Homogenization of Microstructures and Improvement of Mechanical Properties in Cu–Al and Cu–Si Alloys by Rheocasting

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.