Corrosion Under Paint Film of VariousGalvanized Steels

Long term corrosion test for more than 10,000 hrs by means of salt spray test and special cycle test were conducted to study the corrosion resistance of various painted galvanized steels generally used as corrosion resistant materials, in which hot dip galvanized, electro galvanized, galvannealed and cold rolled steel are included.

The results are as follows:

(1) Galvannealed steels are most excellent in corrosion resistance through paint film in both corrosion testings. The reason is considered as follows: Steel under paint film shows clear acid-alkali distribution and galvanized steel does strong alkali after long time exposure. Whereas galvannealed steel shows only neutrality in PH.

Special cycle corrosion test is one of the most valuable corrosion testing methods. And it is concluded that wet-dry cycle and freezing are important factors for corrosion test.