Atomized Filler Powder Compositions Tailoring Microstructural Evolution and Mechanical Properties in Dissimilar High-Strength Aluminum Alloy Laser Welded Joints

Abstract To meet the growing demand for lightweight structures in the aerospace industry, laser welding of dissimilar high-strength aluminum alloys has emerged as a key manufacturing technology. However, the incorporation of filler materials during laser welding significantly influences porosity formation and microstructural evolution, thereby affecting the mechanical properties of the welded joints. Unlike previous studies that have focused on a single filler material, this study systematically investigates, for the first time, the effects of three distinct types of filler materials (atomized powders of AlCu5, AlSi12, and AlMg5) on the macroscopic morphology, microstructure, and mechanical properties of laser-welded joints between dissimilar AA2195 and AA7075 aluminum alloys. The study results demonstrate that, in comparison with the other two filler materials, the grains in the AlSi12-welded joint were significantly refined in both the weld zone (WZ) and the partially melted zone (PMZ), with grain sizes reduced to 31.2 μm and 15.9 μm, respectively. The addition of Si reduces the thermal conductivity of the molten pool, thereby slowing the solidification rate and promoting the escape of hydrogen bubbles, resulting in an internal porosity as low as 1.07% in the joint. Moreover, the AlSi12 welded joint exhibited the highest proportion of high-angle grain boundaries in the PMZ, reaching 91.51%. In addition, the interaction between the second phase and dislocations significantly impeded dislocation motion. Owing to the synergistic effects of multiple mechanisms, the resistance to crack initiation and propagation in the AlSi12 welded joint was significantly improved, with the fracture location shifting from the conventional PMZ to the WZ, and the ultimate tensile strength reached 285 MPa.