Effect of filler-wire composition on microstructure and strength in adjustable ring-mode laser welded joint of 6063 aluminum alloy

To address porosity formation, grain coarsening and mechanical softening in aluminum alloy laser welding, this study investigates the effect of filler wire composition on microstructure evolution and mechanical performance of 6063 aluminum alloy welded joints. Five filler wires were adopted for adjustable ring-mode laser welding of 2 mm-thick 6063 aluminum alloy plates. The results show that high-Si fillers (ER4047) significantly improve weld pool fluidity, enhancing bubble escape and reducing porosity. Al–Mg fillers (ER5356) enrich Mg content and dilute Fe concentration, thereby suppressing the formation of brittle AlFeSi phases. The hybrid filler wire ER4047/ER5356 combines the characteristics of two types of filler materials. It maintains low Fe content and low weld porosity, restrains columnar grain growth, and optimizes the Mg/Si ratio in the molten pool. This facilitates the formation of Mg–Si eutectic clusters and improves solid-solution strengthening, yielding the maximum weld microhardness of 61.9 HV, higher than the base metal (57.2 HV). Meanwhile, the ER4047-filled joint exhibited the highest ultimate tensile strength of 163.1 ± 3.1 MPa, compared with 150.8 ± 4.5 MPa for the autogenous weld, while all filler-assisted joints fractured in the base metal. This work reveals the synergistic mechanism of Mg/Si ratio control and microstructure evolution induced by ER4047/ER5356 hybrid filler, and provides a practical guideline for filler optimization to enhance joint quality and structural performance in lightweight manufacturing.