Visualization of Material Flow during Friction Stir Welding (FSW) of the Same and Dissimilar Aluminum Alloys

This paper investigates the temperature distribution and visualization of material flow in friction-stir welds of aluminum alloys. The flow patterns are clearly revealed by a dissimilar material tracer technique. The 2024 aluminum strips are selected as the tracer material because of the metallographic etching characteristics that differ significantly from those of the 6061 aluminum alloy and the good weldability via the friction stir welding (FSW). The 2.0-mm thick strips are placed at the whole, the bottom, the middle, and the top third of the faying surface along the welding direction to characterize the localized flow of material. The applied forces exerted by the shoulder are measured with the piezoelectric force transducers, while the weld temperature profiles are measured with thermocouples imbedded into different positions of the samples. The inward return flow in the interior of the nugget appears much stronger than the forward surface flow along the weld surface. A dissimilar FSW of 6061 aluminum to 2024 aluminum is performed to further characterize the flow behavior of dissimilar metals. The material flow patterns, the degree of material mixing and interdiffusion, and the thickness of the deformed lamellae highly depend upon the geometry of the threaded tool, welding temperature, and material flow stress.