搅拌摩擦焊接显微组织的一个显著特征就是焊核(Weld Nugget)的形成.采用AZ31镁合金为母材,通过金相和透射电镜分析搅拌摩擦焊接焊核的形成机制及接头不同区域的显微组织特征,并建立AZ31镁合金搅拌摩擦焊接的组织演变模型.结果显示,紧靠轴肩生成厚度约为37 μm～47 μm细密组织层.机械热影响区存在部分动态再结晶和较明显的塑性变形晶粒.焊缝底部有一厚约100μm～130 μm的粗大组织层.熔核区的组织比较细小,沿厚度方向晶粒大小不均匀.同时提出一个焊核晶粒细化的简易模型,分析认为焊接过程中热过程和热机械搅拌作用对FSW接头组织的形成起决定性作用.
The typical microstructure of the friction stirred weld is the formation of the weld nugget. AZ31 magnesium alloy was friction stir welded and the microstructures and the evolution mechanism of the weld were studied using optical microscopy (OM) and transmission electric spectroscopy (TEM) in this paper. The results show that a very thin layer microstructures of about 37 mu m similar to 47 mu m thickness with fine grains is formed under the shoulder. There exist a partly thermodynamic recrystallization, and superplastic grains appear in the thermo-mechanical affected zone. There is a coarse layer of the weld about 100 mu m similar to 130 mu m thickness near the bottom. The weld nugget is composed of fine, re-crystallization grains, and the grain size is different along the thickness direction. The microstructure evolution mechanism is analyzed and a simple model on weld nugget microstructure evolution is also presented in this paper. The mechanism and the factors on microstructures are theoretically analyzed. The heating and the mechanical stirring play the main role in the microstructure evolution.
Rare Metal Materials and Engineering
friction stir welding
thermal mechanical affected zone