7A04铝合金应力腐蚀过程中裂纹萌生和扩展规律研究

为了研究不同拉伸速率对应力腐蚀敏感性及应力腐蚀过程(SCC)中裂纹萌生与扩展规律的影响，本文选用7A04铝合金在3.5%wt NaCl溶液中进行慢应变速率拉伸实验(SSRT)，采用扫描电子显微镜(SEM)、体式显微镜、电化学方法、高分辨透射电子显微镜(HRTEM)等方法进行研究；提出一种原位预测裂纹萌生和扩张的新方法即相移与电化学阻抗谱相结合的方法来系统研究应力腐蚀过程(SCC)中裂纹萌生和扩展规律.结果表明：当拉伸速率为3.0 um/min时，在3 h附近裂纹开始萌生，在8 h附近裂纹发生明显扩展；通过高分辨透射电子显微镜(HRTEM)对裂纹萌生和扩展机理进行研究，验证了新方法的可行性，推测裂纹的萌生和扩展机理可能是由晶界出产生的析出物引起的.
To investigate the effect of different tensile rates on stress corrosion sensitivity and the crack initiation and propagation during the stress corrosion crack (SCC), the slow strain rate test (SSRT) of 7A04 aluminum alloy in 3.5%wt NaCl solution was conducted and scanning electron microscope (SEM), stereomicroscope, electrochemical method and high resolution transmission electron microscope (HRTEM) were used for this research. Meanwhile, a new method for the combination of phase shift and electrochemical impedance spectroscopy was proposed to study the crack initiation and propagation during SCC. The results showed that the crack initiated in the vicinity of 3 h and propagated at near 8 h with the tensile rate of 3.0 um/min; the feasibility of the new method was also verified by studying mechanism of crack initiation and propagation using high resolution transmission electron microscopy (HRTEM) and it's speculated that the mechanism of crack initiation and propagation may be caused by the precipitates produced at grain boundaries.