Influence of pressing temperature on microstructural development in equal-channel angular pressing

Experiments were conducted to evaluate the influence of the pressing temperature when materials are processed by equal-channel angular pressing. The tests were conducted using samples of pure Al, an Al-3% Mg alloy and an Al-3% Mg-0.20% Sc alloy at temperatures up to 573 K. All samples were pressed to sufficiently high strains to give homogeneous microstructures. The results show two important effects. First, the measured grain size tends to increase with increasing pressing temperature. Second, grain refinement is achieved at all temperatures but there is a transition from arrays of high angle boundaries at the lower temperatures to low angle boundaries at temperatures at and above 473 K in pure Al and at 573 K in the Al-3% Mg alloy, whereas the Al-30% Mg-0.2% Sc alloy exhibits high angle boundaries at all pressing temperatures. The inability to achieve high angle boundaries at the higher pressing temperatures in these two materials is attributed to the higher rates of recovery which lead to dislocation annihilation rather than the absorption of dislocations into the subgrain walls. (C) 2000 Elsevier Science S.A. All rights reserved.