Fatigue property of Al-Li alloy friction stir welded lap joints

Through the fatigue test, fracture characteristic and microstructure analyses, the fatigue property of the Al-Li alloy friction stir welded lap joints and the effect of "hooking defect" appearing at the thermal-mechanically affected zone(TMAZ) of advancing side on the joint fatigue property were studied. The results show that the cracks can easily initiate and extend from the location of hooking defect, leading to the decrease in the "effective sheet thickness"(EST) of material and damage to the joint fatigue behavior. The appropriate reduction of the pin length is proved one way of to improve the defects and mechanical property of joints. Furthermore, the established S-N curves show that the fatigue life of lap joints is close to base metal on the high fatigue stress. As the fatigue stress decreasing, the joint fatigue life sharply declines and the fatigue strength of joints at fatigue life N=2 10⁶ is only 80 MPa, only equivalent to 35% that of base metal.