Quench factors and residual stress reduction in 7175-T73 plate

Quenching aluminium alloys with cold water by immersion or spraying produces large thermal gradients in thick components such as large forgings and plate. From a mechanical properties perspective, the consequent rapid cooling is ideal, but can result in high levels of residual stress. These residual stresses can cause warping during machining, dimensional instability and increased susceptibility to stress corrosion cracking. By decreasing the temperature gradients, residual stresses can be reduced. Using an experimentally determined tensile time temperature property curve for 7175-T73, and the application of quench factors, it is possible to cool the alloy to temperatures above the region of rapid transformation and then quench into water, thereby reducing residual stresses with minimal reduction in mechanical properties. Residual stresses have been quantified for these interrupted quenching procedures, and the corresponding tensile properties are reported.