In-depth investigation of microstructure evolution rules and flow localization characteristics in high strain rate deformation is helpful to improve the forming limit and forming accuracy of electromagnetic forming process. In present study, split Hopkinson pressure bar tests were carried out to obtain high velocity deformation with initial strain rate ranging from 1000s-1 to 5000s-1. Then, post-deformation samples of 5A06 alloy were analyzed with the aid of metallographic, SEM and TEM instruments. With the increase of strain rate, equiaxed a grains are elongated with an orientation perpendicular to the loading axis and the aggregated p grains become dispersively distributed along the grain boundaries. Adiabatic shear bands occur with elongated voids and band-like structures inside when the strain rate further increase to 4200s-1. Multi-slips operate at the same time and the dislocation structure patterns change from dislocation clusters to dislocation bands and stack faults and then to grain-like structures of approximately 500nm in size with the increase of strain rate. The absolute temperature of adiabatic shear band zone is calculated to be 442K utilizing mathematical model developed in this work, indicating that the grain-like structures could be in-situ sub-grams rather than recrystallization grains.
Yan, S., Yang, H., Li, H., & Yao, X. (2014). Microstructure evolution and flow localization characteristics of 5A06 alloy in high strain rate forming process. In Procedia Engineering (Vol. 81, pp. 1198–1203). Elsevier Ltd. https://doi.org/10.1016/j.proeng.2014.10.097