Weld Zone Research Articles

Research on the Welding Process and Weld Formation in Multiple Solid-Flux Cored Wires Arc Hybrid Welding Process for Q960E Ultrahigh-Strength Steel.

This paper proposes a novel welding process for ultrahigh-strength steel. The effects of welding parameters on the welding process and weld formation were studied to obtain the optimal parameter window. It was found that the metal transfer modes of solid wires were primarily determined by electrical parameters, while flux-cored wires consistently exhibited multiple droplets per pulse. The one droplet per pulse possessed better welding stability and weld formation, whereas the short-circuiting transfer or one droplet multiple pulses easily caused abnormal arc ignition that decreased welding stability, which could easily lead to a "sawtooth-shaped" weld formation or weld offset towards one side with more spatters. Thus, the electrical parameters corresponding to one droplet per pulse were identified as the optimal parameter window. Furthermore, the weld zone (WZ) was predominantly composed of AF, and the heat-affected zone (HAZ) primarily consisted of TM and LM. Consequently, the welded joint still exhibited excellent mechanical properties, particularly toughness, despite higher welding heat input. The average tensile strength reached 928 MPa, and the impact absorbed energy at -40 °C for the WZ and HAZ were 54 J and 126 J, respectively. In addition, the application of triple-wire welding for ultrahigh-strength steel (UHSS) demonstrated a significant enhancement in post-weld deposition rate, with increases of 106% and 38% compared to single-wire and twin-wire welding techniques, respectively. This process not only utilized flux-cored wire to enhance the mechanical properties of joints but also achieved high deposition rate welding.

Microstructure evolution and strengthening mechanism of Al–Cu–Li–Mg–Ag VPPA welded joint during local three-stage and natural aging treatment

Local three-stage (LTA) and natural aging (NA) treatments were proposed to address the challenges associated with the aging treatment of Al–Li alloy fuel tanks and improve the mechanical properties of VPPA welded joints. The microstructure evolution and mechanical properties of aging welded joints were investigated, followed by a discussion of strengthening mechanisms. The results demonstrated that LTA treatment significantly improved the mechanical properties of VPPA welded joints, with an elongation of 6.8 % and a tensile strength of 501 MPa, representing 88.6 % of the base metal. Following the local double-stage solution (LDS) treatment, the eutectic phases in the welded joints dissolved. During the LTA treatment, there was a consistent decrease in elongation. Initially, the θ'' phase precipitated, followed by the T1(Al2CuLi), σ(Al6Cu5Mg2), and S′(Al2CuMg) phases. With increasing aging time, some θ'' phases transformed into θ′(Al2Cu) phases, while others combined with Mg and Ag to form Ω phases. The precipitated phases continued to grow, increasing the precipitation-free zone (PFZ) width. After 30 h of aging, three types of <110> twinned dendrites were observed in the weld zone (WZ) with (111) twinned planes. The improvement in performance was credited to the elimination of eutectic segregation, as well as the enhanced solid solution and precipitation-strengthening effects. The increase in strength of the LDS state welded joints was primarily due to solid solution strengthening. The strength of the precipitated phase was mainly achieved through the bypass mechanism. The eutectic phases did not dissolve after NA treatment, which resulted in limited strength increment and unchanged elongation (EL). Numerous T1 phases precipitated contributed to the precipitation-strengthening effect.

Enhanced comprehension of the cross-scale forming mechanism in CF/PEEK resistance welding: Analysis of temperature gradients and meso–microscopic phase transitions

