Inert Gas Shielding Research Articles

Latest Developments in MIG Welding - A Review

Abstract: By continually supplying a wire electrode and a shielding gas to protect the weld pool from air contamination, MIG welding has been used to combine two metals or alloys. In comparison to other traditional techniques of combining the alloys using straightforward arc welding processes, the delivery of inert shielding gas provides a number of advantages. Better tensile strength, finer grain hardness, high weld quality and appearance, microstructure improvement, and metallurgical characteristics over the parent metal are a few advantages of this welding process. Therefore, the main goal of this research is to analyse current developments in the MIG welding industry and shed light on those areas that have not yet reached their full potential. As a result, various MIG welding stories are gathered and examined in this study paper based on tests, parameters, and the types of materials used for welding. According to the majority of the publications cited, current was discovered to be the dominant parameter among them, however gas flow rate and angle of weld using modern techniques have not been employed up to that level. Some suggestions for the manufacturing industries are noted below based on the evaluation, which may prove helpful for industrial applications in the future.

Latest Developments in TIG Welding - A Review

Abstract: TIG welding has been used to join two metals or alloys by continuously providing a wire electrode and a shielding gas to protect the weld pool from air contamination. The supply of inert shielding gas offers a number of benefits over other conventional methods of fusing the metals using simple arc welding procedures. A few benefits of this welding method include improved tensile strength, finer grain hardness, excellent weld quality and appearance, microstructure improvement, and metallurgical properties over the source metal. In order to shed light on those sectors that have not yet realised their full potential, the primary objective of this research is to assess current advances in the TIG welding business. Thus, based on tests, parameters, and the kinds of materials used for welding, numerous TIG welding tales are compiled and investigated in this study article. The bulk of the mentioned studies state that the main parameter among them was found to be current, however gas flow rate and angle of weld utilising modern techniques have not been used up to that point. Based on the study, some recommendations for the manufacturing sectors are included below, which might be useful for future industrial applications.

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.

Improvement of mechanical properties through inhibition of oxidation by adding TiC particles in laser aided additive manufacturing of stainless steel 316L

Additive manufacturing has gained significant attention in recent years. However, oxidation is hard to be avoided especially for the directed energy deposition (DED) processes, which are normally operated in an open environment with inert gas shielding. Excessive oxidation will negatively affect the mechanical properties of the deposited materials. In this work, inhibition of oxidation was studied through adding TiC particles for laser aided additive manufacturing (LAAM) of stainless steel 316L. Notably, oxygen content can be reduced significantly, as TiC particles functioned as deoxidizers through chemical reaction with oxygen. Meanwhile, the large Si–Cr–Mn oxides can be changed into uniformly distributed fine TiO2 in the deposited stainless steel 316L. Consequently, ductility of the deposited stainless steel 316L was significantly improved by 54.1% with 5.6% increase in yield strength and 11.4% increase in ultimate tensile strength. This study shows a new way to overcome the negative effects of oxidation on the properties of the additively manufactured materials.

The Toughness of High-Strength Steel Weld Metals

Low-temperature phase transformation (LTPT) welding consumables are a new class of welding wires developed to mitigate hydrogen-induced cracking in the welding of high-strength steels without preheating or postweld heat treatment. LTPT weld metals have a high strength, but their toughness needs further investigation. LTPT weld metals predominately contain a martensite microstructure, which is necessary to achieve high strength; however, martensitic weld metals containing oxide inclusions have relatively poor toughness. Three welding processes — gas metal arc welding (GMAW), gas tungsten arc welding (GTAW), and hot wire GTAW — were investigated. Optical microscopy, scanning electron microscopes, and transmission electron microscopes were employed for characterization. The role of the shielding gas in the formation of oxide inclusions in LTPT weld metals was investigated. The formation of oxide inclusions in the weld metals was related to the CO2 in the shielding gas. When 100% Ar or a pure inert shielding gas mixture was used for all three welding processes, oxide inclusions were greatly reduced, and the weld metal toughness improved considerably, matching the base metal toughness. The mechanism by which inclusions promote fracture propagation in the weld metal was proposed.

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.

A simulation study of local powder bed gas shielding in Selective Laser Sintering / Melting machines

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.

