Effect of natural aging on formability and properties of Al-Cu-Li alloy during creep age forming

As-quenched (AQ) temper due to a good forming potential, is the most common material initial temper used in creep age forming (CAF). The inevitable evolution of microstructure during the natural aging (NA) process may have an effect on the deformation and mechanical properties of alloy during CAF. In this research, a NA regime suitable for CAF of Al-Cu-Li alloy (2195) was obtained by correlation with the creep deformation behavior, microstructures and mechanical properties. The results indicate that the creep deformation of the alloy increases with increasing NA time, after 24 h of NA, the creep deformation reaches a stable value. The creep strain of the NA 24 h temper alloys after creep aging of 21 h is about 1.5 times than that of the AQ temper alloys. The NA 24 h temper alloys present five-stages creep feature, while the creep deformation of the AQ temper presents four-stages creep feature. In addition, this study found that NA before creep aging has a slightly positive effect on age hardening, with increases of 3.9% in yield strength and 3.0% in tensile strength, but with a loss of 5.9% in ductility. The difference in creep deformation and mechanical properties is correlated with dislocation movement and the precipitation and growth of T1 phase. It is recommended to pre-treat Al-Cu-Li alloy (2195) with NA for 24 h to obtain stable creep formability and good mechanical properties.