High strain rate superplasticity of submicrometer grained 5083 Al alloy containing scandium fabricated by severe plastic deformation

High strain rate superplasticity (HSRS) was obtained in a commercial 5083 Al alloy by introducing a ultrafine grained structure of 0.3 μm through severe plastic deformation and by adding a dilute amount of scandium (Sc) as a microstructure stabilizer. Tensile tests were carried out on the as-processed sample at temperatures of 623–823 K and initial strain rates of 1×10−3–1×100 s−1. The maximum elongation to failure of 740% was obtained at 773 K and 1×10−2 s−1. HSRS of the alloy was attributed to the combined effects of dynamic recrystallization and preservation of fine recrystallized grains by the presence of Sc. The mechanical behavior of the alloy at 773 K was characterized by a sigmoidal behavior in a plot of stress vs strain rate in the double logarithmic scale. The origin of the sigmoidal behavior was discussed in terms of microstructural evolution during superplastic deformation. An examination of the fractured samples revealed that failure occurred in a brittle manner related to cavitation rather than necking. Cavity stringers were formed parallel to the tensile axis by interlinkage of jagged-shaped isolated cavities along grain boundaries aligned to the tensile axis.