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Magnesium

AZ31B Magnesium

AZ31B is a wrought magnesium-aluminum-zinc alloy and the lightest structural metal here, at 1.77 g/cm3 — roughly two-thirds the density of aluminum. It pairs 260 MPa tensile and 200 MPa yield with good formability, making it the default choice when extruded, sheet, or forged magnesium parts must shed weight without resorting to die casting.

How AZ31B Magnesium machines

It cuts fast and clean, but magnesium chips and fine dust are flammable. Use flood coolant (mineral-oil based, never water-reactive), sharp tools, high feeds to keep chips chunky, and avoid generating fine swarf. Keep a Class D extinguisher nearby; never let chips accumulate dry. Treated correctly it machines beautifully with low cutting force.

Manufacturing & processing

AZ31B is supplied as extrusions, rolled sheet, and forgings, and the data lists Extrusion, Sheet Metal, CNC, and Forging. It welds well via TIG with magnesium filler. Its limited 120C max service temperature and poor corrosion resistance (2.0/5) mean parts almost always need chromate conversion coating or paint.

Typical applications

Used where mass is the dominant constraint: portable tool and power-tool housings, camera and optics bodies, aerospace brackets, sporting goods, and lightweight structural frames. Best for wrought structures that must be machined or formed rather than cast, where its low density delivers a real strength-to-weight payoff over aluminum.

When to choose it

Choose AZ31B over 6061 aluminum only when shaving every gram matters and the 120C ceiling and corrosion needs are acceptable. If the part is a thin-wall, high-volume housing, switch to AZ91D die casting. If corrosion or temperature is critical, aluminum is the safer, lower-risk default.

Suitable surface finishes

Common finishes for AZ31B Magnesium: chromate/Alodine, powder coating. Use the finish selector →

FAQ

Is machining AZ31B magnesium really a fire hazard?
The bulk part will not ignite, but fine chips and grinding dust can. Standard practice is sharp tooling, generous flood coolant, coarse chip loads, no dry fine swarf, and a Class D extinguisher on hand. Shops machine magnesium routinely; the risk is managed, not eliminated.
How does AZ31B compare to 6061-T6 aluminum?
AZ31B is about 35% lighter (1.77 vs 2.7 g/cm3) but lower in tensile strength (260 vs 310 MPa) and corrosion resistance, with a lower 120C service ceiling. It wins purely on strength-to-weight for weight-critical wrought parts; otherwise aluminum is cheaper and easier.
Does AZ31B need a protective coating?
Almost always. With corrosion resistance rated just 2.0/5, bare magnesium corrodes readily, and especially fast galvanically against steel fasteners. Chromate conversion coating, anodizing (such as Tagnite), or paint is standard practice, plus electrical isolation from dissimilar metals at every joint and contact face.

Property values are typical/nominal for early guidance and vary by temper, grade, supplier and heat treatment. Confirm critical specs against a certified datasheet or with an mfgiq engineer.