Enhanced Dispersion of Initial Oxide Scale in Build-Up Friction Stir Welds of A6061 Aluminum Alloy Plates Using Tools with Wide Pitch Threaded Probe

Friction stir welding (FSW) is difficult to disperse the initial oxide scales in the stir zone when the joint interface is offset from the probe center or the area of weld interface increases by using insert metal. Increasing the pitch of the probe thread is effective to disperse oxide. In the present study, FSW of A6061 aluminum alloy plates supplying bulk build-up metal are performed by two tools with different thread pitch under the welding conditions of being difficult to disperse the initial oxide scales. The present study investigates the effect of the increased thread pitch on the weld microstructure, state of the oxide phase, tensile properties, and temperature history. The welding tool threaded a large thread pitch expands the stir zone in the joint. Increase in thread pitch promotes dispersion of the initial oxide scales in the stir zone. While the thread pitch had no significant effect on tensile properties, it greatly improved oxide dispersion. Therefore, this method is an effective in expanding a deformation area of the material without increasing the probe diameter.