Aluminium die casting alloys: alloy composition,
microstructure, and properties-performance
relationships
L. Wang, M. Makhlouf, and D. Apelian
Since commercial production of aluminium by the
Hall-Heroult process, the use of aluminium and its
alloys has been widespread, and commercial
applications continue to increase. The casting
process has always been a major manufacturing
method for aluminium based products, and parts
have been produced using all the traditional
casting processes. However, recent advances in
die casting technology, coupled with
improvements in die materials, have made the die
casting process the most commonly used method
for producing aluminium alloy castings. Despite
recent innovations and advances in die casting
technology that have significantly expanded the
commercial applications of die cast aluminium
products, the development of complementary new
alloys, the optimisation of existing alloys, and the
documentation of reliable properties data for these
alloys, have all categorically lagged behind.
Realising the potential of research and
development in enhancing the technological
competitiveness of the USA, the North American
Die Casting Association and the US Department of
Energy cooperatively sponsored a research
program at Worcester Polytechnic Institute aimed
at systematically investigating alloymicrostructure-property
interactions in aluminium
die casting alloys. This literature review was
conducted during the early stages of the project.
IMR/284
most commonly used method for producing aluminium castings. The increase in the appeal of the die
casting process may also be attributed to the excellent
die casting characteristics of aluminium alloys, as well
as to the increased demand for large quantities of
identical parts. In the 1980s about 68 of the total
aluminium alloy castings produced in the USA were
made by the die casting process.' In 1992 Japan
produced 63·5% of its total aluminium alloy castings
via the die casting process.' Moreover, among all the
various different alloys which may be die cast, aluminium alloys are predominant. In 1992, 367 000 t of
aluminium were die cast in the USA, in contrast with
only 16700 t of magnesium and 106000 t of zinc."
The report of the North American Die Casting
Association (NADCA) predicted that in 1993, the
sales of die cast components in North America
would total $7 400 000 000; of these, aluminium die
cast components .would account for $5 000 000 000
(Ref. 5).
In addition to advances in manufacturing technology and the increased demands of the market,
research and development efforts dedicated to aluminium alloys have played an important role in the
dramatic growth in the use of these alloys. This is
reflected in the number of publications per year
dedicated to aluminium alloys; inspection of the
Metals Abstracts index, under 'Aluminum base alloys',
shows that the number of papers published annually
increased from about 1000 in 1970 to over 6000 in
1992. However, only a small fraction of published
literature is pertinent to die casting alloys; a search
for technical papers directly related to aluminium die
casting alloys in World Aluminium Abstracts from
1968 to 1992 (now Aluminium Industry Abstracts) and
Metals Abstracts from 1982 to 1992 revealed that
only 200 such papers were published during that time.
Clearly, recent innovations in die casting technology have significantly expanded the commercial
applications of cast aluminium products. However,
the development of complementary new alloys, the
optimisation of existing alloys, and the documentation
of reliable data on mechanical properties for these
alloys have all categorically lagged behind.
Realising the potential of research and development
to enhance technological competitive edge, NADCA
and the US Department of Energy sponsored a major
research programme at Worcester Polytechnic
Institute (WPI) aimed at systematically investigating
alloy-microstructure-property
interactions in die
casting alloys. This literature review was conducted
during the early stages of the project. The review
focuses on collecting and analysing the available
information, and summarising the current understanding of aluminium die casting alloys. It concentrates on production oriented aspects of research and
%
© 1995 The Institute of Materials and ASM International.
The authors are in the Aluminum
Casting Research
Laboratory, Worcester Polytechnic Institute, Worcester,
MA01609, USA.
Introduction
Ever since aluminium was commercially produced by
the Hall-Heroult method, aluminium. and its alloys
have been in widespread use, and their commercial
applications continue to increase. In 1992, the USA
produced 4·1 x 106 t of primary aluminium and consumed 4·6 x 106 t. Worldwide production of primary
aluminium in 1992 was 18·4 x 106 t, and worldwide
consumption was 17·96 x 106 (Ref. 1).
The casting process has always been a major manufacturing method for aluminium based products. The
production of aluminium castings by the 30 major
industrial countries in 1992 totalled 4·1 x 106 t, and
of those the USA accounted for 1·04 x 106 t (Ref. 2).
Generally speaking, cast aluminium alloy components
can be produced by any of the traditional casting
processes. However, advances in die casting technology, especially the development of the cold
chamber die casting process, and improvements in
die materials have made the die casting process the
International
Materials Reviews
1995
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No.6
221
222
Wang et ale Aluminium
die casting alloys
development, which will be of much benefit to the
industrial sector.
Fll:Iidity
The solidification temperature range, the viscosity,
the surface tension of the melt, and the amount of
inclusion present are the major factors which determine the fluidity* of an alloy. Increasing the Si
content of a hypoeutectic AI-Si alloy narrows its
solidification temperature range and thus increases
its fluidity. In addition, owing to the higher latent
heat of Si in comparison with that of aluminium, the
viscosity of molten AI-Si alloys decreases when their
Si content is increased. Accordingly, AI-Si alloys with
Si contents ranging from 7 to 18 wt_%, i.e. the
majority of the AI-Si die casting alloys, have excellent
fluidity. An increase in the Fe content of the alloy
increases the amount of insoluble Fe bearing phases
that form in the alloy and consequently reduces the
alloy's fluidity. Additions of Fe, Mn, Cr, Ni, and Mg
to an Al alloy, if they lead to the formation of
intermetallic inclusions, decrease the alloy's fluidity.
Aluminium-magnesium die casting alloys have
wide solidification temperature ranges, and Mg can
oxidise and \form inclusions in the alloy; moreover,
the oxide film that forms on the melt surface increases
the alloy's surface tension. Accordingly, AI-Mg die
casting alloys in general have poor fluidity.
Resistance to hot tearing
Generally speaking, an alloy with a wide solidification
temperature range, a large solidification shrinkage,
and a low strength at high temperature has a high
tendency for hot tearing. Therefore, alloys with Si
contents close to the eutectic, for example alloy 413.0,
have the highest hot tearing resistance among the
commercial die casting alloys. Iron additions improve
resistance to hot tears because Fe increases the alloy's
high temperature strength. Nickel, Cr, Co, Mo, and
impurity elements with high melting temperatures can
slightly improve high temperature strength and thus
beneficially affect resistance to hot tearing. In contrast,
Zn decreases the high temperature strength and thus
its additions tend to increase the alloys' hot tearing
tendency. Aluminium-magnesium die casting alloys
in general have appreciable hot tearing tendency
because of their wide solidification temperature
ranges.
effect is caused by the relatively homogeneous phase
of the casting. Klein and Wust suggest that, besides
correcting the die and tool design, and adjusting the
operating procedures, a reduction in the sticking
tendencies of an alloy maybe achieved by increasing
its Fe content beyond 0·5%. They also suggest that
melt modification by Na can reduce the sticking
tendencies of the alloy.
Corrosion resistance
Copper additions to aluminium die casting alloys
degrade the alloys' corrosion resistance. Copper easily
disperses in the aluminium oxide film that forms on
an alloy's surface and renders it passive. By dispersing
in the oxide film, Cu damages the film's passivity,
thus degrading the alloy's corrosion resistance.
However, AI-Mg alloys have very good corrosion
resistance, because Mg lowers the electrolytic potential of the alloy; moreover, the specific volume of
magnesium oxide is larger than that of the alloy.
Silicon is inert to most corroding environments, and
its corrosion resistance is the same or better than that
of aluminium in most solutions. So, Si additions to
Al alloys do not, in general, degrade the corrosion
properties of the alloys. Iron in the form of FeAl3
causes pitting and therefore decreases the corrosion
resistance of aluminium alloys. The addition of Mn
may absorb the Fe in Mn-Fe compounds, thus reducing the amount of FeAl3 and its pitting effect.
However, Fe, together with Ni in AI-Si alloys, has a
beneficial effect on resistance to high temperature
water and steam. Impurity elements typically found
in aluminium die casting alloys do not have a significant effect on the corrosion resistance of the alloys,
probably because of their low concentrations (except
Cd, which even at very low concentrations has an
adverse effect on corrosion resistance).
The study on alloy ADC12 (Ref. 8) showed that
the corrosion resistant characteristics depend on
location in the die casting. For example, it was
demonstrated that the corrosion resistance of the chill
zone of a die casting was superior to that of the inner
part in alkaline solutions, while the opposite was true
in acidic solutions. This was attributed to the segregation of Si, Cu, and Fe, which caused the magnitude
of the specific gravity and the lattice constant of the
chill zone to differ considerably from their values in
the inner part of the die casting.
Machinability
Die soldering
Klein and Wust'"? studied the die soldering tendency
of GD AISi9Cu3 alloy. They reported that the main
reason for the steady aluminium sticking on certain
tool parts was the diffusion of Fe from the die into
the boundary zone of the casting, and the subsequent
formation of an AIFeSi phase. The strong sticking
* The term 'fluidity' can be defined as the capability of the molten
metal to fill mould cavities. This term consists of two basic factors:
(i) characteristics of the molten metal such as viscosity, surface
tension, inclusions, and solidification pattern of the alloy; and (ii)
casting parameters such as mould design, mould material and its
surface characteristics, degree of superheat, rate of pouring, and
heat transfer.
International
Materials Reviews
1995
Vol. 40
No.6
and surface finish
Machinability of AI-Si alloys depends mainly on the
amount, size, and morphology of the Si phase, both
primary and eutectic, and also on the type and
amount of intermetallic compound. Generally speak. ing, because Si particles are hard, in commercial die
casting alloys, the higher the Si content of the alloy,
the more difficult it is to machine it. Large, flakelike,
eutectic Si particles and large primary Si particles
have a more detrimental effect on machinability than
small fibrous or granular particles. In most AI-Si die
casting alloys Cu can improve machinability.
Conversely, Fe, when in large amounts and when Mn
is present so that Fe + Mn > 0'8%, may form
Al1s(Mn,FehSi2 as primary angular globules; these
Wang et al.
globules
can considerably
reduce
the alloy's
machinability.
It has been shown? that in Al-Si-Cu alloys with
composition
Fe> 0,6%, Mn > 0'5°AJ, and Si> 8%,
sludge (i.e. the Al1s(Mn,FehSi2
phase) might form as
hard inclusions dispersed in the alloy and cause
difficulties during machining. It has also been shown
that small additions of Mg can improve the machinability of primary 380 alloy.!? However, Mg has a
strong tendency to oxidise and to react with other
elements in the melt and with the refractories; this
forms inclusions and thus degrades the machinability
of aluminium alloys. In general, addition of Mg, Mn,
Sn, Pb, and Bi can improve the machinability of alloy
ADC12 (Ref. 11), and additions of Zn and Cd can
improve the machinability of Al-Si alloys.
Electrical resistance
Shikata and Sato12 studied the effects of Cr, Mn, Ti,
Fe, and Zr on the electrical and mechanical properties
of AI-8'5Si3Cu alloys and came up with the following alloy composition: AI-8'5Si-3Cu-1'OCr-0'5Mn0·3Ti. This alloy was to be used in the cast rotor of
a high starting-torque
motor for hoist and machine
tools. The alloy has an electrical conductivity
of
22-24 %lACS (international
annealed copper standard), a tensile strength
of 18-20 kg mrrr', an
elongation of 2-3%, and good castability.
Currently used aluminium die casting
alloys
Creating a useful alloy requires balancing the elemental ingredients in terms of their function in the alloy
against the alloy's performance requirements. To meet
the varied requirements of designers and end users
of aluminium alloy components, a great number of
Table 1
Compositions
Composition,
of registered aluminium
Aluminium
die casting alloys
223
alloys have been created over the years. By 1980,
there were at least 327 designations issued to aluminium die casting alloys worldwide.P In the USA, the
Aluminum Association registered 239 designations of
aluminium casting alloys and ingots in 1989.14 Of
these, 23 were die casting alloys. The compositions
of these alloys are listed in Table 1 (Ref. 15). In all of
these alloys the major alloying elements are silicon,
copper, magnesium, and iron. These alloys can be
classified into five groups: Al-Si-Cu,
AI-Si-Mg,
Al-Si-Mg-Cu,
Al-Si, and AI-Mg. In the following,
representative
alloys from each group are briefly
discussed.!"
