On this first report, the mechanism of grain refinement of Al by a small addition of Ti was investigated. That is: (a) the effects of Ti contents on the grain size (b) the effects of casting and the melting condition on the grain size (c) the analysis of the precipitates extracted from the slowly cooled ingot and the casting solidified under centrifugal force were studied. The results obtained are as follows:—(1) The Ti content which refined the grain size markedly coincides with the contents at the periptectic point of the Al side diagram of Al-Ti system (0.15%Ti). (2) The range of Ti content effective for grain refining of the castings solidified under centrifugal force and slowly cooled ingots is above 0.15%Ti and the large amount of the precipitates extracted from this range is TiAl
3, though TiC increased when the melt was treated by CCl
4. (3) The grain size depends upon the super-heating temperature, especially in the case the melt is treated by CCl
4, even if the casting temperature is constant. (4) According to (2) and (3), this effect seems to be based on the formation of TiC, and TiC is stable up to about 30° above the liquidus, because the grain size of the specimen cast up to this temperature is refined markerdly. (5) As above mentioned, in the case of grain refining of super pure Al by small addition of Ti, both TiAl
3 and TiC may act as the nuclei during solidification.
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