Suppressing Hydrogen Porosity and Enhancing Strength in LMD-Welded L-PBF AlSi10Mg via Pre-weld Degassing and Er/Zr Microalloying

Fusion welding of L-PBF AlSi10Mg is hindered by severe hydrogen-induced porosity. To address this, a combined strategy of pre-weld hydrogen degassing annealing (PW-HDA, 250–400°C) and Er/Zr microalloying using an AlSi10Mg-Er-Zr filler was employed, followed by low-heat-input laser metal deposition (LMD) butt welding. The results demonstrate that PW-HDA effectively suppressed hydrogen porosity, reducing both pore density and maximum pore size. The AlSi10Mg-Er-Zr filler slightly reduced porosity and refined the α-Al cellular structure and Si-rich eutectic network. Raising the PW-HDA temperature from 250°C to 400°C decreased hydrogen porosity from 3.2% to 0.7% and shifted fracture behavior from microstructure-controlled to ductile, increasing elongation from 5.3% to 19.1%, albeit with a notable reduction in ultimate tensile strength (UTS) at the highest temperature. A relatively low PW-HDA temperature of 250–280°C combined with the AlSi10Mg-Er-Zr filler produced superior mechanical performance, increasing UTS by 4.3–7.2% and elongation by 3.8–94.6% compared with conventional AlSi10Mg filler joints. The optimal condition (280°C PW-HDA + Er/Zr filler) achieved 259.0 MPa UTS and 10.9% elongation, owing to refined α-Al cells and Si-rich eutectic, as well as the minimization of hydrogen pore size and density.