Lowering the temperature for high strain rate superplasticity in an Al–Mg–Zn–Cu alloy via cooled friction stir processing

•The Al 7075-T6 alloy was friction stir processed over two kinds of backing anvils.•The FSPed grain sizes depend on the refrigeration temperature for each backing anvil.•Large refinement down to 0.5 (in air) and 0.3 (N2 refrigerated) μm allows GBS.•Low temperature high strain rate superplastic window at 250–350 °C was obtained.•A eF = 270% record at 250 °C and 10−2 s−1is obtained for the finest FSPed material.

An Al–Zn–Mg–Cu alloy was friction stir processed over two kinds of backing anvils, at two different cooling rates. A finer grain size, 0.3 vs 0.5 μm, was obtained by processing at the highest cooling rate. Both materials showed superplastic behavior with a maximum elongation to fracture of about 510%. Grain boundary sliding was the operative deformation mechanism. Furthermore, the finer grain size material showed high strain rate superplasticity, at 10−2 s−1, at lower temperatures, as low as 250 °C.