Study on the Effect of Sheet Flatness on the Corrosion Resistance of Zirconium Film

Abstract

In order to clarify the relationship between the corrosion resistance of zirconium films and the surface flatness of sheets from amechanism perspective，chemical polishing was used to alter the surface flatness of cold-rolled steel sheets and aluminum alloy sheets.These modified surfaces were compared with untreated cold-rolled and aluminum sheets.Zirconium films were prepared on the sample surfaces，and their micro morphology were observed using scanning electron microscopy (SEM).Electrochemical methods were employed to test the corrosion resistance of the passivation films.The corrosion resistance of the films and the adhesion of paint film was evaluated using salt spray test chamber， cyclic alternation tester and paint adhesion testing equipment.Results showed that the polished cold-rolled steel sheets and aluminum alloy sheets exhibited smooth and even appearances.The zirconium films prepared on these polished surfaces displayed a uniform and dense particle distribution， with significantly reduced roughness.The corrosion current of the zirconium films was lower，and the impedance radius was larger.In contrast， the unpolished cold-rolled and aluminum alloy sheets appeared rough and uneven， and the zirconium films prepared on these surfaces had irregular particle sizes and arrangements.After impact， cup tests and cross-cut adhesion tests， the adhesion of the zirconium films on both cold-rolled and aluminum alloy sheets met the requirements.After 1 000 h of salt spray testing， the maximum single-sided expansion width of the cold-rolled plate paint film on the polished flat surface was approximately 1.9 mm， with no bubbling on the paint surface.For the unpolished cold-rolled sheets， the maximum single-sided expansion width of paint film was about 2.3 mm， also with no bubbling.For the polished aluminum alloy sheets，the paint film exhibited a single-sided expansion width of corrosion of 2.0 mm after 30 cycles of alternating testing，with no bubbling on the paint surface.Conversely， the unpolished aluminum alloy sheets showed a single-sided expansion width of corrosion of 2.6 mm after the same number of cycles， with no bubbling.

Keywords

• cold-rolled sheet； aluminum alloy sheet； zirconium film； adhesion； corrosion resistance