Low Welding Research Articles

Implementation of Manual Metal Arc Welding with Pulsed Current on TIG Modern Inverter Welding Equipment

The TIG welding technique in pulsed current using inverter welding equipment allows the realization of welds at a high technological and qualitative level due to the advantages that the process offers, the control of the welding pool, of the energy introduced in the components, the increase of the arc stability when using low welding currents or when welding at high speeds. Some manufacturers of welding equipment [1, 2] propose the option of using pulsed current on manual metal arc welding sources to increase the technological performance, primarily for the control of the welding pool by using low values of the current frequency below 10Hz, but with limited possibilities to modify the other parameters of the welded joint. The paper proposes the use of TIG welding equipment in pulsed current, in manual metal arc welding using the pulsed welding technique, starting from the advantages that this equipment offers in terms of the much greater possibility of adjusting all the parameters of the pulsed current according to the technological needs. This is possible because the two welding processes use welding equipment with identical external static volt-ampere characteristics.

Microstructure and mechanical properties of ultrasonically welded aluminum to Zn–Mg–Al coated and uncoated mild steels

The gaining popularity of aluminum alloys in the automotive industry demand the development of energy efficient joining methods of Al with other metals such as steel. Among such joining methods, ultrasonic welding is advantageous because it is cost effective and prevents metallurgical defects because of the low welding energy involved. This study evaluates the microstructural changes and mechanical properties of dissimilar ultrasonic welding of Al to Zn–Mg–Al-coated and uncoated mild steels. Various intermetallic compounds (IMCs), such as FeAl3, and Fe2Al5 with different thicknesses and morphologies were observed at the joint interfaces. The Al-to-Zn-Mg-Al-coated steel exhibited mechanical properties that are superior to those of Al-to-uncoated mild steel. The results are discussed in terms of microstructure evolution, joint characteristics, and interfacial reactions in the welds. This study contributes to the understanding of the mechanisms behind strong ultrasonic welding of dissimilar metals.

Simulation of Friction Stir Welding of AZ31 Mg Alloys.

Friction stir welding has been extensively applied for the high-quality bonding of Mg alloys. The welding temperature caused by friction and plastic deformation is essential for determining the joint characteristics, especially the residual stress and weld microstructure. In this work, a modified moving heat source model was proposed by considering the variations in heat generation caused by friction shear stress at both the side and bottom surfaces of the tool. The application of this model was further extended to the entire welding process, especially in the plunging stage. The relative errors between the experimental and simulated peak temperatures at characteristic points were small, with a maximum of 10%, thereby validating the model for accurate temperature prediction. Furthermore, the influence of welding and rotational speed on temperature fields was systematically investigated. At relatively low welding and rotational speeds, the welding temperature increased significantly with either an increase in rotational speed or a decrease in welding speed. However, this effect gradually diminished at higher welding and rotational speeds. These results provide some valuable guidelines for controlling heat generation to improve the quality of Mg alloy welds.

Influence of FSW process on dissimilar T-joint of aluminum alloy to pure copper

ABSTRACT This work investigated the influence of friction stir welding (FSW) parameter on forming the dissimilar T-joint of aluminum alloy 6061 (AA6061) to pure copper (C1100). The experimental outcomes indicated that the hook formation trended to move toward the center of welding line at low welding and/or high rotational speeds. In all cases, the kissing bond (KB) defects were significantly observed in advancing (AS) compared to retreating sides (RS). The thickness of diffusion and intermetallic compound (IMC) layers decreased with increasing welding and/or decreasing rotational speeds. A highest joint efficiency was attained with approximately 74% at 500/125 rev/mm of the skin test and 34% at 500/100 rev/mm of the stringer tests. The fracture process under the stringer test initiated from the AS to the RS along the interface while that of the skin test cracked in the heat affected zone. Improving dissimilar T-joint of AA6061/C1100 was impacted not only by controlling the KB defect but also the IMC layer thickness.

