Grain refinement in aluminum alloy 2219 during ECAP at 250 °C

Grain refinement taking place in a coarse grained 2219 aluminum alloy deformed by equal channel angular pressing (ECAP) at a temperature of 250 °C to a strain of 12 was investigated. The microstructural changes are mainly characterized by the evolution of high density dislocation substructures with relatively low misorientations (∼3–5°) at strains below 2 and deformation bands (DBs) with moderate misorientation angle, which are frequently formed at strains above 3. Repeated ECAP leads to increasing the number and misorientation angle of the boundaries of DBs, so that the misorientation distribution for newly evolved dislocation subboundaries changes from single peak type at low strains to bimodal one at high strains. The fraction of high angle boundaries starts to increase at strain ɛ = 3, then it rapidly rises to about 80% at moderate to high strains and a new fine grains with almost random crystal orientation are fully developed in a whole material. The main mechanism of new fine grained structure formation during ECAP is discussed.