Homogenization of Microstructure and Improvement of Mechanical Properties in Cu-Al and Cu-Si Binary Alloys by Rheocasting

Abstract

An investigation is made on the homogenization of microstructure 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 eutectoid are observed in the rheocast Cu-Al alloys. The elongation values for a strain rate of 1.85×10⁻⁴ s⁻¹ at 973 K are 162% in Cu-8%Al alloy rheocast at a rotation speed of 50 s⁻¹, 178% in Cu-9.5%Al alloy rheocast at 60 s⁻¹, 174% in Cu-10%Al alloy rheocast at 40 s⁻¹ and 141% in Cu-7%Si alloy rheocast at 25 s⁻¹. The elongation values for a strain rate of 1.85×10⁻⁴ s⁻¹ at 1073 K are 176% in Cu-8%Al alloy rheocast at rotation speed of 25 s⁻¹, 148% in Cu-9%Al alloy rheocast at 40 s⁻¹ and 192% in Cu-7%Si alloy rheocast at 25 s⁻¹. It is also 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 the mechanical properties in their rheocast alloy ingots with those in the conventionally cast ones.