Repair of Defective FSW Butt Joints

Kurzfassung

Within the ADO (Airbus-DLR-ONERA research cooperation funded by Airbus) FSW project, scenarios for repairing FSW joints that had turned out to be defective were developed. In the present paper, full-length re-welding of the complete joint line and resulting change in mechanical behaviour was examined. The work was performed on defective butt welds intentionally made at Airbus Operations GmbH in Bremen. At DLR, defective and repaired FSW joints were checked by high frequency ultrasonics and electrical conductivity measurements through the eddy current technique. Mechanical behaviour was characterised in terms of bending, tensile and S-N tests. Defective FSW joints could completely be repaired by a single re-welding process. A second re-welding was not observed to generate any kind of improvement. Conversely, it slightly reduced strength and ductility. The decrease in strength was the lowest for 2024-T3. 2198-T8 and 6156-T6 took a less favourable position, since the artificially aged tempers exhibited higher sensitivity towards additional thermal cycles. However, strength in double repair condition should also be acceptable for these alloys, since weld efficiency never decreased below 72% even for two-pass repair throughout the present study.