Tetsuichi Motegi1, Atsumi Ohno1 and Su-gun Lim2
1Department of Metallurgical Engineering, Chiba Institute of Technology, Narashino
To refine the grain structure of aluminum ingots, a 99.6 mass%Al melt was oscillated in shell, graphite or chill molds using a rod-type oscillator. The variables which affected the ingot structure were the frequency, the amplitude, and the oscillator position. The frequency range was 10 s-1 to 50 s-1 and the amplitude range was 0.2 mm to 4 mm.
Thermal analysis carried out at various positions in the melt showed that the first solidification occurred on the mold wall touching the molten surface. The authors have already demonstrated that at this position equiaxed crystals are repeatedly formed and separated. Consequently, in most experiments, the oscillator was set horizontally near the mold wall, just below the molten surface.
Increase in the frequency and the amplitude of the oscillator enlarged the equiaxed crystal zone and decreased the grain size.
The oscillator must be heated to a temperature over 973 K, in order to prevent the trapping of the oscillator in the solidifying shell when a chill mold is used.
aluminum ingot, grain refinement, solidification, equiaxed crystal, oscillation, frequency, amplitude
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