Effect of H on elastic properties of Mg<sub>2</sub>Si by the first principles calculation

Abstract

The mechanical properties of Al-Mg-Si-type aluminum alloys may degenerate due to the hydrogen damage during servicing in hydrogen environment. The Mg<sub>2</sub>Si is the main strengthening phases in Al-Mg-Si-type aluminum alloys. Therefore, the mechanical properties of Mg<sub>2</sub>Si directly determine the strengths of Al-Mg-Si-type aluminum alloys. In this work, the effects of hydrogen atoms on the mechanical properties of Mg<sub>2</sub>Si are investigated by first principle calculation, which is based on the density function theory. First of all, we calculate the single crystal elasticity constants of <i>C</i><sub>11</sub>, <i>C</i><sub>12</sub> and <i>C</i><sub>44</sub>. Then the elasticity modulus, Poisson’s ratio and hardness of polycrystalline are calculated by using the crystal elasticity constants. Furthermore, we also calculate the tensile properties of Mg<sub>2</sub>Si with and without H atoms. The difference between the densities of states with and without H atoms is used to investigate the change of Mg<sub>2</sub>Si induced by H atoms. The results show that hydrogen atoms significantly reduce the shear modulus and elastic modulus of Mg<sub>2</sub>Si, resulting in the strength and hardness decreasing, but the toughness increasing. The calculations of tensile properties indicate that H atoms reduce the fracture strength but enhance the fracture elongation of Mg<sub>2</sub>Si. The analysis of density of states indicates that hydrogen atoms will induce the properties of Mg<sub>2</sub>Si to transform from semiconductor to metal properties. The calculated results in this paper can provide a reference basis for revealing the mechanism of strength reduction of Mg<sub>2</sub>Si materials in a hydrogen environment.