LY12铝合金摩擦点焊接头组织及性能

Microstructures and properties of friction stir spot welding joints for LY12 aluminum alloy

采用摩擦点焊对厚度为2 mm的LY12铝合金进行焊接实验,分析接头的显微组织及力学性能。根据焊点接头的组织特征可将其分为塑性区、动态静止层、热影响区和母材。结果表明:塑性区和动态静止层的晶粒在热和力作用下发生动态再结晶形成细小的等轴晶,热影响区的晶粒在摩擦热作用下长大变粗;搅拌头旋转速度为2 500 r/min,焊接时间为12 s时,可以获得力学性能较好的焊点,焊点的剪切强度达到9.24 kN;焊点的剪切强度随搅拌头旋转速度的增大而增大,随焊接时间的延长先增大后减小;塑性区的显微硬度较高,但略小于母材,接头显微硬度的最小值分布在热影响区;焊点热输入量较多时,接头为Ⅰ型断裂,焊点的剪切强度较高;焊点热输入量较少时,接头为Ⅱ型断裂,焊点的强度较低。

Friction stir spot welding（FSSW） of LY 12 aluminum sheet with thickness of 2 mm were investigated, the joint microstructures and mechanical properties were analyzed. Based on the structure character of the joint, the microstructure of the joint can be divided into plasticity zone, dynamically quiescent layer, heat affected zone and base metal. The results show that the plasticity zone and dynamically quiescent layer become fine equiaxed recrystallisation under the thermo-mechanical effect, the grains in the heat-affected zone grow up because of the effect of friction heat. When the rotation speed is 2 500 r/min and the welding time is 12 s, good joint is achieved, and the tensile shear strength of the joint reaches 9.24 kN. The tensile shear strength of spot increases with increasing tool rotation speed, with increasing welding time, the strength increases first, while then reduces. The microhardness of plasticity zone is high, but is slightly lower than that of the base metal, the minimum value of microhardness is in the heat affected zone. When the energy input of joint is high, the fracture type of spot is mode I, and the tensile shear strength is high; on the contrary, when the energy input of joint is less the fracture type of spot is mode Ⅱ, and the strength is low.