Aluminium Al6061 is a highly weldable alloy which find applications in the production of aircraft, yacht as well as automobile components. Friction stir welding, being a high quality solid phase metal joining method, is used widely in these industries. Though the quality of welds are claimed to be much higher than that of welds made by conventional welding procedures, tunnel-type, void and root-flaw defects occur frequently depending on the welding parameters. These defects are of very high prominence in industries because of the associated reduction in fatigue life. Main intention of this paper is to specify the defects of butt friction stir welded joints, which can be identified through micrographs taken using scanning electron microscope and non destructive testing methods such as ultrasonic testing and X-radiography, in aforementioned alloys. © Research India Publications.