First-principles study of the mechanical and thermodynamic properties of aluminium-doped magnesium alloys.

Magnesium-aluminum (Mg-Al) alloys are widely used in aerospace, automobile and medical equipment owing to their advantages of easy casting, high strength-to-mass ratio and good biocompatibility. The structural, mechanical, electronic and thermodynamic properties of Mg x Al y alloys ( x + y = 16, x = 1, 2,…, 15) with varying Al-doping contents were studied using the first-principles method. In this work, the structures of Mg x Al y alloys were constructed by replacing Mg atoms in a supercell with Al atoms. The lattice parameters of the Al-doped Mg x Al y alloys decrease with an increasing Al content because of the smaller atomic size of Al than that of Mg. The calculated formation energies show that Mg11 Al5 , Mg5 Al3 and Mg9 Al7 have prominent structural stability. The analyses of the mechanical properties reveal that the doping of Al improves the ductility of Mg x Al y alloys. The elastic moduli increase with an increasing Al content, and Mg9 Al7 has a notable ability to resist deformation, while Mg11 Al5 and Mg5 Al3 have better plasticity. The calculated results of their electronic properties reveal that Mg11 Al5 , Mg5 Al3 and Mg9 Al7 are good conductors without magnetism. Furthermore, CDD analyses show that the inner layer charges of Al atoms migrated to the outer layer, and the charges of Mg atoms accumulated significantly in the outer region of Al atoms. The Debye temperature of Mg9 Al7 is higher than that of Mg11 Al5 and Mg5 Al3 , indicating that it has better thermodynamic stability. Our findings would be helpful for the design of Mg-Al alloys with excellent mechanical and thermodynamic performances.