Ductility enhancement mechanism of laser welded magnesium alloy joints via synergistic effect of Gd powder addition and oscillating laser

Mechanical property of welded joint is an essential and critical factor for the widely application of magnesium alloy in component manufacturing. In this study, the synergistic effects of oscillating laser and Gd powder addition on ductility of laser-MIG hybrid welded magnesium alloy joints were investigated. Furthermore, the ductility enhancement mechanism was elucidated based on grain refinement and crack propagation behavior. The joint elongation was increased by 145.3 % while compared with that of non-oscillating laser welding. The stirring effect of oscillating laser and aggregation of high-melting-point precipitated phases (Mg, Al)₂Gd resulted in the grain refinement. The plastic anisotropy of the weld was reduced due to the randomized grain orientation, which was induced by the homogenic weld microstructure. Consequently, the activation of 〈c + a〉 dislocation slip was enhanced, which was the key factor for plasticity improvement. During the crack propagation process, the grain orientation was rotated by twins and the geometric compatibility of adjacent grains was improved. Consequently, the crack propagation along the grain boundary was hindered efficiently. The findings of this study contribute to the advancement of oscillating laser with power feeding welding technology and provide a valuable reference for enhancing ductility of magnesium alloy welded joints.