Resistance welding technology is an effective solution for connecting thermoplastic composites. However, limited research on non-uniform distribution of interfacial temperature and complex evolution mechanism of phase-change molding hinders its application. This reliance on traditional experimental and trial-and-error methods severely impedes its development. Therefore, this study employed a novel cross-scale numerical simulation method, being applied for the first time in the field of resistance welding for elucidating the underlying mechanism of joint formation through multi-component phase transformation. The constructed model accurately represented the transient heat transfer of a realistic wire mesh structure in three dimensions, while incorporating complex gradient effects arising from both spatial and temporal variations in heating element temperature due to air interference. Further, melting, flow, and consolidation behavior of the resin matrix in resistance welding of carbon fiber/polyetheretherketone (CF/PEEK) thermoplastic composite was investigated herein at a mesoscopic scale. To accomplish this objective, a three-phase flow spatial forming and evolution model for resistance welding was developed at the mesoscopic scale by integrating principles from fluid dynamics. Interestingly, introduction of an air phase reinstated the spatial voids formation and flow in resistance welding, providing robust evidence for the initiation mechanism of internal defects. Moreover, this study revealed variations in the melting mode of PEEK resin across different regions within the weld and highlighted distinct distributions of voids resulting from uneven heat transfer. The interfacial phenomenon and flow diffusion mechanism between components in resistance welding tests were further verified and discussed through analyzing scanning electron microscopy and energy dispersive spectroscopy results. Temporal and spatial correlation in void distribution within the welding zone was observed, which was found to be consistent with simulation results. Specifically, with the progress of the welding process, air near the wire mesh gradually dispersed into the laminate, with significantly more voids at weld seam edges than in central regions. This research methodology based on stepwise scale reduction offers a promising avenue for investigating resistance welding and other connection forming applications, in particular, within the context of engineering underlying logical behavior.

Dissimilar Welding of Thick Ferritic/Austenitic Steels Plates Using Two Simultaneous Laser Beams in a Single Pass

Dissimilar welds between ferritic and austenitic stainless steels are widely used in industrial applications. Taking into account the issues inherent to arc welding, such as the high heat input and the need to carry out multiple passes in the case of thick plates, a procedure with two simultaneous laser beams (working in a single pass) and consumable inserts as filler metal has been considered. Particular attention was paid to the choice of the filler metal (composition and amount), as well as welding parameters, which are crucial to obtain the right dilution necessary for a correct chemical composition in the weld zone. The first experimental investigations confirmed the achievement of a good weldability of the dissimilar pair ASTM A387 ferritic/AISI 304L austenitic steel, having ascertained that the microstructure of the weld zone is austenitic with a little amount of residual primary ferrite, which is the best condition to minimize the risk of hot cracking.

Microstructure and mechanical properties in VPPA keyhole welding of thick aluminum alloy

In this study, the 16 mm thick aluminum alloy was successfully welded using variable polarity plasma arc (VPPA) keyhole welding. The microstructure and microhardness distributions of the weld were systematically measured along its thickness and width. To evaluate tensile strengths along the weld thickness, tensile specimens were divided into upper, middle, and lower sections. The surface temperature distribution of the weld pool, along with the temperature profile through its thickness, was measured using thermometers and thermocouples. Numerical simulations were employed to calculate the pressure oscillations along the keyhole boundary and to analyze the temperature and flow field distributions of the VPPA. The findings initially revealed a homogeneous and refined microstructure distribution within the weld seam. The weld zone exhibited higher microhardness compared to the base metal (BM). The weld demonstrated a tensile strength of 187.86 MPa and an elongation of 24.76%, corresponding to 95.57% and 78.65% of the BM, respectively. The tensile strengths and elongations of the upper, middle, and lower sections displayed a similar distribution to that of the entire weld. The mechanism underlying the microstructure distribution of the weld was significantly influenced by the temperature distribution of the weld pool, dynamic pressure oscillations in the mushy zone, and fluid flow of the weld pool. Specifically, the mechanism whereby pressure oscillations fracture existing nuclei and generate multiple new nuclei has been proposed to explain the refined microstructure distribution. These findings provide crucial insights for optimizing VPPA keyhole welding technology, ensuring stable and high-quality welding of thick aluminum alloys.

A New Approach in Part Design for Friction Stir Welding of 3D-Printed Parts with Different Infill Ratios and Colors.

