12th International Conference on Zinc & Zinc Alloy Coated Steel Sheet - GALVATECH 2021

Electrogalvanized steel sheets are widely used for electrical appliances and OA equipment because of their suitable appearance. It is well known that the lightness, the gloss, the press formability and the corrosion resistance of electrogalvanized steel sheets change depending on the crystal morphology of deposited Zn. Because control of the Zn morphology is important to improve these properties, many studies have been done on the effects of electrolysis conditions. Among the electrolysis conditions, the addition of organic compounds to the bath is known to change the morphology of deposited Zn drastically, however there are still many unexplained parts about the mechanism of changing the morphology of Zn. In this study, as for organic compounds adding to the bath, thiol compounds (R-SH) were used in consideration of adsorption ability to metal surface. Zn was electrodeposited on a steel sheets from the sulfate bath containing thioglycolic acid. Zn electrodeposition was conducted under galvanostatic conditions. The particle size and crystal orientation index of deposited Zn were determined by the result of X-ray diffraction intensity. The particle size of deposited Zn decreased and the crystal orientation index of (0002) Zn increased by the addition of thioglycolic acid. As the result of investigating the electrochemical behavior using the bath containing thioglycolic acid, adding thioglycolic acid reached to decrease of overvoltage for Zn deposition, acceleration of hydrogen reduction reaction and acceleration of Fe dissolution reaction. It is assumed that the increase of orientation index of (0002) Zn by adding thioglycolic is the effect of decrease of overvoltage for Zn deposition.