(i) 380.0 is an AI-Si-Cu
alloy and generally
considered an 'all purpose' die casting alloy
and therefore is most widely used. The alloy
has very good castability, good mechanical
properties,
and generous
limitations
on
impurities. However, it has only fair corrosion
resistance
(ii) 360.0 is an Al-Si-Mg alloy, also considered a
general purpose alloy. It has very good castability and good corrosion resistance, but fair
machinability,
less generous limitations
on
impurities, and slightly lower tensile strength
and elongation than 380.0 alloy
(iii) 390.0 is a hypereutectic Al-Si-Cu-Mg
alloy.
It has outstanding wear resistance, low thermal
expansion, high thermal conductivity, good
elevated temperature
strength and hardness,
and very good castability, but fair corrosion
resistance, low ductility, and poor machinability. It is used mainly as a substitute
for grey cast iron in engine parts and in
applications requiring wear resistance
(iv) 413.0 is a eutectic Al-Si binary alloy which
has excellent castability, very good corrosion
die casting alloys used in cast shapes (after Ref. 15)
wt-%
Others
except AI
Alloy
Si
Fe
Cu
Mn
Mg
Cr
343.0
360.0
A360.0
361.0
6'7-7'7
9'0-10'0
9'0-10'0
9'5-10'5
1'2
2'0
1'3
1'1
0'5-0'9
0'5
0'35
0'35
0'25
0'1
364.0
369.0
380.0
A380.0
8380.0
7'5-9'5
11'0-12'0
7'5-9'5
7'5-9'5
1'5
1'3
2'0
1'3
0'1
0'4-0'6
0'4-0'6
0'4-0'6
0'2-0'4
0'25-0'45
0'1
7'5-9'5
9'5-11'5
10'5-12'0
10'5-12'0
11'0-13'0
16'0-18'0
16'0-18'0
18'0-20'0
21'0-23'0
11'0-13'0
11'0-13'0
1'3
383.0
384.0
A384.0
385.0
390.0
8390.0
392.0
393.0
413.0
A413.0
1'3
1'3
1'3
2'0
1'3
1'3
1'5
1'3
2'0
1'3
2'0-3'0
3'0-4'5
3'0-4'5
2'0-4'0
4'0-5'0
4'0-5'0
0'4-0'8
0'7-1'1
C443.0
515.0
516.0
4'5-6'0
0'5-1'0
0'3-1'5
2'0
1'3
0'35-1'0
518.0
0'35
1'8
* 0'02-0'04%8e;
to'08-0'15%V;
0'6
0'6
0'5
0'2
0'5
3'0-4'0
3'0-4'0
3'0-4'0
0'1
0'35
0'5
0'5
0'5
0'5
0'5
0'5
0'5
0'1
0'5
0'2-0'6
0'1
0'1
0'1
0'1
0'1
0'3
0'45-0'65
0'45-0'65
0'8-1'2
0'7-1'3
0'1
0'1
0'2-0'3
0'25-0'5
0'3-0'4
Ni
0'5
0'5
0'2-0'3
0'15
0'05
0'5
0'5
0'5
0'3
0'5
0'5
0'5
0'1
0'5
2'0-2'5
0'6
0'2
0'3
0'1
0'35
0'35
0'35
0'4-0'6
0'15-0'4
0'1
2'5-4'0
2'5-4'5
0'25-0'04
0'25
0'35
7'5-8'5
0'15
1'0
1'0
0'5
0'5
0'5
Zn
Sn
1'2-2'0
0'5
0'15
0'15
0'5
0'5
0'5
0'15
0'1
0'15
1'0
3'0
3'0
0'1
0'35
0'35
1'0
3'0
3'0
1'0
3'0
0'1
1'5
0'5
0'1
0'5
0'5
0'35
0'15
0'35
0'35
0'3
0'5
0'1
0'2
0'15
0'3
Ti
0'2
Each
Total
AI
0'1
0'35
0'25
0'25
Remainder
Remainder
0'05
0'05*
0'05
0'5
0'5
0'2
0'2
0'2
0'1-0'2
0'1
0'1
0'15
0'05t
0'15
0'15
0'15
0'05
0'1
0'15
0'15
0'15
0'15
0'1-0'2
0'5
0'5
0'5
0'5
0'5
0'2
0'2
0'5
0'15
0'25
0'25
0'25
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
0'15
Remainder
Remainder
Remainder
Remainder
Remainder
Remainder
0'25
Remainder
Remainder
0'05t
t max. 0·1%Pb.
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Materials Reviews
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224
Wang et al.
Aluminium
die casting alloys
resistance, but poor machinability, and it does
not lend itself to producing a good surface
finish. It is suitable for large castings, complex
shapes, and thin wall castings. In comparison,
C443.0 is a hypo eutectic AI-Si binary alloy.
It has high ductility, very good corrosion
resistance, good machinability, but fair castability, and low strength. This alloy is used in
castings where above average ductility coupled
with excellent corrosion resistance is needed
(v) 518.0 is an AI-Mg alloy with excellent corrosion resistance, high strength, high ductility,
excellent machinability, good fatigue properties, and low density. The alloy produces a
good surface finish, but has poor castability. It
is best suited for simple shaped castings where
excellent corrosion resistance is needed.
Compositional effects in aluminium
die casting alloys
In addition to alloying elements, aluminium die casting alloys inevitably contain elements that are not
part of the original alloy design. These elements are
generally referred to as impurities. Although the term
'impurity' implies an unwanted element, all impurity
elements do not necessarily play negative roles in
aluminium die casting alloys. The impurity elements
most commonly found in these alloys include: Mn,
Ni, Cr, Zn, Pb, Sn, and Ti. The effects of the various
elements in aluminium die casting alloys on their
performance are summarised below.
silicon to AI-Mg alloys reduces their ductility and
notch toughness without any noticeable increase in
strength. is
Corrosion behaviour
The electrolytic potential of Si
is - 0·26 V, that of aluminium is - 0·85 V; this large
difference in potential should lead to high corrosion
rates in AI-Si alloys. However, Si is inert to most'
corrosive environments, and the corrosion resistance
of AI-Si alloys in most electrolytes is as good as, or
better than, that of pure aluminium. is
Casting characteristics
Addition of Si to aluminium
produces a simple eutectic system with a fairly narrow
freezing range. The freezing range of the alloy
decreases with increases in the Si content up to the
eutectic composition (at 12·5%Si). Also, increase in
the Si content results in reductions in the alloy fluidity
at a constant temperature. The reduction in alloy
viscosity continues with increased silicon content even
after the eutectic composition is surpassed. This is
because of the high latent heat of fusion of Si, which
is ~ 4·5 times higher than that of an equivalent
volume of aluminium.!" The narrow freezing range
coupled with low viscosity is mostly responsible for
the excellent fluidity of AI-Si alloys, particularly in
the range of 7-18%Si. In addition, silicon expands as
it solidifies; this expansion compensates for part of
the solidification shrinkage of aluminium; consequently, AI-Si alloys have low solidification shrinkage. The solidification volume shrinkage of AI-Si
alloys decreases linearly with increasing Si content
and reaches zero at 25 Si. The low shrinkage and
narrow freezing range of AI-Si alloys are responsible
%
Effect of alloying elements
Silicon
The effects of adding silicon to aluminium were first
investigated by St Claire-Deville in 1856.17 Addition
of Si to aluminium produces an alloy with superior
casting characteristics. Silicon is fairly inexpensive
and is one of the few elements that may be added to
aluminium without increasing its weight.
The coefficient of thermal expansion of aluminium is appreciably reduced by the
addition of increasing amounts of silicon. In the range
27-427°C, the coefficient of linear thermal expansion
of aluminium is 25 x 10-6 K -1. On adding 10%Si it
is lowered to 20 x 10-6 K -\ and to 12 x 10-6 K-1
by adding 40%Si.
Physical properties
The mechanical properties of
AI-Si alloys depend more on the distribution and the
shape of the silicon particles than on the silicon
content. Alloys in which the silicon particles (eutectic
or primary) are small, round, and evenly distributed
are usually highly ductile. On the other hand, alloys
in which the silicon particles are faceted and acicular
are usually much less ductile but "exhibit slightly
higher strength. Figure 1 shows the change in properties of AI-Si alloys as a function of their Si content.
The fatigue resistance of AI-Si alloys is low, particularly if primary Si is present or if the eutectic Si is
unmodified. Artificial aging increases the tensile
strength of AI-Si alloys, but at the expense of their
resistance to fatigue. It is noted that addition of
Mechanical properties
International
Materials Reviews
1995
Vol. 40
No.6
HV
800
W
--I
U5('j
ZI
~ E
w Z 600
~~
~cn
~~
::>Z
,0
::ca:
1-«
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400
UTS
YS
ZCJ)
wa:
~ ~
150
:3>
wO
5=z
., «
>R
0,
'
~
100
Z<.9
Qz
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<.9~
6
CJ)
50
--I
W
25
E
5
10
15
20
Si CONTENT, wt-%
E elongation; HV Vickers hardness; UTS ultimate tensile strength;
YS yield strength
1
Mechanical
properties
of AI-Si
alloys
function of Si content (after Ref. 17)
as
Wang et al. Aluminium
for their resistance to hot tearing, their good weldability, and the soundness of their castings. The
addition of Si to AI-Mg alloys may improve their
fluidity.
In commercial aluminium die casting alloys, Si may
form particles independent of the other elements in
various morphologies and sizes. It may also form
compounds with the other elements. To a large extent,
the Si particles and the compounds constitute the
alloy microstructure and dominate the alloy properties. This will be discussed in more detail in the
following sections.
Copper
Copper is found in aluminium alloys, either dissolved
in the matrix, or forming intermetallics such as CuAl2
(which will form provided that Mg is not present, or
is present in amounts too small to tie up all the Cu,
as CU2MgsSi6AIs). Other elements such as Mn and
Ni may also tie up Cu and form Cu-Mn and Cu-Ni
compounds.
Copper is added to aluminium
alloys to increase their strength. Figure 2 shows the
variation in properties of AI-Cu alloys as a function
of their Cu content. As it increases, alloy hardness
increases. Strength and ductility depend, however, on
whether the Cu is present in solid solution as evenly
distributed spheroidised particles, or as a continuous
network at the grain boundaries. Alloys with dissolved
Cu have the largest increase in strength, and retain
substantial ductility. Conversely, alloys where Cu is
present as a continuous network at grain boundaries
Mechanical properties
~i 400
U5 E
ZZ
w~
r,
wI
~ •....
« (.9 200
~z
- w
o
~a:
:Jr-en
OL-
--'
400
:i
r(.9
ZN
Wi
c:
E
~ Z 200
o~
....J
W
>=
OL--
z
o
~
....•
40~
_
{3~ 20~
Z
o
....J
W
;
4
8
12
16
Cu CONTENT, wt-%
H work hardened; 0 annealed; T4 quenched
T6 quenched and artificially aged
2
and naturally
aged;
Mechanical properties
of AI-Cu alloys
function of Cu content (after Ref. 17)
as
die casting alloys
225
do not show appreciable increase in strength, but
rather a loss of ductility. When spheroidised, evenly
distributed CuAl2 particles are present, the strength
of the alloy becomes a function of the mean free path
between the particles. The modulus of elasticity of
AI-Cu alloys increases proportionally with increasing
Cu content. At temperatures near the melting point
of the alloy, the modulus of elasticity is about
half its room temperature value. The damping
capacity of aluminium is reduced with increasing Cu
additions; copper additions, however, increase the
strength at high temperature of the alloy. Fatigue
strength of AI-Cu alloys increases with Cu additions,
but only if the Cu is in solid solution. In AI-Si-Cu
alloys, Cu improves hardness, strength, fatigue, creep
resistance, and machinability. Addition of Cu to
AI-Mg alloys, when within the content limit, has little
or no effect on mechanical properties.l"
Franek20 studied the structure and distribution of
Cu in an AI- 20Si-4Cu alloy. The alloy was modified
with 0·1%P and cooled at rates ranging between 1
and 100 K min -1. It was found through hardness
measurements that Cu was contained mainly in a
supersaturated solution, which broke up at temperatures in excess of 200°C. Copper increased the hardness of the alloy at temperatures that did not exceed
200°C. Gasparyan et al.21 found that the introduction
of up to 4%Cu in aluminium alloys had a more or
less similar effect on the alloy's mechanical properties
as the introduction of up to 4%Si. Addition of both
Cu and Si significantly increased the alloy's tensile
strength and hardness, but sharply reduced its elongation. Ohuchi'f found that the alloy AI-20%Si, when
containing heat treatable elements such as Cu or Mg,
had a low resistance to thermal shock. Karpachev
et al.23 studied the effect of composition on the
elevated temperature strength of hypoeutectic
AI-Si-Cu alloys and showed that Cu had a very
strong positive effect. Jorstad'" showed that Cu and
Mg improved the machinability of aluminium die
casting alloys. The addition of Cu and Mg improved
the machined surface finish and decreased the
tendency of the alloy to build up on the casting
tool's edge.
