Effect of Heat Treatment Condition on the Flow Behavior and Recrystallization Mechanisms of Aluminum Alloy 7055.

The flow behavior and the microstructural evolution of aluminum alloy 7055 in two heat treatment conditions (homogenized vs. pre-rolled, solution treated, stretched and naturally aged (T3)) were investigated for a height reduction of 60% with deformation temperatures ranging from 370 °C to 450 °C and strain rates ranging from 0.01 s(-1) to 10 s(-1). Flow stress decline ratio maps as a function of deformation temperature and strain rate were produced along with processing maps at a strain of 0.8 to reveal optimum hot-working conditions for deformation at strain rates of 0.01 s(-1) to 0.1 s(-1). The results showed that the stress drop ratio during deformation is higher for the homogenized condition than for the pre-rolled, T3 condition. A higher degree of recrystallization after deformation was observed in the pre-rolled, T3 condition due to finer second phase particles, smaller grain size, and more numerous sub-grains. The mechanism for deformation softening is discussed in the context of grain boundary characteristics.