Calculation of phase equilibrium in Al-Li alloys

Stable and metastable phase equilibria in Al-Li alloys are investigated using a phenomenological free energy model. In this model, short range order in the solid phases is taken into account within the tetrahedron approximation of the Cluster Variation Method. For the liquid phase, a subregular solution model is used. The energy parameters entering the free energy description of each phase are determined by reproducing selected experimental thermodynamic data and equilibrium concentrations in the phase diagram. The entire equilibrium phase diagram is then computed. In addition, metastable equilibrium between the Al-rich f.c.c. solid solution and the Al3 Li phase is analyzed. A metastable miscibility gap is predicted to occur within the Al-rich solid solution below 400 K.