Synergistic Regulation of Heat Input and Interfacial Migration for Defect Suppression and Microstructural Homogenization in Friction Stir Additive Manufacturing of 2060-T3 Al–Li Alloy

Friction stir additive manufacturing (FSAM) is a promising solid-state route for aluminum–lithium (Al–Li) alloy structural fabrication, yet interfacial defects and microstructural heterogeneity remain key challenges. This study investigates the effects of rotational speed, traverse speed, and overlap ratio on defect formation and microstructural evolution in 2060-T3 Al–Li alloy, with postdeposition heat treatment further evaluated for property optimization. At 800 r/min and 300 mm/min, a void-free cross-section is achieved with a nugget zone grain size of 1.45 μm, a dynamic recrystallization fraction of 67.64%, and a high-angle grain boundary (HAGB) fraction of 92.29%; suboptimal speeds produce either internal voids or surface depression and flash. An 80% overlap ratio eliminates hook defects via secondary recrystallization, achieving an effective build width of 7.14 mm versus 5.05 mm at 90% overlap. Solution treatment at 525°C/0.5 h followed by single-stage aging at 145°C/35 h promotes uniform Al ₂ Cu reprecipitation, delivering a peak microhardness of 170.6 HV0.2 and a stable HAGB fraction of 82.1%. These findings establish a three-stage defect control strategy—intrapass optimization, interpass overlap management, and postdeposition heat treatment—providing a systematic pathway for high-performance FSAM of Al–Li alloy structural components.