Abstract
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.
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