In situ synchrotron tomographic investigation of the solidification of an AlMg4.7Si8 alloy

D. Tolnai, P. Townsend, G. Requena, L. Salvo, J. Lendvai, H. P. Degischer

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Abstract

The solidification sequence of an AlMg4.7Si8 alloy is imaged in situ by synchrotron microtomography. Tomograms with (1.4 μm) 3/voxel have been recorded every minute while cooling the melt from 600 °C at a cooling rate of 5 K min -1 to 540 °C in the solid state. The solidification process starts with the three-dimensional evolution of the α-Al dendritic structure at 590 °C. The growth of the α-Al dendrites is described by curvature parameters that represent the coarsening quantitatively, and ends in droplet-like shapes of the secondary dendrite arms at 577 °C. There, the eutectic valley of α-Al/Mg 2Si is reached, forming initially octahedral Mg 2Si particles preferentially at the bases of the secondary dendrite arms. The eutectic grows with seaweed-like Mg 2Si structures, with increasing connectivity. During this solidification stage Fe-aluminides form and expand as thin objects within the interdendritic liquid. Finally, the remaining liquid freezes as ternary α-Al/Mg 2Si/Si eutectic at 558 °C, increasing further the connectivity of the intermetallic phases. The frozen alloy consists of four phases exhibiting morphologies characteristic of their mode of solidification: α-Al dendrites, eutectic α-Al/Mg 2Si "Chinese script" with Fe-aluminides, and interpenetrating α-Al/Mg 2Si/Si ternary eutectic.

Original languageEnglish
Pages (from-to)2568-2577
Number of pages10
JournalActa Materialia
Volume60
Issue number6-7
DOIs
Publication statusPublished - Apr 1 2012

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Keywords

  • 3-D characterization
  • Cast Al-Mg-Si alloys
  • Eutectic solidification
  • In situ
  • Synchrotron radiation computed tomography

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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