Centrifugal casting of Al-Cr semi-solid slurry produced by stir-mix-quenching

摘要

We propose a novel process for producing tubular in-situ composite castings, in which fine intermetallic crystals are concentrated near the outside surface. In this process, two kinds of molten metals with different compositions are mixed with agitation in a mixing vessel to produce semi-solid slurry containing fine intermetallic crystals, and then the slurry is centrifugally cast. The authors call the first stage of the process "stir-mix-quenching." In the stir-mix-quenching experiments, molten aluminum was used for "the first melt" which acts as a coolant, and a hyperperitectic Al-Cr alloy melt with a higher liquidus temperature was used for "the second melt," which is rapidly quenched to precipitate numerous fine primary crystals when it is brought into contact with the first melt. The structure of the composite layer in the cast pipe produced by the centrifugal casting of the mixed-alloy slurry varies with the casting temperature of the slurry. When the casting temperature is higher than the final peritectic temperature, the intermetallic crystals are distributed uniformly in the composite layer. However, when the casting temperature is excessively high (for instance, 50 K higher than the final peritectic temperature), relatively coarse intermetallic crystals form near the boundary between the composite layer and the intermetallic-free region. On the other hand, the growth of the intermetallic crystals is suppressed when the casting temperature is in the neighborhood of the final peritectic temperature.