以镀速和耐蚀性能作为判据,通过正交试验获得了较优的三元Ni-W-P合金镀层工艺, 即镀液组成: 硫酸镍30 g/L, 次亚磷酸钠25~30 g/L, 钨酸钠50 g/L, 柠檬酸钠75 g/L, 乳酸15 mL/L, 硫酸铵30 g/L和添加剂20 mg/L; pH值9.0和镀液温度(90±2)℃. 电化学测试结果表明, Ni-W-P镀层的耐蚀性能优于Ni-P镀层. 研究了高温热处理对Ni-W-P合金镀层耐蚀性能的影响并采用扫描电镜(SEM)和X射线衍射仪(XRD)分析镀层形貌和相组成. 结果表明, 高温热处理导致镀层内部及镀层与基体之间发生了元素的互扩散, 并在镀层表面生成致密的氧化膜, 进而提高镀层的耐蚀性能.
Orthogonal experiments were conducted to find out the optimal process for electroless plating of Ni-W-P coatings. Deposition rate and corrosion resistance were taken as the index for performance assessment. The optimal process is that a solution consisted of NiSO4•6H2O 30 g/L, Na2H2PO2•H2O 25---30 g/L, Na2WO4•2H2O 50 g/L, Na3C6H5O7•2H2O 75 g/L, lactic acid 15 mL/L, (NH4)2SO4 30 g/L and additive 20 mg/L with pH9.0 at temperature (90±2)℃. The corrosion performance of coatings were evaluated by electrochemical tests. The results indicated that the corrosion performance of Ni-W-P coating was superior to Ni-P coating. The corrosion resistance of Ni-W-P coating may be further improved after a proper high temperature heat-treatment. According to the scanning electron microscopy images and X-ray diffraction patterns, after heat treatment there exist an interdiffusion zone between Ni-W-P coating and substrate steel, whilst a compact oxide scale also formed on the surface of the coating, which are considered to be beneficial to the enhancement for the adhesion and corrosion resistance of the coatings.
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