Evolution Mechanisms of Microstructure and Performance of Aluminum Alloy Thin-Walled Components Repaired by Friction Stir Spot Welding

Taking the repair of prefabricated hole defects in 2024 aluminum alloy thin-walled componentsby friction stir spot welding (FSSW) as the research object, the evolution lawsof microstructure and mechanical properties of FSSW-repaired joints of thin-walled componentswere clarified through process experiments and numerical simulations. Thecollaborative effect of the temperature field and material flow field during the FSSW repairprocess and their regulation laws on the microstructure and properties were revealed. Theresults show that as the repair speed increases, the macroscopic surface quality of the FSSWjoint improves. When the repair speed reaches 2000 r/min, a high-quality repaired jointwith a smooth and flat surface and no porosity defects can be obtained. Meanwhile, withinthe repair speed range of 800 to 2000 r/min, the grains undergo dynamic recrystallization(DRX) due to the combined effect of heat and mechanical forces, eventually forming auniform equiaxed grain structure in the weld core area. ABAQUS 2023 simulation verifiesthe temperature distribution during the FSSW repair process. When the repair speed is2000 r/min, the maximum temperature obtained from the simulation is 431.1 ◦C, whichagrees with the measured value from the experiment. The simulation results further revealthat when the repair speed increases from 1200 r/min to 2000 r/min, the material fluiditysignificantly enhances, and the flow velocity on the advancing side is always higher thanthat in other areas. At the rotational speed of 2000 r/min, the plastic material flows continuouslyfrom the periphery and eventually fills the defect area completely. The fracturemode of the FSSW-repaired joint is mainly ductile fracture. With the increase in the repairspeed, the number of dimples at the fracture surface increases significantly. When therotational speed reaches 2000 r/min, the joint achieves the best mechanical properties, andthe FSSW-repaired joint reaches the maximum tensile strength of 169 MPa.