Investigation on the asymmetric creep ageing behaviour of 2195-T84 Al–Li alloy under different tensile and compressive stress levels

Abstract

A comprehensive work has been carried out on the creep ageing behaviour of 2195-T84 Al–Li alloy under both tensile and compressive stresses at 180 °C for 16 h. The corresponding creep deformation and age hardening phenomena have been investigated by creep tests and uniaxial tensile tests. It has been found that the creep strains after tension creep tests are much larger than those after compression creep tests. Meanwhile, after the creep ageing test, the asymmetry of creep strain first decreases gradually and then increases obviously with the increase of the applied stress, and the yield strength of the alloy increases slightly. Moreover, the evolution of microstructures including dislocations and precipitates has been quantitative analyzed by X-ray diffractometer (XRD), scanning/transmission electron microscopy (S/TEM) and differential scanning calorimetry (DSC). It has been found that the dislocation density in the alloy under tensile stress is higher than that under compressive stress during creep ageing process. Besides, the T1 precipitates at the low-angle grain boundaries and the intragranular precipitates of θ′ grow obviously, especially under high stress levels. Furthermore, a set of physically-based creep ageing constitutive model is proposed, and the computed results tally well with the experimental data.