Tailoring model surface and wetting experiment for a fundamental understanding of hot-dip galvanizing

Abstract

The wettability of molten zinc-aluminum on a steel substrate is an important issue in the hot-dip galvanizing process for automotive applications. Especially, the effects of surface oxides have been current topics during recent years. However wetting behavior under the effects of oxide has not been well illustrated due to the complexity of the surface of actually used steel. In this work, wetting experiments using molten zinc-aluminum were applied to tailored model surfaces of iron to investigate its fundamental behavior. Well-defined aluminum oxide islands were successfully patterned on iron surfaces by physical vapor deposition with masks for this purpose. The sessile drop method with zinc-aluminum was conducted in a laboratory- made apparatus. This apparatus included a unique spin-off technique that allowed us to make an interface analysis at the early stage of wetting. The initial contact angles of the patterned samples were revealed to have followed the Cassie equation. This indicates that the wetting of zinc-aluminum on an oxide-iron system can be treated as if it is a static wetting in its initial stage, even though this system is originally considered as a reactive wetting. The molten zinc-aluminum on a patterned sample diffused into the interface between the oxide islands and the substrate in the stage after initial wetting. It is suggested that this manner of zinc-aluminum diffusion plays a key role in the reaction and formation of the interface during the hot-dip galvanizing process. © 2011 ISIJ.