OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 generation, the higher the plastic deformation and material flow, which ultimately results in higher values of UTS and microhardness. Additionally, a group of researchers have observed a correlation between the large and equiaxed dimples observed on the fracture surface with the higher values of UTS and microhardness of FSWed joints [26–28]. Material flow of the shot-peened UVaFSWed AA7075-T651 joints During Friction StirWelding (FSW), the quality of the weld depends on the flow of pasty material beneath the tool. Fig. 10 illustrates the material flow at the Weld Nugget (WN) for the shot-peened UVaFSWed joint of AA7075-T651 at Run P9. At Run P9, the laminar material flow was observed. The microstructure of the shot-peened UVaFSWed AA7075-T651 joints obtained at Run P9 is free of defects and porosity compared to conventional FSW joints [22–25]. Fig. 10 shows that the material flow is unidirectional, indicating proper intermixing of the material in the WN. The proper intermixing of the material improves the mechanical properties of the joints. Due to the ultrasonic vibrations, tunnel defects and micro-voids are eliminated, and fusion between the materials is improved. This results in higher mechanical properties compared to conventional FSWed joints. Fig. 10. Material flow of the shot-peened UVaFSWed AA7075 joint In the current study, it was observed that shot-peened UVaFSWed AA7075-T651 joints exhibit superior mechanical properties, favorable microstructure, and ductile-type fracture behavior as compared to conventional FSWed joints. However, the shot peening and UVaFSW combination yielded even better results. Additional research is necessary to optimize shot-peened UVaFSW while considering various interlayers, process parameters, and tool-pin geometries. Conclusions This study aimed to evaluate the performance of AA7075-T651 joints produced through shot-peened ultrasonic vibration-assisted friction stir welding (UVaFSWed) with a conical threaded pin type tool. The study varied the tool rotation and welding speeds to assess its impact on the joints tensile strength, microhardness, microstructure, and fracture behavior. Additionally, the study examined the grain distribution, material flow at the weld nugget, and joint fracture surfaces after the tensile test using SEM images. From the investigation, the following conclusions were made: ● The joint made by UVaFSW had better tensile strength, microhardness in the WN, and minimum surface roughness in comparison to traditionally FSWed joints. The shot-peened UVaFSWed joint is characterized by a maximum value of UTS (373.43 MPa) and microhardness in the WN (161 HV) at a tool rotation of
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