Computer Coupling of Phase Diagrams and Thermochemistry 32 (2008) 470–477 Contents lists available at ScienceDirect Computer Coupling of Phase Diagrams and Thermochemistry journal homepage: www.elsevier.com/locate/calphad Thermodynamic assessment of the Si–Zn, Mn–Si, Mg–Si–Zn and Mg–Mn–Si systems Adarsh Shukla ∗ , Youn-Bae Kang, Arthur D. Pelton Centre de Recherche en Calcul Thermochimique, Département de Génie Chimique, Ecole Polytechnique, Montréal, Québec, Canada article info Article history: Received 28 April 2008 Received in revised form 1 July 2008 Accepted 2 July 2008 Available online 25 July 2008 Keywords: Silicon Zinc Manganese Magnesium Phase diagrams abstract The binary Si–Zn and Mn–Si systems have been critically evaluated based upon available phase equilibrium and thermodynamic data, and optimized model parameters have been obtained giving the Gibbs energies of all phases as functions of temperature and composition. The liquid solution has been modeled with the Modified Quasichemical Model (MQM) to account for the short-range-ordering. The results have been combined with those of our previous optimizations of the Mg–Si, Mg–Zn and Mg–Mn systems to predict the phase diagrams of the Mg–Si–Zn and Mg–Mn–Si systems. The predictions have been compared with available data. © 2008 Elsevier Ltd. All rights reserved. 1. Introduction Although magnesium-based materials have a long history of important commercial applications, including automotive, there remains much to be learned about the basic properties of the metal and its alloys. With the recent renewed interest in lightweight wrought materials, including both sheet and tube applications, there has been an increased focus on developing a better under- standing of novel magnesium alloys, including those that incorpo- rate additions of such elements as Si, Mn and Zn. These alloy sys- tems, along with other potential candidates, are being actively pur- sued as possible routes to develop magnesium materials with im- proved ductility, or even practical room temperature formability. The properties of cast or wrought material depend first and foremost upon the phases and microstructural constituents (eutec- tics, precipitates, solid solutions, etc.) which are present. In an al- loy with several alloying elements, the phase relationships are very complex. In order to effectively investigate and understand these complex phase relationships, it is very useful to develop thermo- dynamic databases containing model parameters giving the ther- modynamic properties of all phases as functions of temperature and composition. Using Gibbs free energy minimization software such as FactSage [1,2], the automotive and aeronautical industries and their suppliers will be able to access the databases to calculate the amounts and compositions of all phases at equilibrium at any ∗ Corresponding author. E-mail address: adarsh.shukla@polymtl.ca (A. Shukla). temperature and composition in multicomponent alloys, to follow the course of equilibrium or non-equilibrium cooling, to calculate corresponding heat effects, etc. As part of a broader research project to develop a thermody- namic database for Mg alloys with 25 potential alloying metals, the present study reports on the evaluation and optimization of the Si–Zn, Mn–Si, Mg–Si–Zn and Mg–Mn–Si systems. Previous optimizations of the Mn–Si system in the framework of COST 507 [3] and by Chevalier et al. [4] were based upon a Bragg–Williams (BW) random-mixing model for the liquid phase. The liquid in this binary system is expected to exhibit considerable short-range-ordering (SRO) as evidenced by the very negative enthalpy of mixing curve. As has been shown by the present authors [5], the use of a BW model in liquids with a high degree of SRO generally results in unsatisfactory results and in poor predictions of ternary properties from binary model parameters. In the present work, the Modified Quasichemcial Model (MQM) has been used to account for the SRO in the liquids. As well, there are vapor pressure measurements [6,7] of Mn–Si alloys and measurement of the enthalpy of formation [8] of compounds which were not taken into account in previous optimizations. The liquid phase in the Si–Zn system shows slight positive deviations from ideality. This system was optimized previously [9] using a BW random-mixing model. The MQM, which takes clustering into account, was used in the present work in order to obtain a better description and prediction in the Mg–Si–Zn system, and for consistency with the fact that the MQM is used for the other binary subsystems in this ternary system. Hence the Si–Zn and Mn–Si systems have been re-optimized in the present study. 0364-5916/$ – see front matter © 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.calphad.2008.07.002