Effects of Uniaxial Tensile Strain on Mechanical Properties of Al₆MgNb: A First-Principles Study

The effects of uniaxial tensile strain in the x direction (epsilon(x)) on the mechanical properties of the Al6MgNb compound were explored by carrying out first-principles calculations based on the density functional theory (DFT). The calculation results showed that the Al6MgNb compound was stable in mechanics at a uniaxial tensile strain range of 0-12%. The shear modulus G, bulk modulus B and Young's modulus E of the Al6MgNb compound all decreased as the uniaxial tensile strain epsilon(x) grew from 0 to 12%, exhibiting the negative sensitivities of elastic moduli to uniaxial tensile strain. The Poisson ratio nu of the Al6MgNb compound grew with the increase in uniaxial tensile strain epsilon(x) from 0 to 7%, exhibiting the positive sensitivity of Poisson's ratio to uniaxial tensile strain, but it decreased as the uniaxial tensile strain epsilon(x) increased from 7% to 12%, exhibiting its negative sensitivity to the uniaxial tensile strain. The Al6MgNb compound possesses the optimal toughness under a uniaxial tensile strain epsilon(x) of 7% because of the largest value of nu. The Vickers hardness H-V of the Al6MgNb compound decreased first and then remained stable with the growth in uniaxial tensile strain epsilon(x) from 0 to 12%, exhibiting the significant negative sensitivity of the Vickers hardness to tensile uniaxial strain at a strain range of 0-7%. The ratio of the bulk modulus B to the elastic shear modulus G (i.e., B/G) increased first and then decreased with the growth in uniaxial tensile strain epsilon(x) from 0 to 12%. The highest ductility is achieved for the Al6MgNb compound at a strain epsilon(x) of 7% because of the largest value of B/G. The compression anisotropy percentage A(B), shear anisotropy percentage A(G) and the universal anisotropy index A(U) of the Al6MgNb compound all increased as the uniaxial tensile strain epsilon(x) increased from 0 to 12%, exhibiting the positive sensitivity of elastic anisotropy to the uniaxial tensile strain. Our study suggested that the mechanical properties of the Al6MgNb compound can be influenced and regulated by applying proper uniaxial tensile strain. These findings can provide a favorable reference to the study on mechanical performance of Al-Mg-based materials by means of strain modulation.