Search Results (78)

This study investigates the use of YOLOv8 deep learning models to segment and classify thermal images acquired from the rear of the weld pool during the Gas Tungsten Arc Welding (GTAW) process. Thermal data were acquired using a two-color pyrometer under three welding current levels (160 A, 180 A, and 200 A). Models of sizes from nano to extra-large were trained on 66 annotated frames and evaluated with and without data augmentation. The results demonstrate that the YOLOv8m model achieved the best classification performance, with a precision of 83.25% and an inference time of 21.4 ms per frame by using GPU, offering the optimal balance between accuracy and speed. Segmentation accuracy also remained high across all current levels. The YOLOv8n model was the fastest (15.9 ms/frame) but less accurate (75.33%). Classification was most reliable at 160 A, where the thermal field was more stable. The arc reflection class was consistently identified with near-perfect precision, demonstrating the model’s robustness against non-relevant thermal artifacts. These findings confirm the feasibility of using lightweight, dual-task neural networks for reliable weld pool analysis, even with limited training data. Full article

Aluminum alloy, due to its low melting point and high thermal conductivity, deforms and contracts significantly during welding. To mitigate this and achieve full penetration in a single pass, this study uses GTAW (Gas Tungsten Arc Welding) additive manufacturing and optimizes welding groove parameters via the Box-Behnken Response Surface Methodology. The focus is on improving tensile strength and penetration depth by analyzing the effects of groove angle, root face width, and root gap. The results show that groove angle most significantly affects tensile strength and penetration depth. Hardness profiles exhibit a W-shape, with base material hardness decreasing and weld zone hardness increasing as groove angle rises. Root face width reduces hardness fluctuation in the weld zone, and an appropriate root gap compensates for thermal expansion, enhancing joint performance. The interaction between root face width and root gap most impacts tensile strength, while groove angle and root face width interaction most affects penetration depth. The optimal welding parameters for 7xxx aluminum alloy GTAW are a groove angle of 70.8°, root face width of 1.38 mm, and root gap of 0 mm. This results in a tensile strength of 297.95 MPa and penetration depth of 5 mm, a 90.38% increase in tensile strength compared to the RSM experimental worst group. Microstructural analysis reveals the presence of β-Mg₂Si and η-MgZn₂ strengthening phases, which contribute to the material’s enhanced mechanical properties. Fracture surface examination exhibits characteristic ductile fracture features, including dimples and shear lips, confirming the material’s high ductility. The coexistence of these strengthening phases and ductile fracture behavior indicates excellent overall mechanical performance, balancing strength and plasticity. Full article

Welding of maraging steels leads to a microstructural gradient from base material (BM) to weld metal (WM). During post-weld heat treatment (PWHT) the precipitation and reverted austenite (γ_r) reactions will occur defining the mechanical properties. These reactions are affected by the microstructure and local chemical composition of each zone in the “as welded” (AW) condition. This effect has not been clearly described yet nor the evolution of the microstructure. The objective of this work was to analyse the phase transformations at the different zones of the welded joint during the PWHT to explain the microstructure obtained at each zone. Samples of C250 maraging steel were butt-welded by GTAW-P (Gas Tungsten Arc Welding—Pulsed) process without filler material. The AW condition showed an inhomogeneous microhardness profile, associated with a partial precipitation hardening in the subcritical heat affected zone (SC-HAZ) followed by a softening in the intercritical (IC-HAZ) and recrystallized heat affected zone (R-HAZ). A loop-shaped phase was observed between low temperature IC-HAZ and SC-HAZ, associated with γ_r, as well as microsegregation at the weld metal (WM). The microstructural evolution during PWHT (480 °C) was evaluated on samples treated to different times (1–360 min). Microhardness profile along the welded joint was mostly homogeneous after 5 min of PWHT due to precipitation reaction. The microhardness in the WM was lower than in the rest of the joint due to the depletion of Ni, Ti and Mo in the martensite matrix related with the γ_r formation. The isothermal kinetics of precipitation reaction at 480 °C was studied using Differential Scanning Calorimetry (DSC), obtaining a JMAK expression. The average microhardness for each weld zone was proposed for monitoring the precipitation during PWHT, showing a different behaviour for the WM. γ_r in the WM was also quantified and modelled, while in the IC-HAZ tends to increase with PWHT time, affecting the microhardness. Full article

