Phase Equilibria at 500 A°C of the Mg-Gd-La System

The phase equilibria at 500 A degrees C of the Mg-Gd-La system were investigated via a combination of a diffusion couple technique and an equilibrated alloys method, by means of the electron probe microanalyses and x-ray diffraction technique. The LaMg2 and La5Mg41 phases in the Mg-La system were found to exist stably at 500 A degrees C. Continuous solid solutions of (Gd,La)Mg and (Gd,La)Mg-3 form between GdMg and LaMg and between GdMg3 and LaMg3, respectively. No ternary compound was found. Five three-phase equilibria, i.e. (Mg) + LaMg12 + GdMg5, LaMg12 + La2Mg17 + GdMg5, GdMg5 + La5Mg41 + (Gd,La)Mg-3, GdMg2 + (Gd,La)Mg-3 + (Gd,La)Mg and LaMg2 + (Gd,La)Mg-3 + (Gd,La)Mg, were accurately determined. The isothermal section at 500 A degrees C was constructed in the present work.