Dynamic recrystallization kinetics and microstructure evolution of 7055 aluminum alloy during hot compression

7055 aluminum alloy is widely used in manufacture of key components in fields of aerospace. Hot forming is the vital process for manufacture of components. Dynamic recrystallization (DRX) plays a significant role in grain refinement. Hot compressions and metallographic tests are conducted. Equations of DRX kinetics are fitted by least square method and finite element models (FEM) coupled with DRX kinetics equations are established to study the effects of forming parameters on microstructure evolution. The results show that true stress increases with ascending strain rate and decreases with ascending temperature. Large strain, small strain rate and high temperature are beneficial to sufficient DRX fraction and grain refinement. Deformation energy and thermally activated motion of atoms and molecules resulting from large strain and high temperature contribute to dynamic nucleation; meanwhile, small strain rate provides sufficient time for growth of recrystallized grains. The FEM results agree with experiments.

An Explanation of the Small Strain-Rate Sensitivity of Ni3Al

ABSTRACTBased on the superkink model, an explanation is given in this paper for the small strain-rate sensitivity of the anomalous yield stress of Ni3Al. The yield stress is proposed to be the stress needed to destabilise the average superkinks and it varies inversely with superkink height. The yield stress is insensitive to the strain-rate because the superkink height is controlled by the rate at which the superkink widens and is not directly related with the superkink propagation speed.