Friction stir welding assisted by electrical joule effect to overcome lack of penetration in aluminium alloys

Friction Stir Welding (FSW) assisted by electrical Joule effect was developed after the conventional process to eliminate or minimize root defects such as lack of penetration. This type of defect still constitutes a major constrain to a wider dissemination of Friction Stir Welding in industry, especially when aluminium alloys are to be welded. The concept is based on assisting FSW with an external electrical heat source supplied via the tool to increase the temperature in the weld root and improve locally the material viscoplasticity. A new tool was designed, manufactured and implemented. The welds produced were analyzed by metallographic techniques 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 of FSW was shown, as it was possible to reduce the thickness of the weld root defect, even for significant dimensions of lack of penetration, without affecting the grain size of the HAZ in the vicinity of the weld root. © 2014 Trans Tech Publications, Switzerland.