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Friction stir welding of ultra low carbon steel: microstructure, mechanical properties and electrochemical study

In the present investigation, the friction stir welding of ultra low carbon steel was carried out at different tool rotational speeds of 300 to 900 rpm in steps of 150 rpm for 30 mm/min traverse speed. The macro and microstructures were examined to identify the different areas of stir zone, thermomechanically affected zone and heat affected zone of the welded joints. Tensile strength of the welded joints was evaluated and maximum tensile strength of ∼336 MPa was obtained at 450 rpm tool rotational speed. Microhardness was measured along the cross section of the welded joint. The maximum hardness was observed at stir zone when compared to thermomechanically affected zone and heat affected zone. The hardness values decreased with the increase in tool rotational speeds in the stir zone. Electrochemical study was investigated in 0.1 mol/L HCl solution using various electrochemical measurements such as open circuit potential, electrochemical impedance spectroscopy and potentiodynamic polarization. The corrosion rate at stir zone decreased with the increase in tool rotational speed.