Argon Shielding Research Articles

Impact of Electrode Rotation on Aluminum GMAW Bead Shape

Aluminum gas metal arc welding (GMAW) uses inert shielding gas to minimize weld pool oxidation and reduce susceptibility to porosity and incomplete fusion defects. For aluminum shipbuilding, naval welding requirements highly recommend the use of helium-argon mixtures or pure helium shielding gas to provide a broader heat field and better weld toe fusion. Pure argon shielding gas can be used but has been susceptible to incomplete fusion and porosity defects, where argon’s lower thermal conductivity promotes a narrower arc heat field and shallow weld fusion depth. Using helium is a concern because it is a finite resource that costs approximately five times more than argon. The rotating electrode pulsed GMAW process was investigated to improve argon shielding fusion characteristics and reduce helium usage. Argon-shielded bead-on-plate tests were used to evaluate the relationship between ER5183 electrode rotation parameters and arc power on constant deposit area bead shape. These tests were compared to stringer beads (no oscillation) that were made with argon, helium, and helium-argon shielding gases. Electrode rotation improved underbead fusion depth width and toe fusion. With preferred rotation parameters, the bead width and incomplete fusion at weld toes were equivalent to helium-based welds. For weld reinforcement, electrode rotation promoted a nonsymmetric profile with deposit bias on the bead side, where rotation direction was aligned with travel direction. The bead-side deposit bias is an advantage based on preliminary horizontal V-groove welding procedures using ceramic backing. Electrode rotation can offset the effects of gravity, promoting a smoother bead and fusion profile.

GMA welding investigations on the effect of alternating shielding gases on bead profile characteristics of AA6061 aluminum alloy

The bead profile geometry of aluminum alloy has been taken for investigation and the influence of alternate gases in the gas metal arc welding (GMAW) process. In the GMAW process, welding currents of 105 A, 120 A, 135 A, and 150 A are considered for evaluating the weld parameters. Further, the influence of various alternating duration of argon (Ar) and helium (He) shielding gases on the GMAW process has been investigated. Consequently, the alternating duration between shielding gases is used as 0.25 s (He) and 0.75 s (Ar), 0.5 s (He) and 0.5 s (Ar), and pure argon for joining the AA6061 alloy plates. It is found that the 0.5 s (Ar) and 0.5 s (He) shielding gases promoted fewer porosity effects compared with other alternating shielding gas and pure argon. Also, the microhardness and depth of penetration were significantly improved in 0.5 s (Ar) and 0.5 s (He) compared with 0.75 s (Ar) and 0.25 s (He) and pure argon shielding gas. The welded surface morphological study has been conducted for further evaluation of welding currents and shielding gas effects in the GMAW process.

Influence of shielding gas on machining and wear aspects of AISI 310–AISI 2205 dissimilar stainless steel joints

Abstract In this article, the effect of shielding gas combinations on gas tungsten arc-welded dissimilar AISI 310 steel and AISI 2205 steel joints was investigated. Two gases such as nitrogen and carbon dioxide were substituted in argon shielding gas and its corresponding improvement in the mechanical, microstructural, machining, and wear aspects of the dissimilar AISI 310–AISI 2205 joints was studied. Weld bead studies, tensile, and weld region microhardness were conducted. X-ray diffraction studies revealed joint intermetallics, and microstructural evaluation was conducted. Machining studies were conducted using drilling experiments. Using local analysis and global analysis, the cutting force variations in the feed direction and cutting direction were studied. Wear tests revealed that the variations in traction force, specific wear rate, coefficient of friction and tribo wear mass loss were studied. A considerable improvement in wear characteristics of AISI 310–AISI 2205 joints was observed by substituting CO2 and N in shielding gas.

