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 language | English (US) |
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Pages (from-to) | 1700-1715 |
Number of pages | 16 |
Journal | Acta Materialia |
Volume | 59 |
Issue number | 4 |
DOIs | |
State | Published - Feb 2011 |
Funding
This research is supported by the United States Department of Energy (Basic Energy Science) through grant DE–FG02–98ER45721. The LEAP tomography system was purchased and upgraded with funding from NSF-MRI (DMR-0420532) and ONR-DURIP (N00014-0400798, N00014-0610539, and N00014-0910781) grants. ME Krug would like to thank Drs. C. Booth-Morrison and D. Isheim for helpful discussions.
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