H70黄铜冷源辅助搅拌摩擦焊接头微观组织和力学性能分析

采用冷源辅助搅拌摩擦焊对2 mm厚的H70黄铜进行焊接，利用光学显微镜.扫描和透射电子显微镜、电子背散射衍射、显微硬度测试及拉伸试验对焊接接头的微观组织和力学性能进行研究.结果表明，在搅拌摩擦焊的过程中通过采用液氮冷却的方法不仅能降低搅拌区的峰值温度，而且可以显著提高搅拌区的冷却速度，有效抑制了由焊后余热带来的退火软化作用，消除了热影响区.搅拌区组织由高位错密度的超细晶组成，并具有较强的{—1 1 2} < 1 1 0 > 剪切织构.搅拌区抗拉强度较母材提高了58%的同时，断后伸长率没有显著降低，改善了焊缝的强韧性.

Research on microstructure and mechanical properties of cold source assisted friction stir welded H70 brass joint

H70 brass plates with 2-mm-thick were successfully joined by cold source assisted friction stir welding. The microstructure and mechanical properties of the welded joint were investigated by optical microscopy, scanning/transmission electron microscopy, electron backscatter diffraction, microhardness measurement and tensile tests. The obtained results showed that significant reduced peak temperature and increased cooling rate were achieved by using liquid nitrogen cooling. The stir zone showed the ultra-refined grain structure with high dislocation density. The crystallographic shear texture whose dominant component of {-1 1 2}<1 1 0> was also found. The heat-affected zone disappeared as well. As a result, the ultimate tensile strength was enhanced by 58% compared with that of the base metal without ductility loss. A good strength-ductility synergy achieved by using cold source assisted friction stir welding technology.