EFFECTS OF MICROADDITIONS OF VANADIUM AND BORON ON AGE HARDENING AND MECHANICAL-PROPERTIES OF AL-LI ALLOY-8090

The effects of microadditions of vanadium and boron on the age hardening, microstructure, mechanical properties, deformation, and fracture behaviour of Al-Li alloy 8090 have been investigated. The addition of 0.6% V to 8090 alloy increases the peak hardness by 13%, the yield strength by 23%, and the ductility by 85% when optimally aged (190-degrees-C for 22.5 h). The enhancement of these properties is attributed to the refinement of S' and delta' precipitates and the promotion of extensive cross-slip during deformation of the vanadium containing alloys. The same amount of vanadium reduces the impact toughness of 8090 by 50%, which is attributed to the presence of coarse particles of primary Al11 V precipitate. Increasing the cooling rate during solidification, or adding 0.1%B, restores and slightly increases the impact toughness of the vanadium containing alloy. The effect of cooling rate is related to the amount and size of Al11 V precipitates, which decrease with increasing cooling rate. The addition of boron appears to modify the morphology of the Al11 V precipitate.