Precipitation phenomena in impulse friction stir welded 2024 aluminium alloy

• Published in: Materials science & engineering. A, Structural materials : properties, microstructure and processing Structural materials : properties, microstructure and processing, 2022-09, Vol.852, p.143617, Article 143617
• Main Authors: Morozova, Iuliia, Królicka, Aleksandra, Obrosov, Aleksei, Yang, Yitong, Doynov, Nikolay, Weiß, Sabine, Michailov, Vesselin
• Format: Article
• Language: English
• Subjects: AA2024; Deformation; Impulse friction stir welding; Microhardness; S precipitation; Thermal cycle
• ISSN: 0921-5093; 1873-4936
• DOI: 10.1016/j.msea.2022.143617

Microhardness variations across the friction stir welded (FSW) and impulse friction stir welded (IFSW) AA2024–T351 joints have been elucidated by the transformations of the S–Al2CuMg phase with a special focus on a distinguished hardness peak within the heat-affected zone (HAZ) of the impulse welds. The increase in hardness within the stir zone (SZ) originated from the partial re-precipitation of the initial Guinier–Preston-Bagaryatsky zones (GPB) and metastable S needles, previously dissolved.) Formation and growth of stable S precipitates via coalescence accounted for the softening through the thermo-mechanically affected zone (TMAZ). The peak strengthening within the HAZ of the IFSW joints was mainly caused by the dense needle-shaped S particles, which can be explained by a mutual influence of the process specific temperature and strain cycles. Dislocations and subgrain boundaries introduced to the material due to plastic deformation facilitated the nucleation of strengthening S precipitates in the HAZ. It demonstrates that the impact of deformation should be considered by the characterization of the precipitation development in the HAZ.