Microstructure and mechanical properties of laser welded joint of cerium-containing magnesium alloy

The modification of magnesium alloy through the addition of rare-earth elements improves specific properties of magnesium alloy. However, the evolution mechanisms of rare-earth precipitates during thermal cycles are still unclear, particularly during the welding thermal cycles. Therefore, deep research on the influence mechanisms of rare-earth precipitates on the welded joint is necessary. In this paper, Ce-containing Mg alloy was successfully welded by laser welding. The microstructure of the welded joint was deeply analyzed. As a result, the elemental composition and distribution rules of precipitates within the fusion zone were obtained. In addition, heat treatment was carried out for the welded joint, thus deducing the evolution mechanisms of precipitates within the joint. The corresponding results revealed that typical micron/sub-micron-sized particles, consisting of both conventional and rare-earth intermetallics, are formed and neatly distributed within the fusion zone, demonstrating that the rare earth particles inside the fusion zone are much smaller in size than that of Mg₁₇Al₁₂. Tensile test results suggest that these tiny particles significantly improved the strength of the fusion zone, promoting the tensile-shear strength of the joint accounting for 76.6% of that of the base metal. The above approach provides a feasible solution for the welding of rare-earth Mg alloys. (author)