Microstructure characteristics, static and fatigue properties of additive FSW T-joint of 6061 alloy

The weld forming, microstructure, micro-hardness, static performance and fatigue properties of the 6061 aluminum alloy additive T-joint welded by stationary shoulder friction stir welding were evaluated. The surface of shoulder affected region is characterized by super fine grains. The hardness in the skin and stringer decreases at different levels compared to that of the base material. T-joints fail at the heat affected zone during the tensile tests in both skin and stringer direction, the joint coefficients are 0.68 and 0.83 respectively. Using given welding parameter, the characterized fatigue strength is 101.4 MPa at the cycle of 2 × 10⁶. Filling material improves the fatigue property of T-joint evidently. Fatigue crack initiates at the plunge heel due to stress concentration. The fatigue failure mechanism is dominated by transgranular fracture.