Continuous dynamic recrystallization in an Al-Li-Mg-Sc alloy during equal-channel angular extrusion

An Al-Li-Mg-Sc alloy with an initial grain size of similar to 60 mu m was processed by equal-channel angular extrusion (ECAE) at 300 degrees C up to a total strain of 12. Transmission electron microscopy (TEM) and orientation imaging microscopy (OIM) were employed to establish the mechanism of grain refinement. It was found that new ultrafine grains evolved by a strain-induced continuous process, which is termed continuous dynamic recrystallization (CDRX). At epsilon similar to 1, a well-defined subgrain structure had developed. Upon further straining the average mis-orientation of deformation-induced boundaries increased; low-angle boundaries (LAB) gradually converted into true high-angle boundaries (>= 15 degrees) (HAB). At epsilon similar to 4, arrays of boundaries with low and high angle mis-orientations were observed. At epsilon similar to 12, a structure dominated by HAB with an average grain size of similar to 0.9 mu m was formed. This size is roughly similar to that for subgrains developed at preceding strains. It was shown that CDRX occurs homogeneously; the formation of new grains takes place both along initial boundaries and within interiors of original grains as well. (c) 2005 Elsevier B.V. All rights reserved.