Effect of Surface Pre - Oxidation Temperature on the Microstructure of Hot - Dip Galvanized Coating of Ductile Iron

Abstract

In order to improve the quality of hot - dip galvanized coating on ductile iron castings, the scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), and X - ray photoelectron spectroscopy (XPS) and other means were employed to study the effects of pre - oxidation on the formation of oxides on surface of ductile iron, the surface silicon content and hot - dip galvanized coating structure. Results showed that a selective SiO2 oxide layer was formed on the surface of pre - oxidized ductile iron. After pre - oxidation, the silicon content on the surface of ductile iron increased obviously. On the contrary, the silicon content on the surface of ductile iron decreased after alkali washing and acidic pickling. After pre - oxidation at 800 ℃ for 5 h, the silicon content on the surface of ductile iron decreased to 1.86%(mass fraction). Moreover, the thickness of hot dip galvanized alloy coating of ductile iron could be obviously reduced by surface pre - oxidation. After pre - oxidation at 800 ℃ for 5 h, the alloy layer in hot dip galvanizing of ductile iron had the densest structure and the smallest thickness of 20.1 μm. Besides, the variation law of alloy layer thickness with pre - oxidation temperature was basically consistent with the variation law of silicon content on the surface of ductile iron after alkali washing and acidic pickling with pre - oxidation temperature.

Keywords

• surface pre - oxidation|ductile iron|hot - dip galvanizing|coating structure