Effect of cadmium addition on aging phenomena of Al-4%Cu-1%Li alloy

Abstract

Aging behavior of Al-4%Cu-1%Li ternary and Al-4%Cu-1%Li-0.1%Cd quarternary alloys was investigated by means of hardness measurements and transmission electron microscopy. Specimens were normally aged (after water-quenching) or directly aged at 200°250°C for various times. T1' and TB' phases are commonly formed in both alloys, when they are aged at 200°250°C. The precipitation of T1' takes place homogeneously with the aid of excess vacancies, and that of TB' heterogeneously on several kinds of precipitation sites. The distribution of TB' in the quartery alloy becomes finer and denser independently of normal or direct-aging resulting in the increase in age-hardenability. The reason is in the fact that cadmium-rich precipitates are formed numerously at a very early stage of aging, and then TB' is formed on those cadmium-rich precipitates.