Grain refinement in as-cast 7475 aluminum alloy under hot equal-channel angular pressing

Microstructural evolution taking place during equal channel angular pressing (ECAP) was studied in an as-cast 0.16%Zr modified 7475 aluminum alloy at a temperature of 673 K. The structural changes are characterized by development of deformation bands due to large strain inhomogeneity occurring through the ECAP die. Repeated deformation leads to an increasing of number and misorientation angle of the boundaries of deformation bands, finally followed by formation of new fine grains at high strains. The misorientation angle distribution for newly developed boundaries shows a single peak type at relatively low misorientations in low strain and changes to a bimodal distribution with two peaks at low and high misorientations in moderate strain. Pressing to a strain of 12 leads to a full development of new grains surrounded by medium to high angle boundaries with an average size of about 1.7 mum. It is concluded that grain refinement occurs by a deformation-induced continuous reaction, that is essentially similar to continuous dynamic recrystallization.