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The non-consumable tungsten electrode plays a key-role in the tungsten inert gas (TIG) welding process, governing the behavior of the electrical arc that is essential for generating the necessary heat in welding. This study is focused on varying of electric parameters in the purpose to identify the appropriate conditions that promote electrode integrity. The post weld cathode analysis revealed that both the input current intensity and its frequency affect the overall morphology and microstructural and mechanical performance of the refractory electrode. Noticeable physical alterations occur with increased current, leading to larger grains and a reduction in microhardness values. In addition, it causes apparent defects such as perforation and superficial deformation. However, applying higher frequencies mitigates these defects significantly. Based on these findings, it seems crucial to take into consideration the interactive effect of current applied and its frequency to ensure better electrode conservation, thereby enhancing the efficiency of the welding process. [ABSTRACT FROM AUTHOR]

In the present work, dissimilar tungsten inert gas welding of AA6061-T6 to AA5086-H32 has been conducted using pulsed and alternating welding current. Microstructure examination revealed that the extent of the heat-affected zone in pulsed weld joint is narrower than the one obtained by alternating current. Energy-dispersive spectroscopy analysis showed that, regardless the welding process, both alloys contained Fe-rich intermetallic precipitates in base metal and heat-affected zone. Besides, only β-phase is detected in 6061, while Al3Mg2 was found in 5086 alloy. The electrochemical behavior of each zone of the weldments is evaluated in ASTMG69 media according to two setups where the open circuit potential is affected; a second setup is used to check the results. The polarization curves of base metal and heat-affected zone of both alloys overlap each other, and the entire curves exhibit a cathodic plateau with constant current density, while the lowest resistance polarization was obtained in weld zone of both assemblies. Atomic force microscopy and scanning electron microscopy micrographs of the exposed surface suggest that all welding regions suffer from localized corrosion where the intermetallic precipitates act as nucleation sites for corrosion. [ABSTRACT FROM AUTHOR]

Activating flux tungsten inert gas (A-TIG) welding has drawn intense research focus in the present material era to overcome the wide bead geometry and shallow penetration of conventional TIG welding. This work is devoted to investigating the role of halide-based flux on the bead geometry and the microstructural evolution of 7-mm-thick pure titanium plates. Square butt joints were made in the bead on plate configuration by varying arc current in the range of 80–150 A. Halide flux was proven to be effective in narrowing down the bead geometry and increasing the penetration up to 244%. Full penetration was obtained at 150 A, while the maximum penetration was 3.2 mm without flux. The fusion zone microstructure consisted of plate-like α grains and residual β grains. Many grains were filled with lamellar α structure. The microstructure of the fusion zone with and without activating flux showed a similar kind of structure. The hardness of the fusion zone was found to be 25–30% higher to that of base metal. The hardness distribution with and without activating flux was in the same range. [ABSTRACT FROM AUTHOR]

The objective of this research is to examine the impact of welding parameters on the surface roughness, hardness, and tensile strength of welds produced by a single-pass TIG welding process in austenitic stainless-steel plates (AISI 316L). Furthermore, the optimal processing variable settings will be identified in order to provide the highest levels of hardness, lowest levels of surface roughness, and highest levels of tensile strength. This study focuses on three parameters: arc current, voltage, and shielding gas flow rate, which were altered across three levels. A large number of tests were carried out on 3-mm thick AISI 316L stainless steel plates in order to determine the efficient and realistic operating limits of TIG welding settings. The welding process parameters’ operational limitations were determined by visual examination and bead shape. The values of current are taken as 100, 125, and 150 (A); voltage as 16, 18, and 20 (V); and gas flow rate as 6, 9, and 12 (L/min). Their impact on tensile strength, microhardness, and surface roughness was inspected. The experiments were conducted using Taguchi L9 orthogonal array (OA). Each input parameter was found to have an impact on the response. The optimized welding parameters for improved mechanical properties and surface roughness were identified. The results indicated an optimum tensile strength, 624.92 MPa, achieved at the parametric combination of 100 A current, voltage of 16 V, and gas flow of rate 6 L/min. The microhardness results indicated an optimum value, of 319.2 HV, achieved at the parametric combination of a current of 125 A, 16 V of voltage, and a gas flow rate of 9 L/min. A minimum surface roughness, 7.33 µm, was attained at 125 A current, voltage of 16 V, and gas flow rate of 9 L/min. These results highlight the significant impact of welding parameters on the mechanical properties and surface roughness of AISI 316L stainless steel welds. [ABSTRACT FROM AUTHOR]

