Influence of ageing on cyclic deformation behavior and residual stress relaxation of deep rolled as-quenched aluminium alloy AA6110

Deep rolling was applied to solution-heat-treated (as-quenched) AA6110 at room temperature. Subsequently, the deep rolled as-quenched specimens were aged at different temperatures and times. Push-pull fatigue tests were performed at room temperature to evaluate the optimized ageing condition. Cyclic deformation behavior, s/n-curves and depth profiles of near-surface residual stresses and full width at half maximum (FWHM) values of X-ray diffraction peaks as well as hardnesses are presented as compared to the conventional mechanical surface treatment (ageing followed by deep rolling). Thermal residual stress relaxation was investigated by applying a Zener-Wert-Avrami function. It was found that fatigue lifetimes of deep rolled as-quenched AA6110 after ageing were governed by near-surface hardness. Work- as well as precipitation hardening in near-surface regions enhances the fatigue lifetime significantly. Deep rolling after optimized ageing treatment can combine the work- and precipitation hardening in near surface regions and thus results in excellent fatigue strength of AA6110.