Characteristics of Keyhole Refill Process using Friction Stir Spot Welding

Abstract

The characteristics of the application of the friction stir spot welding process to a keyhole which was produced at the friction stir spot welding, 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 toward 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.