Shielding Gas Research Articles

Improving the product of strength and ductility and corrosion resistance by adding He shielding gas in the CMT additive manufacturing process of Ti6Al4V

The cold metal transfer additive manufacturing (CMTAM) of titanium alloys presents a promising solution for the efficient fabrication of large titanium alloy armor components. In this study, different proportions of He gas were added to the welding shielding gas used in the CMTAM of Ti6Al4V, aiming to improve forming quality, the product of strength and ductility and corrosion resistance. Simultaneously, the influence of different He contents on the microstructure, mechanical properties, and corrosion behavior of CMTAM of Ti6Al4V was explored. The research revealed that during the process of CMTAM of Ti6Al4V, as the proportion of He as the shielding gas increased, the arc voltage increases, and the arc becomes more stable. Meanwhile, the wettability of the weld pool improves, resulting in a more spread out weld pool. The fabrication precision of the built material also improved. Microstructural observations indicate that the prior-β grain size gradually increased with the increase in He proportion, the heat input for additive manufacturing also increased，and the martensitic α’ transformed into a basketweave α+β structure. The length and width of the α phase increased, the texture intensity decreased, and the Schmid factor increased. Tensile tests were conducted on samples with different He proportions showed that as the He proportion increased, within the component resulted in a noteworthy enhancement in the product of strength and ductility increase exceeding 50 %. This suggests that He as the shielding gas addition can effectively optimize the strength-plasticity balance in additive manufactured titanium alloys without the need for post-processing heat treatment. Electrochemical tests were conducted in a 3.5 wt% NaCl solution revealed that the addition of He gas significantly improved the corrosion resistance of Ti6Al4V. Specifically, the corrosion resistance was optimal when the shielding gas composition was 50 %He+50 %Ar, far surpassing that of cast Ti6Al4V.

Investigating the Influence Mechanism of Different Shielding Gas Types on Arc Characteristics and Weld Quality in TA2 Laser–Arc Hybrid Welding

The effective welding of a 6 mm thick TA2 pure titanium medium-thickness plate was achieved by laser–arc hybrid welding (LAHW) with helium–argon mixed shielding gas. Conducted research on the influence of helium–argon mixed shielding gas on plasma and arc characteristics during welding, and its further impact on the microstructure, internal porosity defects, tensile properties, and corrosion resistance of welded joints was explored. The study demonstrated that under the shielding gas with 75% helium, the arc width narrowed significantly from 6.96 mm to 2.61 mm, achieving a 63% reduction, which enhanced the concentration of arc heat flux density. Achieved a well-formed weld with no surface spatter and significantly reduced the internal porosity rate from 3.02% to 0.47%, which is an 84% decrease. Tensile fractures are located in the base material, all exhibiting plastic failure. The corrosion resistance of the welded joint initially increased and then decreased with the increase of helium content in the shielding gas, peaking at 75% helium content.

Evolution of Precipitates in a Mechanical Vibration-Assisted Metal Inert Gas Welded Joint of 6082-T6 Aluminum Alloy Made with an ER5356 Filler Wire

Evolution of Precipitates in a Mechanical Vibration-Assisted Metal Inert Gas Welded Joint of 6082-T6 Aluminum Alloy Made with an ER5356 Filler Wire

Effect of TIG remelting on the microstructure, mechanical properties, and corrosion behavior of 5052 aluminum alloy joints in MIG welding

In this work, the effect of tungsten inert gas (TIG) remelting on the microstructure, mechanical properties, and corrosion resistance of 5052 aluminum alloy joints produced by metal inert gas (MIG) welding is investigated. The results indicate that after TIG remelting of MIG welds, the proportion of dendrites increases in the remelted weld zone (WZ), porosity decreases by 76.9%, and the Fe elements in the second phase become coarser and more segregated. In contrast, the Mg elements form a solid solution with a decreased degree of segregation. In addition, the average grain size of the remelted structure decreases, while the proportion of sub-grain boundaries (SGBs) and the kernel average misorientation (KAM) values increase. Moreover, the heat-affected zone (HAZ) widens, and the grains become coarser. An increase of 4.5% in tensile strength and 20.0% in elongation was observed in the TIG-remelted joints after TIG remelting. Electrochemical and immersion tests on the TIG-remelted microstructure showed reduced corrosion resistance. Electrochemical tests mainly exhibited galvanic corrosion, resulting in the formation of pits. The types of corrosions observed in the immersion test differ from those in the electrochemical test, primarily exhibiting exfoliation corrosion and pitting corrosion. A higher geometric dislocation density (ρGND) in the structure increases the susceptibility to corrosion.