Corrosion behaviour
Of all the aluminium alloys,
AI-Cu alloys have the lowest negative potential;
accordingly, they should have the highest resistance
to contact corrosion, but they do not. In pure aluminium and in most corrosion resistant alloys, an oxide
film forms on the metal's surface which causes passivity. In AI-Cu alloys, however, the Cu disperses in
this oxide film and prevents complete passivation;
AI-Cu alloys, therefore, can be severely corroded.
Corrosion may occur not only when the alloy comes
into contact with other materials, but also when the
alloy comes into contact with another AI-Cu alloy
with a different Cu content, or differently cold worked,
or even differently heat treated. In addition, Cu
bearing alloys in the annealed condition tend to pit
severely. In the age hardened condition, they may be
susceptible to intergranular corrosion or to stress
corrosion. The alloy's microstructure plays an important role in its corrosion behaviour. When Cu is in
solid solution, it has a lesser effect on the alloy's
International
Materials Reviews
1995
Vol. 40
No.6
226
Wang et el. Aluminium
die casting alloys
corrosion resistance than when it is present as CuAI2,
provided that the alloy is not aged to the point where
it has become susceptible to intergranular corrosion
or to stress corrosion. Coring is coincidental with
. dendritic growth. As solidification progresses, dendrites of relatively pure Al form, and solute is continuously rejected in the interdendritic liquid, leading to
segregation of the composition on a microscopic scale.
The corrosion resistance of casting alloys with such
cored dendrites and CuAl2 particles in the interdendritic areas is particularly poor. The thermal expansion of AI-Cu alloys increases with increases in the
alloy's Cu content. The electric conductivity is very
sensitive to copper in solution, but is affected only
slightly by the Cu bearing compounds. In an alloy
with 50/0Cu in solution, the electric conductivity is
approximately half that of pure aluminium. is
Casting characteristics Because of the relatively wide
freezing ranges of AI-Cu alloys with 4-6%Cu, their
fluidity, feedability, and resistance to hot tearing are
poor. When the Cu content is increased beyond 6%
castability improves, but the specific gravity of the
alloy increases considerably. In addition to poor
castability and a high specific gravity, AI-Cu alloys
have poor corrosion resistance, and relatively poor
weldability; they are therefore systematically being
replaced by other aluminium alloys, especially in die
casting applications where the parts are not heat
treated.
Magnesium
Magnesium is the principal alloying element in alloys
515, 516, and 518. In alloys, such as 390, and 360,
Mg is also added as an alloying element. However,
in the rest of the aluminium die casting alloys it is
generally considered to be an impurity.
In some aluminium die casting alloys, such as 380,
413, and C443, Mg is specified to be below a certain
level, a maximum of 0·1% in the USA. The reasons
for this limit are not well documented, but could be
attributed to the strong tendency of Mg to react with
other elements to form inclusions and intermetallic
particles. For example, Mg can easily oxidise in the
melt to form MgO micrometre size particles. At high
holding temperatures (i.e. > 745°C), Mg can usually
form spinel, a complex AI-Mg oxide that grows
rapidly as inclusions in the melt.2s Magnesium can
also react with refractories and oxides, and by doing
so may introduce finely dispersed inclusions into the
melt. At higher levels of Mg (i.e. > O·3 0/0),coarse, as
cast Mg2AI particles may precipitate." In commercial aluminium die casting alloys, Mg may form complex intermetallics with other elements, such as
AisFeMg3Si6 and Cu2MgsSi6Als' Because all these
inclusions and intermetallics reduce the alloy's fluidity
and adversely affect its overall properties, Mg levels
in many aluminium die casting alloys had to be
limited. However, for a long time the rationale behind
the low limit on the Mg content has been questioned.
There are three important reasons for questioning
this limit: (i) the knowledge and data currently avail- '
able on the function of Mg in aluminium die casting
alloys are not sufficient to support the set limits;
(ii) allowing a higher Mg content in the alloy can
International
Materials Reviews
1995
Vol. 40
No.6
substantially reduce the cost of the 'demag' * operation; (iii) the limits on Mg set for similar alloys
in countries other than the USA are considerably
higher; for example, the Canadian SC84R alloy
(O·45-0·75%Mg), the German 226/D alloy (O·30/0Mg),
the French A-S9U3A alloy (0·30/0Mg), the Italian
5075 alloy (O·30/0Mg),and the Japanese ADCI0 and
ADC12 alloys (O·3%Mg), are all equal or equivalent
to the US alloy 380, and allow higher Mg contents.
Some work has been done in this respect but the
results are inconsistent. Jorstad!" showed that Mg
(""0·30/0)added to a primary 380 alloy improved the
alloy's machinability. Magnesium hardened the alloy
matrix and thereby reduced the buildup of metal on
the cutting tool's edge. Additions of Mg also resulted
in shorter and tighter chips, reduced the friction
coefficient between the tool and the workpiece, and
provided a better surface finish. The higher level of
Mg gave the primary 380 alloy desirable machining
characteristics comparable to those of a secondary
alloy. Moreover, tool wear rates during machining
the primary alloy with the Mg addition were significantly lower than those for a similar secondary alloy.
Also, Kumagai and Kojima:" indicated that the
addition of Mg (up to 0·50/0)in alloy ADC12 resulted
in an improvement in mechanical properties, while
the addition of Mg, together with Mn, Sn, Pb, and
Bi, improved the alloy's machinability. DasGupta
et al.2S,29 studied the effect of Mg on the microstructure and properties of unmodified 319 alloy with
Mg contents ranging from 0·07 to 0·59% and Sr
modified 319 alloy with Mg contents ranging from
0·08 to 0·630/0.Although 319 is a sand and permanent
mould casting alloy, its composition is similar to 380
die casting alloy except for its lower Si content
(5·5-6·5% for 319 alloy and 7·5-9·50/0 for 380 alloy).
DasGupta's work indicated that increasing Mg did
not significantly change the as cast or the heat treated
microstructure of the alloy. The mechanical properties
of both unmodified and Sr modified specimens in
both the as cast and the heat treated conditions
were also not significantly changed. Joenoes and
Gruzleski/" found that Mg decreased the homogeneity
of the alloy microstructure. At l%Mg, it slightly
refined the Si phase, but had a negative effect on Sr
modification. It was also reported." that the addition
of Mg to aluminium based die casting alloys allowed
a reduction in the stabilisation annealing temperature.
Physical properties
Addition of Mg to aluminium
slightly increases its coefficient of thermal expansion
and its electrical resistivity.
Mechanical properties Aluminium-magnesium alloys
have high strength with good ductility. The AI-Mg
binary phase diagram has a eutectic reaction,
L~Al + MgsAls (35%Mg, 450°C). The solid solubility of Mg in aluminium is 17·4 wt-% at 450°C and
is 1·9 wt- % at 27°C. This is one of the main reasons
that AI-Mg alloys with Mg contents in excess of 60/0
* Removal of the excess magnesium from the aluminium melt
before casting is termed 'demagging'. This operation is performed
to avoid the formation of a brittle intermetallic compound, magnesium silicide, which might break under stress, introducing cracks
in the casting.
Wang et al.
:i
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en
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Mg CONTENT, wt-%
250
200
4
5
10
15
Mg CONTENT, wt-%
HV Vickers hardness; UTS uti mate
strength; H cold worked; 0 annealed
3
die casting alloys
-I
w
a:
••••• 1
en E
W
Aluminium
tensile
strength;
Effect of Mg on tensile properties of AI-Si alloys
in solution heat treated condition, determined
on standard testbars cast in green sand (after
Ref. 17): 1 ksi = 6·89 MN m-2
1·0Zn. The levels of Mg, Mn, and Cr tested were
0·2-2·0%, 0'2-1·6%, and 0-0·6%, respectively. Creep
rupture time and rate were measured at 300 C at a
stress level of 45 MN m -2. The results indicated a
complex relationship between the alloy's heat resistance and its composition. The highest levels of creep
rupture time (>40 h) were achieved with AK5M4
containing 1·13-1·74%Mg, 0·34-0·86%Mn
and
0-0·3%Cr.
D
YS yield
Mechanical properties
of AI-Cu alloys
function of Mg content (after Ref. 17)
as
respond well to heat treatment. Figure 3 shows the
hardness and strength of heat treated or cold worked
AI-Mg alloys as a function of the alloy's Mg content.
In these alloys the hardness, strength, and fatigue
resistance increase, and ductility decreases with
increasing Mg content. The loss of strength with
increasing temperature is less rapid in these alloys
than in other aluminium alloys. The mechanical properties of AI-Mg alloys are sensitive to grain size.
Magnesium is one of the few elements that lowers the
modulus of elasticity of aluminium. Magnesium may
give the Al-Si alloys a very strong heat treatment
response when the proper amount of Mg is added.
During solution treatment of these alloys Mg and Si
dissolve in the aluminium. Upon aging, GP (GuinierPreston) zones or highly dispersed Mg2 Si micrometre
size particles gradually precipitate in the matrix. This
process significantly increases tensile strength, yield
strength, and elongation of the alloy. However, when
Mg in an Al-Si alloy forms coarse as cast Mg2 Si
particles and/or forms Cu2MgsSi6Als particles, when
Cu is also present in the alloy, it has little or no
strengthening effect by heat treatment. The addition
of Mg to aluminium sand casting alloys with 5-11 %Si
increases the alloy's strength and hardness, but
decreases its ductility, as shown in Fig. 4. In addition
to enhancing the alloy's response to heat treatment,
the presence of Mg may increase strength and creep
resistance of Al-Si alloys. is
Karpachev et al.23 studied the effect of Mg
additions, as well as Mn and Cr additions, on the
heat resistance properties of a Russian alloy AK5M4
with composition of AI-5·0Si-4·0Cu-0·8Fe-0·5Ni-
Corrosion behaviour Magnesium lowers the electrolytic potential of aluminium. Moreover, the specific
volume of the oxide film that forms on the surface of
an AI-Mg alloy is larger than the specific volume of
the alloy. Therefore the surface film is very impermeable, particularly if it absorbs water and transforms
it to the hydroxide. Accordingly, AI-Mg alloys have
an excellent corrosion resistance, better than that of
pure aluminium in salt water or in mild alkalis. is
Casting characteristics
The castability of the AI-Mg
alloys is poor, particularly when the Mg contents are
low (2-4%). It improves slightly at higher Mg contents (7-12%). There is also appreciable hot tear
tendency, especially at low Mg contents, because of
the wide freezing range of these alloys. None the less,
AI-Mg alloys produce parts that have excellent surface finish and good weldability. However, Mg has a
strong tendency to react with refractories and oxides,
and introduces finely dispersed inclusions into the
melt. These finely dispersed particles may reduce melt
fluidity and may have an adverse effect on the alloy
properties. In alloys containing Mg, coring is appreciable, and the eutectic phase MgjAl, may appear in
alloys with as little as 3-4%Mg. When these alloys
contain considerable amounts of Fe, a ternary eutectic
reaction (L~AI + FeAl3 + MgsAIs) occurs, most
probably at 0'15%Fe, 33%Mg, 450 C; the eutectic is
completely divorced. The solid solubility of Fe in
aluminium is probably reduced by Mg; the solid
solubility of Mg in aluminium is also reduced by the
D
International
Materials Reviews
1995
Vol. 40
No.6
228
Wang et al.
Aluminium
die casting alloys
Fe. Under non-equilibrium conditions, the tendency
for the divorcing of the eutectic is strongly increased,
so that large, massive crystals of FeAl3 can form even
at low Fe concentrations. Furthermore, the Mg.Al,
compound tends to appear, even at Mg levels of
2-30/0.
