Evolution of microstructure and strengthening of 7050 Al alloy by ECAP combined with heat-treatment

A study was conducted on the structures and properties of industrial 7050 Al alloy produced by severe plastic deformation through equal-channel angular pressing (ECAP). Special attention was paid to effect of heat-treatments on the structures and properties of the material. Four conditions were studied: (1) pre-ECAP annealing and post-ECAP aging; (2) pre-ECAP annealing, post-ECAP short-annealing and aging; (3) pre-ECAP annealing, post-ECAP short-annealing, ECAP repeated and aging and (4) pre-ECAP quenching and post-ECAP aging. The results indicated that condition 4 was most effective in improving strength as compared to other three conditions, whereas, effectiveness of conditions 3, 2 and 1 were more inferior to each other, respectively. Three strengthening mechanisms namely: grain refinement strengthening, precipitation strengthening and dislocation strengthening were dominantly operative in the four conditions. Two grain refinement mechanisms were proposed: (1) some fine grains were formed through cutting off the large grains by the shear bands and (2) some fine grains were formed through recrystallization.