Peeling failure of painted electrogalvanized steel immersed in distilled water was investigated. The relation between paint adhesion and water content of painted film was studied in various environments. The effects of NaCl content and dissolved oxygen in water on paint adhesion were studied. Delaminated surfaces after peeling test were analyzed by x-ray fluorescence analysis and electron probe microanalysis.
It was found that;
1) Paint adhesion after distilled water immersion was the worst.
2) Paint adhesion decreases with increasing NaCl content.
3) Dissolved oxygen affects little paint adhesion.
4) The amount of phosphorus remaining on electrogalvanized steel did not vary during water immersion test and was less than that on cold rolled steel.
5) There is no difference between water content of painted electrogalvanized steel and that of painted cold rolled steel.
The peeling failure of painted electrogalvanized steel in distilled water will not be initiated by corrosion under the film but will occur due to delamination of paint film by higher osmotic pressure of the dipped solution.
As the pressure under the paint film on electrogalvanized steel is thought to be the same that on cold rolled steel, it seems that the weakness of breaking strength of conversion film or adhesion between conversion film and steel surface will cause the poor paint adhesion of painted electrogalvanized steel immersed in distilled water.
