Manufacture

Aluminium, the most common metallic element in the earth's crust, is extracted from the ore bauxite, an impure form of aluminium oxide or alumina. The bauxite is dissolved in caustic soda, filtered, reprecipitated to remove impurities and dried. The pure alumina is then dissolved in fused cryolite (sodium aluminium fluoride) within a carbon-lined electrolytic cell. Electrolysis of the aluminium oxide produces oxygen and the pure aluminium, which is tapped off periodically and cast. The process is highly energy intensive, and typically the production of 1 tonne of aluminium requires 14 000 kWh of electrical energy. In the western world, 60% of this energy is from renewable hydroelectric power. Currently, 63% of new aluminium used in the UK is from recycled sources, and recycling requires only 5% of the energy input compared to primary production. Cast ingots or slabs are hot rolled at 500°C into 5 mm coiled sheet which subsequently can be cold rolled into thinner sheet or foil. Due to the ductility of aluminium, the metal can be extruded into complex shapes or drawn into wire. Forming and machining processes are generally easier than with steel. Aluminium components may also be formed by casting.

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