Journal of Welding Science

In this research, the ultrafine-grained (UFG) composite of AA2024 and AA5083 aluminum alloys was made by accumulative roll bonding (ARB) process and butt-welded by friction stir welding. Friction stir welding (FSW) is the best method for the joining of UFG strips. Microstructural investigations were performed by optical microscope and transmission electron microscope in the stir zone (SZ), thermo-mechanically affected zone (TMAZ) and heat affected zone (HAZ). The fine recrystallized structure with a grain size of about 900 nm was determined in the weldment. Due to the strengthening mechanisms of grain boundaries, nano-meter size precipitates and solid solution strengthening, the high strength of about 403 MPa was achieved. The presence of precipitates with homogeneous distribution in FSWed strips caused a high ductility of about 14% compared to the fabricated composite strips (6.9%). The high hardness of the SZ was caused by the formation of new equiaxed grains and fine precipitates, and also the decrease in the hardness of the HAZ was due to the dissolution and coarsening of T-phase precipitates.

In this study, the Friction Stir Welding process was employed to repair artificial cracks and grooves in 7075 aluminum alloy. Samples with different groove depths (0.5, 1, 1.5, and 2 mm) were prepared and evaluated through experimental tests, metallographic analysis, tensile testing, and numerical simulation using Abaqus software. The results showed that the Friction Stir Welding successfully repaired the defects without creating voids or surface irregularities. Microstructural observations in the stir zone revealed that dynamic recrystallization led to the formation of fine and homogeneous grains, resulting in improved hardness and tensile strength. The specimen with a 1 mm groove depth exhibited the best mechanical performance, with a maximum hardness of approximately 109 HV and the highest tensile strength among all samples. Conversely, samples with 0.5 and 2 mm groove depths showed void formation and reduced strength due to insufficient or excessive heat input and uneven material flow. Both experimental and simulation results confirmed that a groove depth of 1 mm provides optimal conditions for defect repair in 7075 aluminum alloy.

The joining of dissimilar aluminum sheets is an important issue in the optimization of industrial joints due to the differences in physical, mechanical and metallurgical properties. In this study, the mechanical behavior and microstructural changes of bimetallic joints made of AA5052 and AA3105 alloys joined by two methods of TIG welding (TIG) and friction stir welding (FSW) were investigated and compared. First, preliminary experiments were carried out to optimize the parameters of the friction stir welding and TIG welding processes and to select appropriate levels of the process parameters. The results of mechanical experiments showed that in the FSW welded samples, the failure occurred mainly in the weld zone, but in the TIG welded samples, the failure occurred in the base metal. The tensile test results showed that the AA5052 sample had the highest tensile strength (273 MPa) and the highest elongation percentage (20%), and the F 3-5 welded sample with a strength of 89 MPa and 6% elongation performed worse than the T 3-5 welded sample and fractured in the weld area. The microhardness test results showed that the TIG welded sample had a higher hardness in the weld area than the FSW method due to the use of 5356 ER filler. Finally, by analyzing and comparing the results obtained from the tests related to the mechanical properties obtained from each method, it was found that the TIG method performed better than FSW in joining some alloys.