Stress relieving is carried out on metal products in order to minimize the residual compressions in the structure thus reducing the risk of dimensional variations during the manufacture or final use of the component itself.
These compressions can cause unwanted dimensional changes if they are released in an uncontrolled way, for example during a subsequent heat treatment.
Stress relieving normally takes place after roughing and before final finishing such as polishing or grinding. The pieces that have very precise dimensional tolerances and must be subjected to subsequent heat or surface treatments must be stress-relieved.
On aluminum alloys, stress relieving is a fallback treatment, not a practice characterized by parameters such as in the case of solublising, aging or annealing intended as a zero state. The stress relieving of aluminum or its alloys, in fact, is not possible for all alloys and when it is, a specific temperature must be respected in order not to produce structural changes of the material. The temperature holding time is variable and at the end of this period the components must undergo slow cooling to avoid the tensions caused by temperature differences in the material.
Some of the cycles put into practice for stress relieving for aluminum can be for details deriving directly from sand and shell casting or die-casting, for details that have undergone the T6 treatment to increase the mechanical characteristics of the piece and for carpentry obtained from rolled products and welded.
The reasons behind the stress relieving of aluminum are different and can be summarized as follows:
Dimensional stability after mechanical processing
Reduction of hardness to increase cold plastic deformation
Stress relieving ends of the welds on castings recovered for casting defects or welded structures to form bases, molds, frames
To underline the fact that these characteristics have a different thermal profile, as well as the starting condition and the type of alloy.
In the automotive industry, aluminum treatments are possible thanks to the IATF 16949 certification.