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Carbon fiber reinforced polyamide 66 (CF/PA66) sheets are ultrasonically welded by applying nylon meshes as energy directors (EDs) in this paper. The influence of mesh dimensions is revealed by observing the joint formation process, joint mechanical performance, joint cross‐sectional morphology and joint failure mode. Results show that the joint formation process can be divided into wire flattening stage, ED spread stage, tight bonding stage, and mixing stage. The nylon mesh ED with moderate wire spacing, small wire diameter and small mesh area promotes better weld quality. Welding energy will be dispersed rather than concentrated if the mesh area is too large, resulting in reduced failure load. The joints exhibit two fracture modes: interfacial fracture (IF) and workpiece fracture (WF), and the fracture mode of the joints with nylon mesh EDs transits from IF to WF as the welding energy increases. Highlights: Five types of nylon mesh are used as energy directors to join CF/PA66 sheets by ultrasonic welding.The influence of nylon mesh dimensions on the mechanical property and fracture mode of joints is investigated.The formation process of ultrasonically welded joints can be separated into wires flattening stage, ED spread stage, tight bonding stage, and mixing stage. [ABSTRACT FROM AUTHOR]

To ensure comprehensive coverage of welds, multi-axis motions are necessary for the probe during the automatic detection of complex welds. Guaranteeing the effectiveness of ultrasonic data during this process is crucial for ensuring detection accuracy and reliability. Taking tubular Y-joints as an example, this paper presents an adaptive probe posture correction method based on structural signal monitoring: (1) The structural and acoustic model of tubular Y-joints is established to select and predict the target structural signal. (2) Feature extraction and signal tracking algorithms are developed to achieve real-time monitoring of signals. (3) A posture correction method is proposed based on signal characteristics: time-domain characteristics correspond to position adjustments, while amplitudes correspond to orientation corrections. Building upon this, a feedback mechanism for probe posture is established. The effectiveness of the developed method is verified through underwater automatic detection experiments of tubular Y-joints. Results demonstrate that, with the assistance of the probe posture correction method, the coverage of the effective area increases to more than 95%, and embedded defects are fully detected through a single scan. In conclusion, the adaptive probe posture correction method based on structural signal monitoring presents a promising approach for the automatic ultrasonic examination of complex welds. [ABSTRACT FROM AUTHOR]

Friction stir welding of cast and rolled-state aluminum matrix composites is extensively used in many industries, and the speed at which the mixture is stirred profoundly influences the structure and characteristics of the welded connections. The present study investigates the microstructure and mechanical properties of the as-cast and as-rolled (ZrB2 + Al3Zr) particle-reinforced aluminum matrix composites. The welded joints were subjected to friction stir welding at a welding speed of 60 mm/min and stirring speeds of 1000, 1200, and 1400 rpm, separately. At a rotational speed of 1200 rpm, the welded joints exhibit optimal performance with an average hardness of 71.07 HV, a tensile strength of 183.9 Mpa, and an elongation of 16.7%. The weld core region generates precisely shaped equiaxed grains, while the weld matrix facilitates a significant amount of dislocation entanglement. At a rotational speed of 1200 rpm, the grain refinement effect is fully optimized, resulting in an average grain size of 2.94 μm. The recrystallized organization accounts for 70.6% of the grain size. Both types of reinforcing particles are adequately crushed, with the smallest particle size of ZrB2 particles being less than 100 nm and the smallest particle size of Al3Zr particles being less than 1 μm. The two methods of weld reinforcement are fine crystal strengthening and Orowan strengthening. [ABSTRACT FROM AUTHOR]

In this paper, during the heat treatment of TC4 titanium alloy pulsed laser-arc hybrid welded joints, it was found that the degree of V elemental segregation in the β phase of the weld microstructure increased with the slowing down of the cooling rate after holding the weld joint for a certain period above the β phase transition temperature. To reveal the effect of V element segregation in the β phase on the mechanical properties, tensile simulations were carried out using molecular dynamics at different temperatures for different degrees of segregation in the model. The results showed that at the same temperature, when the V elements were segregated in the β phase, the energies of the models were all lower than that of the model with uniform distribution of V elements after relaxation. At the same time, the tensile strengths were all higher than that of the model with a uniform distribution, and the tensile strengths in the x- and y-directions were increased by 17.7% and 8.1%, respectively. In stretching to the maximum stress, the deformation mainly occurred in the β phase, and the deformation mode was a phase transition from BCC to HCP with the formation of nanocrystalline. However, with the increase in temperature and the decrease of the degree of V elemental segregation, the nanocrystalline formed by the deformation gradually decreased, and the grain boundaries also became irregular, which was the main reason for the decrease in the tensile strength. At the same time, after segregation, the start of the BCC phase transition in the tensile process was delayed, which was also beneficial to improving the strength of the model. After exceeding the tensile strength, the deformation was mainly dominated by the slip of dislocations. In addition, with the increase of the degree of V element segregation, the difference in the tensile strength of the model tensile along the parallel and perpendicular grain boundary directions decreased from 0.48 to 0.18 GPa, and the anisotropy of the material was weakened. [ABSTRACT FROM AUTHOR]

Based on the ultrasonic welding technology, this study uses three different welding widths to weld copper cables with different specifications. The influence of welding width on the mechanical properties and microstructure of each group of welded joints was systematically studied for the first time. The thermal shock test was carried out for each group of welded joints under optimum welding width to simulate the influence of severe temperature change environment on joint performance. It is found that the cross-sectional area of joint is 20 mm2 and optimal welding width of joint composed of two and three cables is 7 mm. The optimal welding temperature of the joint composed of four cables is 5 mm. Under the optimal welding width, the average shear strength of two-cable joint reaches 309.4 N. The four-cable joint is only 232.2 N. Moreover, the welding strength weakens significantly as the number of cables and the peak temperature decreases. The high temperature of bonding interface is the key factor to form a good weld. The peak temperature during welding is negatively correlated with the porosity of joint and positively correlated with peeling strength of joint. In addition, the morphology of ultrasonically welded joints has changed obviously after thermal shock test. With the participation of oxygen, the surface of welded joint is gray and bright brass, while the interior of joint is purple due to lack of oxygen. Moreover, the phenomenon of atomic diffusion and thermal expansion generates joints which were initially in a mechanically interlocked form and welding interface of the metallurgical bond under the action of high temperature. So the maximum joint peel strength is slightly improved. [ABSTRACT FROM AUTHOR]

