Journal of Welding Science

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In this paper, laser beam welding of a rectangular piece of steel was simulated using Fluent software. Physical properties of analytical field was constant and its changes with temperature was ignored. In the present work, effect of tool speed and laser power on temperature distribution of workpiece surface and different deeps in the plane of symmetry and also maximum of temperature and depth of penetration were investigated. Using a macro code, geometry generation and meshing of the analytical field by helping required geometric  parameters were provided for software. Moreover, laser radiation power was exerted by writing an UDF in the fluent software. In this case, it was assumed that the workpiece is stationary and gaussian thermal source model defined in UDF moves with the intended speed. Results show that at a constant power, maximum temperature of the workpiece decreases with increasing heat source speed, moreover, in this case, gradient of temperature in front of the workpiece and behind of it, increases and decreases respectively. It is found that the temperature in the depth of the workpiece increases with increasing the power.

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Nowdays, the prediction and prevention of fatigue failures is converted to one of the most concerns for industry owners. Since the processes of fatigue suddenly occur, it is most important and necessary to recognize the effective factors of fatigue life of structures. Mechanical and thermal multiple loading are the important factors of the fatigue failure. In order to appropriate fatigue design, analysis should be validated with experimental results. In present research, fatigue life of A36 welded steel samples obtained from test is compared by finite element results obtained from commercial ansys pakage. In this research, the effects of residual stress, reinforcement, notch and thickness of sampels on fatigue life are studied. Results of analytical simulation and experimental show good agreement. Results also shows the dominant effect of reinforcement on the fatigue life.      

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A517 is a low alloy high-strength steels that due to its high strength, toughness and weldability is used in ship building and submarine hulks. The welded areas of this steel often require repairs. In this study, the effect of number of welding repair on microstructure and mechanical properties of A517 steel is studied. Four samples (samples without repair, once repaired, twice repaired, and three times repaired) were welded by SMAW welding. Microstructural studies were carried out by using optical and scanning electron (SEM) microscopes. The effect of the number of repairs on mechanical properties of samples were investigated by using tensile, bending, impact and hardness The profile of hardness illustrated that the hardness in the heat affected zone near the base metal increased by repeated repairs while the hardness of this zone reduced in the third repaired sample. By repeating the welding repair, tensile and yield strengths of the welding areas were reduced and fracture impact toughness of heat affected zone at -51^○C was increased. Generally, the results of tensile tests of second and third repaired indicated that the strength of these samples were not meet the ASME IX standard requirements, so welding steel A517 in the second and third repairs is not acceptable.
 

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Aluminum to stainless steel joints are broadly used in industries in order to reduce fuel consumption. While fusion welding is not a suitable method to join these metals. solid state welding, like friction welding (FW), is an effective way to this process. However, risk of intermetallic compounds (IMCs) formation is probable in these welds. In previews investigations formation of FeAl₃, Fe₂Al₅ and Fe₄Al1₃ is reported. In this study, effect of different parameters on generated heat and temperature distribution that lead to formation of these compounds in a FW of aluminum alloy to stainless steel is investigated using Finite Element Method (FEM). Additionally, a mathematical modeling of the parameters is performed using Artificial Neural Network (ANN) and the optimum level of the parameters has been found.

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In this research in order to improve the mechanical properties of Aluminium alloy 2024, nanostructure Aluminum sheets were first produced by Cryorolling process and then was welded by resistance spot welding method. For this purpose, the samples solution treated at 495˚C for 55 minute and subsequently cryorolled up to 85% reduction in thickness. For obtaining simultaneous strength and ductility, the cryorolled sheets were then subjected to aged. In this regard the produced samples were then resistance spot welded with different welding parameters, including welding current 60 to 105 KA, electrode force of 3 KN, and welding time of 0.1 s. The highest tensile shear peak load was obtained through welding with 95 KA current.

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In the research presented in this paper, a failure analysis were carried out to identify causes of an incident, which had taken place after an operation to repair a leak in an interstate natural gas pipeline. In this operation, a partial encirclement reinforcement (patch) was welded to the carrier pipe according to an available hot taping procedure, while gas was flowing in the pipeline. The failure analysis commenced with preliminary steps of gathering of background data regarding the repair operation and then several samples were extracted for macroscopic and microscopic metallurgical examinations. In addition to fractographic analyses of fracture surfaces, pipe material was examined because the pipeline had been in service for prolonged period and there was not any official material information available. The analyses disclosed that hydrogen-assisted cracking, wrong design of branch connection, paint coating and pipeline operating conditions were major factors contributing to the failure.
 

