Abstract
Conversion coating on zinc plating film using Cr (III) compound as main constituent were investigated. Corrosion resistance of the film were evaluated by salt spray test and measuring polarization resistance, Rp. Surface analysis were made to determine the elements on the film and depth profile by Auger electron spectroscopy (AES).
Corrosion resistance of the passive film composed of both Cr (III) and silicate was better than those film consisting of each own component. With addition of phosphate and by post-treatment with dipping in colloidal silica sol solution, the corrosion resistance of the film was improved more. The evaluations of the film by measurement of polarization resistance were almost same results. The results of surface analysis using AES indicated that Cr (III) in the film was increased with addition of silicate, and that the thickness of the film was increased with addition of phosphate. These were thought to be responsible for improving the corrosion resistance of those Cr (III) film composed of silicate and phosphate.
