Interfacial sticking and slipping in the friction stir welding process

In friction stir welding (FSW), a rotating threaded weld tool is inserted into a weld seam and literally stirs the edges of the seam together. To determine optimal processing parameters for producing a defect free weld, a physical understanding of the resulting metal deformation flow path is required. Marker studies are the principal method of studying the metal deformation flow path around the FSW weld tool. In our study, we have used a lead wire embedded in the weld seam as a tracer. At the welding temperature of aluminum, the lead becomes molten and is continuously carried with the macro-flow of the weld metal. A through thickness flow of metal was revealed in the X-ray imaging of the lead tracer in addition to revealing a cyclic oscillation in the plasticized metal affected by the process.