Modification of Cast Al-Mg^sub 2^Si Metal Matrix Composite by Li

The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15 pet Mg^sub 2^Si composite were investigated. Adding 0.3 pct Li reduced the average size of Mg^sub 2^Si primary particles from ~30 to ~6 µm. The effect of cooling rate was in...

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Veröffentlicht in:Metallurgical and materials transactions. B, Process metallurgy and materials processing science Process metallurgy and materials processing science, 2009-12, Vol.40 (6), p.822
Hauptverfasser: Hadian, R, Emamy, M, Campbell, J
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Sprache:eng
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Zusammenfassung:The effects of both Li modification and cooling rate on the microstructure and tensile properties of an in-situ prepared Al-15 pet Mg^sub 2^Si composite were investigated. Adding 0.3 pct Li reduced the average size of Mg^sub 2^Si primary particles from ~30 to ~6 µm. The effect of cooling rate was investigated by the use of a mold with different section thicknesses from 3 to 9 mm. The results show a refinement of primary particle size as a result of both Li additions and cooling rate increases, and their effects are additive. Similarly, both effects increased ultimate tensile stress (UTS) and elongation values. The thin sections show somewhat unexpectedly low and scattered tensile results attributed to the casting defects observed in fracture surfaces. The Li-modified alloy displays serrated yielding behavior that is not fully explained here. The refinement by Li and enhanced cooling rate is explained in terms of an analogy with the effect of Sr and cooling rate in Al-Si alloys, and is ultimately attributed to the effect of the alkali and alkaline earth metals deactivating oxide double films (bifilms) suspended in Al melts as favored substrates for intermetallics. [PUBLICATION ABSTRACT]
ISSN:1073-5615
1543-1916