Friction Stir Extrusion: Control Processes and Unique Applications

Abstract

Dissimilar material joining by welding poses unique challenges due to mechanical and chemical incompatibilities between materials. Alternatives such as fasteners and adhesives add cost and weight. Friction Stir Extrusion (FSE), a derivative process of Friction Stir Welding (FSW), sidesteps many issues by forming an in-situ mechanically interlocking join using the plastic flow present in FSW to fill pre-formed geometries. FSE stands out as a derivative process as it extends the capabilities of FSW without requiring additional tooling or equipment and applying to a large variety of material combinations. Multiple research projects demonstrated novel processes and control techniques to improve FSE. First, applying FSE to a new regime of stock material size was accomplished by demonstrating a method of forming the geometry instead of milling or cutting. Second, post-processing FSE welds at a low-temperature precipitation heat treatment improved joint strengths by 23.9% and minimally affected the base material. A torque controller applied to FSE improved tool contact and eliminated surface defects across a wide range of groove cross-sectional areas. A novel weave-tracking algorithm adapted to initial offsets and angular misalignment between the initial weld path and groove location. Finally, Tracer experiments revealed the inner structure and material flow during FSE.