An alloy is a homogeneous mixture of two or more elements, at least one of which is a metal, and where the resulting material has metallic properties. The resulting substance usually has different properties (sometimes substantially different) from those of its components
Alloying one metal with others usually improves on the properties of other elements. For instance, steel is stronger than iron, its primary element. The physical properties of an alloy, such as density, reactivity, Young's modulus, and electrical and thermal conductivity may not differ greatly from the alloy's elements, but engineering properties, such as tensile strength and shear strength can be substantially different from those of the constituent materials. This is sometimes due to the differing sizes of the atoms in the alloy, since larger atoms exert a compressive force on neighboring atoms, and smaller atoms exert a tensile force on their neighbors. This helps the alloy resist deformation, unlike a pure metal where the atoms move more freely. Alloys may exhibit marked differences in behavior even when small amounts of impurities are one element of the alloy; for example impurities in semi conducting ferromagnetic alloys lead to different properties, as first predicted by White, Hogan, Suhl, Tian Abrie and Nakamura.Some alloys are made by melting and mixing two or more metals. Brass is an alloy made from copper and zinc. Bronze, used for statues, ornaments and church bells, is an alloy of tin and copper.
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, rarely, even two! This is called an eutectic mixture.