Search Results (155)

In this study, a three-dimensional transient multi-physics coupled numerical model of narrow-gap tungsten inert gas (TIG) welding of TC4 alloy is established, and the heat transfer, flow behavior of the liquid metal in the molten pool, and the formation mechanism of sidewall lack-of-fusion defects are quantitatively investigated. The results show that, along the groove width direction, the temperature and flow velocity of the liquid metal gradually decrease from the center toward the sidewall. Along the welding direction, the fluid velocity presents multi-peak fluctuation characteristics. As the weld pass increases, the maximum velocity of the liquid metal significantly increases, enhancing the overall fluidity of the molten pool, and the temperature distribution becomes more uniform due to the weakened geometric constraints of the sidewall and the inter-pass heat accumulation effect. Furthermore, excessively high welding speeds (0.2 m/min) or insufficient welding currents (150 A) drastically reduce the per-unit-length heat input, resulting in diminished molten pool volume and decreased maximum liquid metal velocities of 0.075 m/s and 0.1 m/s, respectively. Under these conditions, lateral driving forces generated by the Marangoni effect are insufficient to overcome the viscous resistance of the molten metal. Consequently, the liquid metal solidifies prior to reaching the sidewall, inducing pronounced sidewall lack-of-fusion defects and localized humping on the weld top surface. Full article

The novel martensitic heat-resistant SIMP steel is considered a primary candidate structural material for Accelerator Driven Sub-critical Systems (ADSs) due to its excellent comprehensive properties. However, welding difficulties arising from its high alloy content represent a major bottleneck for its engineering application. This study explored and established optimized manual Tungsten Inert Gas (TIG) welding process parameters suitable for 20 mm thick SIMP steel plates, involving 24 layers and 110 passes, with an average heat input of approximately 4 kJ/cm, successfully achieving well-formed and defect-free welds. The welded joints were investigated using optical microscopy, scanning electron microscopy, and other performance tests. The results revealed the presence of δ-ferrite and a small amount of brittle Laves phase in the weld metal, leading to uneven hardness distribution. Furthermore, poor interfacial coordination between δ-ferrite and tempered martensite significantly reduced the ductility of the joint. Through optimized process parameters, the impact energy of the weld metal reached 183.9 J, while that of the heat-affected zone was 77.9 J. The room temperature ultimate tensile strength and yield strength of the joint were 802.63 MPa and 596.33 MPa, respectively, meeting the weld performance requirements stipulated in GB/T 38875-2020. This research provides data support for promoting the engineering application of SIMP steel in fields such as nuclear power and for enhancing the long-term service reliability of welded structures. Full article

Hot cracking in welding is a very complex phenomenon. It can happen in the weld metal zone during solidification but also in the heat-affected zone (HAZ). Hot cracking defects are material decohesion that occur at high temperatures along grain boundaries when the strain and strain rate exceed a certain level. The cracks can be internal or open to the surface in the weld bead. During a welding operation, different types of hot cracks can appear, such as hot cracking due to solidification, hot cracking due to liquation, hot cracking due to loss of ductility. The main factors favoring hot solidification cracking include the presence of residual elements and impurities, leading to the formation of a low-melting eutectic; the solidification mode; and mechanical restraints. This review paper gives an introduction to solidification cracking in stainless-steel welds, the weldability of the austenite grades, and the causes of solidification cracking occurrence. The main methods with which to detect and inspect cracks are investigated. Particular focus is placed on TIG (tungsten inert gas), also known as Gas Tungsten Arc Welding (GTAW). A review of the literature reveals that considerable progress has been made in terms of the improvement in the properties of the weld joint through the application of mitigation means and strategies. The effort made by researchers in understanding solidification cracking phenomena has been key to enhancing cracking resistance and ensuring the integrity of structures. Full article

Activated Tungsten Inert Gas (ATIG) welding employs an activating flux to increase penetration and improve productivity compared with the conventional Tungsten Inert Gas (TIG) process. Conventional fluxes typically consist of metallic oxides dispersed in alcohol- or acetone-based solvents. In this study, a novel flux composed of SiO₂ and TiO₂ nanoparticles suspended in a sodium-silicate solvent was used for welding Inconel 718. The proposed flux achieved full penetration of a 7 mm thick plate at 160 A DCEN using 60° and 90° electrode tip angles, without visible distortion or defects in the examined cross-sections. Microstructural characterization revealed notable changes in the content, morphology, and size of Nb-rich interdendritic constituents consistent with Laves phase formation compared with welds produced without flux. ATIG specimens contained a lower amount of these brittle intermetallic constituents, which exhibited a less branched and more coagulated morphology despite the lower cooling rate. As a result, a greater fraction of alloying elements remained available for dendrite reinforcement rather than being segregated into Nb-rich interdendritic regions, leading to higher weld-metal microhardness in the ATIG60 specimen than in TIG welds. These observations were attributed to enhanced weld-pool stirring caused by molten metal flow toward the weld center and downward through the weld pool, consistent with the reversal of Marangoni convection. Full article

