Jul 31 2013
Topics Covered
Introduction
Chemical Composition
Physical Properties
Mechanical Properties
Thermal Properties
Other Designations
Fabrication and Heat Treatment
Machinability
Welding
Heat Treatment
Forging
Introduction
Magnesium HM21A-T8 alloy is one of the most widely used precipitation hardening grades. The alloy is soft and ductile under solution annealed condition. It is characterized by high strength, toughness, harness and good corrosion resistance.
The following datasheet gives an overview of magnesium HM21A-T8 alloy.
Chemical Composition
The following table shows the chemical composition of magnesium HM21A-T8 alloy.
|
Element |
Content (%) |
|
Magnesium, Mg |
97 |
|
Thorium, Th |
1.5 - 2.5 |
|
Manganese, Mn |
0.45 - 1.1 |
Physical Properties
The physical properties of magnesium HM21A-T8 alloy are given in the following table.
|
Properties |
Metric |
Imperial |
|
Density |
1.78 g/cm³ |
0.0643 lb/in³ |
Mechanical Properties
The mechanical properties of magnesium HM21A-T8 alloy are listed in the following table.
|
Properties |
Metric |
Imperial |
|
Tensile strength |
235 MPa |
34100 psi |
|
Yield strength |
170 MPa |
24700 psi |
|
Compressive yield strength (at 0.2% offset) |
130 MPa |
18900 psi |
|
Ultimate bearing strength |
415 MPa |
60200 psi |
|
Bearing yield strength |
270 MPa |
39200 psi |
|
Notched tensile strength |
230 MPa |
33400 psi |
|
Shear strength |
125 MPa |
18100 psi |
|
Shear modulus |
17 GPa |
2470 ksi |
|
Elastic modulus |
45 GPa |
6530 ksi |
|
Poisson's ratio |
0.35 |
0.35 |
|
Elongation at break (in 50 mm) |
11% |
11% |
|
Machinability (relative rating, 100=best) |
100 |
100 |
Thermal Properties
The following table outlines the thermal properties of magnesium HM21A-T8 alloy.
|
Properties |
Metric |
Imperial |
|
Thermal expansion co-efficient (@ 0-100°C/32-212°F) |
26.8 µm/m°C |
14.9 µin/in°F |
|
Thermal conductivity |
135 W/mK |
937 BTU in/hr.ft².°F |
Other Designations
An equivalent material to magnesium HM21A-T8 alloy is AMS 4390.
Fabrication and Heat Treatment
Machinability
Magnesium HM21A-T8 alloy is characterized by long, gummy chips. It can be machined in the annealed condition.
Welding
Magnesium HM21A-T8 alloy can be welded using common fusion and resistance methods. Oxyacetylene welding method is not preferred for welding this alloy.
Heat Treatment
Solution-treated magnesium HM21A-T8 alloy is soaked at 760°C (1400°F) for 2 h, air cooled and then re-heated at 620°C (1150°F) for 4 h and air cooled.
Forging
Magnesium HM21A-T8 alloy is forged at 1177°C (2150°F) for 24 h. However, post-work solution treatment is required prior to final hardening