Passive filling friction stir repairing of AISI 304 alloy

The practical development of this master's thesis took place in the months of October and November 2023. Welding processes were carried out using equipment from “stirtec,” installed at the EuroDies Italia Srl’workshop located in Rivoli (TO). All laboratory tests were conducted at the J-Tech laboratory located at the main campus of the Polytechnic University of Turin. The thesis focuses on the application of the passive repair process for filler friction on AISI 304 alloy. The joining process used is Friction Stir Welding (FSW), which offers significant advantages in terms of joint strength and quality. The main material used for the experiments is AISI 304 steel, known for its strength and ductility. Experimental tests were conducted following the specifications of JIS G 3136, with particular attention to the geometry of the test samples and optimal welding conditions. The passive repair process for filler friction was evaluated through the analysis of samples with simulated defects of various sizes (0, 2, 4, and 6 mm) and the insertion of plugs to assess the effectiveness of restoring mechanical properties. The research findings highlight that increasing defect sizes negatively affects the load-carrying capacity of the joints, with greater variability in the obtained values. However, increasing the dwell time during the welding process appears to improve defect closure and standardize load values. In particular, samples with inserted plugs show higher tensile strength, suggesting more effective anchoring of the plug to the sample. In summary, Gianmarco Rimmaudo's research demonstrates that the passive repair process for filler friction can be an effective strategy to restore the mechanical properties of AISI 304 steel joints, with particular attention to defect size and dwell time during the welding process.