Structure Analysis of Thin Corrosion Products Film on Hot-dip Zn-Al Coatings by Synchrotron Radiation Photoemission Spectroscopy

Abstract

Structure of thin corrosion products film (CPF) on hot-dip Zn-Al alloy coated steel sheets were investigated by means of photoemission spectroscopy using synchrotron radiation of 160 eV and μ-FT-IR method, and were compared with those on Zn and Al pure metal sheets. CPF was prepared by 1 h and 16 h exposure in air saturated with water vapor at 323 K under the presence of NaCl particles.
As a result, the dominant component of the CPF on the Zn-0.2%Al coating changed from Zn(OH)₂ to 2ZnCO₃·3Zn(OH)₂, while the CPF of Zn-55%Al alloy coating was consisted mainly of ZnCl₂·4Zn(OH)₂. And it was found that the structure near the surface of CPF, which was composed mainly of Al oxide, was transformed into the surface structure covered with Al chloride by humid exposure under the presence of NaCl.