A Preliminary Assessment of the Zn-rich Corner of the Al-Fe-Zn System and its Implications in Steel Coating

The Al-Zn-Fe system has great importance in the production of corrosion resistant coatings for steel. Aluminum additions to the galvanizing bath can result in significant changes in the process, effecting the growth kinetics of the coating layers, the type of dross formed in the galvanizing pots and, in the case of high aluminum contents, significantly changing the phases present in the coating. The effect of small aluminum additions is frequently ascribed to the change in the first phase that precipitates from the liquid. However, solid liquid phase relations in the Zn-rich corner of the Al-Fe-Zn system are not well established. In this work, the available information on the Al-Fe-Zn system is briefly reviewed and, together with previous assessments of the binary systems, is used to evaluate the applicability of simple thermodynamic models to the phases involved in the solid liquid equilibrium in the zinc-rich corner of the system. The results of this simplified model are compared with laboratory and industrial experimental data from literature and its applicability is discussed, with special emphasis in the present limitations of the models used. © 1999 Carl Hanser Verlag, München.