Thermodynamic Assessment of the Al-Mn and Mg-Al-Mn Systems
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Section I: Basic and Applied Research
Thermodynamic Assessment of the Al-Mn and Mg-Al-Mn Systems Adarsh Shukla and Arthur D. Pelton
(Submitted May 5, 2008; in revised form July 16, 2008) The binary Al-Mn system has 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 to account for short-range ordering. The results have been combined with those of our previous optimizations of the Al-Mg and Mg-Mn systems to evaluate and optimize the Mg-Al-Mn system. All available data for the ternary system are reproduced with only one small ternary model parameter for the liquid phase.
Keywords
aluminum, magnesium, manganese, phase diagrams, thermodynamics
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 understanding of novel magnesium alloys, including those that incorporate additions of Mn and Al. These alloy systems, along with other potential candidates, are being actively pursued as possible routes to develop magnesium materials with improved ductility, or even practical room temperature formability. The properties of cast or wrought material depend first and foremost upon the phases and microstructural constituents (eutectics, precipitates, solid solutions, etc.) which are present. In an alloy with several alloying elements, the phase relationships are very complex. In order to investigate and understand these complex phase relationships effectively, it is very useful to develop thermodynamic databases containing model parameters giving the thermodynamic 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 temperature and composition in multicomponent alloys, to follow the course of equilibrium Adarsh Shukla, and Arthur D. Pelton, De´partement de Ge´nie Chimique, Centre de Recherche en Calcul Thermochimique, Ecole Polytechnique, Montre´al, Que´bec, Canada. Contact e-mail: apelton@ polymtl.ca.
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or non-equilibrium cooling, to calculate corresponding heat effects, etc. Such thermodynamic databases are prepared by critical evaluation, modeling, and optimization. In a thermodynamic ‘‘optimization,’’ adjustable model parameters are calculated using, simultaneously, all available thermodynamic and phase-equilibrium data in order to obtain one set of model equations as functions of temperature
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