| In this paper, we research the Mg-Sn-Mn alloy system, expect to add Sn and Mn into the magnesium alloy to improve the mechanical properties and corrosion resistance of the magnesium alloy. In order to greatly improve the performance of the magnesium alloys, optimize the composition of alloys and the process of heat treatment, this paper uses the Thermo-Calc software from the perspective of phase equilibrium relations and thermodynamic database to research the Mg-Sn-Mn ternary phase diagram, master phase diagram and related thermodynamic information, and characterize the performance of the Mg-Sn-Mn alloys.Using CALPHAD methode, the Mg-Mn, Mg-Sn, Mn-Sn binary phase diagram and thermodynamic data are evaluated. Ordinary substitutional solutions are adapted to model liquid and the terminal solution and all intermetallic phases are treated as stoichiometric compounds. The calculated Mg-Mn binary phase diagram has six phase regions, there are Liquid,Liquid+δMn,Liquid+γMn,Liquid+βMn,Liquid+αMn,Mg+αMn respectively; The calculated Mg-Sn binary phase diagram has seven phase regions, there are Liquid,Liquid+Mg2Sn,Mg2Sn+βS,Liquid+βSn,Mg+Mg2Sn,Liquid+Mg,Mg respectively; The calculated Mn-Sn binary phase diagram has seventeen phase regions, there areLiquid MnSn2+Mn2Sn,Liquid+MnSn2,Liquid+Mn2Sn,Mn19Sn,βMn+Liquid,δMn+βMn,βMn+γMn,γMn+δMn,δMn+Liquid,Liquid+Mn19Sn6,αMn+βMn,δMn,γMn,βMn,αMn respectively. Calculated phase diagram and thermodynamic data are both consistent with experimental work.The Mg-Sn-Mn isothermal section of ternary phase diagram section has been extrapolated using CALPHAD method with Mg-Mn, Mg-Sn, Mn-Sn binary system thermodynamic data. Based on the experiments, the isothermal sections in the Mg-rich corner of the Mg-Sn-Mn ternary system at 673K, 773K are optimized; the thermodynamic properties of the alloy system at 673K,773K is researched. The isothermal sections in the Mg-rich corner of the Mg-Sn-Mn ternary system at 673K,773K have four phase regions; the phase in single-phase region:Mg, the phase in two-phase regions: Mg+Mn and Mg+Mg2Sn, the phase in three-phase region:Mg+Mn+Mg2Sn. In the optimized isothermal section phase diagram in Mg-rich corner at 673K, the Sn mole-frection is 0-0.72% and the Mn mole-frection is 0-0.17%. In the optimized isothermal section phase diagram in Mg-rich corner at 773K, the Sn mole-frection is 0-2.7%, and the Mn mole-frection is 0-0.32%.Although the elements of Sn and Mn can refine the grain of Mg-Sn-Mn alloys the effect of Sn element is more obvious. When the content of Sn element is increased to certain content, Mg2Sn is precipitated in the grain boundary and the secondary dendrite; this is consistent with the results of the phase diagram calculation. Adding Sn element into the alloy significantly increases the hardness of alloys and improves the mechanical properties of the alloys. The hardness of the alloy is related to Mn element on phase composition of alloys. When the alloy phase is composed of single-phase Mg, the hardness of the alloy increases with the increase of Mn content, when the alloy phase is composed of two-phase Mg+Mn, the alloy hardness increases with the decrease of Mn content. Therefore, the hardness of alloys increased first and then decreased with adding Mn element. While the content of Mn element is 0.5%, the alloy reaches the maximum hardness.As the alloy content of Mn and Sn increased, the Mg-Sn-Mn alloys of cast,673K equilibrium treatment,773 K equilibrium treatment get the bette corrosion resistance,but and the Mn element has a great effect than the Sn element, the precipitation of Mn in the alloys can effectively improve the performance of corrosion resistance, achieve the purpose of original design. |
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