Theory Study Of Mg₂ Y (Yb) Enhanced Phase And AMgNi₄ (A=y, La, Ce, Pr And Nd) Alloys

Although pure magnesium is rich in content, and has various excellent properties, such as low density, the high specific strength and rigidity, good damping capacity and electromagnetism shielding property and so on, the poor mechanical properties at room temperature or high temperature limit its application in the modern industry greatly because of its active chemical properties. In order to improve the mechanical properties of magnesium, especially at high temperature, meanwhile, in order to meet the industry demand for a large number of lightweight structural materials, the study of magnesium alloys has become a hot spot, and received a sustaining attention both on experiment and theory. At present, although researches have conducted massive experimental study to the rare earth magnesium alloy, the thorough understanding of Mg alloys and compounds is still very lacking, especially the intrinsic mechanism of structural stability and mechanical properties is not very explicit. Therefore, further theoretical research is needed.In this paper, we used the method of the first principle calculation based on density functional theory, performed a calculation on the property of enhanced phases Mg₂Y and Mg₂Yb. The calculated cohesive energies indicated that both of them were stable, and Mg₂Y was more stable than Mg₂Yb. The obtained equilibrium lattice constants for Mg₂Y and Mg₂Yb were in good agreement with the available experimental values. The calculated results also showed that Mg₂Yb has better plasticity and isotropic property than Mg₂Y, while Mg₂Y has larger value of Cij, so is stiffer than Mg₂Yb.Then the same method was used to research the structural parameters, mechanical properties, electronic structures of the new ternary magnesium alloys AMgNi4 (A= Y, La, Ce, Pr and Nd). The optimized structural parameters were in good agreement with the available experimental datas. The calculated negative cohesive energies and formation enthalpies showed that these alloys had strong structural stability. The calculated results also indicated that alloy YMgNi4 had the largest Cij, bulk modulus B, shear modulus G, Young's modulus E, but the smallest Poisson's ratioυand the worst ductility. Meanwhile, when A= La, Ce, Pr and Nd, the results suggested that the values of Cij, G, B, E and G/B increase with increasing atomic number of A, but Poisson's ratioυand ductility decrease gradually. Finally, the electronic structures of these alloys had been calculated and discussed to reveal the inherent mechanism on the stability, mechanical property.In addition, the structure, mechanical properties of MgCuSn and MgCu₄Sn were also studied. The results showed that they are stable; MgCu₄Sn has larger elastic constants Cij, young's modulus E, body modulus B and shear modulus G than MgCuSn, while MgCuSn has better plasticity, ductility and isotropic property than MgCu₄Sn. Finally, the densities of states are analyzed.