Contribution of grain boundary sliding in low-temperature superplasticity of ultrafine-grained aluminum alloys

Ultrafine-grained (0.6 μm) Al–Mg–Sc alloy with predominant high-angle boundaries was produced by friction stir processing. A superplastic elongation of 210% was obtained at 175 °C, and the optimum strain rate and maximum elongation increased with increasing temperature. Marker lines were scratched on the polished specimen surfaces using a nano-indenter to measure grain boundary sliding (GBS) offsets during deformation, which indicated that the GBS contribution to the strain exceeded 50% at 175 °C and increased with increases in strain and temperature.