First-principle Calculations of Mechanical Properties of Al₂Cu, Al₂CuMg and MgZn₂ Intermetallics in High Strength Aluminum Alloys

Structural stabilities, mechanical properties and electronic structures of Al₂Cu, Al₂CuMg and MgZn₂ intermetallics in Al-Zn-Mg-Cu aluminum alloys were determined from the first-principle calculations by VASP based on the density functional theory. The results show that the cohesive energy (<i>E</i>_coh) decreases in the order MgZn₂ > Al₂CuMg > Al₂Cu, whereas the formation enthalpy (Δ<i>H</i>) decreases in the order MgZn₂ > Al₂Cu > Al₂CuMg. Al₂Cu can act as a strengthening phase for its ductile and high Young's modulus. The Al₂CuMg phase exhibits elastic anisotropy and may act as a crack initiation point. MgZn₂ has good plasticity and low melting point, which is the main strengthening phase in the Al-Zn-Mg-Cu aluminum alloys. Metallic bonding mode coexists with a fractional ionic interaction in Al₂Cu, Al₂CuMg and MgZn₂, and that improves the structural stability. In order to improve the alloys' performance further, the generation of MgZn₂ phase should be promoted by increasing Zn content while Mg and Cu contents are decreased properly