Quantitative and qualitative correlations by atomistic determination for the precipitated phases in Al-Li-Cu system

The atomic cluster structures, stability and properties of the precipitated phases in Al-Li-Cu system, together with the corresponding quantitative and qualitative correlations are investigated by performing atomistic simulations. It is found that the characteristic principal clusters could accurately reflect the local atomic configuration and the short-range-order structural feature of the Al-Li-Cu alloys. These principal atomic clusters are with coordination number (CN) ranging from 10 to 14, and most are with CN12. The mass density of the Al-Li-Cu precipitated phases changes linearly as the solute-concentration. The stability of Al-Li precipitated phases decreases as the solute content, and the cohesive energy of the Al-Cu precipitated phases is higher than that of the Al-Li precipitated phases. Besides, Al4Cu9, AlCu2, AlCu, Al3Li and Al3Li2 phases have larger elastic moduli and higher hardness than the other precipitated phases. The Al-Cu precipitated phases exhibit better plasticity than the Al-Li precipitated phases. All of these Al-Li-Cu precipitated phases are thermodynamically and mechanically stable. Analysis on the band structures and the density of states indicates that these Al-Li-Cu precipitated phases behave the conductive property. There is a negative correlation between the nucleation barrier and the driving force during the precipitation at different aging temperatures, as exemplified by the theta'-Al2Cu precipitate.