Heat treatment of aluminium alloys - Material and recommendations

Aluminum and aluminum alloys are increasingly used in sectors as diverse as the automotive, aerospace, household appliance, electrical and nuclear industries. This is due to the low density of these alloys (approx. 2.6 g/cm ³ ), combined with very interesting forming and application properties.

In particular, these alloys offer a wide range of mechanical properties. Tensile strength ranges from 50 MPa for refined aluminum in the annealed condition to 750 MPa for high-strength alloys of the Al-Zn-Mg-Cu (7049 A) type in the quenched and tempered condition.

Such a range of mechanical properties is obtained by acting jointly on the composition of the alloys and by carrying out heat treatments, which allow either :

• reduce mechanical strength, generally accompanied by an increase in plastic deformability (softening treatments);

• increase mechanical strength (hardening treatments).

However, the aim of heat treatment is not only to affect mechanical strength, but also to influence a large number of other properties that are sometimes very important to users, such as :

• suitability for hot (or cold) processing;

• resistance to corrosion, fatigue and creep ;

• suitability for anodic oxidation ;

• electrical conductivity ;

• dimensional stability, etc.

This article discusses :

• the vocabulary used in this field, in particular state designations and their meaning;

• heat treatment plants ;

• practical recommendations for carrying out heat treatments.