Fatigue crack propagation behavior in friction stir welding of AA6063-T5: Roles of residual stress and microstructure

Behavior of fatigue crack which was propagated at some representative areas in the friction stir welded (FSWed) joint of aluminum alloy 6063-T5 was studied. By extracting the T–L orientation specimens so that the loading axis on the fatigue test and the crack propagation direction were transverse and longitudinal to the welding direction, respectively, the crack propagation tests were carried out for both the as-welded and post-weld heat treated (PWHTed) FSWs at room temperature and 200 °C. The experiments showed that the fatigue crack propagation (FCP) rates were sensitive to the propagating location, the test temperature, and the PWHT condition as well. It was also found that the different FCP rates were driven by the microstructural influences in and around the welded zone. While the residual stress was remarkable in the shoulder limit areas, it had a minor effect on the FCP behavior.

► Crack growth behavior under room temperature and 200 °C is studied.
► Roles of microstructure and mechanical in fatigue crack growth are clarified.
► Different crack growth rates are driven by weld microstructure.
► Role of residual stress is not so significant in nonuniform fatigue crack resistance.