Random meso‐scale defects within welded joints can affect the structural damage process and cause dispersion in the fatigue lifetime of welded joints. In this paper, a meso‐scale stochastic damage approach is used to investigate the effect of random, meso‐scale defects on the fatigue damage lifetime of welded joints under different loads. First, we established an elastic–plastic fatigue damage model considering meso‐defects in the weld metal. Secondly, the fatigue lifetimes for gas tungsten arc welding and gas metal arc welding welded joints were predicted, with most of the predictions within the twofold dispersion factor. Thirdly, the Monte Carlo simulation method was used to investigate the influence of meso‐defect size on the fatigue lifetime dispersion degree, and the fatigue lifetime distribution under different loads was statistically analyzed. Established a fatigue life prediction model considering random meso‐defects in welds.The dispersion effect of meso‐scale random defect size on fatigue life was analyzed.Fatigue life prediction of welded specimens of other materials is also possible. [ABSTRACT FROM AUTHOR]

This study experimentally investigated the effect of temperature conditions on the welding quality of thermoplastic sheets by non-destructive and destructive testing methods. Ultrasonic inspection method was employed for evaluating the fusion welds. Since the thermoplastic materials lead to significant ultrasonic signal attenuation, optimizing the setting condition for the ultrasonic testing was carried out in advance. Then, ultrasonic experiments were performed to evaluate welding qualities with respect to welding temperature conditions. In the partially incomplete welding specimen, two distinct signals were observed, reflected from the intermediate and back wall. The quality factor was defined using the ratio between intermediate and backwall reflection signals to evaluate the welding characteristics according to temperature. Based on this factor, ultrasonic images were produced using a C-scan method for welded thermoplastic specimens to visualize the welding quality. Lap-shear tests were conducted to verify the ultrasonic testing results for the welded specimens. As the welding temperature increased, there was a maximum decrease of 28 % in the percentage of incomplete welds in the C-scan results, and the lap-shear test showed an increase in shear strength. Validation through temperature-dependent shear strength confirmed the effectiveness of C-scan images using ultrasonics. [ABSTRACT FROM AUTHOR]

This review paper presents the current progress in the development of resistance welding techniques for thermoplastic composites, with a particular emphasis on their application in hybrid joints, such as those involving thermosetting composites and metals. Resistance welding, a fusion bonding method, offers significant advantages over adhesive bonding and mechanical joining by eliminating the need for additional adhesive materials and enabling integration into automated manufacturing processes. The study highlights the unique benefits of resistance welding, including lower energy consumption compared to other methods and its compatibility with automated manufacturing, which can reduce production costs by up to 40%. Key findings from the literature indicate that resistance welding is particularly effective in achieving strong, durable joints for complex and large structures, such as those used in the aerospace industry. The review also identifies the main challenges associated with resistance welding, including temperature control, current leakage in carbon-fiber-reinforced polymers, and potential corrosion when using metal meshes. To address these challenges, various strategies are discussed, including surface treatments, the use of nanocomposites, and the integration of carbon nanotubes. The review concludes by emphasizing the need for further research to optimize welding parameters and to develop non-destructive testing methods for industrial applications, ensuring the reliability and long-term performance of welded joints. [ABSTRACT FROM AUTHOR]

In this paper, the influence of Cr element on the mechanical properties of welded joints of gas-shielded solid wire used in oil and gas long-distance pipelines was studied by means of tensile test, impact test, and hardness test, and the microstructure and crack propagation path of weld were characterized by means of an optical microscope, scanning electron microscope, and electron backscattering diffraction. The results show that with the addition of Cr, the strength and toughness of the weld are significantly improved, in which the tensile strength is increased from 607 MPa to 656 MPa, and the impact toughness is increased from 126.37 J to 223.79 J. The proportion of the ferrite side plate in the weld structure is reduced by about 20%, and the effective grain size of acicular ferrite is reduced by about 15%. The reason is that the addition of the Cr element improves the hardenability of the weld structure, inhibits the formation of the ferrite side plate, and promotes the effective refinement of acicular ferrite, which increases the proportion of high-angle grain boundaries in the weld, effectively hindering the crack propagation, improves the crack propagation work, and thus improves the strength and toughness of the weld. [ABSTRACT FROM AUTHOR]

On the load bearing and fatigue behaviour of headed anchor studs with defective welds The welding of headed anchor studs (KBD) is a technically demanding process. The main difficulty for contractors is that it is not yet possible to provide non‐destructive evidence that the product is free of defects. The publication of Allgemeines Rundschreiben Straßenbau (ARS) No. 18/2019 on quality assurance when welding headed stud dowels in bridge construction has significantly tightened the requirements for headed stud dowel welding. Since a company owes a defect‐free trade at the time of handover, but the freedom from defects of headed anchor studs can currently only be proven by means of destructive testing, this creates a considerable entrepreneurial risk for the practice. Although the standards and guidelines provide information on the procedure that can be used to ensure defect‐free bolts, there is no guarantee of success. For this reason, companies had to rely on the tolerance of the acceptance criteria provided by the current standards for headed anchor studs. This article deals with faulty headed anchor stud welds as well as repair methods commonly used in practice to gain initial insights into whether the tightening within the framework of the document Allgemeines Rundschreiben Straßenbau No. 18/2019 was expedient or necessary. Initial results from the PAUT (Phased Array Ultrasound) method will also be examined to determine whether it may be possible in the future to use this method to enable non‐destructive testing of headed anchor studs. [ABSTRACT FROM AUTHOR]

The design of connections of gusset plates, beams, and columns of concentrically braced frame systems is typically based on the forces generated by brace actions without considering the frame actions. This may result in underestimating the design force demand on gusset plates, potentially leading to the failure of interface weld connections at higher lateral drift levels. The present study aims to estimate the force demands at the connection interfaces, typically about a 2% story-drift ratio (SDR), corresponding to the design-level ground motions for braced frame systems. The study considers both the forces of frame and brace action on the corner gusset plate in the design process. It also aims to develop suitable design recommendations to prevent premature weld failures at higher lateral drift. High-fidelity finite-element models of in-plane buckling (IPB) braced frame systems are developed and analyzed under various loading modes. A current standard design method to determine the interface weld size was found to be inadequate to prevent premature failures at the higher drift levels. This is primarily due to the accumulation of the plastic strain at the tip of the gusset at higher drift. The out-of-plane bending of the gusset plate due to geometric imperfection was also found to contribute toward the development of high plastic strain at the tips of gusset plates. Three different connection configurations are considered and analyzed under critical cyclic loading conditions. Finally, design recommendations are presented to avoid stress concentration and premature fracture of gusset plate connections of the IPB braced frame systems. [ABSTRACT FROM AUTHOR]

