Journal
ACTA MATERIALIA
Volume 125, Issue -, Pages 50-57Publisher
PERGAMON-ELSEVIER SCIENCE LTD
DOI: 10.1016/j.actamat.2016.11.056
Keywords
Al alloys; Silver; Interface segregation; Particle; STEM HAADF
Funding
- European Union Seventh Framework Programme [312483 - ESTEEM2]
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The results of a study aimed at investigating the presence of silver in the strengthening phases of age-hardenable AlCuMgSi alloys are presented. HR STEM observations were performed on Al-4Cu-0.55Mg-0.5Si-0.15Zr-0.1Ti-0.5Ag (wt%) alloy samples aged or crept at 200 degrees C to monitor the evolution of secondary phases over long times. Results showed that in the peak aged condition silver mostly segregated at the surface of some strengthening precipitates types. This occurred specifically at the particle/matrix interface of theta' phase while particles, matching the wide compositional range of the quaternary Q' phase were free from Ag. A third population of strengthening particles having the shape of a core-shell rod was also observed. They were characterized by a Mg- and Si-rich core and a Cu- and Ag-rich shell. The exposure at 200 degrees C for up to 570 h, caused an evident coarsening of Q' and theta' plate-like particles, and the Ag surface enrichment of the latter went progressively lost. On the contrary, silver concentrated inhomogeneously on the surface of the core-shell particles for which a relatively low coarsening rate was observed. (C) 2016 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.
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