Theory-guided materials design of multiphase alloys with superior stiffness at finite temperatures

Aiming at designing Mg alloys with a significantly increased stiffness at elevated temperatures, we propose a high-precision multi-scale methodology to compute temperature-dependent elastic modulus of homogeneous multiphase alloys. The proposed method combines (i) first-principles calculations of temperature- and solid solubility-dependent elastic properties in individual phases with (ii) a two-level multiphase homogenization at the continuum level and (iii) a phenomenological thermodynamic modeling by the CALPHAD approach. According to the post-average approximation during the calculation, the stresses and strains of individual phases in the alloy are superimposed before undergoing the average approximation. This is different from the traditional method which consider forces as acting axially assumptions of isostrain and isostress model and followed by numerical averaging. We applied the proposed method in light-weight Mg-alloys, in particular, a three-phase alloy with the composition Mg _0.878Al _0.083Si _0.039, and verified it through experimental measurements. The present work identifies that Mg _xAl _ySi _1-x-y with 0 ≤ x ≤ 0.87 and 0 ≤ y ≤ 0.87- x are candidate compositions with Young`s modulus exceeding 60 GPa at 623 K.