Grain refinement behavior of magnesium alloy AZ31 under torsion extrusion -Research works accomplished by using Electron Microscope System : XXI(3)

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Magnesium alloy AZ3 l was used to investigate the influence of temperature and speed ratio (= die rotation speed / extrusion speed) on the grain refinement behavior and crystal orientation in torsion extrusion using circular type dies with differemt outlet-hole diameters. For each die, the optimum temperature and the speed ratio required to obtain a uniform distribution of 卜2μmfine grains over the entire cross section of the specimen were clarified. The torsion-extruded specimen had a very different crystal orientation than that of the extruded specimen. At a temperature of 443 K, the torsion-extruded specimen tended to form a strong texture along the extrusion axis, especially in the center region of the cross section. In contrast, the conventional extrusion sample had many grains in the direction perpendicular to the extrusion axis. When the outlet-hole diameter was the largest, the torsion-extruded specimen exhibited a strong texture along the extrusion axis over a wide area of the cross section. In conclusion, both the grain size and the texture of the metals could be controlled over a wide range by changing the die-hole diameter and the speed ratio in torsion extrusion.