Magnesium AZ31B properties
Magnesium AZ31B is a wrought magnesium alloy with a density of 1.77 g/cm³ (0.0639 lb/in³), combining high mechanical strength with excellent lightness. Designated under UNS M11311 and manufactured in accordance with ASTM, it contains aluminum and zinc as main alloying elements, and is commonly supplied in plate, sheet, and bar forms. AZ31B stands out for its good machinability, weldability, and strength-to-weight ratio, making it an attractive alternative to aluminum alloys in multiple industrial sectors.
Chemical composition
Section titled “Chemical composition”The magnesium content in AZ31B is 97% as base element.
| Element | Content (%) |
|---|---|
| Magnesium, Mg | 97 |
| Aluminum, Al | 2.50 – 3.50 |
| Zinc, Zn | 0.60 – 1.40 |
| Manganese, Mn | 0.20 max. |
| Silicon, Si | 0.10 max. |
| Copper, Cu | 0.05 max. |
| Calcium, Ca | 0.04 max. |
| Iron, Fe | 0.005 max. |
| Nickel, Ni | 0.005 max. |
Physical properties
Section titled “Physical properties”The AZ31B alloy exhibits a density of 1.77 g/cm³ (0.0639 lb/in³), one of the lowest among structural metals.
| Property | Value |
|---|---|
| Density | 1.77 g/cm³ / 0.0639 lb/in³ |
Mechanical properties
Section titled “Mechanical properties”The tensile strength of AZ31B in extruded condition is 260 MPa (37 700 psi). The following values correspond to extruded material (condition F) and represent typical properties at room temperature.
| Property | Value |
|---|---|
| Tensile strength | 260 MPa / 37 700 psi |
| Yield strength (0.2%) | 200 MPa / 29 000 psi |
| Compressive yield strength (0.2% offset) | 97 MPa / 14 100 psi |
| Ultimate bearing strength | 385 MPa / 55 800 psi |
| Bearing yield strength | 230 MPa / 33 400 psi |
| Shear strength | 130 MPa / 18 900 psi |
| Shear modulus | 17 GPa / 2470 ksi |
| Modulus of elasticity | 44.8 GPa / 6498 ksi |
| Poisson’s ratio | 0.35 |
| Elongation at break (in 50 mm) | 15 % |
| Brinell hardness (500 kg load, 10 mm ball) | 49 HB |
| Charpy impact strength (V-notch specimen) | 4.30 J / 3.17 ft·lb |
Note: Properties vary depending on heat treatment condition and manufacturing process. Conditions such as annealed (O) or hardened rolled (H24) present different strength and ductility combinations; for exact values in those conditions, consult the applicable ASTM standards.
Thermal properties
Section titled “Thermal properties”The thermal conductivity of AZ31B reaches 96 W/m·K (666 BTU·in/h·ft²·°F).
| Property | Value |
|---|---|
| Coefficient of thermal expansion (0–100 °C / 32–212 °F) | 26 µm/m·°C / 14.4 µin/in·°F |
| Thermal conductivity | 96 W/m·K / 666 BTU·in/h·ft²·°F |
Other designations and international equivalents
Section titled “Other designations and international equivalents”AZ31B has UNS number M11311 and has a direct European equivalent EN-MAMgAl3Zn1.
| Standard / Region | Designation |
|---|---|
| ASTM (USA) | AZ31B |
| UNS | M11311 |
| EN (Europe) | EN-MAMgAl3Zn1 |
| ISO | MgAl3Zn1 |
Manufacturing processes and heat treatment
Section titled “Manufacturing processes and heat treatment”AZ31B is primarily processed at temperatures between 300 °C (572 °F) and 400 °C (752 °F). The most common methods include extrusion, rolling, and hot forging. The alloy accepts annealing heat treatment (O) at 340–400 °C (644–752 °F) with controlled cooling to eliminate work hardening. Solution treatment (T4) and aging (T5) treatments can also be applied to adjust the strength-ductility balance, although precipitation hardening is modest in this composition compared to alloys like AZ80.
Machinability
Section titled “Machinability”The typical cutting speed for AZ31B with high-speed steel tools exceeds 100 m/min (328 ft/min). The alloy has excellent machinability, considered the best among common structural metals, producing short, fragmented chips that reduce tool wear. It does not require coolants in most operations as long as excessive heat buildup is avoided. High-quality surface finishes are obtained with low cutting forces.
Forming
Section titled “Forming”Forming of AZ31B is successfully carried out between 230 °C (446 °F) and 370 °C (698 °F). At room temperature ductility is limited due to the hexagonal close-packed structure, so processes such as deep drawing, bending, and stamping require heating. Hot working within the indicated range allows high elongations without cracking. Superplastic forming is also viable under controlled conditions.
