Microstructural Evolution Analysis in Thickness Direction of An Oxygen Free Copper Processed by Accumulative Roll-Bonding Using EBSD Measurement

Abstract

Abstract Microstructural evolution in the thickness direction of an oxygen free copper processed by accumulative roll-bonding (ARB) is investigated by electron back scatter diffraction (EBSD) measurement. For the ARB, two copper alloy sheets1 mm thick, 30 mm wide and 300 mm long are first degreased and wire-brushed for sound bonding. The sheets are then stackedand roll-bonded by about 50 % reduction rolling without lubrication at an ambient temperature. The bonded sheet is then cutto the two pieces of the same dimensions and the same procedure was repeated on the sheets up to eight cycles. The specimenafter 1 cycle showed inhomogeneous microstructure in the thickness direction so that the grains near the surface were finerthan those near the center. This inhomogeneity decreased with an increasing number of ARB cycles, and the grain sizes ofthe specimens after 3 cycles were almost identical. In addition, the aspect ratio of the grains decreased with an increasingnumber of ARB cycles due to the subdivision of the grains by shear deformation. The fraction of grains with high angle grainboundaries also increased with continuing process of the ARB so that it was higher than that of the low angle grain boundariesin specimens after 3 cycles. A discontinuous dynamic recrystallization occurred partially in specimens after 5 cycles.Key wordsaccumulative roll-bonding, oxygen free copper, microstructure, electron back scatter diffraction(EBSD).