Main reinforcement effects of precipitation phase Mg₂Cu₃Si, Mg₂Si and MgCu₂ on Mg-Cu-Si alloys by ab initio investigation

To predict and compare the main reinforcement effects of the key precipitation phases Mg₂Cu₃Si, Mg₂Si and MgCu₂ in Mg-Cu-Si alloy, the structural, mechanical and electronic properties of these phases have been studied by ab initio calculations. The lowest formation enthalpy and cohesive energy indicate that Mg₂Cu₃Si has the strongest alloying ability and structural stability. The mechanical modulus indicates that Mg₂Cu₃Si has the strongest resistance to reversible shear/volume distortion and has maximum hardness. The characterization of brittle (ductile) behavior manifests that MgCu₂ has favorable ductility. Meanwhile the evaluation of elastic anisotropy indicates that Mg₂Si possesses elastic isotropy. Debye temperature prediction shows that Mg₂Si and Mg₂Cu₃Si have better thermal stability. To achieve an unbiased interpretation on the phase stability and mechanical behavior of these precipitation phases, the density of states and differential charge densities are also analyzed. The current study deepens the comprehensive understanding of main reinforcement effects of these precipitation phases on Mg-Cu-Si alloys, and also benefits to optimize the overall performances of Mg-Cu-Si alloy from the hardness, ductility and thermal stability by controlling these second precipitation phases during the heat treatment process.