Unveiling the initiation and evolution mechanisms of adiabatic shear band in extruded 7003 aluminum alloy under high-speed impact load

Abstract

The initiation and evolution of adiabatic shear band (ASB) were investigated in extruded 7003 aluminum alloy. The main objectives are to clarify the sequence of typical events in the high-speed impact deformation process. High-speed impact tests were conducted on cylindrical samples using a split Hopkinson pressure bar (SHPB) at a strain rate of 2200 s−1. The results reveal several key findings. Firstly, ASB initiation occurs after peak stress. In this study, the critical strain required for ASB initiation is 0.33 in the entire sample and 1.95 in the local deformation region. ASB initiation is attributed to material softening caused by temperature rise of the sample under high-speed impact load. Secondly, the temperature rise and recrystallization occurring inside the ASB are the results of the ASB evolution. The initial stage of ASB evolution manifests as deformed ASB (DASB) with elongated fiber grains. Subsequently, rotational dynamic recrystallization takes place within the DASB, eventually transforming into transformed ASB (TASB) characterized by fine equiaxed grains. Furthermore, the plastic deformation within DASB is dominated by strain hardening behavior, while within TASB, it is dominated by softening behavior. Notably, within the DASB, a significant proportion, specifically 81%, of the grain boundaries exhibit small angle of less than 6°. However, within the TASB, the grain boundaries gradually develop into random distributions. The sequence of typical events during high-speed impact deformation is identified as follows: stress peak, temperature rise of the sample, ASB initiation, ASB propagation, temperature rise within ASB, and dynamic recrystallization within ASB.