Corrosion protection of carbon steel using a combination of Zr conversion coating and subsequent zinc-rich silicate coating with a flake ZnAl alloy
Nguyen Huy Hoang, Truong Anh Khoa, Le Thi Nhung, Phan Minh Phuong, Tô Thị Xuân Hằng, Nguyễn Văn, Thanh–Danh Nguyen
Abstract
To improve the corrosion protection properties of zinc-rich silicate coatings on steel, zirconium pretreatment loaded with (3-aminopropyl)triethoxysilane (APTES) 0.025 % (v/v) and the partial replacement of spherical zinc by flake ZnAl alloy were investigated. DC polarization and electrochemical impedance spectroscopy (EIS) show that the zirconium pre-treated layer containing APTES improves the corrosion protection of the bare steel. Zinc-rich silicate coatings containing flake ZnAl with and without pretreatment were evaluated by EIS, salt spray test and pull-off test. Pretreatment with a zirconium conversion layer reduces corrosion products and adhesion loss (from 16.53% to 12.54%) while the performance of corrosion protection significantly increased from 2003 Ω.cm2 to 2640 Ω.cm2 in comparison with the non-pretreated samples. The results show that flake ZnAl pigment (5 wt%) significantly improves corrosion resistance and prolongs the duration of cathodic protection of zinc-rich silicate coatings.