1995 Volume 59 Issue 3 Pages 251-257
Age-hardening characteristics and precipitate structures have been examined in 2091 alloys (Al-2.15%Li-2.04%Cu-1.5%Mg-0.14%Zr) with and without 0.15%V or 0.19%Cr addition, with special attention to the relationship between S′-phase precipitation and the dispersoid particles which are formed during ingot homogenization. It was found that S′-phase precipitates mainly on dislocation loops around incoherent Zr-bearing and V-bearing dispersoid particles. In contrast, coherent Zr-bearing dispersoids and incoherent coarse Cr-bearing ones provided no nucleation site for S′-precipitate. The numerical density of S′-precipitates was not sufficient to contribute to hardening, corresponding to the low density of incoherent Zr-bearing and V-bearing dispersoids. The low density of V-bearing dispersoids was attributed to the low concentration of vanadium in solution before ingot homogenization, which was caused by the formation of a number of coarse V-bearing constituent particles during solidification. To avoid this, small 2091+V alloy ingots were prepared by chill-casting. The density of V-bearing dispersoids was significantly increased, leading to a finer distribution of S′-precipitates as well as a higher hardness level, which was comparable to that obtained in the 2091 alloy T8-treated.
