Transmission electron microscopy observations on the microstructure of naturally aged Al–Mg–Si alloy AA6022 processed with an electric field
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The influence of an electric field applied during the solution heat treatment and during a short subsequent initial natural aging of AA6022 on the nature of the precipitates which occurred after natural aging for a long time (2–3 years) was determined employing transmission electron microscopy and selected area electron diffraction. The precipitates were spherical in shape ranging from 2 nm to 40 nm in diameter d p with an average of 7.9 nm. Their average size was larger than that (4.9 nm) in a specimen processed without field and their size distribution had a greater number of precipitates with d p>∼3 nm. Moreover, their crystal structure differed from that in specimens processed without a field. The increase in yield stress which occurred with the electric field treatments is attributed to an increase in the interaction force between the precipitates and dislocations, which resulted from the larger size and different crystal structure of the precipitates by the field.
KeywordsHigh Resolution Transmission Electron Microscopy Select Area Electron Diffraction High Resolution Transmission Electron Microscopy Natural Aging Select Area Electron Diffraction Pattern
This research was funded by the U.S. Army Research Laboratories and the U.S. Army Research Office under Award DAA1902-1-0315 with Dr. William Mullins as contract monitor. The authors also wish to thank Dr. R. Ramage, Alcoa Technical Center, for providing the AA6022 material and Dr. D. Lloyd, Novelis Global Technology Center, for the chemical analysis and helpful discussions. We also wish to thank Ms. R. O’Connell for typing the manuscript.
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