Effects of Scandium Addition on the Structural Stability and Ideal Strengths of Magnesium-Lithium Alloys

The effects of scandium (Sc) solute addition on the structural stability, mechanical strength, and electronic structure of magnesium-lithium (Mg-Li) ordered alloy were comprehensively studied by first-principles calculations. Two kinds of MgLi-Sc substitutional alloys (Mg-substituted Mg8−xLi8Scx and Li-substituted Mg8Li8−xScx) hold cubic lattice symmetry and become more stable with the increase in Sc content. The mechanical properties, including single crystal elastic constants, polycrystalline elastic moduli, and elastic anisotropy behaviors, have been systematically studied for two considered MgLi-Sc substitutional alloys. It was found that Mg8Li8−xScx exhibits larger elastic moduli than those of Mg8−xLi8Scx with the same Sc content; however, the derived elastic moduli of two substitutional alloys showed nonlinear variations as a function of Sc addition. Calculated stress–strain curves show an increasing of ideal tensile strengths and critical strains of the MgLi-Sc substitutional alloys along the <110> and <111> directions with Sc addition, indicating that the cubic MgLi-Sc substitutional alloy is mechanically harder and less brittle at higher Sc content. Furthermore, the developments of the electronic structures of two types of the studied alloys with increasing Sc addition were also investigated by the density of states and electronic localization function calculations.