异种铝合金回填式搅拌摩擦点焊工艺的研究

目的 研究搅拌头转速和轴套下压量对异质铝合金回填式搅拌摩擦点焊接头的组织及力学性能的影响。方法 采用回填式搅拌摩擦点焊技术对7050铝合金和2524铝合金进行搭接焊试验，焊接完成后利用光镜、体式显微镜、扫描电镜对组织进行观察，另外，测试拉伸剪切载荷和显微硬度分布，最后对断裂行为进行了研究。结果 接头区域可以分为焊核区、热力影响区、热影响区、母材4个区域，焊核区晶粒呈细小等轴状，热力影响区晶粒呈粗大长条状。随搅拌头转速的增大，拉剪载荷降低，当转速为1500 r/min时拉剪载荷值最高，其值为7.499 44 kN。热影响区的显微硬度比母材低，最小值为HV106。接头的断裂方式可以分为剪切型断裂、塞型断裂、剪切-半环型断裂。结论 在一定工艺参数范围内，通过适当降低搅拌头转速能显著提高接头的拉剪载荷，轴套下压量对接头的断裂方式影响显著。

Refill Friction Stir Spot Welding Process of Dissimilar Aluminum Alloy

The aim was to study the effect of tool rotational speed and sleeve plunging depth on microstructure and mechanical properties of refill friction stir spot welded joints of dissimilar aluminium alloy. The lap welding of 7050 and 2524 aluminum alloys were carried out through refill friction stir spot welding technology. After welding, the microstructure evolution was examined with optical microscopy, scanning electron microscopy and stereomicroscopy. In addition, the microhardness distribution and tensile-shear load bearing capacity were measured. Finally, the fracture behavior was studied. The joint area could be divided into four zones: nugget zone, heat affected zone, thermo-mechanically affected zone and base metal. The grains in nugget area were fine equiaxed and the grains in heat affected area were thick and long. The tensile shear load decreased with the increase of the rotational speed of the stir tool. When the rotational speed was 1500 r/min, the tensile shear load was the highest, which was 7.499 44 kN. The microhardness of heat affected zone was lower than that of base metal, and the minimum value was HV106. The fracture modes of joints could be divided into shear fracture, plug fracture and shear-semi-ring fracture. Within a certain range of process parameters, the tensile shear load of the joint can be significantly increased by properly reducing the rotational speed of the stir tool. The sleeve plunging depth has significant effects on the fracture mode of the joint.