Aluminium encyclopaedia

Alloying elements

Aluminium bildet mit fast allen metallischen und mit vielen nicht­metallischen Elementen Legierungen, doch nur wenige finden breite Verwendung. In erster Linie sind dies die Metalle Eisen, Kupfer, Magnesium, Mangan und Zink sowie das Nichtmetall Sili­zium, in geringerem Umfang auch Blei, Bor, Chrom, Nickel, Titan, Wismut, Zinn und Zirkon. Jedes dieser Elemente verbessert schon in geringen Mengen bestimmte Aluminiumeigenschaften, ver­schlechtert aber oft andere, sodass in der Regel ein weiteres Ele­ment zugegeben wird, um die Verschlechterung nach Möglichkeit auszugleichen.

  • Lead, bismuth and tin improve the machinability by causing chips to break off readily. Such aluminium alloys are also called "free-cutting alloys".
  • Boron increases the electrical conductivity of conductor-grade aluminium for use in electrical engineering, because when added too a melt, in quantities of 0.005 to 0.02 per cent, it forms chemical compounds with the elements chromium, titanium and vanadium (which impair the conductivity), which precipitate out in the solid metal as borides that do not affect the conduction of electricity.
  • Copper increases the strength at room temperature but decreases corrosion resistance.
  • Magnesium and manganese make alloys more corrosion resistant and increase the strength.
  • Nickel increases the strength at higher temperatures.
  • Silicon lowers the melting point and the viscosity of the melt (thus improving the castability), but has a detrimental effect on forming.
  • In combination with boron, titanium refines the grain structure.
  • In combination with magnesium, zinc results in the highest strength and high hardness but reduces formability.

Aluminium itself is also used as an alloying element to a significant extent:

  • above all in copper, which on addition of about one per cent becomes harder, more corrosion resistant, easier to melt and tougher
  • in magnesium and titanium alloys
  • in steel production.