Effects of Li additions on precipitation-strengthened Al-Sc and Al-Sc-Yb alloys

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45 Scopus citations

Abstract

Two Al-Sc-based alloys (Al-0.12Sc and Al-0.042Sc-0.009Yb, at.%) and their counterparts with Li additions (Al-2.9Li-0.11Sc and Al-5.53Li-0.048Sc-0.009Yb, at.%) are aged at 325 °C. For both base alloys, the addition of Li results in greater peak hardness from incorporation of Li in the L12- structured α′-Al3(Sc,Li) and α′-Al 3(Sc,Li,Yb) precipitates, and a concomitant increase in number density and volume fraction of the precipitates and a reduction in their mean radius. These changes result from a combination of: (i) an increase in the driving force for precipitate nucleation due to Li; (ii) a decrease in the elastic energy of the coherent misfitting precipitates from a decrease in their lattice parameter mismatch due to their Li content; and (iii) a decrease in the interfacial free energy, as determined from measurements of the relative Gibbsian interfacial excess of Li. In Al-2.9Li-0.11Sc (at.%), the Li concentration of the precipitates decreases from 9.1 at.% in the peak-aged state (8 h) to 5.7 at.% in the over-aged state (1536 h). As a result, the precipitate volume fraction decreases from 0.56% at peak aging time to 0.45% at 1536 h. In Al-5.53Li-0.048Sc-0.009Yb (at.%), the relatively limited Li concentration produces only a small increase in Vickers microhardness from precipitation of metastable δ′-Al3Li upon a second aging at 170 °C following the primary aging at 325 °C.

Original languageEnglish (US)
Pages (from-to)1700-1715
Number of pages16
JournalActa Materialia
Volume59
Issue number4
DOIs
StatePublished - Feb 1 2011

Keywords

  • Aluminum alloys
  • Atom-probe field-ion microscopy
  • Nanostructure
  • Precipitation
  • Rare earth

ASJC Scopus subject areas

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

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