An alloy is a homogenous mixture of two or more metals, or a metal and a non metal. It is prepared by melting the metal and dissolving the other elements in definite proportions. It is then cooled to room temperature. If one of the metals in the alloy is mercury, the alloy is known as amalgam. Sometimes an alloy has lower melting point than any of its constituents. For example solder, an alloy of lead and tin has low melting point and hence it is used in welding.