| 摘要 |
PURPOSE:To reduce the amt. of the surface to be machined and to improve the yield of a product by casting continuously aluminum (alloy) in such a way that the content of boron at the point of >=30mm. thickness from the surface of a ingot in the thickness direction thereof and a cooling rate maintains a specific relation. CONSTITUTION:Aluminum or an aluminum alloy contg. boron is melted. The molten aluminum or aluminum alloy is then continuously cast at the relation between the content B(ppm) of boron at the point of >=33mm. thickness from the surface of a ingot in the thickness direction thereof and a cooling rate R( deg.C/sec) which is so controlled as to attain the area above the straight lines connecting the points a(B=0, R=7), b(B=3, R=7), c(B=3, R=11), d(B=25, R=5) shown in the figure. The outside structure of a fir is thickly formed by the above-mentioned method, by which the amt. of the surface to be machined is reduced and the yield of the product is improved.
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