To improve the efficiency of TIG (Tungsten Inert Gas) welding, our team developed a novel fast-frequency pulsed twin-TIG welding power source and matched welding procedures to overcome the drawbacks of conventional high-efficiency TIG welding. After parameter optimization, stable, high-efficiency and high-quality welding of 316L stainless steel can be realized. Compared with traditional DC TIG welding, the mechanical properties of joints are greatly improved: the weld grain size is refined by 38% under moderate current, while tensile strength, elongation and microhardness rise by 13.6%, 26% and 10% respectively, which achieves simultaneous improvement in strength and ductility. Numerical simulations were carried out to analyze the evolution of molten pool temperature field and velocity vector flow field. The simulation results are highly consistent with experimental data, which verifies the reliability of the model and lays a foundation for the study of molten pool behavior. Combined with molten pool flow characteristics and weld microstructure, the evolution mechanism of microstructure and texture as well as grain refinement in this welding process is revealed. Full article

To address the performance degradation associated with retained high-temperature δ-ferrite in welded joints of high-silicon 20Cr11W2VTaSi steel—a candidate structural material for spallation targets in Accelerator Driven Subcritical Systems—this study systematically investigates the microstructural evolution and mechanical behavior of 20 mm-thick forged joints produced via automated tungsten inert gas (TIG) welding using a 7° U-groove narrow-gap configuration. Results demonstrate that the narrow-gap process—featuring reduced filler metal deposition and low heat input—is believed to suppress macrosegregation of ferrite-stabilizing elements (e.g., Cr, Si, Mo). As a result, the δ-ferrite content in the weld metal is constrained, exhibiting a fine, dispersed, worm-like morphology embedded within a uniform matrix of tempered martensite. Microhardness mapping confirms homogeneous hardness distribution across the joint, closely matching that of the base metal, with no statistically significant localized softening zones identified. Mechanical characterization reveals an optimal balance of strength and toughness: the joint achieves a room-temperature tensile strength of 820 MPa and retains 436 MPa at 550 °C; moreover, the Charpy impact energy at the weld center reaches 171.2 J. Full article

This study proposes a novel high-frequency flat-top longitudinal magnetic field-assisted tungsten inert gas (HF-FTLMF TIG) welding method to improve arc constriction and weld penetration. The effects of magnetic field intensity and frequency on arc morphology, weld appearance, and microstructure were systematically investigated. The results show that, compared with conventional TIG welding, when the frequency of the FTLMF exceeds 1000 Hz, the arc becomes noticeably constricted, the conical angle decreases, and the heat input becomes more concentrated. Under appropriate magnetic field conditions, the arc pressure increases from 251.3 Pa for the free arc to 452.9 Pa, and the weld penetration depth increases from 0.84 mm to 1.09 mm. In addition, HF-FTLMF reduces surface unevenness and improves weld uniformity. Compared with low-frequency FTLMF (<1000 Hz), HF-FTLMF exhibits more stable arc behavior and better weld formation. SEM and EDS results further indicate that the application of HF-FTLMF affects the fusion-zone microstructure and elemental redistribution, and a relatively finer microstructure was observed under the 2000 Hz condition. These findings suggest that HF-FTLMF provides an effective approach for regulating TIG arc behavior and improving weld formation through magnetic field assistance. Full article

This study investigates the influence of specific heat input and weld configuration on heat affected zone hardness and residual stress of S960MC high strength steel welds. In total, five types of weld samples were manufactured by Tungsten Inert Gas (TIG) autogenous welding and Metal Active Gas (MAG) butt welding to simulate the effect of increasing heat input and constraining the relative motion of welded parts during the heating and cooling phase. The obtained results show that the highest axial tensile residual stresses with magnitude above 900 MPa, combined with a hardness drop in a range from 13 up to 18%, occur mostly in the sub-critical heat affected zone, making it the critical zone of the weld. Increasing the heat input during welding does not have a simple correlation with generating more residual stresses and the trends obtained on the surface are different from results evaluated at a depth of 0.2 mm. Restraining the relative part motion during the welding affects mostly the tangential residual stresses, causing an increase in their tensile magnitude localized in the middle of the heat-affected zone while almost no influence on the axial residual stress component was recorded. Full article

