Effects of microadditions of vanadium and boron on age hardening and mechanical properties of Al–Li alloy 8090

The effects of micro additions 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°C for 22·5 h). The enhancement of these properties is attributed to the refinement of S′ and δ′ 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 Al₁₁V 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 Al₁₁V precipitates, which decrease with increasing cooling rate. The addition of boron appears to modify the morphology of the Al₁₁V precipitate.

MST/1584