Nov 13 2012
Topics Covered
IntroductionChemical CompositionPhysical PropertiesMechanical PropertiesThermal PropertiesOther DesignationsFabrication and Heat Treatment Machinability Forming Welding AnnealingApplications
Introduction
Magnesium alloys are light weight and have high machinability. They are often anodized to improve their corrosion resistance. They are designated using the ASTM and SAE system in which the first part indicates the two main alloying elements in the alloy and the second part represents their percentages.
Magnesium AZ31B alloy is available in different forms such as plate, sheet, and bar. It is an alternative to aluminum alloys as it has high strength to weight ratio. It is widely available when compared to other magnesium grades. The following datasheet gives an overview of magnesium AZ31B alloy.
Chemical Composition
The following table shows the chemical composition of magnesium AZ31B alloy.
| Element |
Content (%) |
| Magnesium, Mg |
97 |
| Aluminum, Al |
2.50 - 3.50 |
| Zinc, Zn |
0.60 - 1.40 |
| Manganese, Mn |
0.20 |
| Silicon, Si |
0.10 |
| Copper, Cu |
0.050 |
| Calcium, Ca |
0.040 |
| Iron, Fe |
0.0050 |
| Nickel, Ni |
0.0050 |
Physical Properties
The physical properties of extruded magnesium AZ31B alloy are given in the following table.
| Properties |
Metric |
Imperial |
| Density |
1.77 g/cm3 |
0.0639 lb/in³ |
Mechanical Properties
The mechanical properties of magnesium AZ31B alloy are outlined in the following table.
| Properties |
Metric |
Imperial |
| Tensile strength |
260 MPa |
37700 psi |
| Yield strength (strain 0.200%) |
200 MPa |
29000 psi |
| Compressive yield strength (at 0.2% offset) |
97 MPa |
14100 psi |
| Ultimate bearing strength |
385 MPa |
55800 psi |
| Bearing yield strength |
230 MPa |
33400 psi |
| Shear strength |
130 MPa |
18900 psi |
| Shear modulus |
17 GPa |
2470 ksi |
| Elastic modulus |
44.8 GPa |
6498 ksi |
| Poisson's ratio |
0.35 |
0.35 |
| Elongation at break (in 50 mm) |
15% |
15% |
| Hardness, Brinell (500 kg load, 10 mm ball) |
49 |
49 |
| Charpy impact (V-notch) |
4.30 J |
3.17 ft-lb |
Thermal Properties
The thermal properties of magnesium AZ31B alloy are highlighted in the following table.
| Properties |
Metric |
Imperial |
| Thermal expansion co-efficient (0-100°C/32-212°F) |
26 µm/m°C |
14.4 µin/in°F |
| Thermal conductivity |
96 W/mK |
666 BTU in/hr.ft².°F |
Other Designations
Other designations that are equivalent to magnesium AZ31B alloy include:
- ASTM B107
- ASTM B90
- ASTM B91
Fabrication and Heat Treatment
Machinability
Magnesium AZ31B alloy has good machinability. It is flammable, so extreme care should be taken while performing this process. A lubricant is used to perform machining process. The machinist is required to constantly monitor the operation with a magnesium fire arresting kit.
Forming
Magnesium AZ31B alloy can be formed by preheating at 260°C (500°F).
Welding
Magnesium AZ31B alloy can be welded using metal arc and gas tungsten arc welding techniques.
Annealing
Magnesium AZ31B alloy is stress relieved at 149°C (300°F) for 30 to 60 minutes followed by cooling in air. Full annealing can be done at 344°C (650°F) followed by slowly cooling in the furnace.
Applications
Magnesium AZ31B alloy is mainly used in aerospace applications and general commercial applications.