Achieving defect-free repair in ZM6 magnesium alloy through cold metal transfer welding combined with preheating

ABSTRACT This study explores the influence of Activated Tungsten Inert Gas Welding (ATIG) welding on 6 mm thick UNS S32760 Super Duplex Stainless Steel (SDSS) and UNS S31703 Austenitic Stainless Steel (ASS), materials widely used in marine and chemical processing applications, using SiO2, TiO2, Cr2O3, and Fe2O3 fluxes at currents of 135, 145, and 160 A. The research focuses on analysing weld bead morphology, microstructure, and hardness properties, compared the results with conventional TIG welding. The findings show that every flux considerably increased penetration depth, with TiO2 flux providing 148.51% improved penetration in S32760 steel and SiO2 flux providing 128.44% greater penetration in S31703 steel. Additionally, SiO2 flux consistently produced a higher depth-to-width ratio in both materials. Microstructural analysis revealed that UNS S32760 welds exhibited austenite variants such as Grain Boundary Austenite (GBA), Widmanstätten Austenite (WA), and Intragranular Austenite (IGA), with Chromium Nitride (Cr2N) precipitates in the ferrite matrix, while UNS S31703 welds showed austenite grains such as columnar and equiaxed, with ferrite stringers at the austenite grain boundaries. Hardness tests showed increased weld zone hardness in S32760 steel for both ATIG and conventional TIG welding, whereas S31703 steel exhibited no significant hardness changes.

Abstract This study presents a comprehensive evaluation of autogenous Tungsten Inert Gas (TIG) welding for dissimilar austenitic stainless steel socket joints between SS321 and SS304L tubes, employing both manual and orbital welding techniques. The objective is to assess weld quality, metallurgical integrity, and process feasibility for producing high-reliability dissimilar joints without filler metal, as required in aerospace, pharmaceutical, food processing, and high-purity piping applications. The dissimilar combination of titanium-stabilized SS321 and low-carbon SS304L introduces challenges such as thermal expansion mismatch, elemental diffusion, and sensitization, particularly in constrained socket geometries. Critical welding parameters, including current, pulse settings (orbital), torch angle (manual), arc length, and purge flow rate, were optimized based on tube dimensions. Both techniques achieved full-penetration welds without defects. Post-weld evaluation was conducted through visual inspection, dye penetrant testing, and metallographic analysis, while mechanical performance was assessed via hardness mapping and pressure-based leak testing. Orbital TIG welding demonstrated superior repeatability, narrower heat-affected zones, and consistent weld quality, making it suitable for automated and high-purity applications. Manual TIG welding, though operator-dependent, produced acceptable results under controlled conditions and remains advantageous for field applications. The findings confirm that autogenous TIG welding of SS321 to SS304L socket joints is feasible and capable of producing high-quality dissimilar joints when appropriate process control and joint preparation are maintained. Keywords: TIG welding, SS321, SS304L, dissimilar welding, autogenous welding, orbital welding, socket joint, stainless steel tubing, microstructure, corrosion resistance.

Aluminium 6061 alloy is widely used in aerospace and automotive applications owing to its light weight, corrosion resistance, and machinability. Nevertheless, the poor hardness and limited surface integrity of Al 6061 alloys restrict its prolonged use under extreme conditions. In this work, the properties of Al 6061 alloy has been augmented by developing hard Titanium Carbide (TiC) coatings on its surface by tungsten inert gas (TIG) cladding technique. The developed TiC coatings enhanced the hardness of Al 6061 alloy up to 3 times, with average micro-hardness in the range of 431- 496 HV 0.05 . From this motivation, on the later stage of the work, titanium carbide particles are reinforced in to the weld joints of Al 6061 alloys by TIG arc heat under variable TIG current conditions. The integration of TiC reinforcement into the weld joints enhanced the ultimate tensile strength from 20–29 MPa to 59–83 MPa. Additionally, the maximum hardness attained as 173.72 HV 0.05 , depicting an improvement upto 1.5 times. Further, an Artificial Neural Network (ANN) model using backpropagation accurately predicted mechanical properties, showing strong agreement with experimental data and validating its forecasting capability. It achieved a high co-efficient of determination (R 2 ≈ 0.99) and depicted minimal prediction error, signifying a strong correlation between the experimental data and the predicted outcomes.

