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The purpose of this study was to optimize the conditions of the gas–metal arc welding using CO2 shield gas (CO2 arc welding) with hot-wire feeding technology. A high-speed camera was used to investigate welding phenomena of a butt joint of 36-mm-thick steel plates. The optimum parameters were determined under combinations of the welding current (300 or 400 A) and hot-wire feeding speed (0 to 12.5 m/min) to avoid molten metal precedence. A sound joint was achieved with only four weld passes using optimum conditions. Adequate joint properties, including tensile strength and toughness, were obtained. The optimum conditions provided a welding process with both high efficiency and low heat input.

This fundamental research aims to analyse the effect of heat transfer coefficients, plasticity model of evolved material properties and simplified meshing strategy on substrate deformation induced by wire arc additive manufacturing (WAAM) process with dissimilar materials based on experiment and numerical simulation. Throughout the experiment, stainless steel wire SS316L was used as feedstock to build a five-layer and three-string component on an 8-mm-thick low carbon steel S235 as substrate plate by means of a robotic GMAW system with pure argon as shielding gas and diagonal clamping. In order to define heat transfer coefficients by adjusting simulation to experimental results, the transient thermal distribution was to be measured at specific points located in the component layer using Type K thermocouple inserted during the process and on the substrate implanted beforehand. For modelling and simulation, a non-linear thermo-mechanical method was applied in which the component was modelled using rectangular element shape with optimized hexagonal mesh size obtained through sensitivity analysis in accordance to actual specimen geometry and clamping condition. Non-linear isotropic hardening rule with von Mises yield criterion and temperature-dependent material properties was implemented into the simulation which were generated by means of advanced material modelling software based on elemental composition of evolved component characterized using SEM/EDX. For numerical and experimental validation purpose, substrate deformation was measured using coordinate measurement machine before and after the process. It can be concluded that the result of the computed substrate deformation showed an acceptable agreement compared to experiment within the range of error between 0.5 and 27.5% at each specific measurement points and 10.1% as average single error. This basic investigation can be enhanced in the case where cost-effective WAAM application with dissimilar materials towards single-piece substrate component is concerned.

In order to study the effect of gas atmosphere on forming performance of laser powder bed fusion (LPBF), AlSi10Mg alloy was prepared by direct forming and in situ laser remelting under the shielding gas of argon and nitrogen in this study, and its microstructure and properties were characterized and tested, respectively. The results show that the forming performance of AlSi10Mg under nitrogen atmosphere is better than that of argon. Moreover, in situ laser remelting method can effectively enhance the relative density and mechanical properties of AlSi10Mg, in which the densification is increased to 99.5%. In terms of mechanical properties, after in situ remelting, ultimate tensile strength under argon protection increased from 444.85 ± 8.73 to 489.45 ± 3.20 MPa, and that under nitrogen protection increased from 459.21 ± 13.77 to 500.14 ± 5.15 MPa. In addition, the elongation is nearly doubled and the micro-Vickers hardness is increased by 20%. The research results provide a new regulation control method for the customization of AlSi10Mg properties fabricated by LPBF.

In arc welding, a groove is often used between metal pieces being welded. In tungsten inert gas welding of high-manganese stainless steels with arc voltage control (AVC), the penetration depth was found to increase with groove wall height. The purpose of this study is to understand the influence of the groove on the penetration depth, mainly through numerical simulation. Spectroscopic measurements were also conducted to validate the simulation. The simulation results showed that when no groove is present, several eddies are formed around the arc column and electrode tip, leading to a recirculating flow pattern. When using a groove, shielding gas introduced from the nozzle flows directly into the arc without forming eddies. In the former case, the metal vapour was transported upwards by the recirculating flow into the arc column and the electrode regions. In contrast, in the latter case, the metal vapour was pushed downward to form a dense metal vapour region over the weld pool and was then swept away horizontally. The arc voltage without a groove is about 1 V lower than that with a groove because the metal vapour around the electrode tip increases the arc electrical conductivity. This affects the arc length control when AVC is used. When the arc voltage increases, the AVC shortens the arc length to keep the voltage constant, leading to the deeper penetration by concentrating the heat input and arc pressure. These mechanisms cause the change of penetration depth when the height of the groove wall is changed.

Wire arc additive manufacturing (WAAM) is advantageous for fabricating large-scale metallic components; however, a high geometric accuracy as that of other AM techniques cannot be achieved because of the deposition process with a large layer. This study focuses on the WAAM process based on gas metal arc welding (GMAW). To clarify the influence of shielding gas used to protect a molten metal during fabrication on the geometric accuracy of the built part obtained via the GMAW-based WAAM process, the influence of the metal transfer behavior on the geometry and surface roughness of the fabricated structures was investigated via visualization using a high-speed camera when single and multilayer depositions were performed under different heat inputs and gases. It is known that Ar gas is not suitable for welding steel because it cannot provide the desired arc stability and weld bead characteristics. The results reveal that the arc is stable in the multilayer deposition of the WAAM process, and the short-circuit of the metal transfer at the heat input of 1.17 kJ/cm enables smoothing of the fabricated surface with large irregularities. Better arc stability under Ar gas is achieved when the oxygen content of the fabricated surface is 22 wt%. Furthermore, the short-circuit between the metal droplet and the fabricated surface, where the molten pool is insufficiently formed, resulted in a hump formation. The results indicate that proper use of Ar gas can improve the surface quality when depositing on rough surfaces.

In the present study, type 316L(N) bead-on-plates were welded using Activated-Tungsten Inert Gas (A-TIG) welding process with argon and helium gas at various ratios to evaluate the arc characteristics. The welding process parameters including shielding gas composition were optimized using the design of experiments to join 11 mm thick plate in a single pass. In addition, the A-TIG welding technique using optimized process parameters was developed to weld plates up to 20 mm thickness with significantly reduced heat input. High power density of helium arc shielding leads to constricted arc column that enhances arc efficiency and produces deeper penetration.

