Corrosion Resistance of Organic Film Coated, Metal-organic Composite Coated and Some Zinc Coated Steel Sheets

Abstract

Corrosion behavior of organic film coated steel sheet(ZM), which might be applied to automobile bodies, has been compared with that of metal-organic composite coated steel sheet(WM) and some kinds of zinc coated sheets; (galvanized, galvanealed and zinc-nickel alloy coated shects).
The results obtained are as follows:
(1) Unpainted specimens of ZM and WM show excellent corrosion resistance in cyclic corrosion test (C.C.T.), where a s cathodic E.D. painted specimen of ZM with cross scribes seems to have almost as less corrosion resistance as cold rolled sheet.
(2) 3 coat painted specimen of ZM with cross scribes has also less corrosion resistance than zinc coated sheets in salt spray and weathering test. This shows little sacrificial corrosion preventive effect of zinc powder existing in organic film.
(3) Convex part of ZM exhibits better appearance, but larger perforation than zinc coated sheets after 22 weeks C.C.T., probably because of the surface crack of organic layer.
(4) WM seems to have excellent appearance and less perforation than the others especially in convex part.