Effect of preadsorption of polyethylene glycol on the appearance and morphology of electrogalvanized steel sheets

Zn electrodeposition was performed galvanostatically on a steel sheet at 1 500 A/m2 in an unagitated sulfate solution at 40°C to investigate the effect of preadsorption of polyethylene glycol (PEG) on the lightness and morphology of Zn. The lightness of deposited Zn was increased by the preadsorption at coating masses of 10-80 g/m², except in the initial stage of the deposition. The overpotential for Zn deposition was increased by the preadsorption, and its polarization effect was maintained even when Zn deposition proceeded. The platelet crystals of Zn were smaller and more random in growth direction when Zn deposited on the cathode preadsorbed by PEG. The decrease in size of platelet crystals of Zn with the preadsorption is attributed to both the increase in overpotential for Zn deposition and the decrease in epitaxial growth of Zn. The orientation of {0001 )Zn basal plane decreased because of an increase in overpotential for Zn deposition by the preadsorption of PEG. The lightness of deposited Zn increased in spite of a decrease in orientation of the {0001} plane with the preadsorption. This indicates that the lightness of deposited Zn was more easily affected by the decease in size of Zn platelet crystals than by the crystal orientation of Zn.