On the Principles of the Deformation Methods of Grain Refinement in Aluminum Alloys to Ultrafine Size: II. Ultrafine-Grained Alloys

The applicability and efficiency of the principles of optimum structural heterogeneity and stage-by-stage grain refinement in relation to the formation of an ultrafine-grained (UFG) structure (with a grain size smaller than 1 mu m) in bulk billets during severe plastic deformation are analyzed. The evolution of the criteria of these principles is considered when going from a fine-grained structure to a UFG structure and from conventional deformation treatment to severe deformation treatment. The dependence of the intrinsic mechanisms of grain refinement to ultrafine size on the initial structure of an alloy, including the heterogeneity of the initial structure, is analyzed.