Developing grain refinement and superplasticity in an Al 7075 alloy processed by high-pressure torsion

High pressure torsion (HPT) is one of the most popular severe plastic deformation (SPD) techniques which is used to produce ultra-fine grained or even nano-crystalline materials. In the current research, the effects of high pressure torsion (HPT) processing at different pressure on flow stress and hardness distribution of AA-7075 Al alloy are studied. Using in situ torque measurements versus equivalent strain, the flow stress of the material follows three distinct deformation regions at room temperature. The grain size was 20 μm. The processing by HPT was performed at room temperature with pressure of 6.0 GPa and rotation speed of rpm. Processing of the material was conducted through total number of revolutions, N, of 1/4, 1, and 5. After turn in HPT, the traces of shear deformation appeared. When the turns increased to 3, shear deformation was more severe. After turns, the fibrous structure basically disappeared and ultrafine equiaxed grains were formed. When the deformation proceeded to turns, series of high-angle boundaries were formed in the sample and the average size of equiaxed grains was 500 nm. After HPT processing, the microhardness increased as the numbers of HPT turns increased and the distribution of hardness tended to be relatively homogeneous when the HPT continued to turns. Superplastic deformation tests were performed at initial strain rates in the material processed by HPT and an elongation of 590% was achieved when deforming at 1.0 10-3 s-1.

کلیدواژه ها:

grain refinement ، high-pressure torsion ، microhardness ، superplasticity ، Aluminium alloy