Alloys are important because they have properties that differ from those of pure metals. Because of these properties, they can be adapted to specific uses where a pure metal would be either unsuitable or cost-prohibitive.
An alloy is a metal composed of more than one element and may have properties different from those of its parent elements. While some alloys such as electrum (a mix of silver and gold) and meteoric iron-nickel are found in nature, humans have been creating alloys for their own uses for more than 4,500 years. An early example of a man-made alloy is bronze, which is made from copper and tin but is harder and stronger than either and can be used to make weapons and tools. Another example is steel, a widely used alloy of iron and carbon that is harder and tougher than pure iron.
Properties of a metal that can be altered by alloying include its hardness; its luster; its ability to be permanently shaped, or ductility; its tensile strength, or ability to withstand pulling without breaking; its melting point; and its ability to conduct electrical currents. Alloys can exhibit marked changes in properties based on even small changes in their composition. They are particularly important to the discipline of material engineering, which studies and applies the properties of materials.