THE EFFECT OF THROUGH-THICKNESS ANISOTROPY ON THE CRYOGENIC MECHANICAL-PROPERTIES OF AN AL-CU-LI-ZR ALLOY (VINTAGE-III 2090-T81)

The cryogenic mechanical properties of a 12.7-mm (0.5-in.) Vintage III 2090-T81 (Al-3.05Cu-2.16Li-0.11Zr by weight) plate material were studied. The results indicate that the through-thickness anisotropy in the yield strength of Vintage I 2090-T81 is reduced in the Vintage III material by utilizing a partial recrystallization step during the thermomechanical processing but at some cost to the elongation and cryogenic fracture toughness. Sharp discontinuities in the microstructure resulting from this thermomechanical treatment give rise to distinct differences in the variation of the work hardening behavior with temperature between those regions which undergo recrystallization and those which do not. The lower elongations observed in Vintage III 2090-T81 result from a decrease in work hardenability that appears to be associated with increased slip heterogeneity. The reduced cryogenic toughness is due, in part, to the disruption of the monolithic unrecrystallized grain structure previously observed in Vintage I 2090-T81. The results suggest that a fully unrecrystallized structure is beneficial for cryogenic toughness in the longitudinal orientation.