Superior mechanical performance of 2024 Al alloy fabricated by additive friction stir deposition

Additive friction stir deposition (AFSD) represents an innovative solid-state additive manufacturing paradigm. However, a comprehensive understanding of the microstructural evolution and mechanical properties of 2024 aluminum alloy bulk components processed via AFSD remains limited. This study systematically investigates the microstructural characteristics and mechanical anisotropy of AFSD-processed 2024 aluminum alloy deposits. Results indicate that while minor microstructural gradients exist along the build direction attributable to variations in thermal history and severe viscoelastic deformation, the overall deposit exhibits remarkable homogeneity. Specifically, the lower and middle regions undergo dynamic and static recrystallization induced by cyclic thermal exposure, resulting in minor grain coarsening. Quantitative analysis revealed average grain sizes of 1.78 μm, 2.19 μm, and 2.3 μm for the top, middle, and bottom regions, respectively. Furthermore, micro-Vickers hardness testing revealed a significant gradient along the building direction, contrasting with the uniform distribution observed along the transverse direction. Mechanical testing demonstrated peak tensile strength along the longitudinal direction reaching 425 MPa, with elongation along the transverse direction exceeding 18%. Conversely, mechanical properties along the building direction were notably inferior to those in the planar directions, highlighting the presence of anisotropy despite the process's ability to significantly refine the grain structure.