Magnesium

The lightest structural metal in use, at about two thirds the density of aluminum and a fifth that of steel. The catch is fire: magnesium swarf and thin sections burn fiercely and cannot be put out with water, which is why machining shops treat it differently and why it never went into aircraft interiors. It also corrodes readily unless coated, so magnesium castings are always painted or anodized.

Properties

Density

1,738 kg/m³ — 1.74 g/cm³

Melting point

650 °C

Tensile strength

160–220 MPa

Young's modulus

45 GPa

Thermal conductivity

156 W/(m·K)

Thermal expansion

24.8 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Laptop and camera bodies
• Car steering wheel and seat frames
• Sacrificial anodes in water heaters
• Aluminum alloying

How it compares

Does it rust?

Magnesium does not rust — rust is iron oxide specifically — but it does corrode, forming its own oxide or salts over time.

Is it magnetic?

Magnesium is not ferromagnetic. It is often assumed to be because it is a metal, but most metals are not — only iron, nickel, cobalt and a few alloys are attracted to an ordinary magnet.