This study presents a systematic optimization of GTAW welding parameters to achieve a pipe-to-pipe butt weld with a root height consistently below 2 mm when joining stainless-steel 316L material, employing the Taguchi design of experiments. To the authors’ knowledge, no similar studies have been conducted to explore the optimization of welding parameters specifically aimed at minimizing weld root height under 2 mm in stainless-steel EO pipeline welding applications. This gap in the existing literature highlights the innovative aspect of the current study, which seeks to address these challenges and improve welding precision and joint reliability. Root height, also referred to as weld root reinforcement, is defined as the excess weld metal protruding beyond the inner surface root side of a butt-welded joint. The input parameters considered are the welding current, voltage, speed, and root gap configurations of 1, 1.5, and 2 mm. Welding was performed according to the Taguchi L-09 experimental design. Nine weld samples were evaluated using liquid penetrant testing to detect surface-breaking defects, such as porosity, laps, and cracks; X-ray radiography to identify internal defects; and profile radiography to assess erosion, corrosion, and root height. Among the nine welded plate samples, the optimal root height (less than 2 mm) was selected and further validated through the welding of a one-pipe sample. An additional macro examination was conducted to confirm the root height and assess the overall root weld integrity and quality. Full article

A total of 0.3%C-Cr-Mo-V steel, a high-strength alloy steel widely used in rocket motor housings, suspension systems in high-performance vehicles, etc., is noted due to its high strength-to-weight ratio. However, its high carbon equivalent (CE > 1%) makes it challenging to weld, as it is prone to brittle martensitic formation, which increases the risk of cracking and embrittlement. The present paper focuses on enhancing the microstructure and mechanical properties of 0.3% C-Cr-Mo-V steel by gas tungsten arc welded (GTAW) joints, utilizing post-weld heat treatment and cooling strategies (PWHTCS). A systematic experimental approach was employed to ensure a defect-free weld through dye penetrant testing (DPT) and X-ray radiography techniques. Subsequently, test specimens were extracted from the welded sections and subjected to PWHT protocols, including hardening, tempering, and rapid quenching using air and oil cooling (AC and OC, respectively) mediums. Results show that OC has enhanced tensile strength and hardness while simultaneously maintaining and improving ductility, ensuring a well-balanced combination of strength and toughness. Fractography analysis revealed ductile fracture in AC samples, whereas OC weldments exhibited a mixed ductile–brittle fracture mode. Thus, the findings demonstrate the critical role of PWHTCS, with OC, as an effective method for achieving enhanced mechanical performance and microstructural stability in high-integrity applications. Full article

This study investigates the feasibility of using friction stir extrusion (FSE) recycled aluminum wires as filler metals for gas tungsten arc welding (GTAW) and additive manufacturing applications. A NC-controlled GTAW feeding system was developed to enable the deposition of these recycled wires. The effect of cleaning the machining chips before the FSE process on the quality of the manufactured wires and the resulting welded beads was evaluated. Wires produced from uncleaned chips and cleaned chips were compared in terms of their external appearance, ductility, and the presence of porosity after the weld deposition. The results showed that cleaning the chips before the FSE process is crucial for obtaining more uniform wires with better ductility. Automatic GTAW deposition using cleaned wires resulted in significantly improved bead geometry, reduced external porosity, and overall better quality compared to uncleaned wires. However, both wire types exhibited internal porosity, with uncleaned wires showing the worst performance. The findings demonstrate the potential of using FSE recycled aluminum wires for welding and additive manufacturing while highlighting the importance of chip cleaning and the need for further optimization to minimize porosity in the deposited material. Full article

The high-temperature low-cycle fatigue (LCF) behaviour of Incoloy 800H and its weldments with Haynes 230 and Inconel 82 filler metals, which were fabricated with the gas tungsten arc welding (GTAW) technique, was investigated and compared at 760 °C. The results revealed that the Incoloy 800H weldments showed lower fatigue lifetimes compared to the base metal. However, the weldments with the Haynes 230 filler metal demonstrated an improved fatigue life at the low strain amplitude compared to both Incoloy 800H and the weldment with the Inconel 82 filler metal. The Incoloy 800H base metal showed pronounced initial cyclic hardening with hardening factors increasing with strain amplitudes. In contrast, the weldments with Haynes 230 and Inconel 82 filler metals displayed short initial cyclic hardening and saturation stages, followed by long continuous cyclic softening. The fractography and microstructure after LCF the tests were characterized with scanning electron microscopy (SEM) and transmission electron microscopy (TEM). Transgranular fracture with multiple crack initiations was the predominant failure mode on the fracture surfaces of both Incoloy 800 base metal and the weldments. TEM examination revealed that planar dislocation slips at the low strain amplitude evolved to wavy slips, eventually forming a cell structure at high strain amplitudes in the Incoloy 800H material as the strain amplitudes increased. However, the weld metal exhibited a planar slip mode deformation mechanism regardless of cyclic strain amplitude in the weldment specimens. The differing cyclic hardening and softening behaviours between Incoloy 800H and its weldments are attributed to the higher strength of the weldment specimens compared to the base metal. In the Incoloy 800H base material specimens, the reverse strains during LCF created wavy dislocation structures, which could not fully recover due to the non-reversible nature of the microstructure. As a result, cells or subgrains formed within the microstructure once created. In contrast, the higher strength of the weld metal in the weldment specimens significantly suppressed the formation of wavy dislocation structures, and deformation primarily manifested as planar arrays of dislocations. Full article

