Softening suppression and property improvement by laser pretreatment of FSW AA6061 aluminum alloy

The thermal history associated with welding processes often leads to softening in aluminum alloys, negating their lightweight advantage. To counteract this, this study employs a novel pretreatment strategy using laser beam welding (LBW) prior to friction stir welding (FSW) in AA6061 aluminum alloy. The laser pretreatment, through its high energy density and rapid cooling, promotes grain refinement, creating a greater number of high-angle grain boundaries, and induces the precipitation of fine AlFeMnSi phases. This not only forms a more refined microstructure but also improves uniformity through recrystallization and precipitate pinning effects, which significantly enhances the strength and hardness of the FSW joints. Electron backscatter diffraction (EBSD) analysis revealed that the average grain size in the nugget zone of the pretreated FSW joint was 0.95 μm, which is 32.6 % smaller than the 1.41 μm observed in the conventional FSW joint. This investigation demonstrates an effective approach for achieving robust welds in aluminum alloys, potentially enhancing their application in various industries.