This study investigated the microstructures and properties of deposits protected by seven different proportions of N2 and Ar by performing wire-arc additive manufacturing of the 5356 aluminium alloy. The results show that when the proportion of N2 in the shielding gas was larger than and equal to 50%, flaky nitrides were generated in the deposits. With an increase in the proportion of N2 in the shielding gas, the number and size of nitrides in the deposits as well as the fluctuation frequency and amplitude of the microhardness of the deposits all increase. The existence of flaky nitrides incurs a low ultimate tensile strength of additively manufactured parts protected by a mixed gas containing N2. The presence of large-size flaky nitrides between layers in the deposits leads to a large difference in tensile properties in the horizontal and vertical directions of the deposit. Tensile fracture shows that the deposits were fractured in the mixed mode of ductile and brittle fracture.

Tungsten inert gas (TIG) welding on Duplex stainless steel (DSS) is more easy, comfortable and useful, if the process is precisely understood and controlled through development of the science & technology. TIG welding on DSS has been performed with the help of specific controlled welding process parameters. Welding quality has been strongly depended on these process parameters. In this study, some valuable welding parameters are chosen. These are welding current, shielding gas flow rate and speed of welding. These process parameters of TIG welding for ASTM/UNS 2205 DSS welds are optimized by using Principal Component Analysis (PCA) method and Grey based Taguchi’s L9 Orthogonal array (OA) experimental plan with the conception of signal to noise ratio (N/S). After that, compression results of above mentioned two analyses of TIG welding process parameters have been calculated. The quality of the TIG welding on DSS has been evaluated in term of ultimate tensile strength, yield strength and percentage of elongation. Compression results of both analyses indicate application feasibility for continuous improvement of welding quality on DSS in different components of chemical, oil and gas industries.

The use of pulsed gas metal arc welding (P-GMAW) is fundamental to applications were versatility and control of heat input are required during deposition. However, when welding using pure argon shielding gas, a drawback is the instability derived from wandering of the cathode spots on the weld pool. This work investigates an alternative to weld steels using pure argon shielding gas with cold wire pulsed gas metal arc welding (CW-P-GMAW). A mechanism for enhanced stability is revealed in CW-P-GMAW, related to the migration of cathode spots to the cold wire which prevents the cathode spots from wandering around the weld pool. The migration of cathode spots is likely related to charging of oxides on the cold wire surface by ions formed in the arc plasma. The enhanced arc stability smooths the shape of bead profile, since wandering of the arc due to cathode motion is suppressed.

Automated robotic laser welding is commonly used for the joining of thin-gauge sheet metals for automotive applications due to the precision and speed of the welding process. Without proper process optimization, high-speed laser welding for automotive applications is known to have defects such as porosity, weld concavity, and cyclic humping. Several welding parameters can be adjusted to optimize the laser welding process: decreasing the laser power and the welding speed, changing the intensity distribution of the laser on the surface of the substrate, or by changing the type and flow rate of shielding gas used during welding. However, decreasing the laser power and welding speed leads to a loss in productivity which can be costly in large-scale manufacturing endeavors. This study presents the effect of beam defocusing on the weld pool geometry while holding other parameters constant as the welding mode transitions from full penetration or open keyhole mode (OKM) when the beam is fully focused to partial penetration or closed keyhole mode (CKM) as the beam is defocused. It has been shown that by defocusing the laser beam and controlling the weld pool geometry, the welding process can be stabilized to eliminate defects such as severe concavity without decreasing the laser power or slowing down the welding process. A numerical solution is presented that uses three-dimensional (3D) transient finite element (FE) analysis to calculate the temperature fields and predict the molten weld pool geometry in both the full and partial penetration welding modes using a double conical-Gaussian (DCG) volumetric heat source derived from the classical 3D conical-Gaussian (CG) heat source. The model was calibrated using video imaging of the welding process and known experimental data, and it was validated using an extensive experimental study. The results of this work show that the model can be used to predict the molten weld pool geometry that stabilizes the liquid flow in the melt pool during high-speed laser welding whereby allowing faster speeds to be used in the manufacturing of laser-welded components.

Thin-walled aluminum alloy tube of underwater laser in-situ deposition technique was carried out for the first time, and the influences of laser powers, wire feeding speeds and shielding gas flow rates on the deposition appearance, geometry characteristics, microstructure and microhardness of single track deposited layer were investigated. As the laser power increased, the height of deposited region (DR) and deposition angle decreased, but the height of fusion region (FR) and the width increased. Besides, the deposition appearance became better firstly and then worse. With the wire feeding speed increased, the height of DR, width and deposition angle increased, but the height of FR decreased. In addition, the deposition appearance was greatly improved. As the shielding gas flow rate increased, the height of DR and deposition angle decreased, but the height of FR and width increased. Besides, the deposition appearance deteriorated. The microstructure of FR and DR were columnar dendrites and equiaxial dendrites, respectively. With wire feeding speed increased, the microstructure had a tendency to refine and average microhardness value gradually increased. However, as the laser power and shielding gas flow rate increased, the microstructure became coarse gradually and average microhardness value gradually decreased.

In situ direct formation of titanium carbide (TiC) was realized via tungsten inert gas (TIG) arc surface cladding using titanium dioxide (TiO2) and graphite powders, and the obtained TiC was used for coating structural steel (SS 400). The TIG cladding method was used to directly synthesize TiC by the carbothermal reduction reaction between the raw materials, namely, TiO2, and carbon. The applied shielding gas and electrical current were varied to obtain their optimal combination that has the best effect on the crystallinity of TiC. The optimal result was achieved when the TIG cladding process was performed with an electrical current of 70 A using argon gas shielding. X-ray diffraction (XRD) pattern analysis showed that TiC was formed through the TIG cladding process, indicated by the prominent peaks at 2θ values of approximately 35.97° and 41.82°. Scanning electron microscopy (SEM) investigations of the coated substrate indicated the differences between the morphologies of the TiC-coated and uncoated metal substrate. The microscopic imaging result indicated that the TiC-coated substrate has a smoother surface contour than the untreated metal substrate. Microhardness characterization indicated that the TiC-coated substrate had higher microhardness than the untreated substrate. Furthermore, the proposed technique was shown to have the potential for direct deposition of TiC on a metal substrate to protect the substrate from corrosion.

