Microstructure evolution, enhanced aging kinetics, and mechanical properties of AA7075 alloy after friction extrusion

In the present study we utilized Friction Extrusion (FE); a solid phase processing technique; to produce fully consolidated dense 5 mm rods of AA7075 alloy. The combination of large shear stresses and temperatures at the tool-billet interface during the FE process resulted in the formation of dynamically recrystallized ∼2.0 μm equiaxed grains and fine uniformly distributed stable η (MgZn₂) precipitates ∼25–100 nm in size. Formation of such a microstructure resulted in lower solutionizing temperature and times (flash annealing) as compared to the conventionally extruded counterparts. We demonstrate for the first time that the solutionizing times for the T6 heat treatment of AA7075 can be reduced by three times using this FE process. In addition to being an energy efficient process, FE also serves to improve the performance of AA7075 alloys by retaining their strength while enhancing the ductility of the material. The tensile data for samples that were flash annealed and artificially aged after FE processing showed exceptional increase in ultimate tensile strength by over 19% and yield strength by over 59%, compared with an as-FE-processed sample.