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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The aim of this study was to evaluate the mechanical properties and corrosion behavior of friction stir welding (FSW) connection of A517 (B) steel plate. Mechanical properties and corrosion behavior of weld zone were evaluated after reaching to optimum FSW microstructure with the lowest martensite phase. Thus, after the identifying phase microstructure by SEM and XRD analysis, mechanical properties were analyzed by micro-hardness and tensile test. Micro hardness data shows slight increases in stir zone (SZ) compared with the base metal (BM); although a reduction of about 17% in hardness of heat-affected zone (HAZ) was sensible. Reduction of hardness in the HAZ was appeared as drop by about 12 percent of the yield strength and 19 percent of ultimate strength compared with BM. SEM images from fracture surface of the tensile sample showed bi-modal distribution of large and small Dimples being sings of softness of HAZ .Comparing corrosion behavior in solution consist of 3.5 wt% of NaCl showed that there was no passive layers to prevent dissolution of the metal in the SZ and BM. while BM and SZ had fairly similar corrosion rates, Difference of 50 mV between corrosion potential of SZ and BM showed that in galvanic condition, corrosion resistance of BM could be lower than SZ.

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In this research, lap joint frictionstir welding of IF sheets with thickness of 0.7 mm is investigated. For this purpose, mechanical properties of joints and also microstructural evolutions are studied. It was found that increase in tool rotational speed and decrease in travel speed results in increase in fracture stress of welded joints. Texture study indicates that no changes can be observed in texture components after friction stir welding. This phenomenon in texture components can be related to high stacking fault energy of IF steel and consequently severe dynamic recrystallization during welding. The results show with increase in the tool rotational speed between 900-1400 Rev/min, ultimate force of fracture of friction stir welded joints is increased. Also, it is concluded from results that with increase in tool travel speed between 50-160 mm/min, ultimate force of fracture of welded joints is decreased. Finally it is proved from results of this paper that in the frictionstir welding of IF sheets with thickness of 0.7 mm, maximum force of fracture of welded joints is achieved in rotational speed of 1400 Rev/min and travel speed of 105 mm/min.   

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In this study, commercially pure titanium and aluminum alloy 5083 in connection rotational speed of 1120 rpm and a feed rate of 50 mm per minute for butt welding by friction stir welding has been successfully completed. Micro-structure, hardness and tensile test was conducted on the connection. Welding area is a composite of aluminum and titanium particles that the particles plays an important role in increasing hardness and tensile strength. Welding area is also has three areas. Vickers hardness is 480 times the area of welding means that the hardness in the area of the base metal of titanium and aluminum increased by 16% and 60% for titanium aluminum intermetallic compounds is created in the area is weld.

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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 effects of linear speed and rotational speed of the friction stir welding tool was investigated on the heat generation and distribution of heat,the material flow and weld defect formation of the Polyamide 6 (PA6) workpiece. The commercial CFD Fluent 6.4 software package was used to the simulation of the process with computational fluid dynamic technique. The output results of the simulation showed  higher proportion of rotational speed to the tool linear speed, the material flow in front of the friction stir welding tool became more and the dimension of the welding stir zone became bigger. The maximum simulating generated heat was 220 centigrade degrees and the maximum head and material flow were observed at the advancing side of the join surface. The obtained simulation results were compared with other researchers' experimental results and the simulation outputs displayed acceptable agreement with experimental results.

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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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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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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)

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Friction  Stir Welding  is one of the solid-state processes and today it has been used to join different types of materials. Friction stir welding does not have many problems and limitations due to melting and solidification of weld metal and by controlling its variables, the microstructure and desired mechanical properties can be achieved at the joint. Recently, in most industrial areas, due to its lightness and energy saving, much attention has been paid to the joining of aluminum alloys. The present study investigates the microstructure and evaluation of mechanical properties of friction stir welding in AA2024 and AA6061butt welds. A cylindrical threaded tool was used to join 5 mm thick plates at rotational speeds of 800, 1000 and 1200 rpm and traverse speeds of 30, 50, 70, 90 and 110 mm / min. In order to perform the necessary investigations, metallurgical observations were performed by optical microscope and scanning electron microscope equipped with a chemical analysis system of the elements, as well as mechanical tests of tensile strength and micro hardness. The results showed that the difference between the two alloys causes hardness variations in the nugget zone and a large hardness drop at the transition between the zone composed of both alloys and the 6061 zone. By increasing the traverse speed from 30 to 110 mm / min at constant rotational speeds of 800, 1000 and 1200 rpm, due to reduced input heat, the grain size decreases and the hardness and strength increase. Also, the highest tensile strengths and hardness were 221.6 Mpa and 111.05 Vickers, respectively, for a sample welded at a rotational speed of 1000 rpm and a traverse speed of 110 mm / min.

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In present study, the effect of heat treatment after friction stir welding dissimilar welds T6-7075 and T4-2024 aluminum alloys were investigated. Friction stir welding was performed at a constant rotation speed of 1140 rpm and welding speed 32 mm/min. After welding samples are taken under various heat treatment processes at different aging temperature and time period. Microstructural observations, phase analysis characterization and mechanical properties were performed on welded before and after heat treatment in cross section of welds joint. The results showed that post-weld heat treatment causes abnormal grain growth turns destructive effect on the mechanical properties, while formation of fine and uniform precipitation recovery strength and ductility of welds joints. It is found heat treatment based on T6-7075 and T6-2024 procedure has highest and lowest impact on the restore of weld strength. Tensile test indicate that fracture occurred on the interface between TMAZ and HAZ in retreating side (7075) at as-weld joint, if that failure happens in the stir zone by applying PWHT. Surface fracture suggested fractures in PWHT samples are predominantly inter-granular, while in as-weld joint the fractures of joints are mostly trans-granular.

