Precipitate assemblies formed on dislocation loops in aluminium-silver-copper alloys |
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Authors: | Julian M. Rosalie Laure Bourgeois Barry C. Muddle |
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Affiliation: | 1. Lightweight Alloys Group , Structural Metals Center, National Institute for Materials Science (NIMS) , Japan;2. ARC Centre of Excellence for Design in Light Metals , Australia;3. Department of Materials Engineering , Monash University , Australia rosalie.julianmark@nims.go.jp;5. ARC Centre of Excellence for Design in Light Metals , Australia;6. Department of Materials Engineering , Monash University , Australia;7. Monash Centre for Electron Microscopy , Monash University , Australia;8. Department of Materials Engineering , Monash University , Australia |
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Abstract: | The precipitation microstructure of the γ′ (AlAg2) intermetallic phase has been examined in aluminium-silver-copper alloys. The microstructure developed in an Al-0.90at.%Ag-90at.Cu alloy was significantly different from that reported for binary Al-Ag alloys. The orientation relationship between the matrix and precipitate was unchanged; however, the γ′ phase formed assemblies with a two-dimensional, open arrangement of precipitates. Each such assembly contained two variants of the γ′ phase alternately arranged to form a faceted elliptical unit. The θ′ (Al2Cu) phase formed on these assemblies after further ageing. Each assembly was formed via repeated precipitation of the γ′ phase on dissociated segments of a single dislocation loop. This faceted elliptical assembly has not been previously reported for the γ′ precipitate. The difference between the precipitation behaviour of the γ′ phase in Al-Ag and Al-Ag-Cu alloys was attributed to copper modifying the as-quenched defect structure of the matrix. The formation of faceted elliptical γ′ phase assemblies clarifies earlier observations on the precipitate number density and mechanical properties of aluminium-silver-copper alloys. |
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Keywords: | dislocation loops aluminium alloys dislocations HRTEM intermetallic phases precipitation TEM |
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