Abstract: It has been experimentally confirmed that most alloys exhibit creep asymmetry under tensile and compressive stress states. Although the "stress orientation effect" is potentially able to explain this phenomenon, its detailed mechanism has not been clearly clarified. Here, we studied the tensile-compressive creep deformation relationship of an Al-Cu-Li alloy at an aging temperature of 155 °C. We found that under the same temperature and load conditions, the creep rate of the tensile sample was significantly greater than that of the compressive sample at the initial creep stage, clearly showing the asymmetry of creep behavior under the tension/compression states. Microstructure data revealed that the dislocation loop density in the compressive creep sample was obviously higher than that in the tensile creep sample, and this disparity substantially influences the motion of line-shaped dislocations. On the one hand, dislocation loops inherently act as obstacles to hinder dislocation motion; on the other hand, dislocation loops promote the nucleation and growth of T₁ phases, and those fine T₁ precipitates will also pin and hinder dislocation movement. Our results demonstrate that the tensile-compressive creep asymmetry of an Al-Cu-Li alloy mainly originates from the compression-induced increase in dislocation loop densities, which provides another insight into the mechanism of creep asymmetry of aluminum alloys.

Key words: Creep deformation, Tension-compression loadings, Dislocation loop densities, Al-Cu-Li alloy