Development of High Performance P/M Aluminum Composites Using Fly-Ash Reinforcement

The use of fly-ash, a by-product of coal combustion, as a reinforcing medium in metal-matrix composites is very attractive to make effective use of a material that is otherwise considered to be a nuisance.  However, previous attempts to manufacture aluminum-fly ash composites by traditional stir casting methods have not produced satisfactory results.  In the present study 6061 and 2124 aluminum alloy composites  reinforced with  5-20 vol.% fly ash were produced powder blending and consolidation followed by equal channel angular extrusion (ECAE) processing.  The ECAE step introduces large, homogeneous plastic strains in the billet and produces a final product with 100% density, uniform fly ash particle distribution, and good matrix-reinforcement interfacial strength..  Aging studies were performed in order to determine the optimum time and temperature to produce peak strength.  Flexure testing, tensile testing, and compression testing at ambient and high temperatures were performed to characterize the mechanical properties of the composites.  Property improvements were correlated with the relative volume fractions of the fly ash reinforcement and coherent precipitates, and microstructural refinement produced by ECAE processing.