Application of preheating for defect mitigation and its corresponding effects on mechanical–corrosion performance of friction stir welded AA6082-T6

The present study investigates the influence of induction preheating on weld integrity, microstructural evolution, mechanical and corrosion behaviour of friction stir welded AA6082-T6 joints. The preheating of workpiece material is done prior to the start of friction stir welding (FSW). Induction preheating acted as an additional thermal source intended to promote material plasticisation and improving weld consolidation. The preheating will additionally affect the microstructural evolution, mechanical performance and corrosion behaviour of the joints, consequently making them the part of the present study. Preheating at 150 °C transformed tunnel defects of non-preheated joints into minor voids, while preheating at 250 °C and 350 °C produced defect free joints. Joints preheated at 250 °C resulted in refined grain structure (∼ 0.9 micrometres), improved tensile strength (∼ 12%), enhanced microhardness (∼ 40%). Fractographic analysis using FE-SEM confirmed a ductile mode of fracture with uniformly distributed dimples in the preheated joints. Furthermore, electrochemical corrosion studies revealed improved corrosion resistances (lower corrosion rates) in the induction-preheated joints, evidenced by reduced corrosion potential, reduced current density, and enhanced charge transfer resistance. Overall, induction preheating proved to be an effective approach for improving the structural integrity and performance of FSW joints.