A High cycle fatigue behavior of squeeze cast A356 Al/SiC{sub w} and A390 Al/SiC{sub w} MMCs
- Pennsylvania State Univ., University Park, PA (United States). Dept. of Materials Science and Engineering
- GM Powertrain, Saginaw, MI (United States)
Specimens of A356 Al/SiC{sub w} and A390 Al/SiC{sub w} metal matrix composites (MMCs) were produced by squeeze casting and tested under fully reversed high cycle fatigue conditions at room temperature. A staircase method was employed to determine the mean fatigue strength at 10{sup 7} cycles. The presence of 17 vol. % SiC whiskers in the A356 Al alloy increases the fatigue strength by 29%. In contrast, the A390 Al/SiC{sub w} composite, containing identical whisker reinforcements, showed very little improvement of fatigue strength when compared to the matrix alloy. An analysis of the fracture surfaces of both composites shows that fatigue cracks initiated primarily at pre-existing regions within the preforms which are characterized by the absence of the SiC whiskers. The reinforcement-free regions take two forms: continuous veins, which are very deleterious to fatigue, and discontinuous unreinforced regions, which are deleterious only in certain geometries. An analysis is presented to rationalize the geometry effect. Finally, the authors also identify the importance of large primary Si particles in limiting fatigue life of the A390 Al materials.
- OSTI ID:
- 293095
- Report Number(s):
- CONF-970980--; ISBN 0-87339-382-1
- Country of Publication:
- United States
- Language:
- English
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