Ni-P/Ni-Zn-P双层复合镀层制备及耐蚀性的研究

Preparation and Corrosion Resistance of Bilayered Ni-P/Ni-Zn-P Composite Coating

目的提高金属材料在海洋环境下的耐蚀性。方法采用化学镀方法在Q235碳钢表面施镀Ni-Zn-P合金镀层和Ni-P/Ni-Zn-P双层复合镀层,采用扫描电镜(SEM)和能谱分析仪(EDS)对镀层表面形貌和断面成分进行了分析。结果 Ni-P/Ni-Zn-P双层复合镀层相对于Ni-Zn-P合金镀层胞状组织更加均匀平滑,胞与胞的边界结合更加连续致密。Ni-Zn-P合金镀层断面厚度为6.5μm左右,锌和磷的质量分数分别约为4%和14%。Ni-P/Ni-Zn-P双层复合镀层断面总厚度约7.5μm,内层镀层的厚度约2.3μm,磷的质量分数约为9%;外层镀层厚度约5.2μm,锌和磷的质量分数分别约为5%和11%。在5%Na Cl溶液中腐蚀144 h后,Ni-Zn-P合金镀层遭到了严重的破坏,有许多裂纹,而Ni-P/Ni-Zn-P双层复合镀层仍然连续完整,没有严重的破损,只是局部腐蚀,这说明双层镀层更耐蚀。结论 Ni-P/Ni-Zn-P双层复合镀层腐蚀速率明显低于Ni-Zn-P合金镀层,相对于Ni-Zn-P合金镀层耐蚀性更好。

The work aims to improve corrosion resistance of metal materials in marine environment. Ni-Zn-P alloy coating and Ni-P/Ni-Zn-P bilayered composite coating were prepared on Q235 steel by virtue of chemical plating. Surface morphology and fracture surface of the coatings were analyzed with SEM and EDS. The Ni-P/Ni-Zn-P bilayered composite coating was more uniform and smooth than Ni-Zn-P alloy coating, and the cell boundary was more continuous and dense as well. Cross section thickness of Ni-Zn-P alloy coating was about 6.5 μm, and Zn and P mass fraction nearly 4% and 14% respectively. Overall thickness of Ni-P/Ni-Zn-P bilayered composite coating was about 7.5μm, thickness of inner coating about 2.3 μm, P mass fraction about 9%; the outer coating about 5.2 μm, Zn and P mass fraction of about 5% and 11% respectively. After being corroded for 144 h in 5% solution, the Ni-Zn-P alloy coating was severely damaged and many cracks were present. The Ni-P/Ni-Zn-P bilayered composite coating remained intact and was subject to localized corrosion instead of serious damage, indicating that the bilayered coating was more resistant to corrosion. Corrosion rate of Ni-P Ni-Zn-P bilayered coating was significantly lower than that of Ni-Zn-P alloy coating, corrosion resistance of the former was better as well.