The Properties of Organic Composite Coated Zn-Ni Plated Steel Sheets

In order to improve the performance of zinc-rich painted steel sheets such as Zincrometal®, a thin organic coated steel sheet with excellent performance has been developed. The new pre-painted steel sheet (Tough Coat-III) consists of Zn-Ni alloy electroplated steel as a substrate and a thin organic coating system without containing a large amount of electric conductive pigments. The organic coating includes a special chromate film containing electric conductive pigments and a thin epoxy resin film (about 1µm thickness). The chromate film is design to be reduced at low baking temperature, using reducing agent. Therefore TC-III shows nearly 100% Cr insolubility with maintaining bake-hardnability. The corrosion resistance of TC-III was investigated by cyclic corrosion tests and by impedance measurements. TC-III exhibits excellent corrosion resistance, especially after forming. This excellent corrosion resistance is achieved mainly by adoption of Zn-Ni alloy electroplated steel as the substrate and by removal of conductive pigment from the paint film.