Experimental investigation and thermodynamic modeling of the La–Mg system

Abstract

Phase equilibria of the La–Mg system were studies experimentally by investigating 12 samples in the as-cast and annealed states, by means of X-ray diffraction measurement, scanning electron microscopy, electron probe microanalyses and differential scanning calorimetry. Two invariant reactions were identified experimentally: L→LaMg2+LaMg3 at 762 °C and L + LaMg3→La2Mg17 at 672 °C. The LaMg2 phase was determined to form by the congruent reaction (L→LaMg2) instead of the peritectic reaction (L + LaMg3→LaMg2), and decompose at the temperature ranges of 360–500 °C. The La5Mg41 phase was measured to form from LaMg3+La2Mg17→La5Mg41 at 668 °C and decompose below 500 °C. Then the present experimental results, combined with a critical review of literature data, were used to develop the thermodynamic description of the La–Mg system by means of CALPHAD method. The calculated phase diagram and thermodynamic properties could reproduce the available experimental data reasonably.