Precipitation of Al<SUB>3</SUB>Li from an Al-3%Li Alloy and Some Properties of Al<SUB>3</SUB>Li

Abstract

An X-ray and electron microscopic study on an aged Al-3%Li alloy, containing ordered precipitates, Al3Li, was performed. For the X-ray experiment, single crystals were used. The volume fraction of Al3Li, lattice constant of constrained Al3Li and average lattice constant of the aged alloy were determined from (300) and (400) reflections with their integrated intensities. From analyses of these data with elasticity theory it was found that the misfit parameter of Al3Li is −0.3% and the lattice constant of unconstrained Al3Li is 4.038(3) Å. The diameter of Al3Li was determined directly from electron micrographs. It was found that in the later stage of aging at 200°C, the growth of Al3Li can be described as Ostwald ripening. Interfacial energy between the Al3Li particle and the matrix was determined to be 180 erg/cm2 by using Lifshitz-Wagner’s formula. The antiphase boundary energy on the (111) plane of Al3Li was determined as 195 erg/cm2 by observing the equilibrium separation distance of super dislocations. This value led to a high critical temperature of oder-disorder transition of Al3Li, i.e. 537°C. This conclusion was also supported from the X-ray observation that even in an as-quenched alloy after solution treatment at 550°C for 3 hr, weak super reflection of Al3Li was detected.