An investigation was made for the improvement of microstructures and mechanical properties at an elevated temperature in Al-Cu alloys containing 10, 24, 30 mass% copper, Al-8 mass% Si and Al-4 mass% Ni alloys rheocast with the rotation of a stirrer at a high speed in the range from 20 to 67 rev/s. It was found that the relation among the size, d, of primary solid particles formed by fragmentation of dendritic crystals, copper content, C0, and rotation speed of stirrer can be expressed by the following empirical equation:d=K(33 -C0)n for n=0.32, where K is a constant determined by the stirrer speed. The apparent viscosity of Al-Cu alloys was evaluated during the solidification with high-speed rotation of stirrer. Rheocast microstructures in Al-8%Si and Al-4%Ni alloys are compared with those in Al-Cu alloys on the basis of microscopic observations. The maximum stress and total elongation of the Al-30% alloy ingot rheocast at a rotation speed of 33 s-1 are 24.0-28.5 MPa and 71%, repectively, while those of the Al-24% alloys are 19.7-21.2 MPa and 63-86s at 33 s-1 and 21.2-22.7 MPa and 79-91% at 67 s-1, respectively.
(Received January 30, 1988)
Keywords: rheocasting, stir-casting, aluminum-copper alloy, aluminum-silicon alloy, aluminum-nickel alloy, primary solid particle, grain refinement, apparent viscosity, elevated temperature tensile test, elongation
* A part of this paper was originally published in Japanese in Sosei to Kako (J. Japan Society for Technology of Plasticity), 27 (1986), 403.
** Mechanical Engineering Laboratory, Agency of Industrial Science and Technology, Tsukuba, Ibaraki 305, Japan.
*** Research and Development Center, Suzuki Motor