Annealing of vacancies and ageing in Al-Li alloys

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Abstract
Quenching experiments have been carried out on a set of ‘dilute” Al-Li alloys by using resistivity measurements, and on a ‘concentrate” alloy containing 6·72 at. % Li, by using both resistivity and electron microscopy. A value of 0·25±0·03 eV has been determined for the Li-vacancy binding energy. The recovery after quenching of dilute alloys containing up to 0·38 at. % Li occurs in two stages as in pure Al; the first stage has been ascribed to the annealing of vacancy-Li couples formed during the quenching, whereas the second one has been attributed to the elimination of dislocation loops. By increasing Li content, some anomalies have been observed in the recovery after quenching, ascribed to short-range order phenomena. The concentrate alloy decomposes in the ageing after quenching by forming G.P. zones having an ordered Al3Li internal structure. High quenching temperatures (≥500°C) prevent G.P. zones from reaching the resistivity maximum, a result attributed to a reduction in the lifetime of vacancies caused by the high density of small dislocation loops nucleated by Li atoms.