XAFS Analysis of Corrosion Products Formed at the Cut-edge of Zn‒Al‒Mg Coated Steel in the Early Stage of Corrosion

Abstract

The occupancy sites of Mg in the corrosion products formed on the steel substrate at cut-edge of the Zn‒11Al‒3Mg （mass％） coated steel was investigated by XAFS analysis at the initial corrosion stage. At the cut-edge, corrosion products containing Zn and Mg were formed in the early stages of corrosion. The XRD and XAFS analyses revealed that the corrosion products at the cut-edge of the Zn‒11Al‒3Mg coated steel were Mg-containing Zn₅（OH）₈Cl₂・H₂O. Based on the first-principles calculations, Mg in Zn₅（OH）₈Cl₂・H₂O was more likely to substitute two types of the crystallographic sites of Zn rather than intercalate between the ZnO₆ and ZnO₃Cl layers. Therefore, Zn₅（OH）₈Cl₂・H₂O, with two types of the crystallographic sites of Zn partially substituted by Mg, was thought to be formed at the cut-edge of the steel substrate of Zn‒11Al‒3Mg coated steel at the initial corrosion stage.