| Summary: | This study aims to achieve an ultrafine-grained (UFG) Al 2024 alloy superplasticity at temperatures lower than the traditional ones for commercial Al alloys (400–500 °C). The UFG structure with a mean grain size of 100 nm produced in the alloy by high-pressure torsion at room temperature provided a very high strength—microhardness (HV<sub>0.1</sub>) of 286 ± 4, offset yield strength (σ<sub>0.2</sub>) of 828 ± 9 MPa, and ultimate tensile strength (σ<sub>UTS</sub>) of 871 ± 6 MPa at elongation to failure (δ) of 7 ± 0.2%. Complex tensile tests were performed at temperatures from 190 to 270 °C and strain rates from 10<sup>−2</sup> to 5 × 10<sup>−5</sup> s<sup>−1</sup>, and the values of flow stress, total elongation and strain rate-sensitivity coefficient were determined. The UFG alloy was shown to exhibit superplastic behavior at test temperatures of 240 and 270 °C. For the first time, 400% elongation was achieved in the alloy at an unusually low temperature of 270 °C (0.56 T<sub>m</sub>) and strain rate of 10<sup>−3</sup> s<sup>−1</sup>. The UFG 2024 alloy after superplastic deformation was found to have higher strength (150–160 HV) than that after the standard strengthening heat treatment T6.
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