Microstructural characterization and mechanical properties of nanostructured AA1070 aluminum after equal channel angular extrusion

Abstract

In the present research, equal channel angular extrusion (ECAE) of commercial purity aluminum (1070) was conducted using route B C. For ECAE processing a proper die set was designed and constructed. Electron backscatter diffraction (EBSD) and X-ray diffraction (XRD) analyses were used to evaluate the microstructure and texture of the extruded materials. The results reveal two distinct processing regimes: from 1 to 4 passes the microstructure evolves from elongated subgrains to a rather equiaxed array of ultrafine grains and from 4 to 8 passes there is no strict change in the average grain size. The boundary misorientation angle and the fraction of high-angle boundaries increase rapidly up to 4 passes and at a slower rate from 4 to 8 passes. Also, the variation of hardness and yield stress with number of extrusion was documented up to 8 passes. The present results showed that first ECAE pass has resulted in enhancement of mechanical properties more than four times over the annealed condition. Further ECAE processing has resulted in slight improvement. Based on two strengthening mechanisms, variations of the strength as a function of the pass numbers were related to the calculated dislocation densities and the average boundary spacing.