The alloys were prepared in Mg-rich corner of Mg-Zn-Ce system. Partial phase equilibrium relationships of these alloys at 350 ℃ were identified by using scanning electron microscopy(SEM), electron probe microanalysis(EPMA), X-ray diffraction(XRD) analysis and selected area electron diffraction(SAED) pattern analysis of transmission electron microscopy(TEM). Partial isothermal section of Mg-Zn-Ce system in Mg-rich corner was identified. The results show that there is one ternary compound (T-phase) in Mg-Zn-Ce system. The T-phase is a linear ternary compound in which the content of Ce is about 7.7% (molar fraction); while the content of Zn is changed from 19.3% to 43.6% (molar fraction). The crystal structure of T-phase is C-centered orthorhombic. In addition, one two-phase region of Mg+T-phase and one three-phase region of Mg+T-phase+MgZn(Ce) exist in the Mg-rich corner of Mg-Zn-Ce system at 350 ℃.
Alloys with different compositions in Mg-rich corner of Mg-Zn-La system at 400 ℃ were prepared,the phase equilibrium in the Mg-rich corner of Mg-Zn-La system was determined by scanning electron microscopy(SEM),electron probe microanalysis based on energy dispersive X-ray spectroscopy(EPMA-EDS) and X-ray diffraction(XRD),and the isothermal section at 400 ℃ was established. The results show that there exists a ternary compound(T-phase) with a constant La content and changable Mg/Zn contents in the Mg-Zn-La system. The mole fraction of La in T-phase is about 8%,and that of Zn is from 16% to 43%. There exist a two-phase equilibrium which consists of T-phase plus hcp-Mg and a three-phase equilibrium which is composed of T-phase,hcp-Mg and a liquid phase(L-phase) at 400 ℃ . The L-phase consists of 70% Mg,30% Zn and is free of La.
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 ℃ 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 ℃.
Alloys of Mg-Zn-La system in Mg rich corner at 350℃ have been prepared in this study. Scanning electron microscopy （SEM）, electron probe microanalysis with energy dispersive X-ray spectroscopy （EPMA-EDS）, and X-ray diffraction （XRD） have been used to identify the phase equilibrium and the composition of each phase in the alloys. As a result, the isothermal section of Mg-Zn-La system in Mg rich corner at 350℃ has been determined. The result shows that, in addition to some binary phases, there exists a linear ternary compound called T-phase in Mg-Zn-La system at 350℃, in which the La content is about 8 at. pct ±0.4 at. pct and the Zn content is 8 at. pct- 48 at. pct. The T-phase has a C-centered orthorhombic crystal structure, and the lattice parameters are a=0.965-1.020 nm, b=1.121 1.142 nm, c=0.950-0.977 nm.
The phase equilibria in the Mg-rich comer of the Mg-Zn-La system at 350℃ have been investigated by scanning electron microscopy, X-ray diffraction, and electron probe microanalysis. It has been shown that the linear compound （Mg,Zn）17La2 existed in the Mg-Zn-La system at 350℃. The linear cornpound （so-called Tphase） was with the C-centred orthorhombic crystal structure induced by the solution of significant quantities of the third element. The three-phase region α（Mg） ＋ MgZn（La） ＋ T and the two-phase region composed of the α（Mg） and the linear-compound T phase existed in the Mg-rich comer of the Mg-Zn-La system at 350℃.
LI Hongxiao REN Yuping HUANG Mingli CHEN Qin HAO Shiming