Laser-based powder bed fusion (L-PBF) is an additive manufacturing (AM) technology that uses a high-energy–density laser to scan through a powder bed and completely melts the metal powder. The environment inside the printer chamber, including the flow field of the shielding gas and the spatter particles induced by laser–powder interactions, is essential for product quality. For the first time, this work built a full-size model of printer chamber, and numerically investigated the interaction between the shielding argon flow and the laser induced spatter particles with considering laser temperature. A full-size geometric model of a commercial L-PBF printer with a Gaussian heat source was constructed, as well as a movable particle-release source model for particle injection. The distribution of the argon flow field, the temperature field, and the trajectory and deposition of spatter particles, particularly above the workbench during the L-PBF process were quantitatively analyzed. The results show that the gas flow within 30 mm above the workbench is uniform, and in the upper region of the printer chamber, the flow field is disorderly. The laser can only induce high temperature and upward gas flow in a small region close to the workbench (the height less than 1.6 mm), and the laser induced velocity disturbance in rest regions of the L-PBF printer is negligible. Particles injected towards the outlet (ID4) are mostly blown into the outlet, and in the other four injection directions, more than 90% of spatter particles are deposited inside the printer chamber, especially more than 50% deposited on the workbench. Increasing the laser power (from 100 to 200 W) has little effect on particle deposition on the workbench. Results will be helpful for improving the L-PBF product quality.

The MCAW with rotating electrode process (MCAW-RE) is a variation of the conventional MCAW (metal-cored arc welding) process, where reduced costs and superior productivity are obtained due to narrow gap welding, since the rotational motion of the electrode allows the electric arc to reach peripheral regions of the groove, preventing lack of fusion on the sidewall. Although there is some information about the operational characteristics of this process, the literature studying the mechanical properties is very limited. This work evaluates the mechanical and microstructural properties of high strength steel weld metals obtained by the MCAW-RE using two different mixtures of Ar-CO2 as shielding gas. Multipass welding by MCAW-RE was performed with preheating of 100 °C, in 500 × 150 × 10 mm steel plates. Weld metals were obtained by the MCAW-RE process using a consumable of the class 700 MPa and two mixtures of Ar-CO2 (5% CO2 and 25% CO2) as shielding gas. The results obtained from mechanical tests (hardness and impact Charpy-V) and metallographic examination (optical microscopy, scanning electron microscopy, and electron backscattering diffraction) carried out in samples removed transversally to the weld bead showed equivalent results for all weld metals. These results evidenced that the MCAW-RE process can provide weld metals with satisfactory behavior with different shielding gases. This process has a high potential for replacement of the conventional GMAW process because the weld metals achieved the requirements for several industrial applications.

Gas Metal Arc Welding (GMAW) is a welding process in which an electric arc is formed between a wire electrode and a metal work piece alongside a shielding gas to protect the arc from contaminants. There are several ways in which the molten electrode droplet can be transferred to the weld pool known as metal transfer modes. Identifying the metal transfer mode automatically is essential to monitor and control the welding process, especially in automated processes employed in modern Industry 4.0 manufacturing lines. However, limited research on this topic has been found in literature. This paper explores automatic classification of metal transfer modes in GMAW based on machine learning techniques with various signals from the welding process, including acoustics, current, voltage, and gas flow rate signals. Time and frequency domain features are first extracted from these signals and are used in a support vector machine classifier to detect the metal transfer modes. A feature selection algorithm is proposed to improve the prediction rate from 80% to 99% when all the four signals are utilized. When only the non-intrusive acoustic signal is used, the prediction rates with and without the proposed feature selection algorithm are approximately 96% and 81%, respectively. The high prediction rate demonstrates the feasibility and promising accuracy of the acoustic signal based classification method for future smart welding technology with real-time adaptive feedback control of the welding process.

In this work, gas metal arc welding of AISI 304 stainless steel at varying compositions of argon-CO2 shielding environment was performed using an established optimum parametric combination. Thereafter, investigations on the microstructure of the welded joints and mechanical properties of the weldments were carried out. Weldments of excellent surface quality that are void of spatters and pores were obtained when the shielding gas composition (wt.%) range is between 100% argon and 75% argon - 25% CO2. Increasing percentage composition of CO2 beyond 25% resulted in irregular bead formation characterized with spatters and pores. The hardness of the welded joint became significantly high as the CO2 composition in the shielding gas increased. The highest value of 310 HV was obtained when the shielding gas composition was 5% argon- 95% CO2. The least (220 HV) was obtained when the shielding gas was 100% argon. High ultimate tensile strength (596 - 378 MPa) was achieved when the shielding gas composition range is between 100% argon and 75% argon-25% CO2. The UTS dropped significantly as the CO2 composition in the shielding gas increased beyond 25%. It decreased from 336 MPa at 70% argon-30% CO2 shielding gas composition to 133 MPa when 100% CO2 was utilized as the shielding gas. At the end, the effects of the CO2 addition and suitable composition of CO2 addition to argon shielding environment during GMAW of AISI 304 stainless steel have been established.

Grade 2, the most widely used pure titanium in the industry, has high corrosion resistance, excellent ductility, good weldability and is easily machinable. If titanium is exposed to temperatures above 500 °C due to moisture or hydrocarbons in the air, it is susceptible to taking up oxygen, nitrogen, carbon and hydrogen. This can cause cracks, especially after welding. Therefore, protection of the welding zone from external factors is of great importance during welding. For these reasons, TIG welding is the most widely used method for titanium welding. In this study, Grade 2 pure titanium plates are joined by TIG welding at three (40 A, 60 A and 80 A) current values under the same conditions. For the welding process, 2 wt.-% cerium addition Tungsten tip and high purity (99.99 vol.-%) argon was used as a shielding gas. After a visual inspection of the welded samples, microstructure inspections, macrostructure inspections, hardness measurements, bending tests and tensile tests were performed in accordance with the standards. As a result of the investigations, it was determined that the most suitable current value for the joining of Grade 2 titanium by TIG welding was 60 A.

