New structural and mechanical features of hexagonal materials after room temperature extrusion using the KoBo method

The paper presents results of investigations on texture, microstructure and mechanical properties of magnesium alloy AZ31 and pure zinc after severe plastic deformation using the KoBo extrusion method at room temperature. The KoBo method combines monotonic metal deformation with cyclic changes of deformation path. It allows realization of an extrusion ratio equal to 100 (true strain epsilon = 4.6) at room temperature using a force of less than 1 MN. At the same time the grain structure is refined to the level of a few micrometers and the material attains unusually high mechanical properties not otherwise available regardless of the thermo-mechanical features. Transmission electron microscopy observations in bright and dark field (weak beam technique) contrast conditions allowed identification of clusters of point defects in the extruded wires. In the light of these observations they are the only elements (nano-size elements) of the metals' structure which can be held responsible for the unusual properties of the wires.