First Principles Calculation Of Ag Alloyed Magnesium Alloy

Due to the advantages of low density and high specific strength,magnesium alloy become a hot research direction.Magnesium alloy have been widely used in the industry of automobile,3C,national defense and so on.Our country is rich in magnesium resources,it is of great significance to develop the magnesium alloy with good performance.The structural,mechanical properties,electronic structures of MgAg、Mg₂Ca and AgCa phases were investigated by means of first-principles calculations.The calculated parameters of MgAg 、 Mg2 Ca and AgCa are consistant with those values obtained by experimental results or theorytical analysis.The heats of formation and cohesive energies demonstrated that both the alloying capability and structural stability of MgAg phase are the strongest among the three phases.Further,the elastic constants of MgAg、Mg₂Ca and AgCa phases were calculated in the present study.Base on the elastic constant the mechanical parameters,such as bulk moduli B,shear moduli G,Young’s moduli E,Poisson’s ratio n and ansiotropy A were estimated by using the Voigt-Reuss-Hill（VRH）averaging scheme.The calculated results indicated that among the three phases MgAg and Mg2 Ca are brittle phases,whereas AgCa is ductile phase.AgCa phase has best plasticity while MgAg phase has strongest stiffness,additionally,MgAg phase has the strongest resistance to deformation and shear.The melting points and hardness of the three phases were predicted by using cohesive energy and elastic constants.The density of states（DOS）of MgAg、Mg₂Ca and AgCa phases were investigated as well.According to the above mentioned calculation results,which is the mechanical properties of MgAg and AgCa are better than Mg2 Ca,it can be speculated that the improvement of mechanical properties are arise from the addition of Ag element in Mg-Ca alloy.For the purpose of reveal the variation of electronic structure and mechnical properties with pressure,the mechanical,electronic and thermodynamic properties of MgAg and MgY under pressures were investigated in the present study.The elastic anisotropy of MgAg and MgY were also investigated.The calculated results showed that the deformation resistance and shear resistance increased with the increase pressure,the brittleness of MgAg and MgY were reduced,and as well as maximum density of states.The results also show that thehybrid energy of MgAg and MgY were reduced with pressure.For MgAg,Mg p and Ag p leads to the decrease of hybrid energy.While for MgY,Mg p and Y p leads to the decrease of hybrid energy.The thermodynamic properties of MgAg and MgY at different temperatures and pressures were calculated and discussed by using the anharmonic approximation model.The result shows that the entropy,enthalpy and heat capacity increased with the increasing of temperature,the free energy decreases with the increasing of temperature,and the pressure has little effect on the thermodynamic properties of MgAg and MgY.The electronic structure of Mg-Ag solid solution magnesium alloy was calculated,the reasons for the solid solution strengthening of Ag substituted magnesium atoms are explained.