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

The occupancy sites of Mg in the corrosion products formed on the steel substrate at the 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, at the initial stage of corrosion, it is considered that Zn5(OH)8Cl2·H2O with Mg partially substituting two types of Zn crystallographic sites forms at the cut-edge of the Zn–11Al–3Mg coated steel.