Adjustable-ring-mode (ARM) laser welding displays great potential for improving the stability of the molten pool and the weld quality of aluminum alloys through the coaxial attachment of a large-sized ring-beam spot. In this paper, the author embarked on a systematic study on the impact of varied core powers, ring powers, and core/ring power ratios on the weld morphology, microstructure, and mechanical properties of Al-Mg alloy during the laser welding process with ARM. The results showed that the core power led to higher depth of penetration, and the superheating of the molten pool it created caused grain coarsening and reduced properties. The ring beam effectively decreased weld spatter and enhanced the surface roughness of the weld. Furthermore, the ring beam was more likely to obtain a wider columnar crystal zone and a more homogeneous grain size distribution. The welded joints possessed higher tensile strength values when ring beam power was increased from 1.5 to 2 kW due to the improvement of surface flatness and porosity defects by the ring beam. • The effects of a single beam and different core/ring power ratios on the laser welding of Al-Mg alloys were investigated. • Additional ring beams effectively improved weld surface quality, which is conducive to the increase of tensile strength. • The ring beam could significantly change the width of the columnar crystal zone. • A core/ring power ratio of 1.5 resulted in a more uniform microstructure and performance distribution. [ABSTRACT FROM AUTHOR]

Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

Copyright of Metal Working (1674-165X) is the property of Metal Working Editorial Office and its content may not be copied or emailed to multiple sites or posted to a listserv without the copyright holder's express written permission. However, users may print, download, or email articles for individual use. This abstract may be abridged. No warranty is given about the accuracy of the copy. Users should refer to the original published version of the material for the full abstract. (Copyright applies to all Abstracts.)

AbstractThis study compares dip brazing and TIG welding operations carried out under optimal conditions on the parameters of strength, deformation, and ability to resist shocks for Al-64430 joints, which find extensive use in automobile and telecommunication industries. The fabricated samples were tested for bump test, surface deformation, microhardness and tensile strength, and the joint properties were studied through SEM, EDAX mapping and EDX. Compared to the dip-brazed samples, the TIG welded samples achieved 161% greater strength and 1000% greater elongation but subsequently 1330% higher surface deformation. Both joints were able to pass the bump test; however, some degree of cracks were observed post testing in both samples. Both samples achieved similar joint microhardness values, but notably, compared with the TIG welded sample, the brazed sample showed no HAZ zones in terms of microhardness variation, where a substantial decrease in microhardness was recorded. This absence of the HAZ region was also confirmed through the microstructure. Both primary and secondary silicon were observed in brazed samples, which had finer grain sizes than did the welded samples. Dendrite formation was observed for the brazed samples, whereas a uniform distribution of aluminium was observed for the welded samples. Fractographic analysis revealed brittle intergranular fracture with small dimples present at the fracture point for the brazed joints, while out-of-plane fracture with sharp edges indicated a more ductile nature for welded joints. [ABSTRACT FROM AUTHOR]

Additive manufacturing is a common method for producing diverse functional components. However, its application is constrained by the size limitations imposed by additive manufacturing machines. To address this limitation, continuous drive friction welding emerges as a potential solution to join parts of composite materials together. In this investigation, two welding specimens, composed of polylactic acid (PLA) with copper powder and PLA with aluminum powder, were welded using a turning machine. The assessment of fatigue behaviors in welded joints holds substantial importance in engineering applications. In general, the rotational speed in continuous drive friction welding is fixed. However, there is a lack of research focusing on the fatigue behavior of dissimilar polymer rods filled with metal powder using continuous drive friction welding with different rotational speeds. In addition to fatigue testing, a comprehensive evaluation was performed, including bending tests, surface hardness tests, and material studies such as optical microscopy and differential scanning calorimetry analysis. It was found that the highest temperature in the weld interface are about 150 °C, 136 °C, 108 °C, 96 °C, and 83 °C for rotational speed 1350, 950, 650, 490, and 330 rpm, respectively. The fatigue life of the dissimilar welded parts can be enhanced by approximately 16–30% using enhancing the rotational speed. The bending strength of the dissimilar welded parts can be enhanced by approximately 19–70% using enhancing the rotational speed. The surface hardness in the weld interface can be enhanced by approximately 1–2.5% using enhancing the rotational speed. The weld maintained superior mechanical properties at a rotational speed of 1350 rpm. The findings highlight significant potential applications in the welding industry. [ABSTRACT FROM AUTHOR]

Laser beam welding is the most modern and promising process for the automatic or robotized welding of structures of the highest Execution Class, EXC3-4, which are made of a variety of weldable structural materials, mainly steel, titanium, and nickel alloys, but also a limited range of aluminum, magnesium, and copper alloys, reactive materials, and even thermoplastics. This paper presents a systematic review and analysis of the author's research results, research articles, industrial catalogs, technical notes, etc., regarding laser beam welding (LBW) and laser hybrid welding (LHW) processes. Examples of industrial applications of the melt-in-mode and keyhole-mode laser welding techniques for low-alloy and high-alloy steel joints are analyzed. The influence of basic LBW and LHW parameters on the quality of welded joints proves that the laser beam power, welding speed, and Gas Metal Arc (GMA) welding current firmly decide the quality of welded joints. A brief review of the artificial intelligence (AI)-supported online quality-monitoring systems for LBW and LHW processes indicates the decisive influence on the quality control of welded joints. [ABSTRACT FROM AUTHOR]

The development of high-strength advanced additively manufactured (AM) aluminum alloys is driven by the need for weight reduction in complex-shaped structural applications. In this context, heat-treatable aluminum-scandium alloy, known commercially as Scalmalloy®, offers high strength and lightness, also at high temperatures, due to solution strengthening Al3(Sc, Zr) particles. A widespread diffusion of such AM alloy is also related to welding technologies that could preserve its engineered microstructure. This study investigates the microstructural and mechanical properties of butt friction stir welding (FSW) joints of LPBF Scalmalloy® plates under different welding settings. Joint performance was evaluated under quasi-static and cyclic loading conditions. Porosity in Scalmalloy® and welds was assessed using 3D X-ray computed tomography. An aging heat treatment assessed the extent of precipitation hardening in the FSW joints. Results show that metal stirring during FSW notably reduced the intrinsic porosity of Scalmalloy®, decreasing the equivalent pore diameter from about 200 μm to 60 μm in the welded joints. Under quasi-static loading, welded specimens failed at the interface between the thermo-mechanically affected and the stir zones on the advancing side. The aging heat treatment improved the mechanical strength of Scalmalloy® from approximately 400 to 480 MPa, albeit at the expense of ductility (elongation at fracture decreased from 16 to 4%). The higher heat input and stirring developed at a low welding speed reduced lazy S defects but limited the effectiveness of subsequent aging. In fatigue testing, welded joints consistently failed within the aged base material due to the intrinsic porosity of Scalmalloy®. [ABSTRACT FROM AUTHOR]