Influence of gas atmosphere (Ar or He) on the laser powder bed fusion of a Ni-based alloy

The gaseous atmosphere plays a major role in the quality of the manufactured parts in Laser Powder Bed Fusion (L-PBF) by protecting the metal from high temperature oxidation. If argon and nitrogen are the most commonly used gases, helium has almost never been considered as a possible candidate as a chemically inert shielding gas. To provide a better understanding of the influence of the gas atmosphere on the process stability, a comparative study of L-PBF manufacturing under argon and helium atmospheres has been carried out, considering a nickel-based alloy Inconel® 625 and a single bead configuration. To this end, in-situ process measurements were carried out on a dedicated experimental setup. The melt pool behaviour, the expansion of the vapour plume and the amount of spatters were evaluated with high-speed imaging for the two gases considered, together with the final L-PBF bead dimensions. Results were also compared to single fusion beads carried out in an industrial L-PBF machine for a comparable range of volume energy densities. The influence of the shielding atmosphere on L-PBF single beads was as follows: (1) dimensions of beads were shown to be constant whatever the gas; (2) fewer and smaller spatters were produced under helium atmosphere, especially for high volume energy densities. Physical mechanisms were then discussed to understand those specific effects.

Study on mechanical and metallurgical properties of fiber laser welded Nb-1% Zr-0.1% C alloy

Laser welding of Nb-1% Zr-0.1% C was attempted in butt-welding configuration using top and bottom sided inert gas shielding. The precautionary measure during welding was to limit the reactivity of niobium alloy in ambient atmosphere. The ranges of input parameters, that is, laser power (P), welding speed (V) and beam diameter (D) for full penetration welding were attempted by carrying out bead-on-plate (BOP) experiments. The selection of the combination of process parameters was such that the formed weld area could be minimized without hampering the depth of penetration. Bead-geometry, hardness and tensile strength were quantified to study the influence of input process parameters during laser welding. Base metal had an average hardness of 108 VHN and the average hardness of fusion zone (FZ) was found to lie between 278 and 546 VHN. The steeper increment in microhardness value of the FZ could be due to the grain refinement, dissolution of precipitates and formation of brittle intermetallic phases of carbide and oxides, which were evident by the result of energy dispersive spectroscopy (EDS) and X-ray diffraction (XRD) phase analysis. The weld joint that failed in the weld zone exhibited the brittle failure, and ductile mode was achieved in the joint, where failure occurs at base metal. The range of elongation in laser welded joints varied in between 1.97 and 5.73 mm. The reduction of tensile strength and ductility of the joints could be due to marginal enhancement of microhardness and increment of brittle phase density in fusion zone, as were evident from XRD phase analysis. The main focus of the present work was intended towards the establishment of laser welding as an alternative technique for fabrication of reactive niobium alloy in ambient atmosphere.

Corrosion Resistance and Microstructure of Welded Duplex Stainless Steel Surface Layers on Gray Cast Iron

The degradation of pump components by corrosion and complex, simultaneous damage mechanisms, e.g., erosion–corrosion and cavitation–corrosion leads to high costs through replacement and maintenance of parts. To increase the lifetime of cost-efficient components with superior casting properties, surface welding of duplex stainless steel on gray cast iron parts was performed using inert shielding gas metal arc surface welding (GMA-SW) and plasma transferred arc surface welding (PTA-SW). The thermal conductivity of the used shielding gas and the preheating temperature influenced the dilution of the surface layers, which had a major impact on the corrosion resistance and the microstructure. Lower cooling rates enhanced diffusion and lead to precipitation of carbides. High heat input and prolonged cooling times during surface welding resulted in high dilution and a carbide network. The corrosion resistance in artificial seawater of those surface layers was substantially reduced compared to surface layers with lower heat input and higher cooling rates. The corrosion of the surface layers in the potentiodynamic polarization test was driven by selective corrosion of the phase boundary between Cr–carbides and Cr–depleted austenite. Passive behavior was observed for surface layers with low dilution, which had homogeneous chromium distribution and no carbide networks. In conclusion, the corrosion behavior of gray cast iron was improved by surface welding with duplex stainless steel. The corrosion resistance of the surface layers produced with PTA-SW with no preheating exceeded that of the surface layers produced with GMA-SW and came close to those of a commercially available duplex stainless steel used as reference material.

Effect of Various Parameters on the Bead Geometry and Flexural Strength of MIG Welded Joint

Metal inert gas welding is the process in which a continuous coil of consumable electrode is used with inert gas shielding. It was extensively being used for Aluminum and Mg Alloys. But due to other alternatives available for, the cost of inter gas prohibited the use of MIG welding of steels. After the introduction of carbondioxide as shielding gas the economical viability in welding of steels was realized. The quality of weld joing and its productivity is influenced by the parameters such as arc current, wire feed rate, voltage, welding speed, torch angle, , nozzle to plate distance, welding position and gas flow direction. In the present work effect of gas flow rate, voltage and current are studied using Taguchi L-9 orthogonal array. The flexural strength, tensile strenght and bead geometry for various trails are computed and the optimum combination is obtained.