Mechanical and corrosion properties of TIG welded dissimilar AISI 420 and UNS S32205 stainless steel sheets

Duplex (ferritic-austenitic) stainless steels such as UNS S32205 are especially preferred for their resistance to corrosive environments such as sea water, while providing mechanical properties, which are comparable to those of structural steels. These steels include phases of delta-ferrite and austenite in approximately equal amounts. These alloys are used by traditional industries mainly in water refining systems, bridges, and chemical tanks. Martensitic stainless steels such as AISI 420 are chosen for applications where especially high mechanical properties are a major requirement as well as for their adequate resistance in corrosive media. For economic and technical considerations, these two different types of alloys can be used together in various applications. In this study, 3-mm-thick sheets of UNS S32205 and AISI 420 stainless steels were joined via tungsten inert gas (TIG) welding under pure argon shielding gas using ER312 and ER2209 filler metals. Microstructural examinations of the alloys as received, the weld metals, and the heat affected zones were achieved using both metallurgical and scanning electron microscopes. The composition of the filler material changed the microstructural, mechanical, and corrosion properties of the weld metals. The samples joined with the ER312 and ER2209 fillers yielded weld metal microhardness values of 272 HV and 258 HV, respectively, whereas the impact energy values of the samples were detected as 15 J and 34 J, respectively. The samples joined using ER2209 and ER312 fillers exhibited weld metal corrosion rates of 0.1523 and 0.1331 mm.year -1 . Microstructural, mechanical, and corrosion properties of weldments are investigated after using two types of filler materials in the joining of dissimilar S32205 and 420 stainless steel sheets via TIG welding • S32205 and AISI/SAE 420 stainless steel sheets were joined via TIG welding. • Mechanical properties/joining & corrosion performance of these alloys were examined. • Two filler materials were used to compare their major effects on the weld metals. • Cheaper martensitic has higher mechanical properties; duplex inhibits corrosion better. • Both used together can provide strength/economic & corrosion resistance advantages.

Three-Dimensional Numerical Study on the Metal Rotating Spray Transfer Process of High-Current GMAW

A three-dimensional numerical model based on the volume-of-fluid (VOF) method is typically preferred for studying high-current gas metal arc welding (GMAW) metal transfer mechanism and then controlling it. It is informed that the rotating spray transfer is extremely complicated, and some researchers have focused on simplified models without considering the energy conservation to make analysis manageable for the unstable metal transfer process. Using our created numerical model, the metal transfer of high-current GMAW with shielding gas of different conductivities has been studied by analyzing acting forces and fluid flows in the metal liquid column, especially for the contributions of the self-induced electromagnetic force, equivalent volume force of the capillary pressure of the surface tension (Named surface tension force in this work), static arc pressure. It is found that the unbalanced electromagnetic force greatly promotes the metal rotating motion in 500 A metal inert gas (MIG) welding with pure argon shielding gas and it pushes the metal liquid column to rotate. Considering the arc constricting effect in active shielding gas by simply changing the arc conductivity, it is found that the metal liquid column no longer rotates, it turns to swing since the unbalanced electromagnetic force is large enough to break the rotating motion. The calculated results of the metal liquid column deflected angle and rotating/swing frequency agree well with the experiment of high-speed camera observations.

Microstructure and Corrosion Properties of Austenitic and Duplex Stainless Steel Dissimilar Joints

In several applications duplex stainless steels should be joint welded to conventional austenitic stainless steels. In this research LDX 2101 lean duplex stainless steel sheets were welded to conventional 304 austenitic stainless steels, using gas tungsten arc welding. For the welded joints three different welding rods were used: ER 308L, ER 309LSi, and ER 2209. For gas shielding two different shielding gases were used: argon and argon +2% nitrogen. It was found that the nitrogen addition to the shielding gas promoted austenite formation in the weld metal. It was also found Schaeffler-diagram modified by Outokumpu showed a very good estimation to the ferrite content and chemical composition of the weld metal. The ferrite content estimated by the Outokumpu-diagram, showed a close correlation to measured ferrite contents, the highest error was 30%. In case of the chemical composition of the weld metal, the Cr- and Ni-contents were estimated with a maximum of 15% error. In terms of the corrosion resistance, the best pitting corrosion resistance was achieved using the 308L welding rod with argon shielding gas, where the weight loss was 1.6% after the 24 hours immersion test.

