【摘要】 目的为提高镁合金化学镀Ni-P合金镀层的腐蚀防护性能。方法在AZ31B镁合金表面,先化学镀Ni-Cu-P,再化学镀Ni-P,制备Ni-Cu-P/Ni-P复合镀层。研究复合镀层的表面形貌、成分、厚度和腐蚀电流密度随镀液硫酸铜浓度的变化规律,表征1.0 g/L硫酸铜质量浓度下,复合镀层的截面形貌、成分和晶态结构。结合动电位极化曲线和盐雾试验,分析复合镀层的耐蚀性能和腐蚀防护机理。结果复合镀层中的铜含量随硫酸铜浓度的增加而升高,铜对复合镀层的结构和性能影响很大。通过抑制镀层表面胞状物的生长和增加形核点数量,铜的共沉积能够大幅提高复合镀层的致密性。随硫酸铜浓度的增加,样品表面的催化活性下降,镀液稳定性升高,由此导致复合镀层的厚度随硫酸铜浓度的增加而明显下降。硫酸铜质量浓度为1.0 g/L时,复合镀层均匀致密,并具有可钝化性,按照ISO 9227,其耐盐雾腐蚀时间超过180 h。结论化学镀Ni-Cu-P/Ni-P复合镀层能够赋予镁合金表面优异的耐蚀性能,复合镀层所具有的可钝化性和均匀致密的镀层结构,是镀层腐蚀防护性能提升的主要原因。更多还原

【Abstract】 The work aims to improve the anti-corrosion properties of the electroless Ni-P coatings on magnesium alloys.Ni-Cu-P/Ni-P composite coatings were prepared by plating Ni-Cu-P and Ni-P on AZ31B magnesium alloys. The change rules of surface morphologies, compositions, thicknesses and corrosion current densities of the composite coatings along with the CuSO₄ concentrations in the bath solutions were studied. The cross-section morphology, compositions and crystal structure of the composite coating with CuSO₄ concentration of 1.0 g/L were characterized. Potentiodynamic polarization curves and salt spray tests were conducted to investigate the anti-corrosion properties and mechanisms of the composite coatings. From the experimental results, the copper content in the composite coatings increased with the increasing CuSO₄ concentrations, and copper had significant influences on the structures and properties of the composite coatings. The copper codeposition could enhance the compactness of the composite coatings to a large extent by suppressing the growth of the nodules and producing more nuclei. As the concentration of CuSO₄ increased, the catalytic activity on the sample surface decreased and the stability of bath solution improved, which resulted in the obvious decrease in the coating thicknesses with the increasing CuSO₄ concentrations. The composite coating with a CuSO4 concentration of 1.0 g/L was uniform, compact, and passivable, and the corrosion performance was found to withstand >180 h salt spray test in accordance with ISO 9227. Ni-Cu-P/Ni-P composite coatings can provide a superior corrosion resistance to the magnesium alloy substrates. The passivable and compact coating layers of composite coatings are main factors to improve the anti-corrosion properties.更多还原