Optimal laser welding process parameters and expected weld bead profile for P92 steel

P92 steel is classified as one of the creep strength enhanced ferritic steels, whose welding plays a crucial role in power industries. The best choice for such materials is the laser welding in open atmosphere with an inert gas shield. Compared to the frequently being used Taguchi based grey relational analysis, a simple and systematic approach known as the modified Taguchi design of experiments is utilized for P92 steel to obtain the optimized laser welding process parameters and the expected range of output responses. The complicated non-linear relationship between the laser welding process parameters (viz., laser power, welding speed and focal position) and the welding bead geometry (such as depth of penetration, weld width and heat affected zone width) is developed through empirical relations, which are validated by comparing with existing test results. Most of the test results are found to be within the expected range. From the ANOVA analysis the process parameter, viz. the focal position is found to have negligible variation on the overall mean value of the output responses and hence, the process designer can opt for any one the set levels of the focal position during welding operations.

Effect of inert gas-shielding on the interface and mechanical properties of Mg/Al explosive welding composite plate

Mg alloys oxidize easily in air atmosphere during explosive welding. In this study, explosive welding of Mg/Al composites was shielded using inert gas to improve composite quality. Mg-AZ31B/Al-1060 composite plates were produced under helium atmosphere and compared with identical plates produced under air atmosphere with the same parameters. Microscopic morphology, elemental distribution and the mechanical properties of the bonding interface were evaluated. The interface morphology of the composites welded under helium differs significantly from those welded under air due to the different pressure of shock waves in gaseous media, and almost no oxide formed on the interface of helium bonded composite. In addition, the gain of shear and tensile strength of the helium bonded samples were observed. Therefore, the inert gas plays an important role in improving the properties of Mg-Al composite plates. Inert gas-shielding can be applied as an effective manufacturing method in live wave metal explosive welding.

Dynamics of pore formation during laser powder bed fusion additive manufacturing

Laser powder bed fusion additive manufacturing is an emerging 3D printing technique for the fabrication of advanced metal components. Widespread adoption of it and similar additive technologies is hampered by poor understanding of laser-metal interactions under such extreme thermal regimes. Here, we elucidate the mechanism of pore formation and liquid-solid interface dynamics during typical laser powder bed fusion conditions using in situ X-ray imaging and multi-physics simulations. Pores are revealed to form during changes in laser scan velocity due to the rapid formation then collapse of deep keyhole depressions in the surface which traps inert shielding gas in the solidifying metal. We develop a universal mitigation strategy which eliminates this pore formation process and improves the geometric quality of melt tracks. Our results provide insight into the physics of laser-metal interaction and demonstrate the potential for science-based approaches to improve confidence in components produced by laser powder bed fusion.

Microwave-Assisted Synthesis of Black Titanium Monoxide for Synergistic Tumor Phototherapy.

Black titanium oxide has attracted tremendous interest in tumor phototherapy via converting light energy to heat and reactive oxygen species (ROS). Nevertheless, current synthesis methods suffer from inert gas shielding, high costs, complicated procedures, and expensive facilities, which are fairly impractical for treatment application. Herein, we propose a one-step strategy for fast facile synthesis of black TiO nanoparticles via a microwave-assisted hydrothermal synthesis approach with Ti power, hydrochloric acid, and hydrofluoric acid without the requirement of an reducing agent and high-temperature calcination. The prepared black TiO nanoparticles with an average size of 52 nm exhibit strong absorbance from ultraviolet (UV) to near-infrared light region, favoring a single agent and single light-induced synergistic phototherapy of tumors. The black TiO nanoparticles shows an excellent performance in phototherapy with a photothermal conversion efficiency up to 50% and a prominent ROS generation under 808 nm laser irradiation. The toxicity and therapeutic effect in vitro and in vivo are investigated, and the results elucidate that black TiO nanoparticles possess good biocompatibility and remarkable synergistic tumor therapeutic efficacy. The proposed microwave-assisted method opens up a novel way for the synthesis of titanium-based material in a simple and fast manner, promoting their applications in the biomedical field.

