| An alloy is a combination, either in solution | | | | Classification |
| or compound, of two or more elements, at | | | | |
| least one of which is a metal, and where the | | | | Alloys can be classified by the number of |
| resulting material has metallic properties. | | | | their constituents. An alloy with two |
| The resulting metallic substance usually has | | | | components is called a binary alloy; one with |
| different properties (sometimes significantly | | | | three is a ternary alloy, and so forth. |
| different) from those of its components. | | | | Alloys can be further classified as either |
| | | | substitution alloys or interstitial alloys, |
| Properties | | | | depending on their method of formation. In |
| | | | substitution alloys, the atoms of the |
| Alloys are usually prepared to improve on the | | | | components are approximately the same size |
| properties of their components. For instance, | | | | and the various atoms are simply substituted |
| Steel, is stronger than iron, its primary | | | | for one another in the crystal structure. An |
| component. The physical properties of an | | | | example of a (binary) substitution alloy is |
| alloy, such as density, reactivity and | | | | brass, made up of copper and zinc. |
| electrical and thermal conductivity may not | | | | Interstitial alloys occur when the atoms of |
| differ greatly from the alloy's elements, but | | | | one component are substantially smaller than |
| engineering properties, such as tensile | | | | the other and the smaller atoms fit into the |
| strength, shear strength and Young's modulus, | | | | spaces (interstices) between the larger |
| can be substantially different from those of | | | | atoms. |
| the constituent materials. This is sometimes | | | | |
| due to the differing sizes of the atoms in | | | | Terminology |
| the alloy—larger atoms exert a | | | | |
| compressive force on neighbouring atoms, and | | | | In practice, some alloys are used so |
| smaller atoms exert a tensile force on their | | | | predominantly with respect to their base |
| neighbours. This helps the alloy resist | | | | metals that the name of the primary |
| deformation, unlike a pure metal where the | | | | constituent is also used as the name of the |
| atoms move more freely. | | | | alloy. For example, 14 karat gold is an alloy |
| | | | of gold with other elements. Similarly, the |
| Unlike pure metals, most alloys do not have a | | | | silver used in jewelry and the aluminium used |
| single melting point. Instead, they have a | | | | as a structural building material are also |
| melting range in which the material is a | | | | alloys. |
| mixture of solid and liquid phases. The | | | | |
| temperature at which melting begins is called | | | | The term "alloy" is sometime used in everyday |
| the solidus, and that at which melting is | | | | speech as a synonym for a particular alloy. |
| complete is called the liquidus. However, for | | | | For example, automobile wheels made of |
| most pairs of elements, there is a particular | | | | "aluminium alloy" are commonly referred to as |
| ratio which has a single melting point; this | | | | simply "alloy wheels". The usage is obviously |
| is called the eutectic mixture. | | | | indefinite, since steels and most other |
| | | | metals in practical use are also alloys. |