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研究Al-Mg-Si合金晶界组成相(Al-Mg2Si及Al-Mg2Si-Si)间的电化学行为和动态电化学耦合行为,提出Al-Mg-Si合金的晶间腐蚀机理。研究表明,晶界Si的电位比其边缘Al基体的正,在整个腐蚀过程中作为阴极导致其边缘Al基体的阳极溶解;晶界Mg2Si的电位比其边缘Al基体的负,在腐蚀初期作为阳极发生阳极溶解,然而由于Mg2Si中活性较高的元素Mg的优先溶解,不活泼元素Si的富集,致使Mg2Si电位正移,甚至与其边缘Al基体发生极性转换,导致其边缘Al基体的阳极溶解。当n(Mg)/n(Si)<1.73时,随着腐蚀的进行,合金晶界同时会有Mg2Si析出相和Si粒子,腐蚀首先萌生于Mg2Si相和Si边缘的无沉淀带,而后,Si粒子一方面导致其边缘无沉淀带严重的阳极溶解,另一方面加速Mg2Si和晶界无沉淀带的极性转换,从而促使腐蚀沿晶界Si粒子及Mg2Si粒子边缘向无沉淀带发展。
The electrochemical behavior and the dynamic electrochemical coupling between the grain boundary phases (Al-Mg2Si and Al-Mg2Si-Si) of Al-Mg-Si alloy were studied. The intergranular corrosion mechanism of Al-Mg-Si alloy was proposed. The results show that the potential of the grain boundary Si is more positive than that of the Al matrix at the edge, and the anodic dissolution of the Al matrix at the edge of the Si is caused by the cathode during the whole etching process. The grain boundary Mg2Si has a lower potential than the Al matrix at the edge, However, due to the preferential dissolution of Mg, which is more active in Mg2Si, and the enrichment of Si, which is the active element, the potential of Mg2Si is positively shifted, even with the Al matrix at its edge, leading to the anodic dissolution of Al matrix . When n (Mg) / n (Si) <1.73, as the corrosion proceeds, the Mg2Si precipitated phase and the Si particles are simultaneously present in the grain boundaries of the alloy, and the first precipitated zone is eroded on the edge of Mg2Si phase and Si. On the one hand, the particles lead to no serious anodic dissolution on the edge of the particles, and on the other hand accelerate the polarity conversion of the Mg2Si and non-precipitation bands on the grain boundary to promote the growth of corrosion along the edge of grain boundaries and Mg2Si particles.