The Al-Er-Mg ternary system - Part II: thermodynamic modeling

A thermodynamic modeling and optimization of the Al-Er, Er-Mg, and Al-Er-Mg systems has been carried out, the Al-Mg system having already been optimized in the literature. The sublattice model has been used to describe the thermodynamic functions of both the solution phases and the stoichiometric phases present in the systems. In particular, the order/disorder relationship between the couples of phases A2/B2 and A1/L1(2) present in the system as bcc-(Er,Mg)/Er(Mg1-xAlx) and fcc-(Al)/(Al1-xMgx)(3)Er, respectively, has been taken into account and thermodynamically modeled. Moreover gamma-(Al,Mg) and Er-5(Mg1-xAlx)(24) phases, both related to the cI58-alphaMn (A12) type structure, have been modeled as different sublattice occupations of the same A12 phase. The thermodynamic modeling and the experimental investigation of the phase equilibria (reported in part I of this work) have been carried out by a recursive procedure. As a result, complete descriptions of the solid-solid and solid-liquid phase equilibria have been obtained.