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In this research, the effect of different welding parameters on residual stress and microstructure of the weld region, as well as the comparison of two methods of measuring residual stress using critical fracture longitudinal wave method and preformation method have been investigated. For this purpose, the taguchi DOE methodology is used as a statistical method to optimize four parameters of pulse current, base current, and pulse on time% and pulse frequency to minimize longitudinal residual stresses in austenite 304 AISI stainless steel. After welding, stress measurements were performed using two methods critical fracture longitudinal and perforation, and hardness, tensile and OM tests were performed on the specimens. The tests results show that at all levels of the pulse parameters arranged with the standard L9 Taguchi array, the incident heat input is irrefutable and the effect of this parameter is move then 50%. The optimum conditions obtained while the highest frequency level should be considered. The general trend is achieved from the residual stress measurement charts is consistent with the logic of stress distribution in both methods. Sample number 1 with stress equivalent to 232 MPa and sample number 9 with stress of MPa 126 in ultrasonic method with frequency 4 MHz have the highest and lowest stress among different samples, respectively. The size of the coaxial grains weld was directly related to the incoming heat, so that the least amount of coaxial grains in the welding center was related to specimens NO. 3 and 9 with grain size of 8 µm and 9 µm, which in these samples had the lowest amount of welding heat is measured. The samples 1 and 4 with HV 128 and HV 144 hardness and MPa 633 and MPa 639 have the least hardness and tensile strength and the highest strength and hardness of sampled 3 and 9 with 166 and 161 hardness and tensile strength MPa 703 and MPa 695.
 

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Nowadays, due to the need for miniaturization, small scale resistance spot welding is of interest. The key factor that determines the nugget size is contact resistance. In this paper a new equation is provided to calculate the electrical contact resistance. The model can predict the high temperature contours and the nugget configuration efficiently. Also, a set-up was constructed to verify the model and investigate the effects of parameters on the mechanical properties of Hastelloy X welded joints. DOE analysis is done to recognize the effect of parameters on the nugget diameter, maximum load, and nugget height. It was concluded that the size of the nugget enlarges by increasing welding current and time. The nugget diameter decreases with increase of force.

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Cold roll bonding (CRB) is a solid state welding process, where the bonding is established by compressive plastic deformation of the metals. This process is applicable for a large number of materials. In addition, materials that cannot be bonded by traditional fusion-based processesmight be bonded by CRB process. In this research, cold roll welding of brass and IF steel was studied .The effects of process parameters such as reduction of thickness, pre-rolling annealingconditions and surface roughness on the mechanical propertiesof welded strips were investigated. The peeling and shear punch testswere used to investigate the mechanical properties of welded samples .It was observed that the bond andshear strengthswere enhanced by increasing the reduction and surface roughness. Also, annealing treatment before the CRB process increased the bond strength anddecreasedthe shear strength. Finally, optical and scanning electron microscopes were used to evaluate the fracture surfaces of the tensile and peelingtest specimens.

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In the present research, the parameters of FSW process were optimized for the mechanical properties of thin aluminum- scandium alloys by a design of experiment (DOE) technique. The optimum conditions providing the highest mechanical properties were found by this method. Among the three factors and three levels tested, it was concluded that the tool rotational speed had the most significant effect on the mechanical properties and the travel speed had the next most significant effect. The effect of tool tilt angle was less important when compared to the other factors. The EBSD results demonstrated a recrystallized equi axial structure and the existence of a mixture of B and Ccomponents in the weld nugget.

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Galvanic corrosion is an ever-present problem in all different environments, particularly in tanks. The goal of this project is to develop a finite element model that can be used with experimental data to characterize the corrosion of a galvanic weldments couple in an electrolyte. In this study sample are welded by gas tungsten arc welding and friction stir welding. According to ASTM G8, Evaluation of corrosion properties examined with cyclic polarization test in 0.5 molar H₂SO₄ andthe information required to validate the model was prepared. The finite element model is developed using COMSOL and Math Module through derivation of equations describing corrosion thermodynamics and electrochemical kinetics. The results showed that reducing in heat input to improve galvanic corrosion behavior in the weld sample.In addition to result of simulation reveal sample that welded by gas tungsten arc method had higher current density galvanic corrosion in comparison with friction stir sample.

