Abstract: The low cycle fatigue (LCF) behaviors and cyclic deformation mechanisms of 2195 Al-Li alloy were investigated under low temperatures (-20 °C and -80 °C) and different strain amplitudes (0.6 %, 0.7 %, 0.8 %, and 1.0 %). The LCF stress responses under conditions of -20 °C&0.6 % and -80 °C&0.6 % exhibited initial cyclic hardening followed by cyclic softening. In contrast, the alloy under other LCF conditions displayed continuous cyclic softening. Notably, the alloy demonstrated reduced LCF life under conditions of -80 °C and various strain amplitudes. The fatigue life model based on the total strain energy was developed and proven to be more accurate in predicting fatigue life under diverse LCF conditions. Furthermore, the combined kinematic/isotropic hardening constitutive model exhibited excellent performance in simulating hysteresis loops of the alloy, with corresponding calibration errors all below 14 %. Additionally, fatigue fracture surfaces under various LCF conditions consistently exhibited prominent cleavage fracture characteristics, and the final fracture zone at -80 °C showed increased surface roughness. Finally, the cyclic softening mechanisms were found to be dependent on LCF conditions. The debonding of the interface between the T₁ phases and the Al matrix was identified as the primary cyclic softening mechanism under conditions of -20 °C&0.6 % and -80 °C&0.6 %. Moreover, the cyclic softening effect under -80 °C&1.0 % was closely associated with localized shearing of T₁ phases. Under -20 °C&1.0 %, a more pronounced cyclic softening behavior was observed, which was primarily attributed to the continuous shearing of T₁ phases.

Key words: 2195 Al-Li alloy, Low temperature, Low cycle fatigue behavior, Hysteresis loop simulation, Fatigue life prediction, Cyclic deformation mechanism