Application of the phase-field method to the solidification of hot-dipped galvanized coatings

The growth of dendrites during the solidification of thin metallic films has been modeled using the phase-field method, with appropriate boundary conditions to take into account wetting effects. The model was applied to the growth of zinc dendrites during the solidification of hot-dipped coatings of steel, and the simulation results were compared to recent experimental observations of Strutzenberger and Faderl. It has been found that the presence of a boundary modifies the usual crystallographic growth directions of the dendrite arms as well as their growth velocity. In the case of hcp zinc dendrites in galvanized coatings, wetting effects at the boundary decrease the growth velocity as the inclination angle of the basal plane increases. This model also shows that shiny regions of the coating, characterized by a low density of lead particles and a smooth surface, result from the growth of the dendrite along the outer surface, while dimpled regions, characterized by a high density of lead particles and a rough surface, are due to the growth of the dendrite along the steel substrate.