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Friction stir spot welding (FSSW) is a type of solid state welding that is used in the connection of small pieces and light metals such as aluminum alloy especially. The technical problem during melting of aluminum alloys is one of the most important reasons for developing application of friction stir welding for aluminum alloys. In this research, the effects of important processing parameters such as tool rotation speed, dwell time, plunge depth of tool and sheets thickness on the mechanical properties such as failure force and energy of FSS welded AA-3105 alloy have been experimentally studied using micro hardness and tensile tests. Tensile-shear tests show four different fracture modes of weld failure which consist of shear fracture, circumferential fracture, nugget pull out fracture and fracture in base material modes. The results show that the weld strength drops with increasing the tool rotation speed. Strength and hardness of weld and weld zone increase and then decrease with increasing dwell time of rotational tool which it can be obtained an optimum value of dwell time. Strength and fracture energy and load of welds increases with increasing the sheet thickness

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The effect of heat input of submerged arc welding process on the corrosion bahavior of weld metal of API X42 gas pipeline steel weld joint was investigated. For this purpose, 6 annealed sheets of 15mm thickness were prepared from the X42 microalloyed steel. Submerged arc welding process with varying heat input of 37.8, 18.9 and 12.6 kJ/mm was used for joint welding. Then potentiodynamic polarization and electrochemical impedance spectroscopy methods were used to evaluate the corrosion behavior of the welded joints (in 3.5% NaCl solution). The evaluation of the microstructures of the welded metals in the weld joints were conducted using the scanning electron microscopy. X-ray diffraction was used for the analysis of the phases formed in the weld metal microstructure. Scanning electron microscopy observations and patterns obtained from the X-ray diffraction showed that the increase in heat input resulted in the increase in the amount of ferrite. The grain size also increased. Corrosion test results showed that by increasing the heat input of the weld process, the corrosion resistance increased..

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In this research  the effect of heat treatment offer welding (PWHT) in 650,750 and 8500C for two hours on Sulfide stress corrosion cracking resistance (SSC), welding metal Inconel 625 to low alloy steel 4130 was analyzed that was welded using Automatic TIG welding process then the mechanical properties of the joint was observed using micro hardness measure experiment (weld metal, base metal and the welding heat-affected zone) and welding metal structure using light microscopy, electron SEM(EDX), also XRD. The comparison of the microstructure in different temperatures show the least effect on microstructure in 6500C. In micro hardness measure test after post-weld heat treatment (PWHT) with increasing temperature we observed decreasing hardness of base metal and heat-effected zon and alsoincreasing weld metal micro hardness. when the temperature of post-weld heat treatment reached to 8500C phase γ" changed quickly to delta phase δ.when temperature reached to 8500C secondary phases changed to needle form. After stress testing in Sulfide environment magnetic particles (MT) was done on the samples and results showed that in the post-weld heat treatment sample 8500C tension crack is made. Pictures of stress testing(SSC) SEM sample shows that tension cracks mode is base metal cracks along the grain boundaries and it also extends the base metal to weld metal.

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In this paper, numerical and empirical investigations of the effect of AISI 347 stainless steel interlayer on the microstructure, mechanical properties and fracture mode of AISI 321 stainless steel resistance spot welds have been conducted. For this purpose, two types of joints, the first free from inter layer and the second contains interlayer with 0.05 mm thickness as well as difference currents and times,were evaluated. In order to examine the mechanical properties including maximum force and tensile mode, tensile – shear test of the spot welds was done. The obtained results indicated that an increase in the welding time and current resulted in a change in fracture mode from interfacial to peripheral owing to an increase in fusion zone volume. The change in the chemical composition because of the presence of interlayer and an increase in cooling rate caused the formation of different phases as well as observation of the dispersed Martensite phase in fusion zone.
 

