A full thermodynamic optimization of the Zn-Fe-Al system within the 420-500 °C temperature range

The Zn-Fe-Al system was assessed by using the CALPHAD technique. The optimization was based on three cornerstones. Firstly, crystallographically consistent sublattice models recently proposed by Nakano et al. for all intermetallic phases in the Zn-Fe system made it possible to predict which sublattice(s) would be most capable of hosting aluminum. Secondly, a careful analysis of all available phase diagram data allowed identifying those investigations in which the equilibrium state of the system was unquestionably achieved. Only the results of those studies were employed for the assessment. Thirdly, the PARROT module of Thermo-Calc, which was used for the optimization, was fed with an extensive array of accurate and reliable activities of Al. The activities were derived from electromotive forces measured by Yamaguchi et al. in various two- and three-phase regions. In the past, only a fraction of data collected was published; a complete compilation is presented in this contribution. By comparing calculated quantities and their experimental counterparts, it was demonstrated that the thermodynamic model proposed for the Zn-Fe-Al system could be relied upon within the 420-500 degrees C range, i.e. within the region important for galvanizing and galvannealing. It is difficult to speculate whether the model remains workable outside this temperature interval since almost all experimental data reported in literature were obtained within the limits specified. (c) 2006 Elsevier Ltd. All rights reserved.