Microstructure evolution of ultrafine grained aluminum alloy prepared by large strain extrusion machining during annealing

As a new type of severe plastic deformation (SPD) method for efficiently preparing ultrafine grained (UFG) material, large strain extrusion machining (LSEM) has attracted the attention of researchers. At the same time, the UFG material prepared by the process has a small size, and the influence of external heat is involved in the subsequent utilization. Therefore, in this paper, the microstructure evolution of UFG6061 Al alloy chips prepared by LSEM during annealing has been investigated. The UFG chips were subjected to isochronous and isothermal annealing treatments. The microstructure of UFG chips was characterized by scanning electron microscope (SEM) with electron backscattered diffraction (EBSD) system. The results showed that with the increase of annealing temperature, the UFG aluminum alloy chips underwent three processes of recovery, recrystallization and grain growth. When the annealing temperature was 160 degrees C, with the extension of annealing time, the UFG aluminum alloy chips remained at the recovery stage, the point defects and dislocations were reduced, the dislocation density was reduced, and the grain size was not changed significantly.