Radial macrosegregation and dendrite clustering in directionally solidified Al-7Si and Al-19Cu alloys

M. Ghods, L. Johnson, M. Lauer, R. N. Grugel, S. N. Tewari, David R Poirier

Research output: Contribution to journalArticle

11 Scopus citations

Abstract

Hypoeutectic Al-7 wt% Si and Al-19 wt% Cu alloys were directionally solidified upward in a Bridgman furnace through a range of constant growth speeds and thermal gradients. Though processing is thermo-solutally stable, flow initiated by gravity-independent advection at, slightly leading, central dendrites moves rejected solute out ahead and across the advancing interface. Here any lagging dendrites are further suppressed which promotes a curved solid-liquid interface and the eventual dendrite "clustering" seen in transverse sections (dendrite "steepling" in longitudinal orientations) as well as extensive radial macrosegregation. Both aluminum alloys showed considerable macrosegregation at the low growth speeds (10 and 30 μm s-1) but not at higher speed (72 μm s-1). Distribution of the fraction eutectic-constituent on transverse sections was determined in order to quantitatively describe radial macrosegregation. The convective mechanisms leading to dendrite-steepling were elucidated with numerical simulations, and their results compared with the experimental observations.

Original languageEnglish (US)
Pages (from-to)107-116
Number of pages10
JournalJournal of Crystal Growth
Volume441
DOIs
StatePublished - May 1 2016

Keywords

  • A1. Computer simulation
  • A1. Directional solidification
  • A1. Fluid flows
  • A1. Segregation
  • A2. Bridgman technique
  • Aluminum alloys

ASJC Scopus subject areas

  • Condensed Matter Physics
  • Materials Chemistry
  • Inorganic Chemistry

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