Tensile/compression creep aging behavior of 2195-T34 Al-Li alloy under different stress levels

Abstract

Typically, the influence of compressive stress has been seldom considered during the creep aging process (CAF) of thin-walled components. However, the inclusion of stiffener is known to greatly enhance the compressive stress during CAF, and the influence of compressive stress cannot be ignored. In this work, the tensile creep aging (TCA) and compressive creep aging (CCA) behavior and microstructure evolution were investigated under varying stresses, employing the 2195-T34 Al-Li alloy as the target material. A statistical analysis reveals a disparity in the creep strains of TCA and CCA. Under reduced stress conditions, the creep strain of the former exceeds that of the latter, and the degree of asymmetry gradually decreases as stress levels increase. The asymmetry in the strength of the creep-aged specimens was also observed, with the TCA specimens exhibiting more strength than the CCA specimens and the asymmetry in strength decreased with increasing stress. The stress exponents of TCA and CCA were determined to be n = 0.88 and n = 2.23 respectively, and the creep mechanisms of the two specimens exhibited distinct differences. Microstructural analysis revealed a more pronounced Cu-rich phase at the grain boundaries of the TCA specimens, leading to a reduction in the elongation of the specimens, which was confirmed by differences in fracture morphology. The CCA specimens had a higher concentration of θ′ phases, and the number of these phases declined as the stress increased, which is consistent with the result that the strength of the CCA specimens improved with increasing stress. Furthermore, a constitutive model derived from tensile/compression creep curves is proposed, and the calculated results and actual data exhibit remarkable agreement.