Micro friction stir welding of ultra-thin Al-6061 sheets

The plunging depth of 0.05 mm was optimum for joint formation of 0.5 mm thick Al-6061 sheet by micro friction stir welding. Increasing rotational velocity from 1500 rpm to 2000 rpm was beneficial to sound surface formation, while the taper pin with three flats owned wider process window than the single taper pin. The minimum ratio of thickness reduction of 2% was attained, which enhanced the area of load bearing. The taper pin with three flats owing to the severe stirring actions resulted in the finer grain size, improving tensile property. The maximum tensile strength by the taper pin with three flats reached 217 MPa, equivalent to 90% of base material.