Scanning Kelvin Probe Analysis of Cut Edge Corrosion on Prepainted Galvanized Steel with Chromate-Containing Epoxy Primer

Abstract

Prepainted galvanized steels with chromate-containing and chromate-free primers were prepared to understand the effect of the chromate on cut edge corrosion. The initiation and growth of red rust were investigated with the combination of scanning Kelvin probe techniques and cyclic wet-dry corrosion tests. Chromate was proved to inhibit oxygen reduction reaction on the steel substrate, providing the situation in which the Zn layer readily acts as a sacrificial anode. Even under a thin electrolyte layer of 70 μm, the corrosion potential of cut edge for the chromate-containing specimen was found to be almost the same as that of zinc. In the case of the chromate-free specimen, however, the corrosion potential increased with decreasing thickness of the electrolyte layer to 70 μm, which indicates sacrificial corrosion protection of the Zn layer is no longer effective under thin electrolyte layers. It was also expected that chromate enhances the ability of red rust to prevent the anodic dissolution of the steel substrate.