Aluminium encyclopaedia

Properties

The diverse applications of aluminium are based as a rule on several favourable properties, for example on its low specific weight in combination with high strength. The most important of these properties are listed here in alphabetical order:

  • Alloys: aluminium forms alloys with all industrially used metals and nearly all other metals, and these form the basis for most aluminium products.
  • Chemical affinity: aluminium has a strong tendency to form compounds, especially with non-metals such as oxygen.
  • Combustibility: aluminium does not burn. It is only under specific conditions, i.e. in finely divided form (for example, in powder form), that it reacts strongly in an exothermic manner (as do other metal powders); it is thus used in aluminothermics as a fuel in space travel.
  • Corrosion resistance: thanks to its natural oxide layer, aluminium shows very good corrosion behaviour in contact with water and many other chemicals, and is thus used, for example, in electrical engineering, mechanical engineering, rail and road vehicles, packaging or building construction.
  • Density (specific weight): aluminium has a density of 2.7 grams per cubic centimetre and is thus a light metal (iron, for example, has a density of 7.8 grams per cubic centimetre and is almost three times heavier). This property is used for energy-saving lightweight construction or design, especially in aircraft construction, civil engineering, road or rail vehicles, shipbuilding and packaging.
  • Diffusion resistance: impermeable to gases and liquids even as the thinnest foil, thus very suitable for packaging.
  • Electrical conductivity: aluminium has a conductivity that is some 60 per cent of the (high) conductivity of copper; its specific conductivity, which takes density into account, is even higher than that of copper. It is thus a good conductor and is widely used in electrical engineering and electronics.
  • Magnetisability: aluminium is non-magnetic, a fact that is of importance in electrical engineering, electronics and mechanical engineering. The metal can, however, be magnetised using an eddy current. This is used in industrial applications such as waste separation (eddy-current separators).
  • Melting point: 660 °C and thus low compared with ferrous materials (around 1500 °C), this saves energy when melting and remelting (recycling).
  • No health risk: aluminium does not pose a risk to human health.
  • Processing: possible to process using all common metal processing techniques. Thanks to their high ductility (formability) forming of aluminium and its alloys is easier than with most other industrially used metals, for example ferrous materials.
  • Reflectance: the very high reflectance of light and heat rays is used in aluminium paints and bright-finish alloys.
  • Strength: the strength of aluminium is high in relation to its density, making the metal very suitable for lightweight construction.
  • Thermal conductivity: the conductivity of refined aluminium, for example, is four times higher than that of steel (and half that of silver). For this reason, aluminium is used above all in mechanical engineering applications (for example for pistons in internal combustion engines of road vehicles), in air conditioning technology (for example for heat exchangers and radiators) and in household equipment (for example for cooking pots and heating plates).


Most properties can be influenced in a targeted manner, for example by alloying or heat treatment. As with other metals, one has to accept that due to the improvement in a specific property one or more others will deteriorate. For example, increasing the strength will lead to a reduction in cold workability (ductility).