EBSD characterization of shear band formation in aluminum armor alloys

The shear-compression behavior of four commercial aluminum armor alloys, 2139, 2519, 5083, and 7039, that exhibit enhanced resistance to high-strain-rate deformation, were evaluated using a Split Hopkinson Pressure Bar. Each of the alloys was found to exhibit a characteristic critical equivalent strain beyond which plastic collapse of the material occurred. Microstructural changes were systematically quantified as a function of equivalent strain using electron backscatter diffraction along with the effects of crystallographic orientation, secondary particles, and solid solution strengthening on the accumulation of localized strain within the microstructure. The onset of the plastic collapse was determined to correlate with an equivalent strain where nominally all of the grains within the microstructure exhibited characteristics associated with adiabatic shear band formation. The rapid decline of the flow stress during plastic collapse was found to be enhanced by grain fragmentation and refinement in regions of high stress concentrations. Results from this study suggest that improvements in the performance of these Al armor alloys may potentially be achieved through careful control of their processing, in particular with respect to their texturing and the dispersion of secondary particles in the microstructure.