Bubble-Guidance Breaking Gas Shield for Highly Efficient Overall Water Splitting.

Overall water splitting is a promising technology for sustainable hydrogen production, but the primary challenge is removing bubbles from the electrode surface quickly to increase hydrogen production. Inspired by the directional fluid transport properties of natural biological surfaces like Nepenthes peristome and Morpho butterfly's wings, here a strategy is demonstrated to achieve highly efficient overall water splitting by a bubble-guidance electrode, that is, an anisotropic groove-micro/nanostructured porous electrode (GMPE). Gradient groove micro/nanostructures on the GMPE serve as high-speed bubble transmission channels and exhibit superior bubble-guidance capabilities. The synergistic effect of the asymmetric Laplace pressure generated between microscale porous structure and groove patterns and the buoyancy along the groove patterns pushes the produced bubbles directionally to spread, transport, and detach from the electrode surface in time. Moreover, the low adhesive nanosheet arrays are beneficial to reduce bubble size and increase bubble release frequency, which cooperatively improve mass transfer with the microscale structure. Notably, GMPE outperforms planar-micro/nanostructured porous electrode (PMPE) in hydrogen/oxygen evolution reactions, with GMPE||GMPE showing better water splitting performance than commercially available RuO2||20 wt.% Pt/C. This work improves electrodes for better mass transfer and kinetics in electrochemical reactions at solid-liquid-gas interfaces, offering insight for designing and preparing gas-involved photoelectrochemical electrodes.

A Magnetic Flux Leakage Detector for Ferromagnetic Pipeline Welds with a Magnetization Direction Perpendicular to the Direction of Travel.

For the sake of realizing the safety detection of natural gas and petroleum pipeline welds, this paper designs a ferromagnetic pipeline weld magnetic flux leakage detector based on the calculation of the magnetic circuit of the detection probe, with the magnetization direction perpendicular to the traveling direction. The traditional pipeline magnetic flux leakage detection device uses a detection system mode in which the magnetization direction is parallel to the direction of travel. However, due to the structural characteristics of the weld, the traditional detection system mode is not applicable. Since the weld magnetic flux leakage detector needs to travel along the direction of the weld, the detector designed in this paper rotates the magnetizer 90 degrees along the direction of the weld seam so that the magnetization direction is perpendicular to the direction of travel, breaking through the technical barrier that make traditional magnetic flux leakage detection devices unsuitable for weld detection. The detection device includes a magnetizing structure, a data sampling device, and a driving and traveling device. The magnetic flux leakage signal collected by the detector is converted into a digital image in the form of a grayscale matrix. Using mathematical morphology and chain code algorithms in image processing technology, a pipeline weld defect inversion software system is developed, and a preliminary quantitative analysis of pipeline weld defects is achieved. The application of this technology enables the inspection and protection of oil and gas pipeline welds throughout their life cycle, broadens the scope of existing inspection objects, and is of great safety significance for ensuring national public security.

Microstructural, mechanical and nondestructive characterization of X60 grade steel pipes welded by different processes

Abstract In this paper, the welding quality of API 5L X60 steel pipes was investigated after the application of three different welding scenarios by applying submerged arc welding (SMAW), tungsten inert gas (TIG) and hybrid (TIG + SMAW) welding methods with an average heat input of ca. 1 kJ mm−1 for all passes. For this purpose, the ultrasonic and radiographic tests were done to detect possible discontinuities such as crack and porosity in the welding zones. In addition, the macro and microstructures of weld zones were made to examine different zones in terms of weld quality and phases. Moreover, the hardness, impact toughness and tensile tests were carried out to determine the mechanical properties of the weldments. The tensile strength of the pipe weldments was recorded to be ∼603, 610 and 625 MPa after the welding of pipes by SMAW, TIG + SMAW and TIG welding, respectively. In addition, the impact toughness of the welds was obtained to be 48, 76 and 66 J, for these welding methods, successively. According to the experimental findings, all three welding plans were successfully applied to the steel pipes and found to be suitable regarding the relevant international standards.

