低温对铝合金在SSRT过程中裂纹萌生与扩展规律的影响

Effect of Low Temperature on Crack Initiation and Propagation of Aluminum Alloy during SSRT Process

采用一种电化学阻抗谱(EIS)的解析方法,原位研究低温对7A04铝合金在慢应变速率拉伸过程(SSRT)中裂纹萌生与扩展规律的影响。利用扫描电子显微镜(SEM)观察断口形貌,并通过Kramers-Kronig转换验证EIS实验数据的可靠性。结果表明,裂纹的萌生和扩展过程大致可分为氧化膜溶解、裂纹萌生、动态平衡、裂纹明显扩展四个阶段;温度的降低会改变断裂方式,表现为从混合断裂向脆性穿晶断裂发展;由常温向低温的变化可以有效抑制铝合金在SSRT过程中的裂纹萌生和扩展,具体表现为温度越低对裂纹萌生和扩展的抑制效果越不明显,其中-5℃时抑制效果最强。

The effect of low temperature on crack initiation and propagation of 7A04 aluminum alloy in Slow Strain Rate Tension (SSRT) was studied in situ by using an analytical method of Electrochemical Impedance Spectroscopy (EIS). The fracture morphology was observed by Scanning Electron Microscopy (SEM), and the reliability of EIS experimental data was verified by Krames-Kronig transformation. The results show that the crack initiation and propagation process can be divided into four stages: oxide film dissolution, crack initiation, dynamic equilibrium, and crack propagation. The decrease of temperature will change the fracture mode, which is manifested from mixed fracture to brittle transgranular fracture. The change from normal temperature to low temperature can effectively inhibit the crack initiation and expansion of aluminum alloy during SSRT process. The specific effect is that the lower the temperature, the less obvious the inhibition effect on crack initiation and propagation, and the inhibition effect is the strongest at -5 ℃.