Concurrent precipitation and associated texture evolution in AA 6082 alloy during high pressure torsion (HPT) processing

Abstract

The effect of severe plastic straining by HPT processing on the mechanical properties and the microstructure evolution of a commercial AA 6082 alloy was studied. The HPT processing was carried out by torsion of 0.5 rotation per minute under 2 GPa load, for up to 5 turns. The material was solutionized before HPT. Mechanical homogeneity is achieved after 3 turns with a saturation hardness of ~ 165 HV and further increased to ~ 175 HV after 5 turns, while the alloy showed ~ 68 HV before HPT straining. The increase in hardness during HPT has been attributed to concurrent precipitation during HPT. The development of an ultrafine grained (UFG) microstructure was analyzed by investigating samples prepared from both the centre and the edge of the HPT discs after 1, 3 and 5 turns using TEM. In case of 1 turn, subgrain formation occurred at the edges of the disc while at the centre dislocation cell structure formation was observed. Subgrains are formed at the centre and the edge after 3 HPT turns with an average diameter of ~ 300 nm that further decreased to ~ 200 nm after 5 HPT turns. Texture evolution after 1 turn consists of formation of A*2, C, A and A- components. However, with increasing straining, these components remain stable and no new component arises. This has been attributed to continuous dynamic recrystallisation as the dominating mechanism of grain refinement that can occur in this alloy under the given severe plastic straining.