Role of Activating Flux in Weld Bead Symmetricity during Dissimilar Metal Joining

Ferritic/martensitic steels and austenitic stainless steels are high‐strength steels, and highly recommended in high‐temperature and high‐pressure application. In general, multimetallics with different Inconel alloys are used for joining. This is quite a complex and time‐consuming procedure. The current work demonstrates the efforts made to weld 8 mm‐thick P91 steel and 316L SS plates in a single pass using activating flux tungsten inert gas (A‐TIG) welding process without any interlayers. The main challenge is to get the symmetric weld bead profile. Flux coating is optimized in terms of flux composition, coating density, and coating pattern to get the full penetration with symmetric appearance. The current work discusses the possible cause and their solution of asymmetricity during dissimilar welding. Differential flux coating density is found to be very effective in controlling the arc column shape, fluid flow, and consequently the bead geometry. High coating density is used in the P91 side compared to 316L side. Symmetric weld profile with full penetration is achieved by applying multicomponent flux (33–38% TiO2, 38–43% SiO2, 13–17% NiO, and 8–10% CuO) during A‐TIG welding.

An experimental investigation of nano clay and functionalized nano graphene oxide effects on ablation of carbon/phenolic nanocomposites

This work aims to study thermal stability and ablative behaviors of Carbon/Phenolic composites containing nano clay, nano graphene oxide and hybrid additives. To this end a detailed explained and illustrated process is involved to synthesize factionalized graphene oxide based on Hummers method. The XRD test result shows a major shift in basal plane reflection to below 2θ = 20° in the provided spectrum, which indicates achievement in the functionalization process. Prepared nanoparticles suspensions are then mixed by resol resin with desire wt% to outcome nanocomposites. An in-depth analysis of SEM images with focus on the dispersion, morphology, and interaction of the nanofillers with the resin matrix reveals that nanoparticles are dispersed properly with no agglomeration. 200 gr/m2 carbon woven fabric is then impregnated with prepared nanocomposites employing an own made prepreg machine to use to construct standard flexural as well as oxy acetylene test specimens. Using bending test, thermogravimetric analysis and oxyacetylene torch test, effects of different percentages of considered nanoparticles on the mechanical properties, thermal stability and ablative of carbon/phenolic composites are assessed and the results are reported. According to the results, adding only 0.1 wt% of nano graphene oxide increases char yield around 5% and remain back surface temperature under 100°C during flame test. Moreover samples with 0.2 wt% of nano clay and hybrid (0.05 wt% nano graphene oxide and 0.1 wt% nano clay) additives provides best reaming amount of solid.

Deep Learning-Based Defects Detection in Keyhole TIG Welding with Enhanced Vision.

Keyhole tungsten inert gas (keyhole TIG) welding is renowned for its advanced efficiency, necessitating a real-time defect detection method that integrates deep learning and enhanced vision techniques. This study employs a multi-layer deep neural network trained on an extensive welding image dataset. Neural networks can capture complex nonlinear relationships through multi-layer transformations without manual feature selection. Conversely, the nonlinear modeling ability of support vector machines (SVM) is limited by manually selected kernel functions and parameters, resulting in poor performance for recognizing burn-through and good welds images. SVMs handle only lower-level features such as porosity and excel only in detecting simple edges and shapes. However, neural networks excel in processing deep feature maps of "molten pools" and can encode deep defects that are often confused in keyhole TIG. Applying a four-class classification task to weld pool images, the neural network adeptly distinguishes various weld states, including good welds, burn-through, partial penetration, and undercut. Experimental results demonstrate high accuracy and real-time performance. A comprehensive dataset, prepared through meticulous preprocessing and augmentation, ensures reliable results. This method provides an effective solution for quality control and defect prevention in keyhole TIG welding process.

