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Spurious Grain Formation at Cross-Sectional Expansion During Directional Solidification: Influence of Thermosolutal Convection

  • M. Ghods
  • M. Lauer
  • S. R. Upadhyay
  • R. N. Grugel
  • S. N. Tewari
  • D. R. Poirier
Article
  • 61 Downloads

Abstract

Formation of spurious grains during directional solidification (DS) of Al-7 wt.% Si and Al-19 wt.% Cu alloys through an abrupt increase in cross-sectional area has been examined by experiments and by numerical simulations. Stray grains were observed in the Al-19 wt.% Cu samples and almost none in the Al-7 wt.% Si. The locations of the stray grains correlate well where numerical solutions indicate the solute-rich melt to be flowing up the thermal gradient faster than the isotherm velocity. It is proposed that the spurious grain formation occurred by fragmentation of slender tertiary dendrite arms was enhanced by thermosolutal convection. In Al-7 wt.% Si, the dendrite fragments sink in the surrounding melt and get trapped in the dendritic array growing around them, and therefore they do not grow further. In the Al-19 wt.% Cu alloy, on the other hand, the dendrite fragments float in the surrounding melt and some find conducive thermal conditions for further growth and become stray grains.

Keywords

directional solidification modeling and simulation thermosolutal convection grains formation dendrite fragmentation 

Notes

Acknowledgments

This work was supported by NASA Grants NX10AV40G and NNX14AM18G. The Al-19% Cu and Al-7% Si alloys for this study were kindly provided by Dr. Men G. Chu at ALCOA Technical Center.

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Copyright information

© ASM International 2018

Authors and Affiliations

  1. 1.Chemical Engineering ProgramMiddle East Technical University - Northern Cyprus CampusGüzelyurt via Mersin 10Turkey
  2. 2.Department of Materials Science and EngineeringThe University of ArizonaTucsonUSA
  3. 3.Chemical and Biomedical Engineering DepartmentCleveland State UniversityClevelandUSA
  4. 4.NASA-Marshall Space Flight CenterHuntsvilleUSA
  5. 5.ME Elecmetal Inc.DuluthUSA

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