Abstract
Friction-stir welding of 6061,2024,2219,and 7075 aluminum alloys to themselves as well as dissimilar systems of 6061/2024 and 2219/7075 aluminum alloys are studied to produce sound welds, and to characterize the microstructure, material flow, and properties of their butt joints. The material flow patterns are clearly revealed by the flow visualization marked with a copper-powder tracer technique in the welds of 6061 aluminum alloy. The copper powder is placed at the whole, the top, the middle, and the bottom third of the faying surface along the welding direction. Although all the nugget zones are composed of fine equiaxed grain, structures, significant differences in the plastic deformation and flow patterns have been observed throughout the same and dissimilar friction-stir welds. A significant hardness loss at the thermomechanical affected zone (TMAZ) and the heat affected zone (HAZ) is found throughout all the welds as compared to the nugget zones and the parent metals, The dissimilar metal welds exhibit complex alternative lamellae that produce distinct hardness fluctuations in the nugget zone. At the top surface of the weld, the material transport occurs due to the action of the rotating tool shoulder. The inward return flow in the interior of the nugget zone appears much stronger than the outward surface flow along the weld surface. Dissimilar metal Welds are successfully performed to further characterize the degree of material mixing and interdiffusion, the thickness of the deformed aluminum lamellae.
