Corrosion Behavior of Organic Composite Coated Steel Sheet during Cyclic Corrosion Test

Organic composite coated steel sheets show their excellent corrosion resistance during cyclic corrosion tests (CCT). To clarify corrosion behavior of these sheets, changes in corrosion products and elements of plating, chromate and organic resin layers during CCT were examined. Formation of crystalline ZnCl2·4Zn(OH)2 and superficial amorphous zinc carbonate were detected by X-ray diffraction, fourier transform infrared spectroscopy and Raman spectroscopy. And besides it was found by electron probe micro analysis, chemical analysis and fourier transform infrared spectroscopy that the corrosion products formed on organic resin layer contained silicon as zinc silicate from silica in organic resin layer.Consequently, weight of zinc in plating layer and silica in organic resin layer decreased, while that of nickel in plating layer, chromium in chromate layer and carbon in organic resin layer remained constant, and the corrosion products formed on organic resin layer contained zinc and silicon dissolved from each layer during CCT.