Microstructures and mechanical properties of laser welded joints in Ce-containing rare earth magnesium alloys

During the welding thermal cycle, changes in the distribution and morphology of precipitates within the heat-affected zone (HAZ) often lead to typical softening, making HAZ the weakest region of the welded joints. In this study, a novel welding strategy is proposed by integrating fiber laser welding with thermally stable Ce-containing rare earth precipitates. This approach enables the tailored regulation of precipitate structures in both the fusion zone and HAZ, simultaneously refining precipitate distribution, narrowing the HAZ width and mitigating softening, thereby enhancing the overall mechanical performance of the joint. The results reveal the formation of numerous micron- and submicron-sized precipitates within the fusion zone, which are dispersed along dendritic arm boundaries. These particles serve to effectively pin dislocations and hinder their movement during deformation, contributing to fusion zone strengthening. Meanwhile, the thermally stable rare earth precipitates in the HAZ help preserve the original precipitate structure of the alloy, maintaining the HAZ width at around 100 μm after thermal cycling and substantially reducing microstructural degradation caused by welding. Tensile testing confirms that, with Ce micro alloying and optimized laser welding parameters, the resulting joints exhibit excellent mechanical properties, achieving a lap shear strength of 74.4% relative to the base metal. These findings validate the feasibility and effectiveness of the proposed welding strategy for high-quality joining of rare earth magnesium alloys.