Effect of second phase particles on grain refinement during equal-channel angular pressing of an Al-Mg-Mn alloy

The process of grain refinement under severe plastic deformation was examined in an Al-5.4% Mg-0.5% Mn-0.1% Zr alloy, which was subjected to equal-channel angular pressing (ECAP) in the strain interval from 1 to 12 at a temperature of similar to 300 degrees C. It was shown that the size and distribution of the second phase particles precipitated under homogenization annealing strongly affect grain refinement. Extensive grain refinement under ECAP was provided by a dispersion of Al6Mn particles with an average size of similar to 25 nm that precipitated during the homogenization annealing at an intermediate temperature. The fully recrystallized structure with an average crystallite size of similar to 0.55 mu m evolves through continuous dynamic recrystallization. In contrast, homogenization annealing at a high temperature leads to the formation of coarse Al6Mn particles with a plate-like shape. Under further ECAP, the formation of coarse recrystallized grains takes place in this material due to the discontinuous growth of recrystallized grains during the inter-pass annealing between the ECAP passes. The role of second phases in grain refinement is discussed in terms of pinning and driving forces for recrystallization. (C) 2011 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.