Two distinct interface structures and fracture behavior in oscillating laser welding of Al/Mg dissimilar metals

In this study, high-frequency circular oscillating laser is employed to achieve a more uniform energy distribution and a Ti interlayer is used to suppress the continuous and excessive formation of brittle Al–Mg intermetallic compounds (IMCs). The results show that the joint interface exhibits an optimal “U-shaped” morphology at 3.0 kW with the Ti interlayer melting uniformly. The interface is primarily composed of a 6-μm Al–Mg IMCs layer and a 23-μm Al–Ti IMCs layer. During shear tests, fracture occurs along the Al–Ti IMCs layer. At 3.5 kW, the Ti interlayer is completely penetrated, and the interface transforms into an “n-shaped” configuration consisting of an α-Mg + Al 12 Mg 17 eutectic phase and a dispersed mixture of Al–Ti IMCs. Fracture occurs at the Mg-side fusion line. Neither joint exhibits large-area, single-phase Al–Mg IMCs. Instead of occurring at the conventional Al–Mg interface, fracture is shifted to the Mg-side fusion line, allowing both joints to achieve reliable strengths of ≥2.5 kN.