The equations of dislocation kinetics were used to theoretically analyze the mechanism of strain hardening and the formation of fragmented dislocation structures in metals at large plastic strains. A quantitative analysis of the available data on Al and an Al-Mg alloy showed that strain hardening at large plastic strains and the formation of fragmented dislocation structures were related to the interaction and self-organization of geometrically necessary dislocations. On the micro-scale, the source of the geometrically necessary dislocations was a locally non-uniform plastic deformation induced by a dislocation-density gradient in dislocation-cell boundaries.

Mechanism of Strain Hardening and Dislocation-Structure Formation in Metals Subjected to Severe Plastic Deformation. G.A.Malygin: Physics of the Solid State, 2006, 48[4], 693-9