Experimental investigation of the effect of induction preheating on the microstructure evolution and corrosion behaviour of dissimilar FSW (IN718 and SS316L) joints

Abstract

The present work investigates the microstructure and electrochemical behaviour of the joints formed with and without induction-assisted friction stir welds (FSW) between SS316L and Inconel 718. For this purpose, conventional and induction preheating assisted friction stir welding (I-FSW) was carried out at a rotational speed of 300 rpm and traverse speed of 140 mm/min with 300 °C preheating. The microstructure and phases of the nugget zone were analyzed. The corrosion behaviour of the welded joint and the base metal was investigated in 1 M HCl solution and 3.5 wt% NaCl solution using immersion test and electrochemical techniques. The results show that the induction preheated friction stir welding process produces defect-free joints than the conventional FSW with little increased grain size. Intermetallic compounds (IMCs) at the interface of the nugget zone were not detected due to insufficient heat input. The corrosion result revealed that the corrosion resistance of the I-FSW weld joint was better than the FSW weld joint, and it was lowest in the case of base SS316L, which was confirmed with the immersion test, potentiodynamic polarization test (PDP), and electrochemical impedance spectroscopy (EIS). The presence of blocky carbide particle M23C6 was responsible for the pitting corrosion in the steel region.