| The microstructure and the mechanical properties of squeeze cast SiC whisker-reinforced aluminum composites based on either A356 Al or A390 Al matrices has been studied. One advantage of compositing procedure using SiC whisker preform is the possibility of selectively reinforcing near net-shape components, thus reducing the cost of fabricating a high performance component. Microstructural examination shows that roughly 17 vol. pct. whiskers were randomly oriented and inter-penetrated. Although, SiC preform was applied in squeeze casting procedure in order to get a uniform distribution of SiC whiskers, two types of reinforcement-free regions were identified; (i) continuous `veins` of the matrix alloy which are believed to be caused by cracks formed within the whisker preform during squeeze casting, and (ii) discontinuous `unreinforced areas` also of the matrix alloy, which are a result of small non-uniform distributions of SiC whiskers during preform fabrication. It is observed that there are severe differences of micro-hardness values and chemical compositions in such areas. The differences are caused by the variation of $quot;Mg gettering effect$quot; and the variation is believed to be closely related with the morphology of whiskers. In addition, tension and compression tests shows the addition of 17 vol. pct. of whiskers increased the elastic modulus by about 30-35% and showed discrepancy between tensile yield strength and compressive yield strength. The discrepancy between tensile and compressive strength indicates the presence of thermal residual stress in composite specimen. |
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