A novel method for improving the plastic flow and mechanical properties of spray-formed 7055-T76 (Sc-added) aluminum alloy FSW joint by rotating magnetic field

In order to achieve high-quality welded joint of spray-formed (SF) 7055 aluminum alloy (Sc element added) plate, the electrically-magnetically-assisted friction stir welding (EMAFSW) method was used in this investigation, and the plate was docked by changing the coil current of the rotating magnetic field generator. The effects of rotating magnetic field and different coil currents on the microstructure and mechanical properties of friction stir welds were studied by methods of optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), high resolution transmission electron microscopy (HRTEM) and mechanical properties test. The results show that after applying the rotating electromagnetic field generated by 100 Hz current, and with the increase of coil current, the grain refinement of weld microstructure is obvious, the toughness and ultimate tensile strength of weld joint are improved, and the tensile fracture morphology shows more ductile fracture characteristics. This is due to the fact that the rotating magnetic field weakens the dislocation density and strain of the joint during the FSW process, but the magnetic field plays a role in strengthening the microstructure fine grain simultaneously. The results of this investigation will provide a new welding method for obtaining good cemented aluminum alloy joints, help to better understand the magnetoplastic mechanism, and expand the FSW process window.