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Post-weld heat treatment effects on microstructure, crystal structure, and mechanical properties of donor stir–assisted friction stir welding material of AA6061-T6 alloy

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Friction stir welding (FSW) technology combines heat input from friction and extreme plastic deformation to produce high-quality joints in aluminum and other alloy systems. This necessitates examining the final welded joint’s mechanical and structural properties. Post-weld heat-treated AA6061-T6 alloy that resulted from the application of a Cu donor stir–assisted (CDSA) friction stir welding (FSW) material was examined for crystal structure and mechanical properties. CDSA FSW samples were tested at a constant tool rotational speed of 1400 rpm and a welding translational speed of 1 mm/s. CDSA samples of 20% and 60% thickness of the AA6061-T6 base alloy were selected to assist the FSW joining at the plunge stage. The FSW AA6061-T6 samples were solid solution treated at 540 °C for 1 h, followed by quenching in water at room temperature. The samples were then artificially aged at 180 °C for 6 h, respectively, followed by air cooling. The samples were tested for microstructure, crystal structure, chemical composition, and mechanical properties using optical microscopy, scanning electron microscopy, X-ray diffraction, and nanoindentation. The microstructure shows the additional grain refinement in the stir zone (SZ) due to recovery and recrystallization with increasing aging time. Examination of the chemical contents of the FSW AA6061-T6 alloy samples using scanning electron microscopy with energy-dispersive spectroscopy (EDS) revealed Al (parent material) as the predominant element, while Cu (CDSA) was minimally present as expected. XRD results of the CDSA FSW samples depicted crystal orientations similar to the orientations of the AA6061-T6 alloy. Nanoindentation tests revealed softening effects due to the dissolution of hardening precipitates at the SZ. The hardness of the base metal (BM), left and right regions, is reported as ~ 0.65 GPa, whereas at the SZ, the hardness is ~ 0.55 GPa at a depth of indentation of 4.7 μm.

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The authors acknowledge the Commonwealth Center for Advanced Manufacturing (CCAM) and Amsted Rail for making available the infrastructure required for specimen evaluation. Finally, the valuable contribution of Mr. Geoff Widman in carrying out the experiments is acknowledged and appreciated.


Funding support was received from NASA (grant ID: 80NSSC20M0015). ZW received support from ONR (grant ID: N00014-19-1-2728).

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Mr. A. H. Al-Allaq performed XRD characterization and wrote/revised the manuscript. Dr. S. Bhukya carried out experimentation and data analysis for the CDSA and revised the manuscript. Dr. A.A. Elmustafa conceptualized the research and wrote/revised the manuscript. Dr. Z. Wu secured the funding. Mr. M. Ojha performed the SEM-EDS, and Dr. Y. Mohammed performed the nanoindentation testing.

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Correspondence to Abdelmageed A. Elmustafa.

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Al-Allaq, A.H., Ojha, M., Mohammed, Y.S. et al. Post-weld heat treatment effects on microstructure, crystal structure, and mechanical properties of donor stir–assisted friction stir welding material of AA6061-T6 alloy. Int J Adv Manuf Technol 129, 1845–1854 (2023).

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