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

Abstract

Abstract This study systematically investigates the elastic anisotropy and thermodynamic properties of $$\:{{\upbeta\:}}_{1}^{{\prime\:}}$$ 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 (θd = 366 K), maximum sound velocity (vm=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 $$\:{{\upbeta\:}}_{1}^{{\prime\:}}$$ phase stabilization mechanisms, providing critical guidance for designing high-performance Mg-Zn alloys through phase engineering strategies.