This work investigates the effects of Ar-based shielding gases on the microstructure and phase balance of duplex stainless steel (DSS) depositions. The results are then used for fabrication of DSS walls using wire arc additive manufacturing (WAAM), and the microstructural characteristics and mechanical performance of the products are assessed. WAAM currently poses as one of the most interesting methods of manufacturing by enabling joining of materials to fabricate structures layer by layer. However, the extreme conditions imposed by the process, such as high heat inputs and re-melt and solidification of the deposited layers, could compromise the performance of the products. A detailed microstructural analysis is conducted on single layer and double layer depositions of DSS to assess the effects of different shielding gases on the ferrite/austenite phase balance in the specimens. The results show that the depositions shielded with a small fraction of carbon dioxide (CO2) present better microstructural features in comparison to depositions shielded with the other selected gases. A mixture of 98%Ar + 2%CO2 was employed for fabrication of a 60-layer DSS WAAM-made wall and some mechanical characteristics were studied. The mechanical examinations demonstrate that the properties of the parts fabricated using WAAM are comparable with their wrought counterparts.

Gas protection is very important in arc welding processes and several factors influence its effectiveness. This paper provides a discussion of the applicability of the Schlieren technique to arc welding processes. Tests were performed with different types of shielding gas and with GMAW and GTAW torches, in order to highlight differences associated with the various conditions. The results obtained in conjunction with a review of results reported in the literature allowed an evaluation of the limitations associated with the use of the Schlieren technique in the arc welding processes. The most important limitation is that the visualization is inherently difficult when using pure Ar gas, meaning that in most situations it is not possible to adequately visualize the flow interface with atmospheric air, which is the main region of interest in this type of analysis. However, visualization is possible in regions where pure Ar is heated, or when mixtures with other gases are used. In addition, the results obtained with different sources of light were compared and the test was performed by filming the arc welding or with the gas flowing through the torch without the arc. The differences observed in the results obtained are discussed herein.

Metal matrix composites enhance the wear and corrosion properties of components in heavy-duty industries. This work reports the preliminary effects of process parameters such as current, linear speed, powder flow rate, nozzle angle, powder gas, shield gas, and center gas at the macro-scale and micro-scale of single-track multiple-layer depositions. The use of plasma transferred arc as an additive manufacturing system yields enough energy for a fast solidification rate of the matrix without compromising the carbide in the composite. The results show that the bead height is mainly affected by the powder flow rate, the powder gas, and the travel speed at the macro-scale. The bead width has a close relationship with powder flow rate, powder gas, and current, the latter contributing to the formation of a slumping phenomenon due to heat accumulation. The volumetric deposition is affected by similar parameters to the bead height. At the micro-scale, the process parameters did not show significant carbide changes but demonstrate its homogeneous distribution. The electron microscope observation exhibited the composite’s high quality due to the fast solidification of the process. The results demonstrate that the porosity is mainly affected by the powder flow rate. By understanding the preliminary contribution of process parameters, this manufacturing process can print near net-shaped parts minimizing the post-processing of metal additive manufacturing components. Therefore, this work contributes to implementing a preliminary experimental methodology to understand the deposition process of WC-reinforced composites in plasma transferred arc additive manufacturing.

Background: Duplex stainless steel (DSS) has gained increasing interest in recent years for a number of applications as structural materials in various industrial sectors of the petrochemical process plant, marine engineering and automotive industries. However, this material has experienced hardness and wear failure in the service. Therefore, new development in the surface modification for DSS is required to explore the possibility of producing a hard modified surface layer of SiC resolidified layer by TIG torch surface melting technique. Methods: TIG torch surface melting technique was performed on DSS substrate with preplaced SiC reinforcement. The effects of particle size, SiC preplacement, heat input and shielding gas flow rate on surface topography, hardness and wear rate were investigated through several characterizationsand tests. Results: Inspection of the surface topography reveals rippling marks which proved that the resolidification process occurred during the TIG torch surface melting technique. The obtained result showed that the preplacement of SiC reinforcement on DSS via TIG torch surface melting technique could increase the hardness of DSS by ~ five times. From Taguchi analysis, the optimum combination of parameters obtained for the lowest wear rate of surface layered DSS was: preplacement rate, 1.5 mg/mm2, SiC particles size, 60 μm; heat input, 720 J/mm; and gas flow rate, 15 L/min. Conclusion: The results of this study confirmed that conventional TIG torch melting technology may be used as an alternative to the more expensive laser or plasma technique to create a new composite surface layer on DSS material.

In the automotive industry, it is essential to reduce the weight of the car body to improve fuel efficiency and reduce CO2 gas emissions. As such, the application of advanced high-strength steels is rapidly increasing. However, in the case of gas metal arc (GMA) welding of advanced high-strength steels (AHSS), slag particles are observed to form on the weld surface resulting in poor corrosion resistance. The presence of slag particles on the weld also affects mechanical performance. This paper focuses on the degradation of corrosion resistance due to these slag particles. Current methods to decrease slag islands are costly as they attempt (1) to better protect the weld pool by decreasing the content of oxygen-containing ingredients or increasing argon in the shielding gas and (2) to mechanically clean the weld surface using processes such as shot blasting after gas metal arc welding (GMAW). In this study, the amount of slag was reduced by adjusting the chemical composition of welding consumables. Silicon was decreased to minimize silica/silicate formation, and sulfur was adjusted to affect the surface tension balance of the molten pool. Slag particles were observed to flow along the welding direction to solidify into a large particle in the weld crater that could be removed easily. In a separate consumable, Si and Mn contents were adjusted to form Mn3O4 and SiO2 slag. The use of these two welding consumables reduced the amount of slags, which improved the corrosion resistance. It is not the intent of this paper to compare the performance of these two experimental consumables, however.

Argon–helium mixtures in gas tungsten arc welding of an iron workpiece are investigated using an axisymmetric computational model that includes the cathode, workpiece, and arc plasma in the computational domain. The three-gas combined diffusion coefficient method is used to treat diffusion of helium, argon, and iron vapour. Calculations for argon–helium mixtures without metal vapour are performed; good agreement with previous numerical results is found. A transition from a helium-like to an argon-like arc occurs when the argon mole fraction increases above about 0.3. Calculations for a wide range of argon–helium mixtures including iron vapour are then performed. Adding helium to argon alters the arc properties and affects the weld geometry. Iron vapour cools the arc for all argon–helium mixtures. Iron vapour is present above the workpiece, near the cathode and in the arc fringes for very low argon mole fractions. As the argon mole fraction increases, the iron vapour becomes increasingly confined to the region above the workpiece, with small amounts near the cathode tip. Emission spectroscopy measurements of arcs in argon–helium mixtures with water-cooled copper and uncooled iron workpieces were performed. The measured distributions of atomic helium and iron emission show good agreement with the predictions of the model.

