Abstract

The Mg-Zn-Zr ternary system was experimentally investigated at 450oC using six diffusion couples and 16 key alloys. Four new ternary compounds, namely as IM1, IM2, IM3 and IM4 were detected. The compositions, homogeneity ranges and the XRD patterns of these compounds were identified in this system using Scanning Electron Microscopy coupled with Energy-dispersive X-ray spectroscopy and X-ray Diffraction techniques. The homogeneity ranges of IM1, IM2, IM3 and IM4 are Mg(23-26)Zn66Zr(8-11), Mg(15-16)Zn66Zr(18-19), Mg(10-11)Zn66Zr(23-24), and Mg(9-13)Zn(79-87)Zr(5-8) respectively. IM1 compound is determined to have the same prototype as the MgZn2 phase with the hexagonal structure and P63/mmc space group. The binary compounds do not have extended solid solubility into the ternary system. The XRD patterns of IM2, IM3 and IM4 were obtained from key alloys study. The liquid area in the Mg-Zn-Zr ternary system at 450oC was verified by several key alloys. Although large regions of liquid exist in the binary phase diagrams at 450 oC, the single phase liquid region extended only around 1 at.% into the ternary phase diagram. Two and three-phase regions that contain liquid are up to around 10 at.% Zr. Based on the current experimental results of diffusion couples and equilibrated key alloys, the isothermal section of the Mg-Zn-Zr ternary system at 450oC has been constructed.

Studying this system was challenging due to the large difference in melting points of its components. In order to overcome this problem, Zn-Zr master alloys were prepared to obtain homogenous key samples and to solve the problem of elements evaporation. In addition, two-step annealing methods were used to study the microstructure changes of the key alloys.