Journal
ACTA MATERIALIA
Volume 59, Issue 4, Pages 1700-1715Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2010.11.037
Keywords
Aluminum alloys; Atom-probe field-ion microscopy; Rare earth; Nanostructure; Precipitation
Funding
- United States Department of Energy (Basic Energy Science) [DE-FG02-98ER45721]
- NSF-MRI [DMR-0420532]
- ONR-DURIP [N00014-0400798, N00014-0610539, N00014-0910781]
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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 L1(2)-structured alpha'-Al-3(Sc,Li) and alpha-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 delta'-Al3Li upon a second aging at 170 degrees C following the primary aging at 325 degrees C. (C) 2010 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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