Residual stress reduction in 7175-T73, 6061-T6 and 2017A-T4 aluminium alloys using quench factor analysis

The quenching of aluminium alloys by immersion or spraying using cold water produces large thermal gradients in thick components such as forgings and plate. Whilst the rapid cooling ensures good mechanical properties the thermal gradients can be large enough to produce high levels of residual stress. Reducing the cooling rates during the quench can reduce the magnitude of the residual stresses, however it can also be detrimental to the mechanical properties, particularly for quench sensitive alloys. By generating time temperature property C-curves for each alloy and using quench factor analysis, it is possible to slowly cool the alloy from the solution heat treatment temperature to an intermediate temperature, above the critical temperature region of the C-curve, and then quench to room temperature. The result of this is a reduction in the residual stresses generated during the quench due to a reduced thermal gradient combined with a negligible effect on the mechanical properties of the alloys. The C-curves for the Vickers hardness have been generated for each alloy and temper and are presented. The residual stresses have been quantified for this alternative quenching route for each alloy and the Vickers hardness results are presented.