Al合金表面Ce转化膜成膜机理研究

Ce转化膜作为一种Cr转化膜的理想替代品而日益受到人们的重视，但其成膜机理还不很清楚.本文应用自行研制的扫描微参比电极技术（SMRE），原位测量经CeCl3溶液处理的2024-T3 Al合金表面微区电位分布，并结合X光电子能谱（XPS）和交流阻抗谱（EIS），对Ce转化膜的成膜机理进行探讨.结果表明，在CeCl3溶液中，Ce转化膜的形成过程是 Ce3＋和Cl－相互竞争的动态过程.当由Cl－的不均匀吸附引起的局部腐蚀使pH升高时， Ce(OH)3就会首先在局部位置发生沉积.阴极反应过程产生的H2O2可将Ce(OH)3部分氧化成CeO2.

Investigation on the Formation Mechanism of Ce Conversion Films on 2024 Aluminum Alloy

Many cerium compounds are promising corrosion inhibitors for aluminum alloy. However, the formation mechanism of Ce conversion films is not clear yet. Scanning microreference electrode technique (SMRE) was used to probe the potential imaging of 2024 T3 Al alloy in CeCl3 solution. The pitting corrosion of Al alloy in CeCl3 decreased with immersion time and disappeared finally. Additionally, the competition of inhibition and corrosion between Ce3+ and Cl- on Al alloy was in situ monitored in CeCl3 by SMRE. The results of X ray photoelectron spectroscopy(XPS) showed that the Ce conversion films consisted of Al2O3, CeO2 and Ce2O3(Ce(OH)3), and CeO2/Ce2O3 mass ratio decreased with immersion time. It is concluded that when thecritical pH for Ce(OH)3 formation is reached, Ce(OH)3 will precipitate at micro cathodic area of the Al alloy surface. Consequently, H2O2, the product of the catholic reaction will oxidize part of Ce(OH)3 to CeO2.