| Li is the lightest metal element in the world,and its low density and high plasticity properties are insufficient for the defects of Mg alloy in plasticity and further enhance the advantages of low density of Mg alloy.Mg-Li alloy is the lightest structural material in the world today.It has excellent properties such as high specific strength,low density,and high electromagnetic shielding.It is considered to be the best choice to achieve lightweight development in aerospace,automotive,3C and other industries.But its lower absolute strength has seriously hindered the application and promotion of Mg-Li-Al alloy in industry.In this work,the first-principles calculation method is used to calculate the matrix a-Mg/?-Li interface and ?-Li/AlLi interface between the matrix and the second phase in the dual-phase Mg-Li alloy,and calculate the properties of the second-phase AlLi phase with doping Zn element,which verify the possibility of strengthening the alloy.The enhancement mechanism of the second phase in Mg-Li-Al alloy was revealed at the atomic scale.The conclusion of this work can provide a theoretical basis for the subsequent development of new Mg-Li alloys,shorten the development cycle and reduce the development cost.The main contents and conclusions of this work are as follows:(1)The structural properties of Mg,?-Li and AlLi phases were calculated,and compared with the existing calculated values and experimental values,which verified the reliability of the calculation in this work.This work selected Mg(0001)surface,?-Li(011)surface,?-Li(001)surface and AlLi(011)surface to build ?-Mg(0001)/?-Li(011)interface model and ?-Li(011)/AlLi(004)interface model.The convergence and stability of Mg(0001)surface and ?-Li(011)surface as well as the interface spacing d0 and work of separation Wsep were calculated,and the interface model of ?-Mg(0001)/?-Li(011)and ?-Li(011)/AILi(011)alignment of Bridge type and Hollow type was established,and draw charge density distribution diagrams,differential charge density diagrams,and the partial density of states map of atoms at the interface.It is inferred that the three surfaces of ?-Mg(0001),?-Li(011)and AlLi(011)have the lowest surface energy and the best synthesis computability(high stability and low calculationcost)when they have 6 atomic layers respectively.In addition to the largest outer layer atomic layer spacing distortion rate,the inner layer atom distortion rate tends to be stable and less than 1%,which can be regarded as the inside of the crystal.Moreover,the value of Wsep of the Hollow-type interface is higher,and the charge distribution at the interface is denser,the degree and range of charge transfer are wider,the hybridization between atoms is more intense,so that the interface is tighter.For the ?-Mg(0001)/?-Li(011)and ?-Li(011)/AlLi(011)interfaces,the Hollow type has higher binding ability than Bridge-type interface.(2)The structure,mechanics,electronic and thermodynamic properties of AlLi phase and its doped Zn atoms were calculated.The unit cell model of AlLi,(AI 7/8,Zn 1/8)Li,(Al 6/8,Zn 2/8)Li and(Al 5/8,Zn 3/8)Li were established.After geometric relaxation,calculate their respective lattice constants,formation enthalpy ?H,and binding energy Echo;and after obtaining their respective elastic constants,derive various mechanical property parameters;thereafter,the electronic state density diagrams of the electronic properties are drawn Charge density distribution diagram,phonon dispersion curve diagram of thermodynamic properties,phonon state density diagram,and various thermodynamic state parameters(enthalpy H,entropy S,free energy F and constant volume heat capacity Cv)as a function of temperature were calculated and plotted.The possibility of strengthening AlLi phase and its doping with Zn element to Mg-Li alloy was systematically studied.Zn atoms can be stably doped in AlLi phase,and with the increase of Zn concentration,Al-Li-Zn compound Increase in covalence.The difference in strength and orientation of Li-Li and Zn-Zn bonds reduces the anisotropy of Al-Li-Zn compounds.The elastic constants(B,G and E)of the doped phase are significantly improved,and(Al 7/8,Zn 1/8)Li has the highest elastic constant,and the addition of Zn atoms improves the mechanical stability,ductility and plasticity of the AlLi phase.The AlLi phase and its doped phase can exist stably at high temperature,and(Al 6/8,Zn 2/8)Li has the best stability at high temperature.The calculations in this work show that the binding capacity of the ?-Li/AlLi interface between the matrix and the second phase is much higher than that of the ?-Mg/?-Li interface between the matrix of the two-phase Mg-Li alloy,which proves that the second phase has higher mechanical and thermodynamic properties than the matrix and can produce an interlace with good bonding properties between the matrix and the second phase.It has a role in the development of a new Mg-Lialloy. |
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