Dynamic precipitation in Al-Zn-Mg-Cu Alloys: A comparative analysis of uniaxial tension and cross-die forming

Al-Zn-Mg-Cu alloys are known for their exceptional mechanical properties, primarily achieved through precipitation hardening. This study investigates the dynamic precipitation behaviour in a pre-aged AA7075 alloy under uniaxial tension and cross-die forming at 180 °C. In-situ synchrotron small-angle X-ray scattering (SAXS) revealed a non-monotonic precipitate growth behaviour under uniaxial tension, where growth was initially accelerated but slowed as strain exceeded 7%. Synchrotron SAXS and wide-angle X-ray scattering (WAXS) were used to simultaneously map precipitation and deformation across regions with varied strain conditions in samples subjected to warm cross-die forming demonstrating local variations in precipitation and dislocation arrangement, along with an inverse dependence of precipitate growth on plastic strain. A modified Kampmann-Wagner Numerical (KWN) model was applied to successfully predict the overall precipitation behaviour, highlighting that the competing effects of deformation-induced vacancies enhancing diffusivity and the reduction of supersaturation due to precipitate growth are of primary importance, while the potential influence of strain path in monotonic deformation is of secondary significance.