Study on microstructure and mechanical properties of new generation high-magnesium aluminum alloy cross-welded joints by friction stir welding-friction stir welding

In order to meet the manufacturing requirements of large aluminum alloy ship panels, the cross-welded by friction stir welding-friction stir welding (FSW/FSW) tests of new generation high-magnesium aluminum alloy were carried out. The results show that a well FSW/FSW joint was obtained. Grain size in stir zone (SZ) is the smallest, and there is no obvious directionality of grains morphology in thermo mechanical affected zone (TMAZ). The grain size in the SZ of the FSW/FSW joint is smaller than that of the FSW. Hardness test results show that hardness in the FSW/FSW weld joint has a smaller variation range as compared to the FSW joint. A soft region appears in the advancing side (AS) of the FSW/FSW joint. Tensile test results show that the tensile strength of FSW/FSW joint is 340 MPa, which is around 87% of the base material. The tensile samples fracture in the heat-affected zone (HAZ) is a typical ductile fracture mode along the 45° to the tensile direction. The strength of the FSW/FSW joint is slightly lower than that of FSW joint (358 MPa). The fatigue cycle of the cross-welded joint is up to 2 × 10⁶ times without fracture when the maximum stress is 150 MPa, indicating an excellent anti-fatigue performance. Fatigue cracks main initiate at the bottom of the joint, and the fracture mode of transient fault zone is ductile fracture.