Phase equilibrium of Mg-Zn-La system in Mg-rich corner from 200 to 350 °C

Alloys of Mg-Zn-La system in Mg rich corner were prepared, and the phase relationship was investigated at different temperatures such as 200, 300 and 350 C by scanning electron microscopy (SEM), X-ray diffraction (XRD) and electron probe microanalysis with energy dispersive X-ray spectroscopy (EPMA). Two types of phase equilibrium were identified at the different temperatures. One is two-phase equilibrium contained the Mg solid solution and T-phase. The other is three-phase equilibrium which contained the Mg solid solution, MgZn phase and T-phase. T-phase was stable as the temperature changed. The La content in T-phase is constant which is about 8 +/- 0.3% (atom fraction); but the Mg content and Zn content of that is changed, and the Zn content in T-phase was from 16.1% to 44%. The solubility of La in MgZn phase was increased from 1.2% to 1.6% as the temperature increasing from 200 to 350 degrees C.