Analysis of Corrosion Layers on Electrodeposited Zn-Ni (13wt%) Alloys Using AES, SAM, XPS, SEM and XRD

Abstract

Corrosion layers on electrodeposited Zn-Ni(13wt%) alloys are analyzed using Auger Electron Spectroscopy(AES), Scanning Auger Spectrometer(SAM), X-ray Photoelectron Spectroscopy(XPS), Scanning Electron Microscope(SEM), and X-ray Diffraction(XRD). It was found that surfaces of the alloys corroded by SST (salt spray test) were covered with zinc oxide and zinc hydroxide, and their inner layers consisted of γ phase alloy and ZnCl₂·4Zn(OH)₂. On the other hand, the surface layer of the alloys immersed in 5% NaCl solution consisted of ZnO and ZnCl₂·4Zn(OH)₂. It is pointed out that the enrichment of Ni between the surface and the inner layers does not occur. Chlorine does not exist in the surface layer of the alloys corroded by SST but does in the inner layer. As for the samples immersed in 5% NaCl solution, it is found in the surface layer as well as in the inner layer. It is emphasized that the corrosion mechanism is completely different between SST and immersion in 5% NaCl solution. Chlorine in the inner layer of the alloys corroded by SST is homogeneously distributed. From above results, the mechanism of corrosion by SST for the alloy is discussed.