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An alloy is a combination, either in solution or compound, of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. An alloy with two components is called a binary alloy; one with three is a ternary alloy; one with four is a quaternary alloy. The resulting metallic substance generally has properties significantly different from those of its components.
Alloys are usually designed to have properties that are more desirable than those of their components. For instance, steel is stronger than iron, one of its main elements.
Unlike pure metals, most alloys do not have a single melting point. Instead, they have a melting range in which the material is a mixture of solid and liquid phases. The temperature at which melting begins is called the solidus, and that at which melting is complete is called the liquidus. However, for most pairs of elements, there is a particular ratio which has a single melting point, and this is called a eutectic mixture.
In practice, some alloys are used so predominantly with respect to their base metals that the name of the primary constituent is also used as the name of the alloy. For example, 14 karat (58%) gold is an alloy of gold with other elements. Similarly, the silver used in jewelry and the aluminium used as a structural building material are also alloys.
The term "alloy" is sometimes used in everyday speech as a synonym for "aluminium alloy"; one example of such usage is the "alloy wheels" which might be fitted to an automobile. (This usage is obviously imprecise, since all steels and most other metals in practical use are also alloys.)
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