Effect of Post-Weld Heat Treatments on Microstructure and Mechanical Properties of Friction Stir Welding Joints of AA2014 and AA7075

The present work investigates the influence of post-weld heat treatments (PWHT) on friction stir welded joints of AA2014 and AA7075 dissimilar alloys. Four different PWHT conditions, namely artificial aging (AA), solution treatment and artificial aging, solution treatment (ST), and natural aging (NA), were applied to study their influence on weld strength and microstructural properties. Natural aging showed the best strength of 347.5 ± 7.78 MPa among all the PWHT conditions. In contrast, other PWHT conditions deteriorated the tensile strength compared to as-welded joints. The highest elongation of 10.76 ± 1.27% was observed in NA, while the lowest was in AA among all the welded joints. The fracture location shifted to the stir zone (WNZ) in AA and ST. In contrast, in other PWHT welds, fractures occurred outside the weld region. Abnormal grain growth was observed in the WNZ of the ST joint. Microhardness improvement was observed in WNZ of ST and NA weld, while a lower value was found in the remaining ones. Fracture study revealed that fracture mode was brittle in AA whereas ductile in other joints.