This paper deals with the influence of micro-pulsed direct current on microstructure and mechanical properties of gas tungsten arc welding (GTAW) weldments of Ti-6Al-4V (Ti-64). Bead-on-plate GTA welds were made on the samples in the un-pulsed and micro-pulsed (125 Hz and 250 Hz) conditions. Post-weld heat treatment (PWHT) was performed on a few coupons at 700 °C for 3 h in an inert atmosphere, followed by furnace cooling. In the microstructure, the fusion zone (FZ), base metal (BM), and heat-affected zone (HAZ) can be easily distinguished. The top surface of the FZ has large columnar grains because of lower heat loss to the surrounding atmosphere, and the bottom region of the FZ has comparatively smaller equiaxed grains. The micro-pulsed samples’ FZ grain size was lower than that of those made without pulsing. This shows that high-frequency current has substantially refined prior β grains. The microstructure of the FZ is characterized by an acicular morphology composed of α, martensitic α′, and retained β phases. The FZ’s hardness was higher than the BM due to the presence of martensitic α′. Additionally, the hardness in the HAZ was elevated due to the formation of finer martensitic α′. Micro-pulsed DC welding led to improved mechanical properties, including higher hardness, ultimate tensile strength (UTS), and ductility compared to un-pulsed welding. This enhancement is attributed to the grain refinement achieved with micro-pulsed DC. After PWHT, the prior β grain size remained relatively unchanged compared to the as-welded condition. However, the hardness in the FZ decreased due to the decomposition of α′ into α and β phases. The ductility of all samples improved as a result of the widening of the diffusional α phase. Full article

The cladding process reduces manufacturing costs by depositing super austenitic stainless steel onto low-carbon steel. Arc welding techniques, especially gas tungsten arc welding (GTAW), are commonly used for this purpose. This study evaluates the influence of heat input on cladding performance. Macroscopic analysis showed good fusion of the weld beads to the base metal with no defects. Higher heat input resulted in a lower dilution rate due to increased reinforcement. A microstructural analysis of the heat-affected zones revealed similar characteristics, with martensite formation attributed to cooling conditions. Increased microhardness was observed at the interface between the cladding and base metal, corroborating the microstructural findings. Additionally, a significant enhancement in corrosion resistance was noted in the deposited layers. This research contributes to optimizing cladding processes, ensuring better material performance in industrial applications. Full article

This study aims to analyze the performance of dissimilar titanium alloy Ti-5Al-2.5 Sn and stainless-steel SS 304 joints using three non-destructive testing (NDT) methods such as radiographic testing, visual and microstructural evaluation. Gas tungsten arc welding (GTAW) was performed to join the base metals by incorporating the multi-interlayer of Cu-Nb. The performance of dissimilar joints was evaluated in terms of quality and strength at a welding current of 40 and 60 amperes, and a fixed gas flow rate and welding speed of 20 lit/min and 150 mm/min, respectively. Radiography and visual results indicated severe cracks, voids and incomplete fusion in the specimen welded at a higher current and no such flaws in the specimen welded at a low current. Microstructural results revealed that a dendritic structure was achieved in the fusion zone at a low current that enhanced the ultimate tensile strength (UTS) to 248 MPa while brittle cracks were observed at the Ti-Cu side at higher currents, which reduced the strength to 160 MPa. Full article

The autogenous manual gas tungsten arc welding (GTAW) process was used for cladding austenitic stainless steel 316L using a single pass with various contact tip-to-work distances (CTWDs). Immersion and electrochemical tests were used to evaluate the corrosion resistance of the welded specimens, and a microstructural analysis was conducted to investigate the chemical composition of the molten pool and the heat-affected zone of welding. The key findings of this study indicate that the corrosion resistance improved under a CTWD of 5 mm due to the optimal distribution of ferrite and a refined microstructure. Additionally, the highest hardness was observed in specimens with a CTWD of 3 mm, attributed to the increased ferrite content in the weld metal. As the CTWD increased, the ferrite fraction decreased, and the hardness also diminished. However, in the CTWD 7 mm case, the higher heat input influenced the microstructure and molten pool shape significantly through the Marangoni effect, resulting in a lower corrosion resistance. These results suggest that optimizing the CTWD can enhance the corrosion resistance of welded 316L stainless steel. Full article

