多穴ダイスを組み合わせた異形ダイスによる熱間押出材の結晶粒微細化と高延性化

抄録

  It has been shown using an Al-4.0 mass%Cu alloy as a demonstration material that hot extrusion with the use of a specially-designed die, which is called a heteromorphic die, leads to grain refinement and improvement in ductility. The heteromorphic die consists of two plates and one spacer. One plate is called a strain-giving die and has six holes of 5 mm in diameter, while the other plate is called a shape-giving die and has one rectangular hole of 9 mm×15 mm in side length. The spacer separates these plates at a distance of 10 mm and gives a space between them. The Al-Cu alloy billet was hot-extruded from the strain-giving die into the space between the two dies to produce six thin bars, and all the six bars passed together through the shape-giving die to become a thick rectangular bar. The rectangular bar produced by the present extrusion was tensile-tested at room temperature and the results were compared with those of the un-extruded billet and the bar produced by a conventional hot extrusion using only the shape-giving die. The elongation of the specimens made of the billet, the bar extruded by the conventional method and the one extruded using the present heteromorphic die were 21, 35 and 57%, respectively. The largest elongation found in the sample extruded using the present heteromorphic die should be due to the fine recrystallized grain structure in that sample. It is suggested that the recrystallization is induced by a large strain generated in the present heteromorphic die due to the friction at the large contact area between the die hole wall and the alloy.