This study compares the microstructural evolution and mechanical properties of TC4 (Ti-6Al-4V) titanium alloy joints welded by Tungsten Inert Gas (TIG) and laser processes, following a post-weld annealing treatment at 650 °C for 2 h. Distinct microstructures were obtained: the TIG-welded joint developed a heterogeneous mixture of short-rod α and lamellar β, while the laser-welded joint formed a more homogeneous equiaxed α structure with uniformly distributed β-phase nanoparticles. Electron backscatter diffraction (EBSD) results confirmed that the annealing treatment significantly weakened the strong welding-induced texture and disrupted the epitaxial growth mode of columnar grains. Mechanical testing demonstrated that annealing improved the strength-toughness balance, but the extent and mechanism differed between the two processes. For the TIG-welded joint, the ultimate tensile strength slightly decreased, while elongation and impact toughness increased by 18% and 10.4%, respectively. In contrast, the laser-welded joint maintained its original strength while achieving greater improvements in ductility and toughness, with elongation and impact toughness increasing by 20% and 15.2%, respectively. This divergence is attributed to insufficient recrystallization and the persistence of residual coarse grains, limiting the TIG joint’s performance. However, in the laser-welded joint, the pinning effect of β-phase nanoparticles and associated grain refinement enhanced ductility without compromising strength. Full article

This study addresses the challenge of through-hole defects in ZM6 cast magnesium alloy components by proposing an innovative repair strategy using ultrasonic-assisted Tungsten Inert Gas (U-TIG) welding. The microstructure and mechanical properties of the repaired joint were systematically characterized through optical microscopy, scanning electron microscopy (SEM), X-ray diffraction (XRD), and room-temperature tensile testing. The results indicate that, assisted by the ultrasonic energy field, the repair zone successfully reconstitutes a typical and optimized triple-phase microstructure: (1) the matrix: α-Mg solid solution (dark gray), supersaturated with Nd and Zr; (2) the strengthening phase: a eutectic Mg₁₂Nd phase (light gray), rich in Nd, distributed along grain boundaries acting as the primary strengthening component; (3) the grain refiner: dispersed Zr-rich particles (bright white spots), which effectively pin grain boundaries. Crucially, the application of ultrasound significantly refined the α-Mg grains and transformed the continuous network of the Mg₁₂Nd phase into a more fragmented and uniform dispersion. This refined microstructure synergistically integrates the strengthening mechanisms of solid solution, precipitation hardening, and grain refinement. Consequently, the repaired joint exhibits excellent mechanical properties, achieving over 90% of the base metal’s tensile strength and elongation at room temperature. This work not only validates the feasibility of U-TIG welding for repairing ZM6 alloys but also provides a solid theoretical foundation and a promising technical pathway for the in-service repair and remanufacturing of high-performance magnesium alloy components. Full article

The paper investigates the arc behavior and molten metal flow during Keyhole tungsten inert gas (K-TIG) welding of dissimilar materials, Invar 36 and stainless steel (types 304, 316, 309, and 310) specifically. A high-speed camera was used to capture the contour of the molten pool in real time. Results showed that in stainless steel welding, the arc shape is bell-shaped, and the distance from the tip of the molten pool to the keyhole decreases with increasing thermal conductivity (6.76–10.86 mm). When Invar 36 was butt-welded, the arc contracted. However, when Invar 36 was welded with dissimilar materials of stainless steel, the arc deflected to the Invar 36 side. The deflection angle ranged from 29.9° to 37°, resulting in an asymmetric arc shape. The distance from the tip of the molten pool to the keyhole increased to 10.88–13.33 mm, which was about 42% higher than that of the same material welding. Metallographic analysis showed that the width of the heat affected zone on the Invar 36 side increases with the decrease in thermal conductivity of the stainless steel (1.77–2.03 mm). Differences in thermophysical properties and viscosity further led to asymmetric molten pool flow and metal accumulation behavior. This study quantified the formation mechanism of arc deflection and weld pool asymmetry in K-TIG welding of dissimilar materials. Full article