Low and High Gas Tungsten Arc Welding Heat Inputs Influence on Corrosion of Stainless Steel Weldments

In this study, influence of low and high heat inputs on corrosion susceptibility of 304L austenitic stainless steel (ASS) in simulated 0.5 molar solution of NaCl was investigated. Gas tungsten arc welding (GTAW) was used to generate low and high levels welding heat input. Microstructures of the weldments were examined, using metallurgical optical microscope (OMM) (Olympus GX51), while the corrosion behaviours were evaluated by potentiodynamic polarization tests, and corrosion data were recorded, using a computer-based data logging system – Autolab PGSTAT 204N. From the results, the evolving microstructures of the weldments before corrosion were characteristically heterogeneous; austenite (γ) was the leading phase, while ferrite (α) grains were dispersed within the γ matrix. Fusion zone (FZ) and heat affected zone (HAZ) microstructures after corrosion were characterised by pits of varying sizes with different alignments. And at GTAW speed, current and voltage of 7.2 mm/s, 200A and 40V, corresponding to low heat inputs, there were few number and size of pits relative to 1.7 mm/s, 200A and 40V, corresponding to high heat input. Shift in corrosion potentials (Ecorr) toward less negative direction, that is more nobility was observed at the low heat inputs induced GTAW parameters as compared to the corresponding high heat inputs induced GTAW parameters. In general, corrosion susceptibility of 304L ASS in the simulated 0.5 molar solution of NaCl was heightened at high heat inputs induced GTAW parameters as compared to the corresponding low heat inputs parameters.

Microstructures and mechanical properties of friction stir welded additively manufactured Scalmalloy®

The development of high-strength advanced additively manufactured (AM) aluminum alloys is driven by the need for weight reduction in complex-shaped structural applications. In this context, heat-treatable aluminum-scandium alloy, known commercially as Scalmalloy®, offers high strength and lightness, also at high temperatures, due to solution strengthening Al3(Sc, Zr) particles. A widespread diffusion of such AM alloy is also related to welding technologies that could preserve its engineered microstructure. This study investigates the microstructural and mechanical properties of butt friction stir welding (FSW) joints of LPBF Scalmalloy® plates under different welding settings. Joint performance was evaluated under quasi-static and cyclic loading conditions. Porosity in Scalmalloy® and welds was assessed using 3D X-ray computed tomography. An aging heat treatment assessed the extent of precipitation hardening in the FSW joints. Results show that metal stirring during FSW notably reduced the intrinsic porosity of Scalmalloy®, decreasing the equivalent pore diameter from about 200 μm to 60 μm in the welded joints. Under quasi-static loading, welded specimens failed at the interface between the thermo-mechanically affected and the stir zones on the advancing side. The aging heat treatment improved the mechanical strength of Scalmalloy® from approximately 400 to 480 MPa, albeit at the expense of ductility (elongation at fracture decreased from 16 to 4%). The higher heat input and stirring developed at a low welding speed reduced lazy S defects but limited the effectiveness of subsequent aging. In fatigue testing, welded joints consistently failed within the aged base material due to the intrinsic porosity of Scalmalloy®.

Grain Structure and Texture Evolution in the Bottom Zone of Dissimilar Friction-Stir-Welded AA2024-T351 and AA7075-T651 Joints.

High-strength dissimilar aluminum alloys are difficult to connect by fusion welding, while they can be successfully joined by friction stir welding (FSW). However, the asymmetrical deformation and heat input that occur during FSW result in the formation of a heterogeneous microstructure in their welded zone. In this work, the grain structure and texture evolution in the bottom zones of dissimilar FSW AA2024-T351 and AA7075-T651 joints at different welding speeds (feeding speeds) were quantitatively investigated. The results indicated that dynamic recrystallization occurs in the bottom zones of dissimilar FSW joints, and equiaxed grains with low grain sizes are formed at the welding speed of 60-240 mm/min. A high fraction of the recrystallized grains were generated in the bottom zones of the joints at a low welding speed, while a high fraction of the substructured grains are produced at a high welding speed. Different types of shear textures are produced in the bottom zones of the joints; the number fraction of shear texture types depends on different welding speeds. This study helps to understand the mechanism of microstructure homogenization in dissimilar FSW joints and provides a basis for further improving the microstructure of the welded zone for engineering applications.

