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Metals 2018, 8(5), 324; https://doi.org/10.3390/met8050324

Numerically Based Phase Transformation Maps for Dissimilar Aluminum Alloys Joined by Friction Stir-Welding

1
Department of Mechanical and Manufacturing Engineering, College of Engineering and Computing, Miami University, Oxford, OH 45056, USA
2
Faculty of Metal Engineering and Industrial Computer Science, AGH University of Science and Technology, 30-059 Krakow, Poland
3
Department of the Testing of Materials Weldability and Welded Construction, Institute of Welding, 44-100 Gliwice, Poland
*
Author to whom correspondence should be addressed.
Received: 31 March 2018 / Revised: 30 April 2018 / Accepted: 4 May 2018 / Published: 8 May 2018
(This article belongs to the Special Issue Phase Transformations in Alloy Processing)
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Abstract

Sheets of aluminum 2017A-T451 and 7075-T651 were friction stir-welded in a butt-weld configuration. An existing computational model of the welding process for temperature distribution and material flow was adapted to estimate the phase transformations that occur across the weld zone. Near the weld center, process temperatures are sufficient to fully dissolve the equilibrium η phase in 7075 and partially dissolve the equilibrium S phase in 2017A. Upon cooling, Guinier–Preston (GP) and Guinier–Preston–Bagaryatsky (GPB) zones re-precipitate, and hardness recovers. Due to the more complete dissolution of the equilibrium phase in 7075, the hardness recovery skews toward whichever side of the weld, i.e., the advancing or retreating side, represents the 7075 workpiece. Phase transformation maps generated by the numerical simulation align not only with the hardness profiles taken across the weld zone, but also with positron lifetimes obtained through positron annihilation lifetime spectroscopy (PALS). Boundaries between the aluminum matrix and the secondary phases provide open volumes to trap positrons; therefore, positron lifetimes across the weld correspond with the phase transformations that occur in 7075 and 2017A during processing. View Full-Text
Keywords: friction stir-welding; dissimilar materials; aluminum; material flow; temperature; phase transformations friction stir-welding; dissimilar materials; aluminum; material flow; temperature; phase transformations
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This is an open access article distributed under the Creative Commons Attribution License which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited (CC BY 4.0).
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Hamilton, C.; Dymek, S.; Kopyściański, M.; Węglowska, A.; Pietras, A. Numerically Based Phase Transformation Maps for Dissimilar Aluminum Alloys Joined by Friction Stir-Welding. Metals 2018, 8, 324.

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