Effect of Precipitation Hardening on the Residual Stress Behavior in Aluminum 7075

The phase changes in precipitation hardenable aluminum alloys throughout the heat treatment process are often used advantageously to enhance mechanical properties. However, the presence of precipitates may also result in residual stresses within the alloy. In this research, two sets of solution annealed Al-7075 samples were subjected to aging heat-treatments to form secondary phase precipitates at different kinetic rates. Following heat treatment, x-ray diffraction was used to analyze precipitate phases and surface residual stress (using the sin²ψ method). Crystallite size and volume fraction of the precipitates were determined from XRD pattern data and microstructural analyses. Results show strong correlation between the magnitude of compressive residual stress in the Al-7075 surface and aging time, precipitate size, and precipitate volume fraction.