An isothermal section of the Mg-Nd-Gd ternary system at 723 K was established by diffusion triple technique and electron probe microanalysis （EPMA）. Mg3Gd and Mg3Nd form a continuous solid solution （Gd,Nd）3Mg, and a continuous solid solution （Gd,Nd）Mg is also formed between MgGd and MgNd. Mg7Gd, Mg5Gd, Mg2Gd, Mg41Nd5, （Gd,Nd）3Mg and （Gd,Nd）Mg are found in the ternary system. In these intermetallic phases, Mg7Gd has been reported to be a metastable phase in previous literatures. The solubilities of Mg, Gd and Nd in all the phases were detected. Furthermore, four three-phase equilibria, α（Mg）＋Mg7Gd＋Mg41Nd5, Mg7Gd＋Mg5Gd＋Mg41Nd5, Mg5Gd＋Mg41Nd5＋（Gd,Nd）3Mg and （Gd,Nd）3Mg＋（Gd,Nd）Mg＋Mg2Gd, were identified in the isothermal section.
The phase equilibria in Mg-rich corner of Mg-Ca-Gd and Mg-Ca-Nd ternary systems at 400℃ were determined through the equilibrated alloy method by using XRD, SEM, EPMA and DSC. Partial isothermal sections in Mg-rich corner of Mg-Ca-Gd and Mg-Ca-Nd ternary systems at 400 ℃ were constructed from 13 alloys. A three-phase region of a-Mg, Mg41RE5 and Mg2Ca was determined in both ternary systems. It is formed by a similar ternary eutectic reaction L→a-Mg＋Mg2Ca＋Mg41RE5 at 499.6 ℃ and 505.6 ℃, respectively. It is found that the maximum solubility of Ca in Mg5Gd is 3.68% （molar fraction） and 3% of Gd can be dissolved in Mg2Ca in the Mg-Ca-Gd system at 400 ℃. While in the Mg-Ca-Nd system, the maximum solubility of Ca in Mg41Nd5 is 3.57% and 1.24% of Nd can be dissolved in Mg2Ca at 400 ℃. Other three-phase equilibria existing in Mg-rich corner of Mg-Ca-Gd system are a-Mg＋MgsGd＋T and MgsGd＋Mg2Ca＋T and the three-phase equilibrium in Mg-rich corner of Mg-Ca-Nd system is Mg3Nd＋Mg2Ca＋ Mg41Nd5.
