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Friction Stir Welding Assisted by Electrical Joule Effect to Overcome Lack of Penetration in Aluminium Alloys

Friction stir welding assisted by electrical joule effect is a development of conventional friction stir welding with the ability to eliminate or minimize the root defects by lack of penetration. The lack of penetration, mainly relevant in the welding of aluminium alloys, still constitute one major constrain to a wider dissemination of friction stir welding into industrial applications. The concept is based on assisting friction stir welding by an external electrical heat source integrated in the FSW tool. The innovative tool feature enables to increase the temperature in the weld root by Joule effect and improve material viscoplasticity in this region. A new tool was designed, manufactured and implemented. The resulting welds produced were analyzed via metallography and Electrical conductivity measurements that have proven to be a valuable technique to identify the different zones of solid-state welded joints with a good correlation with the microstructure and hardness. The potential of this variant was shown reducing the thickness of weld root defect, even for significant levels of lack of penetration, although affecting the grain size of the HAZ in the vicinity of the root surface.