2015 Volume 64 Issue 6 Pages 251-258
The behavior of under-film corrosion was investigated by Raman imaging using multivariate analysis of corrosion products, which were generated by CCT and SST. Effect of the conversion coatings on the corrosion under the wetdry cyclic conditions was considered by comparing between zinc phosphate conversion coating and zirconium oxide conversion coating covered by cation electrodeposited coatings. The following findings were obtained. Under the zinc phosphate conversion coating, β-FeOOH was formed near the corrosion tip because corrosion products were deposited just under the scratch and macrocell corrosion was caused. Under the zirconium oxide conversion coating, β-FeOOH was not formed. It was considered that macrocell corrosion was not induced because of the smaller amount of corrosion products under the scratch and the higher anti-corrosion properties of the coating. It was confirmed that Raman imaging using multivariate analysis was useful for the analysis of under-film corrosion.