Hiroshi Sawamura and ShirMorita
The authors have observed, in the previous paper [this journal, 6 (1942), 27] regarding the running quality of binary aluminium alloys containing silicium up to 15.69%, the following experimental results that the silicium content of the alloy, taking the minimum value of the running quality is between 3% and 4%, and that this content is higher in silicium than the composition of the maximum solidification temperature range and that the running quality of the hyper-eutectic alloy containing 15.69%Si is far more than that of the eutectic alloy. These phenomena could not be explained by using the solidification range theory of the running qaulity of alloys brought forward by A. Portevin and his collaborators. Therefore, the authors have studied the microscopic structures of the cross sections of the running quality test specimens and have confirmed that it is necessary to take into consideration the super-cooling phenomena in the solidification process of molten alloy flowing in the test mould for clarifying the nature of the running quality. Then, the phenomena above mentioned are reasonably explained as follows : the degree of the super-cooling of the hyper-eutectic alloy containing 15.69%Si is far more than that of the eutectic alloy and as the authors have poured the molten alloy into the test mould at about 50° above the liquidus temperature on the equilibrium diagram, the difference between the pouring temperature and the temperature of the primary crystallization of the hypereutectic alloy is more than that of the eutectic alloy. Consequently,the time interval where the perfectly liquid alloy flows in the test mould in the case of the hyper-eutectic alloy is far more than in the case of the eutectic alloy and the length of flow of the former alloy filled up the test mould is longer than that of the latter. The phenomenon that the running quality of the alloy containing silicium between 3% and 4% takes the mimimum value has not been sufficiently clarified by means of the microscopic study only, but it has been suporsed that the degree of the super-cooling of the alloy containing 3% and 4%Si is less than that of the Si 1.6%-alloy, and consequently this phenomenon takes place.
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