MICROSTRUCTURES AND TENSILE PROPERTIES OF RHEOCAST AL-CU, BI-SN AND BI-PB EUTECTIC ALLOYS

An investigation is made on the microstructures and properties in Al-Cu, Bi-Sn and Bi-Pb eutectic alloys rheocast at a high rotation speed of 70 rev/s of a stirrer, which has been immersed in the vacuum-melted alloys, inside a water-cooling outer tube. The results are summarized as follows. (1) It is observed that the microstructure of Al-33 mass%Cu alloy ingot rheocast at a rotation speed of 70 s-1 is a colony structure in which the eutectics with a dense lamella of two phases are surrounded by those of a coarse lamella of two phases. This morphology is almost the same as the microstructure of conventionally cast Al-33%Cu alloy ingot. (2) It is observed that the microstructures of Bi-43 mass%Sn and Bi-44.5 mass%Pb alloy ingots are “Chinese script” eutectic structures with scattering oval regions in the discontinuous eutectic matrix. The structures of the oval regions are primary solid particles in both alloys, but the eutectics are formed with the precipitation of lamellae of two phases will be formed with precipitation of bismuth crystals in the oval region after the solidification of the Bi-44.5%Pb alloy. (3) The elongation value of Al-33%Cu alloy ingot rheocast at a rotation speed of 70 s_1 is 263% for a strain rate of 9.26 × 10-4 s-1 at a temperature of 773 K. (4) The elongation values of Bi-43 %Sn alloy ingot rheocast at a rotation speed of 70 s-l are 25 to 31% for a strain rate from 0.93 × 10-4 to 4.63 × 10-4 s-1 at 293 K. (5) The elongation values of Sn-44.5%Pb alloy ingot rheocast at a rotation speed of 70 s-1 are 31 to 40% for a strain rate of 0.93 × 10-4 to 4.63 × 10-4 s-1 at 293 K. The elongation value of the alloy ingot is 75% for a strain rate of 1.85 × l0-4s-1 at 323 K. © 1990, The Japan Institute of Metals. All rights reserved.