Effects of Alkaline Zinc Bath Formulations on Electrochemical Corrosion Behavior of Electrogalvanized Coatings Available to Purchase

The effects of alkaline noncyanide zinc plating bath formulation on the plating characteristics and deposit properties are investigated. Scanning electron microscope and x-ray diffractometer are used to study the surface morphology and texture of the zinc deposits, respectively. Uniform and compact coatings with a dominant (110) texture are obtained for all of the bath formulations. Nevertheless, significant differences in surface morphology and relative preferences for the (110) and (100) planes were found to result from the concentrations of zinc and sodium hydroxide in the bath. Electrochemical impedance spectroscopy and potentiodynamic polarization scan were used to evaluate the corrosion resistance. The coatings with a moderate Zn (8 g/L to 11 g/L) and controlled NaOH (120 g/L) contents show good corrosion resistance, with the corrosion current and corrosion rate being the lowest at 8 g/L of Zn and 120 g/L of NaOH. The ratios of texture coefficient, morphology, and compressive residual stress from different bath composition contribute to the corrosion-resistant property. The findings from this work should provide useful information regarding electrogalvanized zinc coatings with enhanced corrosion resistance.