The effect of Sr and Fe additions on the microstructure and mechanical properties of a direct squeeze cast Al-7Si-0.3Mg alloy |
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Authors: | J X Dong P A Karnezis G Durrant B Cantor |
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Affiliation: | (1) Department of Mining and Metallurgical Engineering, McGill University, H3A 2T5 Montreal, PQ, Canada;(2) Present address: Oxford Centre for Advanced Materials and Composites, Department of Materials, University of Oxford, Rolls Royce Plc, DE24 8BJ Derby, United Kingdom;(3) Department of Materials, University of Oxford, OX1 3PH Oxford, United Kingdom |
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Abstract: | This article describes the results of an investigation into the microstructure and mechanical properties of a gravity die
cast and direct squeeze cast LM25 alloy (Al-7Si-0.3Mg-0.3Fe). The direct squeeze cast LM25 alloy has superior mechanical properties
compared to the gravity die cast LM25 alloy, especially with regard to ductility, which is increased from ∼1.7 pct for the
gravity die cast LM25 alloy to ∼8.0 pct for the direct squeeze cast LM25 alloy in the T6 heat-treated condition. This increase
in ductility is due to (1) the removal of porosity, (2) a decrease in Si particle size, and (3) a refinement of the Fe-Si-aluminide
particles. High cooling rates in direct squeeze casting result in quench modification of the Si particles, such that chemical
modification with Sr or Na may not be required. In addition, direct squeeze casting is more tolerant of Fe impurities in the
alloy, due to the formation of smaller Fe-Si-aluminide particles than those in gravity die cast material. The direct squeeze
cast LM25+Fe alloy (Al-7Si-0.3Mg-1.0Fe) has a ductility of ∼6.5 pct, compared to that of ∼0.5 pct for the gravity die cast
LM25 + Fe alloy in the T6 heat-treated condition. This increase in tolerance to Fe impurities can lead to a substantial reduction
in manufacturing costs due to (1) reduced raw-material costs, (2) reduced die sticking, and (3) improved die life. |
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