高速列车铝合金MIG接头应力腐蚀失效研究

Research on stress corrosion crack failure of MIG joints on aluminum alloy of high-speed trains

为提升高速列车服役安全性,探究焊接接头应力腐蚀失效断裂机制,采用金相显微镜、透射电镜(TEM)、扫描电镜(SEM)、硬度测试、室温拉伸、恒载荷应力腐蚀等测试方法,研究6005A铝合金熔化极惰性气体(MIG)保护焊接头微观组织、力学性能和应力腐蚀性能。结果表明:焊接热影响下热影响区(HAZ)晶内析出相粗化及回溶、晶界无沉淀析出带(PFZ)宽化;接头硬度分布呈W型,硬度最低点位于HAZ区,且室温拉伸和恒载荷应力腐蚀试验中接头均断裂于HAZ区。随着加载应力的增大接头应力腐蚀敏感性增大,加快接头沿晶应力腐蚀失效断裂,且高应力水平(0.9 R_(p 0.2))下,接头平均断裂时间约为42 h。

In order to improve service safety of high-speed trains and explore stress corrosion cracking fracture mechanism of welded joints,microstructure,mechanical properties,and stress corrosion cracking properties of MIG welding joints of 6005A aluminum alloy were investigated by adopting optical microscopy,transmission electron microscope(TEM),scanning electron microscope(SEM),hardness test,tensile test,constant stress corrosion load test and so on.The results show that under the effect of welding heat,intragranular precipitates is coarsened and redissolved in heat affected zone(HAZ),and precipitation free zone(PFZ)is widened at grain boundary.Hardness distribution of the joints is"W"type,with minimal-hardness point located in HAZ zone,and MIG joints also fracture at HAZ zone in room temperature tensile test and constant load stress corrosion test.Along with the increase of loading stress,stress corrosion cracking sensitivity will increase,and intergranular stress corrosion cracking failure fracture will accelerate.And average fracture time of the joints reaches about 42 h under high load stress(0.9 R_(p 0.2)).