Effect of micro-additions of Ge, In or Sn on precipitation in dilute Al-Sc-Zr alloys

Philipp Okle, Jeffrey D. Lin, Tianyu Zhu, David C. Dunand, David N. Seidman*

*Corresponding author for this work

Research output: Contribution to journalArticle

4 Scopus citations

Abstract

Trace amounts of inoculants - germanium (0.02 at%), indium (0.02 at%) or tin (0.01 at%) - were added to a ternary Al-0.06Sc-0.06Zr at% alloy to study their effects on Al3(Sc,Zr) precipitation. During isothermal aging at 300 °C, the In- and Sn-containing alloys exhibit an early microhardness increases, which is attributed to In or Sn clustering. Peak isothermal microhardness due to Al3(Sc,Zr) precipitation is achieved simultaneously (~4 h) for the three inoculated alloys and an inoculant-free alloy. Isochronal aging produces a low-temperature microhardening response for the In- and Sn-containing alloys, followed by two microhardness peaks at 350 and 450 °C for all four alloys, associated with precipitation of Sc and Zr, respectively. Atom-probe tomography demonstrates partitioning of Ge and Sn (up to 0.5 at%) from the matrix to the Al3(Sc,Zr) precipitates, with partitioning to Sc-rich precipitate cores (for isothermal aging) or to both Sc-rich cores and Zr-rich shells (for isochronal aging). Inoculant partitioning at precipitate cores and early low-temperature microhardness increases are consistent with inoculant clustering to form nucleation sites for Sc and Zr precipitation. Inoculant segregation at the precipitate shells can be explained by co-precipitation of the fast-diffusing inoculant element and the slow-diffusing Zr, between which an attractive binding energy exists. When compared to the inoculant-free control alloy with a somewhat higher Sc content, the three inoculated alloys exhibit a 2- to 10-fold decrease in creep rates at 300 °C for stresses above ~18 MPa, but a small reduction in creep threshold stresses from 12 to ~10 MPa.

Original languageEnglish (US)
Pages (from-to)427-436
Number of pages10
JournalMaterials Science and Engineering A
Volume739
DOIs
StatePublished - Jan 2 2019

Keywords

  • Aluminum alloys
  • Atom probe
  • Microhardness
  • Scandium
  • Zirconium

ASJC Scopus subject areas

  • Materials Science(all)
  • Condensed Matter Physics
  • Mechanics of Materials
  • Mechanical Engineering

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