日本金属学会誌

J. Japan Inst. Metals, Vol. 17, No. 8 (1953),
pp. 397-401

On Casting Segregation of Al Alloys (1st Report)

Shigeo Muromachi


Abstract:

The phenomenon of the ``inverse segregation'' in Al alloys, especially in duralumin ingots is well known, but the mechanism of the phenomenon is not clear yet, and so, the author made an investigation on the said phenomenon. Specimens were prepared from Al-Cu (4%) ingots which were melted and crystallized in a mould cooled on one side (Fig. 1). From the cooled plane to the other side of the ingots, the hardness of each grain was measured using a micro-hardness tester, and chemical analyses and microscopic determinations were made. Similar experiments were carried out with Al-Si and Al-Cu-Si ingots. Between the chill and columnar layer of the ingots, the auther has found a minimum in Cu content and also in the hardness of the α phase, and the position of this minimum point (Fig. 7) differs from that hitherto known. This minimum point moves towards the inside of the ingot with the increase of cooling rate. The occurrence of this minimum point seems to be explained by the theory of super-cooling. Besides, the auther has found a maximum in Cu content and also in the hardness of α phase at the end of the columnar layer, and moreover, it has been found that two kinds of dendrites having different hardness occur at the same end of the columnar layer (Fig. 8). These phenomena may be explained by the volume contraction theory, that is, the volume contraction due to the rapid solidification acts to attract the residual melt of high concentration, and the melt crystallizes there into dendrites of high concentration and also into eutectics.


(Received 1953/2/26)

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