Large straining behavior and microstructure refinement of several metals by torsion extrusion process

A torsion extrusion process is proposed as a new method for introducing very large strain into metals in order to get very fine grained structure. This method is characterized by rotation of a die or a container along its axis during an extrusion process. Experiments were performed to investigate the deformation characteristics and inspect microscopic structure, using an aluminum and a magnesium alloy specimen. From these experiments, it became clear that there exist an optimum die condition and a temperature condition, in which fracture does not occur on the specimen surface and the grain size becomes very fine. The mean representative strain in the cross section of the specimen reached about 40 in the case of 40 rotations of the die. The mean size of grains was found to be under I micrometer in both the aluminum and the magnesium alloy used. The torsion extrusion process may have a possibility to become a mass production process for so-called ultrafine-grained metals, as the very high strain can be induced to metals by only one pass deformation without repetition of working.