Residual stress analysis of additive friction stir deposition of AA 7050 with varying traverse speeds

Additive friction stir deposition (AFSD) is a state-of-the-art solid-state additive manufacturing process that provides refined microstructures, compared to fusion-based techniques, and is apposite for point-of-need applications. However, residual stress development remains a critical concern for process scalability and structural performance. In this work, the influence of traverse speed on residual stress evolution, thermal behaviour, and microstructure in lubricant-free AFSD of AA7050-T7451 was investigated. Deposits were fabricated using two traverse speeds in a serpentine rastering pattern under identical set point temperature control conditions. In situ temperature data were collected using a thermocouple embedded in the tool during deposition. Residual stresses were quantified using grazing incidence X-ray diffraction (GI-XRD) in the build’s planar and through-thickness directions, while microstructural characteristics were assessed via electron backscatter diffraction (EBSD). The results indicate that increasing traverse speed leads to a reduction in the magnitude of compressive residual stresses in all three directions, with significantly larger differences observed in the through-thickness direction. EBSD analysis revealed that the slower traverse speed resulted in pronounced grain coarsening toward the end of the build, whereas grain size remained relatively uniform along the build for the faster traverse speed. The results also support that the faster traverse speed resulted in a more uniform thermal gradient in the deposit. These findings demonstrate that traverse speed is an effective parameter for tailoring residual stress distributions and microstructural uniformity in AFSD deposits, providing guidance for optimizing process parameters for performance-critical applications.