This study investigates the dissimilar welding of austenitic stainless steel AISI 304L and ferritic stainless steel AISI 409M using Tungsten Inert Gas (TIG) welding. Welding experiments were designed using a Taguchi L9 orthogonal array considering welding current, shielding gas flow rate, and travel speed as process parameters. Butt joints were fabricated and evaluated through visual inspection, X-ray radiography, tensile testing, and microstructural characterization. The results indicate that tensile strength of the welded joints varied significantly with process parameters and ranged from 522 to 644MPa. Among the samples, specimen S6A exhibited the highest tensile strength (644.5MPa) with 30.6% elongation due to the formation of a refined ferrite-austenite microstructure with reduced dendritic spacing. Microstructural analysis revealed the presence of lacy and vermicular ferrite within the austenitic matrix along with Widmanstätten ferrite near grain boundaries. Taguchi optimization identified the optimal welding condition as C2G3S3 corresponding to 105 A welding current, 20 L/min shielding gas flow rate, and 3mm/s travel speed. The study establishes a correlation between welding parameters, heat input, microstructural evolution, and mechanical performance in dissimilar stainless-steel TIG welding. Unlike previous studies, the present work establishes a direct correlation between heat input, solidification behavior, and resulting microstructural features in AISI 304L-409M dissimilar welds. The study provides new insight into the process-structure-property relationship specific to ferritic-austenitic stainless steel combinations.

Abstract. Tubes with non-uniform thickness are needed to even out wall thickness in draw bending and provide higher stiffness in specific directions in some applications. Tailored local heating of the tubes in tube sinking operations should reduce the local flow stresses and facilitate differential deformation along the circumference of tubes to form tubes with uneven wall thicknesses. Local heating of tubes prior to entry into the die in tube sinking is implemented in this research to form tubes with higher thickness in desired directions. Initial experiments are conducted using plasma heating by tungsten inert gas (TIG) welding equipment on EN AW 6060 AlMgSi0.5 aluminum tubes. The process window is described by varying the process temperature (weld current between 50 A and 80 A) while altering the degree of deformation, the tube diameter, and tube thickness. Tubes with no defects were formed at 50 A. Increasing the weld current led to a higher wall thickness (up to 25% thickness increase), however, high weld currents also favored the formation of surface defects, wrinkle formation, or burn-through holes depending on the process setup. The process window was larger for tubes with higher wall thickness.

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.

Ti‐6.5Al‐3.5Mo‐1.5Zr‐0.3Si titanium alloy was produced using tungsten inert gas wire and arc additive manufacture (WAAM) technology. The study investigated the impact of WAAM process parameters and their interactions on weld bead size and microstructure. The columnar‐equiaxed transformation model was utilized to analyze the solidification process of the titanium alloy weld pool. The findings revealed that bead width increases with higher welding current and decreases with increased welding speed. Conversely, bead height decreases with higher welding current and speed but increases with increased wire feeding speed. Notably, welding current and speed, as well as welding current and wire feeding speed, exhibited significant interactions on bead width and height. The optimized process parameters for arc additive manufacturing of titanium alloy were determined as follows: wire feeding speed of 149 cm/min, welding speed of 25.2 cm/min, and welding current of 140 A. During the weld solidification process, the temperature gradient decreased from bottom to top, while the solidification speed increased in the same direction. Furthermore, an increase in welding current and a decrease in welding speed shifted the solidification conditions towards the columnar crystal region, thereby promoting the growth and formation of columnar crystals.

This study investigates the high-temperature dry-sliding wear behavior of base alloy (Ti-6Al-4V, also called Ti64) and its surface-engineered variants developed through conventional tungsten inert gas (TIG) arc treatment both with and without ceramic reinforcements (SiC and B4C). Pin-on-disk wear tests were conducted at room temperature, 150 °C, and 300 °C under normal loads of 3 kg and 6 kg to simulate realistic thermomechanical service conditions. Microstructural and phase evolution were analyzed using optical microscopy, field emission scanning electron microscopy (FESEM), and energy-dispersive x-ray spectroscopy (EDS), while the mechanical response was evaluated through microhardness and high temperature wear testing. TIG arc surface modification led to significant refinement in microstructure and a notable hardness enhancement from ∼250 HV in the base metal to ∼840 HV in B4C-reinforced samples corresponding to ∼232% increase due to the formation of hard phases like TiB and TiC. This improvement in mechanical properties translated into remarkable wear resistance at elevated temperatures. The B4C + TIG samples exhibited the most superior performance achieving wear depth reductions of up to ∼52% at room temperature, ∼85% at 150 °C, and maintaining wear increase below 10% even at 300 °C under high load, outperforming SiC + TIG, BM + TIG, and unmodified Ti64. Overall, TIG arc surface engineering particularly with B4C reinforcement proves to be an effective strategy to enhance the high-temperature tribological performance of base alloy ,making it highly suitable for aerospace, biomedical, and automotive applications.

