Sc microalloying enhanced strength-ductility synergy in FSW joints of 1561 aluminum alloy

Joint softening commonly occurs during friction stir welding (FSW) of work-hardened Al–Mg alloys, limiting their structural applications. In this study, 0.05 wt% Sc was added to the 1561 aluminum alloy to form Al 3 (Sc, Zr) phases. The work investigates how these phases influence the microstructural evolution and mechanical properties of the alloy before and after friction stir welding. It was found that primary Al 3 (Sc, Zr) particles refined the grain size, reduced dendritic segregation, and improved the pre-weld microstructure. The pinning effect of nanoscale coherent Al 3 (Sc, Zr) dispersoids effectively suppressed grain boundary migration. Consequently, the nugget zone (NZ) of the 1561Sc FSW joint exhibited relatively fine grains, a large fraction of high-angle grain boundaries (HAGBs), and a weak texture intensity. Microstructural analysis reveals the combined effects of grain refinement and precipitation strengthening from Al 3 (Sc, Zr) phases increased the tensile strength, yield strength and elongation of the FSW joint by 37 MPa, 67 MPa and 1.9 %, respectively, thereby achieving FSW joints of 1561 aluminum alloy with both high strength and ductility.