Flux-cored arc welding of 316L austenitic stainless steel: the effect of different shielding gas mixtures on microstructural features and weld performance

ABSTRACT Double-pass flux cored arc welding (FCAW) of 316 L austenitic stainless steel was performed using different shielding gas mixtures. Microstructural features and weld performance were evaluated. Based on the Creq/Nieq ratio of fusion zone and cooling rate, different morphologies of ferrite (skeletal, lathy, and dendritic) and austenite with various volume fractions were produced. An increase in Creq/Nieq ratio can increase the strength level because the presence of ferrite in the weld metal acts as a second-phase strengthening agent. On the other hand, ferrite is a suitable place for sigma phase precipitation. Highest joint efficiency resulted in the specimen welded via GTAW. The ductility of welds was ranked as CO2 +Ar shielded FCAW > GTAW > CO2 shielded FCAW > self-shielded FCAW. At room temperature, variation of delta-ferrite content (Creq/Nieq ratio) does not affect toughness. However, an increased amount of CO2 in shielding gas will result in decreased toughness values because of the enhanced formation of oxide inclusions. Increasing CO2 content of shielding gas from 0% to 18% and finally to 100% will result in decreasing toughness values from the highest value of 76J to 40 J and finally the lowest value of 38J.

Monitoring Welding Torch Position and Posture Using Reversed Electrode Images – Part II, Experimental and Analysis for the REI-TPA Model

This paper is a sequel to the previous paper. In the previous research (Ref. 1), a REI-TPA model was established to quantitively relate reversed electrode images (REIs) to welding torch position and attitude (TPA). In this research, the REI-TPA model was validated with bead-on-plate welding experiments on S304 stainless steel plates. The contours of the REI and electrode as well as the weld pool geometry were extracted from the image with a developed, robust algorithm, and the arc length was calculated with welding voltage. The offset distance and deflection angle of the welding torch relative to the correct position and attitude were calculated by inputting the extracted parameters into the REI-TPA model. The computational result was compared to the experimental data. The result showed that the model is correct and the monitoring of the welding torch with the REI-TPA model is available. The REITPA model can be applied to real-time control of TPA, which is a supplement to the application of the weld passive visual image and an extension of multiinformation acquisition and processing methods in the welding process.

Influence of filler metal and arc pulsation on P91 steel weldments developed by activated TIG welding and its effect on stress corrosion cracking

This study examines the influence of arc pulsation and ErNiCrMo-3 filler metal on stress corrosion cracking (SCC) in P91 steel weld joints using activated tungsten inert gas (A-TIG) welding. The constant current joint without filler showed the lowest resistance to SCC, while the pulsed current joint with filler exhibited the highest SCC resistance. Arc pulsation reduced chromium carbide precipitates, enhancing microstructural refinement and crack growth thereby increasing tensile strength and SCC resistance. Filler introduced minor austenitic phases inside martensitic microstructure with reduced hydrogen content contributed to increased SCC resistance. The joint fractography among all welds revealed a complete transgranular fracture.

Fabrication of boron carbide ceramics reinforced with silicon carbide fibers

In the present study, the boron carbide ceramics reinforced with silicon carbide fibers (B4C-SiCf) were fabricated by incorporating various contents of SiCf ranging from 2.5 to 10 wt%. The B4C-SiCf powder mixtures were sintered using the Field Assisted Sintering Technique (FAST), also known as Spark Plasma Sintering (SPS), at temperatures of 1800 °C and 2000 °C for 5 min by applying a pressure of 70 MPa in argon atmosphere, while heating and cooling rates were maintained at 100 °C/min and 50 °C/min, respectively. The influence of the initial powder ratio on the sintering behavior, relative density, microstructural development, and mechanical properties of the obtained B4C-SiCf composites was investigated. The results indicated that the sintered ceramic materials contained only the initial compounds, i.e. B4C and SiC phases. Scanning Electron Microscopy (SEM) showed that the sintered composites consisted of densely compacted B4C grains. The highest relative density (>99 %) was achieved for the sample with 95 wt%B4C and 5 wt%SiCf, sintered at 2000 °C. Depending on the constituent content and the densification temperature the obtained composites demonstrated hardness values ranging from 29 to 43 GPa. The maximal hardness was attained in the composite with 95 wt%B4C sintered at 2000 °C. To assess the performance of the composites under extreme conditions, the ablation resistance was evaluated using a flowing oxyacetylene torch test. The material containing 5 wt%SiCf exhibited superior ablation resistance when compared to the other compositions. The attained results of this study showed that the SPS technique is a highly effective method for the densification of additive-free B4C-SiCf ceramic composites, showcasing promising properties for applications in extreme environments.

