残留结晶相对Al-Mg-Si-Cu合金晶间腐蚀行为的影响

摘要

采用光学显微镜、透射电镜、X射线衍射、扫描电镜及能谱等研究中性和酸性NaC1腐蚀溶液中残留结晶相对A1-Mg-Si-Cu合金晶间腐蚀行为的影响.结果表明:实验合金含有Mg2Si和Al4.01(MnFeCrCu) Si0.74两种残留结晶相.在中性和酸性溶液中,Mg2Si相通过Mg优先溶解,由阳极转换成阴极,进而造成基体点蚀.Al4.01(MnFeCrCu)Si0.74相在中性溶液中作为阴极,导致周围Al基体发生点蚀,而在酸性溶液中只发生自身腐蚀.当点蚀发生在晶界上时,能直接诱发晶间腐蚀；而当点蚀发生在晶内时,则需点蚀扩展至晶界才能诱发晶间腐蚀.不同于中性溶液,酸性溶液中的晶间腐蚀也可以由晶界直接形成.%The optical microscopy, transmission electron microscopy (TEM), X-ray diffractometry (XRD), scanning electron microscopy (SEM) and energy dispersive spectrum (EDS) were employed to study the effect of residual constituents on the intergranular corrosion (IGC) behavior of Al-Mg-Si-Cu alloy in the neutral and acidic solutions. The results show that the alloy includes two types of constituent phases, Mg2Si and Al4.01(MnFeCrCu)Si0.74. In the neutral and acidic solutions, the anodic Mg2Si phase first undergoes the preferential dissolution of Mg and converts into the cathodic one, which gives rise to the point corroding of adjacent matrix. The Al4.01(MnFeCrCu)Si0.74 phase leads to the anodic dissolution of matrix at its adjacent periphery in the neutral solution. But the self-corrosion of Al4.01(MnFeCrCu)Si0.74 occurs in the acidic solution. It is the pitting corrosion occurring at the grain boundary that can directly induce IGC. However, IGC does not occur until the pit grows up and contacts with the grain boundary when the pits are in the grain interior. Besides, unlike the corrosion behavior of alloy in the neutral solution, IGC can occur spontaneously by grain boundary in the acidic condition.