The extended use of laser welding in the industry requires a less sensitive process in terms of geometrical tolerances of the joint edges. As the industrial availability of laser systems increases, the demand to use laser welding technology possibly with parts coming from less precise production steps is increasing. Gap formation is often caused by the edge quality of the parts coming from previous manufacturing steps such as sheet forming. Al alloy sheets deformed to box-shaped 3D forms often require welded joints on the edges in lap, but, and corner joint configurations. These joints are hard to carry out by laser welding due to the large gap formation caused by the tolerances of the deformation processes involved. Laser welding of Al alloys is already challenging in the absence of gap formation, while these joint configurations have been not feasible with a stationary beam due to incomplete fusion and defect formation. Laser welding with beam oscillation and wire feeding can improve the weldability of these joints. The oscillating motion of the high-intensity beam can achieve a deep weld together with a wider seam. Combined with wire feeding, the process can close gaps in the butt, lap, and corner joint configurations. On the other hand, the added oscillation and wire-related parameters require extending the experimental space, which requires a methodological study to identify feasible conditions. Accordingly, this work proposes a methodological approach to identify and set laser welding process parameters with beam oscillation and wire feeding for an EN AW 5083. Process parameters were initially studied using a simple analytical model that depicts the beam trajectory. Bead-on-plate tests were conducted to assess beam size, power, and weld speed ranges. Lap, butt, and corner joint conditions with a 0.5-mm gap were welded with high quality by manipulating the laser power, oscillation amplitude, and wire feed rate. The results show that welding speeds could be maintained as high as 55 mm/s with complete filling of gaps of up to 0.5 mm, eliminating the surface undercuts and achieving weld widths in the order of 2.5 mm. Moreover the results show the possibility control the depth of the welds from 3 mm to full-penetration conditions. [ABSTRACT FROM AUTHOR]

To solve the technical problems of poor strength–plasticity–toughness matching of titanium alloy welded joints, the optimized multi-stranded wires are used as the filler metal for narrow gap laser welding of TC4 titanium, and the welded joints obtained using high-temperature annealing were heat-treated at 850 °C holding 2 h. The macrostructure, microstructure and texture of both welded joints were compared by employing an optical microscope, scanning electron microscope and transmission electron microscope, and the tensile and impact properties were also evaluated. The results show that after heat treatment of the welded zone acicular α' martensite decomposition into lamellar α-phase + β-phase, the welded joint microhardness distribution tends to be smooth, the average tensile strength of the welded joints is 902 MPa, elongation is 14.5%, about 4.1% lower than the as-welded of the welded joints tensile strength, but elongation increased 3.5%, and room-temperature impact energy is 18.5 J, increased by about 54% than the as-welded impact energy, achieving a reasonable match of strength–plasticity–toughness of titanium alloy welded joints. [ABSTRACT FROM AUTHOR]

AbstractMost published works related to gas metal arc welding processes focus on quality criteria, while energy consumed has not been considered. In this study, key parameters of the gas metal arc welding (GMAW) operation of the AISI 1045 steel, including the current (I), voltage (V), flow rate (F), and nozzle stand-off distance (D) are optimized to minimize energy consumed (EC) and enhance the ultimate tensile strength (TS) as well as elongation (EL). The radial basis function network (RBFN) is employed to propose GMAW responses. The Entropy method, modified grey wolf optimizer (MGWO), and Multi-Attributive Border Approximation Area Comparison (MABAC) were utilized to compute the weights, generate feasible solutions, and determine the best optimality. As a result, the optimal I, V, F, and D were 137 A, 23 V, 12 L/min, and 12 mm, respectively. The EC was reduced by 5.8%, while the TS and EL were improved by 3.3% and 20.7%, respectively, at the optimality. The EC and EL models were primarily affected by the I, V, F, and D, respectively. The TS model was mainly influenced by the I, D, F, and V, respectively. The RBFN-MGWO could be employed to present non-linear data and achieve better optimal results, as compared to the traditional approach. The obtained outcomes could be used to produce high-quality welds with minimizing environmental impacts. [ABSTRACT FROM AUTHOR]

Heat-resistant nickel alloys are promising materials for manufacturing structural elements used in high-temperature nuclear power plants. Nickel alloys are characterized as difficult-to-weld materials; this is one of the main factors limiting their use. This paper presents the results of the development and industrial exploitation of welding technology for heat-resistant nickel alloy grade CrNi62MoCh2-VI (EC 199-VI). The quality control results of the obtained welded joints are presented. Notably, the welded joints of the CrNi62MoCh2-VI alloy exhibit resistance to intercrystalline corrosion and demonstrate improved mechanical characteristics. [ABSTRACT FROM AUTHOR]

The use of an integrated approach to determining the static strength of operated main pipelines with surface defects makes it possible to take into account the effect of residual weld stresses in combination with operational loads. In this case, it is important to determine the nature of the welding stress distribution for welded structures made of high-strength steels. Here, there is non-uniformity of stresses concerning magnitude and gradient, which is due to technological methods. A mathematical model of the experimental-calculation method is proposed. Such a model allows describing such stresses. A two-parameter criterion for brittle-tough fracture of a material which takes into account the influence of residual stresses is used. It is shown that the combination of residual stresses and operating loads has a significant effect on the safety factor. At the same time, conditions are possible under which compressive residual stresses have a favourable effect on the static strength of a pipeline with a defect. [ABSTRACT FROM AUTHOR]

This paper is a study of mechanical properties and microstructure of rotary friction welded tungsten heavy alloy with aluminum alloy (AA). A plastic deformation is visible on AA side. Effects of friction time (FT) and friction pressure (FP) on the ultimate tensile strength (UTS) were studied by plotting graphs. The UTS of joints increases with increasing FP and FT and then decreases after reaching the maximum value. The fracture proceeds through the cleavage planes at the interface. Scanning electron microscopy for investigation of the fracture morphology and phase transformations taking place during friction welding process was used. Chemical compositions of the interfaces of the welded joints were determined by using energy-dispersive X-ray spectroscopy (EDS). EDS analyses across the interface of tungsten and nickel have not confirmed the diffusion to AA side. Microstructure of friction welds consisted of equiaxed grains formed due to dynamic recrystallization and coarse grains in the periphery region on AA side. [ABSTRACT FROM AUTHOR]

Welding experiments were conducted under different currents for single-pass butt welding of high-strength steel flat plates. The microstructure of welded joints was characterized using OM, SEM, and EBSD, and the welding process was numerically simulated using a finite element method. According to the grain size obtained by electron microscope characterization and the temperature data obtained by simulation, the microstructure and mechanical properties of coarse grain and fine grain areas of the heat-affected zone were predicted by using the material microstructure and property simulation software. Finally, the results of mechanical properties simulation were verified through mechanical property testing. [ABSTRACT FROM AUTHOR]

To fully exploit the advantages of steel, the welding connection of dissimilar steels has been developed. In this work, the metallographic microstructures, elemental distributions, and electrochemical corrosion properties of the Q235 and 304 welds under different bias arcs were investigated. The arc bias caused the Q235-side heat-affected zone to widen, the microstructure consisted of ferrite and pearlite, and the ratio varied with decreasing distance from the fusion line. Elemental scans show that Cr and Ni concentration gradients exist near the fusion line. The 304-stainless-steel-side heat-affected zone was mainly composed of austenite grains, and the fusion zone was narrower but prone to cracking. Electrochemical tests revealed that 304 stainless steel had the best corrosion resistance, while Q235 had the worst corrosion resistance, and that the welded joints with an arc bias toward the 304 side had the best corrosion resistance. The samples' the passivation film which formed via electrochemical polarization had limited stability, but the over-passivation potential could be used as a reference for corrosion resistance. Overall, the arc bias and weld material properties significantly affected the microstructure and corrosion resistance of the joints. [ABSTRACT FROM AUTHOR]

