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2006 CASTING SOURCE DIRECTORY ENGINEERED CASTING SOLUTIONS 41
Magnesium Alloys
Table 1. Typical Mechanical Properties of Magnesium at Room Temperature
Property Unit AZ91 AM60 AM50 AM20 AS41 AS21 AE42
Ultimate Tensile Strength MPa 240 225 210 190 215 175 230
 (250) (240) (230) (210) (240) (220) (230)
Tensile Yield Strength MPa 160 130 125 90 140 110 145
(0.2% offset ) (160) (130) (125) (90) (140) (120) (145)
Compressive Yield Strength MPa 160 130 125 90 140 110 145
Fracture Elongation % 3 8 10 12 6 9 10
 (7) (13) (15) (20) (15) (13) (11)
Elastic Modulus, tension GPa 45 45 45 45 45 45 45
Elastic Modulus, shear GPa 17 17 17 17 17 17 17
Brinell Hardness 70 65 60 45 60 55 60
Impact Strength J 6 17 18 18 4 5 5
Charpy un-notched test bars (9) (18) (18) (18) (16) (12) (12)
Note: Values in parentheses show mean property values obtained from separately diecast test bars.
Table 2. Typical Physical Properties of Magnesium
Property Unit Temp (F) AZ91 AM60 AM50 AM20 AS41 AS21 AE42
Density g/cu cm 68 1.81 1.8 1.77 1.75 1.77 1.76 1.79
Liquidus Temperature F 1,110 1,139 1,148 1,182 1,144 1,169 1,157 
Incipient Melting 
Temperature F 788-815 788-815 788-815 788-815 788-815 788-815 1094 
Linear Thermal 
Expansion Coeffi cient µm/m 68-212 26 26 26 26 26.1 26.1 26.1
Specifi c Heat of Fusion kJ/kg 370 370 370 370 370 370 370
Specifi c Heat kJ/kg*K 68 1.02 1.02 1.02 1.02 1.02 1.02 1.02
Thermal Conductivity W/K*m 68 51 61 65 94 68 84 84
Electrical Conductivity MS/m 68 6.6 nm 9.1 13.1 nm 10.8 11.7
 
Cast magnesium alloys have gained more popularity in recent years due 
to their ability to maintain high 
strengths at light weights. Mag-
nesium possesses unique 
properties that can open the 
door to important markets 
for structural applications 
and has gained widespread 
use in automotive compo-
nents. Further, non-automo-
tive applications, spurred on 
by the computer, electronics 
and power tool industries, con-
tinue to expand.
Magnesium has a density two-
thirds that of aluminum and only 
slightly higher than that of fi ber-reinforced 
plastics and possesses excellent mechanical 
and physical properties (Tables 1-2). When 
coupled with the inherent advantages 
of the metalcasting process, magnesium 
alloys yield cost-effective solutions to 
product needs by allowing for part con-
solidation and weight savings over other 
materials and manufacturing methods. 
Advantages of Magnesium
Magnesium alloy properties can pro-
vide a casting designer with several ad-
vantages as an engineering material over 
other lightweight alloys.
Weight—The lightest of all structural 
metals, magnesium preserves the light 
weight of a design without sacrificing 
strength and rigidity (Fig. 1). This benefi t 
is important when portability is a key 
element of the product design, such as 
with chainsaws, pneumatic nailers, circu-
lar saws, luggage, laptop computers and 
cellular phones. Automobiles and other 
transportation equipment continue to take 
advantage of magnesium’s low density in 
expanding application areas ranging from 
under-hood and driveline uses found 
in engine brackets and transfer cases to 
numerous interior parts, such as steering 
column components, pedal brackets, in-
strument panel supports and seating.
Damping Capacity—Magnesium 
is unique among metals because of 
its ability to absorb energy. Increased 
vibration absorption capacity provides 
for quieter operation of equipment 
when magnesium castings are used for 
housings and enclosures.
Dimensional Stability—Annealing, ar-
tifi cial-aging or stress-relieving treatments 
normally are not necessary to achieve 
stable fi nal dimensions. 
Metallurgical changes in the 
structure of some metals can affect 
dimensions after prolonged exposure to 
elevated temperatures, but this is not the 
case with magnesium al-
loys. As a result, there have 
been few problems associ-
ated with the dimensional 
change of castings in assem-
blies. Magnesium shrinkage 
rates are more consistent and 
predictable in comparison 
to other nonferrous metals. 
Components release from the 
die with minimal force and 
distortion, hence they have 
minimal residual casting stress. 
Impact & Dent Resistance—
The elastic energy absorption 
characteristics of magnesium result 
in good impact and dent resistance 
and energy management, which is 
one reason magnesium castings can 
be used for automotive safety-related 
The conversion of this military helicopter 
transmission housing from a fabrication to 
a magnesium casting allowed for a 30% 
cost reduction and lowered scrap 
rate by 40%. 
The American Foundry Society Technical Dept., Schaumburg, Illiniois
42 ENGINEERED CASTING SOLUTIONS 2006 CASTING SOURCE DIRECTORY
Fig. 1. Magnesium’s light weight has allowed it to become the alloy of choice 
for a number of new markets and applications, such as the automotive, power 
tool, computer and electronics industries.
applications, such as air 
bag systems. Portable tools 
and handheld electron-
ics also benefit from this 
combination of proper-
ties, offering mechanical 
shock resistance.
Anti-Galling—Magne-
sium alloys possess a low 
galling tendency and can 
be used as a bearing sur-
face in conjunction with 
a shaft hardness above 400 
Brinell measurement.
