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Characteristics of keyhole refill process using friction stir spot welding

ABSTRACT The characteristics of the application of the friction stir spot welding (FSSW) process to a keyhole which was produced at the FSSW, to refill the hole and make it disappear, were investigated. This paper focused on the material flow caused by a rotational tool, using a scrolled groove tool without a probe that could produce a material flow towards the rotating centre. The keyholes in lap joints of aluminium alloy disappeared when the FSSW conditions were a tool rotational speed of 1500 rpm, a plunging depth of 0.7 mm and a dwell time of 4 s, although gaps in the bottom of the keyhole was observed in some of them. From the observation results of the material flow conditions in this case, to eliminate the non-refill space and to transmit the rotary torque to the stir zone, it is suggested that it is important that the material flow to refill a keyhole and the deformation of the keyhole edges reach to the bottom of the keyhole at approximately the same time.