This study investigates a maintenance robot for the electric heating tube sheaths in nuclear pressurizers and the optimization of welding parameters for autogenous tungsten inert gas (TIG) butt welding of 304 austenitic stainless steel circular pipes suitable for this robot. Numerical simulations were carried out to analyze the effects of welding current and dwell time on temperature fields, weld morphology, and residual stress. The results revealed that a welding current of 105 A achieved complete penetration, while a dwell time of 4 s ensures full fusion at the weld starting point. However, prolonged dwell time significantly increased residual stress. Through systematic autogenous TIG welding experiments, the optimal welding current and dwell time for achieving superior weld morphology were determined. The results demonstrate that at a travel speed of 100 mm/min, defect-free welds with full penetration and no collapse can be achieved when the welding current is set to 105 or 115 A. Furthermore, under the conditions of a welding current of 115 A, an arc voltage of 10.5 V, and a dwell time of 4 s, the weld root width at the starting point remains stable and the residual stress is maintained within an acceptable range, ensuring weld reliability.

Fatigue characteristics improvement of the TIG-welded 316L specimens with T-joint geometry using laser shock peening

Titanium and its alloys are widely used in aerospace, biomedical, and structural applications due to their exceptional strength-to-weight ratio and corrosion resistance. However, welding of titanium, particularly using tungsten inert gas (TIG) welding, introduces residual stresses and microstructural variations that influence its fracture behaviour. This study focuses on evaluating fracture toughness of TIG-welded titanium tube from single edge notch tension (SENT) testing and numerical simulations. Single edge notch tension specimens provide a realistic assessment of crack propagation under tensile loading, offering insights into fracture resistance of welded joints. Additionally, extended finite element method (XFEM) was employed to simulate crack initiation and propagation, complementing experimental findings. Fracture toughness of weld metal is found to be 65.32 MPa m (experimentally) and 59.84 MPa m (XFEM analysis). Around 16% increase in fracture toughness is observed in weld metal from base metal. The results contribute to fundamental understanding of fracture mechanics in welded titanium structures and aid in development of optimized welding procedures to enhance performance in critical engineering application.

Abstract Repairing is considered as a practical and economic scheme to effectively extend the lifetime of components made of Inconel 738 (IN 738), which has been widely used in hot sections of jet engines and industrial gas turbines. In this study, the feasibility of repairing IN 738 substrates was investigated using InterPulse tungsten inert gas (TIG) welding with Inconel 625 (IN 625) and Pmet 838 as feeding materials. It was shown that single-pass deposition achieved a sound metallurgical bonding under three different TIG parameters, with no cracks observed in any of the specimens. Under multi-pass repairing, γ′ dissolution was observed in the heat-affected zone (HAZ), and cracks were observed neither in the multi-pass deposited layers nor the HAZ. The Pmet 838 deposited layer was quasi-homogeneous and entirely devoid of γ′; the IN 625 multi-pass deposited layer, however, exhibits pronounced mesoscopic segregation with significantly lower hardness than the IN 738 substrate. The Pmet 838 deposited layer demonstrates considerably higher hardness than that of the IN 738 substrate, primarily attributed to the existence of dense cellular structures. The hardness in the HAZ of both specimens decreases with increasing the distance from the fusion line to the base metal, which may be associated with gradient variations of the cellular structures. After annealing at 920 °C for 150 h, the average Vickers hardness of the Pmet 838 multi-pass deposited layer decreased from 486.1±13.9 HV 0.2 to 378.2±6.2 HV 0.2 , even though copious precipitation of γ′ was observed in it, which is attributable to the disappearance of the cellular structure; in contrast, the IN 625 deposited layer exhibited heterogeneously distributed γ′ precipitates and needle-like δ phase, corresponding to the aforementioned mesoscopic segregation, resulting in an increase in the average Vickers hardness from 252.1±6.6 HV 0.2 to 317.6±17.4 HV 0.2 .