Metal Transfer Behavior of Metal-Cored Arc Welding in Pure Argon Shielding Gas

The metal transfer behavior of gas metal arc welding in a pure argon shielding gas was evaluated through experiments using a standard solid wire and a metal-cored wire. The investigation was conducted using observation techniques based on recording images by a high-speed camera equipped with laser assistance and bandpass filters in a range of welding currents. It was observed that the metal transfer mode became a streaming transfer mode when the welding current increased in the solid wire. Meanwhile, in the metal-cored wire, the droplet transfer frequency increased, and the droplet diameter decreased without changing the metal transfer mode in the globular transfer mode. We surmised that the streaming transfer in the solid wire would be caused by the spread of argon plasma at the wire tip, which decreases the effect of the electromagnetic force on droplet detachment. Conversely, due to the presence of flux inside the metal-cored wire, the argon plasma could not spread and was attached close to the iron vapor plasma at the overhead of the droplet. Hence, the electromagnetic force acting on the side of the unmelted flux was ineffective at promoting droplet detachment, preventing the transition to a streaming transfer mode. Furthermore, weld bead formation in the metal-cored wire was better than that in a conventional solid wire.

Strengthening of additively manufactured tungsten by use of hydrogen in argon shielding gas

Additively manufactured tungsten was printed in atmospheres of pure argon and argon-3% hydrogen and compared on the basis of microstructure, chemical composition, and three point bend tests. The argon-3% hydrogen atmosphere refined microstructure and markedly increased flexural strength, achieving a maximum of 985 MPa. Chemical composition analysis revealed high levels of oxygen in argon-3% hydrogen parts compared to pure argon. It is proposed that the argon-3% hydrogen atmosphere aided the formation of tungsten oxides and slowed their sublimation. These oxides likely led to grain refinement by grain boundary pinning. The grain refinement produced a ribbon-like microstructure which resulted in higher strength transgranular fracture

Preparation and characterization of Fe-SiO2 soft magnetic composites prepared by classic and modified Stöber Method

In this study, gas atomized iron powder with the particle size of 10 - 100 μm was coated in two different ways. The coating was created by a chemical procedure, the powder was treated for different periods of time with the classical and modified Stöber process. Toroidal samples were then prepared using different pressures. These samples were heat treated in an argon shielding gas. The complex permeability spectra of the green and heat-treated samples were measured and the effect of pressure, chemical coating time and heat treatment was investigated. The formation of the coatings in each case was confirmed by scanning electron microscopic examinations. Samples with long-term chemical treatment and without heat treatment were appropriate in high-frequency applications (μstat = 50, fFMR = 5 − 15 MHz). After the heat treatment, the relative initial permeability has increased significantly (160-180) and the resonance frequency has decreased (400-4000Hz). Furthermore, it can be stated that a more coherent, thicker coating can be obtained with the modified Stöber method.

Effects of filler material selection on the microstructural, mechanical and corrosion properties of TIG welded AISI/SAE 304L stainless steel sheets and rings

Abstract Austenitic stainless steels are mainly preferred especially for resistance to aggressive oxidizing medias and high temperature applications such as equipments and mechanical parts which are used in defense and conventional industries. In this study; 3 mm thick 304L austenitic stainless steel sheets and rings are joined to each other by using Tungsten Inert Gas welding method under pure argon shielding gas with ER316L and ER2209 filler metals. Weld metals and heat-affected zones of welded joints were examined by metallurgical and scanning electron microscopes. Microhardness, tensile and Charpy impact tests of weld regions are investigated. It has been determined that the filler metals have dominantly changed the microstructure of weld metals. The microhardness values of the welded samples joined with ER2209 filler metal was lower than the sample joined with ER316L filler metal in weld metal regions. Besides, corrosion tests indicated that the corrosion rates of welded samples joined with ER2209 filler metal is lower than the samples joined with ER316L filler metal.

