Effect of preadsorption of organic additives on the appearance and morphology of electrogalvanized steel sheets

Zn electrodeposition was performed galvanostatically on a steel sheet at 1500 A/m2 in an agitated sulfate solution at 40°C to investigate the effect of preadsorption of organic additives on the lightness and morphology of Zn. The organic additives preadsorbed were classified into two types: 1) polyethylene glycol (PEG), gelatin and stearyl dimethyl benzyl ammonium chloride (SDBAC) (type I), which exhibit the polarization effect on Zn deposition; 2) saccharin and sodium lauryl sulfate (type II), which exhibit no polarization effect on Zn deposition. The platelet crystals of deposited Zn became small by preadsorption of all kinds of organic additives. 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 significantly because of an increase in overpotential for Zn deposition by the preadsorption of PEG and gelatin, and the orientation decreased slightly by saccharin and sodium lauryl sulfate in spite of no polarization effect on Zn deposition. The surface roughness of deposited Zn decreased by the preadsorption of organic additives with the exception of SDBAC. This is due to decrease in size of platelet crystals of Zn. The lightness of deposited Zn was increased by the preadsorption of organic additives with the exception of SDBAC. Because Zn deposited ununiformly by the preadsorption of SDBAC, the surface roughness of Zn increased and the lightness decreased.