Microstructural characteristics and formation mechanism of adiabatic shear bands in Al-Zn-Mg-Cu alloy under dynamic shear loading

The microstructural characteristics and formation mechanism of adiabatic shear bands in ultra-high strength aluminum alloy are studied under dynamic shear loading. It is found that thermal softening alone is insufficient to trigger the initiation of adiabatic shear bands (ASBs). Dynamic recrystallization induced softening is attributed to be the main cause of ASB initiation, with temperature rise playing a secondary role by accelerating the deformation localization process. It is believed that abrupt temperature rise takes place after ASB initiation, and the temperature rise prior to ASB formation is relatively small. Recrystallized ultrafine grains with a strong texture of {112} < 110 > are formed in ASBs, based on a progressive subgrain misorientation recrystallization mechanism. It is proposed that the translational-rotational motion of the dynamically recrystallized nanograins in the form of vortexes at the mesoscale can account for the microstructural softening, thus causing shear instability, eventually leading to fracture by the combination of ductile and brittle failure mechanisms.