Mg-Gd-Y Alloy Calphad, Experimental Varity And Application In The Navol Mg Alloy Development

The development of computation materials science impelled the advancement of materials design and become the main development directions of computation material thermodynamics. CALPHAD(Calcaluation of Phase Diagram) technology can forecast the products, transformation temperature and the phase fractions with different temperature, as well as provides the crucial theory instruction for the material preparation and the design of heat-treatment processing.Magnesium alloys have caused widespread attention of the astronautics, the aviation and the automobile industry, because of its excellent castability, machinability , bio-compability and high specific strength. But its peer high-temperature mechanical properties limited the alloys application in loading-structure .So there is an urgent need for the development of high-strength magnesium alloys if we want to fully exploit the potential of this fascinating lightweight material. With the development of magnesium alloys, Mg-Gd-Y alloy system are of interest around the world because of their excellet high-temperature properties and good casting characteristics.However, the reports about phase diagram in this alloy is limited, specially for vertical phase diagram at present, the design of alloy component and heat-treatment processing is mainly completed by experiments. While experiments on developing a new alloys are expensive and time consuming.In this paper, the phase equilibrium computation theoretical model are introduced at first , and then the binaty phase diagram of Mg-Gd,Mg-Y,Gd-Y alloys and ternary Mg-Gd-Y system alloys in Mg-rich corner were calculated using Calphad software Pandat and the Mg alloy database. The phase equilibria and solidification sequences of the alloys Mg-5Gd-2Y,Mg-1Gd-7Y and Mg-xGd-4Y(x=1,9,15) were compared with the experimental results of SEM, SEM-EDS spectrum analysis and DSC curves. The results show that thermodynamics database of Pandat software is reliable and the thermodynamic calculated phase equilibria agree well with the experimental results.The phase diagram of Mg-Gd-Y-Zn-Zr alloy in Mg-rich corner was calculated using Calphad software Pandat. A new alloy of Mg-9Gd-3Y-0.6Zn-0.5Zr and its heat treatment process was designed under the guide of this phase diagram. The result shows that the phase diagram of Mg-9Gd-3Y-0.6Zn-0.5Zr is feasibility for the design of the heat treatment process in this alloy ,the heat treatment process for as-extruded Mg-9Gd-3Y-0.6Zn-0.5Zr is aging at 200℃for 63 hours and the tensile strength up to 430MPa.