AZ91D镁合金磷酸盐-高锰酸盐体系化学转化工艺

Chemical conversion process of AZ91D magnesium alloy based on phosphate-permanganate electrolyte

通过正交试验研究了以磷酸盐-高锰酸盐为基础的镁合金无铬转化工艺,讨论了工艺参数对转化膜厚度及其有机涂层耐蚀性的影响,并通过扫描电镜、能谱等方法分析了转化膜的微观形貌和化学成分。研究表明,当磷酸二氢铵为10～15g/L、高锰酸钾为5～10g/L时,磷酸盐-高锰酸的最佳处理工艺为:ZnSO43g/L,NaF3g/L,pH3,温度45°C。转化液pH对膜层厚度及有机涂层的耐蚀性有显著的影响。在试验参数范围内,转化膜的厚度及后续有机涂层的耐蚀性能随pH的减小而大幅度提高。经该工艺处理后,后续有机涂层的耐蚀性能提高10倍以上。

A process for chromium-free conversion of magnesium alloys based on phosphate-permanganate electrolyte was studied by orthogonal test. The effects of process parameters on the thickness of conversion film and the corrosion resistance of organic coating on it were discussed. The microscopic morphology and chemical composition of the conversion film were analyzed by SEM and energy-dispersive spectroscopy. For an electrolyte containing NH4H2PO4 10-15 g/L and KMnO4 5-10g/L, the optimal process conditions are as follows： ZnSO4 3 g/L, NaF 3 g/L, temperature 45 ℃, and pH 3. The thickness of conversion film and the corrosion resistance of subsequently prepared organic coating are greatly affected by the pH of electrolyte, since they are increased greatly with the decreasing of pH in the test range. The corrosion resistance of subsequent organic coating is improved by more than 10 times after treatment by the process.