Development of ultrafine-grained microstructure and low temperature (0.48 Tm) superplasticity in friction stir processed Al-Mg-Zr

Friction stir processing (FSP) was applied to extruded Al-4Mg-1Zr to produce fine-grained microstructure with grains sized 0.7-1.6 μm. Low temperature deformation behavior was investigated at 175 °C and initial strain rates of 5 × 10−5-3 × 10−3 s−1. Low temperature superplasticity was observed in ultrafine-grained material. A maximum superplastic elongation of 240% was obtained in ultrafine-grained (0.7 μm) FSP sample at an initial strain rate of 1 × 10−4 s−1 where a maximum strain rate sensitivity of 0.34 was observed.