The influence of oxide layer pattern size created on the surface of C45 steel on laser light absorption during laser quenching procedure

An increase in surface absorptivity can be helpful with a number of laser heat treatment processes. This study examines the relationship between the surface condition and its influence on interaction with a laser beam. The aim of this paper is to examine the effect of the oxide layer pattern size on the absorption of IR radiation and the influence of the ambient atmosphere. The process was carried with inert gas shielding. The oxide layers are created by the controlled heating method. The controlled heating method uses a scanning laser system to create oxide layers of different thickness on steel EN 10083-2: C45. Subsequently, the absorbency of the formed oxide layer was measured, depending on the irradiation energy emitted into the surface. According to recent experiments has been found that the higher the thickness of the oxide layer increases absorption. These results have shown that the use of surface oxidation increases the coupling of laser energy to material surface in the order of tens of percent. The thickness and hardness of the laser hardened layer were considered. That paper describes possibilities of precise laser quenching of the oxidized C45 material surface.

Investigation of the oxides film on 304L base metal produced during welding process without inert gas shielding

Control rod drive mechanism Canopy-seal weld mockup of PWR was taken as the object of study. The microstructure of oxidation film and the oxidation mechanism on the surface of 304L base metal near the weld, under the gas tungsten arc welding without inert gas shielding on the base metal, were investigated. The morphology, composition and structure of the oxide film were characterized by optical microscopy, scanning electron microscopy, energy disperse spectroscopy, laser Raman spectroscopy, Auger electron spectroscopy, transmission electron microscopy and X-ray photoelectron spectroscopy. With decrease of distance to fusion line, oxygen content on the surface of the base metal increased, the size of oxide particles grew up, and cracks appeared on the oxide film, gradually. In the region at 2 mm distance from the fusion line, surface oxide film was mainly Cr2O3 and Cr-O amorphous. In the region at 7 mm distance from the fusion line, surface oxide film was mainly comprised of Fe3O4 with a few FeCr2O4 and Cr2O3. The temperature on the base metal during welding affected the growth rate, particle size, oxide species of oxide film on the surface of base metal. When the oxygen potential of the metal atom and the partial pressure of ambient oxygen are determined, the influence of temperature on diffusion is the main factor determining the composition of the oxide film.

Effects of shielding gas on GMAW of 10Ni5CrMoV HSLA steel using high Cr-Ni austenitic wire

The composition of shielding gas was investigated for gas metal arc welding (GMAW) of the 10Ni5CrMoV steel using high Cr-Ni austenitic wire. Adding CO2 into the inert shielding gas can improve the arc stiffness and reduce the incomplete fusion of sidewall. The optimal shielding gas of 40%Ar + 58%He + 2%CO2 was applied into multi-layer multi-pass GMAW of 10Ni5CrMoV steel with austenitic wire. No welding porosity, incomplete fusion and cracks were found in the welding joint. The chemical composition of the deposited metal reached the requirement for forming austenite weld. The highest hardness of welding joint was less than 350 HV and no obvious hardening tendency occurred in the welding joint. The tensile test and impact test indicated that the multi-layer multi-pass welding joint of 10Ni5CrMoV steel using austenitic wire had excellent comprehensive mechanical properties.

Sensitivity of Ti-6Al-4V components to oxidation during out of chamber Wire + Arc Additive Manufacturing

Reactive metals including titanium readily oxidise and should be protected from the atmosphere during Additive Manufacturing processes. This work explores the sensitivity of Ti-6Al-4V components to oxidation contamination during out of chamber Wire + Arc Additive Manufacturing when using inert gas trailing shields. Five Ti-6Al-4V components were produced with varying argon trailing shield configurations that range from ideal inert gas shielding (resulting in no surface contamination) through to very poor inert gas shielding that results in substantial surface oxidation. Despite significant changes in the degree of surface oxide contamination between each component, the overall increase in oxygen concentration in the bulk alloys was minimal and had negligible influence on the tensile strength and ductility.

Surface modification of AZ91 magnesium alloy using GTAW technology

AbstractIn this study, surface remelting treatment of the AZ91 magnesium alloy by means of welding using a non-consumable electrode in an inert gas shield was carried out. Three variants of surface treatment were used, i.e. the single torch variant with a single heat source without cooling down the samples, the single torch variant with a single heat source and a cooling system with liquid nitrogen, and the double welding torch variant with a double heat source in the torches operating in a tandem configuration. Experimental verification of the applied apparatus solutions was based on both macro- and microstructural assessment of the obtained effects. Comparative analysis of the variants used and the obtained microstructural results allowed the authors to indicate the deficiencies and limitations of particular solutions and to single out the best solution that would be useful for modifying the surface layers of magnesium alloys, as well as other materials having a strong oxygen affinity.