Microstructure quantification and correlation with flow stress of ultrafine grained commercially pure Al fabricated by equal channel angular pressing (ECAP)

Commercial purity Al was severely deformed by equal channel angular pressing (ECAP) up to eight passes using route BC. The deformation microstructure was characterized quantitatively by electron-backscattered diffraction (EBSD) and transmission electron microscopy (TEM). The microstructural homogeneity was investigated by EBSD at various locations from center to surface of the samples on a longitudinal section parallel to the pressing direction. Structural parameters including mean boundary spacing, boundary misorientation angle and fraction of high angle grain boundaries were measured and characterized through the section of the ECAP samples. EBSD scans revealed a homogeneous ultrafine grained microstructure after 8 passes. The analysis showed that the fraction of high angle grain boundaries was more than 70% at most locations of the sample section. Also, an average boundary spacing of 380 nm was obtained by the linear intercept method. TEM analysis was used for more detailed characterization of the microstructure, such as low angle boundaries with misorientation angles smaller than 2°. Using the structural parameters–flow stress relationship, the flow stress was estimated based on the EBSD and TEM/Kikuchi-line analyses and compared with measured values.