The quality of welded joints depends on the most optimal welding parameters and the selection of shielding gas type. The shielding gas was selected for joining stainless steels through gas metal arc welding methods by considering properties such as chemical-metallurgical interaction of shielding gas and the molten weld metal during the welding process, heat transmission capability of the gas and cost. In this study, the effect of different shielding gas combinations on the mechanical and microstructural properties of 316 austenitic stainless steel joined by the metal inert gas (MIG) welding method was investigated. In the welding process, pure argon (100 % Ar), 98.5 % Ar + 1.5 % H2and 95 % Ar + 5 % H2were used as shielding gases. Tensile, hardness, and bending tests were conducted to determine mechanical properties of the welded samples. In addition, metallographic examinations were carried out to detect the macrostructural and microstructural properties of weld zones. According to the results obtained from the study, the highest tensile strength was obtained from the joints welded using 100 % Ar shielding gas. When the addition of H2into the Ar gas increased, the tensile strength of the welded samples decreased. As a result of the tensile test, fractures occurred in the base metal in all welded samples. In all welding parameters, the hardness of the weld metal was lower as compared to the heat affected zone (HAZ) and the base metal. As a result of the bending test, crack and tearing defects were found in the weld zone.

In Selective Laser Sintering and Melting it is necessary to protect metal powder deposited on the powder bed from contact with atmospheric air, which may lead to oxidation and downgrading of the properties of the powder in the presence of high temperature that is necessary for achieving full or partial melting. Thus, the building chamber of commercially available SLS/SLM machines is fully isolated and filled with inert shielding gas which may need to be replenished before each build session thereby raising both machine building and consumables costs. In this paper, it is examined using Computational Fluid Dynamics how protection of the powder area around the laser spot can be achieved by locally insulating it from air by gas circulation in a suitably designed box moving with the laser beam. Full coverage of the respective area and at the same time no disturbance of the powder particles within it are critical requirements. Two concept variants are studied and simulated with promising results.

The effect of a shielding gas on the plasma flow of an electric arc and molten metal is studied. The effect of the shielding gas on the plasma flow of the electric arc of molten metal is simulated, and a mathematical model is developed that describes the flow of the plasma-forming gas inside a device that forms the necessary directions of plasma flows to form a droplet of molten electrode metal of the required size. It is established that the shielding gas and its pressure affect the gas outflow rate and the formation and size of an electrode metal drop. The time of the formation and detachment of the droplet changes at the increase in the pressure of the shielding gas, the higher the gas pressure, the smaller the volume of the droplet. Argon and carbon dioxide have different effects on the plasma flow of the electric arc, the length of the arc, the formation and detachment of the droplet. The process of the droplet formation can be controlled by changing the gas composition, pressure, and gas velocity. It is determined that the gas flow rate increases from 1.2 to 5.2 m/s and the volume of a droplet of molten electrode metal decreases at the increase in the gas flow from 10 to 30 L/min. The droplet volume can be changed on average by 65% depending on the shielding gas.

Tungsten Inert Gas (TIG) Welding is a type of arc welding process which has its major application in the pressure equipment industries. The shielding gas used in TIG welding avoids the contamination of weld and it also enhances the weld characteristics. Normally, the inert gases are used as shielding gas. The aim of this study is to investigate the weld characteristics of alloy steels with pure argon and argon (80%) mixed with carbon dioxide as shielding gas. During the study, the weld penetration and the number of root passes were monitored. Then the weld characteristics were analyzed by mechanical testing of the welded specimen were examined. Finally, a thorough technical comparison is made for the different shielding gases in detail.

In tungsten inert gas (TIG) welding, less penetration depth is achieved in a single pass which adversely affects productivity, Activated TIG (A-TIG) welding techniques achieve better performances and higher penetration depths compared to conventional TIG welding. Pure argon does not have the potential to provide adequate penetration in austenitic stainless steel. Argon–hydrogen shielding gas mixture provides high heat flux, thereby influencing the arc voltage and penetration. In the present study, hydrogen is added to base shielding gas argon to study the effect on weld geometry during TIG and A-TIG of 310S stainless steel. The result shows a higher weld depth to width ratio and a significant reduction in the angular distortion. Also, higher tensile strength is obtained in A-TIG weld metal with 1% hydrogen addition, due to more efficient cooling of the weldment. However, increasing the hydrogen concentration in shielding gas resulted in defect formations in the weldment due to the interaction between activated flux and the hydrogen.

Friction stir welding (FSW) process has gained popularity due to its energy efficiency in joining similar or dissimilar materials as compared to traditional way of joining materials and as it involves no use of shielding gas and little harmful emissions due to which it is regarded as ‘green technology’. It’s a solid-state joining process in which plastic deformation takes place to join the similar or dissimilar materials rather than melting. Due to this its applications can be found in the field of industries ranging from aerospace to ship building and rail to electronics. FSW plays a key role in joining many ‘non-weldable’ aluminium alloys such as from 2xxx series alloys (Al-Cu) and 7xxx series alloys (Al-Zn) which is not possible with conventional process leads to softening of weld plates which leads to decrease in the mechanical properties. Hence, the study of various interlayers such as zinc, copper, brass, nickel, tin etc. has become a hot topic for researchers. The joining of dissimilar material is often difficult due to difference in physical properties and composition and hence use of interlayer in FSW helps in effective joining. Insertion of interlayer between the interface of plates to be joined not only enhances the tensile strength of the weld joint but also restricts the excessive formation of hard and brittle intermetallic compounds (IMCs) and leads to controlled formation of fine and uniformly distribution of IMCs and reduces the residual stresses and further increases the joint efficiency. This work contains the review of some important research papers on FSW of similar alloys (Al-Al), dissimilar alloys (Al-Mg), and effects of interlayer on similar alloys (Al/Cu/Al) and dissimilar alloys (Al/Zn/Mg). This paper also throws light on effects of process parameters such as (tool rotation, tool transverse speed, tool materials) on joining of materials by FSW has been discussed along with the suggestions of the researchers.

