Theoretical investigation of typical fcc precipitates in Mg-based alloys

First-principles calculations were performed to study structural, elastic and electronic properties of typical face-centered cubic (fcc) precipitates of Mg-based alloys (Mg3Gd, Mg3Gd0.5Y0.5 and Mg3Zn3Y2) within the generalized gradient approximation. The calculated results show that the substitution of part of the Gd with Y in Mg3Gd leads to a slight decrease in the cell volume (0.35%), and the lattice parameters obtained after full relaxation of crystalline cells are in good agreement with the experimental data. The calculated negative formation enthalpies and the cohesive energies show that these typical fcc precipitates of Mg-based alloys have good alloying ability and structural stability. According to the calculated density of states of these phases, it is found that the highest structural stability of Mg3Zn3Y2 is attributed to an increase in the bonding electron numbers below the Fermi level. In addition, the elastic constants Cij of these phases were also calculated, and the bulk modulus B, shear modulus G, Young’s modulus E, Poisson’s ratio ν and anisotropy value A of polycrystalline materials were derived from the elastic constants. The mechanical properties are further discussed.