First-principles calculations to investigate stability, mechanical and thermo-dynamic properties of AlxTMy intermetallics in aluminum alloys

Abstract

The mechanical, thermal and electrical properties of 8 types of common AlxTMy (TM = Sc–Zn, Y–Cd, Hf–Hg) intermetallics in Al based alloys at various temperatures and pressures have been investigated by combining first-principles calculations with the Debye model. The results clearly show that the stability and mechanical property are closely related to the types of configurations and TM elements. The electronic structure for AlRh and AlCd alloys are used to study the characteristics of stable compounds, and it is found that more transferred electrons will make the lattice mismatch δ larger. The Cauchy pressure C12–C44 and electric local function (ELF) present underlying characteristics of bonds and physical mechanisms. Further, the Helmholtz free energies F of both Al bulk and stable AlxTMy intermetallics are decreased with increasing temperature, while the entropy S, heat capacity CV and coefficient of expansion aT show the opposite trends. And the smaller F leads to the lower aT; that is the compounds constitute of elements of IB ∼ IVB have larger F and aT, while the compounds with VB ∼ VIIB possess smaller F and aT. In short, all calculated parameters in this work show the same change with the atomic number in for three periods 3-5d, indicating that the structure of the TM valence electron layers are the main reason for the underlying mechanisms. This work is helpful for the study of high-performance of structural Al-based alloys.