Microstructural evolution and mechanical properties of an aluminum alloy processed by equal-channel angular pressing and high-pressure torsion

2014-07-07A commercial Al-7075 alloy was processed by severe plastic deformation (SPD) techniques, namely equal‐channel angular pressing (ECAP) and high‐pressure torsion (HPT) or a combination of the two processes. After processing, the microstructural properties were examined, microhardness measurements were recorded across the disk diameters, and miniature tensile specimens were pulled to failure at a temperature of 623 K. ❧ Using TEM and EBSD techniques, it is demonstrated that the three SPD processing techniques have a potential for producing an ultrafine‐grain structure containing reasonably equiaxed grains with high‐angle grain boundary misorientations. However, microstructures were refined to different levels depending on the processing operation. It is shown that the most refined grain structure was achieved after processing by a combination of ECAP for 8 passes and HPT. The grain refinement mechanisms are primarily governed by dislocation activities. ❧ It is shown that the maximum saturation hardness achieved at high equivalent strains by different processing techniques increases with increasing amounts of deformation and it is the highest after processing by a combination of ECAP for 8 passes and HPT. The saturation hardness values were ~231 after processing by HPT, ~249 after processing by ECAP for 4 passes + HPT and ~273 after processing by ECAP for 8 passes + HPT. ❧ Tensile testings show that the elongations to failure increase by increasing the amount of deformation. It is shown that after ECAP for 8 passes + HPT samples of the Al-7075 alloy have lower flow stresses and superplastic elongations up to >1000% when pulling to failure at 623 K. Superplastic elongations were not achieved after processing only by ECAP because of the non‐uniform grain size and the presence of many larger grains