How is friction stir welding applied to aerospace aluminum structures?

Friction stir welding (FSW) is solid-state joining process for aluminum. Process: Rotating tool with shoulder and pin plunges into joint, Friction heat softens material below melting, Tool traverses along joint mixing material, Forges joint as tool passes. Advantages: Solid-state (no melting) - No porosity, hot cracking; Can join unweldable alloys (2xxx, 7xxx), Superior mechanical properties to fusion welding, Minimal distortion, and Automated, repeatable process. Applications: Fuselage longitudinal joints (Eclipse, A380), Fuel tanks (Space Shuttle External Tank), Wing skin panels, and Integrally stiffened structures. Parameters: Rotation speed, traverse speed, plunge force, and tool geometry. Metallurgy: Heat affected zone (HAZ) with property reduction, Thermomechanically affected zone (TMAZ), and Nugget (stir zone) with fine grain. Design: Joint design differs from riveted, Allows integral rather than mechanically joined structure, and Weight savings from reduced overlap. Certification requires extensive characterization of joint properties, process window, and NDT capability.