Abstract: A process is described for recycling scrap aluminum-matrix composites, e.g. gates and risers from a casting operation. A melt of the scrap composite is provided in a treatment vessel by heating at a temperature of 720.degree.-750.degree. C., such as to avoid unwanted stirring and contamination of the melt. While mixing with the impeller, a gas is injected through a gas outlet beneath the surface of the melt and near the rotating impeller. This melt is mixed with a vaned rotor impeller such that no vortex is formed and oxide film is not drawn into the melt. This treatment gas comprises a mixture of a major proportion of an inert gas and a minor proportion of reactive gas. The gas injection is continued only until small gas bubbles have been well distributed through the melt but before the gas causes the reinforcing parties to start rising to the surface. After the gas is stopped, the melt is allowed to rest for a period of time at the reaction temperature of 720.degree.-750.degree. C.

Abstract: Gas is dispersed into molten metal by immersing a shaft-supported impeller into the molten metal and by pumping gas through the shaft and out of the impeller. The impeller is in the form of a rectangular prism having sharp-edged corners that shear the gas into finely divided bubbles. The particular shape of the impeller provides an especially effective bubble-shearing and bubble-dispersing action.

Abstract: An apparatus and process are described for treating molten metal. The invention comprises: (a) a heated vessel having inlet and outlet means for the continuous flow of molten metal downwardly through the vessel, (b) a perforated plate extending horizontally across the vessel dividing it into an upper treatment section and a lower treatment section, this plate forming an intermediate treatment section, and (c) a device for injecting gas in the form of small discrete bubbles into the metal in the lower treatment section, this device comprising a hollow rotatable shaft extending downwardly through an opening in the plate with drive means coupled to the upper end of the shaft, a vaned rotor fixedly attached to the lower end of the shaft within the lower treatment section, with one or more passageways within the rotor for conducting gas from the interior of the shaft to the metal in the lower treatment section.