Ni-Zn-P合金镀层在人工模拟海水中腐蚀行为的研究

目的 提高金属材料在海洋环境中的耐腐蚀性和使用寿命.方法 采用碱式化学镀方法 在Q235碳钢表面施镀Ni-P镀层和Ni-Zn-P合金镀层,镀液配方NiSO4·6H2 O 20~25 g/L,C6 H5 O7 Na3·2H2 O 50~70 g/L,NH4Cl 25~30 g/L,NaH2PO2·H2O 15~25 g/L.制备Ni-Zn-P合金镀层时,在以上配方中加入0.4~0.8 g/L ZnSO4·7H2 O.采用金相显微镜和扫描电子显微镜(SEM)观察镀层在人工模拟海水中腐蚀前后的组织形貌,用能谱分析仪(EDS)分析镀层腐蚀前后表面成分.结果 Ni-P镀层和Ni-Zn-P合金镀层中的P质量分数分别为11.26%和9.97%.从P含量和镀层组织形貌,可以确定得到的两种镀层是连续致密的非晶镀层.Ni-Zn-P合金镀层比Ni-P镀层的胞状组织更加均匀平滑,胞与胞的边界结合更加连续致密.在人工模拟海水中腐蚀144 h后,Ni-P镀层出现明显的点蚀坑,Ni-Zn-P合金镀层仍然连续完整.Ni-Zn-P合金镀层腐蚀后,Zn含量明显下降,并出现少量的Fe和O,表明合金镀层腐蚀过程是Zn优先被腐蚀,然后镀层逐渐被腐蚀破坏,最后基体发生腐蚀.Ni-Zn-P合金镀层的腐蚀速率明显低于Ni-P镀层的.结论 Ni-Zn-P合金镀层的胞状组织比Ni-P镀层的更加均匀平滑,胞与胞的边界结合更加连续致密,Ni-Zn-P合金镀层腐蚀速率明显低于Ni-P镀层.

Corrosion Behavior of Ni-Zn-P Alloy Coating in Artificial Seawater

Objective To improve the service life and corrosion resistance of metal materials in the marine environment. Methods The Ni-P coating and Ni-Zn-P alloy coatings were prepared on Q235 steel by alkaline electroless plating technique. The bath formula was: NiSO4·6H2O 20 ~25 g/ L,C6H5O7Na3·2H2O 50 ~70 g/ L, NH4Cl 25 ~30 g/ L, NaH2PO2·H2O 15 ~25 g/ L. Ni-Zn-P alloy coating was prepared by adding 0. 4 ~0. 8 g/ L of ZnSO4·7H2O into the above formula. The surface morphology of coatings before and after corrosion in artificial simulated seawater was observed by optical microscope and SEM. The surface composition of coatings before and after corrosion was analyzed by EDS. Results The P contents of Ni-P plating and Ni-Zn-P alloy coating were 11. 26 wt% and 9. 97 wt% , respectively. From the P content and coating microstructure, it ccould be determined that the two coatings obtained were continuous dense amorphous coatings. The Ni-Zn-P alloy coating was more uniform and smooth than the Ni-P coating, and the cell boundary was more continuous and denser. After 144 h corrosion in artificial simulated seawater, Ni-P coating showed obvious pitting, while the Ni-Zn-P alloy coating was still intact without damage and localized corrosion. After corrosion, the content of Zn decreased obviously and a small amount of Fe and O appeared in the Ni-Zn-P alloy coating, indicating that Zn was first corroded in the corrosion process of the alloy coating, then the coating was gradually corroded, and finally, the substrate was corroded. The corrosion rate of Ni-Zn-P alloy coating was significantly lower than that of Ni-P coating. Conclusion The Ni-Zn-P alloy coating was more uniform and smooth than the Ni-P coating, and the cell boundary was more continuous and denser. The corrosion rate of Ni-Zn-P alloy coating was significantly lower than that of Ni-P coating.