The lap welding process for 304L stainless steel welded using the pulsed gas tungsten arc welding (P-GTAW) procedure was studied, and the effects of the pulse welding parameters (the peak current, background current, duty cycle, pulse frequency, and welding speed) on the macroscopic morphology, microstructure, and mechanical properties of the resultant lap joints were investigated. Tensile tests, hardness measurements, and SEM/EDS/XRD analyses were conducted to reveal the characterization of the joint. The relationships between the welding parameters; certain joint characteristic dimensions (the weld width, D; the weld width on the lower plate, L_a; the weld depth on the lower plate, P; and the minimum fusion radius, R); and the maximum tensile bearing capacity were studied. The weld zone was primarily composed of vermicular ferrite, skeletal ferrite, and austenite, and no obvious welding defects, precipitation, or phase transformations were evident in the weld. Microhardness tests demonstrated that the weld microhardness was highest in the base metal zone and lowest in the weld zone. As the heat input increased, the average microhardness decreased. The hardness difference reached 17.6 Hv10 due to the uneven grain size and the transformation of the structure to ferrite in the weld. The fracture location in welded joints varied as the heat input changed. In some parameter combinations, the weld tensile strength was significantly higher than that of the base material, with fractures occurring in the weld. Scanning electron microscopy results exhibited an obvious dimple morphology, which is a typical form of ductile fracture. XRD revealed no significant phase changes in the weld zone, with a higher intensity of the austenite diffraction peaks compared to the ferrite diffraction peaks. Full article

Austenitic stainless steels used in structural applications suffer from stress corrosion cracking due to residual stresses during welding. Much research is being conducted to prevent the stress corrosion cracking of austenitic steels by inducing compressive residual stresses. One method is ultrasonic shot peening (USP), which is used to apply compressive stress by modifying the mechanical properties of the material’s surface. In this study, 304L stainless steel was butt-welded by gas tungsten arc welding (GTAW) and subsequently subjected to compressive residual stress to a depth of 1 mm from the surface by a USP treatment. The influence of USP on microstructural changes in the base metal, the HAZ and weldment, and the corrosion properties was analyzed. A microstructural analysis was conducted using SEM-EDS, XRD, and EBSD methods alongside residual stress measurements. The surface and cross-sectional corrosion behavior was evaluated and analyzed using a potentiodynamic polarization test, electrochemical impedance spectroscopy (EIS) measurements, a double-loop electrochemical potentiokinetic reactivation (DL-EPR) test, and an ASTM A262 Pr. C test. The surface was deformed and roughened by the USP. The deformed areas formed crevices, and the inside of the crevices contained some cracks. The crevices and internal cracks caused pitting, which reduced the resistance of the passivation film. The cross-section was subjected to compressive residual stress to a depth of 1 mm from the surface, and the outermost area of the cross-section had fine grain refinement, forming a solid passivation film that improved the corrosion resistance. Full article

This study investigated how welding affects the thermal deformation of square cells produced for casks, which are dry storage containers for spent nuclear fuel. We aimed to minimize structural deformation by utilizing STS316L as the material for the square cells. We explored a method of subdividing the square cells and joining them through butt welding. Keeping the upper plate thickness constant, GTA butt welding was conducted while varying the column’s wall thickness, followed by measurement with a laser vision sensor. The heat conduction and thermal strain were then calculated using a finite element analysis (FEM). Both experimental and analytical results confirmed that there was significant thermal deformation in the cases of thick-walled columns due to variations in heat conduction distribution, with the resulting deformation patterns depending on thickness. Full article

Mg alloy AZ31B was directly bonded to SK7 with a low alloy content, DP980 with a high Mn content, 316L with a high Cr and high Ni content by laser-gas tungsten arc welding (GTAW) and hybrid direct lap welding. The results showed that the tensile loads of AZ31B/SK7 and AZ31B/DP980 joints were 283 N/mm and 285 N/mm respectively, while the tensile load of AZ31B/316L joint was only 115 N/mm. The fracture and interface microstructures were observed using scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and identified through X-ray diffractometry (XRD). For AZ31B/SK7 and AZ31B/DP980, the interface of the front reaction area and the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase. However, for AZ31B/316L, the interface of the keyhole reaction area was mainly composed of an Fe-Al phase and an Al-Mn phase, but a multi-layer composite structure consisting of the Mg₁₇Al₁₂ compound layer and eutectic layer was formed in the front reaction area, which led to a deterioration in the joint property. The influencing mechanism of Mn, Cr and Ni elements in steel on the properties and interface structure of the laser-GTAW lap joint between the Mg alloy and the steel was systematically analyzed. Full article