Tadayoshi Takahashi1, Masayuki Kudoh1 and Keiichi Yodoshi2
1Department of Metallurgical Engineering, Faculty of Engineering, Hokkaido University, Sapporo
Using the authors' method that an artificial hole was made in the solid-liquid coexisting zone, the interdendritic liquid was allowed to flow into the cylindrical hole or the wedgewise concavity for different fractions of solid. The healing phenomena in relation to hot tearing were pursued by the formation mechanism of dendrites within the liquid flowing into the hole.
The results on an Al-3 mass%Si alloy are summarized as follows.
(1) When the diameter of the cylindrical hole was above 4 mm, the occurrence of crystals was recognized in the hole and the hole was healed. In case of the hole of 2 mm diameter, a narrow shrinkage pipe was observed in the central part of the hole.
(2) The formation of the dendrites within the hole becomes possible with increasing diffusion distance of solute in the liquid in front of the dendrites developing from the wall of the hole towards the center of it, because the degree of constitutional undercooling in the central part of the hole increases with increasing the diffusion distance. In the hole of 2 mm diameter without crystallization, the liquid in front of growing dendrites is promoted to be enriched in solute and the solute-rich liquid is utilized as the source of feeding against the solidification contraction of the specimen, so that a shrinkage pipe is formed.
(3) The experimental results of the healing phenomena in case with holes of several diameters could be reappeared with the wedgewise concavity which was made by the procedure similar to the formation of the cylindrical hole in the solid-liquid coexisting zone.
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