Experimental study on the effect of argon shielding gas on the suppression of nitrogen arc anode ablation

The high heat flux density of the DC arc often leads to severe anode ablation, which is a key factor limiting the wider use of the DC plasma torches. In this study, a series of comparative experimental studies are conducted with the goal of suppressing nitrogen arc anode ablation by combining argon shielding flow and anode structure. It is found that for the planar electrode structure, the use of argon shielding gas can alleviate the ablation of the anode by nitrogen arc to some extent. If a boron nitride channel is installed on the anode surface to constrain the argon shielding flow, the electrode ablation can be significantly reduced. The experimental results show that there is no significant ablation on the anode surface after 1 h of operation of the nitrogen arc device with an arc current of 100 A. Further analysis reveals that, on the one hand, argon shielding gas can extend the range of motion of the nitrogen arc root along the anode surface and increase the speed of arc root motion, which has the effect of expanding the time-averaged arc anode attachment area. On the other hand, argon shielding gas can also increase the size of the nitrogen arc root and decrease the temperature of the arc root. The use of constraining channels can effectively control the range of motion of the arc root along the anode surface and strengthen the influence of argon shielding gas. The combination of these effects can substantially suppress the anode ablation of the DC arc device.

Tensile properties of Ti-6Al-4V as-built by laser metal deposition: The relationship between heat affected zone bands, strain localization and anisotropy in ductility

Expanded structural applications of additively fabricated or repaired components rely on a thorough understanding of relationships between the anisotropic microstructure and macroscopic mechanical properties. In the present study, Ti‐6Al‐4V as-built by laser metal deposition using a powder feedstock was investigated through an extensive characterization of microstructure, porosity and tensile properties along different loading directions. While no significant anisotropy in strength was noticed, the ductility was observed to vary significantly depending on the loading direction. Higher ductility along the build direction was found to result from strain delocalization using in-situ tensile tests combined with digital image correlation. Differences in mesoscale strain localization patterns stem from a specific distribution of α’ plates in relation to HAZ bands. In addition, the influence of a variety of other features including the crystallographic textures, the β grain morphology, the distance to the free surface, the porosity and the argon shielding during manufacturing on tensile properties was also examined and discussed in light of existing literature.

Influence of shielding gas flow on the uniformity of additively manufactured martensitic stainless steel

Shielding gas flow is essential to the additive manufacturing (AM) process, and the effects of argon shielding gas flow variation on the macroscopic homogeneity of additive manufactured stainless steel parts have been studied using an open-architecture AM system. Such a variation manifests itself layer-by-layer within one part and part-by-part across the build plate. Within one build, a combination of balling behavior, conduction melting and keyhole melting is observed across the build plate using the same laser parameters. Quantitative characterization of the melt pool shapes show that the melt pool width and the penetration depth exhibit the largest variations. Possible relations between the gas flow condition and macroscopic structure variations are discussed and guidelines for improved design of a gas flow system as well as future research directions are suggested for achieving macroscopically uniform metal AM.

Phase Equilibrium and Microstructure Examinations of Eutectic Fe-C-Mn-B Alloys.

In this study, we analyzed the quaternary Fe-C-Mn-B system to create new eutectic cast alloys for coating deposition and additive manufacturing. Experimental samples were fabricated via the wire arc manufacturing method with argon shielding using Kemppi Pro 5200 Evolution equipment. Annealing was performed in a vacuum electric furnace at 1273 K for 350 h. For phase analyses, Jeol Superprobe 733 equipment was used. Metallographic and differential thermal analyses were used to reveal the eutectic structure of the samples. Examinations of the quaternary Fe-C-Mn-B system demonstrated that several eutectic alloys existed in the system. Four isothermal pseudo-ternary sections of the Fe-C-Mn-B system were studied: “Fe3B”-Fe3C-“Fe3Mn”; Fe2B-“Fe2C”-“Fe2Mn”; “Fe3B”-Fe3C-“Fe1.2Mn”; “Fe23B6”-“Fe23C6”-“Fe23Mn”. Broad eutectic concentrations enabled us to overcome parameter fluctuations during additive manufacturing. In each isothermal section, two dissimilar phase regions were determined: one with a ternary Fe-C-B composition and the other with a ternary Fe-C-Mn composition. Depending on the manganese content, two types of solid solutions could be formed: (Fe, Mn)α or (Fe, Mn)γ.