Alloy Families
Magnesium alloys can 
be used in multiple ap-
plications, but they easily 
can be divided into two 
groups: sand casting alloys and diecast-
ing alloys. Alloys also can be classified as 
general purpose, high-duc-
tility and high-temperature 
with higher levels of iron, 
nickel and copper. Sand 
casting alloys often are 
produced with a fine grain 
structure due to small ad-
ditions of zirconium.
Aluminum is the prin-
cipal alloying element for 
many magnesium alloys as 
it can improve the mechan-
ical strength, corrosion 
properties and castability 
of magnesium castings. 
The most widely used gen-
eral purpose sand casting 
alloy is AZ91. In the alloy 
nomenclature, the letters 
A and Z denote the ma-
jor alloy. However, not all 
properties improve with 
aluminum and zinc additions. Ductil-
ity and fracture toughness are gradually 
reduced when more aluminum is added. 
This effect led to the introduction of a 
series of alloys with reduced aluminum 
contents (the AM series), which is used 
extensively for automotive safety-related 
components. These include manganese, 
which is added to control the iron content 
of the alloys. Several alloys, such as AM60 
(6% aluminum, 0.05% manganese), have 
found widespread applications in parts, 
including instrument panel supports, steer-
ing wheel armatures and seat parts. 
Some applications expose the cast-
ing to higher operating temperatures or 
continuous stresses that lead to concerns 
about long-term deformation and creep. 
Castings for use in higher temperature 
service conditions can be produced in al-
loys, such as the AS and AE series, based 
on the addition of either silicon or rare 
earth elements (E), which promote the 
formation of fi nely dispersed particles at 
the grain boundaries. 
Recent property and castability im-
provements have been shown with new 
magnesium creep-resistant alloys that 
use specialized rare earth elements, such 
as calcium or strontium, as the signifi cant 
alloying elements. These new alloys can 
produce cast components with superior 
alloys. Most magnesium alloys are pro-
duced as high-purity versions 
to reduce potential corro-
sion problems associated 
This engine cradle for a high-performance sports 
car was redesigned from a low-pressure alumi-
num permanent mold casting to two different 
processes: a magnesium vacuum die casting 
(top), which helped lower porosity defects; and 
a low-pressure permanent mold magnesiumcasting (bottom), which allowed for a sand 
core to form a hollow cross support beam 
rather than the ribbed support design of 
the die casting.
2006 CASTING SOURCE DIRECTORY ENGINEERED CASTING SOLUTIONS 43
mechanical properties at in-service higher 
temperature ranges. 
Casting Processes
Along with magnesium’s multiple al-
loys, the material can be cast by a variety 
of methods, including high-pressure 
diecasting, permanent mold casting, sand 
casting, semi-solid and squeeze casting. 
Different alloys may be specifi ed for these 
different processes, but in cases where the 
same alloy is used with different casting 
processes, the properties of the fi nished 
castings will depend on the method. 
The most prevalent casting method for 
magnesium is diecasting. In this process, 
complex, thin-walled parts are produced 
at high production rates aided by the low-
heat content per volume of molten metal. 
Both hot chamber and cold chamber ma-
chines currently are used for magnesium. 
For optimum performance, it is recom-
mended that higher shot speeds are used 
for magnesium compared to aluminum, 
especially for thin-walled parts. Diecast-
ing process variants (such as vacuum 
diecasting) can produce components with 
lower porosity and better properties than 
standard diecasting. 
Magnesium also is conducive to using 
semi-solid casting methods, typically with 
magnesium alloy granules or partially 
solidifi ed alloys rather than liquid mag-
nesium. Semi-solid molding commonly is 
used for smaller parts, such as those used 
in the electronics industry. 
Design Considerations
When evaluating the various alloys 
and processes for a magnesium casting, 
there are a number of characteristics to 
consider to obtain a quality, low-cost 
component. This includes the 
end-use application, the post-
casting operations and how 
casting magnesium will factor 
into tooling costs. 
High Stiffness-to-Weight Ra-
tio—This characteristic is important 
where resistance to defl ection is desired 
in a lightweight component.
Improved Die Life—Unlike molten 
aluminum, molten magnesium does 
not react with tool steels, resulting in 
longer die life and increased productiv-
ity. Because of low erosion and reduced 
heat input, which reduce the propensity 
for thermal fatigue (heat checking of the 
die), casting magnesium can warrant 
three to four times the die life than if 
aluminum were used. 
Machining—Magnesium is recognized 
as the easiest of structural metals to 
Cast through the rubber plaster molding process in AZ91D 
magnesium alloy, this projector frame and interface offered the 
customer improved durability and rigidity, high heat tolerance 
and eliminated EMI plating requirements when compared to its 
previous plastic injection mold design. 
This 2.3-lb AM60B magnesium shift tower 
assembly is a one-piece diecast component. 
Converted from a multiple steel fabrication, 
the magnesium casting design resulted in a 
75% weight savings.
machine and is the “standard” of the 
cutting tool industry when comparing 
machinability of metals. The low power 
requirements for machining magnesium 
alloys permit the use of deeper cuts and 
higher feed rates, thus permitting fast 
and efficient machining when compared 
to other metals. Magnesium alloys also 
normally produce well-broken chips, 
which are easy to handle. ECS
This article was adapted with permission 
from materials prepared by the Interna-
tional Magnesium Assn., McLean, Va., 
and the North American Die Casting 
Assn., Wheeling, Ill.