日本金属学会誌

J. Japan Inst. Metals, Vol. 51, No. 11 (1987),
pp. 1076-1083

Formation of Accumulation Zone Composed of Equiaxed Crystals in Al-Cu Alloy Ingot

Masayuki Kudoh1 and Tadayoshi Takahashi1

1Department of Metallurgical Engineering, Faculty of Engineering, Hokkaido University, Sapporo

Abstract:

As the molten metal in the upper part of a crucible was stirred, equiaxed crystals occured in the stirred part, settled down, and accumulated succesively on the bottom of the crucible.
In this study, the method was applied to an Al-4 masal%Cu molten alloy in the graphite crucible placed in a furnace having a temperature gradient. When the temperature in the lower part of the melt was lower than that in the upper part of it, chrysanthemum-like crystals and comparatively large liquid areas are observed in the accumulation zone, and the liquid areas may result in the formations of porosity and semimacrosegregation. Inversely, when the temperature in the lower part of the melt was high, the morphology of crystals was changed from chrysanthemum shape to granular one and they were filled in uniformly in the accumulated zone. The volume fractions of solid of the specimens under both thermal conditions, which were quenched at various stages of the stirring, were larger than that estimated by Pfann's equation, but the measured values agreed approximately with the estimated ones in the cooling process after stirring. Furthermore, a fraction solid, above which the liquid cannot flow through the networks of the equiaxed crystals, is about 0.55.


(Received 1987/5/16)

Keywords:

equiaxed crystal stirring, accumulation, liquid pare, porosity, semimacrosegregation, solidification zone, aluminum-copper allay, ingot structure


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