(V) Enhancing mechanical properties of uniformly distributed nano TiB2/2024 Al composite rolling sheet by pre-stretch aging

The effects of pre-stretching prior to natural aging on the behavior of dislocation evolution, the precipitation behavior, microstructure and mechanical properties of an in-situ TiB₂/2024 Al composite were investigated. Pre-stretching introduced a strong increment in the dislocation density, and meanwhile facilitated uniform distribution of dislocations. The dislocation structure evolved from parallel dislocation lines to dislocation cells, and finally formed uniform dislocation networks. The heterogeneous nucleation of the S’’ precipitates occurred on the more uniform-distributed dislocations. Finer and more evenly distributed S’’ precipitates were achieved. Based on these refined microstructure features, the mechanical properties of TiB₂/2024 Al composite presented a significant increase in yield strength and tensile strength, from 306 ± 6 MPa and 508 ± 3 MPa without pre-stretching to 504 ± 3 MPa and 542 ± 5 MPa for the composite subjected to 8% nominal strain pre-stretching, respectively. Meanwhile, a loss of plasticity took place on the pre-stretching composites. The results in this work provided important insight into tuning the thermo-mechanical treatment which possesses improved mechanical properties.