Mechanical and thermodynamic behaviors of the second phases in Al–Zn–Mg–Cu alloys

The mechanical and thermodynamic behaviors of intermetallics in Al–Zn–Mg–Cu alloys are studied by first-principles calculations. All studied second phases have negative values of formation enthalpy and cohesive energy indicating their excellent thermodynamic stability. Al 3 Er_D0[Formula: see text] has the most significant metallic nature, while Mg 2 Si shows the least metallicity. TiAl 3 shows the highest bulk, shear, and Young’s moduli. All Al 3 M polymorphs, Mg 2 Si and TiAl 3 phases show covalent/metallic hybrid bonding. The mechanical anisotropic behaviors obey the trend of: MgZn[Formula: see text]Er_D0[Formula: see text]Sc_D0[Formula: see text]Sc_D0[Formula: see text]Er_D0[Formula: see text]Er_L1[Formula: see text]Sc_L1[Formula: see text]Si, where MgZn 2 is the most mechanically anisotropic phase. The calculated room-temperature linear thermal expansion coefficient values for the studied phases are from [Formula: see text] K[Formula: see text] to [Formula: see text] K[Formula: see text]; where Al 3 Er_L1 2 has the highest value ([Formula: see text] K[Formula: see text], followed by Al 3 Sc_L1 2 ([Formula: see text] K[Formula: see text]; both of which are close to that of the Al matrix, thus making the relatively lower thermal misfit.