Parts produced using a 3D printer are combined with friction stir welding (FSW). In the FSW processing of parts with a low infill ratio, welding errors occur due to a lack of material. In this study, plates were created using two different-colored PLA Plus filaments with different infill ratios in the weld area (20%, 60%, and 100%). Triangular pin geometry, different feed rates (20, 40, and 60 mm/min), and different tool rotation speeds (1250, 1750, and 2250 rpm) were used as FSW process parameters. Tensile testing was performed to determine weld strength and hardness measurements, and visual inspections were performed. Color measurements were made on the test samples before and after the welding process, and the relationship between welding performance and color was evaluated. The best welding strength was obtained as 17.83 ± 0.68 MPa at a feed rate of 20 mm/min, a tool rotation speed of 1750 rpm, and a part with a 60% infill ratio in the welding zone. In the sample with the best weld strength, the temperature was measured as 198.97 °C. Color changes in the weld area of parts with 60% and 100% infill ratios were measured between 78.9-82.2 and 79.1-84.5, respectively. It was determined that the color change decreases as the weld strength increases in these parts. The results show that with the proposed new part design, the FSW method can be used at low infill ratios, and the weld strength can be evaluated based on the color changes in the weld zone.

Cold Metal Transfer Welding of Ferritic and Austenitic Stainless Steel: Microstructural, Mechanical, and Electrochemical Studies

In the present study, cold metal transfer arc welding was employed to weld the 304L austenitic stainless steel (ASS) and Ti-stabilized 439 ferritic stainless steel (FSS) using a 309L filler electrode. Dissimilar joints were prepared using low heat input (HI; W1 ~ 247 J/mm) and high HI (W2 ~ 282 J/mm). The solidification mode for both weldments were the ferritic-austenitic mode and the weld zone (WZ) regions of both the weldments consists of columnar austenites, lathy and skeletal ferrite phases. The interfaces between WZ and ASS base metal showed the unmixed zone, whereas a conventional heat-affected zone (HAZ) was formed between the WZ and FSS base metals. The formation of ferrite stringers were observed in the unmixed zone, whereas peppery features of chromium-rich carbides were observed in HAZ. Moreover, electron backscattered diffraction technique was used to distinguish the microstructural differences between W1 and W2 weldments. Increase in the HIs resulted in decreased ferrite fraction in WZ as well as decrease in the mechanical strength of the joints. The W1 weldment depicted higher values of average micro-hardness (WZ ≈ 334.32 HV) than W2 (WZ ≈ 310.92 HV)) weldment. The electrochemical behaviour of the weldments was analysed for both the base metals and WZ of weldments. The higher degree of sensitization (DOS ~ 9.24%) of W1-WZ showed lower intergranular corrosion resistance than W2-WZ (DOS ~ 7.77%), however, the opposite trend was observed for impedance and pitting resistance.

Microstructure and Mechanical Properties of Dissimilar Resistance Spot Welded Zn-Coated DP800–TBF1180 Automotive Steels Using MFDC Technology

The use of advanced high-strength steel in the automotive industry is increasing in last decade. This is due to the restrictions to reduce fuel consumption and thereby decrease harmful carbon dioxide emissions. This paper aims to investigate welding properties of dissimilar resistance spot welded hot dip galvanized DP800–TBF1180 automotive steels using MFDC (Mid Frequency Direct Current) technology. LME crack occurrence due to the zinc coating was determined by magnetic particle test. The mechanical properties of welded joints were determined by tensile-shear, cross-tension and hardness measurements. The micro structural characterization was also performed in the weld zones of the joints. The appropriate welding parameter range were selected for welding processes by MFDC technology. Therefore, LME crack formation were not observed according to magnetic particle test. The highest strength was obtained as 17.60 kN and 5.51 kN by tensile-shear and cross tension tests, respectively with a welding current of 8 kA. In addition, a soft zone was found in the HAZ for both base metals. The hardness decrease in HAZ is more pronounced on the TBF1180 side. The soft zone hardness values of the sample S4 were approximately 330 HV, and the hardness values of the base material were measured in the range of 376-386 HV.

