8 mm thick extruded Al-5.3Mg-0.23Sc alloy plates was subjected to friction stir processing (FSP) at a tool rotation rate of 400 rpm and 25 mm/min. Microstructural examinations indicated that fine and equiaxed microstructure with a grain size of 2.0 µm and high ratio of high-angle grain boundaries was produced. Superplastic behavior of the FSP alloy was investigated at initial strain rates of 1×10-2 - 1 s-1 and temperatures of 425-500°C. It was showed that superplastic elongations of >1000% were obtained at a wide temperature range of 450-500oC and high strain rate range of 3×10-2 - 3×10-1 s-1. A maximum elongation of 1500% was achieved at 475°C and a high strain rate of 1×10-1 s-1. The analyses of the superplastic data and SEM examinations on the surfaces of deformed specimens indicated that grain boundary sliding is the main deformation mechanism for the FSP Al-Mg-Sc alloy. Furthermore, the FSP alloy exhibited enhanced superplastic deformation kinetics compared to that predicted by the constitutive relationship for superplasticity in fine-grained aluminum alloys.
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