Effect of microstructural heterogeneity on the balanced-biaxial and tensile behavior of a Zn alloy sheet

Abstract

A 0.65 mm thick Zn sheet was processed at room temperature by equal channel angular sheet extrusion (ECASE), which allowed for the fabrication of a heterogeneous material. The processed sheet's heterogeneity manifested as larger dislocation clusters and smaller grain sizes on the surface than in the sheet's center, generating as well a 35% increase in yield strength while preserving a fracture elongation of 26%. ECASE processing resulted in a slightly higher deformation limit than that of the as-received material with a weight reduction of 9%. The improvement in the processed sheet's mechanical properties was associated with the formation of twins on the surface, resulting in a smaller grain size and heterogeneity between the twins-free and twinned grains. These two microstructures produced a combination of hard and soft zones. ECASE processing formed twins in particular grains that in turn created a high density of geometrically necessary dislocation (GND) arrays in twin-free neighboring grains. It should be noted that the twinned grains had a low density of geometrically necessary dislocations (GND). In addition to the heterogeneity between twinned and twin free grains, a heterogeneous GND distribution was formed between the surface and the processed sheet's center, with the basal slip system dominating.