OBRABOTKAMETALLOV technology Vol. 26 No. 2 2024 zinc, and copper as the main alloying elements. Due to solidification and liquation cracking in the fusion welding, Friction stir welding (FSW) is preferred to joining aluminum alloys [1]. The FSW process is preferred for joining difficult-to-weld similar and dissimilar aluminum alloys. As a solid-state joining process, FSW tends to lower distortion and residual stress in the welded joints. In comparison to the fusion welding techniques, FSW provides better joints. A specially designed rotating tool is inserted into the edges of the workpiece to be joined and moved along the interface of two plates in the FSW process. Consequently, the softened material near the tool is transported from the advancing side to the retreating side to form a joint [2]. In the FSW, a high downward force and spindle torque are required to generate a large amount of heat. The heat generated softens the material, providing the adequate plastic flow next to the tool. This leads to an increase in the volume of welding equipment and a greater welding load [3]. The FSW tool pin profile is subjected to higher stress during welding, which causes rapid tool degradation, leading to premature failure. Moreover, tool wear causes poor weld quality, resulting in higher production costs. Also, the higher welding load in the FSW limits the welding speed. These difficulties can be solved using different secondary energy sources during FSW. A group of researchers applied ultrasonic vibrations during FSW. Ultrasonic vibration-assisted friction stir welding (UVaFSW) assists in softening of the material without substantial heating [4–6]. Liu et al. [7] found that ultrasonic vibration-assisted FSW improved the joint mechanical properties, the quality of the weld, and the heat input at the localized area. According to Xu et al. [8], brazing with ultrasonic vibration assistance created a junction with a smaller grain size that improved corrosion resistance and ultimate tensile strength (UTS). Liu et al. [9], while investigating UVaFSW of AA1060 aluminum alloy, have found that ultrasonic energy enhanced the flow velocity, the volume of deformed material, and the strain rate. In aerospace, defense sectors and industrial applications, joint efficiency, and joint strength, play a key role, especially for joints made of similar and dissimilar aluminum alloys. It has been widely reported that joint efficiency and strength can be substantially improved using post-welding treatment. In the last few years, researchers have focused on post-weld treatment for aluminum joints. Shot peening and laser shock peening treatments are prominently reported in the literature as post-weld treatment, since both processes induce residual compressive stresses in the welded specimen and improve fatigue life, grain structure, and tensile strength. Fig. 1, a and b shows the schematic diagrams of laser shock peening and shot peening, respectively. a b Fig. 1. Schematics of (a) Laser shock peening process, (b) Shot peening process Amuda et al. in [10] inspected the effect of cryogenic cooling and the addition of element metal powder during the gas tungsten arc welding of the AISI 430 plate. Their study showed that both strategies refined the grain structure. However, with the accumulation of metal powder, a significant decrease in the zone of thermal influence (HAZ) is found to be up to 50 %, and cryogenic cooling reduces HAZ to 36 %. On the
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