在转速1600 r/min, 焊速200 mm/min; 转速800 r/min, 焊速200 mm/min; 转速400 r/min, 焊速400 mm/min 3组参数下对2 mm厚的退火态7B04铝合金薄板进行搅拌摩擦焊接, 研究了焊接参数对焊缝质量及微观组织的影响, 并分析了焊核区的低温超塑性变形行为. 结果表明, 通过控制焊接参数, 可获得良好的焊接质量, 接头强度系数达100%. 焊核区发生动态再结晶, 生成细小等轴晶, 母材晶粒尺寸约为300 μm, 转速为1600, 800和 400 r/min时晶粒尺寸分别为2, 1和0.6 μm. 这种细晶组织有利于焊核区超塑变形, 在300 ℃, 焊核区在1×10^-3和3×10^-4 s^-1应变速率下获得了160%~590%的延伸率, 在350 ℃, 1×10^-3 s^-1条件下获得高达790%的最大延伸率, 在约400 ℃时超塑性变形行为消失.

Annealed 7B04 Al sheets in thickness of 2 mm were subjected to friction stir welding (FSW) under three rotation rate and welding speed parameters of 1600 r/min, 200 mm/min; 800 r/min, 200 mm/min and 400 r/min, 400 mm/min, respectively. The effect of welding parameters on the tensile property and microstructure of the FSW joints were investigated, with more efforts focusing on the low-temperature superplasticity of the nugget zones (NZs). The results showed that FSW joints with high quality could be produced by controlling welding parameters, with a joint strength coefficient of 100% being obtained. Dynamic recrystallization took place in the NZs with fine and equiaxed grains generated. The grain size of the base material was about 300 μm, while it was significantly decreased in the NZs with decreasing the rotation rate: about 2, 1 and 0.6 μm for the above three samples, respectively. The fine grain structure of the NZs could facilitate their superplastic deformation. The NZs exhibited superplastic elongations ranged from 160% to 590% at 300 ℃ at strain rates of 1×10^-3 and 3×10^-4 s^-1. The maximum superplasticity of 790% was obtained at 350 ℃ at the strain rate of 1×10^-3 s^-1. The ability to superplastic deformation disappeared in the NZs at 400 ℃.