Electroslag welding is widely used in column joints. However, the process of Electroslag welding has a higher heat input than other welding processes, which results in dramatic changes in microstructure and mechanical properties, especially grain size and toughness. These connections are very vulnerable when subjected to dynamic loads and earthquakes. Therefore, the study of heat transfers and its effect on the mechanical properties of these joints is important. Considering the importance of this, in the present study, a finite element model is proposed to study the thermal behavior of this process, then the accuracy of the model is measured according to the practical experiments of the microcontroller. For verification, several practical examples of welding were performed and then, to evaluate the size of the pit pool, welded sections of the macrovar were prepared to confirm the assumptions of the model. In the next step, the validated model is used to study the thermal behavior of the system and the distribution of temperature according to the variables of current, voltage and speed. In this regard, due to the complexity of the process, it is not possible to carry out all simulations with software menus, so much of the simulation was written with the language of the ANSYS software.

This study focused on the effect of Electroslag remelting process (ESR) on microstructure and composition of as-cast Cu-Cr-Zr alloy. The results revealed that applying ESR process resulted in a more uniform distribution of alloying elements. However, slight aggregation of large precipitates and inclusions existed in as-cast ingot. It was observed that impurities like P, S and Mg which had significant effect on electrical property were eliminated after ESR process. Moreover, further optimization of alloy composition which in turn would affect its mechanical and electrical properties was obtained through using ESR technique, successfully.

Welded tubular joints are widely used in various industry structures for high efficiency subjected to pressure, bending and twisting. Welded structures are the main parts of structures, buildings, bridges, gas pipes, pressure vessels and power transmission equipment in the ship building, construction, oil, gas, petrochemical industries and power plants. A sample of pipe-welded joints is a X-tubular joint that has been investigated in this study. The main objective of the present work is to investigate the heat transfer and residual stress caused by the three-stage welding process in Xtubular joint made of St52 using Simufact welding software. The welding process involves three welding steps using arc welding. The finite element model contains the thermal and mechanical properties of base metal and welding metal as a function of temperature. Also, advanced modeling tools such as mesh adaptation during the process and meshing compatible with the welding site, the birth and death technique of the element and the source of heat transfer have been used. welding simulation showed that significant residual stresses were created in the joint after welding. Comparison of the results shows that the numerical results and empirical measurements are in good agreement with each other and the existing model can provide a good prediction of temperature distribution and stress control in this welding process.

In welding process, stresses after cooling, which remain in body, are called residual stresses. Sometimes, the magnitude of stresses is high and reduces the strength of welded pieces, moreover, they cause crack in the weld. To predict welding residual stresses, it is necessary to do thermal and mechanical analysis.In this paper, some parameters which influence the welding using ANSYS software are investigated. Results show that even by decreasing the travel speed of torch, it makes no differences in the amount of residual stresses, but preheating causes decreasing the produced stresses about 22 percentages. Suitable welding sequences also, decreases residual stresses up to 25 percentages.

Friction stir welding (FSW) can be defined as a green technology, because the consumption of energy during this process is less than other welding methods. In addition, during the process there is no gas, filler material or other consumables. It should be noted that, complex curved shapes are now commonly used in different industries in a bid to have lightweight structures. According to the above-mentioned descriptions, several investigations into the potential benefits of adopting Friction Stir welding (FSW) in the production and joining different materials are being undertaken. The work presented in this paper is focused on thermal behavior of the curved FSW and its benefits for the green technology. Due to the robust nature of FSW process aluminum 6061-T6 alloy has been selected as the welding material. The results of the study showed that, the total peak temperature value of 300° C happened at time, t = 3 s at the plunge stage (outside of the welding seam). Meanwhile, at the dwell stage (between t = 3 s to t = 5 s), there is a stable situation in the amount of the generated heat from the plastic deformation as well as the contact shear stress at the tool-workpiece contact interfaces, thus the interfacial temperature is found to be stable. By the end of the dwelling step, the total generated heat is stable to the maximum value of 300° C. At the step time of t = 12. 8 s, the temperature is distributed asymmetrically across the workpiece until the time step of 19. 6 s which at this point the asymmetric contour expanded in the stir zone.

The main purpose of this study is optimization of resistance spot welding of AZ61 Mg alloy to achieve maximum nugget size and minimum tensile residual stresses in welding area. Since the stability and strength of a welded structure is strongly dependent on the nugget size and the residual stresses, an integrated artificial neural networks and genetic algorithm is utilized to optimize the welding parameters. In this study, the resistance spot welding process is simulated by a 2D fully coupled structural-electrical-thermal finite element model. The finite element model is developed to predict of the nugget size and the residual stresses in the welding area. In order to validate the FE model, the results are compared with the obtained results from the experimental tests. The results show that the FE model has a good agreement with the experimental tests. The input parameters for optimization are: electrical current, welding time and electrode force. The results show that the integrated optimization algorithm is successful in determining the optimized welding parameters. Based on the optimization results, the maximum nugget size 6. 33 mm and the minimum tensile residual stress 228 MPa are achievable by using 16kA, 16 Cycles and 848 N as current, welding time and electrode force respectively.

Some Micro structural Aspects of Explosive welding Interface between Aluminum and Steel which welded in Different Conditions have been studied. Wavelength, amplitude and Interlayer Phase Dimensions Formed in the welding Interface have been measured by means of an Optical Microscope. By Comparing Welded Samples, it is Determined that the Greater Stand off Distance, the Larger Interface Dimensions, But Interface Wavelength and Amplitude have not been Changed with Stand off Distance Variations. It has been concluded which an Increase in Explosive Mass and a Decrease in Flyer Tube Thickness, Will Result in Increase in Wavelength and Amplitude and Interlayer Phase Dimensions.

The application of ultrafine-grained or nanostructured aluminum is very interesting owing to its high strength to weight ratio. welding of these materials is one of the main challenges. Regarding the potential of the solid-state friction stir welding in joining of nanostructured materials, in the current research different equipment and techniques like optical and scanning and transmitted electron microscopes, Vickers microhardness, and uniaxial tensile tests were employed to study the effect of major welding parameters on the bonding quality of friction stir welded ultrafine-grained Al 1050 alloy produced via accumulative roll-bonding (ARB) method. The studied parameters were rotation and traveling speeds, pin geometry as well as welding atmosphere temperature. The results show the microhardness enhancement of the weld zone by decreasing the rotation speed or increment of traveling speed due to lower heat generation within the stir zone. Investigation of the pin geometry depicts an insignificant impact of this variable on the weld tensile properties. Only in the case of a threaded pin, a slight enhancement in the tensile properties was achieved. Submerge or underwater welding could improve joint strength. However, the application of extremely cold water with respect to 25°,C water shows a reverse effect and leads to severe weld quality degradation owing to defects formation (like internal channels and surface discontinuity).