Unveiling the origins of elastic anisotropy and thermodynamic stability in Mg Zn alloy strengthening phases via first principles

This study systematically investigates the elastic anisotropy and thermodynamic properties of [Formula: see text] phase in Mg-Zn alloys through first-principles calculations combined with Debye-Grüneisen theory. Three critical intermetallic phases - monoclinic Mg₄Zn₇, cubic MgZn₂ (C-MgZn₂), and hexagonal MgZn₂ (H-MgZn₂) phases were comparatively analyzed. Electronic structure analysis reveals that C-MgZn₂ and H-MgZn₂ exhibit stronger chemical bonding stability compared to Mg₄Zn₇. Phonon dispersion characteristics demonstrate distinct vibrational patterns: C-MgZn₂ and Mg₄Zn₇ display enhanced phonon modes at both low and high frequency ranges, while H-MgZn₂ shows predominant medium-frequency vibrational modes. Elastic anisotropy evaluation identifies Mg₄Zn₇ as moderately anisotropic, H-MgZn₂ as significantly anisotropic, and C-MgZn₂ as nearly isotropic. Thermodynamic analysis predicts superior thermal stability for C-MgZn₂, evidenced by its highest Debye temperature (θ_d = 366 K), maximum sound velocity (v_m=3.468 m/s), and minimal Grüneisen parameter (γ = 0.641), correlating with its exceptional thermal conductivity. In contrast, Mg₄Zn₇ exhibits the highest thermal expansion coefficient among the investigated phases. These findings establish fundamental structure-property relationships that advance the understanding of [Formula: see text] phase stabilization mechanisms, providing critical guidance for designing high-performance Mg-Zn alloys through phase engineering strategies.