Thermodynamic Optimization And Calculation Of The Mg-Gd-Ag Ternary System

Mg-Gd based alloys are very promising structural materials due to the great aging hardening response and high creep resistance performance. Especially, Mg-Gd-Ag alloys attract a lot of attention, as some researches indicate that certain amount of Ag to Mg-Gd based alloys could result in a significant mechanical property increase. In order to further improve the mechanical property effectively, optimize alloy composition and select proper processing parameters, it is necessary to investigate the phase diagrams and thermodynamic data of the Mg-Gd-Ag ternary system.In this study, experimental/calculation method was employed to conduct the scientific research and thermodynamic description of the Mg-Gd-Ag ternary system was developed for the first time. The major achievements of the present work are as follows:(1) Phase equilibria of the Mg-Gd-Ag system focused on Mg-rich region at 400○C and 450○C were experimentally studied through evaluation of six selected compositions under the long annealed states.(2) Thermodynamic descriptions of the Mg-Gd, Mg-Ag and Ag-Gd systems were carefully assessed and reliable parameters were selected respectively for three constituent bianry systems.(3) Based on the phase equilibrium data of the Mg-Gd-Ag system obtained in our study, thermodynamic assessment was performed on the Mg-Gd-Ag ternary system and a set of self-consistent thermodynamic parameters was obtained. Reasonable agreement is achieved between the calculated results and experimental data.(4) Under the guidence of thermodynamic calculated results, the chemical compositions of Mg-Gd-Ag alloys were designed and the relevant heat treatment technologies were seleced. The mechanical properties of the Mg-Gd-Ag alloys were also tested. The experimental results further confirmed the reliability of the thermodynamic parameters of the Mg-Gd-Ag system.