Microstructures and mechanical properties of micro friction stir welding (μFSW) of 6061-T4 aluminum alloy

Micro friction stir welding (μFSW) was successfully performed to join the ultra-thin 6061-T4 sheet with the thickness of 0.5 mm. The optimum plunging depth of 0.05 mm was obtained and reduction ratio was lower than 0.2%. Based on better dynamic flow induced by the triflat pin, the good surface appearance at the wider process window was obtained, while the grain size at the nugget zone was finer than that by the taper pin. Increasing welding speed caused that tensile property increased firstly and then decreased with high welding speed than 500 mm/min. The maximum values of tensile strength and elongation of the μFSW joint using the triflat pin reached 220.3 MPa and 11.7%, which were 91.9% and 54.4% of base material, respectively.