The purpose of the presented research was to determine the suitability of using ultrasonic testing (UT) to inspect heterogeneous, from a material point of view, welded joints on the example of the joints of a ferritic steel element with elements made of an austenitic steel. The echo technique with transverse (SEK) and longitudinal wave heads (SEL) addressed this issue. Due to the widespread use of 13CrMo4-5 and X2CrNiMo17-12-2 steel grades in the energy industry, they were selected as the test materials for the study. The objects of the presented research were welded joint specimens with thicknesses of 8, 12, and 16 mm and dimensions of 300 × 300 mm, made using the 135 metal active gas (MAG) process with the use of the Lincoln 309LSi wire—a ferritic–austenitic filler material. The stages of the research task were (1) making distance–amplitude curve (DAC) patterns from the test materials; (2) preparation of specimens of welded joints with artificial discontinuities in the form of through-holes; (3) performing UT tests on welded joints with artificial discontinuities using heads with 60° and 70° angles for the transverse wave and angle heads for longitudinal waves with similar beam insertion angles; (4) selection, by radiographic testing (RT), of welded joint specimens with natural discontinuities in the form of a lack of sidewall fusion; (5) performing UT tests on welded joints with natural discontinuities, using heads as welded joints with artificial discontinuities. It was found that (1) the highest sensitivity of discontinuity detection was obtained by performing tests on the ferritic steel side, which is due to the lower attenuation of the ultrasonic wave propagating in ferritic steel compared to austenitic steel; (2) the best detection of discontinuities could be obtained using a longitudinal ultrasonic wave; (3) there is a relationship between the thickness of the welded elements, the angle of the ultrasonic beam introduction, and the effectiveness of discontinuity detection. [ABSTRACT FROM AUTHOR]

Metal 3-D printing, such as laser powder bed fusion, is capable of printing intricate parts with limitless design freedom. Despite design freedom, the maximum size that can be printed is a hindrance to the emerging technology. Therefore, joining and evaluating welded joints are critical for making them more viable for a wider range of applications. Thus, the present study examines the impact of tool rotational speeds on friction-stir-welded joints, revealing that an increase from 600 to 1200 revolutions per minute (RPM) raises the stir zone's temperature from 270.0 to 329.9 °C and residual stresses from 46.7 to 93.1 MPa. An optimum tensile strength of 260 MPa was observed at 800 RPM with a grain size of 2.6 µm, whereas the lowest strength of 172 MPa occurred at 1200 RPM with a 4.21 µm grain size. Additionally, the corrosion resistance decreased with increasing residual stress, showing the highest resistance at 600 RPM (Ecorr = − 1.0737 V) and the lowest at 800 RPM (Ecorr = − 1.2027 V). The study also found a decrease in grain density with higher rotational speeds and localized corrosion due to microgalvanic coupling between Si particles and the α-Al matrix. Moreover, the shear components C {001} < 1 1 ¯ 0 > were identified as being particularly susceptible to corrosion attacks. This specific component significantly contributes to the reduced corrosion resistance observed in the joints. [ABSTRACT FROM AUTHOR]

Images of titanium alloy welds detected by time-of-flight diffraction (TOFD) have problems, including large noise signals and many interference streaks around the defects, all of which seriously limit the accuracy and effectiveness of defect recognition. Existing image denoising methods lack the knowledge of the noise characteristics of TOFD images of titanium alloy weld and the preprocessing experience of technicians in the field. In addition, it is difficult to select the parameters of the preprocessing methods, and they are easily influenced by the level of technical personnel, resulting in low efficiency and poor consistency in preprocessing. To address these problems, we proposed a denoising method based on the combination of wavelet band features and deep-learning theory for TOFD images of titanium alloy weld. First, based on the wavelet preprocessing method and the experience of nondestructive testing (NDT) technicians, we constructed an image pair dataset consisting of the original TOFD images of titanium alloy weld and the desired target images to realize the accumulation of engineers' preprocessing knowledge. Second, we constructed a multiband wavelet feature fusion U-net image denoising model (WU-net) and designed a loss function under three constraints of image consistency, image texture information consistency, and structural similarity. This model was able to learn to achieve end-to-end adaptive denoising for TOFD images of titanium alloy weld. Third, we illustrated and validated the effectiveness of TOFD image preprocessing for titanium alloy weld. The results showed that the proposed method effectively eliminated TOFD image noise and improved the accuracy of defect recognition. [ABSTRACT FROM AUTHOR]

The effects of laser beam welding (LBW) process parameters on the characteristics of Nd:YAG laser butt welding 1.5 mm thick 2205 duplex stainless steel. Specifically, the study focuses on the depth of penetration, bead width, ultimate tensile strength (UTS) and elongation. To achieve this, a parametric study is conducted using a central composite design (CCD) with response surface methodology (RSM) to establish mathematical regression equations that identify the key process parameters and their effects on the responses. The investigations showed that the size of the meltpool at the fusion zone (FZ) increases as the laser power increases. This leads to the formation of wider and deeper weld beads, ultimately leading to stronger and more flexible joints. Similarly, pulse width and scanning speed have a significant impact on the weld bead geometry, UTS, and elongation. It is observed that the FZ is free of any visible cracks, voids, or porosity. The LBW process parameters have been optimized to reduce operating costs by lowering the line energy, without compromising the welding quality. The optimal UTS value for the welded joint is around 865 MPa, which is almost equivalent to 99% of the UTS of the 2205 duplex stainless steel base material (BM). To obtain high-quality welded joints, it is recommended to use a laser power ranging from 423 to 425 W, scanning speed of 5.3 mm/s and pulse width of 5.4 ms. [ABSTRACT FROM AUTHOR]

Two types of filler materials, FeCoCrNiMn and Al-10Si-0.3 Mg powder, were utilized to achieve lap welding of 5083 aluminum alloy to DP780 steel using laser deposition welding at various laser powers. By conducting a comparative analysis of the macroscopic morphology, microstructure, hardness, and shear properties of two groups of welded joints, the effects of multi-principal filler material and heat input on the weld formation, microstructure evolution, and shear properties of dissimilar lap joints were evaluated and discussed. An interesting finding was that, compared to the Al-10Si-0.3 Mg powder, the FeCoCrNiMn powder used as filler material had significant advantages in reducing the hardness of the weld zone and improving the shear properties of the lap-welded joints. The multi-principal powder of FeCoCrNiMn was unable to prevent the formation of Fe-Al intermetallic compounds in the weld metal. However, it did alter the elemental compositions and grain morphologies in the weld metal when compared to the Al-10Si-0.3 Mg powder. Moreover, selecting welding parameters with a low heat input was appropriate for the dissimilar metal joining of aluminum to steel using laser deposition welding. [ABSTRACT FROM AUTHOR]

