Blistering Phenomena of Painted Zn Alloy Electroplated Steel Sheets

Abstract

Corrosion behavior of painted Zn-Fe and Zn electroplated steel sheets was investegated using the salt spray test (SST).
Corrosion resistance of electrophoretically coated Zn-Fe electroplated steel sheet was superior to that of Zn electroplated steel sheet. This was considered to be caused by the difference between their corrosion resistances against OH^- ions formed by cathodic reaction under the paint film. In the case of painted specimens with cross scribes, the corrosion resistance to the alkaline solution of Zn-Fe electroplated steel sheet was higher than that of Zn electroplated steel sheet. This result agreed with the result of SST. On the other hand, the corrosion resistance to alkaline solution of unpainted Zn-Fe electroplated steel sheet was not higher than that of Zn electroplated steel sheet. When cathodic current was applied in the same solution, Zn-Fe electroplated steel sheet showed a higher resistance. The resistance to blistering of Zn-Fe electroplated steel sheet was due to the corrosion resistance to alkali in the cathodically polarized state.