7003铝合金动车柜体的应力腐蚀开裂

Stress Corrosion Cracking of Cabinet of 7003 Aluminum Alloy

采用光学显微镜、扫描电镜、能谱分析等手段,对某动车7003铝合金柜体的裂纹进行原因分析。裂纹为沿晶扩展,且有分枝,断口为冰糖状花样,晶面上有发纹、鸡爪纹,经分析裂纹为氢脆起主导作用的应力腐蚀裂纹。通过慢应变速率拉伸实验及恒位移应力腐蚀实验对7003铝合金的应力腐蚀倾向进行评价。慢拉伸实验表明,7003铝合金在3.5%NaCl溶液中的断裂为穿晶与沿晶的混合断裂,在穿晶断裂部分有大量的二次裂纹、解理台阶及河流花样,应力腐蚀敏感指数达0.2。恒位移实验结果显示:经28天腐蚀后,7003铝合金已发生裂纹扩展,长度达700μm,断口的应力腐蚀区存在"舌状凸起"和"凹槽"等形貌,有较明显的应力腐蚀敏感性。

Cracks,discovered on the edge of 7003Al-alloy cabinet of the high speed train was analyzed by means of optical microscope,scanning electric microscope（SEM）and electronic differential system（EDS）.It is found that cracks with many branches propagated along the grain boundaries,the fracture is sugar candy pattern,and capillary and chicken claw cracks are on the grain plane.The crack is stress corrosion crack（SCC）induced by the hydrogen embrittlement.The SCC sensitivity of 7003 Alalloy was evaluated by slow strain rate test（SSRT）and constant displacement test.The result of SSRT shows that the sensitivity index of 7003Al-alloy is 0.2.Its fracture is mixture fracture of transgranular and intergranular in 3.5% NaCl solution.There are many second cracks,cleavage steps and river patterns on the transgranular fracture.The result of constant displacement test indicates that the cracks propagate to 700μm after corrosion for 28 days,and tongue protrusions and grooves occur in the stress corrosion zone.The 7003Al-alloy is obviously sensitive to the SCC.