EBSD and TEM characterization of ultrafine grained high purity aluminum produced by accumulative roll-bonding

High purity aluminum (99.99% purity) was severely deformed by accumulative roll-bonding (ARB) to a thickness reduction of 98.4%. Quantitative microstructural characterization of the deformed sample was carried out by electron backscatter diffraction (EBSD) and transmission electron microscopy (TEM). EBSD scans at various locations from the sample surface to the mid-thickness revealed a fairly uniform and equiaxed structure, although a small fraction of an elongated structure parallel to rolling direction (RD) was also observed. Misorientation angle distributions for grain boundaries of which misorientation angle was larger than 2° were evaluated by EBSD, showing that more than 70% of the boundaries were high-angle ones (>15°). More detailed structural features, such as low-angle boundaries (<2°) and dislocations between boundaries were characterized by TEM. The TEM results indicated that about 17% of the boundaries have misorientations <2° and that the fraction of high-angle boundaries is about 52%. An estimated yield strength based on the structural parameters determined by TEM was in good agreement with the measured value.