Prediction Method for Perforation Corrosion Life of Coated Steel Sheets in Actual Automobiles

Abstract

Many kinds of corrosion testing methods are being used to evaluate corrosion resistance of coated steel sheets for automobiles. In this study, perforation corrosion behavior of Zn coated steel sheets analyzed in various corrosion testing was compared with that of actual vehicles used in North America. It was found that the influence of weight and type of coating on perforation corrosion behavior changed depend on the conditions of combined cyclic corrosion tests. In order to establish practicability of CCTs, our study focused on corrosion rate ratio of steel to Zn coating in the perforation corrosion process to introduce a new index of PCI (Perforation Corrosion Index). The corrosion behavior in CCTs and actual vehicles can be correlated using the PCI values and perforation corrosion resistance of zinc-alloy coated steel in actual vehicles can be predicted based on the tendency of corrosion resistance as a function of PCI. It is also important to make the lapped specimen with adequate clearance and bare area so that the corrosion mechanism in CCTs be equivalent with that in actual environment. It is expected that coated steel sheets will be developed appropriately and efficiently applying this corrosion prediction method.