Effect of beryllium on age hardening, defect structure, and S′ formation in Al–2·5Cu–1·2Mg alloy

Abstract

AbstractThe effect of micro additions of Be on the aging behaviour, defect structure, and S′ phase formation in Al–2·5Cu–1·2Mg alloy is investigated. It is shown that the addition of 0·15%Be significantly increases the peak hardness and overall precipitation rate for the alloy. An analysis of the kinetic data shows that S′ precipitation obeys the Avrami equation, and that the Be addition does not affect the growth dependent parameter or activation energy, but significantly increases the nuclei density dependent parameter, which is consistent with the higher density of S precipitates in the microstructures of the alloy containing Be. Analysis using transmission electron microscopy shows that Be reduces the dislocation loop density during the early stages of aging, which is attributed to the high Be–vacancy binding energy, and promotes formation of dislocation helices. The enhanced nucleation of S′, notwithstanding the lower density of dislocation loops, which stimulate S′ nucleation, suggests the operation...