Friction Stir Welding (FSW) is a novel solid state welding process for joining of metallic alloys and has emerged as an alternative technology used in alloys that are difficult to join with conventional techniques. It uses a non consumable rotating welding tool to generate frictional heat and plastic deformation at the welded location while the material is in solid state. In this paper, the mechanical properties of welded joints of AA 6061 alloy were investigated to determine the effect on the mechanical properties of welding joints. FSW process was carried out at the various rotational speeds (1000, 1200 rpm) with welding speed 15 mm/min by using Half Groove Threaded (HGT) tool. Micrographs showed proper mixing at the higher rotational speed and at lower feed rate. The results in this study show that maximum welding efficiency of AA 6061 in terms of ultimate tensile strength, using 1200 RPM rotational speed, 15 mm/min traveling speed. By correlation of mechanical and metallurgical properties of welded sample at lower feed rate performed better in terms of ductility. © 2017 Elsevier Ltd. All rights reserved.