WELLCOME
MAGNESIUM
A favorable strength-to-weight ratio
makes magnesium a
desirable material for automotive and
aerospace parts
New interest in magnesium has been recently
aroused due to the expansion of use of
magnesium alloys in the 1990s and, especially,
due to an appearance of high-strength magnesium
matrix composites as lightweight advanced
structural materials for automotive and aerospace.
Magnesium alloys are considered as possible
replacements for aluminum, plastics, and steels,
primarily because of their higher ductility, greater
toughness, and better castability.
Production of magnesium almost tripled
last decade, and the world production
capacity reached 515,000 tons per year in
2009 . Both the increased production of
magnesium and applications of new highperformance magnesium alloys have posed
a scientific and technical challenge to the
brazing engineering community.
Characterization of Base Metals
• Magnesium is the eighth most abundant element
and constitutes about 2% of the Earth's crust, and
it is the third most plentiful element dissolved in
seawater.
•
Although magnesium is found in over 60
minerals, only dolomite, magnesite, brucite,
carnallite, and olivine are of commercial
importance.
•
•Magnesium and other magnesium compounds
are also produced from seawater, well and lake
brines and bitterns.
Magnesium is the lightest and one of
the cheapest structural metals. Magnesium
alloys are environmentally friendly, lighter
than aluminum (only 2⁄3 of aluminum and
1⁄3 of titanium specific weights), better in
heat dissipation and heat transfer due to
high thermal conductivity of 51 W/m·K,
and exhibit excellent ability in shielding
electromagnetic interruption.
Low density, ~1.75 g/cm3, in combination
with A relatively a high tensile strength of 228–
290 MPa, heat resistance up to (450°C), and
oxidation resistance up to 500°C make
magnesium alloys attractive for various structures
in the automotive industries.
Especially, the magnesium alloys are attractive for
various aerospace industries, as well as in textile and
printing machines where lightweight magnesium parts
are used to minimize inertial forces at high speed .
Moreover, magnesium alloys are recyclable, which
minimizes their environmental impact. However, the
surface of magnesium alloys should be protected
because they corrode easily when exposed to
atmosphere.
• Mechanical properties (especially plasticity) of
magnesium Alloys depend on the fabrication
parameters and the testing temperature. For
example, a considerable change in mechanical
properties was observed for Alloy AZ31
fabricated by casting, extrusion, and rolling .
• The strength weakening is accompanied by a
remarkable increase in ductility. The elongation
increased from 21.5% to 66.5% as the test
temperature changed from RT to 250°C.
• Magnesium alloys with reduced aluminum
content AM60, AM50, and AM20 are suitable for
applications requiring improved fracture
toughness. However, the reduction in aluminum
results in a slight decrease in strength for AM
alloys .
• Alloys AS41, AS21, and AE42 are employed for
applications requiring long-term exposure at
temperatures above 120°C and creep resistance.
•
Magnesium compounds, primarily magnesium oxide,
are used mainly as refractory material in furnace linings
for producing iron and steel, nonferrous metals, glass, and
cement.
•
Magnesium oxide and other compounds also are used in
agricultural, chemical, and construction industries.
•
Magnesium alloys also are used as structural
components of machinery.
• Magnesium also is used to remove sulfur from
iron and steel.
•
Magnesium Alloy – Wire
The highly accurate magnesium alloy wire is 20 percent stronger than
extruded magnesium bar, which can be bent and coiled at the room
temperature. SEI' magnesium alloy wire is high specific strength.
* Tensile Strength 1.2 - 1.6 times (vs. Extruded)
1.3 - 1.8 times (vs. Die Cast)
* 0.2% Proof Stress 1.4 - 2.0 times (vs. Extruded)
1.6 - 2.5 times (vs. Die Cast)
Tolerance of dimensional accuracy is =<1/100mm.
Magnesium Alloy – Tube
The technology of wiredrawing skill would be used to produce for
magnesium alloy tube. Mechanical properties of pipe are further more
improved than conventional method. * Tensile
Strength 270MPa Achieved
* Dimensional Accuracy +/-0.1mm Achieved
* Linearity Error 1mm/m Achieved
* Bending Formability 2.8D Almost Achieved
Let us
summarize
!
Magnesium is the third most commonly used
structural metal, following Fe and Al.
The main applications of Mg are in order:
• component of aluminium alloys;
• in die-casting (alloyed with Zn);
• to remove S in the production of iron and
steel;
• the production of titanium in the Kroll
process.
Microstructures and Macrostructures
• Optical micrograph: Mg-ZnZr-(RE) alloy, cast and aged
(no soln treatment).
• Note coarse gb ppts.
Electron micrograph: MgNd-Zr alloy, cast, soln
treated and aged to peak
hardness. (Note PFZ at gbs)
Mg-Zr-Zn-(RE) helicopter
gearbox casing Bicycle
frame (alloy unspecified !
“6% additives”)
Magnesium alloy cast parts are gaining increasing attention
from the automotive sector where the aim is weight reduction.
However, the casting of magnesium alloys is still plagued with
problems that are difficult to solve: porosity, macrosegregation, oxide
entrainment, irregularity of microstructure, corrosion, machining
safety, etc.