Effective toughening of dissimilar Ti alloy friction welded joint by combining electropulsing thermal and athermal effects

To address the low toughness issue in titanium alloy friction weld joints, this study employs electropulsing treatment to synergistically control the microstructure of TC11/TC17 linear friction welded (LFWed) joint through thermal and athermal effects, transforming equiaxed grains into a basketweave structure in the weld zone. The toughness of the joint increased from 9.3 J/cm2 to 33.5 J/cm2, while the strength maintained surpasses that of both parent materials.

Use of threaded cylindrical pin tools to reduce macroscopic defects in dissimilar welded joints of AA7075-T6 and AZ31B alloys by the FSW process

The continued increase in greenhouse gas emissions has had dire consequences for the global climate. In order to reduce such emissions, several efforts have been made by researchers in the transport sector, such as the development of electric motorization, the development of hybrid engines, the use of biofuels and the use of light alloys. The use of light alloys such as aluminum and magnesium in vehicles can reduce the emission per kilogram of vehicles drastically, however, it is still necessary to develop effective and more agile methods of the dissimilar joints of these materials. Some authors have studied the friction stir welding of AZ31B magnesium alloys and AA7075-T6 aluminum alloys in order to determine better process parameters to enable this bond, however, few articles have been published in order to evaluate the influence of tool geometry on such properties. In this sense, this article aims to evaluate the influence of friction welding tool pin geometry as smooth cylindrical pin, threaded cylindrical pin, conical and hexagonal pin configurations in the formation of the mixed zone of welds manufactured by the FSW process. For this purpose, AZ31B and AA7075-T6 alloys were welded by FSW with welding speed of 75 mm/min, tool rotation speed of 565 rpm, offset of 0.5mm and inclination of the tool geometry in relation to the plates to be welded of 3º, the joints were evaluated for their macro and microstructures and Vickers hardness with a load of 100 gf. It was possible to observe that the joints welded with the threaded cylindrical pin tool presented stir zones free of macroscopic defects, similar hardness values for the four tools studied and the presence of a thin layer of intermetallics between TMAZ and SZ on the AZ31B side.

On the mechanisms of charge weld evolution in aluminum extrusion

This study aims to provide new insights into the governing mechanisms of material property evolution within the charge weld zone in the hot extrusion process of aluminum profiles. A set of 6xxx series aluminum alloy tubular profiles was produced through carefully designed industrial experiments of billet-to-billet extrusion. The evolution of material integrity within the charge weld zones was experimentally characterized by microhardness tests, optical microscopy, scanning electron microscopy (SEM), and drift-expansion tests. The experimental analyses reveal that the material integrity of charge welds gradually increases from the onset to the end, primarily driven by the ‘local’ pressure history experienced. Towards the end of the charge weld zone, grooves and holes, and oxide particles gradually vanish, leading to enhanced material integrity. A through-process finite element (FE) model was developed using QForm-Extrusion software to analyze the thermo-mechanical history of charge weld formation, providing a deeper understanding of how material properties evolve and the underlying mechanisms governing this evolution. The model was experimentally validated in terms of the extrusion load and distribution of the charge welds in extruded profiles. Overall, the new insights gained in this study offer valuable knowledge for enhancing the process and quality control in billet-to-billet extrusion, as well as reducing in-process scrap towards more sustainable production of aluminum profiles.

Effect of tool rotational speeds on material flow and strain rates during friction stir butt welding of AA2219-T87 plates

ABSTRACT Friction stir welding (FSW) process is widely used for joining Al-Cu alloy (AA2219-T87) plates because of its high joint efficiency and low residual stresses in contrast to fusion-based joining techniques. A two-way coupled, 3D thermal-material flow model has been developed in COMSOL software, and the effect of tool rotational speeds on thermal and material flow fields, strain rates, thermal histories, and size of weld zones are being studied. The non-uniform net heat generation during the FSW process is due to the friction between workpiece and tool materials and the deformation energy of plasticized material flow sheared by the rotating tool. An approximate range of temperatures for the weld zones has been proposed and found to be appropriate because the predicted sizes are in good agreement with the experiments. Furthermore, the authors suggested that a quality FSW joint must have the nugget zone smaller and the heat-affected zone larger than the tool shoulder diameter.

