厚板铝锂合金SSFSW接头组织非均质性及力学性能

Microstructure heterogeneity and mechanical properties of SSFSW joints for Al-Li alloy thick plates

对12 mm厚板2195-T8铝锂合金进行静止轴肩搅拌摩擦焊(Stationary shoulder friction stir welding,SSFSW)工艺试验,探讨工艺参数对接头组织非均质性和力学性能的影响。结果表明:转速在300~500 r/min及焊接速度在30~80 mm/min范围内可获得表面光滑、无缺陷的焊缝。转速为300 r/min时,焊核区(Welding nugget zone,WNZ)呈梯形截面且沿厚度分布比较均匀;转速为400~500 r/min时,WNZ形状明显不规则并在焊缝表面附近形成异常流动的回填区,WNZ沿厚度方向的晶粒尺寸相差2~3倍;转速降低为300 r/min时,晶粒尺寸差别明显减小。转速为300 r/min时,WNZ硬度沿厚度方向分布均匀;转速为400~500 r/min时,WNZ底部硬度值远小于中间和顶部。在转速为300 r/min及焊接速度为80 mm/min的优化工艺条件下,WNZ抗拉强度可达到母材的71.57%。拉伸试样的断裂位置发生在热力影响区和热影响区交界处或WNZ底部,具有典型的塑性断裂特征。

The stationary shoulder friction stir welding(SSFSW)process tests were carried out on 12-mm-thick 2195-T8 Al-Li alloy plates,and the effects of welding process parameters on the microstructure heterogeneity and mechanical properties of the joints were discussed.The results show that smooth weld surface and completely dense defect-free weld can be obtained when the spindle speed is 300-500 r/min and the welding speed is 30-80mm/min.When the rotating speed is 300 r/min,the welding nugget zone(WNZ)is trapezoidal,and the section is homogeneously distributed along the thickness direction.At 400-500 r/min,the shape of WNZ is obviously irregular,and refill zone(RZ)with abnormal flow is formed near the weld surface.The grain size difference along the thickness direction is 2-3 times at 400-500 r/min.When the rotating speed is reduced to 300 r/min,the grain size difference along the thickness direction decreases significantly.At 300 r/min,the hardness of the WNZ is homogeneous along the thickness direction while the hardness value at the bottom of WNZ is much lower than that at the middle and top at 400-500 r/min.Under the optimized process of 300 r/min-80 mm/min,the ultimate tensile strength of the joint can reach 71.57%of the base metal.The fracture location of tensile specimens mostly occurs at the interface between TMAZ and HAZ or at the bottom of the WNZ,which has typical plastic fracture characteristics.