The strength-toughness combination of the aluminum-lithium alloys 2090 and 2091 at cryogenic temperatures

Abstract

The strength-toughness combination of the aluminum-lithium alloys 2090 (nominal composition Al-2.7 Cu-2.2 Li-0.1 Zr in wt. %) and 2091 (Al-2.2 Cu-2.0 Li-1.5 Mg-0.1 Zr) plate at cryogenic temperatures was investigated. Aluminum-lithium alloys have lower density and higher stiffness than conventional aluminum alloys and were developed for aircraft applications. This study was motivated by the possibility of using aluminumlithium alloys for cryogenic tankage of spacecraft, an application in which light weight, weldability and good cryogenic mechanical properties are at a premium. Alloy 2090-T81 has a strength-toughness combination that improves with decreasing temperature between 300 and 4 K under some conditions. This improvement is accompanied by an increase in the tensile elongation and strain hardening rate, but the large increase in fracture toughness is not reflected in the primary fracture mode. The goal of this study was to develop an understanding of the mechanisms responsible for the increase in fracture toughness at cryogenic temperatures. The mechanical properties of alloy 2090 in other metallurgical conditions and a second alloy, 2091, were also considered.