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A family of metal matrix composites comprised of 7000 series alloys reinforced with aluminum oxide particulate is under development. The matrices include the high strength 7050, 7075 and 7178 alloys as well as 7005. The reinforcement level in the composites varies between 10 and 20 volume percent (14 and 27 weight percent). The particulate is carefully graded aluminum oxide powder ranging in size from 10 to 21 microns. The powders were introduced into the aluminum matrix using ingot metallurgy processing and then DC cast into 178 mm diameter billet. The billet was extruded into bars, heat treated and the mechanical properties evaluated. Elastic modulii in all composites increased with the volume fraction of reinforcement. Uniaxial yield and tensile strengths in excess of 590 MPa and 660 MPa respectively were measured in the 7075 composites. Fatigue strengths of 7005 composites are shown as a function of volume fraction and loading conditions.

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.