First-Principles Study On The Mechanical Properties Of LaMg₃and LaCuMg₂

Magnesium alloys are the excellent materials because of the high specific stiffness and good workability. Furthermore, the Mg alloys are also the promising hydrogen storage due to the high hydrogen storage capacity. Therefore, magnesium alloys have attracted a great deal of interest. However, the application of magnesium alloys in modern industry is still limited due to the restrained properties, and/or the slow kinetics and high temperature in hydrogen absorption-desorption. In order to overcome above problems, addition of other elements is known to be one the most effective ways to improve the mechanical properties of the magnesium alloys. In this paper, the first-principles calculations based on density functional theory are carried out to investigate the mechanical properties of LaMg3and LaCuMg2. The obtained main conclusions are as follows:The calculation lattice parameters of LaMg3and LaCuMg2phases have been found to be in excellent agreement with the available experimental value. The obtained formation enthalpy shows structural stability of the two phases and the LaMg3phase is more stable. The computed elastic constants satisfy Born criteria, showing that these two phases are elastically stable. With the substitution of part Mg in LaMg3by Cu, the elastic constants C11,C12increase while C44decrease, implying an enhanced Poisson effect and smaller resistance to<001>(100) shear. Furthermore, the bulk modulus B is increased, while the shear modulus G, Young’s modulus E, and anisotropic ratio A are reduced. The calculated Debye temperature of LaCuMg2is lower, implying the weaker interaction between atoms in LaCuMg2. Then, the stress-strain curves in entire range and the ideal strength at critical strain were studied. The present results show that the lowest ideal tensile strength for LaMg3and LaCuMg2are in the [100] direction. The ideal shear strength on the<110>(110) slip system of LaMg3is bigger than LaCuMg2. The variation of electron density distribution reveals the underlying mechanism of the mechanical properties of LaMg3and LaCuMg2.