Search Results

The Effects of Fe-P flash electro-coating on several properties of galvannealed sheet steel with coating of 60 g/m2 were investigated to apply galvannealed sheet steel not only to inner panels but also to exposed panels. The allowable range of Fe content in galvannealed coating for anti-powdering property is from 7 wt% to 9.5 wt%. However, this range of Fe content gives higher coefficient of friction for the galvannealed sheet steel against die due to the existence of soft phase, ζ, at surface. The amount of Zn peeling off by flaking increases with the decrease in Fe content below 10 wt% in the case of no lubrication. Fe-P flash electro-coating on galvannealed sheet steel is effective to decrease the coefficient of friction and the amount of Zn peeling off by flaking, and does not influence the anti-powdering property.

Organic composite coated steel sheets retain their excellent corrosion resistance during cyclic corrosion tests (CCT). To clarify the corrosion behavior of these sheets during CCT, variations in corrosion products and coating components were examined. Moreover, the contribution of the corrosion products, organic composite coating, and chromate film to corrosion resistance was examined by AC impedance measurements. Formation of crystalline ZnCl2·4Zn(OH)2 and amorphous zinc carbonate were detected by X-ray diffraction (XRD) and Fourier transformation infrared spectroscopy (FT-IR). Crystalline ZnCl2·4Zn(OH)2 is formed during CCT on and under the organic composite coating. The corrosion products formed on the coating contain silicates from the silica in the organic composite coating. Consequently, the contents of zinc and silica in the coating decrease, while nickel and chromium in the chromate film and carbon in the coating remain constant during CCT.

Al2O3 -dispersed Zn-Co-Cr alloy electroplated has been developed for automobile use. Optimum coating composition ranges from 0.5 to 2.0wt% for Co, 0.3 to 1.0wt% for Cr, and 0.1 to 2.0wt% for Al2O3. The coating showed excellent corrosion resistance with and without paint. Superior anti-corrosive property of the coating results from the formation of the mechanically and chemically stable corrosion products, ZnCl2 −4Zn (OH)2, and the passivation in anodic polarization. The coating also showed good stone chipping resistance as well as paintability, formability, and weldability. Accordingly Al2O3 -dispersed Zn-Co-Cr alloy electroplated is suitable for application to both unexposed and exposure parts, including interior and exterior surfaces.