Effect of Welding Process Parameters on Fatigue Property of 7B04-T6 Aluminum Alloy Friction Stir Spot Welded Joint

7B04-T6 aluminum alloy plate with thickness of 1.5 mm was welded by refill non-keyhole friction stir spot welding with different refill time, insertion time, insertion depth, and rotation speed, and then tensile-tensile fatigue tests were carried out on the joint. The effect of welding process parameters on fatigue property of the joint was studied. The results show that the joints under different welding processes were all composed of nugget zone, thermo-mechanically affected zone, heat affected zone and base metal. Hook defects were present in the junction zone of the two plates in the thermo-mechanically affected zone. The order of influences of welding parameters on fatigue life of the joint from weak to strong was refill time, insertion time, insertion depth and rotation speed. With the rotation speed of 2 500 r·min^-1, the refill time of 2 s, the insertion depth of 1.9 mm, and the insertion time of 3 s, the fatigue life of the joint was the longest of 211 919 cycles. The fatigue crack initiated at hook defects in the junction zone between the two plates.