Evolution of {Omega} phase in an Al-Cu-Mg-Ag alloy -- A three-dimensional atom probe study
- National Research Inst. for Metals, Sengen, Tsukuba (Japan)
Evolution of plate-like precipitates of the {Omega} phase in an Al-1.9Cu-0.3Mg-0.2Ag (at.%) alloy has been investigated by three-dimensional atom probe (3DAP) and transmission electron microscope (TEM) techniques. In an as-quenched alloy, all solute atoms are uniformly dissolved. After 5 s aging at 180 C, co-clusters of Ag and Mg atoms are present. Initially, these co-clusters do not have well-defined shape, but after aging for 120 s, they are aligned on the {l_brace}111{r_brace} planes incorporating Cu atoms. Initially, they do not have the distinct structure consistent with the {Omega} phase, thus these are designated as {l_brace}111{r_brace}GP zones. The {Omega} platelet which appears after the {l_brace}111{r_brace}GP zones contain all solute elements within the precipitate having a composition of approximately 25 at.% Cu, 20 at.% Mg and 10 at.% Ag. In the well-defined {Omega} phase which appears after 2 and 10 h aging at 180 C, Ag and Mg atoms are strongly segregated to the broad face monolayer interfaces of {alpha}/{Omega}. No Mg and Ag are incorporated within the platelet, and its chemical composition is Al-33 at.% Cu. Based on these observations, it is concluded that the {Omega} phase evolves from co-clusters to plate-like precipitates continuously, rather than precipitating discretely by heterogeneous nucleation to their precursors. In a well-grown {Omega} plate, elemental mapping near a ledge was observed by 3DAP for the first time.
- OSTI ID:
- 302346
- Journal Information:
- Acta Materialia, Vol. 46, Issue 17; Other Information: PBD: 2 Nov 1998
- Country of Publication:
- United States
- Language:
- English
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