Improvement of mechanical properties of Mg₂Si phase system by doping transition metals: a first-principles study

To further improve the application and promotion of 6xxx Al alloys, we researched the mechanical properties of the Mg₂Si brittle phase. The influence of different transition metals (M = Sc, Ti, V, Cr Y, and Nb) on the stability and mechanical properties of the Mg₂Si phase was studied using first-principles calculations. The results indicate that transition metals can effectively reduce the cohesive energy of the Mg₂SiM phase compared to pure Mg₂Si (Pure Mg₂Si: − 2.831 eV; Sc–Mg-1: − 3.099 eV; Ti–Mg-1: − 3.197 eV; V–Mg-1: − 3.229 eV; Cr–Mg-1: − 3.243 eV; Y–Mg-1: − 3.097 eV; Nb–Mg-1: − 3.367 eV), thereby enhancing the material’s energy stability. In terms of mechanical properties, Nb–Mg-1 exhibits superior toughness and lower hardness compared to the pure Mg₂Si phase (Pure Mg₂Si: Pugh’s ratio = 1.184, H_V = 11.337 GPa; Nb–Mg-1: Pugh’s ratio = 1.639, H_V = 6.431 GPa). The other five transition metals also contribute to improved toughness and reduced hardness in the Mg₂SiM phase to varying degrees (Ti–Mg-1: Pugh’s ratio = 1.617, H_V = 6.692 GPa; Y–Mg-1: Pugh’s ratio = 1.603, H_V = 6.526 GPa; Cr–Mg-1: Pugh’s ratio = 1.577, HV = 6.917 GPa; V–Mg-1: Pugh’s ratio = 1.507, HV = 7.155 GPa; Sc–Mg-1: Pugh’s ratio = 1.351, HV = 8.559 GPa). This is because the addition of Nb promotes orbital hybridization between Si and Nb, reduces the energy required for dislocation slip, and improves the mechanical properties of the material. The differential charge density and charge transfer also confirm this phenomenon. This study provides valuable insights into enhancing the ductility of the Mg₂Si phase and improving the application of 6xxx Al alloys.