An investigation has been made on the homogenization of microstructures and the improvement of mechanical properties in Cu-Al binary alloys containing 8, 9, 9.5 and 10 mass% aluminum and Cu-7 mass% Si alloy produced by the vacuum rheocasting, in which solidifying alloys are vigorously agitated at high rotation speeds from 16 to 60 rev/s of a stirrer immersed in the alloys. The results are as follows: The torque values in Cu-8%Al and Cu-7%Si alloys with rotation of stirrer at a speed of 50 s-1 are higher than those at a speed of 25 s-1. Homogeneous microstructures are formed by fragmentation of columnar dendritic crystals by the rotation of stirrer at high speeds during the solidification of Cu-8% Al, Cu-9%Al and Cu-9.5%Al alloys. Oval primary solid particles coexisting with eutectoids are observed in the rheocast Cu-Al alloys. The tensile tests of the rheocast and conventionally cast Cu-Al and Cu-Si alloy pieces have been also done for the strain rates of 0.93× 10-4 to 9.26×10-4 s-1 at 973 and 1073 K. It is found that the ductility in Cu-Al and Cu-Si alloys at elevated temperatures is strongly improved only by the high-speed rheocasting in comparison with that in the conventionally cast ones.
(Received April 21, 1989)
Keywords: rheocasting, stir-casting, solidification microstructure, homogenization, primary solid particle, copper-aluminum alloy, copper-silicon alloy, elongation, ductility, elevated temperature tensile test
*This paper was originally published in Japanese in J. Japan Inst. Metals, 52 (1988), 109.
**Mechanical Engineering Laboratory, Agency of Industrial Science and Technology, Tsukuba, Ibaraki 305, Japan.
***Research and Development Center, Suzuki Motor Co., Ltd., Kami-mura, Shizuoka 432-91, Japan.