Brass

Copper and zinc, with the ratio setting both the colour and the behaviour: 70/30 cartridge brass draws deeply without splitting, 60/40 is stronger and cheaper, and free-machining brass adds a little lead so it cuts like chalk. It is the standard against which machinability is measured, which is why small turned parts default to it. Brass in contact with ammonia or with residual forming stresses can crack spontaneously — season cracking — which is why drawn cases are stress-relieved.

Properties

Density

8,500 kg/m³ (8,400–8,730) — 8.50 g/cm³

Melting range

900–955 °C

Tensile strength

300–550 MPa

Young's modulus

110 GPa

Thermal conductivity

120 W/(m·K)

Thermal expansion

20 µm/(m·K)

Floats in water

No

Magnetic

No

What it is used for

• Plumbing fittings and valves
• Door handles, locks and hinges
• Cartridge cases and musical instruments
• Machined electrical terminals

How it compares

Does it rust?

No. Copper and its alloys cannot rust, since rust is iron oxide. They form a patina instead — copper oxide first, turning to the familiar green carbonate over decades — and that layer is adherent and protective, which is why copper roofs last centuries.

Is it magnetic?

Brass 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.