Morphology Control of Zinc Deposits of Electrogalvanized Steel Sheets

Abstract

The visual appearance, press formability and the corrosion resistance of electrogalvanized steel sheets change depending on the morphology of deposited Zn. In this paper, the effects of plating factors such as the surface condition of steel substrate, electrolysis factors and the bath condition on the morphology of deposited Zn were systematically discussed both from a crystallographic viewpoint of the epitaxy between Zn/steel and from an electrochemical viewpoint of the overpotential for Zn deposition. The crystal orientation index of Zn basal plane and the crystal size of Zn are decreased with increasing the overpotential for Zn deposition. They are also decreased with decreasing the epitaxy between Zn/steel even when the overpotential is kept constant. When the overpotential for Zn deposition is increased, the surface roughness of deposited Zn becomes larger because of an increase in the inclination of Zn basal plane to steel substrate. When the epitaxy between Zn/steel is decreased without changing the overpotential, the surface roughness becomes smaller because of the decrease in crystal size of Zn although the inclination of Zn basal plane is somewhat increased.