High strength rebars are generally developed by increasing carbon and manganese contents depending on the size and strength capacity requirement. These elements in steel beyond certain level adversely affect weldability and impact toughness which are very critical for structural steels. In this study, an attempt has been made to analyse and optimize the welding parameters on higher carbon equivalent (0.60) of 36-mm-diameter structural rebar by Arc and TIG welding process to arrive at exact preheating temperature for obtaining desired weld properties at minimum possible cost. The basic aim of this work is to establish the welding process parameters on structural steel to use as an earthquake-resistant steel without compromising the properties such as yield strength, tensile strength, tensile strength to yield strength ratio, and minimum uniform elongation. Before and after the welding, changes in the microstructure and mechanical properties in the fusion zone and heat affected zone (HAZ) of the welds were investigated. From the results, it was observed that 150 °C is the optimum preheating temperature to obtain good welds. The microstructural studies revealed that martensite is not present in the HAZ of the 150 °C preheated sample and the same was substantiated from resultant mechanical properties also. [ABSTRACT FROM AUTHOR]

This paper presents an automated or intermittent wire feeding method in tungsten inert gas (TIG) welding. The preliminary investigation shows the macrostructure, microstructure, and mechanical property effects on various welding parameters using one combination proportion of filler metal with various welding parameters. The result of microstructure has shown that the localized segregation occurred at the center area weld metal with high-density eutectic phase and energy dispersive X-ray spectroscopy (EDS) study has found that Mg content was higher compared to the outside region. Other sample microstructure shows columnar structure was formed in dilution boundaries, and it reveals that fast cooling rates happened when the filler wire was inserted. Also, microstructure on weld traverse section shows that the wavy-like structure depended on the heat input. The fracture mode shows that lack of heat input is susceptible to oxidation; therefore, the fracture tends to occur at weld metal in the brittle manner with reduced strength of more than 40%. Also this article presented the method to calculate length ratio (RL) and the volume ratio (RV) to estimate the minimum value of ratio under the condition of a good welded surface profile. [ABSTRACT FROM AUTHOR]

A tungsten inert gas (TIG) welding process was utilized successfully to produce a dense and hard iron aluminide coating on an aluminized plain carbon steel substrate. The aluminized surface of the steel sheets was melted using different currents in the range of 30 to 50 A. The surface and cross section of the alloyed layers were studied using optical microscopy, scanning electron microscopy, X-ray diffraction and a nano-hardness test. The results showed that the volume of the pool formed during the surface melting had a critical influence on the phases formed during the process. Forty amperes was found to be the optimum TIG current, at which a Fe-rich aluminide consisting mainly of Fe3Al formed on the steel substrate. [ABSTRACT FROM AUTHOR]

A uniform design method was used to obtain the active flux formula for direct current electrode negative polarity activated tungsten inert gas (DCEN A-TIG) welding of 2219 aluminum alloy. According to the test results of the tensile strength of welded joint, a mathematical model was established to determine the best component of each component in the active agent and the correctness of the regression equation was verified. Compared with conventional TIG welding without active agent, DCEN A-TIG welding can effectively avoid the presentation of macroscopic and microscopic weld porosity, increasing penetration and strength of the welded joint. The three surfaces in the DCEN A-TIG weld zone presented different morphologies. The upper surface of the weld zone was composed of strong directional dendrites, whereas the cross section and longitudinal section of the weld zone were mainly composed of equiaxed dendrites. Cellular crystals were also observed on the bottom of the longitudinal section. The base metal of the joint was the hardest, and the hardness in the heat-affected zone was higher than that of the weld zone. The weakest area in the welded joint was near the fusion zone. Compared with conventional TIG welding, DCEN A-TIG welding can provide advantages. [ABSTRACT FROM AUTHOR]

