The Evolution Mechanisms of Intermetallic Compounds within the Fusion Zone and Heat-Affected Zone of Laser-Welded Joint of Cerium-Containing Magnesium Alloy

Softening of the heat-affected zone (HAZ) is a major cause of weld failure, highlighting the importance of mitigating HAZ softening to achieve high-quality welded joints. Therefore, in-depth research on the evolution mechanisms of intermetallic compounds (IMCs) within the weld is crucial. In this paper, Ce-containing Mg alloy was joined by fiber laser welding. The formation mechanism of the welded joint and the evolution rules of IMCs within both the HAZ and the fusion zone are investigated. The results indicate that during the welding operation, precipitates composed of conventional elements within the HAZ melt, flow, and form agglomerates with coral-like internal structures, contributing to the HAZ softening and subsequent joint failure. In contrast, precipitates consisting of rare-earth elements preserve their original morphology, mitigating the microstructural variations and softening of the HAZ. Additionally, fine particles with sizes < 1 μm are generated and uniformly distributed in the fusion zone, enhancing the mechanical performance of the fusion zone. Utilizing microstructural and compositional analysis along with phase diagrams, the dynamic evolution of IMCs in both the HAZ and fusion zone is elucidated, providing valuable insights for improving the quality of Mg alloy welds.