Microstructure transformation from lamellar to equiaxed microduplex through equal-channel angular pressing in an Al-33 pct Cu eutectic alloy

Strain-driven transformation of a lamellar structure into a homogeneous equiaxed microduplex structure was investigated in an eutectic Al-33 pct Cu alloy deformed by equal-channel angular pressing at 400 °C via route Bc. In route Bc, the rotation of sample is always 90 deg in the same sense, i.e., clockwise or counterclockwise. The transformation follows the subdivision of the colonies into smaller lamellar blocks, the separation of these lamellar blocks into isolated islands, and, finally, the shrinkage of these islands to disappear, through the breaking down of the lamellae near the boundaries of the lamellar block-and-equiaxed region. The kinetics of the strain-driven microstructure transformation process, described by the dependence of the relative lamellar area fraction on equivalent true strain accumulated by equal-channel angular pressing (ECAP), physiognomically resembles that of the thermally activated transformation process described by the Johnson-Mehl-Avrami-Kolmogorov (JMAK) model for the recrystallization process.