Dislocation density-me diate d creep ageing behavior of an Al-Cu-Li alloy

Creep aging is well-known to be a time-dependent, coupled process of deformation and precipitation strengthening for age-hardening alloys. Its existing mechanisms are mainly attributed to those interactions between atomic diffusion and dislocation motion. However, an understanding of the relationship between dislocation density and a special multistage creep behavior, i.e., double steady creep feature, is still far limited. Here we investigate the effect of various dislocation density levels on such an abnormal multistage creep of an Al-Cu-Li alloy. We find that the increased dislocation densities enable an apparent time decrease (from 6.2 h to 0.8 h) of their first steady II -stage. The yield strength of post-aged samples increases from 425.0 MPa to 580.0 MPa while the corresponding elongation decreases from 12.3% to 7.3% for the creep-aged samples #1 to #4. Microstructural results also reveal that a great difference in dislocation configuration, tailored by various density levels, results in varying creep processes of the II -stage. This stage is closely related to the nucleation and early growth of T 1 precipitates. Their number densities (maximum: 2.9 x 10 19 m -3 ) and the average length (maximum: 21.3 nm) of T 1 precipitates are much smaller than those of the stable peak-aged T 1 phases, suggesting that creep II -stage of all three creep-aged samples is dominant by the nucleation and initial growth of those T 1 precipitates. This study provides valuable insights into the dislocation density-mediated creep deformation of an Al-Cu-Li alloy. & COPY; 2023 Published by Elsevier Ltd on behalf of The editorial office of Journal of Materials Science & Technology.