Mechanical properties of directionally solidified Al--Si eutectic

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Abstract
The effect of directional solidification on the yield strength of the Al-Si eutectic alloy has been studied. Eutectic alloys (Al-12.7 wt. % Si) were directionally frozen at growth rates, R, between 0.097 cm/h and 47.0 cm/h through a temperature gradient of about 80/sup 0/C/cm. As found by Day and Hellawell, an oriented (001) Si fiber texture is obtained for rates less than 1.0 cm/hr, and at higher growth rates microstructures similar to the as-cast eutectic are found. At the lower growth rates, banded structures alternating rich in Si and lean in Si were also observed. Tensile measurements indicated that the yield strength is independent of R at growth rates less than ca. 1.0 cm/h, while at higher growth rates the strength increases linearly with R/sup 1/4/. Composite strengthening due to aligned Si microstructure at low R was not exhibited due to the preferential yielding within the banded structures. Yield strengths for higher growth rates are controlled by a precipitate spacing effect.

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