Thermodynamic assessment and determination of phase diagram including spinodal lines in Al-Mg binary alloy

Although several thermodynamic modelling have been carried out for the Al-Mg alloy system, no previous thermodynamic descriptions could calculate the metastable phase diagram of L12-type ordered GP zones (Al3Mg). In this study, Calphad-type thermodynamic assessment of Al-Mg binary alloys was performed to determine not only the miscibility gap but also the spinodal lines of GP zones. The Gibbs energies of fcc-Al solid solution and ordered GP zones were expressed by a four-sublattice model (split compound energy formalism), and a complete thermodynamic description was obtained from available experimental data; e.g. miscibility gap of GP zones or equilibrium phases, and thermal quantities of mixing enthalpy and activity. The calculated miscibility gap and spinodal lines could satisfactorily reproduce experimentally reported reliable data, and thus the equilibrium between fcc-Al solid solution and ordered GP zones was successfully evaluated for the first time.