Engineering tensile properties by controlling welding parameters and microstructure in a mild steel processed by friction stir welding

In order to evaluate the effects of welding parameters on microstructure and tensile properties, a mild steel was stir welded under various conditions. The results revealed that carrying out the friction stir welding (FSW) process in lower rotation speeds or higher welding speeds due to lack of heat input and low flow-ability of the welding material, tunnel defect and flaky surface is appeared. In contrary, in higher rotation speed or lower welding speed, the temperature of stir zone (SZ) reached to single austenite region owing to significant increment of heat input. Consequently, refined microstructure involving ferrite and pearlite transformed from new fresh austenite can be formed. Tensile behavior of the FSW processed specimens exhibited relatively higher amount of yield strength and limited uniform elongation in comparison with the starting material. But, the samples has tunneling defect or any other welding defects showed very limited uniform elongation.