Metal alloys: why mixing metals changes properties
Design & Technology · Key Stage 3 · The School
What an alloy is
An ALLOY is a mixture of a metal with one or more other elements, often another metal. Pure metals are rarely used alone in products, because alloying can fix a weakness a pure metal has — pure iron rusts easily and is relatively soft, for instance.
A property neither parent has alone
STEEL is an alloy of iron and a small amount of carbon. Pure iron is soft; steel is far harder and stronger, from a tiny addition of carbon changing how the iron's internal structure locks together. The improvement is not a simple average of iron and carbon's own properties — it is a genuinely new behaviour that comes from the mixture.
Choosing an alloy for a job
Different alloys of the same base metal suit different jobs. STAINLESS STEEL adds chromium to ordinary steel, which resists rust — useful for cutlery and kitchen equipment. BRASS, an alloy of copper and zinc, is more workable than pure copper and resists corrosion well, useful for fittings and musical instruments.
Aluminium alone is light but not very strong. Alloying it with a small amount of copper, magnesium or other metals produces AIRCRAFT-GRADE aluminium alloys that keep most of the lightness while gaining real strength — essential for a plane, where every extra kilogram of structure costs fuel to carry. A different aluminium alloy, mixed for corrosion resistance rather than strength, suits window frames instead, where strength matters less than surviving years of weather. Same base metal. Different alloying elements. Different properties. Different jobs. This is exactly why product designers specify not just "aluminium" but a particular aluminium alloy by name — the base metal alone does not tell you enough about what the material can actually do.