Assessment And Optimization Of The Mg-Gd-Y System Phase Diagram

Magnesium alloys exhibit low density, high specific and specific,great specific elastic modulus and good damping. Therefore, they have wide application potential in the modern electronics industry, and aerospace and other fields. However, research and development (R&D) of magnesium alloys almost uses the traditional trial and error method, which is time consuming and expensive. Phase diagram is of importance in the process of materials R&D to provide guideline in composition design and formulation of heat treatment process. CALPHAD, calculating phase diagram by combining the computer software with the corresponding, turns the material design from practice experiment method to scientific one. However, there are limitations in the database of existing phase diagram calculation softwares. For example, there is almost no simulation module for mechanical properties of magnesium alloys in JMatPro phase diagram calculation software. In the Pandat software, the database of magnesium alloy has limitations as well, Gd content is restricted in the range of 0-1% wt, Y is restricted in the range of 0-1% wt. When content of Gd, Y is more than 1% wt, a larger error between the calculated phase diagram and experimental phase diagram. Therefore, in order to accurately design the composition and microstructure of magnesium alloys, it is primarily needed to establish the relative thermodynamic model, optimize the thermodynamic parameters and update the database.In the present work, the experimental data of Mg-Gd and Gd-Y binary system were evaluated and the relevant thermodynamic parameters were optimized by PanOptimization Pandat software modules. In addition, Mg-Gd-Y ternary phase diagram was obtained by extrapolation based on the reported self-consistent thermodynamic parameters of Mg-Y binary in literature and optimized thermodynamic parameters. The following conclusions can be drawn.1) Thermodynamic parameters of Mg-Gd binary system was optimized by using PanOptimization module of the Pandat software and the optimized Mg-Gd binary phase diagram was obtain. The transition temperature of the reaction with no variables was about 548 ℃ in the optimized phase diagram. The maximum solid solubility of Gd in the Mg was 4.6 at%, which was much close to the experimental data 548 ± 2 ℃,4.53 at%, suggesting good agreement between the experimental data and calculated data.2) Thermodynamic parameters of Gd-Y binary system was optimized by PanOptimization module of the Pandat software. The optimized phase diagram was in good agreement with the experimental phase diagram.3) Thermodynamic parameters of ternary Mg-Gd-Y system was obtained by using the optimized Mg-Gd and Gd-Y binary thermodynamic parameters as well as parameters in literature for Mg-Y binary system. Mg-Gd-Y ternary phase diagrams inculding the vertical section and isothermal section of the Mg-9Gd-3Y at 200 ℃,400 ℃,600 ℃.