A metal alloy is a substance that combines more than one metal or mixes a metal with other non-metallic elements. For example, brass is an alloy of two metals: copper and zinc. Steel is an alloy of a metallic element (iron) and a small amount — up to 2% — of a non-metallic element (carbon). When compared to metals, alloys differ in their properties and characteristics, such as composition, applications, how they're made, and cost.