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The dynamical, mechanical, anisotropic, and thermodynamic properties of Mg-XL-Y (XL = Zn, Al) alloys based on three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) have been investigated systematically by first-principles calculations. The LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys are thermodynamically, dynamically, and mechanically stable. The each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. According to universal elastic anisotropic index, percent shear anisotropy, 3D surface structures of Young's moulus, and sound velocities, the LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy. Besides, all LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys possess low lattice thermal conductivity due to the strong anharmonicity. The calculated adsorption energies indicate that the 14H(001) surface of Mg–Al–Y system at the hollow site is more sensitive to absorb O atom. • Three long-period stacking ordered (LPSO) phases (ie, 10H, 14H, and 18R) are thermodynamically, dynamically, and mechanically stable. • Each LPSO phase of Mg–Al–Y alloys has superior mechanical properties with larger resistances to deformation under applied stress and shear pressure, stiffness, as well as hardness than those of corresponding to LPSO phases of Mg–Zn–Y alloys. • LPSO phases of Mg-XL-Y (XL = Zn, Al) alloys exhibit obvious anisotropy and low lattice thermal conductivity. [ABSTRACT FROM AUTHOR]

The crystal structures, mechanical properties, anisotropic properties, and lattice thermal conductivities of Mg–Bi alloys have been investigated by particle swarm optimization structure prediction method and first-principles calculations. Apart from the well-known stoichiometry of Mg 3 Bi 2 , the novel stable stoichiometry of Mg 4 Bi, as well as several metastable stoichiometries (i.e., Mg 3 Bi, Mg 2 Bi, and MgBi) are predicted. Meanwhile, the calculated phonon dispersion curves and elastic constants show that the above five Mg–Bi alloys are dynamically and mechanically stable, respectively. Moreover, the calculated mechanical properties indicate that the studied Mg–Bi alloys with various stoichiometries behave ductility. Simultaneously, they exhibit obvious anisotropic characters and the degree of anisotropy follows the order of MgBi > Mg 2 Bi > Mg 3 Bi > Mg 4 Bi > Mg 3 Bi 2. More importantly, the minimum lattice thermal conductivities of MgBi and Mg 2 Bi are smaller than that of the well-known Mg 3 Bi 2. The adsorption of O atom on the Mg 3 Bi (001) surface is more sensitive compared with other four Mg–Bi (001) surfaces. • Apart from the well-known stoichiometry of Mg 3 Bi 2 , the novel stable stoichiometry of Mg 4 Bi, as well as several metastable stoichiometries (i.e., Mg 3 Bi, Mg 2 Bi, and MgBi) are predicted. • The five Mg–Bi alloys are dynamically and mechanically stable. • The five Mg–Bi alloys behave ductility and obvious anisotropy. • The minimum lattice thermal conductivities of MgBi and Mg 2 Bi are smaller than that of Mg 3 Bi 2. [ABSTRACT FROM AUTHOR]

• Mg 15 Al, Mg 3 Al and MgAl searched using CALYPSO are the newly found structures. • The addition of Al element can increase the tensile and compressive strength of Mg-Al alloys. • Mg 15 Al, Mg 3 Al and MgAl all exhibit ductility and anisotropy. Magnesium-aluminium (Mg-Al) alloys with different mass ratios and crystal structures can exhibit different physicochemical properties. The stable/metastable crystal structures of Mg x Al y (y/(x + y) = 1/16 ~ 15/16) were investigated using the CALYPSO (Crystal structure Analysis by Particle Swarm Optimization) method in combination with ab initio calculations. Mg 15 Al, Mg 3 Al and MgAl were determined to be the most stable structures by comparing formation energies with other studies. We calculated their elastic constants, moduli, anisotropy, hardness and thermodynamic properties. Our results demonstrate that all these structures exhibit ductility and anisotropy, and Mg 15 Al has the greatest hardness. [ABSTRACT FROM AUTHOR]

• The work function and surface energy of the new nonstoichiometries structure of Mg-Al and Mg-Y alloys evaluated previously have been investigated by means of the first principles calculations. The calculated results are summarized as follows: • The calculated results indicate that the electron work functions of Mg 15 Al and MgY are close to or less than that of magnesium matrix, further implying Mg 15 Al and MgY will not accelerate the local galvanic corrosion to the degree that other compounds do. • The work function and surface energy of Mg 15 Al have the different trend with different end surfaces, which is consistent with pure metal Mg reported previously. The reason may be due to the lower aluminum content, which makes the properties of Mg 15 Al closer to those of a simple substances rather than an alloying compound. • By comparing the work function calculations of Mg 3 Y, MgY and MgY 3 with six surfaces, it can be seen that as the Y content increases, the work function of the Mg-Y alloys is lower than that of the magnesium matrix increasingly, indicating the corrosion resistance of Mg-Y tends to increase with the increasing of Y content. • The analyzing of densities of states further indicates the strong covalent bond exists between Mg and Al in Mg-Al alloys and the conduction band is predominated by Y 4 d orbital mainly in Mg-Y alloys. The first principles are carried out to investigate the electronic work function, surface energy and electronic properties based on the new compositions evaluated previously for binary Mg-Al alloys and Mg-Y alloys. The calculated results imply that Mg 15 Al and MgY could be good corrosion resistant materials due to the work function close to or less than that of magnesium matrix. Meanwhile, the work function and surface energy of Mg 15 Al show the opposite trend with different end surfaces, which is different from the Mg 3 Al, MgAl and similar to the Mg monomer reported previously. It may be attributed to the properties of Mg 15 Al with lower aluminum content close to those of a monomer rather than an alloying compound. Compared with Mg-Al alloys, the corrosion resistance of Mg-Y alloys tends to increase with the increasing of Y content. Our results provide considerable insight into the stabilities of Mg-Al alloys and Mg-Y alloys surface, provide the data of the corrosion resistance design of magnesium alloys. [Display omitted] [ABSTRACT FROM AUTHOR]