First-principles study on the thermodynamic, electronic and mechanical properties of Mg–Al–Si ternary compounds

The alloys used in lightweight equipment such as magnesium (Mg) alloys are not only required the considerable strength but also the good stiffness, i.e., the Young's modulus (E) is relatively high. Herein, the first-principle density functional theory is adopted to efficiently and economically explore the thermodynamic, mechanical, and electronic properties of Mg-aluminum (Al)-silicon (Si) ternary compounds. The current calculated results show that the Mg–Al–Si ternary compounds are dynamically stable. In addition, the calculated cohesive energies of these compounds are negative, indicating that they are thermodynamically stable. Moreover, the calculated bulk modulus (B) of Mg–Al–Si ternary compounds is gradually enhanced with decreasing Mg content, and Mg2Al3Si6 has the largest B with a value of 72.6 GPa, while MgAlSi has the largest shear modulus, E with values of 44.5 and 109.7 GPa, respectively, which is beneficial for increasing the stiffness of Mg alloys. Electronic density and weighted average bond length are used to probe the electronic basis of mechanical properties, and the results show that the weighted average length of Mg2Al3Si6 is tighter than other compounds, resulting in higher B.