Iron
Iron is always present in commercial aluminium
alloys. It is often added unintentionally through the
use of steel tools during melting and casting, and the
use of remelting materials containing Fe or rust. For
most aluminium foundry alloys, the presence of Fe is
detrimental, and efforts are made to keep its levels as
low as economically possible. However, in aluminium
die casting alloys it is added purposely to minimise
die soldering. Various Fe bearing phases may form in
aluminium alloys, and the effects of Fe depend to a
large extent on the type of morphology of the phases
it forms.
Types and morphologies of Fe bearing phases
In a
binary AI-Fe system, the equilibrium solid solubility
of iron in aluminium is about 0,03-0,050/0 at the
eutectic temperature (655°C) and even much lower at
room temperature. The phase in equilibrium with
aluminium is usually designated as FeAl3 (40·7%Fe).
In the AI-Fe-Si system, several ternary phases can
be in equilibrium with aluminium: Fe2SiAIs (a),
FeSiAls ([3), FeSi2Al4 (£5) in high Si alloys, and
FeSiAl3 (y) in high Fe and high Si alloys. More ternary
phases form at higher Fe and Si contents. The
invariant reactions in the aluminium corner are shown
in Table 2. Under non-equilibrium conditions when
small amounts of Mn, Cr, and Cu are present, another
phase with a composition of 27-35 0/0Fe and 6-8%Si
may form. This phase is similar to the MnSiAI or
CrSiAI type phases in which most of the Mn or Cr is
replaced by Fe. For most commercial casting alloys,
because of non-equilibrium solidification, it is not
uncommon to find alloys in which FeAI6, FeAI3,
Fe2SiAls, FeSiAls, and FeSi2Al4 coexist with one
another and with Si. In Al-Si alloys when Cu is
present, the AI-FeSiAls-Si eutectic forms as thin
platelets (needles). If there is more than 0'8%Fe,
primary FeSiAls crystals may appear. Fast cooling
tends to shift the eutectic towards higher Fe contents
and to disperse the FeSiAls crystals. Occasionally,
especially in alloys with a low Si content or in alloys
containing Mg, Cu, or Zn, FeSiAls may appear as
Table 2
Invariant reactions at the aluminium
end of the AI-Fe-Si system hitter Ref. 18)
Composition,
Temperature,
Liquid
Reaction
DC
Fe
L--+AI* + FeAI3t
L--+AI* +Sit
655
577
1'9
L--+AI* + Sit + FeSiAlst
L + FeAI3* --+Fe2SiAIat + FeSiAI3t
L + FeSiAI3* --+Fe2SiAIat + FeSiAlst
L + FeSiAI3* + FeSiAI4 t --+FeSiAlst
576
710
675
0'7
7'5
6'0
7'0
2'5
L + FeAI3* --+Alt + Fe2SiAIat
L + Fe2SiAla* ~Alt + FeSiAlst
L + FeSi2AI4* --+FeSiAlst + Sit
700
630
612
596
Materials Reviews
1995
B
Fe
Si
0'05
12'5
12'0
12'5
13'0
14'0
4'0
6'5
14'0
1'7
1'5
Vol. 40
wt-%
A
Si
Compositions:
* phase A, t phase B, t phase C.
§ x may vary from 0 to 9.
International
Chinese script; when Cu is present, Fe may be associated with it; the compound probably becomes
CU2FeAI7' In the presence of Mg, the compound
FeMg3 Si6Als may form as Chinese script (when it is
a eutectic) or as globules (when it is primary). Iron
forms Al1s(Fe,MnhSi2 with Mn, often in the shape
of Chinese script, thus removing the embrittling effect
of the needle shaped FeSiAls. The phases formed by
Ni, together with Cu and Fe, are not known with
certainty. As mentioned earlier in the AI-Fe-Mg
ternary system the eutectic, L ~ Al + FeAl3 + Mg, A13,
is completely divorced. Under non-equilibrium conditions, massive crystals of FeAl3 can form, even at
low Fe concentrations.!"
The morphology and size of Fe bearing phases in
aluminium casting alloys depend on the alloy's composition and casting conditions. In commercial castings the Fe bearing phases may appear as Chinese
script, needles (platelets), or angular globules, and
sometimes they appear in the form of petal-like
particles. The size of these phases generally becomes
smaller at faster cooling rates. As mentioned earlier,
the FeSiAls phase may form as Chinese script, a shape
usually associated with Fe2SiAls, or as platelets
(needles), usually associated with FeSi2AI4• Hence,
the identification of these Fe bearing phases by shape
alone may be misleading. Yet, in recent publications,
e.g., in Backerud et al.'s work,32 the Chinese script
phase is generally referred to as Al1s(Fe,MnhSi2, and
the needle shaped phase as FeSiAls.
Backerud et ale indicated that in 380 alloy the
Chinese script phase may solidify ahead of the a-AI
dendrites as large primary particles at low 'cooling
rates, e.g. < 0·2 K s -1, or precipitates together with
the eutectic Si particles in the interdendritic regions
at higher cooling rates, e.g. > 6 K S -1. The addition
of Mn expands the composition range in which the
Chinese script phase Al1s(Fe,MnhSi2 may form. Since
the Chinese script shape is less detrimental to the
tensile properties of the alloys than the needles, it is
preferable to shift more of the Fe bearing phases from
the needles to the Chinese script shape. Usually, Mn
serves as an Fe corrector; however, if the total content
of Mn plus Fe exceeds 0'8%, the Al1s(Fe,MnhSi2
particles become 'primary and appear as angular
globules (although the compound itself has a cubic
crystal structure). These globules do not embrittle the
alloy, but they may appreciably reduce its machinability; hence, the Mn content is often controlled only
No.6
0'01
36'0
34'0
34'0
36'0
33'0
25'5
Fe
C
Si
Fe
Si
",25'0
34'0
25'0
'" 15'0
17'0
15'0
25'0
33'0
25'0
13'0
7'0
13'0
<0'1
99'8+
36'0
1'65
1'60
0'2
17'0
17'0
D"
7'0
25'5
O'OX§
33'0
33'0
25'5
0'05
0'04
25'0
99'9
99'8
7'0
7'0
25'5
0'6
1'1
13'0
Wang et al.
partially to correct the Fe and thus to prevent the
formation of the primary particles. Chromium and
Ni may also correct the Fe, but (Cr,Fe)4Si4AI13 or
(Cr,FehSisAh
and FeNiAl9 compounds may form.
These' compounds are elongated in shape and can
cause brittleness. The best Fe corrector is probably
Co: it does not combine with Si, and thus the number
of extraneous particles formed in the alloy is limited.
Physical properties
Increasing the Fe content of an
AI-Fe alloy reduces its thermal conductivity. The
electrical
resistivity
of aluminium
increases
to
approximately 2·75 x 10-s Q m with the addition of
O'050/0Fe and to 2·9 x 10-s Q m with the addition
of 10/0Fe.
Corrosion behaviour
The difference in electrolytic
potential between the FeAl3 particles that are usually
present in AI-Fe alloys (ranges between -0·39 and
-0,58 V) and the ·aluminium matrix (~-0'85
V)
leads to a reduction in the corrosion resistance of
aluminium upon adding Fe, especially pitting corrosion. However, Fe, together with Ni in AI-Si alloys,
produces particularly good resistance to the effects of
high temperature water or steam. In AI-Mg alloys,
Fe tends to reduce corrosion resistance, but has little
or no effect on stress corrosion or exfoliation."
Mechanical properties
As mentioned earlier, the
effect of Fe on mechanical properties depends on the
type and morphology of the compounds it forms, as
well as on their quantities. Generally speaking, the
Fe bearing phases increase the alloy's hardness but
decrease its ductility. The compounds are essentially
insoluble and may be responsible for an improvement
in strength, particularly at elevated temperatures. In
AI-Mg alloys, the MgsAls' compound may form as
coarse particles (when Mg > 2 %) that reduce the
alloy's ductility, creep, and fatigue resistance.
Karpachev et al.'s work " showed that additions of
Cu had a strong positive effect on the high temperature strength of the AI-Si alloys, and additions of
Fe and Ni made it possible to reduce the Cu content without reducing the alloy's high temperature
strength. It was reported'" that addition of Fe to
BS LM24 alloy reduced the alloy's tendency for hot
tearing and minimised segregation. Holecek33 studied
the negative effects of Fe, at levels less than 2%, on
the mechanical properties of AI-Si alloys. The alloys
investigated
contained
12-13%Si
and 1'5-2%Cu,
and were Na or P modified. Counteracting the effects
of iron by adding Mn, Cr, Mo, Co, and/or V was
also studied and recommended
for alloys with
high Fe contents that had unacceptable mechanical
properties.
Kobayashi et a1.34 and Egashira et al.3s studied the
effects of Fe, Mg, and Mn on the fatigue crack
propagation
characteristics
of high purity AI-Si
system casting alloys (between the hypo- and hypereutectic range). It was found that the crack propagation rate in the high stress intensity range was
retarded by the addition of Fe and Mn to an
AI-Si-Mg
alloy. A statistical investigation
of the
microstructural feature, which caused fatigue fracture
in aluminium alloy castings, was conducted. It was
found that Fe content had a pronounced influence. A
Aluminium
die casting alloys
229
patent issued to Toyota Jidosha " claims that hot
tearing in aluminium die casting alloys can be prevented by controlling the alloy's Fe, Mn, and Ni
contents, even when recovered scrap alloys or chips
are used.
Casting characteristics
Generally, in aluminium die
casting alloys Fe improves resistance to hot tearing
and decreases the tendency for die sticking or soldcring.l" As the fraction of the insoluble Fe bearing
phases increases with increasing Fe content, the flowability and feeding characteristics become adversely
affected. In AI-Mg alloys, Fe has some grain refining
effect. The solidification shrinkage of AI-Fe alloys
decreases linearly with increasing Fe content and is
approximately 3% at 5%Fe. The fluidity of the molten
alloys decreases with Fe additions, but there is no
appreciable change in surface tension. Fe may participate in the formation of 'sludging' phases with Mn,
Cr, and other elements.
Richard?" found that in A1Si9Cu3 die casting alloys,
the Fe and Mn formed intermetallic hard spots. These
spots were particularly coarse and dense and resulted
from decanting at a low holding temperature. Richard
expressed the decanting temperature and the minimum
holding
temperature
in terms
of the
(Fe + 2Mn + 3Cr) content of the alloy. Flores et al.9
studied the kinetics of formation, growth, and sedimentation of the Al1s(Fe,MnhSi2 phase in AI-Si-Cu
alloys. They found that when the composition
exceeded 0·6 0/0Fe, 0·5%Mn,
and 80/0Si, at temperatures in the 610-660°C range, some AI(Fe,Mn)Si
type phases would form. These phases, commonly
referred to as 'sludge', led to the formation and
sedimentation
of very hard inclusions that had a
detrimental effect on the mechanical properties of
the alloys.
Awano et al.3s studied the non-equilibrium crystallisation of AIFeSi type compounds in AI-Si alloy
castings made from superheated melts. They indicated
that the morphology of the AIFeSi type compound
changed from needles to Chinese script when the melt
was superheated and Fe correctors were not added.
The factors affecting this phenomenon and the effect
of melt superheating on the strength were also investigated for squeeze castings made from alloy lIS AC4C.
This alloy has the composition: AI-( 6·5-:-7·5)Si-0·5Fe0·2Cu-0·3Mn-(0·2-0·4)Mg-0·3Zn-0·2Ti,
which
is
equivalent to 356.0 alloy with a high Fe content.
Under non-equilibrium
conditions the AIFeSi type
compound crystallised in the needle form during the
earlier stages of solidification and in the Chinese
script form during the later stages of solidification,
regardless of the thermal history of the melt after
superheating. The addition of Mg, however, inhibited
the crystallisation of the compound in the Chinese
script form. The toughness of T6 treated squeeze
castings increased when they were superheated at an
elevated temperature. This was caused not only by
the crystallisation
of the compound in a Chinese
script form, but also by a reduction in the particle
size of the compound that formed in the needle form.
Klein and Wust"? studied the die soldering tendencies of alloy GD AISi9Cu3. During die casting, this
alloy, and also alloy GD AISi7MgSb, tend to adhere
International
Materials Reviews
1995
Vol. 40
No.6
230
Wang et al.
