异质结构改善α-黄铜快速冷却搅拌摩擦焊缝的强塑性

Heterogeneous structure-induced strength and ductility synergy of α-brass subjected to rapid cooling friction stir welding

采用传统搅拌摩擦焊(空冷)和快速冷却搅拌摩擦焊(液态二氧化碳)成功焊接2 mm厚的α-黄铜薄板。利用电子背散射衍射和透射电子显微术对焊缝的显微组织和力学性能进行研究。结果表明:传统搅拌摩擦焊缝为均匀等轴晶组织,而快速冷却搅拌摩擦焊缝呈现出含有大量位错和纳米孪晶的异质晶结构。快速冷却搅拌摩擦焊缝的屈服强度和抗拉强度较传统搅拌摩擦焊分别提高31%和24%。屈服强度和应变硬化能力的改善归因于晶界强化和位错强化,同时,纳米孪晶可缓解塑性变形引起的应力集中,使焊缝表现出良好的塑性。

The 2 mm-thickα-brass plates were successfully joined using conventional friction stir welding(CFSW)with air cooling and rapid cooling friction stir welding(RCFSW)with liquid CO2 cooling.The microstructure and mechanical properties of the two welds were carefully investigated by electron back-scattered diffraction and transmission electron microscopy.The stir zone of CFSW exhibited homogeneous equiaxed grains,while the stir zone of RCFSW showed a heterogeneous grain structure,i.e.ultrafine grains containing massive dislocations and nano twins.Compared with the CFSW,yield strength and ultimate tensile strength of RCFSW were increased by 31%and 24%,respectively.The enhanced yield strength and improved strain hardening capacity were attributed to grain boundary strengthening and dislocation strengthening.Furthermore,good ductility was achieved due to the released stress concentration of the nano twins caused by the plastic deformation.