A critical evaluation of the processing of an aluminum 7075 alloy using a combination of ECAP and HPT

Experiments were conducted on a commercial Al-7075 alloy by processing by ECAP for 4 passes and then processing by HPT for up to a maximum of 20 turns. Measurements show that the grains were refined to ~680 nm after ECAP and to ~310 nm in the center of the disk after ECAP+HPT. Tensile testing at a temperature of 623 K revealed lower flow stresses and higher elongations to failure after processing by ECAP+HPT. Thus, the alloy was not superplastic after processing by ECAP but superplasticity was achieved with elongations up to ~800% after processing by ECAP+HPT. By plotting the Vickers microhardness against equivalent strain, it is shown that the hardness saturates at Hv≈250 after ECAP+HPT. This saturation hardness is higher than the value of Hv≈230 recorded after processing by HPT without a preceding step of ECAP. The results demonstrate that processing by ECAP+HPT produces higher hardness and greater grain refinement than processing only by HPT.