Mechanical response and microstructural evolution of a composite joint fabricated by green laser dissimilar welding of VCoNi medium entropy alloy and 17-4PH stainless steel

In engineering structures, the application of advanced alloys, such as the VCoNi medium-entropy alloy (VCoNi-MEA), with remarkable tensile strength (> 1 GPa) and superior ductility necessitates the employment of dissimilar joints. This study pioneers the dissimilar joining of VCoNi-MEA and 17–4 precipitation hardening stainless steel (17–4PH STS) using state-of-the-art green laser beam welding (LBW). To evaluate and optimize the experimental parameters, two welding speeds (200 and 300 mm/s) along with post-weld heat treatment (PWHT) were incorporated. High-quality welded joints with a single-phase face-centered cubic (FCC) structure in the fusion zone (FZ), minimal precipitates (< 1.6 %), and no visible cracks were successfully created. The LBW process demonstrated effective low-heat input characteristics, evident from a considerably narrow heat-affected zone (HAZ). Control over FZ width and grain size was achieved, measuring 600 and 112 μm at low welding speed and 250 and 49 μm at high welding speed, respectively, significantly lower than previous studies. A remarkably high yield strength (YS) of ∼620 MPa and ultimate tensile strength (UTS) up to 845 MPa were observed in the as-welded conditions, improving to ∼645 and 875 MPa, respectively, after PWHT. This enhancement in mechanical properties is primarily attributed to lattice friction induced by V addition. PWHT also improved joint ductility, increasing from 3.5 % to 8.6 % (low-speed) and from 6.3 % to 9.2 % (high-speed). The reduction in crystallographic orientation achieved using a higher welding speed and PWHT emerged as a major reason for improved mechanical properties. Slip-based deformation mechanisms dominated across all conditions, featuring crystallographically aligned slip bands. Interactions between existing and additional slip bands formed a dense dislocation network crucial for enhanced elongation after PWHT. Thermodynamic parameters elucidating phase stability in the observed FZs and contributions to superior YS were calculated and comprehensively discussed.

Enhancing hardness in SMAW welded joints with low-frequency vibration assistance: an experimental and analytical study

Vibration assisted welding has gained popularity over the years for creating high quality welds and achieving better mechanical properties. The main objective of this research is to use low frequency vibration-assisted welding to optimise the process parameters. This study uses a novel vibratory technique to vibrate the workpiece during shielded metal arc welding at frequencies ranging from 0 to 100 Hz in order to examine the hardness of mild steel plates butt-welded to a thickness of 5 mm. Taguchi Methodology has been applied to optimise the hardness of welded specimens by varying the input variables viz. Current, vibration duration, and vibration frequency. Additionally, the microstructure of welded mild steel plates has been studied using SEM, optical micrographs, and XRD analysis. Results indicated that a low heat input of 80 Amp frequency of vibration of 100 Hz, and duration of vibration of 100 sec demonstrated optimum performance in terms of hardness of welded MS plates. Frequency of vibration has been found to be the most important parameter determining the hardness of the welded joint. Maximum hardness of 97.1643RHN has been found at optimal parameters. As the weld pool is being excited, vibration-assisted welded butt joints exhibit a finer grain structure, suggesting higher hardness values.

Tempering Procedure Effects On the Impact Toughness in Simulated Haz of Grade 22 Steel

Abstract Welding of thick low alloy steel components without elevated preheat imposes rapid cooling rates that may promote martensite formation in the CGHAZ. Freshly formed martensite contains a distorted and supersaturated matrix with high dislocation densities. As a result, impact toughness properties of these regions are inherently low and post weld tempering procedures are typically required. Conventional PWHT involves extended isothermal holds at elevated temperature which allows for considerable softening of the martensitic structure but has been found to have less effect on improving impact toughness. In contrast, short-term tempering processes with rapid heating and cooling rates and short exposures to elevated temperatures have been shown to greatly improve impact toughness through a shift in the kinetics of martensite tempering that produces high number densities of refined carbides. Temper bead welding (TBW) was developed for in-service repair of thick steel components where PWHT is impractical or not possible. With TBW, the heat-affected-zone is tempered by one or more rapid re-heat cycles from overlapping weld beads or weld layers. This study compares the CVN impact toughness and fracture morphology of the CGHAZ in the as-welded condition, with conventional PWHT, with a single TBW reheat, and with multiple TBW reheats for an SA-387 Grade 22 alloy steel.