Welding
Section titled “Welding”Gas tungsten arc welding (GTAW) of AZ31B typically uses preheating between 150 °C (302 °F) and 200 °C (392 °F). The alloy has good weldability with arc processes (GTAW, GMAW) and resistance welding, using filler material of similar composition (AZ61 or AZ92). It is essential to remove oxides and protect the area with inert gas (argon) to avoid porosity. After welding, a stress relief anneal at 260–343 °C (500–650 °F) is recommended to restore mechanical properties.
Applications
Section titled “Applications”Thanks to its low density of 1.77 g/cm³ (0.0639 lb/in³), AZ31B is used in sectors where weight savings are critical.
| Industry | Typical applications |
|---|---|
| Aeronautics and aerospace | Interior panels, seat frames, secondary structural components |
| Automotive | Engine brackets, transmission cases, lightweight chassis parts |
| Consumer electronics | Camera bodies, laptop housings, phone frames |
| Sports | Bicycle frames, racket components, hiking poles |
| Defense | Ammunition boxes, portable systems |
| General industry | Jigs, handling devices, lightweight machinery parts |
Comparison with similar materials
Section titled “Comparison with similar materials”Compared to AZ91C, AZ31B exhibits approximately three times greater elongation although its tensile strength is slightly lower.
| Property | AZ31B (extruded) | AZ91C (cast) | Aluminum 6061-T6 |
|---|---|---|---|
| Density | 1.77 g/cm³ / 0.0639 lb/in³ | 1.81 g/cm³ / 0.0654 lb/in³ | 2.70 g/cm³ / 0.0975 lb/in³ |
| Tensile strength | 260 MPa / 37 700 psi | 275 MPa / 39 900 psi | 310 MPa / 45 000 psi |
| Yield strength | 200 MPa / 29 000 psi | 160 MPa / 23 200 psi | 276 MPa / 40 000 psi |
| Elongation (50 mm) | 15 % | 3 % | 12 % |
| Modulus of elasticity | 44.8 GPa / 6498 ksi | 45 GPa / 6526 ksi | 68.9 GPa / 10 000 ksi |
| Thermal conductivity | 96 W/m·K / 666 BTU·in/h·ft²·°F | 51 W/m·K / 354 BTU·in/h·ft²·°F | 167 W/m·K / 1157 BTU·in/h·ft²·°F |
AZ31B offers the best strength-ductility ratio among general-purpose wrought magnesium alloys. Compared to aluminum 6061-T6, it provides a 34% mass reduction for comparable absolute strength, although with lower stiffness.
Frequently Asked Questions (FAQ)
Section titled “Frequently Asked Questions (FAQ)”What is the density of magnesium AZ31B?
Section titled “What is the density of magnesium AZ31B?”The density of AZ31B is 1.77 g/cm³ (0.0639 lb/in³), making it one of the lightest structural metals.
What does the designation AZ31B mean?
Section titled “What does the designation AZ31B mean?”The letter “A” indicates aluminum as the first alloying element (~3%), “Z” indicates zinc as the second alloying element (~1%), “31” reflects the nominal percentages (3% Al, 1% Zn), and “B” is a serial letter denoting a modification in impurity limits compared to the A version.
Can AZ31B be welded with MIG process?
Section titled “Can AZ31B be welded with MIG process?”Yes, it can be welded with GMAW (MIG) using argon as shielding gas and a filler wire of AZ61 or AZ92 alloy, provided the surface is thoroughly cleaned and a light preheat is maintained.
Is AZ31B suitable for anodizing?
Section titled “Is AZ31B suitable for anodizing?”Yes, like other magnesium alloys, AZ31B can be anodized to improve corrosion resistance and provide a base for subsequent coatings.
What is the maximum service temperature of AZ31B?
Section titled “What is the maximum service temperature of AZ31B?”It is recommended not to exceed 150 °C (302 °F) in continuous service, as above this temperature mechanical strength and dimensional stability begin to degrade significantly.
Is AZ31B more expensive than aluminum?
Section titled “Is AZ31B more expensive than aluminum?”The price per kilogram of magnesium AZ31B is usually higher than that of aluminum 6061, but the lower weight often offsets the cost in applications where mass reduction is a priority.
Sources Consulted
Section titled “Sources Consulted”- azom.com: https://www.azom.com/article.aspx?ArticleID=6707
- engineeringtoolbox.com: https://www.engineeringtoolbox.com/metal-alloys-densities-d_50.html
- steelnumber.com: https://www.steelnumber.com/en/equivalent_alloy_eu.php?zname_id=12092