DEFINITION: An alloy is a metal (parent metal) combined with other substances (alloying agents), resulting in superior properties such as; strength, hardness, durability, ductility, tensile strength and toughness. The parent metal is the majority of the alloy. For example, mild steel is 0.1 - 0.3% Carbon and 99.9 - 99.7% Iron.

Alloys are sometimes described as a mixture of two or more metals. However, this is misleading, as often alloys are composed of just one metal, as well as other non-metal elements. Cast iron is an example, as it is a combination of iron (metal) and carbon (non-metal).

Metal alloys have specific enhanced properties compared to their ‘parent’ metals.
For example, steel. Steel is itself an alloy of iron and carbon. Iron is a very brittle metal, likely to break or snap if it receives a sudden blow/shock. Adding the alloying agent carbon, gives the new alloy the property of toughness and tensile strength. Steel can be used in the construction industry for bridges and large buildings. A bridge manufactured only from the parent metal, iron, would eventually collapse due to its inability to absorb shocks/blows. The table below gives three alloying elements that can be added to the alloy steel, to further improve its physical properties.