Effects of aluminum concentration on the formation of inhibition layer during hot-dip galvanizing

The formation of inhibition layer (IL) during hot-dip galvanizing with Al concentration varying from 0.0 to 0.8 wt pct. is studied by both experiments and numerical simulations. Using EDS and XRD, the IL is identified mainly as Zn-bearing Fe₂Al₅. SEM results reveal that the IL thickness increases with Al concentration in zinc bath, and the particles of Fe₂Al₅ on the surface of IL formed in 0.8 wt pct. Al bath are smaller than those formed in 0.2 wt pct. Al bath. On the surface of IL generated in 0.8 wt pct. Al bath there are some tiny particles with size about tens of nanometers randomly dispersing on the larger ones, indicating that the growth of IL is so fast that the growth mode changes and nucleation occurs at the IL/zinc interface. Using a mesoscopic model based on the lattice Boltzmann method, numerical simulations are also performed to study the reactive transport phenomena during IL formation under different Al concentrations. The simulations reveal complex coupled mechanisms between Fe and Al diffusion, Fe dissolution, as well as nucleation and growth of Fe₂Al₅ and the results agree with the experiments.