The root pass represents a challenge for welders. Being the first pass of the joint, it requires full penetration and is more prone to metallurgical defects. There needs to be a balance between the forces acting on the molten pool to avoid incomplete penetration or burnthrough. Additionally, the hardness in the heat affected zone (HAZ) should not exceed 350 HV, beyond which there is susceptibility to cold cracking. When different thicknesses are present in the joints, it is often thought that greater thicknesses require higher welding energy (the ratio between power and welding speed). This has also been verified in the literature. The present work aims to test if it be possible to weld the root pass of four plates of different thicknesses (7 mm, 10 mm, 12.7 mm, and 25.4 mm) considering a similar welding energy. This would make the parameterization robust, as the welder would not need to change the welding energy to perform the process under different conditions. An experimental evaluation was conducted on shipbuilding steel ASTM A131 DH36 using the GMAW process, evaluating both the geometric characteristics of the weld bead and the microstructure at different thicknesses. Cooling rates were predicted based on an in-house finite volume method (FVM) computational code. The results indicated that although all welds met the main requirement of full penetration, the metallurgical requirement of a maximum hardness of 350 HV in the HAZ was only achieved at thicknesses of 7 mm and 10 mm. This occurred because, in greater thicknesses (12.7 mm and 25.4 mm), the cooling rate was elevated due to the thickness itself and the use of a higher feed rate. Consequently, in the coarse grain heat affected zone (CGHAZ), there was a shift from the ferritic field to the bainitic field. To meet the requirements, it is advisable to adjust parameters, such as increasing weld energy or applying preheat treatment. Another alternative involves planning subsequent passes to induce a tempering effect on the root. In summary, for geometrical purposes, a constant energy can be used, whereas metallurgical objectives might necessitate greater energy input with increasing thickness. [ABSTRACT FROM AUTHOR]

A novel friction processing method is used to join Al-Cu sheets in lap configuration without any significant deformation or thickness depletion of parent metals. A pin less, flat shouldered tool is rotated and plunged against a sacrificial top sheet to initiate localised melting at the joint interface. Effect of addition of SiC particles at the joint interface on resulting weld microstructure, interface strength, and joint electrical resistance is studied in this work. Diffusion reaction of SiC particles with Al and Cu results in melting of the interface at around 530 °C. The peak temperature in weld zone with SiC particles is significantly lower than the Al-Cu eutectic temperature and melting points of Al, Cu. Cross-sectional scanning electron micrographs, fractographs, electron dispersive spectroscopy, X-ray diffraction, lap shear, T peel tests, and joint electrical resistance measurements are used to investigate pure Al-Cu and Al-SiC-Cu weld joints for different SiC particle concentrations. SiC particles are found to enhance joint strength through generation of fine eutectic microstructures with sub-micron lamellar spacing and through formation of uniformly distributed nano-precipitates. The highest peel strength achieved with the SiC interlayer is around 70 % higher than that for corresponding pure Al-Cu welds. Despite formation of thick hypereutectic region towards Cu side, with larger volume percentage of "lumps of intermetallics", there is a clear diversion of fracture path from the intermetallics rich region towards the SiC-eutectic boundary of the interface region in Al-SiC-Cu welds. Additionally, SiC interlayer is seen to result in lower percentage rise in joint resistance with temperature. However, SiC interlayer results in a marginal increase in joint electrical resistance. Thus, addition of SiC particles at Al-Cu joint interface is recommended for significantly enhancing the joint strength with no significant change in joint electrical resistance. [Display omitted] • Diffusion of Si from SiC particles into Al-Cu melt reduces the interface melting temperature. • SiC particles expose nascent surfaces of Al-Cu, promote interdiffusion and enhance wetting. • Nanoprecipitates are seen to form in the ''crumbled" eutectic melt region. • SiC particles increase the fracture energy with a highly jagged fracture surface. • Joints with SiC interlayer exhibit higher joint strength at nearly similar electrical resistance. [ABSTRACT FROM AUTHOR]

High-entropy alloys (HEAs) are newly developed materials that have many excellent properties, such as a high strength-to-weight ratio and excellent tensile properties. If high-entropy alloys and stainless steel are joined by welding, the advantages of their properties can be balanced. In this paper, dissimilar lap joining of Al 0.3 CoCrFeNi-HEA with 304 stainless steel was achieved using gas tungsten arc welding (GTAW) with different heat inputs. Macroscopic morphology, microstructure analysis and mechanical property tests of the welded joints were carried out. The results showed that the macroscopic morphology of the dissimilar welded joints is well-formed under different heat inputs. The penetration and width of the weld seam increased with the heat input, and the lap area of the welded joint also increased. There was the same microstructure in the weld seam with different heat inputs, including columnar dendrites near the fusion line and equiaxed dendrites at the weld centre. The ultimate shear strength of the welded joints increased from 442 MPa to 560 MPa with increasing heat input, and the elongation of the welded joints increased from 26 % to 41 %. With increasing heat input, the average microhardness of the weld zone (WZ) was approximately 145 HV. [ABSTRACT FROM AUTHOR]

Wire arc-directed energy deposition (WA-DED) is a promising additive manufacturing (AM) technique for building large, complex near-net-shape parts, combining high deposition rates and fully dense builds. The goal of this study was to explore the advantages of WA-DED for local property optimization by joining a high-strength nickel-based alloy with a wear-resistant cobalt-based alloy. Single-pass depositions of the IN718 Ni-based alloy on round L605 Co-based alloy stock were prepared, using a Fronius cold metal transfer (CMT) WA-DED system to achieve low heat input and clean weld passes. The influence of varying process control settings during the deposition process on the final porosity and interface integrity, as well as resultant variations in microstructure and mechanical property, were evaluated. The results indicate that the process did successfully produce crack-free, non-porous, and continuous welds. In the as-deposited condition, the weld metal showed the presence of Nb-enriched regions and phases, and variation in process control settings resulted in a change of mean precipitate size. The interface regions showed increases in hardness, likely due to precipitate strengthening during extended cooling times. Lastly, the general microstructure and mechanical properties showed relative insensitivity to changes in processing setting during WA-DED using the CMT system, allowing for greater flexibility during manufacturing. [ABSTRACT FROM AUTHOR]