Joining Behaviour of Thick Plate Using High-Frequency Induction Assisted Arc Welding

Combining a preheating source with conventional arc welding is a promising method to study the weld quality and improvement of strength for high-strength super-alloy materials. The present research used an induction preheating source with plasma arc welding (PAW) to weld Inconel 625 thick plates. The investigation was performed at a constant induction current of 600 A, welding speed of 100 mm/min and a plasma welding current of 135 A. The induction-assisted plasma arc welding (IAPAW) demonstrated that a weld joint was possible with static induction preheating and a high plasma welding current at low welding speed. The microstructural observation showed various dendritic structures in the fusion zone (FZ). The FESEM and EDX analysis confirmed the formation of Laves phase in the interdendritic structure of the FZ. The ultimate tensile strength of the IAPAW joint reached to 658 MPa. The tensile fracture surface of the welded sample revealed a lower number of dimples, indicating the reduction of ductility. The XRD analysis was carried out at various zones and it confirmed the peak shifting towards the higher 2-theta value of the FZ.

Dissimilar linear friction welding of AZ31 magnesium alloy and AA5052-H34 aluminum alloy

The intermetallic compound (IMC) layer, tensile properties, and fracture behavior of dissimilar Mg/Al joints and their relationship during linear friction welding (LFW) are investigated to develop a strategy to obtain high-strength Mg/Al dissimilar materials. The thickness of the Mg/Al-based IMC layer decreases as the applied pressure increases and the frequency decreases. The IMC layer is mainly composed of Mg17Al12 and Mg2Al3 at the weld interface. The tensile strength of the joints fabricated at an appropriate frequency of 50 Hz and a high pressure of 200 MPa during LFW is 235 MPa, which is 94 % the tensile strength of AZ31 and is attributed to the effective suppression of the Mg2Al3 IMC layer growth. At a lower frequency, large defects and pores are formed near the weld interface edge on the Mg side owing to the low welding temperature. The joint fabricated at a higher frequency exhibits a thick and brittle Mg2Al3 IMC layer at the weld interface because of the high growth rate; thus, the dissimilar joints fractured primarily at the Mg2Al3 IMC layer. The inhibition of the Mg2Al3 IMC layer growth yields superior tensile properties in Mg/Al dissimilar materials.

Inline Monitoring of continous Ultrasonic Welding Processes of Thermoplastic Composites via a custom polyCMUT based Ultrasound Array

Ultrasonic welding (UW) of thermoplastic composites (TCs) is an emerging technology in the field of composite joining techniques in the aerospace sector. Through a mechanical oscillator, ultrasound at a frequency of 20kHz is induced into the material via a welding horn, where microscopic friction and damping effects melt the thermoplastic. Under further pressure the weld area cools down, permanently joining both parts together. Like all joining processes in the aerospace industry the resulting joints need to be tested for their quality and structural integrity. The traditional testing method using water-coupled ultrasound includes extra steps. This process could be considerably improved by assessing the quality of the weld directly after or even during the welding process, allowing for immediate rework or discard of the parts in question. Ultrasound is still the best solution for this quality assessment, being inexpensive, well understood, and able to create B-Mode images, allowing a look into the cross-section of the weld. However, there are several major problems: To increase the system complexity as little as possible it is necessary to attach the ultrasound unit next to the welding equipment, and as close to the welding horn and compactor as possible to save space and keep the end- effector manoeuvrable. This brings problems for classic piezoelectric ultrasonic arrays: The low welding frequency and its resonance modes reach into the lower resonance modes of the piezoelectric sensors leading to immense noise, hiding any potential echo from the welding zone. Classic piezoelectric crystals are also very brittle and can suffer damage from sustained exposure to this violent environment. The authors present a novel solution: a custom-made polymer-based capacitive micromachined ultrasonic transducer array (polyCMUT). polyCMUTs are tiny drums with two electrodes. One on the bottom and the other suspended over a cavity sandwiched between two layers of polymers. By applying a DC-bias an electrical field is created and the membrane is set under tension. If then an AC voltage is applied, the strength of the electric field decreases, allowing the membrane to snap back into its original position. If done at the resonance frequency of the membrane, a strong ultrasonic signal is created. To receive this signal the polyCMUT is charged with a DC-bias, allowing it to receive the echo of the transmitted signal by measuring the changing capacitance. Not only is the polymer robust and inexpensive to fabricate, the general architecture of CMUTs also allows a design where the first mode of resonance is the actual mode the CMUT is operating in. By designing for a resonance frequency over 5 MHz all noise from the initial welding process is ignored, leading to a working pulse echo imaging system. The array is then mounted onto a PEEK block attached to the compactor unit of the welding end-effector. This publication is intended to present initial results, the design process of the custom array and the tests leading there.

