A study on microstructure development and mechanical properties during friction stir welding in a AISI 1018 mild steel

In this study, change in microstructures and corresponding mechanical properties during friction stir welding are investigated. Microstructural analysis was carried out by optical microscope and electron microscope. Tensile test is done by uniaxial tensile test machine. The results proved that Abrasion of welding tool happened when the transverse speed is relatively low and as a result some WC particles originated from the welding tool is observed in the weldment. In contrast, in relatively high transverse speed causes formation of tunneling defect in weldment. The results from uniaxial tensile test illustrated that the specimen welded by transverse speed of 100 mm/min was fractured from base metal, however in case of transverse speed of 50 mm/min fractured was appeared in weldment area. Significant grain refinement in welded specimens resulted in increment of yield strength. Furthermore, harness measurements demonstrated that in weldment area the hardness value increased from 155 HV to 210 HV.