An evidence of high strain rate superplasticity at intermediate homologous temperatures in an Al–Zn–Mg–Cu alloy processed by high-pressure torsion

A commercial Al–Zn–Mg-Cu alloy, 7075 Al, was processed by high-pressure torsion in unconstrained conditions at room temperature to five complete turns under load of 6 GPa. Microstructural characterization was performed by transmission electron microscopy in the peripheral region of the processed samples, showing equiaxed and submicron grain sizes of 100–150 nm. Vickers microhardness measurements revealed large strengthening at ambient temperature as a consequence of the grain refinement. Small punch testing, having the same axial symmetry as high-pressure torsion processing, was performed to evaluate the mechanical properties at intermediate temperatures. The processed disks showed high strain rate superplasticity at 250 and 300 °C.