| Mg is a small metal material of relatively small density,the density is only about 2/3 of aluminium and about 1/4 of iron.It is one of the most important light materials.Because of its relatively light material,Mg and its alloys are important position in lightweight.In addition,the specific strength,specific stiffness of Mg alloy is very high,and it has the excellent characteristics of easy recovery and utilization.It is widely used in the field of aerospace and automobile.However,Mg and Mg alloy are hexagonal closed-packed structure(HCP),which have low symmetry(c/a=1.624),the plane are able to slip less.At room temperature,only the base plance can provide two independent slip systems,which can not achieve the requirements of the five independent slip systems in the Von-Mises criterion.Consequently,the plasticity of Mg alloy at room temperature is poor,and it is difficult to deform,which limits its application.In addition,Mg is a relatively active metal,that leads to its poor corrosion resistance.Although the Mg alloy with high specific strength,the strength is lower than that of Al alloy.Therefore,the essence of plastic deformation of Mg alloy is studied,looking for ways to improve the toughness and plastic deformation of Mg alloy,improving corrosion resistance of Mg alloy.As the final Mg alloy development,design and processing to provide theory has important guiding significance.In this paper,we apply the first principles which based on density functional theory.The generalized stacking fault energy in Mg crystal,Mg-Al,Mg-Zn,Mg-Mn two element alloy and Mg-Al-Zn three alloy has been calculated by using VASP software.Firstly,the intrinsic stacking fault energy and the unstable stacking fault energy of the different sizes of the base plane are calculated,calculations were carried out using 1×2 x 12 cells.The generalized stacking fault energy,charge density and density of states of 4 major slip plane(base plane{0001}<1120>,cylindrical plane{1010}<1120>,I type pyramidal plane{1011}<1120>and Ⅱ type pyramidal plane {1122}<1123>)of Mg single crystals has been calculated.The analysis shows that the base plane is most likely to slip,the most difficult sliding of Ⅱ type pyramidal plane,the difficulty of slip between cylindrical and I type pyramidal plane is not much difference.The electron hybridization between different orbitals is analyzed by using charge density diagram and density of state diagram.In addition due to doping can improve the plasticity of magnesium alloy.This paper calculated the Al,Zn,Mn atoms are substitutional doping of Mg atoms of the stacking fault energy,charge density and density of states.It is found that the Zn element can best reduce the stacking fault energy,Mn times,and Al is the worst.The electron transfer and orbital hybridization of Mg-Al and Mg-Zn alloys were analyzed by charge density diagram and density of state diagram.The average stacking fault energy of each slip surface is calculated by the weighted model of generalized stacking fault energy.Finally,the stacking fault energy of Mg-Al-Zn three element Mg alloy is calculated.Because the substitutional sites of the double elements are more doped,this article first through the determination of enthalpy of formation to determine the doping position elements Mg-Al-Zn alloy containing 32 atoms.The generalized stacking fault energy of Mg-Al-Zn three element Mg alloy is also calculated and it is found that the generalized stacking fault energy of Mg-Al-Zn three element Mg alloy is lower than that of Mg-Al,Mg-Zn alloy.Therefore,the Mg-Al-Zn alloy has better plasticity. |