Fatigue damage represents a key failure mode in ship structures. Such damage typically begins at vulnerable points in the structure, like welded joints, stress concentration areas, and cracks. Cyclic loading, particularly from waves, encountered by ships during their operational life is a major cause of fatigue damage, which is the main focus of this study. There are various methods to address different sea state conditions, though they can sometimes be approximate. This paper aims to review the most commonly used methods to highlight their strengths and weaknesses and to provide essential background knowledge for developing reliable theoretical and numerical models for predicting the fatigue life of ship structures exposed to various sea states over their lifetime. The primary theoretical approaches discussed include energy spectral methods in both time and frequency domains, which are used to quantify wave-related energy and amplitude characteristics and evaluate wave loads for predicting the fatigue life of structures and welded joints. The discussion also covers the determination of cyclic stress in specific structural details of the hull girder and welded joints to identify the relevant maximum stress range for subsequent fatigue studies conducted using finite element analysis. [ABSTRACT FROM AUTHOR]

In this study, a new deep-penetration variable-polarity tungsten inert gas (DP-VPTIG) welding process, which is performed by a triple-frequency-modulated pulse, was employed in the welding fabrication of 8 mm AA7075 aluminum plates. The electric signal, arc shape, and weld pool morphology of the welding process were obtained by means of high-speed photography and an electric signal acquisition system under varying parameters of the intermediate frequency (IF) pulse current. The principle of the arc characteristics and the dynamic mechanism of the weld melting during the process are explained. In addition, the macroforming, microstructure, and microhardness of the welded joints were investigated. The results indicate that, with an intermediate frequency pulse of 750 Hz, the arc displayed a higher energy density and a more effective arc contraction, which improved weld appearance and penetration. Moreover, the impact and stirring action of the arc refined the microstructure grains of the weld center. Therefore, this new welding method is feasible for welding medium-thickness aluminum alloy plates without a groove. [ABSTRACT FROM AUTHOR]

The welded joints of high/medium entropy alloys (H/MEAs) have shown sound mechanical properties, indicating high promise for the industrial application of this new type of metal alloy. However, these joints possess either relatively low strength or low ductility. In this paper, we used ultrasonic-assisted laser welding to weld CrCoNi MEA with the nitrogen as shielding gas. The results showed that the tensile strength of the joint at room and cryogenic temperature is 686 MPa and 1071 MPa, respectively. The elongation at room and cryogenic temperature is 26.8% and 27.7%, respectively. The combination of the strength and ductility in our joints exceeds that of other welded H/MEA joints. We attributed this excellent combination to the refined dendrite, the solution of nitrogen into the matrix, and the low stacking fault energy of the CrCoNi MEA. The findings in this paper not only provide a novel way to weld H/MEAs with high strength and ductility, also are useful for additively manufacturing the high-performance component of H/MEAs. [ABSTRACT FROM AUTHOR]

There is a growing number of welded steel bridges in the world that are reaching the end of their design life. Repair of fatigue damage (cracks) or replacement with new modern designs is becoming an increasing issue. Fatigue damage is now one of the main design and construction risks associated with the construction of new dynamically stressed steel structures. Fatigue damage is now one of the main design and engineering risks associated with the construction of new dynamically stressed steel structures. Increasing fatigue life can be achieved by HFMI treatment that can be applied to new weld as well as existing welded joints. This paper presents the results of experiments focused on HFMI treatment to new and repaired butt welds of higher thicknesses. [ABSTRACT FROM AUTHOR]

Titanium alloys are widely applied in the aerospace field owing to their exceptional properties, but coarse grains can easily form during the welding process, seriously diminishing the mechanical properties of the welded joint. To address this problem, a pulsed current was introduced to refine the grain structure of titanium alloy welds. In this study, we investigated the effect of varying the pulsed current frequency on grain refinement in titanium alloy welds and explored the mechanism of grain refinement using the "overlap welding" method. The results showed that the grain refinement improved with increasing pulse current frequency, particularly at the original β and α grain boundaries. Compared to non-pulsed welding, the original β grain boundary decreased from 305 to 158 μm, and the maximum α grain size decreased from 93.236 to 46.693 μm when the pulse frequency was 100 Hz. Moreover, dendrite fragmentation was identified as the primary mechanism of grain refinement in pulsed plasma arc welding of the Ti6Al4V alloy. The repeated heating of the molten pool by application of the pulsed current caused the dendrite tip to remelt in the pasting region, promoting dendrite fragmentation. [ABSTRACT FROM AUTHOR]

In this work, the results from the electron beam welding of copper and Al6082T6 aluminum alloy with a titanium filler are presented. The influence of the filler on the structure and mechanical properties of the welded joint is studied in comparison with one without filler. The X-ray diffraction (XRD) method was used to obtain the phase composition of the welded joints. Scanning electron microscopy (SEM) was used for the study of the microstructure of the welds. Energy-dispersive X-ray spectroscopy (EDX) was applied to investigate the chemical composition. The mechanical properties were studied by means of microhardness measurements and tensile tests. A three-phase structure was obtained in the fusion zone consisting of an aluminum matrix, an intermetallic compound CuAl2, and pure copper. The application of Ti filler significantly decreased the amount of molten copper introduced in the molten pool and the number of intermetallic compounds (IMCs). This improved the strength of the joint; however, some quantity of IMCs was still present in the zone of fusion (FZ), which reflected the microhardness of the samples. The application of a titanium filler resulted in refining the electron beam weld's structure. The finer structure and the reduced amount of the brittle intermetallic phases has led to an increase in the strength of the joint. [ABSTRACT FROM AUTHOR]

This review paper explores the impact of various weld cladding techniques, such as MIG and TIG, alongside innovative methods like Cold Metal Transfer (CMT), on enhancing the microstructure, corrosion resistance and mechanical properties of metals and alloys. Welding dissimilar metals with traditional methods presents challenges, but the CMT process, a modified version of MIG welding, addresses these with its rapid deposition rate, improved bead aesthetics and low thermal heat input. Robotic welding further enhances microstructural characteristics. Advancements in conventional TIG, MIG and CMT processes, including A-TIG, Keyhole-TIG, Pulsed MIG, Plasma-MIG, CMT Pulse and CMT Advanced, improve capabilities such as weld penetration, heat-affected zone width, weld finish, and defect reduction. This paper summarises how different welding techniques improve weld quality in terms of microstructure, electrochemical and mechanical properties. Additionally, it compares conventional welds and their variants to identify the best welding technology for Austenitic SS316 in marine environments. Highlighting the applications and benefits of weld cladding in industries like aerospace, shipbuilding and power generation, the paper underscores the significance of a comparative study on TIG, MIG and CMT weld cladding using Ni-Cr-Mo filler on SS316 base metal for optimal corrosion resistance and mechanical performance in marine settings. [ABSTRACT FROM AUTHOR]