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In this research, the dissimilar welding of St52 plain carbon steel to W400 wear resistant steel and its effect on the microstructure and wear properties of the wear resistant steel was investigated. The wear resistant steel was produced via direct quenching with nominal hardness of 400 HB. Gas tungsten arc welding was used for joining process. The results showed that welding led to hardness reduction, wear rate increase and also significant changes in microstructure of the heat affected zone of the wear resistant steel. According to the results, by increasing the heat input for about 9%, the hardness and wear rate of the heat affected zone was decreased 8% and increased 250%, respectively. According to the scanning electron microscopy observations the main wear mechanisms of the base metal were adhesion and abrasion. However, the wear mechanisms of the heat affected zone were mainly adhesion and delamination. By increasing the heat input, the delamination was increased significantly. 

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In this research, gas tungsten arc welding of dissimilar joint between 4130 low alloy steel and AISI 201 austenitic stainless steel was investigated. Four filler metals i. e. ERNiCr-3, ER 309L, ER 308L and ER 80SB2 were used. After welding, microstructural features of various areas and also fracture surfaces were examined using optical microscopy and scanning electron microscopy. Tensile test was conducted in order to study the mechanical properties of each joint. It was found that ERNiCr-3 is fractured from fusion zone and the others were fractured from 4130 base metal. Also, some second phase particles such as NbC were seen in the ERNiCr-3 weld joint. SEM observation showed that the fracture behavior of ERNiCr-3 weld joint is semi brittle and the others are ductile. The fusion zone of ERNiCr-3 weld joint was fully austenitic and consisted of equiaxed grains and no crack was seen in this area. The fusion zone of ER 308L and ER 309L were composed from cellular dendrite and finally ER 80S-B2 weld joint was consisted of lath martensite.

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The purpose of this study was to examine the effect of adding Nano particles such as Nano Carbon Tube during Friction Stir Welding (FSW) on dissimilar Al alloy joints. More specifically, both FSW and Friction Stir Processing (FSP) were performed simultaneously to investigate the effect of adding Nano particles on mechanical properties and microstructure of the weld zone for joining AA5754-H22 and AA6063-T4aluminum alloys. Reliability of the joints was tested by non-destructive tests such as visual inspection, ultrasonic, and radiography. The global mechanical behaviors of dissimilar welds were similar to that of the base material. Important losses in ductility were also reported for dissimilar welds. Microstructural evaluation of fractured surfaces indicated that ductile fracture was the major mechanism of similar and dissimilar welds. We expected that the locks for dislocation moving would improve the mechanical properties of the weld zone. Also, the friction coefficient in the two-passes welded sample was about 30% lower than the friction coefficient of the base metal. On the bases of the wear resistance of hardness and the coefficient of friction, it was concluded that the wear resistance of the surface Nano-composite produced had also increased in the stir zone.

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In the TIG-MIG hybrid welding, higher weld efficiency and better weld quality are obtained with respect to each individual TIG and MIG welding methods. Moreover, in this method, the MIG arc is more stable in pure argon shielding gas. Therefore, in this study, the influence of TIG-MIG hybrid welding parameters on the welds appearance quality and welds depth to width ratio of a 316L austenitic stainless steel was investigated using optimum parameters of Taguchi design of experiments (DOE). Microstructure of the heat affected zone (HAZ) obtained from the hybrid welding was compared with those of each individual MIG and TIG welding techniques under equal heat-input condition. The results indicated that the most important parameter in the hybrid method to obtain the best appearance quality and the highest depth to width ratio is the distance between the two arcs. The MIG and TIG currents are the next influencing parameters. The width of HAZ and the size of constituent grains in hybrid welding with optimum parameter, were smaller than those of each individual TIG and MIG processes due to the higher associated cooling rate in the hybrid welding technique.

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Solid state joining of powder metallurgy (P/M) processed and sintered by spark plasma sintering through friction stir welding (FSW) was studied. The nanocomposites were prepared via mechanical milling followed by spark plasma sintering. The microstructural and mechanical of the joints were evaluated as a function of the different processing parameters such as rotating and advancing speeds of the tool. The achieved finding revelled that the FSW of the nanocomposites produced by P/M containing bimodal sized Al2O3 reinforcement have a working window are affected by the heat input. The joint evolution revelled that the microstructure and mechanical properties of those was related to the generated heat input during the welding. It is known that dynamic recrystallization (DRX) caused grain size refinement of aluminium into stir zone. Meanwhile, it was revealed that the pinning effect of Al2O3 nanoparticles retarded grain growth of the recrystallized grains caused by dynamic recrystallization (DRX)