Actively inducing multiple dynamic recrystallization events to suppress grain coarsening in wire-based friction stir additively manufactured layers

Wire-based friction stir additive manufacturing (W-FSAM) avoids the defects inherent in fusion-based processes and improves the continuity of feedstock feeding, positioning it as a highly promising technology for aluminum alloy additive manufacturing. However, thermal cycling during multi-layer deposition readily affects the previously deposited layers, leading to microstructural coarsening, residual stress, and property deterioration. To address this issue, the present study designed a tool with a long stirring pin that actively induces more extensive dynamic recrystallization (DRX) to refine the microstructure of the previously deposited layers. Through finite element simulation and experimental validation, it was determined that the 2.5 mm-long stirring pin could induce DRX simultaneously in two deposited layers, successfully suppressing the coarsening of the underlying layer. The high-temperature, high-strain zone generated by the stirring pin promoted DRX behavior in the deposited layer at this location and led to pronounced {100}〈001〉 oriented nucleation. Furthermore, this work elucidates the complex microstructural evolution behavior under severe plastic deformation and reveals the relationship between the microstructure and the mechanical properties.