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目的：提高AZ91 D镁合金的耐腐蚀性能,扩大其应用范围。方法先在AZ91 D镁合金表面化学镀Ni-P镀层,再化学镀Ni-Sn-P镀层,形成Ni-P/Ni-Sn-P双镀层。研究Ni-P/Ni-Sn-P双镀层的表面形貌和耐腐蚀性能,并与Ni-P单镀层进行对比。结果 Ni-P/Ni-Sn-P双镀层表面分布更均匀平整,缺陷较少,孔隙率较低,具有无定形结构。二次Ni-Sn-P镀层的腐蚀电位约为-0.77 V,略低于一次化学镀Ni-P层(约-0.68 V),两镀层间的电位差使得其构成了微腐蚀电偶,Ni-P层作为阴极,Ni-Sn-P层作为阳极,阳极优先被腐蚀。结论 Ni-P/Ni-Sn-P双镀层的Ni-Sn-P外层能为Ni-P内层提供阴极保护,较好地横向分散腐蚀电流,从而增强AZ91 D镁合金基底的耐腐蚀性能。

ABSTRACT:Objective To improve the corrosion resistance of AZ91D magnesium alloy and expand the range of application. Methods Ni-P coating was first prepared on AZ91D magnesium alloy by electroless plating, then Ni-Sn-P coating was prepared on this basis, forming Ni-P/Ni-Sn-P duplex coatings. The microstructure and corrosion resistance of Ni-P/Ni-Sn-P duplex coatings were investigated and compared with those of Ni-P coating. Results The results showed that the surface of Ni-P/Ni-Sn-P duplex coatings was more uniform, compact, with fewer defects, lower porosity and amorphous structure. The corrosion potential of the secondary Ni-Sn-P coating was about -0. 77 V, which was lower than that of the first Ni-P coating (-0. 68 V). The potential difference between the two coatings formed micro etching point, with Ni-P coating as the cathode, and Ni-Sn-P coating as the an-ode, and the anode was corroded first. Conclusion The outer layer of Ni-Sn-P coating in the Ni-P/Ni-Sn-P duplex coatings could protect the first Ni-P coating from corroding and diffuse the corrosion current in the horizontal direction, thus greatly enhancing the corrosion resistance of AZ91D magnesium alloy.