The objective of the research was to determine the exact process parameters required for spot-welding AA2014 and AISI316 alloys. The main focus was on achieving particular welding results, including nugget diameter, hardness, and tensile shear fracture load (TSFL). The central composite rotatable design model within the framework of a Response Surface Methodology (RSM) optimization approach, the study sought to intensify key spot weld process factors. The mechanical characteristics and nugget diameter of the welded joints were analyzed by carefully examining these factors to determine their significant effects. The investigation yielded crucial insights, revealing that the highest strength of welded joints, characterized by a nugget diameter of 5.982 mm, hardness of 149.6 VHN, and TSFL of 2.355 KN, was achieved at 3.4 kgf, when accompanied by 60 W power and a 2.5s duration. Notably, power emerged as the predominant factor driving the spot-welding process. Furthermore, microhardness and TSFL displayed direct correlations with power, while nugget diameter exhibited an inverse relationship. Moreover, rigorous statistical analyses, including F-tests and ANOVA, provided robust validation, indicating that the observed values fell comfortably within a 99.5% confidence interval for hardness, nugget diameter, and TSFL. These meticulously derived conclusions represent a significant stride towards establishing more standardized and efficient spot-welding protocols, particularly beneficial for the manufacturing sectors dealing with mild steel and aluminium materials. [ABSTRACT FROM AUTHOR]

In this study, a new method for welding an API 5L X65 steel pipe that is internally clad with Alloy 625 cladding using Alloy 22 and AWS ER100S-G steel was developed. The first and second weld passes were made using Alloy 22 to provide excellent corrosion resistance for the Alloy 625 cladding region. The remaining weld passes were made using 100S-G steel to provide high mechanical strength. The welded joints were evaluated for their microstructure and mechanical properties. No significant solidification defects were found in the welded joints, as confirmed by bending and transverse tensile tests. The yield strength of the welded joint showed that welding was capable of delivering the necessary strength compatible with API 5L X65, X70, and X80 steels for subsequent installation using the reel lay process. The microstructure of the welded joint was complex, with the first two weld passes having a soft Ni-fcc matrix composed mainly of Alloy 22, while the first three 100S-G steel weld passes had a hard martensite matrix. The main region of the welded joint had a soft acicular ferritic matrix. Impact toughness testing showed that the energy absorbed by the notch positioned at the first steel weld pass was better than that for the notch positioned at the steel weld pass without a dilution effect for Alloy 22 (approximately 46 J and 14 J, respectively). The toughness of the weld pass increased due to the high Ni incorporation by dilution with Alloy 22, even at − 15 °C, while the steel weld passes that were not affected by dilution with Alloy 22 exhibited very low energy absorption, which is characteristic of steel materials assessed under conditions below the ductile-to-brittle transition temperature (DBTT). The fracture toughness tests confirmed this result, as the major steel weld passes exhibited brittle features that caused abrupt failure during the test at − 15 °C. [ABSTRACT FROM AUTHOR]

Welding techniques are widely utilized for permanent material joining. The tungsten inert gas (TIG) welding process is notable for its exceptional precision, controlled heat input, and affordable equipment. It is widely employed for joining different grades of steel. Currently, extensive research is being conducted to enhance the quality of welded joints. This involves exploring various welding methods and adjusting welding parameters to improve characteristics such as strength, ductility, formability, appearance, and corrosion resistance. The current investigation's main aim consists of studying the effect of the welding parameters, i.e., the welding current and the gas flow rate, on the mechanical properties of welded joints of low-carbon steel with a thickness of 1 mm. The yield strength, tensile strength, and strain at break are selected as responses. The analysis of variance (ANOVA) is utilized to check the impact of welding parameters on the responses, while the Gray Relational Analysis (GRA) is used to optimize the welding parameters to maximize the chosen responses. Results show that welding current possesses the most influence on the three responses, i.e., the yield strength, tensile strength, and strain at break. The combination of 65 A welding current and 15 l/min gas flow rate allows the maximization of the three responses. [ABSTRACT FROM AUTHOR]

Tungsten argon arc welding (TIG), cold metal transfer (CMT) welding and flash butt welding (FBW) are used to join M390 and 304. The mechanical properties of M390 and 304 welded joints with different welding methods were compared by tensile and microhardness experiments. The microstructure evolution and phase changes of TIG, CMT and FBW welded joints were compared and analyzed by scanning electron microscope (SEM) and x-ray diffraction. The grain size of weld metal (WM) and M390 heat-affected zone of three types of welded joints were measured by Image J software. Corrosion resistance of three types of weld joints was characterized by electrochemical corrosion tests, and the microstructure of post-corrosion test specimens was characterized by SEM and EDS. The results show that three types of welded joints without cracks and voids can be obtained between dissimilar metals M390 and 304. The microstructure of TIG weld metal is composed of martensite and the carbides M7C3 and M23C6 due to higher heat input during TIG welding processes. Because extensive C, Cr and Ni element diffusion occurs during FBW welding due to low heat input, the microstructure of the weld metal is composed of martensite and austenite matrix and carbides of M7C3 and M23C6. The filling of nickel-based alloys during CMT welding processes make the microstructure include austenite and (Al, Ni, Ti) carbide. The tensile strength and elongation of CMT welded joint can reach 501 MPa and 21.8%, the corrosion current density is 4 mA cm−2, and the corrosion voltage is − 21 mV, which is the best mechanical properties among the three types of welded joints. The welded joints with the three welding methods are all fractured at WM position. [ABSTRACT FROM AUTHOR]

Defective welds substantially hinder the quality of a welded joint, and choosing the best process parameter to ensure tunnel defect-free welds requires extensive experimentation. A coupled Eulerian–Lagrangian (CEL) finite element (FE) model was proposed to predict the defect formation, thermal history, and material flow behavior of the friction stir welding (FSW) process. The formation of defects was examined by varying tool rotation speed (TRS) between 600 and 1800 rpm and welding speed (WS) between 30 and 90 mm/min, with a constant tilt angle of 0°. It was evident that selecting appropriate process parameters established the condition for a tunnel defect-free joint. Less temperature of 300.2 °C can't initiate proper material plasticization, leading to reduced material consolidation and more flash generation, thereby generating a long-stretched tunnel defect sample (S1). In contrast, a maximum temperature rise of 595.6 °C in the tunnel defect-free specimen (S2) ensures sufficient frictional contact between the tool-workpiece, thereby increasing material plasticization and enhancing material flow. Variation of less than 10% was found between the observed and simulated transient thermal histories. A minor percentage error of 5.44% in length and 1.28% in width was measured between the experimental and numerical tunnel defect morphology of S1. Contrarily, percentage errors of 4.16% in length and 3.75% in width were recorded for S2. Complete dynamic recrystallization in S2 hinders the formation of lamellar grain structures and flow segregation, leading to fine granular morphology. Maximum von Mises residual stress of 370 MPa was evident to spread all over the welded path in S1, thus hindering its service life. In comparison, 470 MPa were recorded at the crown of the chips of S2, which can be machined. A percentage error of 11.9% for sample S1 and 4.07% for S2 was marked when validating for average axial force data deviation. The proposed methodology was fairly well validated with the experimental trials. [ABSTRACT FROM AUTHOR]