Thermodynamic Study On The Phase Equilibria In The Mg-Sn-Zn-Ca Systems

Magnesium alloys are the lightest structural metal materials.in engineering application.They are widely used in aerospace,automobile and electronics industry for their outstanding characteristics,such as high strength-to-weight ratio,excellent cast ability,good heat conductivity,electromagnetic shielding property,machinability,damping property and recycle characteristics.However,the low yield strength,ductility and poor elevated temperature creep limit the applications of the magnesium alloys.In order to optimize alloy compositions and choose reasonable technology to improve performances,it is important to acquire precise phase diagrams information,which should besed on an thermodynamic database of magnesium alloys.In this paper,thermodynamic calculations are carried out by the CALPHAD approach to the phase equilibria of the Mg-rich region in the Mg-Zn-Ca and Mg-Zn-Ca-Sn systems.The main research results are as follows:(1)The experimental data of the Mg-Zn-Ca ternary phase diagrams and thermodynamic properties have been systematically analyzed.The CALPHAD method has been used for the re_optimization and calculation of Mg-Zn-Ca ternary system,and then thermodynamic parameters of Mg-Zn-Ca ternary system have been established.Phase diagram of the calculated and experimental results coincide very well.(2)Based on.the thermodynamic and experimental phase diagram data of Mg-Ca-Sn ternary system reported in the literature,using CALPHAD method,the isothermal sections of the Mg-Ca-Sn system at 500 ? have been thermodynamically calculated,and the calculated results are identical with the experimental data.The thermodynamic calculation reproduces the eutectic reaction:L(?)>(Mg)+Mg2Ca+CaMgSn at 519 ?,L(?)(Mg)+Mg2Sn+ CaMgSn at 560 ?.(3)The thermodynamic database of Mg-Sn-Zn-Ca quaternary system has been established,and by using this database,isothermal sections and veritical sections of the phase diagrams have been calculated,which provides a theoretical basis for the design of magnesium-based alloys.