The following figure shows that SEM image of oxide films on two
opposite sides of a fracture surface of a tensile test specimen taken
from AZ91 sample.
Some magnesium matrix composites exhibited
impressive increases in mechanical performance in
contrast with nonreinforced matrix alloys. For example,
the composite consisting of Mg-14Li-1Al matrix and 30
vol-% of steel fibers has a tensile strength 600–700 MPa
at room temperature and 450–480 MPa at 200°C, while
the matrix alloy exhibits only 144 MPa at room
temperature, and 14 MPa at 200°C.
Magnesium matrix composites
₪ Advanced Mg-based materials have great potential to
improve mechanical performance. New nontraditional
reinforcing systems reach strength characteristics
comparable with some steels or titanium alloys.
₪ For instance, the squeeze-casting composite of the matrix
AZ91D alloy reinforced with 10 vol-% of Al18B4O33
particles exhibits a tensile strength 480 MPa .
• Even the low-alloyed magnesium matrix MB15
reinforced with 30 vol-% of Al18B4O33 whiskers
demonstrates a yield strength of 230 MPa and
very good rigidity characterized with Young’s
modulus 76 GPa and 0.5% elongation. An
increase in volume fraction of the reinforcing
component can result in drastic change of
For
mechanical properties.
example:
• The Swiss company EMPA recently reported
about the super-strength composite MgAl1/T300
containing 60 vol-% of graphite fibers. This
material exhibited tensile strength of 1470 MPa
and Young’s modulus 155 GPa.
 Magnesium matrix composites also have potential for
high-damping to reduce mechanical vibrations. For
example, undirectional solidification of Mg-2Si alloy
yields Mg/Mg2Si composite structure with a mechanical
strength as high as the industrial cast Alloy AZ63 but with
a damping capacity 100 times higher .
A similar Mg-10Ni alloy with
Mg/Mg2Ni structure provides a
damping capacity 40 times higher than
that of AZ63 cast. Moreover, Mg-2Si
alloy reinforced with long carbon fibers
has a Young’s modulus of ~200 GPa
with a damping capacity of 0.01 for
strain amplitude of 10–5.
• Due to the low solidus limitation of the matrix,
only low-temperature filler metals such as
P380Mg and P430Mg can be used for joining
casting composites based on ZK51A and QE22A
matrix alloys, or forged composites based on
ZK60A and ZC71 matrix alloys.
• Joining other cast or forged composites can be
performed by placing filler metal GA432 or
P380Mg between the brazed parts and heating to
390°–400°C thoroughly controlling temperature.
Joining of wrought magnesium composites based
on Mg-Zn matrixes is preferably carried out by
soldering with Zn-Al solders.
• Creep-resistant alloys Mg-Al-Ca-Sn and Mg-AlCa-Zn were recently developed , and they showed
yield strengths of 190–203 MPa, ultimate tensile
strengths of 240–250 MPa, and elongations of 3–
5% at room temperature.
• The minimum creep rate was less than 0.9 x 10–9
s–1 at 200°C under loading of 55 MPa. Similar
improvement of creep resistance was also
measured for the Ca-added Mg-Al-Mn Alloy
AM60B. It showed at least 10 times lower creep
rate at 200°C at the load of 90 MPa than Ca-free
cast alloy.
• Experiments with composite Mg-based filler
metals were recently started and will be
finished in the near future to respond to
strength requirements of new high-strength
base materials such as magnesium matrix
composites. Filler metal matrix reinforced
with fine ceramic particles can increase yield
strength in brazed joints by at least 20% and
creep strength by 50–70% .
• The Mg-Al-Li system, which has a eutectic
Mg-36.4Al-6.6Li (wt-%) composition at
418°C , looks like a possible candidate in
the liquid phase to prepare and test for
composite brazing filler metals. There are
also other low-melting Mg-based alloys
that might have good plasticity in solid
state.
• Another alloy of this system Mg-8Li-5Al-1Zn is a
filler metal with a melting point around 560°C.
This alloy demonstrates an unusually high tensile
strength of 220 MPa after age hardening.
Supposedly, the strength can be further increased
by adding a small amount of zirconium.
Typical Applications for Magnesium
Alloys
• The use of magnesium alloys in car design is
expanding, and now includes ultralightweight
matrix composites. Typical automotive
applications are engine blocks, cylinder liners,
pushrods, valve spring retainers, instrument
panels, clutch and brake pedal support brackets,
steering column lock housings, and transmission
housings .
Joining of magnesium alloys!
• Material-handling equipment and commercial applications
include parts for magnesium dockboards, grain shovels,
gravity conveyors, luggage, computer housings, digital
camera housings, electrical conductors, and hand-held
tools.
• In the aerospace industry, lightweight and stiff magnesium
alloys are employed in various units and devices, for
example, aircraft transmission systems and their auxiliary
components, gear housings, rotor housings, and generator
housings in cold areas of engines.
• In audio, video, computer, and communication equipment,
plastics are being replaced by magnesium alloys that have
advantages in strength, heat sink, and service life.
Consequently, thin magnesium net shapes are used now in
many models of cellular phones, laptop computers, and
camcorders.