A series of metal-matrix composites were formed by extrusion freeform, fabr
ication of a sinterable aluminum alloy in combination with silicon carbide
particles and whiskers, carbon fibers, alumina particles, and hollow flyash
cenospheres. Silicon carbide particles were most successful in that the co
mposites retained high density with up to 20 vol% of reinforcement and the
strength approximately doubles over the strength of the metal matrix alone.
Comparison with simple models suggests that this unexpectedly high degree
of reinforcement can be attributed to the concentration of small silicon ca
rbide particles around the larger metal powder. This fabrication method als
o allows composites to be formed with hollow spheres that cannot be formed
by other powder or melt methods.