Electroplastic friction stir spot welding for joining AA6061-T6 aluminum to galvanized DP590 steel

The friction stir spot welding has shown great potential for joining low-ductility aluminum to high-strength steels. In the last decade, wide researches were done to achieve high strength and tool life enhancement in friction stir spot welding. The electroplastic effect, with its environmentally friendly nature and high efficiency, has resulted in a reduction of flow stress and tool wear, improvement of plasticity and material flow for various processes. On the other hand, adding nanoparticles to the friction stir spot welded area joint increased the tool wear despite the improved strength. In this paper, the joint strength and spindle output power are investigated in electroplastic friction stir spot welding process for joining of AA6061-T6 with 1 mm thickness to DP590 steel sheet of 1.5 mm. A 2K design was used for statistical analysis considering four parameters of rotational velocity (1000, 2000 rpm), dwell time (2, 4s), electrical current (250, 500A), and adding SiC reinforcing nanoparticles. A quantitative study of the current density was performed by the finite element code with thermal-electric coupling. Results showed that electroplastic effect had a compatible impact with nanoparticles on strength improvement by accelerating the occurrence of dynamic recovery and recrystallization, and neutralized the negative effect of nanoparticles on tool life since created joints with failure loads above 7 kN.