Welding of powder metallurgy (P/M) materials continues to be challenging due to the complexities in terms of thermal and metallurgical processes as a result of porosity. Though fusion welding may reduce or totally eliminate porosity levels in the weld zone, metallurgical changes in the heat-affected zone (HAZ) and PMZ may pose problems relating to strength of the welded joints. The present research work aims to study the mechanical and metallurgical changes in a sinter-forged pre-alloy Atomet 4601 (Fe-0.54 % molybdenum (Mo)-1.8 % nickel (Ni)+0.3 %C) low alloy steel subjected to tungsten inert gas (TIG) welding. Green cylindrical compacts were sintered in a nitrogen-purged muffle furnace at a temperature of 1120 °C for 20 min and subjected to cold upsetting to get various densities of specimens. TIG welding was performed on the forged alloy steel plates with suitable filler material. The TIG-welded alloy steel was subjected to tensile and micro hardness tests, in addition to micro-examination and SEM fractographs of the fractured surfaces. Weld metal porosity has been observed in the case of parent metals with lower density. Increasing the density of alloy steel is found to enhance the tensile strength of parent metal and welded joint of alloy steels-partly due to absence of weld metal porosity. Formation of lamellar acicular ferrite at the fusion zone makes the welded joint stronger than the parent metal. The SEM image of fractured surface reveals brittle mode of fracture of the welded joint during tensile testing. [ABSTRACT FROM AUTHOR]

The angular distortion is a typical out-of-plane distortion, and it has negative effects on the performance of welded structures. However, the researches on angular distortion of welded structures using intelligent algorithm and mathematical analysis are comparatively less. In this article, the influence from the bead profile on the angular distortion is analyzed, and the angular distortion of tungsten inert gas arc welding with no gap would be predicted by back propagation neural network and the novel inherent strain considering the actual bead geometry model, and the prediction accuracy is also evaluated through comparative analysis of the results with each other. The average relative error of the model built using inherent strain considering the actual bead geometry model method is only 1.289 % and better than that predicted by back propagation neural network algorithm (4.772 %). Meanwhile, the inherent strain considering the actual bead geometry model prediction stability that is estimated using standard deviation is also clearly better than that of back propagation neural network. Actually, the prediction methods by back propagation neural network algorithm and inherent strain considering the actual bead geometry model are proved to be correct and stable. Therefore, the proposed methods can be used to predict the angular distortion of the welded structures with no gap butt joint and guide the actual welding process to decrease the welding deformation. [ABSTRACT FROM AUTHOR]

This paper presents a method for automatic control of arc length in tungsten inert gas (TIG) welding process using the arc voltage. By using this method, the role of operator in arc length control is played by an automatic control system based on a predefined arc voltage value for any special welding operation. A dynamic model for feed-rate mechanism and the relation between variations of arc length and voltage are described in details. Using a proportional-integral controller, variations of arc length in welding path is compensated with an automatic feed-rate mechanism in a normal direction to the welding path. By keeping the voltage constant during the process, a stable weld with higher quality and better appearance is obtained specially in welding of uneven surfaces. Theoretical and practical investigations show that the suggested method is able to control the TIG welding process successfully. Test results show that an accurate weld is obtained without the interference of the operator, and by comparing the predefined values of arc voltage with what is practically obtained, the welding gap is automatically adjusted. [ABSTRACT FROM AUTHOR]