In industrial applications, various types of materials are used and strength of weldment of two alloys is a major cause of interest among engineering community. In this study P11 and P22 steels were welded using ER −70 - S6 wire electrode with metal inert gas (MIG) welding process using CO2 as shielding gas. The strength of the weldment was tested by impact testing, Hardness by Micro Vicker hardness and Microstructure of weldment before and after the failure was examined using a metallurgical microscope. The results of experiments performed on the specimen on impact testing machine showed that the impact energy of welded specimen was 49 J in Charpy impact test, whereas, that of parent metal P11 was 48 J and for P22, it was 64 J. The result of impact test shows that the impact energy of weldment of P11 and P22 lies between the impact energy of parent alloys. The microhardness at Heat affected zone (HAZ) was highest and at base metal, it was lowest whereas, at weldment microhardness value lies in between microhardness value of base metal and HAZ. Specimen were heat treated in a furnace in an air environment at 700, 800 and 900 °C for 2 h and subsequently cooled in the furnace. The results of impact test show increased strength of weldment after post weld heat treatment (PWHT) at all temperatures however, the strength was found to decrease with increase in temperature of PWHTs.

The present work aimed at evaluating the effect of O2 content in argon-based shielding gases over the arc cathodic emission behavior (which can lead to arc wandering) in wire + arc additive manufacturing (WAAM) of thin aluminum walls and its consequences over layer formation. The effect of O2 content on arc wandering was assessed by analyzing cathodic spot behavior through high-speed videography during Gas metal arc (GMA-AM) depositions. Superficial and geometric aspects were analyzed, as well as the sputtering zone width on the wall sides. Through a proposed model, a parallel effect of wire-introduced oxides was weighted to explain arc wandering, searching for oxides in the wall sides (deviating from its action only on the pool). The main finding was that no influence of O2 from the shielding gas was observed on arc wandering, consequently on layer formation, when its content was up to 200 ppm. When an O2 content of 20,000 ppm was employed, oxide searching by the arc in the wall sides was no longer perceived due to enough oxide availability from the shielding gas. However, this favorable condition to layer formation entailed excessive layer oxidation. From the cathodic emission point of view, it can be said that high-purity shielding gases or special mixtures with small additions of O2 (up to 200 ppm) provide no significant advantages for WAAM of aluminum thin walls, at least for the hereby tested alloy and parameters.

The effect of shielding gas on the mechanical and microstructural characteristics of ER410NiMo martensitic stainless steel weldments was investigated. Three weldments with various inclusion contents were manufactured using different shielding gas compositions and welding processes: gas metal arc welding (GMAW) with 100% argon (Ar), GMAW 85% Ar/15% carbon dioxide (CO2), and flux cored arc welding (FCAW) 75% Ar/25% CO2. The inclusions in each weldment were characterized by means of scanning electron microscope observations and energy-dispersive spectroscopy analysis. The weldments underwent postweld heat treatment, after which the chemical composition and reformed austenite proportion were measured to account for microstructural effects. Hardness measurements, tensile tests, and impact toughness tests using the Charpy method were performed. The results showed that the Charpy V-notch (CVN) absorbed energy decreases with increasing inclusion content. The highest CVN absorbed energy, 195 J, was obtained for the GMAW 100% Ar weld, which had the lowest inclusion content. GMAW 85% Ar/15% CO2, with four times more inclusions than the former, had a CVN absorbed energy of 63 J. The current manufacturing process, FCAW 75% Ar/25% CO2, was found to have an inclusion content three times higher than the GMAW 100% Ar weld but a CVN absorbed energy of 66 J, which is close to the GMAW 85% Ar/15% CO2 weld. The results showed that using GMAW 100% Ar as a replacement to FCAW 75% Ar/25 % CO2 would lead to a three-fold improvement in terms of absorbed impact energy. The effect of inclusions on tensile properties, which was not clearly identified as several factors, in addition to inclusion content, affects the weld strength and elongation. Overall, the yield and ultimate tensile strengths differed slightly: 724 and 918 MPa for GMAW 100% Ar, 746 and 927 MPa for GMAW 85% Ar/15% CO2, and 711 and 864 MPa for FCAW 75% Ar/25% CO2, respectively.

Ti6Al4V alloys are widely preferred in the biomedical industries owing to its higher corrosion resistance in human body environment. Welding plays a critical role in the manufacture of complicated biomedical components. Hence, the necessity to identify suitable joining process for joining Ti6Al4V is very important. In this work, an attempt is made to study the CO2 laser welding of titanium sheets (Ti6Al4V) having dimensions of 100 × 60 × 3 mm. Laser welding was done based on L9 Taguchi array with welding speed(v), laser power(P), and shielding gas flow rate(f) as input parameters. The weld quality was analysed by measuring the depth of penetration (DOP), bead width (BW), and hardness values. Full penetration was observed only in two welding trials. The optimized parameters were identified by using the VlseKriterijumska Optimizacija I Kompromisno Resenje (VIKOR) multi-objective optimization technique. Analytic Hierarchy Process (AHP) is used for determining the weights of the relative importance of the output factors. VIKOR method identified that the 7th experimental run (power = 1.3 kW, speed = 0.3 m/min, shielding gas flow rate = 20 L/min) as the optimized parameter for getting the weld with full depth of penetration, lesser bead width, higher microhardness values in the fusion zone (FZ) and heat affected zone (HAZ). The metallurgical characterization of the optimized weld is also dicussed with the aid of microstructures taken from Scanning Electron Microscope (SEM).

Aluminum alloys are currently used in aircraft and automotive parts such as chassis because of its strength and lightweight structure. This work studies the outcomes of welding parameters on 5 mm thick AA6061 sample welded by using the gas tungsten arc welding. TIG welding process is chosen because of its superior technique and better economy. For the selected parameters, the welding was carried on the sample as per the standard American Welding Society (AWS) in four passes by using MGS 525/409 as the filler metal using argon as the shielding gas. Microstructure, hardness and tensile strength were determined to analyze the properties and various parameters of the welded joint. The yield and tensile strength of the sample welded at 160A was found to be 245 MPa and 105 MPa which represents 20% reduction in the ultimate tensile strength and reduction of 61% in yield stress. The hardness was found to be highest for the sample welded at 190A at the metal surface, heat-affected zone and weld zone measured was 103 HRC, 90 HRC and 87 HRC respectively. The Sample welded with 190A showed good bending strength and represented a low included angle. Microstructure showed fine and equiaxed grains uniformly distributed in the welding region.

