First-principles study of the properties of Li, Al and Cd doped Mg alloys

The major mechanical and electronic properties of the Li, Al and Cd doped Mg solid solutions were investigated by employing the first principles density functional theory methods. The solute atoms were chosen since they have a larger range of solubility. Each of the alloy models consists of fifteen Mg atoms and one solute atom. The elastic parameters C_ij were evaluated, and the bulk modulus (B), shear modulus (G), Young's modulus (E) and Poisson's ratio (ν) were further derived. The results show that the B/G ratio (an estimation of the metal ductility) of Mg, Mg-Al, Mg-Li and Mg-Cd are 1.92, 1.80, 1.47 and 2.17, respectively, which indicates that the Mg-Al and Mg-Cd alloys are ductile and the Mg-Li alloy is slightly brittle. For the Mg-Cd alloy, its plasticity might be better than that of the others due to a larger Poisson's ratio and lower values of C₁₁ - C₁₂ and E. The tensile test simulation of the Mg metal and Mg-Al, Mg-Li and Mg-Cd alloys reaches the strengths of 5.05, 5.32, 5.28 and 4.89 GPa, respectively.