Compositional characterization of Cu-rich phase particles present in as-cast Al-Cu-Mg(-Li) alloys containing Ag
- Defence Metallurgical Research Lab., Hyderabad (India)
The effects of small additions of Ag on the aging of wrought Al-Cu-Mg(-Li) alloys, involving widespread nucleation of Cu-rich {Omega} (and T{sub 1}) phase precipitates, are known. This article examines the influence of small additions of Ag on the nature of Cu-rich {theta}-Al{sub 2}Cu, S-Al{sub 2}CuMg, and T{sub 1}-Al{sub 2}CuLi phases present in appropriate as-cast Al-Cu, Al-Cu-Mg, and Al-Cu-Li-Mg alloys. Using a combination of light microscopy, scanning electron microscopy (SEM), and electron probe microanalysis (EPMA), it is shown that neither independent nor combined additions of Ag and Mg to the binary Al-Cu alloy after the composition of the {theta} phase; however, there are differences in the ways the {theta} phase is evolved in Al-Cu-Mg alloys with and without Ag. Ag additions to the Al-Cu-Mg alloy result in the formation of an Al-Cu-Mg-based ternary phase, having a Cu content similar to that of the {theta} phase and containing small amounts of Mg; rapid rates of cooling cause the retention of this phase in the as-cast alloy. Relatively large amounts of both Ag and Mg are always located in the peripheral regions of such a phase. This phase is readily replaced by {theta} phase upon annealing at 450 C. The S phase of the ternary Al-Cu-Mg system is identified in this alloy and is found to dissolve small amounts of Ag. In the case of the Al-Cu-Li-Mg-Ag alloy, two major changes are observed; both Ag and Mg are always present in relatively large amounts in the peripheral regions of the T{sub 1} phase, and the S-phase particles are once again found to dissolve small amounts of Ag. These results are discussed in light of the known compositional features of the precipitates formed in the artificially aged Al-Cu-Mg(-Li)-Ag alloys, to reveal that examination of phases present in the as-cast microstructure is a contributory step toward determining the locations of trace alloy additions in the phase precipitates of interest.
- Sponsoring Organization:
- USDOE
- OSTI ID:
- 677979
- Journal Information:
- Metallurgical and Materials Transactions. A, Physical Metallurgy and Materials Science, Vol. 30, Issue 7; Other Information: PBD: Jul 1999
- Country of Publication:
- United States
- Language:
- English
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