The composition of shielding gas exerts a crucial influence on high nitrogen austenitic stainless steel (HNASS) deposited by gas metal arc additive manufacturing. The proportion of N2 in shielding gas greatly affected the formation quality and microstructure of deposited parts. As N2 proportion improved, the formation quality became worse gradually and the nitrogen concentration of deposition metal increased. The maximum nitrogen concentration of deposition metal was more than 1%. However, N2 porosity in the deposition metal became serious when the N2 content was over 10 %. The microstructure of the deposition metal changed from two phases of austenite and ferrite in shielding gas of 0∼10 %N2 to complete austenite with 15 %∼25 %N2 content in shielding gas. With optimal shielding gas of 5%N2+2%O2+10%He+83%Ar, the deposited parts of HNASS demonstrated good formation and excellent properties. The average ultimate tensile strength of 920 MPa was achieved and the elongation was 27.7%.

This research work is the first step in evaluating the feasibility of producing industrial components by using Laser Metal Deposition with duplex stainless steel Wire (LMDw). The influence of Ar and N2 shielding gases was investigated in terms of nitrogen loss and in the microstructure and austenite content of different deposited geometries. The evolution of the microstructure in the build-up direction of the Ar and N2-shielded blocks was compared in the heat-treated and as-deposited conditions. The susceptibility for oxygen pick-up in the LMDw deposits was also analyzed, and oxygen was found to be in the range of conventional gas-shielded weldments. Nitrogen loss occurred when Ar-shielding was used; however, the use of N2-shielding prevented nitrogen loss. Austenite content was nearly doubled by using N2-shielding instead of Ar-shielding. The heat treatment resulted in an increase of the austenite content and of the homogeneity in the microstructure regardless of the shielding gas used. The similarity in microstructure and the low spread in the phase balance for the as-deposited geometries is a sign of having achieved a stable and consistent LMDw process in order to proceed with the build-up of more complex geometries closer to industrial full-size components.

It has been well known that, in GMA welding, various welding phenomena are largely affected by the type of shielding gas used. However, up to the present time, almost no attempt has been made to ut...

The effect of chromium carbide introduced into the charge of a flux cored wire on the structure and properties of the hardfacing deposit is considered. Hardfacing is performed in a shielding gas atmosphere using a flux cored wire. The composition of the flux cored wire is selected so that the iron-based hardfacing deposit alloyed with the Cr–B–Nb–C system is achieved. In hardfacing, chromium carbide decomposes and alloys the hardfacing deposit with chromium and carbon; this leads to the formation of chromium carbides in the hardfacing deposit and to an increase in its hardness. On average, the presence of chromium carbide in the charge of a flux cored wire leads to an increase in the wear resistance of the hardfacing deposit.

An inert gas environment is required during the laser metal deposition of titanium alloys due to oxidation. A nozzle with local shielding device is more flexible than the inert gas chamber, and size of the components produced is not restricted. In this study, a coaxial double-deck gas shielding nozzle was designed to provide a local shielding for the laser metal deposition of Ti-6Al-4V alloy. Numerical simulation of flow field under four different gas flow rates was carried out, and the corresponding Ti-6Al-4V single clads as well as components were produced. Experimental results revealed that the effective protection length increased and then became steady with the gas rate getting larger. Every component showed significant change in the degree of surface discoloration. Among that when the gas flow rate exceeded 30 L/min, surface of the formed bulk components showed yellowish and shiny silver and the internal oxygen content was below 2000 ppm, which had a minimal raise from the powder. In addition, the microhardness of the components showed little increase compared with the rolled substrate.

Purpose The purpose of this paper is to find a theoretical reference to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition in wire arc additive manufacturing (WAAM) and ensure the effect of the gas shielding and stable heat and mass transfer in deposition process. The multiphysical numerical simulation and physical experiment are used for validation. Design/methodology/approach In this study, welding torch tilt deposition and external parallel magnetic field–assisted deposition are presented to adjust the unsymmetrical arc shape and plasma flow of overlapping deposition, and a three-dimensional numerical model is developed to simulate the arc of torch tilt overlapping deposition and external parallel magnetic field–assisted overlapping deposition. Findings The comparison of simulated results indicate that the angle of welding torch tilt equal to 20° and the magnetic flux density of external transverse magnetic field equal to 0.001 Tesla are capable of balancing the electric arc and shielding gas effectively, respectively. The arc profiles captured by a high-speed camera match well with simulated results. Originality/value These studies of this paper can provide a theoretical basis and reference for the calibration and optimization of WAAM process parameters.

The surface modification of Ti6Al4V alloy using a TIG re-melting process with a non-consumable electrode under Ar and Ar + N2 shielding gases has been investigated. The re-melted layers were characterized using optical and scanning electron microscopy and x-ray diffraction. The corrosion behavior of samples was also examined by potentiostat analysis. Based on the results, the TIG surface re-melting process of Ti6Al4V alloy under Ar shielding gas has negative effects on hardness and corrosion behavior of coatings. In contrast, Ti6Al4V/TiN composite coatings were successfully formed during TIG re-melting process in the presence of N2 in shielding gas. The prepared coatings showed the hardness value of about 890-910 Hv which was over four times higher than the substrate (220 Hv). The hardness showed an increasing tendency by increasing the TIG current up to 115 A. By annealing the produced coatings, the metastable TiN phase was transformed into a stable Ti2AlN phase, and the hardness value increased to about 980 Hv. Moreover, the corrosion resistance of re-melted coatings was improved during the annealing process.

