Aluminum

Almost exactly a third the density of steel, which is the whole reason it exists in aircraft and bicycles. Pure aluminum is soft — the 40-130 MPa span covers fully annealed to heavily cold-worked foil and sheet — so structural parts are always alloyed, and 6061 or 7075 is what you actually buy. It expands about twice as much as steel for the same temperature rise, which is why aluminum-framed windows need bigger gaps than steel ones.

Properties

Density

2,700 kg/m³ — 2.70 g/cm³

Melting point

660.3 °C

Tensile strength

40–130 MPa

Young's modulus

70 GPa

Thermal conductivity

237 W/(m·K)

Thermal expansion

23.1 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Beverage cans and foil
• Window and door frames
• Heat sinks and LED housings
• Overhead power transmission line cores

How it compares

Does it rust?

No — aluminium cannot rust, because rust is specifically iron oxide and there is no iron in it. It does oxidise, immediately and constantly, but aluminium oxide is hard, tightly bonded and only a few nanometres thick, and it protects the metal beneath rather than flaking away. It does corrode galvanically when in contact with a dissimilar metal in a damp environment, which is a different mechanism.

Is it magnetic?

Aluminum 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.