What is an alloy?
An alloy is a mixture of a metal with one or more other elements, which may be other metals or small amounts of a non-metal such as carbon. The parts are usually melted together and then allowed to solidify. Alloys are made because a pure metal is often too soft, too weak, or corrodes too easily for everyday use.
Why alloys are harder
In a pure metal the atoms are the same size and lie in neat, orderly layers. When a force is applied, these layers can slide over one another, so the metal is soft and easily bent. When atoms of a different size are added, they disturb the orderly arrangement and stop the layers from sliding. This makes the alloy harder and stronger than the pure metal.
Key idea
Foreign atoms of a different size disrupt the regular layers of metal atoms, preventing them from sliding – so the alloy is harder and stronger than the pure metal.
Common alloys
| Alloy | Main elements | Use |
|---|---|---|
| Steel | iron + carbon | buildings, cars, tools |
| Stainless steel | iron + chromium + nickel | cutlery, sinks (resists rust) |
| Brass | copper + zinc | musical instruments, taps |
| Bronze | copper + tin | medals, statues, bells |
| Duralumin | aluminium + copper + magnesium | aircraft bodies (light and strong) |
Advantages of alloying
- Greater hardness and strength than the pure metal.
- Better resistance to corrosion (for example, stainless steel does not rust easily).
- An improved appearance, useful for jewellery and decoration.
Example
The kitchen sinks and cutlery in a Malaysian home are usually made of stainless steel. The added chromium forms a thin protective layer, so the metal stays shiny and does not rust in our humid, rainy climate.
Remember
An alloy is a mixture, not a compound – the metals are not chemically bonded in a fixed ratio, and the composition can be adjusted to suit the job.