Homogeneous mixing of Al, varying amounts of Cu, Mg and Zn metal powders and SiC ceramic powders and mechanical alloys of metal powders by using high energy ball milling were carried out in the Retsch MM400 model mixer device, which performs movement in a spex manner. After this process, X-ray diffraction (XRD) was applied to the powdered mixtures. With the data obtained from XRD graphics; The crystallite size was calculated using the Scherrer equation, and the lattice stresses were calculated using the Williamson-Hall equation and comparisons between these two data were made. It was observed that the amount of Cu by weight, both the crystallite size, did not make a notable change for this property. Then, powder mixtures were sintered in hot isostatic press in argon atmosphere, which is a shielding gas, and turned into samples. These samples were polished and scanning electron microscopy (SEM) images were taken.

High nitrogen stainless steel has extensive applied foreground in industries. But the weldability limits the use of the steel. The weld without nitrogen can become the weakness of the joint in corrosion resistance and strength. In this study, response surface methodology was applied to optimize the Ar-N2-CO2 ternary shielding gas for a nitrogen-containing filler metal in high nitrogen stainless welding. The influence of the proportion of N2 and CO2 on the nitrogen content, the impact energy and the tensile strength were investigated by the statistical regression models. The results show that the tensile strength, nitrogen content and impact energy increase and then decrease with the increasing of CO2, which indicates that CO2 content should not be too high. N2 addition can increase the nitrogen content of the weld obviously. But the impact energy decreases when N2 content exceeds about 7%. Integrating the mathematic models of the three performances, the optimal shielding gas compositions were determined to be 87 %Ar-6.5 %N2-6.5 %CO2. With this optimal shielding gas, the tensile strength and impact energy reached 956.7 MPa and 166.8 J, respectively. The deviation between the experimental value and the predicted value was below 2%.

Low nickel 200 series grade austenitic stainless steels are popular due to their low price and the welding of these materials is of interest to engineers and fabricators. Therefore, the dissimilar joining of AISI 205 and AISI 216 stainless steels are examined in this paper. The study used a TIG welding process with an ER307 filler metal and stepped up welding speeds with varying mixtures of H2 in the argon shielding gas. The weldments on the weld bead (shape and size), solidification mode (predicted on WRC-1992) and the delta-ferrite content (compared between the predicted and calculated lath ferrite with vermicular ferrite) were examined. The microstructure (volume and formation of delta-ferrite in the austenite matrix), mechanical properties (hardness and tensile strength tests) and pitting corrosion resistance (pitting potential and pitted initial) are also studied. The results indicate that the welding speed can be stepped up from a minimum of 1 to a maximum of 3.5 mm/sec. This parameter affected to an increase weld bead size, delta-ferrite, hardness, tensile strength and pitting corrosion resistance of the weld metals. The role of H2 can help heat collection in the weld pool during welding allowing the welding speed to increase up to a maximum 5.2 mm/sec. This was achieved with a 6 vol.% of H2 in the argon shielding gas. These results can help increase productivity and thus be considered a successful outcome for this work.

CO2 gas-shielded arc welding, which is widely used in the industrial world, has been recognized as an efficient and economical GMA welding process. However, its characteristic repelled transfer pro...

Aerosol processing is gaining much interest in fabricating particles for various applications due to its easy application and good control of particle characteristics. In this study, spherical alumina particles were prepared using a transferred arc plasma aerosol system with argon shield gas and nitrogen carrier gas. The operating conditions for spheroidization were controlled by comparing the particle heating and particle residence times in plasma to obtain the calculated critical particle size. Nitrogen fractions (10%–63%) and plasma powers (1–2.5 kW) were used as control parameters to verify the process design for the average injected particle sizes of 10 μm and 100 μm. The spherical particle sizes were examined by using field-emission scanning electron microscopy. Results showed that the particle size limits for melting ( d P , L M ) and vaporization ( d P , L V ) increased with increasing plasma power. Higher plasma power is required to fabricate spherical shapes from larger injected particles at nitrogen fractions of 10% and 63% because of the longer residence time needed to reach the melting state of the raw materials.

In this research, studied was the microstructure of AW5083 aluminium alloy butt laser weld joint fabricated under the Ar + 30 vol. % He shielding gas. The light and electron microscopy, computed tomography, microhardness measurements and tensile testing were used for evaluation of the weld joint properties. Porosity volume in the weld metal (WM) was observed by the computed tomography (CT). The volume of porosity in the weld No. 1 was 0.05 mm3, while that in the weld No. 2 was 1.45 mm3. The width of the weld No. 1 was 4.69 mm, the average tensile strength was 309 MPa, and the average microhardness was 55.7 HV0.1. Polyhedral grains with an average grain size diameter of 48 μm were present in the heat-affected zone. The fusion zone (FZ) was of a dendritic structure with an average grain size of 20 μm. Three intermetallic compounds β-Al3Mg2, γ-Al12Mg17 and Al49Mg32, which were identified by transmission electron microscope (TEM) analysis, were present in inter-dendritic areas of the WM. The weld joint was characterized by ductile fracture in the base metal (BM). In the FZ, a small number of Al2O3 particles of irregular shapes were observed.

In this work, the thermal characteristics of the weld pool during Yb:YAG laser welding of the AA5083-H111 aluminum alloy were captured using an infrared thermal imaging camera and a numerical model was developed to predict the temperature fields using COMSOL Multiphysics software. On comparing the measured and predicted temperature of the weld pool surface, the deviation was below 10 °C and the average experimental error was not more than 1%. It shows the reliability of IR camera used in this investigation. Also, it was apparent from the thermal images that at a higher beam power, an erratic molten pool was created due to the instability of keyhole and spatters were ejected from the molten pool. The higher recoil pressure built at the walls of keyhole due to the high intensity of the laser beam and instigation of the ejected fluid flow mechanism was responsible for this occurrence. Also, the formation and floating mechanisms of process-induced porosities were analyzed. Porosities were identified in the weldments processed with longer shielding gas blown distance (30 mm), whereas other welds had no porosities. Since the gas blown distance was more, gas pressure over the molten pool was not sufficient to suppress the plasma plume and, thereby, results in porosity formation. Interestingly, a high number of porosities were evident at the toe of the weld bead and it was assumed to be caused by the high thermal gradient-induced Marangoni flow. This study provides a better understanding of molten pool behavior, porosity formation and its floating mechanism.