Ab initio simulations of vacancy-solute clusters in Al-Mg-Si and Al-Zn-Mg alloys

摘要

The coherent fcc (face-centred-cubic) based cluster stability of Al-Mg-Si and Al-Zn-Mg alloys is studied theoretically using augmented plane wave density functional theory calculations of a periodically repeated supercell containing 32 atoms. In particular, the presence of vacancies within the structure of Mg_a-Si_b±Va_c and Zn_d-Mg_e±Va_f clusters is investigated in detail. These fcc type arrays of solutes are considered to bind with vacancies. The binding energies between two substitutional elements, Mg and Si as well as Zn and Mg, and same arrangements bound to one vacancy in a fcc aluminium matrix are calculated. The binding energies of the co-clusters are taken as reference energies to compare the binding energies of two atom co-clusters to a vacancy in different constellations. These energies are used to predict formations of very early clusters containing single vacancies. Energetically more favourable structures are obtained and discussed.