Formation of grain boundaries in magnesium single crystal during equal channel angular pressing

Abstract

Magnesium single crystal was deformed by equal channel angular pressing (ECAP) in order to investigate formation of grain boundaries from the boundary-free structure. Microstructure and microtexture were analysed with electron backscattered diffraction technique before and after passing the theoretical shear plane of the ECAP die. The microstructure of the single crystal deformed in compression before passing the theoretical shear plane consisted of massive {1 0 2} twins. After passing the shear plane, the twinned microstructure was gradually fragmented via shear. Simultaneously, continuous dynamic recrystallization was observed, starting with formation of low-angle grain boundaries (LABs) with different misorientations. New recrystallized grains were formed on LABs via bulging and close to high-angle boundaries via accumulation of dislocations. Long and straight LABs formed perpendicular to the (0 0 0 1) slip plane with misorientations around 〈1 0 0〉 axis were frequently observed in twins interiors and were found to be formed further within the recrystallized grains causing fragmentation into smaller grains. While in twinned areas, the recrystallization was enhanced, in fragments with initial orientation (c-axis parallel to transverse direction of the ECAP die), it was suppressed.