Effect of Inconel 718 Filler on the Microstructure and Mechanical Properties of Inconel 690 Joint by Ultrasonic Frequency Pulse Assisted TIG Welding.

Ultrasonic frequency pulse assisted TIG welding (UFP-TIG) experiments were conducted to join Inconel 690 alloy (IN690) by adding Inconel 718 alloy (IN718) as the filler. The effect of the filler on the microstructure, mechanical properties, and ductility dip cracking (DDC) susceptibility of IN690 joints were investigated. The results show that a variety of precipitates, including MC-type carbide and Laves phases, are formed in the weld zone (WZ), which are uniformly dispersed in the interdendritic region and grain boundaries (GBs). The increase in the thickness of the IN718 filler facilitates the precipitation and growth of Laves phases and MC carbides. However, the formation of Laves phases in the WZ exhibits a lower bonding force with the matrix and deteriorates the tensile strength of IN690 joints. Due to the moderate content of Laves phases in the WZ, the IN690 joint with 1.0 mm filler reaches the maximum tensile strength (627 MPa), which is about 96.5% of that of the base metal (BM). The joint with 1.0 mm filler also achieves the highest elongation (35.4%). In addition, the strain-to-fracture tests indicate that the total length of cracks in the joint with the IN718 filler decreases by 66.49% under a 3.8% strain. As a result, the addition of the IN718 filler significantly improves the mechanical properties and DDC resistance of IN690 joints.

Microstructural, texture, and crystallographic analysis of SiC particle incorporation in double-sided friction stir welding of dissimilar aluminium alloys

This paper investigates the impact of incorporating SiC nanoparticles into the welded interface joint of dissimilar aluminium alloys 2024 and 7075. Double-sided friction stir welding (DS-FSW) was performed to investigate the impact of added nanoparticles on the joint's mechanical properties and crack growth rate. Microstructural analysis of the fractured surface was conducted to assess the influence of nanoparticles on crack propagation, while field emission scanning electron microscopy (FESEM) was utilized to examine the grain size distribution across different weld zones. On analyzing the DS-FSW joint with SiC-reinforced particles using electron backscattered diffraction (EBSD), predominant shear texture components such as B/B̅ and C are observed. Additionally, there are deformed textures like Rotating cube (H) {001} <110> and F {111} <112>, along with recrystallization texture elements such as Goss {110} <001>, P {011} <112>, and Cube {001} <101>. Mechanical properties, determined through hardness and tensile tests, were compared between nanocomposite weldments and base metal to assess the improvement in mechanical properties following the inclusion of SiC particles. Crack growth tests were performed using compact test (CT) specimens at a maximum load of 5 kN and a stress ratio of R = 0.1. The addition of SiC nanoparticles to the joint area led to a significant decrease in grain size and an increase in hardness within the stir zone, compared to the base metal and samples without the powder. The tests revealed an approximately 62 % increase in tensile strength and a notable increase in microhardness of the weld zone of the aluminium alloy metal matrix composite (AAMMCs).

Rotary friction welding applied to Cu11.8Al0.45Be shape memory alloy

The feasibility of welding a CuAlBe SMA by continuous drive friction welding was evaluated. The metallurgical state (annealed/quenched) before welding and frictional pressure (5 and 10 MPa) were varied and their effects on joint quality were analyzed. Static tensile tests, microhardness, thermal analysis by DSC, and optical microscopy were carried out to characterize the welded joint. The results indicated joints of excellent thermomechanical quality. The welding zones are well-defined, narrow, and have a very refined microstructure compared to the base metal. The phase transition temperatures along the welded assemblies were not changed when welding was performed on the quenched samples, except in the welding zone of the sample welded with 10 MPa. Maximum tensile strength was obtained by using maximum friction pressure during welding of the annealed alloy (quenching after welding). To fill the gap in bibliographical research in this field of study, this work innovatively presents the possibility of welding Cu-based SMAs by rotary friction, including the welding of quenched parts without the need for subsequent heat treatments and without compromising the shape memory effect.

