Flake-like ZnAl alloy powder modified waterborne epoxy coatings with enhanced corrosion resistance

Abstract

Zinc-rich epoxy coatings (ZRECs) have been widely used to protect steel against corrosion because of their excellent corrosion resistance. However, the ZRECs preparation usually used a large amount of Zn powders and organic solvents, which not only wasted resources but also produced a great quantity of volatile organic compounds (VOC). Therefore, it was necessary to develop a method which can prepare epoxy coatings with low Zn content, great corrosion resistance and green environmental protection. In this paper, three different flake metal powders (Zn, ZnAl alloy and ZnAlMg alloy) were used to replace spherical Zn powders to develop environmentally friendly coatings with low pigment content. The coatings were evaluated by salt spray test and electrochemical test. The results show that the use of flake metal powders instead of spherical zinc pigments can enhance the electrical connection between metal particles, prolong the path of corrosive medium infiltration into the coatings, enhance the physical shielding effect of the coatings, and reduce the pigment content by one third. Among them, the ZnAl coatings displayed the best anti-corrosion performance resisting salt fog corrosion for 28 days. In addition, the experimental results show that the self-healing ability of the coatings also plays an important role in the immersion middle and late stages. In short, the waterborne epoxy ZnAl coatings are suitable for large-scale application in harsh environments.