Friction Stir Welding of Ultra Low Carbon Steel Microstructure Mechanical properties and Electrochemical Study

Abstract

The present automobile industry, with an increase in aerodynamic designs, the formability property of structural materials is a fundamental requirement. This requirement demands high ductility in materials. The properties of ultra-low carbon steel fulfil this to a certain extent. On the other hand, aerodynamics in automobiles also requires uni-body designs. Friction stir welding is a solution to this problem. In friction stir welding (FSW), two work piece materials form a bond without melting along their interface region. The absence of welding fumes in FSW encourages environmental sustainability. This fumeless welding process is sometimes called a green welding process. The end-product of FSW is free of most of the defects (for example, porosity, undercut, lamellar tearing, hot cracking, distortion, etc.) that are found in regular fusion welding techniques. In the present work, friction stir welding has been performed on the ULC steel at different tool rotational and traverse speeds to find out the optimal operating processing parameters for achieving maximum strength. Therefore, this work attempted to reach the scientific basis behind the one-to-one or/ one-to-many relationship between the process parameters (such as tool rotational and traverse speed), structure, mechanical properties, and electrochemical behaviour of the friction stir welded ULC steel joints. The welding parameters, such as the tool rotational speed, varied from 300 to 900 rpm instep of 150 rpm, and the tool traverse speed has been varied from 15 to 75 mm/min instep of 15 mm/min. The other process parameters, such as tool tilt angle and axial thrust, have been kept constant during the welding, and the experiments have been conducted with a suitable design of experiments. Firstly, the fabrication of butt joints of 3 mm thickness ULC steel using friction stir welding was performed for the varying tool rotational speed with constant tool traverse speed, which was chosen after the analysis of the available literature. The structural analysis of