Abstract The effect of pre-ageing at 0°C on the subsequent ageing at 40°C (two-step ageing) in Al-Zn 10% alloy is investigated by X-ray small-angle scattering and resistivity measurements. The size of G.P. zones at the end of the two-step ageing is found to increase on increasing the time of pre-ageing, a result which is related to the influence of temperature on zone size in single-stage ageing.
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.
