1993-03-01

The Recycling and Reclamation of Metal-Matrix Composites 930182

The recycling and reclamation of metal-matrix composites (MMC's) are critical aspects of the commercialization process. By recycling, we mean the economic processing of MMC scrap for reuse as composite. Reclamation refers to the separation and recovery of the individual components of the composite, i.e., the various aluminum alloys and ceramic particles.Three forms of MMC wrought alloy scrap have been considered; i.e., D. C. (direct chill) cast log ends, extrusion butts, and cut extrusion scrap. Recycling each of these forms of scrap back into D. C. cast extrusion billet has been demonstrated. This has been accomplished by recycling the scrap back through the basic mixing process. Various ratios of scrap to virgin composite have been explored and optimum blends are being studied. Similarly, for MMC foundry alloy (high silicon) gates and risers produced in shape-casting, fluxing and degassing techniques have been developed so these may be recycled back into useful castings. These fluxing and degassing processes have been confirmed at commercial foundries and are described in detail. Finally, when MMC scrap can no longer be recycled, the alumina particles in the wrought alloys, or the silicon carbide particles in the foundry alloys may be removed by common salt or other fluxing techniques. Methods are used which are similar to the way oxide films or insoluble “dirt” are removed from ordinary aluminum. Rotary salt furnace (RSF) technology has been shown to be effective for this approach and the results of large RSF trials are reported.

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