The Microstructure and Mechanical Stability of Sc-Doped Mg2Si/Al Composite: Experiments and First Principles Calculation

A Sc-doped Mg2Si/Al composite was prepared in situ to show the effect of Sc addition on the microstructure and deforming behaviors of the composite. More attention was paid to the refining effect of Sc addition on the primary Mg2Si phases and the tensile behavior of secondary phases with first principles calculation in order to demonstrate the structural stability from the atomic view. The experimental results reveal that Sc would promote the refinement of primary Mg2Si particles and the increase in tensile strength. The elastic properties and electronic structure of Sc-doped Mg2Si/Al were calculated by first principles based on density functional theory (DFT). Mg7Si4Sc exhibited the strongest alloying ability and stability. The brittleness of Mg2Si was significantly improved due to the increase in Poisson's ratio (v) and the reductions in Young's modulus (E) and G/B ratio by Sc addition. The bonding types (Mg-Si, Mg-Sc and Si-Sc) were determined by the density and covalent bond energy of the elements. Mechanical deformation modes of Mg2Si, Mg7Si4Sc and Mg8Si4Sc along [100], [110] and [111] orientations were investigated by first principles calculation. The results show that Mg7Si4Sc possessed the largest tensile strength in [100] direction, because Mg-Si and Si-Sc bonds played the dominant role in the fracture process with reduction in Mg-Si bond population and increase in Si-Sc bond population.