A substance which has metallic properties, and that consists of two or more elements; usually, at least one of which is a metal.

1. A mixture of a metal with smaller quantities of other metals, or even nonmetals, to make it harder, to survive high temperatures, or to improve it in other ways: Alloy wheels on vehicles use strong, lightweight alloys, that are based on aluminum.

2. Any of various materials having metallic properties and composed of two or more closely mixed chemical elements, of which at least one is a metal: Brass is an alloy of copper and zinc.

Alloys are produced to obtain some desirable quality, such as greater hardness, strength, lightness, or durability.

Alloys have been known since virtually the beginning of recorded history; a prehistoric age, in fact, is known as the Bronze Age, indicating the advent of human's ability to smelt bronze, an alloy of copper and tin.

Other well-known alloys include brass, an alloy of copper and zinc; and steel, an alloy of iron and carbon.

Alloys have been created by mixing metals with semi-metals like arsenic and antimony and with nonmetals like carbon and silicon.

Most alloys are developed for a specific physical characteristic; such as, malleability or strength.

Alloys are most often created during the molten stage of a metal, and the alloying element is usually added during the refinement process.

Steel is made by introducing carbon from the coke used in the refinement of iron ore.

Alloys are also divided into ferrous (iron based) and non-ferrous, in which the base is usually copper, aluminum, or titanium.

Titanium is particularly important for providing extreme durability (about the same as steel) and at very light (half the weight of steel), both considerations in the construction of high-performance aircraft.

However, the alloys used in jet and rocket engines; especially, in areas of intense heat and stress, are usually nickel-based or cobalt-based.

Alloys are often far less conductive of electricity and less reactive to living bodily tissue than pure metal, which makes them ideal for use in prosthetic devices, heart pacemakers, and in dentistry.