This study tackles the challenges of inconsistent weld quality and limited real-time monitoring in Tungsten Inert Gas (TIG) welding by developing a digital twin for the process. The primary objective is to enhance process efficiency and quality control by creating a high-fidelity virtual model of TIG welding that enables real-time monitoring and control. To achieve this, the study employs Desirability Function Analysis (DFA) to optimize multiple quality characteristics. The methodology integrates advanced sensors and IoT technologies to gather real-time data on critical welding parameters such as current, voltage, travel speed, and gas flow rate. This data is used to create a simulation model that accurately replicates the physical welding process. The experiments are conducted using digital twin on SS304 thin which is widely used in industrial applications. By applying DFA, the study converts multiple quality characteristics into a single composite desirability score, offering a quantitative assessment of process efficiency and output quality. The experimental results demonstrate the digital twin’s ability to accurately predict and control welding outcomes, significantly improving productivity and quality control. This research highlights the transformative potential of digital twin technology in TIG welding, paving the way for smarter, data-driven decision-making in industrial settings.

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.

Abstract This study investigates a novel tungsten inert gas double-electrode (TIG-DE) welding process with integrated coaxial hot-wire feeding for additive manufacturing applications. By combining arcs generated by multiple cathodes with independent wire preheating, the process aims to overcome the limitations of conventional single-electrode TIG systems, particularly with respect to directional dependence and limited deposition rates. A custom-built demonstrator system was used to systematically analyze the arc behavior, weld bead formation, and process stability under various parameter conditions. Arc pressure measurements confirmed the isotropy of the arc shape under optimized electrode configurations. Blind seam trials in orthogonal directions revealed minimal geometric deviations, verifying the directional independence of the process, which is a major advantage over conventional processes. The integration of an ohmic preheating unit enabled stable wire feeding at high speeds and significantly reduced eccentricities of the weld bead. Compared to the cold-wire TIG process, the hot-wire process exhibited a broader process window and higher productivity, with deposition rates exceeding 1 kg h $$^{-1}$$ - 1 and seam height deviations consistently below 1 mm. These findings highlight the capability of the developed process to enable geometrically consistent and directionally independent layer buildup, providing a robust foundation for further development of wire-based additive manufacturing using TIG technology.

In this study, 5% hydroxyapatite (HA)-95% titanium (Ti) composite coatings were fabricated on Ti-6Al-4V (Ti64) substrates using the Tungsten Inert Gas (TIG) welding method at welding currents of 90A, 100A, and 110A. The effects of welding current on the microstructural, mechanical, electrochemical, and biological properties were systematically investigated. According to ASTM E190 bending tests, interfacial adhesion strength increased with increasing welding current. Electrochemical in vitro corrosion tests showed limited dependence on current, though the 100A coating exhibited the lowest corrosion current density (6.93×10-2 μA·cm-2) and highest polarization resistance (12800 Ω), indicating the most passive surface behavior. In vitro simulated body fluid (SBF) tests demonstrated that the 90A coating promoted optimal apatite-like layer formation. Overall, the welding current strongly affected the coatings’ microstructure, chemical stability, mechanical strength, corrosion resistance, and bioactivity. Among all, 90A was optimal for structural stability, 100A for electrochemical performance, and 110A for mechanical adhesion. Thus, the TIG welding process is a promising approach for producing biofunctional coatings on metallic substrates.

Effect of process parameters on mechanical properties and microstructure of TIG welded joints between AA 5052-T0 and AA 7075-T0

The current strategy for joining ITER divertor cooling pipes is to conduct semi-automated autogenous Tungsten Inert Gas (TIG) welding on thin-walled pipes using an inserted flat washer filler ring. In this approach, the positioning of the filler ring and the alignment of the pipe stubs so far can only be achieved manually. However, it has limitations for future maintenance because human interventions may be limited or completely prohibited in contaminated environments, requiring the need for remotely operated tools and systems. In addition, maintenance of cooling pipes will involve cutting and re-welding of the parts. However, components have limited lifespan for reuse. Additive manufacturing (AM) is an advanced technique that provides one potential way to overcome the limitations. This work investigates the use of the AM method to deposit material as an alternative approach to using filler rings, which a flange feature was firstly built on the pipe end using laser blown powder direct energy deposition (DED). Thereafter, semi-automated autogenous TIG welding was conducted on the AM modified pipe stubs. The results suggest that using the AM produced parts has achieved compliant pipe joins, implying possible improvements to maintenance strategies for future fusion power plants and experimental devices.

Synergistic effects of PWHT and FSP on the microstructure, texture and mechanical properties of tungsten inert gas–welded dissimilar AA7075-T6/AA6061-T6 joints