Inhomogeneous Strain Behaviors of the High Strength Pipeline Girth Weld under Longitudinal Loading.

Unforeseen failures in girth welds present a significant challenge for the pipeline industry. This study utilizes 3D Digital Image Correlation (DIC) assisted cross-weld tensile testing to analyze the strain response of high-strength thick-walled pipelines, providing essential insights into the strain migration and fracture mechanisms specific to girth welds. The results reveal that the welding process significantly affects the mechanical distribution within the girth weld. The tested Shielded Metal Arc Welded (SMAW-ed) pipe exhibited undermatched girth welds due to high heat input, while Gas Metal Arc Welding (GMAW) introduced a narrower weld and Heat-Affected Zone (HAZ) with higher hardness than the base metal, indicative of overmatched girth welds. Strain migration, resulting from a combination of metallurgical heterogeneous materials and geometrical reinforcement strengthening, progressed from the softer HAZ to the base metal in the SMAW-ed sample with reinforcement, ultimately leading to fracture in the base metal. In contrast, the GMAW-ed sample shows no strain migration. Reinforcement significantly improves the tensile strength of girth welds and effectively prevents failure in the weld region. Sufficient reinforcement is crucial for minimizing the risk of failure in critical areas such as the weld metal and HAZ, particularly in SMAW-ed pipes.

Effect of shoulder diameter, tool rotation speed, and arrangement of plates on mechanical and metallurgical properties of dissimilar aluminum 2024-T3 and 7075-T6 friction stir spot welding (FSSW)

In most studies conducted on friction stir spot welding, the focus has been on process parameters and the tool pin geometry. One of the influential parameters in this process, which has received less attention, is the tool shoulder diameter. The spread or concentration of the weld can significantly affect the weld strength and mechanical properties of the joint. In this research, two tools made of H13 hot-work steel with different shoulder diameters of 20 and 25 mm were prepared. Three rotation speeds of 1000, 1600, and 2400 rpm were considered for the welding process. The arrangement of aluminum plates on top of each other was varied in two configurations, parallel and overlapped. Mechanical properties, including tensile shear strength and Vickers micro-hardness, were investigated. The microstructure of different weld zones was also examined using an optical microscope. The results showed that increasing the tool shoulder diameter could enhance the breaking force and tensile shear strength of the joints. Meanwhile, the rotation speed had an optimal value, and with its increase, the breaking force initially increased and then decreased. Placing the 2024-T3 aluminum plate on top of the stack also increased the tensile shear strength of the samples. The fracture mode of the broken specimens was entirely nugget pull-out, which became more pronounced during the use of optimal parameters. Micro-hardness in the region influenced by heat decreased, reaching a minimum in the thermo-mechanically affected zone. In the stir zone, micro-hardness increased significantly due to intense plastic deformation and material compression. The microstructure in the nugget region appeared fine-grained and compact, while the region affected by coarse grain experienced significant heat effects. Increasing the tool shoulder diameter led to an increase in the nugget zone and the length of the bonded region. However, it did not have a significant effect on grain size in the nugget region.

Mechanisms affecting the difference in fatigue resistance between welds and base materials were investigated based on in-situ fatigue method

Coiled tubing (CT) is manufactured using plastic processing and weld molding techniques, rendering the weld zone (WZ) susceptible to fatigue fractures under the continuous action of complex alternating loads during field applications. While this risk has garnered significant attention, the underlying mechanisms of its fatigue failure remain elusive. To address this knowledge gap, this study employs an in-situ SEM fatigue test method, coupled with metallographic analysis, hardness testing, SEM observation, and EBSD characterization, to deeply analyze the fatigue microdamage mechanism in the WZ by comparing the fatigue performance of the base material (BM) of the CT with that of WZ. It is found that the microstructure of the BM consists of different scales and shapes of ferrite and a small amount of pearlite nested and intertwined with each other, which has a strong coordinated deformation ability and can effectively relieve stress concentration, delay crack initiation and form a single fatigue source. In contrast, the WZ’s ferrite organization is large, uniform, and independent, making it prone to early-stage plastic deformation with weak inter-grain coordination, resulting in the formation of numerous slip bands and multiple crack sources. During the crack propagation stage, the abundant grain boundaries in the BM effectively deflect the crack expansion direction and slow down its progression; while multiple secondary cracks in the weld expand simultaneously and connect with each other, resulting in a higher crack expansion rate than the BM. The research findings provide crucial insights and guidance for enhancing the overall fatigue performance of CT.