Aluminium
die casting alloys
to dies made of hot worked tool steel.It was observed
that die erosion occurred with GD AlSi7MgSb alloy
and not with GD AISi9Cu3 alloy. The sticking of the
alloy on certain tool parts was found to be caused by
the diffusion of iron from the die into the boundary
zone of the casting and the formation of an AIFeSi
type phase. Klein and Wust suggested raising the Fe
content of aluminium die casting alloys 'to above
0.5°/0 and modifying the melt with Na as possible
ways of reducing sticking.
Effect of impurity elements
Commercial aluminium casting alloys almost always
contain impurity elements. Most of these elements,
because of their low concentrations, dissolve in the
aluminium and have a minimal influence on alloy
properties. Under certain conditions, however,
impurity elements may form intermetallic compounds;
these compounds may have appreciable effects on the
alloy properties. Except for Zn, impurity elements in
AI-Si alloys tend to decrease the fluidity of the molten
alloy and to enhance the alloy's resistance to hot
tearing. The impurity elements most commonly found
in aluminium die casting alloys, together with their
effects on the alloy properties are described in the
following.
Manganese
The solubility of Mn in aluminium is
1·80/0at 657°C, 1·00/0at 627°C, and 0·20/0at 427°C.
At low Mn contents, the phase in equilibrium with
aluminium is MnAI6• The solubility of Mn in aluminium is reduced by the presence of Fe and Si, leading
to the formation of some compounds, such as
Al1s(Fe,MnhSiz, and (Fe,Mn)AI6• Manganese is usually added to wrought alloys as a hardener to enhance
the strength of these alloys by work hardening, and
as a corrector for Fe. In aluminium casting alloys,
where work hardening is not employed, Mn offers no
significant strengthening benefits. However, secondary aluminium casting alloys always contain high
levels of Mn brought into the melt in scraps of
wrought materials. The presence of Mn in AI-Si
alloys may slightly improve the alloy's high temperature properties, enhance its fatigue resistance, and
reduce its shrinkage." Manganese and Zn in secondary alloys, where many elements are present in small
amounts, compensate for Cu and Ni, and enhance
the corrosion resistance of the alloy to a level that is
comparable to that of primary alloys. Over 2°/oMn
in AI-Mg alloys tends to form coarse particles and
to slightly increase the low temperature properties
and the creep resistance of the alloy. There is also
evidence" that a high volume fraction of MnAl6 may
beneficially influence internal casting soundness. Hard
inclusions, e.g. Al1s(Fe,MnhSiz sludge, may form in
alloys with compositions exceeding 0·6%Fe, O'5°A>Mn
and 8%Si at temperatures around 610-660°C.
This phase has a detrimental effect on the alloy's
mechanical properties." It is also reported " that Mn,
together with Fe and Ni, is strongly related to hot
tearing.
Manganese is usually added to aluminium die
casting alloys in amounts that do not exceed half the
alloy's Fe content to act as an Fe corrector. As
International Materials Reviews
1995
Vol. 40
No.6
mentioned earlier, .Mn can compensate for the negative effects of Fe by favouring the formation of the
compound Al1s(Fe,MnhSiz in the shape of Chinese
script, and minimising the embrittling needle shaped
phase, FeSiAls. Manganese may absorb Fe and form
compounds such as (Fe,Mn)AI6• This compound has
an electrolytic potential approximately equal to that
of aluminium, and therefore can alleviate the pitting
effects of FeAI3• Manganese is also employed to alter
the response to chemical finishing and anodising.
However, if the total Mn plus Fe content in the alloy
exceeds 0'80/0,primary Al1s(Fe,MnhSiz crystals may
form as angular globules and degrade the alloy's
machinability. High concentrations of Mn in an aluminium based alloy detracts from the alloy's castability and casting soundness. Therefore, the Mn
content of these alloys is often controlled to correct
only partially the Fe and not to allow the formation
of the primary Al1s(Fe,MnhSiz crystals.
Nickel When Ni is present in AI-Si alloys it slightly
increases the alloy's strength at both room and elevated temperatures, and it may also slightly increase
ductility, but only if it acts as an Fe corrector;
otherwise Ni reduces ductility. Nickel reduces the
coefficient of thermal expansion of aluminium based
alloys; and Ni and Fe together in AI-Si alloys enhance
the alloys' resistance to attack by high temperature
water and by steam.
Chromium
Chromium, like Mn, is usually used as
an Fe corrector. When present in AI-Si alloys, it
slightly increases the alloy's strength at room and
also at elevated temperatures and slightly reduces
ductility. Chromium may form sludge with Mn and
Fe. Also, like Mn, Cr in AI->20/0Mg alloys tends to
form coarse particles and increases the low temperature properties of the alloys and also their creep
resistance.
Zinc Zinc in amounts up to 1% in aluminium alloys
is in solid solution and does not form any visibly
detectable phases. High levels of Zn, together with
Mg, may lead to the formation of MgZnz• Zinc up
to '" 3% has no effect on the corrosion properties of
aluminium based alloys. When present in Al-Si alloys
Zn decreases high temperature strength, tends to
increase the tendency for hot tearing, but improves
the alloy's machinability. As mentioned earlier, in
secondary alloys, Zn and Mn compensate for Cu and
Ni, and enhance the alloy's corrosion resistance.
When present in AI-Mg alloys Zn enhances the
alloy's castability and also its strength. Because the
detrimental effects of Zn are not very pronounced,
Zn is specified in many alloys at higher levels than
other impurities, e.g. up to 3% in some aluminium
die casting alloys.
Klein39 studied the effects of Zn on the mechanical
properties
of aluminium
die casting alloy
GD AISi8Cu3. He tested die cast flat testbars with
Zn contents of 1·2 and 20/0.His results indicated that
the alloy with 20/0Zn had a higher tensile strength
than that with 1'20/0Zn,even after aging for one year.
Tin and lead Tin and lead, if present together with
Mg in Al-Si alloys, tend to enter into a Mg, Si phase.
Wang et al.
In AI-Si alloys, Sn and Pb decrease the alloy's high
te~perature strength, and improve the alloy's machinability; Sn, however, has a deleterious effect on corrosio~ res~s.tance. Lead in AI-Mg alloys may improve
machinability, supposedly without a loss of strength
or a loss of corrosion resistance.
Other elements
The presence of Be in quantities as
low as a few parts per million in aluminium based
a~loys may effectively reduce the alloy's oxidation at
high temperatures, especially when the alloy is in the
molten state. At higher levels (> 0·04%) Be can act
as an ~e. corrector, and affect the morphology and
composition of the Fe bearing intermetallics. In this
capacity,. ~e markedly ~mproves the alloy's strength
and ductility, However, If not acting as a Fe corrector,
Be rna y decrease these properties.
C~balt and Mo are Fe correctors. In fact, Co is
considered to be the most effective of all the known
F~ corre.ctors. In AI-Si alloys, both Co and Mo may
slightly Increase the alloy's strength at room tempera~ure and at elevated temperatures,
and may also
slightly increase ductility, but only if they act as Fe
correctors. Otherwise, Co and Mo reduce the alloy's
strength and ductility. In addition, Co may increase
the alloy's fatigue resistance.
Bismuth in AI-Si alloys improves wear resistance
a~d machina!Jility. Silver is reported to increase elongation, Vanadium at 0·1-0·2% is reported to refine the
FeMn compounds.
Zirconium
slightly increases
strength, reduces ductility, and has a grain refining
~ffect. Cadmium in concentrations
exceeding 0·1 %
Improves machinability. Rare earth elements increase
creep resistance and reduce gas porosity. Calcium has
a deleterious effect on corrosion resistance, increases
H solubility, and is responsible for casting porosity
at trace concentration levels.
Effect of melt treating elements
Several elements may have a grain refining effect on
aluminiu:m castin~ al~oys, and the most commonly
used grain refiner IS TI-B master alloy. Titanium and
B are usually added in amounts well within their
solid solubility limits and do not form any separate
phase. Iron reduces their solubility so that in the
presence of Fe, less Ti and B are needed. However
Ti is often employed at levels greater than those
required for grain refinement to reduce cracking
ten~encies i~ compositions
that are prone to hot
teanng. Sodium, Sr, and Sb are effective modifiers of
hypoeutectic AI-Si alloys. Phosphorus has an effect
on refining primary Si particles of hypereutectic AI-Si
alloys. However, additions of Na and Sr increase
porosity. Antimony improves alloy machinability but
by combining with Mg reduces the response to heat
treatment. Sodium has an embrittling effect on AI-Mg
alloys. In hypoeutectic AI-Si alloys, P may react with
N a .and Sr, diminishing their modifying effect. Though
grain refinement renders little or no improvement in
~~chanical pr~p~rties of aluminium die casting alloys,
It .Improves. fluidity, .consequently resulting in castings
WIth a uniform microstructure
and a decrease in
number of defects. Its beneficial effect on refining and
evenly distributing
porosity may also have some
benefits to die castings.
Aluminium
die casting alloys
231
Solidification and microstructure
development in typical aluminium die
casting alloys
Backerud et al.32 studied the solidification characteristics .a~d the m~crostructures that develop in typical
aluminium casting alloys under strictly controlled
laboratory
conditions. A unique thermal analysis
method was used in combination with metallography
and modern microanalytical techniques. The thermal
analysis method consisted of two thermocouples
placed in a small cylindrical mould; one thermocouple
was placed close to the inner wall of the mould and
the other at its centre. During solidification
the
melt, the thermocouples recorded the cooling curves
at both locations. The cooling curve at the specimen
centre, its first derivative, and the temperature difference between the centre and the wall of the mould
were p~otted as a function of time and then analysed.
The microstructures
and the compositions of all the
phases present in the specimen were investigated using
metallography,
energy dispersive X-ray (EDX), and
X-ray powder diffraction (XRD) techniques. From
the analysis the solidification characteristics
of the
alloys were quantitatively
determined. The information collected included: cooling rate, dendrite arm
spacing (D.AS), solidification temperature range and
time, rea~tIons occurring during solidification (temperature Interval, phases formed, and fraction of solid
pr~cipitated in each reaction), and the point of dendnte coherency* (temperature and fraction of solid
formed at this point). Typical hypoeutectic, eutectic,
and hypereutectic AI-Si die casting alloys, namely
380, 413, and 390 alloys, were investigated. Also, the
AI-Mg alloy 518 was analysed. The main results from
this study are summarised in the following.
df
AI-Si alloys
Hypoeutectic alloys
Various 380 type alloys were investigated. For a
typi~al 380 alloy, the DAS was 74, 57, and 28 urn at
cooling rates of 0·2, 0·6, and 5·0 K s -1, respectively.
In general, an increase in the cooling rate was
accompanied by an expansion in the solidification
temperature range that resulted from a drop in the
end temperature.
Solidification
of these alloys is
accompanied
by the reactions shown in Table 3.
The phases observed in the solidified samples are
presented in Table 4.
During solidification of a typical 380 alloy (9·1 %Si,
1·00~Fe, 3·2%Cu, 0·38%Mn, 0·34%Mg, 1·1O~Zn), formatl.o~ o~ the dendritic network was followed by
precipitation of an AISiFe type phase. At low cooling
rates, e.g. 0·2 K S-l, this phase was Al1s(Mn Fe)· Si
Chimese scnpt.
.
3
2
On the other hand, at higher 'cooling
rates, e.g. 0·6-5·0 K s -1, it was Als FeSi needles. The
co-eutectic precipitation
of the Fe bearing phase
occurred as the Als phase at the intermediate cooling
rate. (0·6 K s -1), but as the AIlS phase at higher
cooling rates, such as 5 K s-t, and up to 200 K S-l.
* The point of dendrite coherency is the point at which the solid
p~ase network is established throughout the entire casting; from
thIS.moment on, macrosegregation, shrinkage, porosity, and hot
teanng start to develop.
International
Materials Reviews
1995
Vol. 40
No.6
/
232
Wang et al.
Table 3
Aluminium
Reactions during
type alloys
die casting alloys
solidification
of
380
Reactions
during
solidification
Reaction
I no.
no.
Reaction
1
2
3
4*
Development of dendritic network
Precipitation of AIMnFe containing phases
Main eutectic reaction involving precipitation
Mn-Fe containing phases
Precipitation of Mg2Si
5
Precipitation
Formation
of Si and
of AI2Cu
of complex
of
the
413.0 alloy
Reaction
6
Table 5
eutectics, containing
Suggested
temp.,oC
Reaction
1
Development
2a
2b
2c
L~AI +AlsFeSi
L ~ AI + AI,s (Mn,FebSi2
L ~ primary Si
574
572
572
572
3a
3b
L~AI
L~AI
575
573
of dendritic
network
+ Si + AlsFeSi
+ Si + AI,s(Mn,FebSi2
AI2 Cu and
AIsMgaSi2Cu2
* Only observed
in samples with a high Mg content.
