Metallurgical and Materials Transactions A

, Volume 30, Issue 10, pp 2611–2618 | Cite as

The effect of Mg on the microstructure and mechanical behavior of Al-Si-Mg casting alloys

  • C. H. Caceres
  • C. J. Davidson
  • J. R. Griffiths
  • Q. G. Wang


The microstructure and tensile behavior of two Al-7 pct Si-Mg casting alloys, with magnesium contents of 0.4 and 0.7 pct, have been studied. Different microstructures were produced by varying the solidification rate and by modification with strontium. An extraction technique was used to determine the maximum size of the eutectic silicon flakes and particles. The eutectic Si particles in the unmodified alloys and, to a lesser extent, in the Sr-modified alloys are larger in the alloys with higher Mg content. Large Fe-rich π-phase (Al9FeMg3Si5) particles are formed in the 0.7 pct Mg alloys together with some smaller β-phase (Al5FeSi) plates; in contrast, only β-phase plates are observed in the 0.4 pct Mg alloys. The yield stress increases with the Mg content, although, at 0.7 pct Mg, it is less than expected, possibly because some of the Mg is lost to π-phase intermetallics. The tensile ductility is less in the higher Mg alloys, especially in the Sr-modified alloys, compared with the lower Mg alloys. The loss of ductility of the unmodified alloy seems to be caused by the larger Si particles, while the presence of large π-phase intermetallic particles accounts for the loss in ductility of the Sr-modified alloy.


Material Transaction Tensile Ductility Unmodified Alloy Dendrite Cell Size Area Equivalent Diameter 
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Copyright information

© ASM International & TMS-The Minerals, Metals and Materials Society 1999

Authors and Affiliations

  • C. H. Caceres
    • 1
  • C. J. Davidson
    • 2
  • J. R. Griffiths
    • 2
  • Q. G. Wang
    • 3
  1. 1.the CRC for Alloy and Solidification Technology (CAST), Department of Mining, Minerals and Materials EngineeringThe University of QueenslandBrisbaneAustralia
  2. 2.CSIRO Manufacturing Science and TechnologyKenmoreAustralia
  3. 3.Metal Processing InstituteSPIWorcester

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