Effect of interactions between bubbles and graphite particles in copper alloy melts on microstructure formed during centrifugal casting: Part II. Experiments

During centrifugal casting of copper alloys containing graphite particles, both particles and bubbles move under the influence of centrifugal forces a nd influence the final microstructure, including porosity and the distribut ion of graphite. The movement of graphite particles and bubbles in the melt s of copper alloys, originally containing 7 and 13 vol pet graphite particl es and centrifugally cast at 800 and 1900 rpm in horizontal rotating molds, has been examined. Microstructural observations of sections of these centr ifugal castings show that the graphite particles are segregated near the in ner periphery and the amount of porosity in the graphite-rich zone is highe r than the porosity in the graphite-free and transition zones. The intimate association of porosity with graphite particles in the graphite-rich zone was explained on the basis of attachment of graphite particles to bubbles i n the melt and the viscosity of the melt, which increases with increasing c oncentration of graphite particles near the inner periphery of the castings . It was found that the amount of the porosity in the graphite-rich zone in creases with volume fraction of graphite particles used in this study; the size of the porosity in the graphite-rich zone also increases with increasi ng rotational speed of the mold. This suggests that the graphite particles and bubbles were attached to each other in the melt and they did not get se parated during centrifugal casting conditions of the present study. The pre sent experiments qualitatively confirm theoretical computations.([10])