At the higher cooling rates, the growth kinetics obviously favoured the formation of the cubic AIlS phase
over the monoclinic Al, phase for the given composition. At the end of the solidification process, the
precipitation of Al2 Cu (no. 5 in Table 4) and the more
complex eutectic reaction (no. 6 in Table 4) took
place. Compact AIlS particles might sediment at the
very low cooling rates; these particles form what is
usually called sludge.
Backerud et al.'s work'? also indicated that the
solidification process and the resulting microstructure
of the 380 type alloys were determined by the alloy
composition, as well as the cooling rate. When the
alloy had low Si (7'2%), Cu (1'20/0),Fe (0'52%), and
Mn (0,180/0) contents; the pre-eutectic part of the
sample, as expected, was very large (-- 500/0 of the
fraction of solid) and dendrites made up a large
fraction of the total volume. In the eutectic regions
of AIlS phase and the Als phase were observed. This
mix of phases was seen at cooling rates up to 50 K S-l,
while the AIlSphase dominated the structure at higher
cooling rates. It was clearly shown that the amount
of final eutectic was low in this alloy because of its
low Cu content. When the alloy had a very high Si
content (11'00/0),but low Cu (1'50/0)and Mn (0'110/0)
contents, solidification began with the formation of a
dendritic network, although the alloy composition
was very close to that of the eutectic. This led to
supersaturation of Si in the remaining liquid, and
some primary Si particles formed before the start of
the main eutectic reaction. Even at very high cooling
rates, the Al, phase was the only Fe bearing phase
that precipitated. This is expected because of the low
Mn content of this alloy. When the alloy had a high
Mg content (0'59%), but a low Mn content (0'110/0),
the high Mg content led to the formation of the
Mg2Si phase in addition to Si, AIFeSi, AI2Cu, and
Table 4
Phases observed by optical and scanning
electron microscopy (SEM), and energy
dispersive X-ray anal.ysis (EDX) in 380·
alloy
No.
Characteristics
oc-AI*
AI,sMn3Si2*
AlsFeSi
Dendrites
Brown Chinese script
Needles
5
Si*
AI2Cu*
Grey
Pink particles
6
7
AIsCu2MgaSis
Mg2Si*
3
4
* Confirmed
by X-ray diffraction
International
Eutectic alloy 413
Solidification of alloy 413 (11'4%Si, 0·46%Fe,
0'090/0Cu,0'180/0Mn, O'030/0Mg,l·l%Zn) began with
the formation of the dendritic network, which, owing
to growth kinetics, occupied aIarger volume of the
sample than was expected based on the equilibrium
diagram. While the dendrites grew, Si was enriched
in the interdendritic regions, leading to formation of
primary Si particles in the structure. During the
eutectic reaction, Al, particles dominated as the Fe
bearing phase at low cooling rates (e.g. 0·3 K S-l),
and AIlSphase dominated at the higher cooling rates
(e.g. 5 K s- 1). The solidification reactions and the
resulting phases are presented in Tables 5 and 6.
Hypereutectic alloy 390
Two compositions of 390 alloy were investigated. One
was 390.0 (15'00/0Si, 0·30/0Fe, 5'50/0Cu, O'Ol%Mn,
0'650/0Mg, 0'00650/0Zn, O'Ol%Ti, without Padded).
The other was B390.1 (17'450/0Si,0·74%Fe, 4·81%Cu,
O'27%Mn, O'560/0Mg,1·00%Zn, 0'060/0Ti,and minor
amount of Pl. The solidification reactions and the
resulting phases formed in these two alloys are listed
in Tables 7 and 8.
In alloy 390.0, because it had no P, the primary Si
crystals were very large." The eutectic areas showed
Table 6
Phase
1
2
other complex eutectics. Because of the low Mn
content of this alloy, the Als phase was the only Fe
bearing phase observed at cooling rates between
0·6 K S-l and 100 K S-l. When the alloy had a high
Fe content (1'32%), but a low Mn content (0'12%),
the second reaction following the formation of dendrites was the formation of very large Al, particles.
These large particles were found even at high cooling
rates (e.g. 100-150 K s -1). When the alloy had a high
Fe content (1'35%) and the Mn content was 0·48%
(Fe/Mn = 2'8), a strong reaction occurred resulting
in the precipitation of a mixture of AIlS and Al, preeutectic particles. When the alloy contained low Fe
(0'63%) and high Mn (0·4%; Fe/Mn = 1'6), the AIlS
phase dominated as the Fe bearing compound, and
no trace of the Al, phase was found over a wide
range of cooling rates (0'7-100 K s -1).
No.
Phase
Characteristics
1
oc-AI*
Primary Si
Dendrites
Big grey particles
Si
AlsFeSi
Grey
Needle
AI,sMn3Si2*
Brown Chinese script
2
3
4
5
Black
* Confirmed
(XRD).
Materials Reviews
1995
Vol. 40
No.6
Phases observed by optical microscopy,
SEM, and EDX in 413.0 alloy
by XRD.
Wang et a/.
Table 7
Reactions during
and 8390.1 alloys
Reaction
no.
Reaction
1
2
Primary Si
Development
3
L-AI
L-AI
in 390.0
solidification
of dendritic
network
+ Si + AlsFeSi
+ Si +AI1S(Mn,FebSi2t
3at
3bt
4
5
L-AI + Si +AlsFeSit
L-AI + Si + Mg2Si
L+ Mg2Si
6
-AI +S1 +AI2Cu +AlsMgaCu2Sia
L-AI +AI2Cu +AlsMnaCU2Sia+Si
Suggested
temp.,oC
Reaction
no.
636*, 670t
561*, 557t
575
1
2
573t
575t
555
507
eutectic Si, Als needles, large amounts of Al2 Cu, and
some AIsMgsCu2Si6 particles. Most of the Mg2Si
seemed to have consumed during reaction no. 5
(Table 7). In alloy B390.1, due to the higher Si content
and the more effective nucleation, the primary Si
particle density was higher. Increasing the cooling
rate from 0·5 to 4 K S-l did not seem to influence the
primary precipitation to any significant extent. A
difference from the 390.0 alloy was that in the eutectic
reaction of B390.1 alloy, the AIls phase, as well as
the Al, phase, formed simultaneously with the other
phases.
AI-Mg alloys
Alloy 518.2 (O'l%Si, 0'16%Fe, 0·01%Cu, 0·01%Mn,
7'6%Mg, 0'02%Zn) was investigated. The solidification reactions, and the various phases formed are
presented in Tables 9 and 10.
The solidification sequence started with the development of a dendritic network at --610°C. In an
AI-Mg binary alloy system, one would expect a final
eutectic reaction involving the precipitation of the
Al, Mg, phase to occur at 450°C. However, in this
alloy, because the Fe concentration (initially 0'160/0)
increases in the interdendritic areas and reaches a
level above 1·8% at temperatures below 550°C, Al3 Fe
needles precipitate. At the low level of Si in this alloy
(0'1 %), some Mg2Si might also form together with
A13Fe. Finally, a complex eutectic reaction completes
solidification
L ~ Al + Al3Fe + Mg2Si + AIsMgs
The equilibrium temperature for this reaction is
449°C. The actual reaction was experimentally
detected at 430-440°C. Due to segregation, the relative rate of the final eutectic reaction and the quantity
of eutectic formed increased with increasing the
cooling rate.
Phases observed by optical microscopy,
SEM, and EDX in 390.0 and 8390.1 alloys
No.
Phase
Cha racteristics
1
a-AI
Primary Si
Dendrites
Big grey*
Grey, large bulk]
Grey
2
3
Si
4
AI1S(Mn,FebSi2
5
6
AlsFeSi
AI2Cu
Brown Chinese script
Needle
Pink
7
AIsMgaCu2Sia
Grey, brown bulk
* 390.0 alloy only; t 8390.1 alloy only.
Reactions
alloy
during
die casting alloys
solidification
3
4
5
in 518.2
Suggested
temp.,oC
Reaction
Development
233
of dendritic
612
612
network
L-AI
L-AI
+ AI3Fe
+ AI3Fe + Mg2Si
L-AI
L-AI
+ Si + M92Si
+AI3Fe + Mg2Si +AlaMgs
587
555
448
512
* 390.0 alloy only; t B390.1 alloy only.
Table 8
Table 9
Aluminium
Jaquet and Hotz40 developed a procedure for quantitatively describing the microstructure of aluminium
foundry alloys. In this procedure, the microconstituents considered to be relevant were aluminium, silicon, AI-Si eutectic phase, intermetallic particles, and
microporosity. The parameters calculated in order to
describe quantitatively the microstructure were area
fraction of the eutectic phase, mean chord of the
aluminium and AI-Si eutectic phase, area fraction,
length, breadth, shape factor, and distribution of the
Si plus intermetallic particles, as well as the volume
fraction, length, and shape factor of the micropores.
The analysis indicated that a relationship existed
between the mean chord and the secondary dendrite
arm spacing of the aluminium phase.
Properties of typical aluminium die
casting alloys
Tables 11-14 (Refs. 15, 41) present selected mechanical properties, physical properties, and performance characteristics of typical aluminium die casting
alloys.
Effect of process parameters
Effect of die casting conditions
Yamamoto et ai.42 studied the metal flow and the
solidification behaviour of die castings made from
aluminium alloys ADC10 and ADC12. In their experiments the molten metal was poured into the shot
sleeve of the die casting machine at 640°C. It was
found that the temperature of the metal decreased
and reached the solidifying temperature rapidly so
that the metal injected into the die cavity was in a
liquid-solid state. Nishi et ai.43 investigated the solidification phenomena inside the shot sleeve and the
development of the microstructure of ADCI0 alloy
die castings. The samples were produced using a 90 t
locking force cold chamber die casting machine. The
as die cast microstructure of ADCI0 alloy consisted
of a coarse (X-AI phase with DAS > 5 urn, and fine
eutectic structures. The amount of coarse (X-AI
increased as the time between pouring the molten
metal into the shot sleeve and injection increased,
Table 10
Phases observed by optical microscopy,
SEM, and EDX in 518.2 alloy
No.
Phase
1
a-AI
Dendrites
2
3
AI3Fe
Mg2Si
Grey needles
Light brown particles
4
AlaMgs
Black particles
International
Characteristics
Materials Reviews
1995
Vol. 40
No.6
234
Wang et al.
Table 11
Aluminium
die casting alloys
Typical mechanical properties
Tensile strength,
MN m-2
of aluminium
die casting alloys (after Ref. 15, except where stated)
Yield strength
Elongation
(0'2% offset), MN m-2
in 50 mm, %
After
After
After
After
After
Hardness,
Fatigue strength
(R. R. Moore
Alloy
Temper
Ref. 41
Ref. 15
Ref. 41
Ref. 15
Ref. 41
Ref. 15
H8*
Shear
strength,
MN m-2
360.0
Ft
170
170
2·5
F
324
317
172
A360.0
364.0
380.0
300
320
165
159
3'5
3'0
5'0
7'5
75
75
190
180
140
120
160
160
165
159
2'5
3·5
3'0
4'0
80
75
190
140
190
140
200
140
120
80
80
170
170
50
50
130
130
130
120
80
200
140
After
A380.0
383.0
384.0
390.0
390.0
8390.0
392.0
413.0
A413.0
C433.0
443.0
513.0
515'0
518.0
296
F
F
F
320
331
324
320
310
F
F
324
279
296
330
280
T5
320
290
300
290
230
F
F
F
250
270
140
130
100
290
296
241
F
F
228
276
283
310
F
F
150
170
240
310
3'5
2'5
172
241
265
<1
1'0
1'0
1'0
262
145
110
<1
<1
2'5
3'5
9
<0'5
2'5
3'5
110
152
190
9'0
10'0
10'0
186
5
8'0
specimen,
5 x 108 cycles),
MNm-2
*500 kg load on 10 mm ball.
tAs cast.
and also as the pouring temperature decreased. It
was also found that the coarse a-AI phase formed in
the shot sleeve before injection.
