Friction stir welding of additively manufactured A20X and effects of post-weld heat treatments

This work investigates the microstructural evolution and mechanical performance of the A20X aluminum alloy produced by laser powder bed fusion (LPBF), joined by friction stir welding (FSW), and finally heat treated. The as-built material exhibited an ultrafine equiaxed grain structure (1.23 ± 0.5 μm) with relatively high strength (YS of 304 MPa; UTS of 391 MPa). After FSW, the joints showed a stir zone with fine grains (2.01 ± 0.94 μm) and a moderate hardness increase. Direct aging proved ineffective in enhancing strength, whereas the T6 treatment at the peak-hardness condition (i.e., solutionizing at 530 °C for 2.5 h and aging at 195 °C for 2 h) significantly improved mechanical properties. TEM analysis clarified that precipitation strengthening was achieved after the heat treatment. Peak-aged specimens exhibited the highest hardness (about 150 HV) and strength (UTS of 442 MPa in the base metal, 418 MPa in the joints) with only a limited reduction in ductility. However, some peak-aged joints exhibited markedly lower ductility, with elongation at fracture below 3%, likely associated with the presence of internal weld defects. Overall, the combination of LPBF, FSW, and optimized T6 heat treatment enables the fabrication of high-strength A20X joints suitable for advanced applications.