<p>This study investigates the repair of blind-hole defects in Al-Mg-Li alloy using Additive Friction Stir Deposition (AFSD). The effects of hole geometry (diameter and depth) on filling behavior, interfacial bonding, microstructure evolution, and mechanical properties were systematically examined. Results reveal a distinct “reparable window”: holes with a diameter of ~ 8&#xa0;mm and depth ≤ 4&#xa0;mm could be fully filled due to matched frictional heating and material flow. Beyond this range, incomplete filling and interfacial defects occurred. Microstructural analysis showed that the near-center region developed a {111} &lt;110 &gt; shear texture with coarse grains, while the periphery formed a fine-grained &lt; 111&gt; fiber texture with a directional banded structure under constrained flow. The bottom edge region (BEBR) exhibited the weakest bonding due to insufficient heat input, pressure attenuation, and localized Al₂O₃ formation. The repair zone displayed refined nano-scale <i>δ</i>′-Al₃Li precipitates via dissolution–reprecipitation, leading to recovered hardness. Tensile strength reached ~ 379&#xa0;MPa at well-bonded shallow regions but dropped sharply to ~ 54&#xa0;MPa at poorly bonded deep regions, where fracture occurred along the interface. This work provides a fundamental understanding of AFSD-based repair of constrained 3D defects in high-strength Al alloys.</p>