镁合金搅拌摩擦焊接组织特征研究

Research on Microstructure of Magnesium Alloy by Friction Stir Welding

  • 摘要: 通过对镁合金AZ31进行搅拌摩擦焊获得了成型良好的焊缝,采用金相显微镜对焊缝组织进行了分析,并采用透射电镜和X射线能谱仪对晶粒形貌和晶界析出的第二相进行了观测分析。结果表明,镁合金搅拌摩擦焊可以获得组织致密的焊缝,焊缝区域根据组织特点可以分为焊核区、热机影响区和热影响区;焊核区“洋葱环”之间呈现层片状结构,晶界强化相数量减少且尺寸变小;热机影响区在前进侧和焊核区有明显的分界,晶粒呈细长条状,后退侧和焊核区分界相对不明显,晶粒变形较小;热影响区在前进侧较窄,组织与母材组织相比变化较小,而后退侧热影响区较宽,晶粒尺寸有所增长,这与搅拌摩擦过程中金属切削迁移的堆积过程有关。

     

    Abstract: AZ31 magnesium alloy weld in good shape was produced by friction stir welding. Metallographic microscope was adopted to observe the microstructure of the weld, and by transmission electron microscopy (TEM) and X ray energy spectrum instrument, grain shape and the second phase precipated at the grain boundry were observed and analyzed. The results showed that magnesium alloy friction stir welding could produce weld of dense tissue. According to the characteristics of the grain microstructure, the weld area could be divided into the weld nugget zone, thermo-mechanically affected zone and the heat affected zone. The onion rings of weld nugget zone presented lamellar structure, and the quantity and size of strengthening phases in the grain boundary decreased. The boundary of the advancing side in thermo mechanically affected zone and the weld nugget zone was obvious, and the grains were elongated strips. The boundary of the retreating side and the nugget zone was relatively unobvious, and the grain deformation was smaller. The advancing side in the heat affected zone was relatively narrow, and the microstructural change was small, almost the same with that of the parent material. The retreating side of the heat affected zone was wide, and the grain size had grown larger. The differences in the retreating side and advancing side were caused by the migration and accumulation of metal in the process of friction stir welding.

     

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