Abstract:The superplastic-like deformation behavior of 7075 aluminum alloy sheets was studied by high-temperature tensile tests under deformation temperature range of 400–500 ℃ and strain rate range of 0.0001–0.1 s–1. The relationship between deformation behavior and microstructural evolution was analyzed using scanning electron microscope and electron backscatter diffraction techniques. A hyperbolic sine constitutive model was established to characterize the plastic flow behavior. The results indicate that dynamic recovery is the predominant softening mechanism at high strain rates, while a transition to dynamic recrystallization occurs at lower strain rates, accompanied by a notable increase in the proportion of high-angle grain boundaries (HAGBs). Nonetheless, excessively low strain rates can lead to grain coarsening. At 450 ℃/0.01 s–1, the maximum elongation of 72% is achieved, which is attributed to the presence of fine equiaxed grains, a high fraction of HAGBs, and a low dislocation density. With the increase in temperature, dynamic recrystallization becomes more obvious, resulting in a reduction in average grain size and a gradual enhancement in elongation. However, excessively high deformation temperatures promote atomic diffusion at grain boundaries due to more intense atomic thermal motion, leading to diminished bond strength and a sharp decline in elongation. Examination of microscopic fractures at 450 ℃/0.01 s–1 reveals a multitude of uniformly distributed ductile dimples, indicative of a typical ductile fracture. As the deformation temperature rises, the fracture mechanism progressively shifts towards brittle fracture. Conversely, at constant temperature, higher strain rates predominantly induce ductile fracture, which transitions to localized brittle fracture as strain rates decrease, consequently reducing post-fracture elongation. This study investigates the deformation mechanisms of coarse-grained aluminum alloys, which helps to reduce the cumbersome pretreatment processes required for these materials. The findings hold significant importance for optimizing the processing techniques and mechanical properties of 7075 aluminum alloy, thereby promoting its broader industrial applications.