We report atomic resolution imaging of Cu-planar precipitates in aged Al-Cu alloys, known as Guinier-Preston (GP) zones, by high-angle annular detector dark-field scanning transmission electron microscopy. Single layered GP-I zones as small as 2 nm in length were resolved among densely populated GP-I zones, whereas double layered GP zones were clearly identified. The images of GP-II zones showed not only the commonly accepted structure, in which single Cu layers are separated by three Al layers, but also a variant, in which double Cu layers are separated by a single Al layer.
- Aged alloy
- Guinier-Preston zone
- Scanning transmission electron microscopy
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