Aluminum alloys (or aluminum alloys; see spelling differences) are alloys in which aluminium (Al) is the predominant metal. The typical alloying elements are copper, magnesium, manganese, silicon, tin and zinc. There are two principal classifications, namely casting alloys and wrought alloys, both of which are further subdivided into the categories heat-treatable and non-heat treatable. About 85% of aluminum is used for wrought products, for example rolled
plate, foils and extrusions. Cast aluminum alloys yield cost-effective products due to the low melting point, although they generally have lower tensile strengths than wrought alloys. The most important cast aluminum alloy system is Al¨CSi, where the high levels of silicon (4.0¨C13%) contribute to give good casting characteristics.
Aluminum alloys are widely used in engineering structures and components where light weight or corrosion resistance is required. Alloys composed mostly of aluminum have been very important in aerospace manufacturing since the introduction of metal skinned aircraft.
Aluminum-magnesium alloys are both lighter than other aluminum alloys and much less flammable than alloys that contain a very high percentage of magnesium.
Aluminum alloy surfaces will develop a white, protective layer of
aluminum oxide if left unprotected by anodizing and/or correct painting procedures. In a wet environment, galvanic corrosion can occur when an aluminum alloy is placed in electrical contact with other metals with more positive corrosion potentials than aluminum, and an electrolyte is present that allows ion exchange. Referred to as dissimilar-metal corrosion, this process can occur as exfoliation or as inter granular corrosion. Aluminum alloys can be improperly heat treated. This causes internal element separation, and the metal then corrodes from the inside out. Aircraft mechanics deal daily with aluminum alloy corrosion. Aluminum alloy compositions are registered with The
Aluminum Association. Many organizations publish more specific standards for the manufacture of aluminum alloy, including the Society of Automotive Engineers standards organization, specifically its aerospace standards subgroups, and ASTM International.