Ni-P/Ni-Zn-P三层复合镀层的制备与耐腐蚀性能研究

目的制备具有不同电位差的多层阳极Ni-P/Ni-Zn-P复合镀层。方法采用化学镀的方法,在Q235钢基体表面制备内层为低磷Ni-P合金、中层为高磷Ni-P合金、外层为Ni-Zn-P合金镀层的三层复合镀层。通过金相显微镜、扫描电子显微镜(SEM)、X射线能谱仪(EDS)、X射线衍射仪(XRD)、电化学工作站等仪器对复合镀层表面形貌、成分结构及腐蚀电位进行分析。结果相较于低磷Ni-P镀层和高磷Ni-P镀层,Ni-P/Ni-Zn-P三层复合镀层的晶胞大小均匀一致且胞与胞之间致密平滑。内层低磷Ni-P镀层断面厚度约为14.5μm,镍的质量分数约为96.5%,磷的质量分数为3.5%;中层高磷Ni-P镀层断面厚度约为17.6μm,镍的质量分数约为90.2%,磷的质量分数约为9.8%;Ni-P/Ni-Zn-P三层复合镀层断面总厚度约为40μm,镍的质量分数约为80.7%,锌和磷的质量分数分别为7.6%和11.7%。在Tafel极化曲线中,Ni-P/Ni-Zn-P三层复合镀层的腐蚀电流密度最小,为3.815×10^(-6) A/cm^(2),具有更好的耐蚀性。在模拟海水环境(5%NaCl溶液)中腐蚀220 h后,内层、中层组织腐蚀成片,出现孔洞且有点蚀,而Ni-P/Ni-Zn-P三层复合镀层几乎没有腐蚀,只有部分区域出现点蚀,组织较为完整,说明三层镀层较单层、双层镀层具有更好的耐腐蚀性。结论制备具有电位差的多层阳极Ni-P/Ni-Zn-P复合镀层具有更好的性能,且相较于内层单层、中层双层Ni-P合金镀层,其腐蚀速率也明显降低,耐腐蚀性能更好。

Corrosion protection of composite coating combining ceramic layer,copper layer and benzotriazole layer on magnesium alloy

A novel composite coating was fabricated on AZ91 magnesium alloy by applying a composite surface treatment which combined the methods of plasma electrolytic oxidation(PEO)pre-treatment,electroless copper and benzotriazole(BTA)passivation. The cross-section microstructures and chemical compositions of coating were examined using scanning electron microscopy(SEM) equipped with energy dispersive analysis of X-rays(EDX).Potentiodynamic polarization curves and salt spray tests were employed to evaluate corrosion protection of the coating to substrate in 5%NaCl solution.It is indicated that electroless copper produces a rough interface between the electroless copper layer and the ceramic layer.The corrosion potential shifts to the positive direction significantly and the current density decreases by more than one order of magnitude.There is no visible galvanic corrosion pits on the surface of the composite coating combination of PEO and electroless copper after 168 h neutral salt spray testing.The color of copper after BTA immersion could be held more than 60 d.