This paper presents a study on an application of genetic algorithm (GA) for edge detection of molten pool in fixed pipe welding. As circumferential butt-welded pipes are frequently used in power stations, offshore structures, and process industries, it is important to investigate the characteristic of the welding process. In pipe welding using constant arc current and welding speed, the bead width becomes wider as the circumferential welding of small-diameter pipes progresses. In order to avoid the errors and to maintain the uniform weld bead over the entire circumference of the pipe, the welding conditions should be controlled as the welding proceeds. This research studies the intelligent welding process of aluminum alloy pipe 6063S-T5 in fixed position using the AC welding machine. The monitoring system used an omnidirectional camera to monitor backside image of molten pool. A method of optimization for image processing algorithm using GA was proposed and has been implemented into a process to recognize the edge of molten pool. The result of detection, which is back bead width, was delivered into a fuzzy inference system to control welding speed. The experimental results show the effectiveness of the control system that is confirmed by a sound weld of the experimental results. [ABSTRACT FROM AUTHOR]

In order to improve the weldability of invar alloy, temperature field distribution is studied using finite element analysis method and real experiment under different welding parameters and different thickness of welded materials. Temperature field distribution and welding penetration is also disclosed by real experiment and finite element method analysis. Finally, the effect of welding parameters on temperature distribution and welding penetration is discussed. The results show that Ni48Fe52 invar alloys can be welded to carbon steel with full penetration using welding parameters of I = 132 A, U = 17.1 V, v = 4 mm/s, and δ = 1.88 mm. [ABSTRACT FROM AUTHOR]

Input-output relationships of tungsten inert gas (TIG) welding and abrasive flow machining (AFM) processes were determined using radial basis function networks (RBFNs). A batch mode of training was adopted to implement the principle of back-propagation (BP) algorithm (which works based on a steepest descent algorithm) and a genetic algorithm (GA), separately. The performances of RBFN tuned by a BP algorithm and that trained by a GA were compared, on some test cases related to the above two manufacturing processes. The GA-optimized RBFN was found to perform slightly better than the BP-tuned RBFN. The back-propagation algorithm works based on the principle of a steepest descent method, whose solutions have the chance of getting stuck at the local minima, whereas the probability of the GA-solutions for being trapped at the local minima is less. However, their performances may depend on the nature of the deviation (error) function. [ABSTRACT FROM AUTHOR]

This paper describes the effects of pulsed TIG welding process parameters (pulse duration, peak current, and pulse frequency) on the microstructure and microhardness of Al-0.8%Mg-0.5%Si (6061) alloys. It was observed that pulse TIG welding produced finer grain structure of weld metal than conventional TIG welding (without arc pulsation). An increase in the pulse frequency has been found to refine the aluminium and eutectic grain structure of weld metal especially when welding is done using short pulse duration. Long pulse duration lowers the pulse frequency up to which refinement of constituents in weld metal takes place. Effect of the pulse frequency on the grain structure was found to be determined by pulse duration. For a given pulse frequency, long pulse duration produced a coarser structure than short pulse duration. An increase in the peak current coarsened the grain structure. [ABSTRACT FROM AUTHOR]

An image sensing system for the TIG (tungsten inert-gas arc) welding process of aluminium alloy was established. The relationships between the image sensing system and the characteristic of welding current were discussed in detail. Front and back images of the weld pool were obtained with different welding parameters. In order to process the image, the characteristics of an aluminium alloy were analysed. Image processing and pattern recognition were first used to obtain information from the TIG welding process for aluminium alloy. The image of the weld pool was pre-processed using a series of methods: a weighted median filter, a statistical threshold by expectation and the projection method. A neural network method was used to extract the edge of the images of the weld pool. The result of detecting the edge with a BP neural network were excellent. The symmetry of the weld pool for aluminium alloy was studied when the welding current is large. The edge of the image of the whole weld pool is obtained in a single side image and an accurate method for measuring the weld pool geometry parameter is provided. Experiments show that using the image sensing to control the TIG weld width for aluminium alloy is an effective method. [ABSTRACT FROM AUTHOR]