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

Experiments were conducted to evaluate the influence of the pressing temper ature when materials are processed by equal-channel angular pressing. The t ests 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 t o sufficiently high strains to give homogeneous microstructures. The result s show two important effects. First, the measured grain size tends to incre ase with increasing pressing temperature. Second, grain refinement is achie ved at all temperatures but there is a transition from arrays of high angle boundaries at the lower temperatures to low angle boundaries at temperatur es at and above 473 K in pure Al and at 573 K in the Al-3% Mg alloy, wherea s the Al-30% Mg-0.2% Sc alloy exhibits high angle boundaries at all pressin g temperatures. The inability to achieve high angle boundaries at the highe r pressing temperatures in these two materials is attributed to the higher rates of recovery which lead to dislocation annihilation rather than the ab sorption of dislocations into the subgrain walls. (C) 2000 Elsevier Science S.A. All rights reserved.