Relationship between La and Ce additions on microstructure and corrosion resistance of hot-dip galvanized steel

Abstract

Scanning electron microscopy, X-ray diffraction, a neutral salt spray test, and electrochemical methods were applied to observe the microstructure and test the corrosion resistance of hot-dip galvanized steel before and after the addition of La and Ce. La/Ce mixture existed in the form of (La, Ce)Zn13 on the coated surface, decreased the coating thickness and accelerated the zinc dendritic growth. The corrosion current density of Zn–0.1La–0.1Ce coating was 63% less than that of pure Zn coating. This phenomenon can be explained that La/Ce mixture inhibited the transformation of Zn5(OH)8Cl2·H2O into Zn5(CO3)2(OH)6 or ZnO, reduced the time for appearance of red rust, and thus enhanced the stability of corrosion products and delayed the oxidation and corrosion processes of galvanized coating. La/Ce mixture improved the corrosion resistance compared to a single La or a single Ce addition. A competitive relationship between La and Ce was observed in the corrosion resistance improvement of hot-dip galvanized steel.