Numerical simulation of efficient welding for thick plates in shipbuilding using simufact welding

In the welding process of medium-thick plates, it is common to create grooves and perform double-sided multi-pass welding. However, this approach leads to low welding efficiency and high costs. Hence, this study utilizes a groove-free, double-sided double-pass welding method to enhance welding efficiency and decrease shipbuilding expenses. A finite element model of groove-free submerged arc welding for medium-thick plates was established using SolidWorks software, and mesh division was carried out. Subsequently, numerical simulations of high-voltage, high-current double-sided double-pass submerged arc welding for medium-thick plates were conducted using Simufact Welding software. In the simulation, a mobile double ellipsoid heat source was utilized to replicate the dynamic alterations throughout the entire welding process. Subsequently, the temperature field of the welded material was computed. Finally, utilizing the temperature field results, the residual stress distribution within the welded material was computed through the thermal-structural coupling feature. The simulation results revealed a significant temperature gradient at the center of the heat source during the welding process, with a slower temperature change observed behind the heat source. Around 4000 seconds, the weldment cooled to room temperature. At this point, the thermal stress mainly concentrated around the weld seam. This numerical welding simulation serves as a crucial reference for designing welding process parameters and researching residual stress distribution. Consequently, it enhances welding efficiency in the field of shipbuilding.

Evolution of microstructure and mechanical properties of GTAW joint for magnesium alloy thin plate by post-weld reinforcement compression treatment

Gas tungsten arc welding (GTAW) joints of magnesium alloy thin plates generally exhibit low welding coefficients. Therefore, post-weld reinforcement compression treatment is utilized to improve mechanical properties of the joints in this experiment. The study shows that the grain shapes and sizes in various zones of the treated welded joints alter significantly, and the presence of twins is also detected especially in the base material (BM) and heat-affected zone (HAZ). The strength of the welded joints progressively rises with the increase in the compression reduction. The welding coefficient of the C3-joint reaches 91.6% when the compression reduction is 1 mm. The ultimate tensile strength (UTS), yield strength (YS), and elongation (EL) are 271 MPa,173 MPa and 7.2% respectively. The post-weld reinforcement compression treatment introduces abundant dislocations in the fusion zone (FZ), contributing significantly to the increase in joint strength. In addition, solid solution strengthening and texture strengthening also exert a role.

Optimization and Simulation Parameters of the Resistance Spot Welding for Commercial Aluminium (AA1050) at Low Power Welding Machine

This study aims to find the best conditions of resistance spot welding in commercial Aluminium AA1050 to obtain the maximum tensile shear strength of the joint using a low-power supply welding machine. The chosen parameters for this study were welding current, welding time, and electrode force using a 90 kVA welding machine. The investigation used the DoE method with Taguchi’s technique to reduce the number of experiments where two sheet thicknesses (1 mm and 2 mm) were used in this work. The software program Minitab 18 analyzed the results using the main effects plots and the interaction plots to identify the most significant parameters and their effect on the joint strength. The best conditions for maximum tensile shear force were 14.85 kA welding current and 0.79 kN electrode force for both thicknesses and two cycles and 12 cycles welding time for 1 mm and 2 mm sheet thickness, respectively. The maximum tensile strength obtained was 250 N and 225 N for 1mm and 2mm sheet thickness, respectively. A mathematical equation was developed to predict the shear force with 19.9 % and 17.9 % error for 1 mm and 2 mm thicknesses, respectively. The best conditions were applied in ANSYS 2022R1 multi-physics to obtain the temperature distribution with time history, where the result shows the nugget size according to the molten temperature. The percentage of discrepancy between actual and numerical nugget size was 8 %.

