Influence of Residual Stress and Microstructure on the Fatigue Crack Growth Behavior of Intersecting Friction Stir Welded Joints

Friction stir welding (FSW) is extensively applied in aerospace. In practice, welds are often required to intersect, resulting in complicated stress states and significant microstructural variability. This study investigates intersecting FSW joints of 2024-T3 aluminum alloy under different process parameters. Fatigue crack growth behavior was examined through experiments and finite element simulations, while electron backscatter diffraction (EBSD) characterized microstructural evolution. Results show that compressive residual stress delays crack propagation, with cracks along Weld 1 exhibiting a distinct “retardation and acceleration” pattern, particularly at higher rotational speeds. Welding sequence significantly influences grain refinement and fatigue resistance. Weld 1 undergoes more extensive refinement than Weld 2; the intersecting region shows the greatest refinement, and the advancing side shows microstructural heterogeneity and localized strain concentration. The coupled influence of residual stresses and microstructural attributes jointly determines the fatigue crack growth behavior of intersecting FSW joints.