Journal of Welding Science

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Today, steel to aluminum joints are used to facilitate transportation and fuel consumption. These joints are applied from nuclear, aerospace and naval to automobile and kitchen industries. According to previous studies fusion welding processes are not suitable methods for these joints, solid-state welding, especially friction stir welding, is a proper way to use for these joints. However, using this method for these two metals needs adequate prediction of temperature distribution and material flow to obtain enhanced joints. In this study, a finite element method is used to predict the temperature distribution. In addition, a computational fluid dynamics solution is coupled with the thermal solution. Therefore, the flow rate, strain rate and dynamic viscosity is obtained. Also, the joint morphology is predicted using the Level Set method. It is shown the material flow depends on flow rate, strain rate and dynamic viscosity and is intensively function of rotational speed. Additionally, offset to the aluminum side improves the morphology of the stir zone.

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High-strength low alloy steels are a class of steels used in applications that require high strength and good weldability, including ship hulls, gas pipelines and oil industry. One way to build parts is fusion welding that create areas with a large grain size in the heat-affected zone and increased susceptibility to hydrogen cracking. One way to solve this problem is to use solid state friction stir welding process. In this study, microstructural evaluation and mechanical properties of friction stir welding X-60 cross sections examined by optical microscope and by tensile and micro-hardness tests. The results indicate that changing welding parameters and thereby, change the heat input during friction stir welding have a great impact on maximum temperature and cooling rate that cause creating ferrite and bainitic ferrite in the weld zone. This change in microstructure of weld zone cause to improve mechanical properties that increase yield strength from 380 MPa to 420 MPa .Also, the friction stir process cause increasing hardness of 220 Vickers to an average of 280 Vickers and uniform distribution of hardness in the cross-section of friction stir joints.

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In this study, the corrosion behavior of super duplex stainless steel UNS S32750 and tungsten arc welding with filler metals AWS ER2594 duplex stainless steel in acidic solution containing chloride ions have been investigated. Microstructure of weld joints evaluateby light and electron microscope and corrosion behavior examine by open circuit potential and cyclic polarization tests.The results showed that increas in heat input leads to a change in the distribution of alloying elements, formation of intermetallic phases around grain boundaries and the shifting balance between austenite and ferritein phases in weld region. Based on the cyclic polarization tests, cross-weld and base  metal active behavior and have good corrosion resistance due to the presence of high alloying elements. As well as increase in heat input leads  to  an increase in current density and decrease in the pitting potential.

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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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Transient liquid phase bonding of  UNS S32750 super duplex stainless steel to AISI 304 austenitic stainless steel using BNi-2 interlayer was carried out at 1050 oC for 45 min. Microstructure analyses of the joint were carried out using optical microscopy, scanning electron microscopy and energy-dispersive X-ray spectroscopy. Microhardness indentation and shear strength test were performed to assess mechanical behavior of the joint. No eutectic contents was seen at the joint and thus Isothermal solidification was completed at 45 min bonding time. The shear strength of the joint was about 0.7 of duplex stainless steel shear strength. Froctographic studies revealed that the fracture mode was completely ductile in the case of the joint made at bonding time of 45 min.

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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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In this study, corrosion behavior of Ti-6Al-4V titanium alloy joint by friction stir welding with a rotational speed of 375 rpm and a travel speed of 100 mm/min was investigated. The welding procedure was carried out under β-transus temperature that was consisted of equiaxed grains in the stir zone. The corrosion behavior of the welded joint was investigated in 3.5% NaCl solution at temperatures of 25, 37 and 80 . Microstructure investigation of sample surfaces after electrochemical experiments was conducted using SEM. results revealed that the β phase was mainly corroded at all three testing temperatures, however the corrosion in the sample tested at 80 °C was more considerable.

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