Investigation of exit-hole repairing on dissimilar aluminum-copper friction stir welded joints

Exit-holes in friction stir welded dissimilar aluminum-copper (Al-Cu) joints are repaired by using probeless tools, forcing the surrounding material to fill the exit-hole cavity. The repair by refilling the same base materials is performed in two steps using probeless tools of different diameters. In this study, two different conditions are investigated, keeping the processing parameters constant and varying the tool shoulder diameters. Namely, the repair is performed using a two steps sequence of probeless tools with shoulder diameters of: (1) 12 and 19 mm, and (2) 12 and 27 mm. The refill action is achieved using only the base materials. A comprehensive experimental campaign, including tensile tests, microhardness measurements, scanning electron microscopy and energy dispersive x-ray spectroscopy investigations, have been conducted to evaluate the effectiveness of the repairing. The results showed that the usage of probeless tool is an effective strategy to repair the exit-hole of dissimilar Al-Cu friction stir welds, with exclusive contribution from the same Al and Cu base materials in the cavity of the exit-hole. The original FSW joint with exit hole, with a diameter of about 8 mm, repaired by shoulder diameters of 12 and 19 mm exhibited ultimate tensile strength about 13% higher than the values provided by the samples taken in the steady-state region of the weld bead The maximum and minimum hardness of the repairing zone made with shoulder diameters of 12 and 19 mm are 240 and 80 HV0.1, respectively, which are within the range of the friction stir welded regions indicated in previous studies. (c) 2021 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY license (http://creativecommons.org/licenses/by/4.0/).