Electrochemical Behavior of Electrodeposited Zinc-Iron Alloys in Alkaline Solutions

Abstract

As a basis to elucidate the mechanism of underfilm corrosion of Zn-Fe alloy electroplated steel, the electrochemical behavior of electrodeposited Zn-Fe alloys was investigated in alkaline solution of pH ranging from 9.5 to 13.6.(1)In 5%NaCl solution of pH=9.5 and 11.7, low corrosion current density was observed in the range of low Fe content in the alloy due to the suppression action of oxygen reduction reaction caused by the initial oxide film formed on the alloys, which was observed also in neutral 5%NaCl solution.(2)In 5%NaCl solution of pH=13.6, the corrosion current density tended to increase with increasing Fe content in the alloy in the range of 50% or less Fe content and it significantly increased compared with that in the solution of pH=9.5 and 11.7 in the same Fe content range as above, presumably resulting from the change in both anodic and cathodic reactions.(3)In NaCl-free solution of pH=12, electrodeposited Zn and Zn-Fe alloys were passivated, thus leading to anodic control of corrosion. Furthermore, the corrosion current density decreased with increasing Fe content in the alloy in the solution. It was suggested that the decrease in the corrosion current density resulted from reinforcement of the surface film by iron in the alloys and passivation of iron in the alloys.