Thermodynamic study of the galvanizing process in a Zn-0.1%Ni bath

The addition of alloying elements to the zinc bath is one of the best solut ion to reduce overthicknesses of the coating when galvanizing silicon-kille d steels. The use of nickel addition to the molten zinc offers industrial a dvantages, especially in the modification of the Sandelin curve related to the reactivity of steels towards the galvanizing bath. However, dress forma tion in a 0.1 wt % Ni bath is the main drawback of the process. Bending on thermodynamic description of the ternary Fe-Zn-Ni system at 450 degrees C, the reaction between a pure iron substrate and a nickel added zi nc bath is modelled at 450 degrees C. The approach of the extension of the liquid phase in the quaternary Fe-Zn-Si-Ni system leads to understanding of the effect of nickel addition to the zinc bath when galvanizing reactive s ilicon steels. These thermodynamic interpretations lead to understanding of experimental phenomena during the galvanizing process: dress formation, re duction of the coating thickness, smoothing the solid-liquid interface when nickel is added to the zinc bath at 450 degrees C. Based on morphological and kinetic observations, steel-zinc reactions are clearly investigated sho wing the important effect of allowing elements to the substrate or to the b ath. (C) 1998 Kluwer Academic Publishers.