What is an alloy?

Generally speaking, an alloy is a mixture of a metal with one or more alloying elements, which can be metallic or non-metallic. Materials that contain at least one metallic element, and behave in the same way as a metal, are thus called ‘alloys’.

Alloying often has the advantage that it allows the properties of the basis metal to be improved. In particular, strength and corrosion resistance can be improved in this way.

Alloys are named after the element that is present in the largest amount; the other alloying elements are then listed in the order of decreasing composition. Thus, in an aluminium-silicon-copper alloy, aluminium is the basis metal and silicon and copper are the other alloying elements, with silicon having the higher content of the two.

What role do alloys play in the aluminium industry?

For practical applications, aluminium is usually alloyed with other elements, mostly with other metals. This enables the properties of the basis metal to be improved considerably. Alloying produces improvements in aluminium’s properties, such as protection against corrosion by certain substances. A few per cent magnesium, for example, make it resistant to seawater and thus suitable for shipbuilding. Generally speaking, by choosing the right alloying elements, aluminium can be optimised for a specific application. Not least because of this, aluminium alloys have acquired a special importance in many technical fields.

Strictly speaking, commercial-purity aluminium, with an aluminium content of up to 99.9%, is also an alloy. Although the iron and silicon contents here are regarded as impurities, they affect the properties of aluminium significantly.

In the aluminium industry, one generally differentiates between casting and wrought alloys: casting alloys can only be shaped by casting and are not subjected to subsequent forming. Here, magnesium, silicon and copper are the alloying elements most widely used. By contrast, wrought alloys are intended to undergo deformation using processes such as extrusion, rolling or forging and thus need to have good formability. Important alloying elements here are magnesium, silicon, copper, manganese, zinc and iron.