Metallurgical, mechanical, and corrosion behavior of AISI 304L joints welded using variable arc energy inputs and subjected to thermal aging

The effect of three levels of welding arc energy input on the metallurgical, mechanical, and corrosion behavior of AISI 304L stainless steel was studied with the aim of investigating and recommending the most useful range of process parameters for improved performance of engineering structures made from this industrially important alloy. The gas tungsten arc welding process was employed, and all the joints were butt-welded using a single-V groove design. With an increase in heat input, the δ-ferrite phase changed from lathy to vermicular, besides the heat-affected zones of all the welds exhibiting grain coarsening effects. Postweld thermal aging led to the preferential occurrence of carbides in the interdendritic regions, which degraded their corrosion performance. Thermal aging did not affect the tensile strength of these welds, but their ductility was significantly impacted. The extent of segregation of Cr and C, especially, was observed to be the least in the case of low heat input welds. This study establishes that while designing welding procedures for AISI 304L structures, low welding arc energy should be used as it promotes better mechanical as well as corrosion properties.

Friction stir extrusion of thin AA 7075-T6 into low-carbon steel: Effects of low weld pitch value

Friction stir extrusion, a derivative process of friction stir welding, forms a mechanical joint between workpieces by forging one into a prefabricated geometry within the other. Thin sheet AA7075-T651 extrusion joints were made into an O-ring dovetail channel within a low-carbon steel workpiece. The effects of low weld pitch process parameters on joint characteristics between the extruded thin sheet AA7075-T651 and low-carbon steel were observed. The weld pitch was varied from 0.02 to 0.05 mm rev−1. No material mixing was observed. Tensile-shear test results were normalised by sample width. The 0.04 mm rev−1 weld pitch group yielded the highest average joint strength at 493 N mm−1. The weld pitch parameters reduced machine in-process forces without a large decrease in joint strength.

Influence of reduced pressure on arc and weld pool properties in TIG welding

In this article, transient transport phenomena in the arc and weld pool for different ambient pressures during tungsten inert gas welding were reported. Arc plasma and weld pool behaviour vary with ambient pressure because of changes in arc thermophysical properties. The maximum arc temperature decreases with decreasing ambient pressure because of reduced plasma electrical conductivity. Decreased arc mass density results in a lower maximum weld pool surface temperature and a decrease in maximum metal vapour content as ambient pressure decreases. Arc pressure decreases with decrease in ambient pressure, resulting in shallower penetration. Calculated arc temperature distribution and weld cross-section are compared with experiments to validate the modeling method for simulating heat and mass transfer phenomena in low ambient pressure welding.

Effect of welding parameters on properties of HDPE geomembrane extrusion welds

The stress crack resistance (SCR) of high-density polyethylene (HDPE) geomembrane extrusion welds is examined for a 1.5 mm HDPE geomembrane and three different welding parameter combinations (denoted as “Cool”, “Good”, and “Overheated”). Results are reported for unnotched welds, unnotched sheet, and notched sheet. The average SCR for a Good extrusion weld is 23% of that of the unnotched sheet SCR. Little variation is found between the three welding parameter combinations for low geometry irregularity SCR weld specimens. There is no statistically significant difference between a good-quality fusion and extrusion weld. However, operator-dependent weld induced geometric irregularity (WIGI) greatly affects the SCR of extrusion welds. Extrusion welds with high WIGI have an average unnotched SCR of only 9% of the unnotched sheet. Extrusion welds with an overground surface can have an unnotched SCR as little as 1% of the best extrusion weld. Deleterious weld bead geometries are identified to provide a framework with which engineers can identify “high-risk” extrusion welds with respect to stress cracking.