Microstructure of Polycrystalline Zinc Subjected to Plastic Deformation by Complex Loading / Mikrostruktura Polikrystalicznego Cynku Odkształconego Plastycznie W Złozonym Schemacie Deformacji

Abstract

Polycrystalline, high purity (99,995%) zinc ingot was subjected to KoBo type extrusion in room temperature. Material was extruded to form of a 2 mm diameter wire, extrusion die oscillated during process by an angle ±8_ at a frequency of 5 Hz and the extrusion speed was 0.5 mm/s. Final product was tested for tensile strength and yielded R0;2 ≈ 150MPa and Rm ≈ 250MPa. Microstructure of both extruded and initial materials was investigated by means of high resolution Electron Backscatter Diffraction (EBSD) in Quanta 3D FEG scanning electron microscope (SEM). Observations revealed that microstructure of extruded zinc sample is highly heterogeneous and consists of grains elongated slightly in the direction of extrusion. Grains dimensions ranges from over one hundred microns down to submicron scale while grains in the non-deformed material are equiaxed with mean diameter of approximately 200 microns. Other microstructure features such as intergranular bands and partly fragmented primary grains with subgrain structure are observed. Furthermore detailed study of local microstrains by Imaqe Quality Factor analysis are performed. Presence of Geometrically Necessary and Statistically Stored Dislocations is assessed. Thick areas of highly distorted lattice adjacent to High Angle Grain Boundaries are revealed. Microstrain mapping suggest composite-like microstructure of deformed material, that might explain its superior mechanical properties.