Effects of Ag and Ni Additives on Zn Diffusion in Steel Hot-Dip Galvanizing: An ab Initio Molecular Dynamics Simulation

An ab initio molecular dynamics study has been performed to investigate the effects of Ag and Ni additives on Zn diffusion in steel hot-dip galvanizing. Ag-Zn, Ni-Zn, and Zn-Zn ensembles are selected to model the industry process. For the Zn-Zn ensemble, the calculated pair correlation function, first peak position, and coordination number are in good agreement with available experimental data. We examine differences in the structural and electronic properties among Ag-Zn, Ni-Zn, and Zn-Zn ensembles. For Zn self-diffusion, we obtain a diffusion constant of 2.48 × 10^-9 m^2/s, very close to the experimental value of 2.37 × 10^-9 m^2/s. The Zn diffusion constants of different ensembles increase in the following order: Ag-Zn (almost equal)Zn-Zn > Ni-Zn, which is in agreement with the additive effects on the thickness of coatings in galvanizing, where Ag increases the coating thickness, but Ni decreases it. Our molecular dynamics simulations reveal that the role of additives in controlling the zinc coating thickness is to alter zinc diffusion speed before reaching the substrate. These suggestions may be useful for screening chemical additives to control the zinc coating thickness.