Thermodynamic re-assessment of the Al-Li-Zn system

Abstract

Aluminum-lithium alloys are a kind of highly promising material due to low density, high strength and excellent modulus properties. The proper addition of Zn can effectively promote the precipitation of the main metastable strengthening phase δ′(Al₃Li). As a crucial sub-system of Al-Li alloys, literature data on phase diagram and thermodynamic properties of the Al-Li-Zn system as well as the Al-Li and Li-Zn binary systems were comprehensively evaluated by the CALPHAD approach. The Li-Zn system was reassessed mainly by considering the newly reported data on formation enthalpy and activity and a 2-sublattice (SL) model was applied to describe the βLiZn₄ phase. The Al-Li system was modified by considering AlLi₂ and describing the metastable phase δ′(Al₃Li) with interconvertible 4SL and 2SL ordered-disordered models. The predicted metastable fcc solvus was in perfect agreement with the measurements. Considering the available experimental data, the ternary Al-Li-Zn system was then re-optimized and a self-consistent thermodynamic description of the ternary Al-Li-Zn system was presented. The predicted metastable two-phase region of (Al)+δ’(Al₃Li) in Al-Li-Zn system can be coupled with the accessible experimental data, which can be expected to well assist in designing high-strength Al-Li alloys.