Long-term corrosion protection of arc spray Zn-Al-Si coating system in dilute chloride solutions and sulfate solutions

Abstract

In order to study the corrosion protective mechanism of arc spray Zn-Al-Si coating system in soil environment, carbon steel specimens covered with arc spray Zn-Al-Si coating system were immersed in dilute chloride solutions and sulfate solutions for over 500 days, and the corrosion behavior of the coated steel specimens was examined. The evolution of the open-circuit potential (OCP) of the immersed specimens and the anodic polarization curves of the arc spraying Zn-Al-Si layer were investigated. The corrosion products were characterized and the local polarizations at the cross-shaped scratch were performed after immersion test. The results showed that red rust of steel occurred in sulfate solutions but was inhibited in chloride solutions. The OCP of specimens increased with immersion time due to depressed anodic reaction. The corrosion products of arc spraying Zn-Al-Si layer were mainly Zn(OH)2, ZnO and Zn5(OH)6(CO3)2 in sulfate solutions, and Zn5(OH)6(CO3)2 and layered double hydroxide Zn0.70Al0.30(OH)2(CO3)0.15·xH2O in chloride solutions. Long-term corrosion protection of arc spray Zn-Al-Si coating system in chloride solutions is attributed to the formation of Zn0.70Al0.30(OH)2(CO3)0.15·xH2O and absence of ZnO.