| Budget Amount *help |
¥2,100,000 (Direct Cost: ¥2,100,000)
Fiscal Year 1987: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1986: ¥600,000 (Direct Cost: ¥600,000)
Fiscal Year 1985: ¥900,000 (Direct Cost: ¥900,000)
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| Research Abstract |
In this study, promoting factors for the occurence of fine equiaxed crystals were found by the suitable selection of casting conditions, and methods for the control of the area and grain size of the equiaxed crystals were established. The results obtained were summarized as follows.
(1) As the columnar dendrite with a peaked tip morphology grew rapidly in the liquid with high temperature, the degree of supercooling decreased in the liquid in front of the dendrite and the tip morphology varied elliptical shape according to the slow growth of the dendrite. Subsequently a chance of nucleation in the liqued occurred because the conditions for the nucleation and the stability of the equiaxed crystals were established according to both effects of the drop of solidification temperature due to solute enrichment and fall in actual temperature of the liquid, although the chance of the nucleation did not occur in the stage of rapid growth of the dendrite because of insufficient time for the nucleation.
(2)(a) As a concrete casting method for the promotion of the transition from columnar to equiaxed, it is effective to use, in laboratory scale, the graphite mold with a thin thickness. (b) The duplex casting is also effective one. For an example, a large amount of A1-3mass%Si alloy as a primary molten metal is poured into the mold, and when the columnar growth is delayed, a small amount of pure aluminum as a secondary molten metal is poured into the solidifying primary molten metal in order to elevate the solidification temperature and stimulate the occurence of the equiaxed crystals.
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