The electrochemical corrosion performance of aluminum alloys grade 6082-T6 weld repair

This research investigated the corrosion behavior of standard current metal inert gas weld repair for 6082-T6 aluminum alloy using ER5356 filler metal. The new and repaired (NW and RW) welds were studied. The welds comprised the weld metal (WM), the heat affected zone (HAZ) (solid solution and softened zones), and the base metal (BM). The study focused on investigating electrochemical corrosion using polarization and electrochemical impedance spectroscopy (EIS) methods in 3.5% NaCl solutions, especially in HAZ, including metallurgical and mechanical examinations. The BM containing an α-Al matrix with Al(Fe,Mn)Si and Mg2Si phases exhibited the maximum hardness (70–104 HV0.1). The WM hardness decreased (67–76 HV0.1) with the α-Al, β-Mg3Al2, and Mg2Si phases. Despite having comparable phases to BM, HAZs showed lower hardness (Solid HAZ: 70–82 HV0.1) due to more intermetallic phases. The RW’s softened HAZ revealed the minimum hardness (52–63 HV0.1) compared to that of the NW (55–70 HV0.1). Besides, the tensile strength of the RW (179.7 MPa) was also lower than that of the NW (174.4 MPa) because of the reheating effect. The electrochemical corrosion results indicated that the BM exhibited the maximum corrosion resistance (the lowest corrosion current density (icorr), the highest corrosion potential (Ecorr), and the charge transfer resistance (Rct)), followed by the HAZ and the WM, respectively. The softened HAZ demonstrated better corrosion resistance than the solid solution HAZ. Conversely, the over-aging effect reduced the softened zone’s pitting corrosion resistance (Ep) compared to the solid solution zone. The RW exhibited inferior corrosion resistance compared to the NW due to increased intermetallic phases, which was consistent with the mechanical results. However, the RW’s softened HAZ corrosion characteristics were inconsistent with its mechanical properties; its hardness and tensile strength were the lowest, but its corrosion resistance was not. Pitting corrosion was observed on the weld surfaces using the SEM.

Plume active control in high-power fiber laser welding based on high-speed shielding gas microbeam

Plume is an inherent physical phenomenon in fiber laser keyhole welding, negatively affecting welding quality. This paper proposes a new type of high-speed shielding gas microbeam (HSGM) based on the limitation of conventional shielding gas regulating plumes. The gas flow characteristics of the HSGM on the molten pool surface were explored using numerical simulation. Then, the coaxial double-layer shielding nozzle was trial-manufactured to clarify the regulation law for the HSGM on the plume. The gas velocity and pressure produced by the HSGM on the molten pool surface were positively correlated with the shielding gas flow rate, and the gas flow pattern was an acute triangle shape. The suitable HSGM can significantly restrain plume formation, improve the weld surface forming quality, increase the weld penetration depth (about 15.4%), and reduce the mass loss of the weld (about 58.7%). The significant blowing pressure effect of HSGM on plumes and splashes was the key to regulating the welding process. Compared with conventional shielding gas, the use of HSGM was significantly reduced.

Effect of double-pulse frequency and post-weld heat treatment on microstructure and mechanical properties of metal-inert gas welded Al–Mg–Si alloy joints

The Al–Mg–Si alloy welded structure is widely used in aerospace, marine ship, automotive and other industries. However, the mechanical properties of welded joint were seriously weakened due to the microstructure coarsening and heat affected zone (HAZ) softening, making its service life decayed. In this paper, in order to enhance the mechanical properties of Al–Mg–Si alloy welded joint, a coupled method including double pulsed Metal Inert Gas (DP-MIG) welding technology and post-weld heat treatment (PWHT) were applied on the joining process of Al–Mg–Si alloy. With the increase of DP frequency from 2 Hz to 5 Hz, the average grain size of fusion zone decreased from 113.7 μm to 88.4 μm. And the tensile strength of welded joint was at the interval of 180∼190 MPa. After a suitable heat treatment (solution treatment at 530 °C for 2 h and aging treatment at 180 °C for 8 h), the tensile strength of welded joint increased to 318.3–333.8 MPa, which exceeds 90 % of the base metal (BM). Under the comprehensive effect of solid solution strengthening, fine grain strengthening, and precipitation strengthening, the mechanical properties of Al–Mg–Si alloy welded joint were significantly improved. And the research results in this paper can provide a research basis for high quality connection of Al–Mg–Si alloys.

