T-phase Precipitation induced by the Addition of Silver to an Aluminium–Copper–Magnesium Alloy

Abstract

RECENTLY attention has been directed to the effects of small amounts (approximately 0.1 atomic per cent) of silver on the structure and properties of certain age-hardening aluminium alloys, since the changes that occur are thought to have both fundamental and practical significance^1–7. As part of this work, a detailed investigation is being made of silver additions to a wide range of aluminium–copper–magnesium alloys and some interesting results have been obtained for aluminium–2.5 per cent copper–1.5 per cent magnesium (contents expressed in weight percentages). As reported previously⁵, the addition of 0.5 per cent silver to this alloy both accelerates the rate of ageing and causes increased hardening in the medium temperature range (120°–240° C) (Fig. 1). Reasons for these changes have now been sought using X-ray diffraction and transmission electron microscopy to investigate alloys which were solution-treated at 500° C, cold-water quenched, and aged at 200° C in a salt bath. Results are shown in Figs. 1 and 2.