Formation and Evolution of Corrosion Products on Eutectic Microstructures: A Novel Study to Understand Corrosion Protection of Zn–Al–Mg Coatings

Abstract

Zn–Al–Mg coatings contain Zn phase and Zn/Mg–Zn, Zn/Al, and Zn/Al/Mg–Zn eutectics. The formation and evolution of corrosion products on different eutectics that affect the corrosion resistance of Zn–Al–Mg coatings require further exploration. In this work, the formation and evolution of corrosion products on different microstructures were investigated. The results show that while the corrosion products on different microstructures are mainly Zn5(OH)8Cl2, the phase composition and morphology of corrosion products vary significantly. These differences in corrosion products on each microstructure were discussed in detail. The corrosion protective properties of corrosion products on different microstructures were compared. The protective properties of corrosion products are closely related to the content and morphology of Zn5(OH)8Cl2 and Zn6Al2(OH)16CO3. The corrosion products on Zn/Al/Mg2Zn11 eutectic are the finest and densest, with high content of Zn5(OH)8Cl2 and Zn6Al2(OH)16CO3, showing good protective performance. Increasing the content of Zn/Al/Mg–Zn eutectic to enhance the corrosion resistance of Zn–Al–Mg coatings should be considered in the subsequent work.