AWS WHC-3.07:2008

Friction Stir Welding
Scope : Friction stir welding (FSW) is a variant of friction welding that produces a weld between two (or more) workpieces by the heating and plastic material displacement caused by a rapidly rotating tool that traverses the weld joint.1, 2 Heating is believed to be caused by both frictional rubbing between the tool and workpiece and by visco-plastic dissipation of the deforming material at high strain rates. Like conventional friction welding processes, the FSW process is solid state in nature. Both friction welding and friction stir welding produce a volume of hot-worked metal along the bond line. However, friction stir welding differs from friction welding in one important aspect: in friction welding, the relative motion is between the workpieces that are held in compression, whereas the relative motion in FSW is between the workpieces and a rotating tool. Friction stir welding has been in existence since the early 1990s and was developed mainly for the welding of aluminum alloys. The significant benefits of this process were quickly recognized, motivating considerable research and development during the next decade that expanded the technology to other materials. Information in this chapter provides a basic understanding of the friction stir welding process and a variation of the process, friction stir spot welding. Topics include equipment and controls, process variables, materials and applications, mechanical properties, weld quality, economics, and safe practices. Additional topics discussed in this chapter are heat transfer, material flow, residual stress, nondestructive examination, and corrosion. Lists of technical papers that have been used in compiling this chapter are provided in the Bibliography. An important feature of the Bibliography is the grouping of these papers according to the specific alloys welded with the friction stir process.