ELECTROCHEMICAL-BEHAVIOR OF ELECTRODEPOSITED ZINC-IRON ALLOYS IN 5-PERCENT-NACL SOLUTION

The electrochemical behavior of electrodeposited Zn-Fe alloys in neutral (pH = 5.6) 5%NaCl solution was investigated as a basis to elucidate the corrosion behavior of Zn-Fe alloy electroplated steel. (1) Electrodeposited Zn-Fe alloys containing 4 approximately 27%Fe exhibited the suppression action of oxygen reduction reaction in neutral 5%NaCl solution. The corrosion current density of the alloys was remarkably decreased due to the suppression of oxygen reduction reaction compared with that of electrodeposited Zn and Zn-Fe alloys containing more than 30%Fe. (2) The suppression action of oxygen reduction reaction was considered to be attributed to suppression of electron transfer through the initial oxide film formed on the alloys, because the suppression occurred in the presence of the surface oxide film and anomalously large Tafel slope of ca. -4RT/F equivalent to that explained by dual barrier model was observed. (3) The initial oxide film was not stable in 5%NaCl solution, thus losing most of the suppression action after several hour immersion. The suppression action, however, was recovered after a short time exposure to the air, indicating that the oxide film having the suppression action was formed again.