Definition · Plain-language
Alloy
An alloy is a mixture of a metal with one or more other elements, made to give it more useful properties than the pure metal.
The step most authors miss
Doing CRediT right? Don’t stop at the statement.
A CRediT statement credits you inside one paper. The recognition CRediT was built for happens when those roles are tied to you, persistently. Sign in with your ORCID — free — and claim your CRediT contributions on casrai.org, the home of the standard. They become a verified, portable part of your identity, not a line that disappears into one PDF.
Free: claim your contributions, then export a journal-ready CRediT statement, schema.org structured data, JATS XML, CSV or BibTeX — and preview your public profile. A membership publishes that profile publicly and verifies the journals you serve.
A metal mixed with other elements
An alloy is made by mixing a base metal with one or more other elements, usually while molten so they blend thoroughly, then letting the mixture solidify. The added elements may be other metals or non-metals such as carbon. The result is still essentially metallic in character but has different, usually improved, properties. Because the components are mixed rather than chemically bonded in a fixed ratio, an alloy is classed as a mixture — more precisely a solid solution — not a compound. The proportions can be varied to fine-tune the properties.
Why alloys are usually stronger
Pure metals are often too soft for practical use because their atoms are all the same size and arranged in neat layers that can slide over one another easily. Alloying introduces atoms of a different size, which disrupt these regular layers and make it harder for them to slip. This is why alloys are typically harder and stronger than the pure metal they are based on. Alloying can also lower the melting point, improve resistance to corrosion, or change appearance, depending on which elements are added and in what amounts.
Everyday and important alloys
Alloys are among the most useful materials we have. Steel is iron mixed with a small amount of carbon, far stronger than pure iron and the backbone of construction; adding chromium and nickel gives stainless steel, which resists rust. Brass is copper and zinc, used for fittings and instruments; bronze is copper and tin. Solder is a low-melting alloy used to join metals. Even coins and the aluminium in aircraft are alloys, chosen so their properties suit the job.
Key facts
At a glance
- Definition: a mixture of a metal with one or more other elements
- Classed as: a mixture (solid solution), not a compound
- Why made: to improve strength, hardness or corrosion resistance
- Steel: iron + carbon
- Brass: copper + zinc
- Bronze: copper + tin
Common misconceptions
What people often get wrong
Often heard: An alloy is a chemical compound of its metals.
Actually: An alloy is a mixture, usually a solid solution, not a compound. Its components are not chemically bonded in a fixed ratio, and the proportions can be varied to adjust the properties.
Often heard: Alloys are always weaker than pure metals.
Actually: Alloys are usually stronger and harder than the pure base metal, because the differently sized added atoms disrupt the regular layers and stop them sliding. That is the main reason alloys are made.
Often heard: An alloy can only be made from two or more metals.
Actually: An alloy must contain a metal, but the other elements need not be metals. Steel, the most important alloy, is iron mixed with carbon, which is a non-metal.
Going deeper