Investigation on the mechanical properties and microstructural analysis of dissimilar friction stir welding of AA5154/AA7150

Butt welds were produced on AA5154/AA7150 using the FSW method, and measurements were taken for the hardness and elongation percentage of each joint. Regression analysis was utilized to investigate the significance of each parameter and formulate a mathematical relationship. Welding was performed at 1200 rpm, with a welding speed of 90 mm/min and a tool diameter of 28 mm, resulting in defect-free welds. Failures were commonly observed at the pin and the side of AA7150. To decrease the ultimate tensile strength (UTS), the welding speed (WS) or tool rotational speed (TRS) was increased. As both TRS and WS constitute the nugget zone, variations in hardness distribution were noted across the weld zones. ANOVA was applied in this study to establish the relative importance and influence of each factor on UTS. The ANOVA results indicated that all parameters significantly impacted UTS. Specifically, WS contributed 41.42%, diameter contributed 17.57%, and TRS contributed 13.27%. A quadratic model was also developed to describe the relationship between the factors and UTS values. Based on the data, a range of 0.41% to 10.36% differences existed between projected and actual values. The strength of the model was evaluated using R-Squared (R-Sq.), resulting in an obtained R-Sq. value of 0.892. This value indicates a robust relationship between the predicted and actual values.

Исследования соединений AA7075, сваренных трением с перемешиванием и ультразвуковым воздействием: механические свойства и анализ разрушения

Introduction. Joint efficiency and strength, particularly in aluminum alloys, are crucial in aerospace, defense, and industrial applications. Post-welding treatments like shot peening and laser shock peening significantly improve joint efficiency and strength, enhancing fatigue life, grain structure, and tensile strength. The purpose of the work. The literature reviewed shows that the ultrasonic vibration-assisted friction stir welding (UVaFSW) and post-weld treatment improved the mechanical properties and material flow. However, limited studies have been observed on the UVaFSW joints of AA7075-T651, considering the consequence of welding speed, tool rotation, and post-weld shot peeing treatment. The methods of investigation. The study investigates the ultrasonic vibration-assisted friction stir welded (UVaFSwed) AA7075-T651 joint's tensile strength, microhardness, microstructure, and fracture behavior, considering the impact of tool rotation, welding speed, and post-weld shot peening treatment. Results and Discussion. The post-weld treated shot-peened UVaFSWed joints demonstrated the maximum tensile strength of 373.43 MPa, the microhardness of 161 HV, and the lowest surface roughness of 15.16 µm at 40 mm/min welding speed when compared to the friction stir-welded (FSWed) joints. These results indicate that shot peening improved the mechanical properties and surface quality of the UVaFSWed joints. The high tensile strength and low surface roughness make these joints suitable for applications requiring strength and aesthetics. The fracture for the shot peened UVaFSWed joints mainly occurred in the heat-affected zone (HAZ) during the tensile test. It could be attributed to the higher temperature experienced during welding, which resulted in grain growth and decreased material strength in the HAZ. The shot-peened UVaFSWed joint has a more uniform grain distribution than the FSWed one, which contributed to the joint's higher tensile strength. The fractured surface of the shot peened UVaFSWed joints showed larger, equiaxed, and shallow dimples, resulting in higher ultimate tensile strength (UTS) and microhardness compared to the conventional FSWed joints. The mechanical properties and microstructure observed in the welding zones of shot peened UVaFSWed joints are superior to those of conventional FSW joints. However, further investigation is required to determine the specific factors contributing to this localized failure at HAZ, considering the effects of shot peening parameters. This study also suggests the potential for optimizing shot peened UVaFSWed joints of AA7075-T651.