Fatigue Behavior of Friction Stir Welded Lap Joints for Dissimilar AA7150-AA2524 Aluminum Alloy

The detail fatigue rating (DFR) value of friction stir welded (FSW) lap joints for dissimilar AA7150-AA2524 aluminum alloy was experimentally investigated. The metallographic analysis was carried out on by optical microscope (OM). Fatigue fractography was observed under scanning electron microscope (SEM). The results indicate that DFR value of AA7150-AA2524 FSW lap joints is 191.54MPa. There is no distinct different boundary between HAZ and BM of the upper AA7150 sheet. The grains in the upper NZ of AA7150 are coarser than those in the bottom NZ of AA2524. Fracture morphologies shows that lots of hook defects in the FSW lap joint. Fractography indicates that fatigue crack is initiated from the AA2524 bottom surface around the weld center, where weak-bonding defects can be seen. The hook defects and weak-bonding defects have obvious influence on the fatigue property of friction stir welding lap joints, which seriously reduce the fatigue strength.