In addition to the coarse a-AI phase, there were
two other types of abnormal structures which formed
in the shot sleeve and remained in the final microstructure. The first was a scattered structure that
exhibited a planar interface with the matrix. The
second was a massive structure that agglomerated
coarse a-AI phase and coarse eutectic Si. Iwahori?"
studied the scattered structure and indicated that
commercial aluminium die castings of alloy ADe12
often included a number of scattered structures that
are caused by the breakdown of solidified layers in
the metal sleeve. The quantity of scattered structures
was governed by the solidification behaviour of the
molten metal in the sleeve at the shot and may be
estimated from the heat capacity of the molten metal
per unit area of the sleeve. Nishi et al.45 found that
with increasing the injection velocity and/or the temperature, the microstructure of die cast aluminium
Typical physical properties
Table 12
Specific
gravity*
Density,
kg m3
F
F
2'68
2'68
2'63
2'76
F
F
2'76
2'70
F
2'73
2'73
2'66
2685
2685
2630
2740
2740
2713
2740
Alloy
Temper
360.0
A360.0
364.0
380.0
A380.0
384.0
390.0
390.0
F~
413'0
A413.0
443.0
518'0
A535.0
F
T5
F
F
F
F
F
2'66
2'69
2'53
2'54
* Specific gravity and weight
t International
2740
2657
2657
2685
2519
2547
of aluminium
t'-I
die cast alloys (after Ref. 15)
Approxi mate
melting range,
Electrical
conductivity,
°c
%IAcst
570-590
570-590
560-600
520-590
520-590
480-580
510-650
510-650
37
37
575-585
575-585
575-630
540-620
550-620
39
39
37
30
27
27
23
25
24
24
23
data in this table assume solid (void free) metal.
annealed copper standard.
~As cast.
lnternational
alloys became finer, and the measured mechanical
properties (particularly tensile and Charpy impact)
improved. On the other hand, excessive shrinkage
microporosity and a coarse dendrite structure were
characteristic of specimens produced under low
pressure.
Kainov et ai.46 also studied the effect of cooling
rate on the microstructure and properties of AI-Si
die casting alloy A12. Using ADCl2 aluminium alloy
(ll'82°~Si and 2'06%Cu), Suzuki et al.47-found that
the dendrite cell size of die cast specimens was less
than a tenth that of sand cast specimens, and increased
linearly from the surface towards the centre of the
casting. The eutectic Si was spherical and
1 urn in
diameter in the layer 0,05-0,1 mm from the surface
of the casting, and became acicular and larger towards
the centre. The axis ratio for the acicular Si particles
varied between 3·4 and 13·8. The amount of crystallised a-AI rapidly increased within a layer 0·5 mm
away from the surface, and remained constant from
that point inwards towards the centre.
Materials Reviews
1995 Vol. 40
NO.6
Thermal
conductivity
at 25°C,
Wm-1 K-1
0'35
0'35
0-29
0'26
0'26
Coefficient of thermal
perK x 10-6
expansion
20-100°C
20-300°C
20'9
21-1
22'9
22'9
22'9
22'5
22'7
22'1
20'9
21'2
21'1
20'3
18'5
18'0
0'23
0'32
0'32
0'37
20'5
22;5
0'37
0'34
0'24
0'24
24'1
24'1
26'1
26-1
Wang et ale Aluminium
Table 13
Die casting and other characteristics
Alloy
360.0
A360.0
380.0
A380.0
383.0
384.0
390.0
8390.0
392.0
413.0
A413.0
C443.0
518.0
to hot
cracking
Pressure
tightness
1
1
2
2
2
2
2
2
2
4
4
3
1
1
3
5
2
1
2
4
4
4
1
1
3
5
(ASTM standard 85-92a) (after Ref. 41)
Other characteristics
Die casting characteristics
Resistance
Die
filling
capacity
Antisoldering
to die
3
3
2
2
1
1
1
1
1
1
1
4
2
2
1
1
2
2
2
2
2
1
1
4
5
5
Strength
Resistance
to
corrosion
Machining
Polishing
Electroplating
Anodising
(appearance)
3
3
3
3
2
3
3
3
2
2
1
1
1
2
3
3
3
3
3
2
5
3
3
3
3
3
4
5
5
5
5
5
2
1
2
2
4
4
3
5
3
3
2
2
2
3
5
5
5
4
4
2
1
5
1
3
3
3
5
5
5
5
5
4
1
Rating system: alloys are rated 1 to 5 according to the positive to negative qualities in the listed categories;
Alloy
360.0
A360.0
364.0
380.0
A380.0
484.0
390.0
413.0
C443.0
515.0
518.0
319.0 (S,P)*
A356.0 (S,P)
Characteristics
Resistance to
hot tearing
1
1
2
2
2
2
2
1
2
4
5
2
1
A443.0 (S)
1
443.0IP)
1
2
2
1
380.0t
390.0t
413.0t
of aluminium
2
1
1 denotes the best performance;
5 the poorest.
%
Shrinkage
tendency
1
2
2
2
2
2
3
3
2
2
3
3
3
3
3
5
4
Effect of casting design
Fluidity
1
1
1
temps.
1
1
3
3
4
4
4
5
5
5
5
3
3
die casting alloys (after Ref. 15, except where stated)
Pressure
2
3
5
5
2
1
of
elevated
The effects of dimensional parameters on the mechanical properties of aluminium die castings were studied
by Pushmashev." The alloy tested contained 9'2%Si,
l'40/0Cu, 0'6s%Mg, O'S%Mn, 0'2%Cr, 0'20/0Ti, and
0·4 Fe. The casting temperature was varied between
600 and 7S0°C, and the die temperature was varied
between SOand 2S0°C. Part properties were evaluated
as functions of the ratio of the area of the crosssection to its perimeter (spr). The results indicated
that tensile properties in general were inversely related
to spr and that as spr increased, the scatter in the
data decreased noticeably.
Suzuki et aI.52 studied the 'mass effect' caused by
changes in casting wall thickness on various properties of AI-12%Si-2'S%Cu (ADC12) die castings.
The wall thicknesses studied ranged from 2 to 10 mm.
Their study showed that the specific gravity,
coefficient of thermal expansion, modulus of elasticity,
hardness, ultimate tensile strength, 0·20/0 yield
tightness
1
2
1
2
2
2
Chemical
oxide
coating
dimension instability and is both time and energy
efficient.
In aluminium die castings, the surface layer had a
Vickers microhardness > lOS and an a-phase content
< 60%. This layer is usually referred to as the 'chill
zone'." The chill zone is usually thinner in heavy ..
section castings. Casting parameters, such as metal
temperature, injection pressure, and gate velocity, had
little effect on the formation of the chill zone, but the
die temperature had a significant effect. Metal flowline
patterns were observed in aluminium die castings."
These flowline patterns were the result of differences
in the solidified structure. They appeared as bright
and dark regions with thicknesses ranging from S to
SOurn. Presumably the bright regions were rich in
primary aluminium, and the dark regions were rich
in eutectic Si. The orientation of these patterns was
totally random.
Lin et aI.50 indicated that metastable phases and
residual stresses may be present in aluminium die
castings (ADC12 alloy) if the castings are cooled
rapidly. These metastable phases and residual stresses
can cause dimensional instability of the castings. The
mechanism of formation of the instability was studied,
and a two stage aging technique was developed. Lin
et al. claim that this aging technique eliminates the
Table 14
235
die casting alloys
1
2
2
1
2
1
3
5
5
2
1
1
2
2
2
1
Corrosion
resistance
3
3
4
2
3
5
4
2
2
2
1
1
3
3
3
4
4
5
2
1
2
1
3
2
1
1
2
2
5
2
2
3
Machinability
Weldability
4
4
3
4
4
4
2
4
4
4
4
3
2
2
4
3
4
5
3
4
4
1
4
2
4
*
S sand casting, P permanent mould casting, listed for comparison.
t Data for these alloys after Ref. 26.
Rating system as for Table 13.
International
Materials Reviews
1995
Vol. 40
No.6
236
Wang et al.
Aluminium
die casting alloys
strength, elongation, bending strength, flexibility,
compressive strength, compressive yield strength,
compressive strain, shear strength, impact strength,
and fatigue strength were all dependent on the casting's wall thickness. The wall thickness t was related
to the strength S by the general equation: S = at?",
where a and n are empirical constants. In another
study, Suzuki et ai.8 found that the segregation of Si,
Cu, and Fe caused a difference in the specific gravity,
the coefficient of thermal expansion, and the lattice
constant between the chill zone and the inner parts
of the casting. This segregation is also claimed to' be
responsible for a 30-65 % increase in the mechanical
properties of the chill zone over those of the inner
regions of the casting. On the other hand, the hardness
and the wear resistance of the castings were reduced
due to the formation of primary a-crystal in the
chilled surface.
Hotta et ai.53 investigated the scatter in strength
values obtained for die castings of alloys ADC10 and
ADC12. The strength of specimens obtained from
different parts of die castings was measured. It was
found that specimens cut from locations less than
150-200 mm away from the gate had strength values
ranging between 200 and 350MN m -2. These specimens were found to be generally defect free and their
strength varied with the casting thickness. Specimens
cut from locations beyond 150-200 mm from the gate
had strength values <200 MN m -2. These specimens
generally contained defects - particularly lumped,
thin, and scattered defects - and their apparent
specific gravities were low. While the lumped defects
were responsible for reducing both apparent specific
gravity and tensile strength, and thin and scattered
defects reduced the tensile strength, but hardly affected the apparent specific gravity. Hotta et al. also
noted that the tensile strength for these specimens
varied almost linearly with the fraction of defect area
in the fracture surface.
Effect of process parameters
Czikel''" investigated methods of preparing testbars
for obtaining reliable data on die casting alloys. The
effect of the position of the testbar in the mould, the
testbar density, and the casting time and temperature
on the hardness, strength, elongation, and toughness
of GD AISi9Cu3 alloy were studied. The study clearly
showed that data obtained from testbars prepared in
different ways differed significantly. Czikel et ai.55 also
evaluated several properties of die cast specimens
made from this alloy. A modified die was used to
prepare the test specimens. In this die impact bending
test specimens and tensile test specimens were produced together. The measured data included density,
impact bending strength, hardness, and other mechanical properties. It was found that pouring temperature,
as well as pouring rate, affected all properties.
Nishi et ai.45 showed that the pressure applied
during metal filling affected the mechanical properties
of ADC10 alloy. With an increase in injection velocity
and/or a rise in temperature, the microstructure
became finer and the measured mechanical properties
(tensile and Charpy impact) were enhanced. Maglia
et ai.56 also showed that the mechanical properties of
International
Materials Reviews
1995
Vol. 40
No.6
PN 424352 alloy were affected by changes in the
speed of filling and by changes in melt temperature.
Bratukhin et ai.57 studied the effects of additional
pressure applied during solidification on the structure,
porosity, and mechanical properties of die casting,
high temperature, aluminium alloys ATSR-IV and
VAL8. They found that porosity decreased and ductility increased when the alloys solidified under
pressure.
Iwahori''" determined the tensile strength of the
'scattered' structure/normal structure interface and
found it to be only 9 kg mm - 2. Therefore, the presence
of the scattered structure, which depended on the
solidification behaviour of the metal in the sleeve at
the shot, lowered the strength of commercial die
castings and caused pressure leakage defects near
the gate.
Effect of heat treatment
Jacob'" studied the effect of heat treatment on elongation of die castings of a 9'95%Si, 3'6%Cu, 0'5°A>Fe,
0'50/0Zn,and 0·020/0Ti alloy. In his experiments, cylindrical samples 6·18 mm dia. were cast in a machine
having an injection pressure of 110 MPa and a closing
force of 1200 kN. Samples were divided into three
groups. Group I was untreated. Groups II and III
were heat treated for 4 h at 300°C. Group III was
cooled slowly in the oven while group II was instantly
removed after the 4 h. The results showed a 400/0
improvement in elongation combined with a 20°A>
decrease in rupture strength and Brinell hardness
in both heat treated groups of samples. Work on
alloy LM24 (Ref. 31) showed that Mg additions
(0'3% max.) allowed a reduction in the stabilisation
annealing temperature.
