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Last edited 28 Jan 2020
An alloy is an impure substance (admixture) comprising a mixture of metals, or a metal to which small additions of other metals and non-metals have been added to give it special or desired properties. The result is a compound that is likely to be superior in performance to the pure metal and may be more economical in use.
Creating an alloy may provide enhanced tensile strength, ductility, malleability, corrosion resistance, etc. The resulting alloy will retain many of the properties of the original metal, such as electrical conductivity, in addition to the new properties.
Typical alloys (and their main components) are:
- Steel (iron plus carbon and other additives)
- Bronze (copper and tin), stainless steel,
- Brass (zinc and copper),
- Red gold (gold and copper)
- White gold (gold and silver)
- Sterling silver (silver and copper)
- Aluminium alloy (aluminium and magnesium).
Other alloys include pewter, solder and silicon steel. Ferrous metals can generally be thought of as alloys because they are essentially iron ore with various amounts of carbon added to create wrought iron, cast iron, mild steel and high tensile steel. A stainless-steel alloy can be created by adding chromium and nickel to iron ore.
Steel alloys are used widely in construction (mild steel, reinforcement steel etc). Carbon steel is prized for its strength and hardness and is used for structural applications in buildings, bridges, highways and other civil engineering works, as well as for rebar and hollow structural sections.
After steel, aluminium alloy is the second most widely specified metal in building construction. Pure aluminium has relatively low in strength, but when alloyed can be used for extrusions and other manufactured components. However, even as an alloy it still boasts around 92% purity. It is ductile, workable and versatile and can be almost completely recycled. About 40% of all aluminium produced in the UK is used for construction – around 150,000 tonnes per year. Typical applications include windows, cladding, structural glazing, architectural hardware, heating and ventilation, and partitions.
Fusible alloys are characterised by their relatively low melting points – usually below 150°C. This can be exploited in various uses such as in solder, and in sprinklers which are activated when the alloy is melted by the heat from a fire. Fuses to stop electrical flow when the current begins to overload are another application.
 Other applications
Dentists use various alloys for filling dental cavities which are a cheaper version of more old-fashioned varieties such as gold and silver. These new composites can include titanium, molybdenum, chromium, chromium, cobalt and other ingredients.
Alloys can also be mixtures of other materials. Super plastics are relatively recent formulations which can be stretched to twice their length and so are useful for various industrial applications such as mould injection.
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