Flow localization in an Al-2.5Mg alloy after severe plastic deformation

AA5052 was subjected to severe plastic deformation using the equal channel angular pressing (ECAP) technique. The microstructure, quantified using electron backscattered diffraction, showed that ECAP refined the grain size, increased the fraction of high angle boundaries (from 0.46 to 0.75) and increased total boundary area per unit volume of AA5052. ECAP increased the flow stress from about 325 to 425 MPa and strain rate sensitivity from 0.005 to 0.012 and reduced strain hardening exponent from 0.34 to 0.25. Shear localization in the ECAP as well as unpressed AA5052 was studied using hat-shaped samples deformed at both quasi-static strain rates in a screw-driven machine and dynamic strain rates in a split-Hopkinson bar. The shear band formation in the hat-shaped sample was narrow and well defined for the ECAP condition as compared to the unpressed condition where the shear band was broad and diffuse, implying an increased propensity for shear localization as compared to the unpressed condition. The microstructure within the shear band of the ECAP condition sample showed that the boundary area per unit volume decreased as compared to that away from the shear band.