Superplastic behaviour at low temperatures of an Al-4.1Mg-2.0Li-0.16Sc-0.08Zr (wt pct) alloy fabricated by casting and subjected to equal channel angular extrusion (ECAE) with a total strain of ~16 at 325ºC is analyzed. Intense plastic straining resulted in a uniform structure with an average grain size of 0.8 µm. The alloy exhibited superplasticity in the temperature range 150-250ºC at strain rates ranging from 1.4x10-5 to 5.6x10-2 s-1. A maximum elongation-to-failure of 440 pct was observed at 175ºC (~0.5 Tm, where Tm is the melting point) and a strain rate of 2.8x10-5 s-1, where a maximum strain rate sensitivity of 0.32. It was shown that mechanisms resulting in superplastic elongation at high temperatures and low temperatures are essentially the same. The difference in the strain rate coefficient for high temperature superplasticity (at T=450°C the m value was found to be 0.5) and low temperature superplasticity is caused by effect of high stress at the head of dislocation pile-up formed near grain boundaries. Detailed consideration of mechanism of low temperature superplasticity is presented.
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