Coating Structure and Corrosion Mechanism of Zn-19%Al-6%Mg Alloy Coating Layer

Abstract

The purpose of this report is to compare the coating structure and corrosion mechanism of newly developed Zn-19%Al-6Mg-Si with conventional Zn-Al-Mg alloy coating Zn-11%Al-3%Mg-0.2%Si. In past papers the corrosion resistance of Zn-Al-Mg alloy coating layers was mainly discussed based on analysis methods that focus on one aspect of early corrosion stage. However, this report focuses on the changes in the corrosion mechanism until the end of the coating lifespan and picks up the factors of the coating layer that contribute to corrosion resistance.

The results of the corrosion cross section images of the Zn-Al-Mg alloy coating layer after cyclic corrosion test suggested that corrosion of the coating layer progresses selectively in each phase, which means each phase has its own electrochemical potential. Considering the differences in the corrosion mechanisms of these two coated steel sheets, it was suggested that the phase proportion of the coating layer and the unique potential determine the corrosion resistance of the coating layer.