以磷酸盐–高锰酸钾体系化学转化作为前处理的AZ91D镁合金化学镀镍工艺

Process of electroless nickel plating on AZ91D magnesium alloy pretreated by chemical conversion in phosphate–potassium permanganate system

以磷酸盐-高锰酸钾体系化学转化膜作为化学镀Ni—P层和AZ91D镁合金基体之间的中间层，以取代传统的HF活化前处理。化学转化液组成和工艺条件为：KMnO4 31．6g／L，Na3PO4·12H2O 0．5g／L，CH3COONa·3H2O4．1g/L，CH3COOH 10．0g／L，室温，5min。化学镀镍液组成和工艺为：NiSO4·6H2O 20g／L，NaH2PO2·H2O 20g／L，C6H5Na3O7·2H2O 10g／L，NH4F 10g／L，pH8．0，80～85℃，2h。分别采用扫描电镜、能谱仪、X射线衍射仪等研究了Ni—P镀层的微观形貌、成分和结构，并采用电化学方法表征了Ni-P镀层的耐蚀性。结果表明，所得Ni-P合金镀层均匀、致密，厚度约为45μm，可显著提高基体的耐腐蚀性能。

A phosphate-potassium permanganate chemical conversion coating was used as the interlayer between electroless Ni-P coating and AZ91D magnesium alloy substrate to replace the traditional HF activation pretreatment. The bath composition and process conditions are KMnO4 31.6 g/L, Na3PO4·12H2O 0.5 g/L, CH3COONa·3H2O 4.1 g/L, CH3COOH 10.0 g/L, room temperature, and 5 min for the chemical conversion treatment, and NiSO4·6H2O 20 g/L, NaH2PO2·H20 20 g/L, C6H5Na3O7·2H2O 10 g/L, NH4F 10 g/L, pH 8.0, 80-85 ℃, and 2 h for the electroless nickel plating. The micromorphology, elemental composition, and microstructure of the Ni-P coating were studied using scanning electron microscope, energy-dispersive spectrometer, and X ray diffraction,respectively. The corrosion resistance of the Ni-P coating was characterized by electrochemical method. The results showed that the obtained Ni-P alloy coating is uniform, compact, and 45 μm thick, and can significantly improve the corrosion resistance of magnesium alloy substrate.