Study on tensile/compressive asymmetry in creep ageing behavior of Al–Cu alloy under different stress levels

Abstract

Creep-ageing behavior of an Al–Cu alloy has been investigated under both tensile and compressive stress ageing conditions, with different stress levels at 165 °C for 9 h. The corresponding creep strain and age strengthening of the samples were studied by creep tests and uniaxial tensile tests. Microstructures observations of specimens have been examined by Scanning TEM (STEM) and X-Ray Diffraction (XRD). It has been found that the creep strains after tension creep tests are significantly greater than those after compression creep tests, and the asymmetry of creep strain decreases with increasing stress level. However, the yield strength of the creep aged-samples in compressive stresses are higher than those in tensile stresses, but the asymmetry of yield strength does not change significantly with the stress level. The stress exponents were found to be n = 2.95 and n = 4.21 for tension and compression creep test, respectively. The corresponding variance in dislocation density and the size of precipitates are the main reasons for the asymmetry of creep strain and yield strength, and the decreasing asymmetry in creep ageing behavior with increasing stress level is also related to the above two factors. In addition, the asymmetric creep ageing behavior of the Al–Cu alloy is discussed from both the macro and the micro aspect and a deeper understanding is achieved.