含Ce稀土镁合金激光焊接接头的微观组织及力学性能

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

摘要

焊接热循环过程中，热影响区内析出相分布特征与微观形貌的改变，极易导致焊接接头出现典型的热影响区软化，使其成为整个接头中最薄弱的环节。本工作提出一种融合光纤激光焊接工艺与高热稳定含Ce稀土析出相协同作用的焊接策略，通过调控熔化区和热影响区的析出相结构，一方面改善焊缝熔化区和热影响区析出相结构，另一方面显著缩窄热影响区尺寸、降低热影响区软化，进而整体提升焊接接头力学性能。结果表明：焊缝熔化区内形成大量微米/亚微米级析出相颗粒，这些颗粒弥散分布在枝晶臂边缘，有效钉扎位错、阻碍变形过程中位错的运动，从而强化熔化区；同时，热影响区内保留的高热稳定的稀土析出相则一定程度地维持合金原有的组织结构，使热循环过后热影响区的宽度控制在100 μm左右，显著降低焊接热循环对热影响区微观组织的影响。拉伸性能结果表明，经Ce元素微合金化及激光焊工艺优化后，焊接接头表现出良好的力学性能，所得接头拉剪强度达母材的74.4%，证明该焊接策略在实现稀土镁合金高质量连接方面的可行性与有效性。

Abstract

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.

关键词

稀土 / 镁合金 / 激光焊接 / 微观组织 / 调控机制

Key words

rare earth / magnesium alloy / laser welding / microstructure / control mechanism

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基金资助

湖南省教育厅科学研究项目优秀青年项目(24B0986)