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

Abstract

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_xAl_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_xAl_y alloys were constructed by replacing Mg atoms in a supercell with Al atoms. The lattice parameters of the Al-doped Mg_xAl_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 Mg₁₁Al₅, Mg₅Al₃ and Mg₉Al₇ have prominent structural stability. The analyses of the mechanical properties reveal that the doping of Al improves the ductility of Mg_xAl_y alloys. The elastic moduli increase with an increasing Al content, and Mg₉Al₇ has a notable ability to resist deformation, while Mg₁₁Al₅ and Mg₅Al₃ have better plasticity. The calculated results of their electronic properties reveal that Mg₁₁Al₅, Mg₅Al₃ and Mg₉Al₇ 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 Mg₉Al₇ is higher than that of Mg₁₁Al₅ and Mg₅Al₃, 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.