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Home > Aluminium alloys brief introduction

Aluminium alloys brief introduction


Pure aluminium is relatively soft. To overcome this, the metal can be alloyed and/or cold worked. Most of the aluminium reaching the marketplace has been alloyed with at least one other element.

There is a long-established international system for identifying aluminium alloys (see the table below). The first digit in the four-digit alloy code identifies the major alloying element.

The European standard uses the same codes.

The table below gives the broad outline of the systems.

Alloying element

Alloy code

Alloy type

None (pure aluminium)

1000 series

Not hardenable


2000 series



3000 series

Not hardenable


4000 series

Not hardenable


5000 series

Not hardenable

Magnesium + silicon

6000 series



7000 series



8000 series



The 6000 series is by far the most widely used alloy in aluminium extrusion.

As cold working is the only way to increase the strength of the alloys that cannot be hardened, most of these go for rolling. In extrusion, on the other hand, hardenable alloys are the most commonly used.

The 6000 series, which has silicon and magnesium as the alloying elements, is by far the most widely used in extrusion. In a 7021 alloy, zinc and magnesium are responsible for the hardening effect. Some alloys use manganese, zirconium or chrome to increase toughness.

Iron, which is found in all commercial aluminium, can have a negative effect on toughness and finish (amongst other things) if present in high quantities.

Two hardening methods are used on alloys in the extrusion process. ‘Solution’ heat treatment is carried out during extrusion by carefully controlling the temperature of the emerging profile. ‘Precipitation’ hardening (ageing), which takes a few hours, occurs in special furnaces after the extrusion process.

Amongst the factors affecting the choice of the right alloy for an extruded product are:
– Strength, finish, suitability for decorative anodizing, corrosion resistance, suitability for machining and forming, weldability and production costs.