Tool geometry optimization for enhanced mechanical properties in friction stir welding of carbon steel

Friction stir welding (FSW) is known for its environmentally friendly characteristics and energy efficiency. The geometry of the tool holds significant importance in FSW, playing a crucial role in ensuring satisfactory welds. In the present work, optimization of tool geometry is carried out for the FSW of 3 mm thick AISI 1018 carbon steel. A tungsten carbide tool containing 7 wt.% cobalt with a tapered pin profile—identified as the optimal configuration—was employed for the welding process. The FSW joint was subjected to microstructure examination and tensile testing for weld quality. The results revealed that optimized tool geometry enhanced the weld quality. The welded joints revealed an 18% increase in ultimate tensile strength (UTS) than the base metal (BM). Microstructural observations in the thermo-mechanically affected zone (TMAZ) and heat-affected zone (HAZ) were conducted using Scanning Electron Microscopy (SEM) and analyzed with ImageJ software. The present study demonstrated a significant increment in the ultimate tensile strength of the joint obtained by incorporating the optimized parameters, additionally, the microstructures were uniform throughout the TMAZ and HAZ. Fractography of the ruptured sample revealed a dimpled region indicating ductile failure.