Plastic deformation in relation to microstructure and texture evolution in AA 2017-T451 and AA 2624-T351 aluminum alloys under dynamic impact loading

Abstract

Mechanical and microstructural responses of AA 2017-T451 and AA 2624-T351 aluminum alloys to dynamic impact loading were investigated using the split Hopkinson pressure bar (SHPB) and electron backscattered diffraction (EBSD) analysis. Although both alloys were subjected to the same impact loads, the strain rate developed in the AA 2017 alloy was higher and the peak stress in the dynamic stress–strain curve is observed to be higher for the AA 2624 alloy. The higher deformation resistance observed in the AA 2624 alloy under dynamic impact loading is a consequence of its higher capacity for strain hardening that effectively overcomes the effects of thermal softening and dynamic recovery during impact loading. Strain hardening is quickly dominated by thermal softening in AA 2017-T451 alloy leading to a lower resistance to deformation and a higher tendency to form transformed adiabatic shear bands consisting of dynamic recrystallized (DRX) grains as observed in the EBSD measurements. Although shear bands were also observed in the AA 2624 alloy, EBSD analyses suggest that the shear band region consist of deformed grains with high intensity of localized strains and dislocation accumulation. Whereas both alloys exhibited nearly the same high angle grain boundary fractions before dynamic impact loading, a higher in-grain (kernel) misorientation were observed in the AA 2624 alloy after impact. Larger fraction of high angle grain boundaries (HAGBs) was observed in the impacted AA 2017 alloy. The results of the EBSD measurements on both the as-received alloys and the impacted specimens such as grain boundary fractions, area fractions of selected fibers as well as Schmid factor and the corresponding Schmid factor distribution are discussed. The study provides a consolidated understanding of the microstructure developments during deformation and its relation to the mechanical response of the alloys to dynamic impact loading.