Additive manufacturing (AM), particularly laser-based powder bed fusion (PBF-LB), enables the production of high-strength, lightweight components made of aluminum alloys such as AlSi10Mg. However, joining these parts via welding remains a significant challenge due to weld seam porosity caused by hydrogen entrapment. This study investigated the influence of the PBF-LB process parameters, tungsten inert gas (TIG) welding settings, filler material, and post-weld T6 heat treatment on the tensile strength and porosity of welded AlSi10Mg components. Using two different layer heights (30 µm and 60 µm), plate thicknesses (3 mm and 5 mm), and varying welding conditions, a series of 10 TIG-welded sample groups were fabricated and analyzed. Microstructural, hardness, porosity, and tensile tests revealed that porosity was high across all samples (11–19%). A subsequent T6 heat treatment improved the tensile strength. Higher layer heights and thinner plates led to a higher tensile strength of the weld seam, while the addition of a filler material showed limited benefits. No other influencing factors or interactions could be found. The results emphasize the need to optimize hydrogen control in the processes, melt pool dynamics, and weld seam geometry to receive reliable joints in lightweight manufacturing of PBF-LB AlSi10Mg parts. Full article

To accurately assess the residual stress distribution on the superficial layer of the weld for a pure copper butt-welded joint after laser shock peening (LSP), a coupled model was established by integrating experimental measurements with numerical simulations. This model simulates both the tungsten inert gas (TIG) welding process of pure copper and the subsequent LSP treatment applied to the weld. On this basis, the effects of the spot overlapping rate, number of impact layers, and pulse width on the weld residual stress profile were evaluated via multi-point LSP simulations. The findings imply that LSP converts the weld’s superficial residual stress from tensile to compressive, which verifies the accuracy of the simulations through the experimental data. Multi-point LSP numerical simulations demonstrate that elevating the spot overlapping rate and number of impact layers enhances the amplitude and affected depth of the surface compressive residual stress (CRS). A slight decrease in the CRS on the superficial layer of the weld was observed with an increase in pulse width. Compared with increasing the overlapping rate and pulse width, increasing the number of impact layers has a more significant strengthening effect. When the impact layer reached 3 times, the surface CRS reached −219.4 MPa, and the influence depth was 1.3 mm. Full article

Stainless steel welding plays a critical role in industrial manufacturing due to its superior corrosion resistance and structural reliability. The keyhole tungsten inert gas (K-TIG) welding, renowned for its high efficiency, high precision, and cost-effectiveness, demonstrates particular advantages in medium-to-thick plate joining. In order to synergistically leverage the properties of 2205 duplex stainless steel (DSS) and 316L austenitic stainless steel (ASS), we have implemented K-TIG welding with a single variable under control: a constant current and voltage travelling speeds spanning 280–360 mm/min. Defect-free dissimilar joints were consistently achieved within the 280–320 mm/min speed window. The effects of welding speed on microstructural characteristics, mechanical properties, and corrosion behavior of the weld seams were systematically investigated. The percentage of austenite in the weld zone decreases from 84.7% to 59.9% as the welding speed increases. At a welding speed of 280 mm/min, the microstructural features in the regions near the weld seam and fusion zone were investigated. All obtained joints exhibited excellent tensile properties, with their tensile strengths surpassing those of the 316L base metal. The optimal impact toughness of 142 J was achieved at a welding speed of 320 mm/min. The obtained joints exceeded the hardness of TIG joints by 19%. Notably, the grain refinement in the weld zone not only enhanced the hardness of the welded joint but also improved its corrosion resistance. This study provides valuable process references in dissimilar stainless steel K-TIG welding applications. Full article

This study investigates the application of the Keyhole–Tungsten Inert Gas Welding (K-TIG) hot-wire filling welding technique with mechanical arc oscillation to weld a 95 mm-thick Ti-6Al-4V titanium alloy plate. The root layer thickness achieved with this technique reaches up to 17 mm, with an average filling thickness of 2.5 mm. The weld bead displays a smooth, shiny appearance, and no significant welding defects are observed in the cross-section of the welded joint. Experimental results show that the welded joint consists of the α phase in different forms, as well as fine α+β microstructures. Compared to the base material, both the weld metal and the heat-affected zone exhibit a lower crystallographic texture strength, with more complex texture types. The impact toughness of the welded joint is excellent, with no significant weaknesses. The impact toughness of the weld metal significantly surpasses that of both the base material and the heat-affected zone. The engagement strengthening effect induced by high-current filling plays a crucial role in enhancing the impact toughness of the weld metal. Full article