THERMODYNAMIC STUDIES AND THE PHASE-DIAGRAM OF THE LI-MG SYSTEM

Li activities for liquid and solid alloys at the (Mg), (Li), and (Mg) + (Li) two-phase region of the Li-Mg system were determined. Liquid al loys were examined at temperatures from 638 to 889 K at various Li con centrations. The (Mg) solid solutions were investigated in two series: at constant temperatures between 773 and 876 K, with varying Li conte nt, and at fixed Li concentrations, equal to 0.125 and 0.160 molar fra ctions, at different temperatures between 772 and 849 K. At the two-ph ase region, (Mg) + (Li), emf measurements were performed in the temper ature range 773 to 838 K, with fixed Li concentrations equal to 0.20, 0.25, and 0.275 molar fractions. For (Li) solid alloys, experiments we re done at temperatures 773 to 849 K for several constant Li concentra tions, between 0.30 to 0.45 molar fractions, respectively. Studies on solid alloys enabled us also to determine the boundaries (Li)/[(Mg) (Li)] and (Mg)/[(Mg) + (Li)] at temperatures 773 to 831. K. The result ing thermodynamic and phase boundary data of this study were used with other selected references for a critical assessment of the Li-Mg syst em. The Lukas BINGSS optimization program and BINFKT for the calculati on of the thermodynamic functions and of the phase diagram were used. The calculated equilibrium phase diagram at temperatures below 750 K i ndicates a slightly lower solid solubility of Mg in (Li) in comparison with results from thermal analysis and the recently published Saunder s evaluation.