An alloy is a mixture of a metal with at least one other element, usually another metal. Pure metals are soft because the layers of identical atoms slide over each other easily. In an alloy the atoms are of different sizes, which disturbs the layers, so they slide less easily and the alloy is usually harder and stronger than the pure metal.
- Steel is iron with a small amount of carbon. It is harder and stronger than pure iron. Low-carbon steel is easy to shape and is used for car bodies. High-carbon steel is harder but more brittle and is used for tools. Stainless steel also contains chromium, so it resists corrosion and is used for cutlery.
- Brass is copper and zinc. It is harder than copper but still easy to shape, and is used for taps, door handles and musical instruments.
- Bronze is copper and tin. It is hard and resists corrosion, and is used for statues, bells and ships' propellers.
- Solder is an alloy of tin and lead, although many modern solders are lead-free. It has a low melting point and is used to join electrical components.
- Duralumin is aluminium with small amounts of copper and magnesium. It is strong but has a low density, so it is used in aircraft parts.
