DAY 18: FERROUS ALLOYS, ALUMINUM
AND MORE
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Cast Iron
Aluminum
Titanium
Copper
Goals for tomorrow: Whatever we miss today +
Zn, Mg, other metals. Review. Material
selection discussion.
TYPES OF CAST IRON
1.
2.
3.
4.
5.

Grey
White
Malleable
Ductile
Compact Graphite
The form in which the carbon appears in the
iron matrix is very important, and determines
the use and properties.
CAST IRON
Notes:
1. Significance of
Eutectic
(ledeburite is the
name of the
eutectic mix of g
and Fe3C.)
2. Silicon is often
an important 3rd
component
steel
Cast iron
FE-C TRUE EQUILIBRIUM DIAGRAM
T(°C)
1600
Graphite formation
promoted by
L
1400
• Si > 1 wt%
g
Austenite
1200
• slow cooling
Liquid +
Graphite
g +L
1153°C
4.2 wt% C
1000
g + Graphite
+g
800
0.65
740°C
600
Adapted from Fig.
11.2,Callister 7e. (Fig. 11.2
adapted from Binary Alloy
Phase Diagrams, 2nd ed.,
Vol. 1, T.B. Massalski (Ed.in-Chief), ASM International,
Materials Park, OH, 1990.)
400
(Fe)
 + Graphite
0
1
2
3
4
90
100
Co , wt% C
4
GRAY CAST IRON
By far the cheapest and most common.
 Presence of Silicon + slow cooling rate causes
graphite to form instead of cementite, Fe3C.
 The graphite is in flake form. See micrograph.
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What we have:
1. Graphite flakes.
Look like
cornflakes
2. Pearlite matrix
http://www.nikonsmallworld.com/gallery/search/description
s/cast+iron/1
MORE ON GRAY IRON
The presence of the sharp-cornered flakes creates
stress risers which make gray iron very brittle.
 However, there are good results as well

1.
2.
3.
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Low shrinkage – very castable!
Excellent machinability
Excellent damping
This material is very useful in situations where
no tensile strength is required.
PROPERTIES
AND
USES
About 3.5% C, 2% Si.
 UTS about 40 Ksi
 Ductility and yield strength not given, because it’s
really brittle.
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How do the properties of
cast iron make it such an
ideal material for this
application?
WHITE CAST IRON
We cool fast enough and with less Silicon so that
graphite flakes do not form.
 The result is a material with lots of cementite,
Fe3C. Extremely hard and brittle. Result:
1. Not easily machined
2. Often you have white iron on the surface and
grey iron in the interior of the casting. This is a
chilled casting and is desirable.
3. Uses: where very hard, wear resistant surface
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WHITE CAST IRON
Massive cementite – white + Pearlite
DUCTILE CAST IRON
Nodular iron or Spherical. We take away as
much S as possible and innoculate with a Mg
alloy. This causes graphite to form in spherical
clumps instead of flakes. This has a tremendous
effect on mechanical properties.
 Yield: 276 MPA, 40 Ksi
 Ultimate: 414 MPA, 60 Ksi
 Ductile: 18% EL
 Please note that this stuff is castable. This is
very important – has steel like properties in a
casting!
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NODULAR / SPHERICAL CAST IRON
USES OF DUCTILE IRON
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Complex geometries + need for tensile strength.
Valve body
Shafts which take tension
Pump housings
Gears
Engine blocks
Ductile Iron can be really strengthened by austempering. That
way the spherical graphite lives in a bainite matrix.
http://www.ductile.org/didata/section4/4intro.htm
MALLEABLE IRON - BLACKHEART
This has similar properties to the previous iron.
But to get it, we start with white cast iron and
reheat it for an extended period of time (hours).
 The cementite decomposes into graphite in
clumps. (Recall that grey iron has sharp flakes).
 Consequently, we have ductility.
 This approach is not used as frequently now as it
was in the past.
 White cast iron is hard to get in thick sections,
therefore the same is true for malleable iron.
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COMPACT GRAPHITE IRON
A relatively new approach – get somewhere in
between gray and ductile as far as properties go.
 I’ll let you do the research. This one will not be
on the next quiz.
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TYPES OF CAST IRON
Gray iron
 graphite flakes
 weak & brittle under tension
 stronger under compression
 excellent vibrational dampening
 wear resistant
Adapted from Fig. 11.3(a) & (b), Callister 7e.
Ductile iron
 add Mg or Ce
 graphite in nodules not flakes
 matrix often pearlite - better
ductility
16
TYPES OF CAST IRON
White iron
 <1wt% Si so harder but brittle
 more cementite
Adapted from Fig. 11.3(c) & (d), Callister 7e.
Malleable iron
 heat treat at 800-900ºC
 graphite in rosettes
 more ductile
17
PRODUCTION OF CAST IRON
Adapted from Fig.11.5,
Callister 7e.
18
ALUMINUM FACTS
Light metal: 2.7 g/cm3 vs 7.9 g/cm3 for steel.