Fatigue properties
The die casting process is known to be capable of
producing very high fatigue properties. Oedcgaard'"
reviewed static and dynamic mechanical properties of
aluminium casting alloys and focused on the fatigue
mechanisms. His review indicated that three major
microstructural parameters had significant effects on
the fatigue properties of a 'wide range of aluminium
die casting alloys: (i) porosity 'and shrinkage defects;
(ii) DAS; and (iii) fraction, size, and crystallographic
orientation of intermetallic compounds. Klein and
Wust60 studied the effects of filling velocity, final
pressure during solidification, and specimen crosssectional area on the fatigue properties of alloy
GD AISi9Cu3. The results show a marked dependence
of fatigue properties on die casting conditions.
Chijiiwa et ai.61 measured the fatigue crack growth
in alloy ADC12 using specimens of thicknesses ranging from 2·9 mm to 25·4 mm. Their results indicated
that both the fatigue toughness K1c, and the threshold
stress intensity factor Kth, were independent of the
specimen thickness. Heat treatment of the alloy
caused an increase in Kfc, and a slight change in Kth•
Egashira et ai.35 investigated the effects of Si particle
size, strength of matrix, and addition of Mn and Fe
on the fatigue crack propagation in high purity AI-Si
casting alloys. They found that a fine distribution of
Si particles caused a decrease in the crack propagation
rate in an AI-12%Si alloy. In an AI-70/oSi alloy and
Wang et al.
an AI-6·3 Si-0·32%Mg
alloy the. decrease in crack
propagation rate was pronounced in the high stress
intensity range, when the strength of the matrix was
high. In the threshold region, however, the crack
propagation rate was reduced when the matrix had a
low strength due to crack closure effects. Egashira
et al.35 also showed that the fatigue crack propagation
rate in the high stress intensity range was reduced
by the addition of Mn and Fe to AI-Si-Mg alloys.
It was also found that the Fe content of alloy
GK AISi12CuNiMg had a noticeable effect on the
alloy's fatigue fracture characteristics.
%
Shrinkage
Garber et a1.62 studied the density and shrinkage
characteristics of A380 alloy and found that the
pouring temperature did not have an effect on either
property. However, they reported that the internal
volumetric shrinkage decreased and the external volumetric shrinkage increased when the solidification
and the cooling rate were increased. The total volumetric shrinkage, however, remained constant, equalling the sum of the internal and external values and
independent of the solidification and cooling rates. It
was rcported'" that Mn additions to alloy LM24
(0'5% max.) could reduce shrinkage.
Conclusion
Recent developments in die casting technology have
significantly expanded the commercial applications of
die cast aluminium products. This is manifested in
the sales of die cast aluminium parts in the USA
which exceeded $5 000 000 000 in 1995. However, it
is evident that the development of new die casting
alloys, the optimisation of existing alloys, and the
accurate measurement and documentation of reliable
mechanical and physical properties for these alloys
have categorically lagged behind. Realising the need
in these areas, the North American Die Casting
Association and the US Department of Energy are
jointly sponsoring a project at Worcester Polytechnic
Institute aimed at characterising the interactions
between alloy chemistry, die cast microstructure, and
alloy properties. This literature review which focuses
on collecting and critically analysing the published
information on aluminium die casting alloys was
prepared during the early stages of the project.
Acknowledgements
This review was supported. by the US Department
of Energy and the North American Die Casting
Association (NADCA).
References
1. 'Non-ferrous
metal data 1992', 90-91;
1993, New York,
American Bureau of Metal Statistics.
2. D. P. KANICKI (ed.) Mod. Cast., 1993, 83, (12), 20~21.
3. 'Aluminum .statistical review for 1988', 9; 1989, Washington,
DC, The Aluminum Association.
4. c. E. MOBLEY: 'Quality of die casting', presented at Defining the
State of Die Casting Technology Workshop, Worcester, MA,
USA, March 1993, US Department of Energy/North
American
Die Casting Association/University
of Northern Iowa.
Aluminium
die casting alloys
237
5. R. w. NEGEL: Die Cast., 1993, 37, (1), 12-14.
6. F. KLEIN and J. WUST: Giesserei, 14 May 1990, 77, (10),344-351.
7. F. KLEIN and J. WUST: Lioarski Vestn., 1989,36, (5-6), 126-146.
8. M. SUZUKI: J. Jpn Inst. Light Met., March 1971,21, (3), 111-119
(in Japanese).
9. A. FLORES, J. C. ESCOBEDO, M. MENDEZ, and 1. MENDEZ: in Proc,
16th Int. Die Casting Congo and Exposition, Detroit, MI, USA,
September-October
1991, North
American
Die Casting
Association, 293-297.
10. J. L. JORSTAD: in Proc. SDCE-79, 10th Int. Die Casting Cong.,
St. Louis, MO, USA, March 1979, Society of Die Casting
Engineers,9.
11. S. KUMAGAI and Y. KOJIMA: Aluminum (Japan), April 1979,
(154), 41-54.
12. T. SmKATA and K. SATO: J. Jpn Inst. Light Met., March 1973,
23, (3), 99-105 (in Japanese).
.
13. w. F. KEHLER: 'Handbook
of international
alloy compositions
and designations',
Vol. 3, 'Aluminum';
1980, Columbus, OH,
Metals and Ceramics Information
Center, Battelle Columbus
Laboratories.
14. 'Metals and alloys in the United Numbering System', 5th edn;
1989, Warrendale, PA, Society of Automotive Engineers.
15. D. M. STEFANESCU, J. R. DAVIS, and J. D. DESTEFANI (eds.): 'ASM
metals handbook',
9th edn, Vol. 15, 'Casting'; 1988, Metals
Park, OH, ASM International.
16. Alloy Dig., AI-308, October
1990; AI-311, January
1991;
AI-313, March 1991; AI-215,.May
1984; AI-315, April 1991;
AI':"'-242,January 1983.
17. L. F. MONDOLFO: 'Metallography
of aluminum alloys'; 1943,
London, Chapman & Hall.
18. L. F. MONDOLFO: 'Aluminum alloys: structure and properties';
1976, London, Butterworths.
19. J. L. JORSTAD: Trans. AFS, 1971, 79, 85-90.
20. A. FRANEK: Sb. Vys. Sk. Chem.-Technol. Prate Anorg. Chem.
Technol. B, 1973, 17, 67-72.
21. L. A. GASPARYAN,L. A. KRYUKOVA, and s. A. AKOPYAN: Mezhuvuz.
Sb. Nauchn. Tr. Erevan. Politekh. Inst., 1978, (2), 37-43.
22. H. OHUcm: J. Jpn Inst. Light Met., April 1983, 33, (4),188-194.
23. v. M. KARPACHEV, A. A. OFENGENDEN, and v. s. ZOLOTOREVSKII:
Tsvetn. Met., June 1990, (6), 90-92.
24. J. L. JORSTAD: 'Influence of aluminum casting alloy metallurgical
factors on machinability',
Report SAE No. 800486, Society of
Automotive Engineers, Warrendale, PA, 1980.
25. E. L. ROOY: in 'ASM metals handbook',
9th edn, Vol. 15,
'Casting', (ed. D. M. Stefanescu et al.), 743-770; 1988, Metals
Park, OH, ASM International.
26. J. E. GRUZLESKI: 'The treatment. of liquid aluminum-silicon
alloys'; 1990, Des Plaines, IL, American Foundrymen's
Society.
27. S. KUMAGAI and Y. KOJIMA: Aluminum (Japan), April 1979,
(154), 41-54.
28. R. DasGUPTA, C. C. BROWN, and s. MAREK: Trans. AFS, May
1989, 97, 245-254.
29. R. DasGUPTA, C. C. BROWN, and s. MAREK: in Proc. Int. Conf. on
'Advanced aluminium and magnesium alloys', Amsterdam, The
Netherlands, June 1990, ASM Europe, 485-492.
30. A. T. JOENOES and J. E. GRUZLESKI: Cast. Met., 1991,4, (2),62-71.
31. Stoperitidende, 1983, 49, (2), 49-50.
32. L. BACKERUD, G. CHAI, and J. TAMMINEN: 'Solidification characteristics of aluminum alloys', Vol. 2, 'Foundry alloys'; 1990, Des
Plaines, IL, American Foundrymen's
Society.
33. S. HOLECEK: Sb. Vys. Sk. Chem.- Technol. Praie Anorg. Chem.
Technol. B, 1983,28, 39-53.
34. T. KOBAYASm, M. NIINOMI, I. HIROTA, and H. EGASlllRA: in Proc.
RASELM '91 on 'Recent advances in science and engineering
of light metals', Sendai, Japan, October 1991.
35. H. EGASlllRA, M. NIINOMI, T. KOBAYASm, and s. KOHMURA: J. Jpn
Inst. Light Met., December 1989, 39, (12), 878-885.
36. TOYOTA JIDOSHA: 'Aluminum
alloy for die casting',
Pat.
no. JP8619753A-KoKai,
Japan, 7 July, 1984.
37. M. RICHARD: Fonderie, October 1978, (382), 281-285.
38. Y. AWANO and Y. SlllMIZU: Trans. AFS, 1990, 98, 889-895.
39. F. KLEIN: Giesserei, 19 March 1979, 66, (6), 138-142.
40. J. C. JAQUET and w. HOTZ: Cast. Met., 1992,4, (4), 200-225.
41. '1993 Annual Book of ASTM standards',
Vol. 02.02; 1993,
Warrendale, PA, ASTM.
42. Y. YAMAMOTO, Y. IWATA, and M. NAKAMURA: Imono (J. Jpn
Foundrymen's Soc.), 60, (12), 770-776.
43. N. xtstn, T. KOMAZAKI, and Y. TAKAHASm: Imono (J. Jpn
Foundrymen's Soc.), 1991, 63, (4), 347-352.
International
Materials Reviews
1995
Vol. 40
No.6
238
Wang et al.
Aluminium
die casting alloys
44. H. IWAHORI: J. Jpn Inst. Light Met., September 1984,34, (9), 13.
45. N. NISHI, H. SASAKI, T. HIRAKAWA, and Y. TAKAHASI: Imono
(J. Jpn Foundrymen's Soc.), December 1988, 60, (12), 777-783.
46. v. M. KAINOV, v: V. KUZNETSOVA, and L. A. URGALKINA: Sov.
Cast. Technol., June 1990, (6), 14-16.
47. M. SUZUKI and K. FURUMOTO: J. Jpn Inst. Light Met., May 1971,
21, (5), 350-357.
48. M. SUZUKI, K. FURUMOTO, and K. SAKAMOTO: J. Jpn Inst. Light
Met., June 1971, 21, (6), 379-384.
49. M. SUZUKI and A. SASAZAKI: J. Jpn Inst. Light Met., July 1971,
21, (7), 456-462.
50. w. LlU, C. CHEN, S. ZHANG, and z. DENG: J. Cent.-South Inst.
Min. Metall., October 1987, 18, (5), 542-547.
51. P. I. PUSHMASHEV: Liteinoe Proizvod., July 1980, (7), 17-19.
52. M. SUZUKI and K. FURUMOTO: J. Jpn Inst. Light Met., January
1971, 21, (1), 36-45.
53. S. HOTTA, K. SARUKI, T. ASANO, and M. NAKAMURA: J. Jpn Inst.
Light Met., March 1989,39, (3), 203-209.
International
Materials Reviews
1995
Vol. 40
No.6
54. J. CZIKEL: Livarski Vestn., 1988, 35, (4), 97-108.
55. J.
CZIKEL,
G. .
SABATH,
and
G.
SCHINDELBACHER:
Giessereiforschung, 1988, 40, (1), 23-32.
56. P. MAGLIA, V. TALIAN, and P. MOKRY: Slevarenstvi, June 1983,
31, (7), 330-333.
57. v. A. BRATUKHIN, S. Z. ZLOTIN, Y. I. TRIFONOV, A. V. SHCHEKIN,
and M. Y. TRIFONOV: Sov. Cast. Technol., November 1990,
(11), 28-31.
58. S. JACOB: Fonderie Fondeur Aujourd'hui, Feburary 1988, 72,
38-39.
59. J. A. OEDEGAARD: Gov. Res.
Announc.
Index,
PB
92-103027jXAB,
28 May 1991, 99.
60. F. KLEIN and J. WUST: Metall, June'1990, 44, (6), 568-573.
61. K. CHIJIIWA, K. KANAZAWA, and K. MINAMI: Imono (J. Jpn
Foundrymen's Soc.), December 1988,60, (12), 784-789.
62. L. W. GARBER and A. B. DRAPER: Die Cast Eng., NovemberDecember 1979, 23, (6), 46-49.