Experimental investigation and thermodynamic modeling of the La-Mg system

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.