 Can be very strong: UTS up to 80 ksi.
Competitive with steel at a fraction of the weight.
 Very corrosion resistant. Forms a tenacious
passive oxide layer on the surface.
 Extremely plentiful in earth’s crust, yet very
hard to extract from its ore. Hall-Heroult process
requires extensive electricity for electrolysis.
 Very recyclable.
 Not good at high temperatures.
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PRECIPITATION HARDENING IN ALUMINUM
Super-saturated
Ageing- get
coherent precips
and get max
strength
Over-aging.
Precipitates
no longer
coherent.
AGEING CURVES
UTS
Ductility
A precipitation hardened Al alloy will be sensitive to exposure
to high temperatures over extended time, will be difficult to
weld and will be more prone to corrode.
TYPES OF ALUMINUM ALLOYS
Wrought, no heat treatment, but may be
strengthed with cold work.
 Wrought, heat-treatable and cold worked
 Cast, Heat treatable. Aluminum is very castable.
Lots of die casting is done. Due to low mp, about
660C.
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Fact: Al has a modulus of elasticity about 1/3
that of steel. Al structures will be far less stiff
than steel for the same geometry.
WROUGHT ALLOY
1100 series alloy. Basically commercially pure
Al. According to Matweb
 Yield: 103 Mpa, 15 Ksi.
 UTS: 110 Mpa, 16 Ksi.
 Ductility: 25%EL. (in 50mm)
 Widely used in cheap aluminum products. Not
for strength.
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WROUGHT – HEAT TREATABLE
The strongest Al is 7075. Alloys are Zn, Mg, and
a little Cu. This alloy depends of precipitation
hardening.
 Yield: 462 Mpa, 67 Ksi. (Competitive with steel.)
 UTS: 524 Mpa, 76 Ksi.
 Ductility: 11%EL. (in 50mm)
 Widely used in aerospace applications where a
superior strength to weight ratio is needed.
Aircraft structural parts.
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HOW IS ALUMINUM USED IN CARS
http://www.autoaluminum.org/main/newsreleases/automotive-aluminum-use-reaches-all-time-high-in
http://www.autoaluminum.org/main/aluminum-processes-andmaterials/aluminum-processes-and-materials
TITANIUM
Light metal: 4.5 g/cm3 vs 7.9 g/cm3 for steel.
 Can be very strong: UTS up to 200 ksi.
Competitive with steel at a fraction of the weight,
but you have to pay the price.
 Very corrosion resistant. Forms a tenacious
passive oxide layer on the surface.
 Very reactive at high temperatures. Has to be
produced in special process. Expensive.
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MORE ON TITANIUM
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Wikipedia says up to 77 tons will be used in each
A-380.
Extremely corrosion resistant.
Now also seeing commodity use. Be
careful, it might be a fake. I.e. golf
clubs!
Komsomolets: Soviet era
attack sub had Titanium
hull.
OR DID IT?
COPPER
Heavier than Fe, about 9.0 gm/cc.
 One of the earliest metals. MP 1100C.
 In unalloyed form, not very strong, but extremely
ductile. Yield: 5 Ksi, UTS: 30.5 Ksi, %EL = 60%.
 Electical conductivity is key to its use in all kinds
of electrical equipment and conductors.
 Copper is also the base metal for two families of
alloys:
1. Brasses (with Zn)
2. Bronzes (with Sn and other metals)
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Copper
Property
Industry/Type of Application
Aesthetics
Architecture, sculpture, jewelry, clocks, cutlery.
Door hardware, marine internal combustion engines, crop
Bactericide
treatments.
Plumbing tubes and fittings, roofing, general and marine
engineering, shipbuilding; chemical engineering, industrial processes
Corrosion resistance
including pickling, etching and distilling; domestic plumbing,
architecture, desalination, textiles, papermaking.
Electrical
conductivity
Low temperature
properties
Mechanical
strength/ductility
Non-magnetic
Non-sparking
Elasticity
Thermal
conductivity
Electrical power generation, transmission and distribution,
communications, resistance welding, electronics.
Cryogenics, liquid gas handling, superconductors.
General engineering, marine engineering, defense, aerospace.
Instrumentation, geological survey equipment, minesweepers,
offshore drilling.
Mining and other safety tools, oxygen distribution.
Electrical springs and contacts, safety pins, instrument bellows,
electronic packaging.
Heat exchangers and air-conditioning/refrigeration equipment,
automotive radiators, internal combustion engines, mining.
Copper
BRASS
Very attractive metal.
 Excellent corrosion resistance.
 Excellent ductility
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Cartridge brass: 30%Zn
Yield 63 Ksi
UTS 76 Ksi
Ductility %EL = 8%
(After cold working.)
BRONZE
Numerous alloys based on Sn, Ni, Aluminum, etc.
 Tin bronze: UTS is 45 ksi, Yield is 22 ksi, %EL =
25%. (Cast alloy)
 Used for bearings, bushings, fittings and gears.
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