Effect of oxides on the reaction kinetics during hot-dip galvanizing of high strength steels

Selective oxidation of the minor alloying elements during annealing prior to hot-dip galvanizing cause poor wetting with liquid zinc, resulting in bare spot defects. The effect of surface coverage, morphology (i.e., size and distribution) of the oxides on the reaction kinetics was examined. The Zn wettability has been determined by sessile drop contact angle measurement method and the Fe–Al interfacial layer was investigated by the use of a novel hot temperature spinning process. It has been found that besides the overall surface oxide coverage, size of the oxide islands is a dominant factor in affecting the reaction kinetics.

► Overall wetting kinetics is governed by the size of the oxide islands.
► Larger oxide islands are problematic in reactive wetting during hot-dip galvanizing.
► Growth of Fe–Al interfacial layer is hindered by larger oxide islands.
► Wetting kinetics is described by introducing Avrami growth law into Cassie equation.