Keyhole critical failure criteria and variation rule under different thicknesses and multiple materials in K-TIG welding

The stability of keyhole was important to determine both the process and welding quality in keyhole tungsten inert gas (K-TIG) welding. In this study, the welding experiments were conducted on three kinds of materials (TC4 alloy, 304 stainless steel, Q235 carbon steel) with four kinds of thicknesses (2 mm, 4 mm, 6 mm and 8 mm). The keyhole critical failure criteria of K-TIG welding for different materials and thicknesses was established based on Gibbsian surface thermodynamics and regression analysis. Critical stability coefficient Kc was calculated by the values of upper width (Wf) of fusion zone and lower width (Wr) of fusion zone. When Kc>G/WfWr, the keyhole collapse failure would occur. Otherwise, a stable penetration could be obtained. On the other hand, the values of Kc increase with the increase of plate thickness, which meant the keyhole stable range would be smaller. The Kc values of TC4 alloy were smallest and the corresponding stable penetration range was largest. While the values and range of Q235 carbon steel were the largest. This was consistent with the rule reflected by the fitting curves of critical heat input. Furthermore, the difference in criteria variation rule of different materials and different thicknesses were discussed.

Intelligent seam tracking in foils joining based on spatial–temporal deep learning from molten pool serial images

Vision-based weld seam tracking has become one of the key technologies to realize intelligent robotic welding, and weld deviation detection is an essential step. However, accurate and robust detection of weld deviations during the microwelding of ultrathin metal foils remains a significant challenge. This challenge can be attributed to the fusion zone at the mesoscopic scale and the complex time-varying interference (pulsed arcs and reflected light from the workpiece surface). In this paper, an intelligent seam tracking approach for foils joining based on spatial–temporal deep learning from molten pool serial images is proposed. More specifically, a microscopic passive vision sensor is designed to capture molten pool and seam trajectory images under pulsed arc lights. A 3D convolutional neural network (3DCNN) and long short-term memory (LSTM)-based welding torch offset prediction network (WTOP-net) is established to implement highly accurate deviation prediction by capturing long-term dependence of spatial–temporal features. Then, expert knowledge is further incorporated into the spatio-temporal features to improve the robustness of the model. In addition, the slime mould algorithm (SMA) is used to prevent local optima and improve accuracy, efficiency of WTOP-net. The experimental results indicate that the maximum error detected by our method fluctuates within ± 0.08 mm and the average error is within ± 0.011 mm when joining two 0.12 mm thickness stainless steel diaphragms. The proposed approach provides a basis for automated robotic seam tracking and intelligent precision manufacturing of ultrathin sheets welded components in aerospace and other fields.

Penetration state recognition for tungsten inert gas welding via an alternating cusp-shaped magnetic field-assisted molten pool-oscillation

To ensure optimal penetration in direct current (DC) argon tungsten arc welding, a method was proposed to recognize the molten pool penetration during molten pool oscillation under alternating cusp-shaped magnetic field (ACSMF). An arc discharge model is established to analyze the oscillation mechanism of the molten pool under ACSMF. The periodic variation of arc shape induces the periodic oscillation to establish a mapping relationship with the fluctuation of arc voltage waveform. At the excitation current of 3 A and frequency of 10 Hz, the arc voltage waveform undergoes abrupt changes at 1.26 V and 1.37 V, corresponding to the critical and the full penetration states, respectively. The errors in identifying moving penetration are 0.8 % and 0.7 %, with a full penetration weld, demonstrating a penetration rate of 100 %, indicating effective penetration recognition. Arc sensing technology for tungsten inert gas (TIG) welding under ACSMF is poised for gradual application in single-side welding and double-side forming of medium and thick plates. It is anticipated to evolve towards real-time identification technology for molten pool penetration monitoring.