January 22, 2010

Aluminum Metal and Aluminum Alloy

Aluminum was discovered in 1827 by Friedrich Wohler. Its importance was established after the inventing of the dynamo (1887) because a great deal of electricity is consumed in its extraction.

Occurrence and extraction
Aluminum does not occur naturally in the pure form. In compound, it is the commonest metal on the earth (about 8% of the earth’s crust). The mineral richest in aluminum is bauxite. Among the EEC countries, France, Italy and Greece have significant reserves. Corundum is crystalline aluminum oxide. When pure and clear, it takes the form of gemstones’ (sapphire, ruby, topaz, amethyst).

To begin with, pure aluminum oxide (Al2O2) or alumina is extracted from bauxite. The Oxygen is then removed from alumina by electrolysis. Kryolith (Na2AlF6) is added as fluxing agent, in order to reduce the melting point from 2000 oC to 960 oC. The end of aluminum product uses in semi-finished goods (sheets, rods, profile, tubes) are super pure aluminum, Al 99.98 R or aluminum, e.g. 99.5 (DIN 1712T3).

Properties of Aluminum
Physical Properties:Melting Point: 658 oC
Density: 2.7 kg/dm3
Best electrical conductor after silver and copper.

Chemical Properties:
Corrosion resistant, impermeable oxide layer.

Mechanical Properties:
Tensile strength cast 160 to 320 N/mm2 rolled 150 to 400 N/mm2
Extensibility: 2% to 35 %

Technological:
Aluminum can be forged, rolled (down to thin foils), stretched, milled, cast, welded and soldered. Thermite, for instance, which is used in welding together bars, is a mixture of aluminum powder  and iron oxide. In aluminum coating, a mixture containing powdered aluminum can be sprayed on to steel and then burned in by annealing.