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Magnesium Casting Alloys Typical Mechanical Properties

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Magnesium Casting Alloys Typical Mechanical Properties, Elongation, Tensile Temper, Shear Strength, Hardness, Electrical Conductivity

Magnesium is the lightest metal of structural importance [108 lb/ft3 (1.740 g/cm3)]. The principal uses for pure magnesium are in aluminum alloys, steel desulfurization, and production of nodular iron. Principal uses for magnesium alloys are die castings (for automotive and computer applications), wrought products, and, to a lesser extent, gravity castings (usually for aircraft and aerospace components). Because of its chemical reactivity, magnesium can be used in pyrotechnic material and for sacrificial galvanic protection of other metals. Since magnesium in its molten state reacts with the oxygen in air, a protective atmosphere containing sulfur hexafluoride is employed as a controlled atmosphere.

Commercially pure magnesium contains 99.8 percent magnesium and is produced by extraction from seawater or by reduction from magnesite and dolomite ores. Chief impurities are iron, silicon, manganese, and aluminum. The major use of magnesium, consuming about 50 percent of total magnesium production, is as a component of aluminum alloys for beverage can stock. Another use for primary magnesium is in steel desulfurization. Magnesium, usually mixed with lime or calcium carbide, is injected beneath the surface of molten steel to reduce the sulfur content.

A growing application for magnesium alloys is die cast automotive components. Their light weight can be used to help achieve reduced fuel consumption, while high-ductility alloys are used for interior components which must absorb impact energy during collisions. These alloys can be cast by hot or cold chamber die-casting methods, producing a diverse group of components ranging from gear cases to steering wheel frames. Some vehicles use magnesium die castings as structural members to serve as instrument panel support beams and steering columns.

Designs employing magnesium must account for the relatively low value of the modulus of elasticity (6.5 x 106 lb/in2) and high thermal coefficient of expansion [14 x 10-6 per °F at 32°F (0°C) and 16 x 10-6 for 68 to 752°F (20 to 400°C)]. (See Table below)

The development of jet engines and high-velocity aircraft, missiles, and spacecraft led to the development of magnesium alloys with improved elevated-temperature properties. These alloys employ the addition of some combination of rare earth elements, yttrium, manganese, zirconium, or, in the past, thorium. Such alloys have extended the useful temperatures at which magnesium can serve in structural applications to as high as 700 to 800°F.

Alloy
Condition
or
temper*
Tensile
strength,
ksi
Tensile
yield
strength,
ksi
Elongation,
%,
in 2 in
Shear
strength,
ksi
Strength,
ksi
Hardness
BHN
Electrical
conductivity,
% IACS‡
Tensile
Yield
Permanent mold and sand casting alloys:
AM100A
- T6
40
22
1
22
-
-
70
14
AZ63A
- F
29
14
6
18
60
40
50
14
- T4
40
13
12
17
60
44
55
12
- T5
30
14
4
17
60
40
55
- T6
40
19
5
20
75
52
73
15
AZ81A
- T4
40
12
15
17
60
44
55
12
AZ91E
- F
24
14
2
18
60
40
52
13
- T4
40
12
14
17
60
44
53
11
- T5
26
17
3
-
-
-
-
-
- T6
40
19
5
20
75
52
66
13
AZ92A
- F
24
14
2
18
50
46
65
12
- T4
40
14
9
20
68
46
63
10
- T5
26
16
2
19
50
46
70
-
- T6
40
21
2
22
80
65
84
14
EZ33A
- T5
23
15
3
22
57
40
50
25
K1A
- F
25
7
19
8
-
-
-
31
QE22A
- T6
40
30
4
23
-
-
-
25
-
-
-
-
-
-
-
-
-
ZE41A
- T5
30
20
3.5
22
70
51
62
31
ZK51A
- T5
40
24
8
22
72
47
65
27
ZK61A
- T6
45
28
10
26
70
27
Die casting alloys:
AZ91D
- F
34
23
3
20
-
-
75
-
AM60B
- F
32
19
6 – 8
-
-
-
62
-
AM50A
- F
32
18
8 – 10
-
-
-
57
-
AS41B
- F
31
18
6
-
-
-
75
-
AE42X1
- F
33
20
8 – 10
-
-
-
57
-

ksi x 6.898 = MPa
* - F = as cast; - T4 = artificially aged; - T5 = solution heat-treated; - T6 = solution heat-treated.
†RE = rare-earth mixture.
‡ Percent electrical conductivity/100 approximately equals thermal conductivity in cgs units.

Reference:

‘‘Metals Handbook,’’ ASM. Beck, ‘‘Technology of Magnesium and Its Alloys.’’ Annual Book of Standards, ASTM. Publications of the Dow Chemical Co

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