Refinement and Localization of Primary Intermetallic Compound in Hyperperitectic Al–Cr Alloy by Centrifugal Duplex Casting

A novel process named Centrifugal Duplex Casting has been proposed: It is a manufacturing process of an aluminum cast pipe with an in-situ composite layer which contains fine intermetallic crystals. In this process, two kinds of molten metal, i.e. molten aluminum (the first melt) and molten Al–Cr alloy with higher liquidus temperature (the second melt), are cast in sequence at a given interval into the rotating mold of a centrifugal caster. The second melt collides with the meniscus of the first melt, and is dispersed as a great number of fine fluid clumps. These fluid clumps are rapidly quenched, migrate toward the outer periphery, and accumulate to form the composite layer. The particle size of the intermetallic crystals in this composite layer is much smaller than that of the Al–Cr alloy centrifugally cast by a conventional process. The solidification structure of the cast pipe produced by Centrifugal Duplex Casting is controlled by cooling capacity of the first melt. For instance, when the first melt has superheat at the moment of the second-melt casting, coarse intermetallic crystals grow inside of the refined composite layer. On the other hand, when the first melt has partially been solidified, the growth of the intermetallic crystals is suppressed. Therefore, the time interval between the two casting operations is an important parameter in this process