Laser Welding of 316L Austenitic Stainless Steel in an Air and a Water Environment.

Laser welding is an innovative method that is frequently used and required by different disciplines and represents a technique of choice in a wide range of applications due to important advantages such as precision, speed, and flexibility. However, the welding method must be used properly otherwise it may deteriorate the mechanical properties of the welded metal and its environment. Therefore, the laser parameters should be precisely determined and carefully applied to the sample. The primary objective of this study was to investigate and propose optimal welding parameters that should be adjusted during the neodymium-doped yttrium aluminum garnet (Nd: YAG)-pulsed laser welding of austenitic stainless steel 316L in an air welding environment by using Argon shielding gas and in wet welding settings in serum medium. The investigation of the welding process in serum medium was conducted in order to propose the most suitable welding parameters being important for future possible medical applications of laser welding in in-vivo settings and thus to investigate the possibilities of the welding process inside the human body. In order to evaluate the quality of welding in air and of wet welding (in serum), a detailed parameter study has been conducted by variation of the laser energy, the welding speed and the focal position. The relationship between the depth of penetration and specific point energy (SPE) was also evaluated. The microstructure of the welded metal was examined by an optical microscope and scanning electron microscope (SEM). Based on the microscopy results, it was found that the largest depth of penetration (1380 µm) was achieved with 19 J laser energy in air medium, while the depth reached the largest value (1240 µm) in serum medium at 28 J laser energy. The increasing energy level showed opposite behavior for air and serum. The results of our study imply that when welding of 316L stainless steel is implemented properly in the body fluid, it would be a promising start for future in-vivo studies.

Investigating the Microstructural Properties and Phase Distributions of TIG Welded AISI/SAE 304L Stainless Steel Runners in TNT Filled Ammunutions

Among the stainless steels, the most widely used group is austenitic stainless steels. The prominent reason why austenitic stainless steels are preferred in welded stainless steel fabrications is their good weldability. AISI/SAE 304L austenitic stainless steels exhibit adequate corrosion resistance in oxidizing environments. AISI/SAE 304L austenitic stainless steels are also used in filling interfaces of runners between the Tri-Nitro-Toluen filling vessel and ammunitions in defense industry. For the manufacture of the runners, the stainless steel plates and the stainless steel pipes are mainly joined by fusion welding. These runners are cleaned with hot tapping water at 70°C after each filling of ammunitions by TNT so that cleaning operation can deteriorate the corrosion properties of runners especially weld zones. Austenitic stainless steel weldments include basically delta-ferrite and austenite phases on weld regions. Delta ferrite phase exhibits resistance to chloride bearing medias while austenite phase is more resistive to high temperature oxidizing ambients In this study; 3 mm thick 304L austenitic stainless steel plates and rings are welded to each other with two different filler weld wires of ER316L and ER2209 by Tungsten Inert Gas welding method under pure argon shielding gas. Weld metals and heat-affected zones of welded joints were examined using optical metallurgical microscope. It has been determined that the additional filler weld wires have changed the weld metal and the heat affected zone microstructures and phase distributions dominantly. Microstructures of all welded joints have been compared. Besides, phase distributions of weld metals and heat effected zones are made by image analysis software and Schaefflers diagram. ER2209 welding filler metal increased the phase fraction of delta-ferrite in weld metals while it decreased the austenite phase fraction as compared to ER316L filler metal.

