H对Mg2Si力学性能影响的第一性原理研究

Effect of H on elastic properties of Mg2Si by the first principles calculation

Al-Mg-Si系铝合金在氢环境服役时,因遭受氢损伤而导致力学性能退化.Mg2Si是Al-Mg-Si系铝合金主要的热处理强化相,其力学性能直接决定着Al-Mg-Si系铝合金的强度.本文采用基于密度泛函数理论的第一性原理计算方法,研究了间隙H原子对Mg2Si力学性能的影响.首先计算了Mg2Si的单晶体弹性常数C11,C12和C44,在通过Hill模型计算了多晶体的弹性模量、泊松比及硬度,并进一步计算了H对Mg2Si晶粒拉伸性能的影响,最后对H原子掺杂引起的Mg2Si晶体态密度变化进行了分析.结果表明:H原子的引入显著降低Mg2Si晶体的剪切模量和弹性模量,从而使得体系强度、硬度降低,韧性提高.拉伸性能计算也表明H原子引起Mg2Si晶体断裂强度降低、断裂延伸率提高.态密度分析表明,Mg2Si晶体中引入氢原子,将引起Mg2Si晶体由半导体性质向金属性质的转变,从而造成体系强度、硬度的降低,韧性增加.本文计算结果可以为揭示以Mg2Si为增强相的材料在氢环境中强度降低机理提供参考依据.

The mechanical properties of Al-Mg-Si-type aluminum alloys may degenerate due to the hydrogen damage during servicing in hydrogen environment.The Mg2 Si is the main strengthening phases in Al-Mg-Si-type aluminum alloys.Therefore,the mechanical properties of Mg2 Si directly determine the strengths of Al-Mg-Sitype aluminum alloys.In this work,the effects of hydrogen atoms on the mechanical properties of Mg2 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 C11,C12 and C44.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 Mg2 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 Mg2 Si induced by H atoms.The results show that hydrogen atoms significantly reduce the shear modulus and elastic modulus of Mg2 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 Mg2 Si.The analysis of density of states indicates that hydrogen atoms will induce the properties of Mg2 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 Mg2 Si materials in a hydrogen environment.