Mechanism of grain refinement during equal-channel angular pressing in an Al-Mg-Sc alloy

The mechanism of grain refinement of an Al-5.4Mg-0.4Mn-0.2Sc-0.09Zr alloy subjected to equal-channel angular pressing (ECAP) with a back pressure (BP) for up to 12 passes via route BC at 573K (300 °C) was studied. New grains form through a specific mechanism of continuous dynamic recrystallization (CDRX). The formation of microshear bands (MSB) enclosed by a pair of geometrically necessary boundaries (GNBs) and the splitting of initial boundaries to pairs of mutually parallel boundaries plays a vital role in initiation of recrystallization process. Transformation of the 2D lamellar structure to 3D crystallites occurs through the intersection of primary MSBs by secondary MSBs, mainly. Upon further deformation the GNBs evolve to planar sub-boundaries and then to high-angle boundaries. The formation of primary MSBs is associated with the appearance of texture α-fiber, and the appearance of a new type of shear texture, which is an axial {112} texture of orientation around the transverse direction accompanies the formation of ultra-fine grains. © 2016 Advanced Study Center Co. Ltd.