Analysis of Laser beam welding of SS316L butt joints using Design of Experiments

Process control plays a significant role in increasing customer demand for quality, performance, cost; safety and reliability are essential for continuous growth, securing a process that allows least distortion after the laser welding process by applying with Experimentation Design. In the current experiments, the parameters of Laser power, welding speed, and Argon shielding are being used with L4 orthogonal array. These variables were checked to find the best control level combination of output and its related least distortion and maximum tensile strength. The X-ray radiography has tested the welds’ consistency and found that they are free from the surface and internal defects. The results show that welding speed, weld processes are critical parameter, and a shielding gas are not critical.

Development of Low-Magnetic-Permeability Welds of 316L Stainless Steel

Austenitic stainless steel is often used as the construction material for particle accelerator vacuum chambers. It is also a strong candidate construction material for helium vessels of superconducting radiofrequency cavities of highenergy, high-power particle accelerators. One of the major limitations of austenitic stainless steels for their application in particle accelerators is the relatively higher magnetic permeability of its welds. The present paper describes an experimental study to obtain a low-magnetic-permeability gas tungsten arc weld of 316L stainless steel while using ER 316L stainless steel filler metal through controlled addition of nitrogen in the argon shielding gas. It was demonstrated that 316L stainless steel welds, made with the addition of 1.5% nitrogen in the argon shielding gas, were associated with magnetic permeability close to that of the base metal. The welds exhibited good strength and ductility in addition to qualifying the impact test requirement of the American Society of Mechanical Engineers Boiler & Pressure Vessel Code (BPVC) for operation at room temperature and liquid helium temperature (4 K). The technique is important for the fabrication of BPVC-compliant 316L stainless steel vacuum chambers and pressure vessels of particle accelerators, including helium vessels of superconducting radiofrequency cavities.

Effects of Active Gases on Droplet Transfer and Weld Morphology in Pulsed-Current NG-GMAW of Mild Steel

The current research of narrow-gap gas metal arc welding (NG-GMAW) primarily focuses on improving the sidewall fusion and avoiding the lack-of-fusion defect. However, the high cost and operation difficulty of the methods limit the industrial application. In this study, small amount of active gases CO2 and O2 were added into pure argon inert shielding gas to improve the weld formation of pulsed-current narrow-gap gas metal arc welding (NG-GMAW) of mild steel. Their effects on droplet transfer and arc behavior were investigated. A high-speed visual sensing system was utilized to observe the metal transfer process and arc morphology. When the proportion of CO2, being added into the pure argon shielding gas, changes from 5% to 25%, the metal transfer mode changes from pulsed spray streaming transfer to pulsed projected spray transfer, while it remains the pulsed spray streaming transfer when 2% to 10% O2 is added. Both CO2 and O2 are favorable to stabilizing arc and welding process. O2 is even more effective than CO2. However, O2 is more likely to cause slags on the weld surface, while CO2 can improve the weld appearance in some sense. The weld surface concavity in NG-GMAW is greatly influenced by the addition of active gas, but the weld width and weld penetration almost keep constant. This study proposes a new method which is beneficial to improving the weld bead formation and welding process stability.

Laser Welding of Laser Powder Bed Fusion (LPBF) Manufactured 316L Stainless Steel Lap Joint

The aim of the study was to determine the static strength of laser welded lap joint in laser powder bed fusion (LPBF) printed stainless steel material and also a joint formed of printed and commercial sheet metal. Printed 316L test pieces with a thickness of 2 mm and a similar commercial 2 mm thin plate were used as test material. A laser welded lap joint made of a commercial sheet metal was used as a reference. Yb:YAG disk laser with wavelength 1030 nm and maximum output power 4 kW was used in welding tests. All test sets were welded with the same welding parameters and argon shielding gas. One fully penetrated keyhole weld was made to the lap joint. The static strength of the lap joints was determined by tensile tests. The measured shear strength was highest in the reference joint. In other cases, shear strength was only 8-11% lower compared to the reference joint. The cross-sections of the welds were analyzed on the basis of images taken with an optical microscope. Based on the results, the printed 316L is highly laser weldable material.