镀锌钢上钼酸盐/硅烷复合膜的组成与耐蚀性

Composition and Corrosion Resistance of Molybdate/Silane Composite Films on Galvanized Steel

分别采用一步法和两步法在热镀锌钢板表面获得钼酸盐/硅烷复合膜,通过X射线光电子能谱分析(XPS)、俄歇电子能谱剥层分析(AES)、盐雾腐蚀试验(NSS)及Tafel极化曲线等对两种复合膜的化学成分和耐蚀性能进行了研究,并将它们与单独的钼酸盐转化膜、硅烷膜进行对比。结果表明:一步法和两步法制备的复合膜具有相似的双层结构,内层以钼酸盐转化膜(含O、Mo、Zn、P)为主,外层以硅烷膜(含C、O、Si)为主,内外层之间及膜与锌基体之间的化学成分呈梯度变化;与单独的钼酸盐膜、硅烷膜相比,两种复合膜对腐蚀的阴极过程的抑制明显增强,自腐蚀电流减小至单层膜的1/5以下,耐蚀性显著提高;两步法制备的复合膜耐蚀性超过常规铬酸盐钝化膜,而一步法制备的复合膜的耐蚀性比由两步法制备的稍差,但仍接近常规铬酸盐钝化膜。

Two kinds of molybdate/silane composite films were prepared using a one-step method and a two-step one on hot-dip galvanized steel sheets, respectively. The chemical composition and corrosion resistance of the two composite films were then investigated by means of XPS, AES, neutral salt spray （NSS） test and Tafel polarization curve measurement, and were compared with those of single-layer molybdate and silane films. The results show that （ 1 ） both the two films are of the same double-layer structure, and the inner layer, similar to molybdate conversion film, mainly contains O, Mo, Zn and P, while the outer layer, similar to silane film, mainly contains C, O and Si; （2） the chemical composition of the composite films gradually changes from the film to the substrate and from the inner layer to the outer one; （3） as compared with the single-layer molybdate and silane films, the composite films are of an evidently-inhibited cathode polarization process, with a self-corrosion current decreasing to less than 1/5 of that of the single-layer films and a remarkably-improved corrosion resistance; and （4） the two-step method results in a corrosion resistance stronger than that of the conventional chromate passivation film, while the one-step method results in a slightly poor corrosion resistance which is close to that of the conventional chromate passivation film.