Heat treatment: Non-age-hardenable wrought alloys

Hardening mechanisms:

This group includes unalloyed aluminium and the AlMg, AlMn and AlMgMn type alloys. With these alloys, increases in tensile strength are achieved by means of cold working and solid-solution hardening.

The tensile strength Rm is usually used as the characteristic value to evaluate strength properties. The diagram alongside shows the ranges of values that can be achieved for this property.

To some extent, other material properties, such as proof stress Rp0.2, elongation at fracture A5, notch sensitivity and corrosion resistance, exhibit contrary behaviour. Therefore for a specific application, the material and heat treatment must be chosen so that the material properties satisfy the requirements of the component during manufacturing and subsequent service.

Solid-solution hardening is achieved by introducing foreign atoms into the aluminium crystal lattice. Up to a certain fraction, this effect increases with the number of foreign atoms in solution. The presence of the alloying atoms strains the aluminium crystal lattice and this leads to higher strength values.

Work hardening occurs as a result of the dislocation of lattice planes during plastic deformation, whereby the dislocations interact with each other and thus cause an increase in tensile strength.

During the production of non-age-hardenable semi-finished products, work hardening has the greatest influence on tensile strength. The figure alongside clearly shows the effect of solid-solution hardening for an AlMg system and the work hardening of an AlMgMn type alloy.