轨道交通用7003铝合金型材失效行为分析

摘要

采用金相、扫描电镜和透射电镜观察以及慢应变速率拉伸应力腐蚀实验等分析测试方法对轨道交通用7003铝合金型材的失效原因进行分析.研究结果表明:型材失效件的裂纹为沿晶扩展,且有支裂纹向外扩展;失效件断口形貌呈冰糖块状花样特征,断口表面附集着铝、锌的氧化物,还有少量氯化物和硫化物,经分析失效型材的裂纹是由应力腐蚀导致的沿晶脆性断裂.型材试样在30 g/L NaCl+10 mL/L HCl腐蚀溶液中的抗拉强度为181.5 MPa,断裂时间为5.1 h,在空气中的抗拉强度为320.3 MPa,断裂时间为27.7 h,试样的应力腐蚀敏感指数(ISSRT)为0.46.晶界析出相尺寸较小、密度大,且呈链状连续分布,在腐蚀过程中,晶界连续析出相易成为阳极腐蚀通道,是较高的应力腐蚀敏感性的主要原因.%The failure behavior analysis of rail railway 7003 aluminum alloy extrusions was studied by optical microstructure, scanning electron microscopy(SEM), transmission electron microscopy (TEM) and slow strain rate tensile stress corrosion testing, etc. The results show that the crack of extrusions extends along the grain boundary and bits of branch crack extend outward. Fracture morphology of failure extrusions is sugar lump pattern features, and also the fracture surface is attached to aluminum, zinc oxide and bits of chlorides and sulfides. The intergranular brittle fracture is caused by stress corrosion. The tensile strength and break time of extrusions sample are respectively 181.5 MPa and 5.1 h in 30 g/L NaCl+10 mL/L HCl corrosion solution; The tensile strength and break time of extrusions sample in air are 320.3 MPa and 27.7 h, respectively. Stress corrosion sensitivity index (ISSRT) is 0.46. The small size, high density and continuous chain distribution of grain boundries precipiates which easily become anodic corrosion channel during the corrosion process, are the main causes of high sensitivity to stress corrosion.