LF21铝合金稀土转化膜的开裂及其钼酸盐后处理

Molybdate Pro-teatment for Rear Earth Conversion film on LF21 Aluminum Alloy to Improve Corrosion Resistance

用化学沉积法在LF21铝合金表面制备了均匀连续的稀土铈化学转化膜,通过电镜、能谱、极化曲线测试和盐雾试验等方法研究了膜的开裂行为以及钼酸盐后处理对膜耐蚀性能的改善作用。结果表明,沉积时间对膜的开裂倾向有显著影响,随沉积时间延长,开裂倾向增大,裂纹更深更宽。在10 g/L的钼酸钠溶液、50℃、浸泡30min的条件下对稀土转化膜进行后处理以后,裂纹程度有所减弱,耐蚀性能明显改善,维钝电流下降约一个数量级,耐盐雾性能也明显提高。钼酸盐后处理提高稀土转化膜耐蚀性的机理可能包括钼酸盐膜在裂纹部位的沉积、钼酸盐的缓蚀作用和稀土转化膜的"自封闭"作用。

Cerium conversion film was prepared on LF21 aluminum alloy by chemical deposition, and the cracking behavior and improvement of corrosion resistance of the film by molybdate pro-treatment were studied with methods of SEM, EDX, polarization testing and salt fog testing. The results show that deposition time had significant influence on cracking of the filro. With the deposition time prolonged, cracking tendency of the film increased and the cracks were wider and deeper. After the film was treated in 10g/L molybdate solution at 50 ℃ for 30 minutes, the cracking degree was alleviated and corrosion resistance of the film was increased. The passive current density decreased by almost an order of magnitude and the property to resist salt fog testing was also improved. The mechanisms for molyMate treatment to improve corrosion resistance may include the deposition of molybdate film at cracking sites, the inhibitive effect of molybdate and the ＂self sealing＂ effect of cerium conversion film.