Wetting Behavior of Zn-Al Liquid on Si-Containing Steel After Surface Oxidation and Reduction Treatment

In the hot-dip galvanization of steel products, surface oxidation–reduction treatment has been proposed recently to improve the wettability of liquid Zn-Al alloy on Si, Mn-containing high-strength steel. During surface oxidation–reduction treatment, an iron-oxide layer with a nanoscale thickness is formed on the steel surface, which is reduced to a metallic iron layer. Although elemental Si and Mn in steel react with oxygen in the atmosphere to form oxide phases, these oxides are expected to be trapped under a reduced iron layer. However, optimum oxidation–reduction conditions have been explored to achieve a good wettability of the liquid Zn-Al alloy on the steel surface. In this study, the dynamic wetting behavior of liquid Zn-Al alloy on the surface of the Si-containing steel after oxidation–reduction treatment was observed by the sessile drop method. It was found that the wettability of the liquid Zn-Al alloy on Si-containing steel depends significantly on the oxidation–reduction condition of steel, despite the Si content in steel being fixed. A porous structure formed in the reduced iron layer accelerates liquid Zn-Al alloy wetting through a capillary force, whereas oxide phases exposed to the steel surface prevent liquid alloy wetting.