Investigating strength increasing modifications to a friction stir welded AA7075 T-peel joint’s exit location: a modeling led study

Modifying the friction stir welding (FSW) process to improve the strength of the joint requires knowledge of process-structure–property relationships. Exit holes in friction-stir welded joints, unavoidable artifacts of FSW, are known to reduce joint strength. However, the aspect of the AA7075 T-peel joint’s structure at the exit location that is the most detrimental to the strength remains to be discovered. This study used finite element simulations to explore the effect of two modifications to the joint’s structure at the exit location on joint strength. The two modifications were eliminating the exit hole and producing an effective bond around the exit hole. The simulations relied on characterizing the weld’s structure and local hardness distributions and considered fracture property variation. Through modeling, it was predicted that effective bonding around the exit hole would significantly increase joint strength even with the presence of the exit hole. In the subsequent experimental task, the rotating tool “dwelled” at the exit hole before it exited the workpiece. In other words, the welding process was modified to include dwell time at the exit location, and as a result, effective bonding around the hole was observed. Using dwell times of 1, 2, and 5 s increased the T-peel joint’s strength by 29%, 31%, and 41%, respectively.