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is not willing to face additional costs for the use of such materials. For all these reasons, metal matrix compos- ites are only at the beginning of the evolution curve of modern materials. As lightweight, stiff, wear-resistant applications become of greater value to transportation and other industries, more high volume uses will evolve; brake rotors, pistons and drive yokes are examples. MMC production melting metal-


lurgy and pouring presently are of greater technical importance than using powder metallurgy composite material. Casting is more economi- cal and has the advantage of being able to use well proven processes such as investment casting. Cast- ing also offers the engineer more freedom than other processes. An objective in the development of light metal composite materi- als may be to increase the modulus


Fig. 7. Shown is an A356 micrograph (unetched, 100x), without silicon carbide particulates, to compare to the MMC microstructure.


Fig. 1. MMC 30, Unetched (50x)


Fig. 2. MMC 30, Unetched (100x)


Fig. 3. MMC 30, Unetched (500x)


Fig. 4. MMC 30 Etched (50x)


Fig. 5. MMC30, Etched (100x)


Fig. 6. MMC 30, Etched (500x)


Figures 1-6 show the metallography of a 28% F500 MMC at magnifications of 50x/100x/500x in the etched and unetched conditions. (Twenty-eight percent is the concentration by volume and F500 refers to the size of the silicon carbide particulates.) The micrographs show the uniformly distributed silicon carbide particulates (brown) in the aluminum (tan) matrix. Also shown are intermittent interdendritic voids (black indicates shrinkage cavities).


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