Microstructure and Corrosion Behavior of ZnAl12Mg3Si0.3 Double-Batch Hot-Dip Coatings

This article presents the microstructure (SEM) and corrosion behavior of ZnAl12Mg3Si0.3 (ZAMS) coatings obtained by the double hot-dip method on Sebisty steel with increased strength. On the basis of chemical composition studies in micro-areas (EDS) and phase composition studies (XRD), structural components of the coating and corrosion products formed on the coating surface after exposure to the neutral salt spray (NSS) test (EN ISO 9227) were identified. The presence of the Fe(Al,Si,Zn)₃ intermetallic phase was found in the Fe-Al intermetallic layer, while in the outer layer, dendrites rich in Al and Zn were identified. In these dendrites, the eutectics of Zn/MgZn₂ and precipitates of the MgZn₂ phase and Si were located. The NSS test showed better corrosion resistance of ZAMS coatings compared to conventional zinc hot-dip coatings. The increase in corrosion resistance is due to the formation of favorable corrosion products: simonkolleite-Zn₅(OH)₈Cl₂·H₂O and hydrozincite-Zn₅(OH)₆(CO₃)₂, and the presence of the MgZn₂ phase in the coating, which is more anodic than other structural components.