硅氧烷硫化物与铈盐复合膜对铝合金耐点蚀能力的影响

Effects of Siloxane Sulfide and Cerium Salt Complex Conversion Film on Corrosion Resistance of Aluminum Alloy

通过在AA6063铝合金表面预沉积Ce^(3+),再浸涂双-[三-(乙氧基)硅丙基]四硫化物(BTST)的分步沉积工艺,制备了一种高耐蚀性的CeO_2/BTST复合转化膜。结果表明:单独CeO_2膜仅可使铝合金在3%NaCl溶液中的极化电阻提高一个数量级;但复合膜则可使之提高两个数量级,且点蚀电位上升近400 m V。CeO_2/BTST复合膜对铝合金亚稳态或稳态点蚀发展有强烈抑制作用,其噪声电阻达到10 MΩ·cm^2以上,在浸泡168 h内基本无亚稳态点蚀发生,而单独的CeO_2膜或BTST自组装膜的耐蚀性均有限,在3%NaCl溶液中浸泡168 h后铝合金表面即出现大量点蚀。由于CeO_2能优先吸附于第二相(AlFeSi)组织表面,抑制亚稳态点蚀生长;而硅氧烷与Al—O键结合能高,能有效提高Al基体的全面保护能力,得益于二者的协同作用,采用顺序沉积铈盐/硅氧烷所制备的复合保护层,能同时显著提升铝合金的全面腐蚀与局部腐蚀抗力。

A complex chemical conversion film of CeO2-siloxane was prepared on AA6063 alumi- num alloy by successively dipping the alloy in CeCl3 aqueous solution and then in bis-[triethoxysi- lypropyl] tetra-sulfide （BTST） alcohol solution. Electrochemical tests show that the polarization re- sistance of the bare A1 alloy in 3%NaC1 solution can be enhanced by an order of magnitude with the CeO2 conversion film alone. But the complex film can rise both the polarization resistance by two orders of magnitude and the pitting potential by ca 400 mV. The enhancement of corrosion re- sistance of the alloy is limited by applying either CeO2 conversion film or BTST film alone, while a lot of pits can be observed on the A1 electrode surface after immersed in 3%NaC1 for 300 h. Howev- er, after the CeOdBTST complex film was formed, no noise peaks can be found from the ECN curves when A1 electrode immersed in 3%NaC1 for 168 h, indicating that the complex film has a strong inhibition effect on the propagation of metastable- and steady-pits on the alumlnlum alloy. Since CeO： can be absorbed preferentially on the second phase （A1FeSi）, it can inhibit the growth of metastable pits; and the siloxane has a high binding energy with Al--O bond, therefore, the syn- ergistic effect of Ce02 and siloxane may be beneficial to the excellent protectiveness of the com- plex film.