Precipitation in an aluminium-14at.% lithium alloy

Abstract

Abstract The early stages of low-temperature ageing of an Al–14 at.% Li alloy have been studied by differential scanning calorimetry, X-ray diffraction and transmission electron microscopy. Results show precursor structures form before δ′ (Al3Li) precipitation and these have been attributed to congruent ordering and spinodal decomposition. The development of the precursor structures are shown to be controlled by excess quenched-in vacancies and therefore very sensitive to quench rate, hold time at room temperature and small amounts of cold work applied between quenching and ageing. Large amounts of cold work (95%) do not completely destroy the ordered structure of the as-quenched alloy but the high-diffusivity channels arising from the presence of dislocations are found to influence both the precursor events and the δ′ precipitation.