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In the present Study, a dissimilar joint of carbon steel sheet EN 10025 with 316 L has been welded by FSW and the welding parameters were optimized by RSM software method. For investigation of mechanical properties and microstructural analysis carried out by using optical, scanning electron microscopes with EDS analysis, tensile and hardness test of different area of joints, SZ, TMAZ, HAZ, their interfaces and Base metal. The optimized result were shown that best of joints within maximum strength (UTS) 312 MPa by rotational speed 950 rpm, transverse speed 90 mm/min and tool angle 3° was achieved. The failures were happened at base metal of EN 10025 to advancing side. Metallographic results were shown that grain size at SZ is 10 to 20 time more reduced caused improved of mechanical properties. Also chemical analysis and hardness result on welded samples by optimized parameters were shown that quite good mixing was happened at SZ.

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In this study, friction stir butt welding of Mg and Al alloys with applying Zn interlayer was performed. To obtain optimum condition, a combination of two travel and three rotation speeds were selected. Mg-Zn and Mg-Al-Zn IMCs, Al solid solution and residual Zn, were the most common phases in the stirred zone, which eliminated the formation of Al-Mg intermetallics. The maximum mechanical properties were achieved for the joint fabricated at 35 mm/min and 600 rpm, caused to 24% improvement in tensile strength and around 3 times enhancement of elongation compared with Zn free sample FSWed at the same conditions. The fracture micrographs were consistent with corresponding ductility results. Fracture surfaces of Zn-added samples presented a fine texture with a mixture of brittle and ductile fracture feature, which was different from the coarse cleavage plane and fully brittle fracture of the joint without Zn interlayer. 

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Dissimilar joint with good quality and mechanical properties is one of the major problems the industries. One of the most commonly used methods to solve this problem is friction stir welding process. In this paper two different tool pin with simple cylindrical and screwed profile were used to finding optimization of friction stir welding parameters to reach best mixing flow, composite structure and maximum tensile strength in dissimilar joint between AA6065 aluminum alloy and pure copper. In this research 1130 rpm tool rotation, 24, 40 and 65 mm/min travelling speed, 0.3 mm plunge depth and 3o tool tilt angle were carried out. The results shows that internal material flow that produced with screw pin was better than simple cylindrical in constant process parameters. According to the results, at lower tool travelling speed the strength of joint increases. The tensile test results revealed the maximum strength of joint of screw pin was 345MPa with 2.6mm elongation and simple cylindrical pin was 272MPa with 2.2mm elongation which welded with 1130 rpm and 24 mm/min travelling speed.

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In this study, the effect of tool's advance velocity on the mechanical behavior of the Al-7075 alloy during friction stir welding was simulated. In this simulation, the Lagrangian method with rigid-Visco-plastic material was used. The results of the process temperature obtained by the simulation method were verified by the experimental welding test. Using the characteristic stress, strain and temperature relationships in the Al-7075 alloy, the changes and the relationship between the material strength during the welding process by simulation was studied. The generated simulation defects was verified by experimental test.

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Friction stir welding (FSW) was conducted on AISI 304 austenitic stainless steel plate with 2 mm thickness. The FSW was performed at a welding and rotational speeds of 50 mm/min and 400 rpm, respectively. Microstructure observations by the optical microscopy showed that a severe grain refinement occurred in the stir zone (SZ). Electron backscattered diffraction analysis (EBSD) results indicated that high fraction of low angle grain boundaries (LAGBs) developed in the thermo-mechanically affected zone (TMAZ) through the occurrence of the dynamic recovery. Moreover, in the path from the TMAZ towards the SZ, the fraction of high angle grain boundaries (HAGBs) increased with decreasing the fraction of LAGBs through the occurrence of continuous dynamic recrystallization (CDRX). 100 Pole figure showed the formation of shear texture components of A*1 and A*2 in the SZ which implied the occurrence of CDRX mechanism.
 

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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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Today in addition to Join by friction stir welding, the composite fabrication process is also performed simultaneously. The main purpose of the present research is to investigate the effect of pin geometry on the property of Aluminum 6061- alumina nanocomposite created by friction stir welding. For this purpose friction stir welding was carried out by selecting five types of pin geometries on Aluminum 6061 in which Al2O3 particles were deposited and the samples were examined by tensile and hardness tests, optical and electron microscope. Samples were investigated by tensile and hardness test, optical and electronic microscopy. Regular hexagonal pins due to having six smooth face and impulsive movement during rotation, caused a good perturbation which resulted in maximum tensile strength and elongation percentage of 198 MPa and 10.25 and minimum grain size of 13.3 micron, respectively. In the sample welded by a threaded cylindrical pin due to non-impact during rotation, inappropriate flow of reinforcing particles and its accumulation at perturbation the lowest tensile strength and elongation percentage of 133.5 MPa and 1.95%, respectively, were observed.

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Friction stir welding (FSW) is an economic and high quality technique at aluminum welding and joining methods. The most important factor in the soundness of this type of welding, is the mechanism of material transfer in each tool rotation. The materials transfer during the welding process involves horizontal and vertical movement that caused by extrusion process and forging force (the tilt angle due to forging force and on the other hand, shape of pin due to the extrusion process). One of the most important parameters in FSW process is the effect of rotational speed in the welded zone. In this study, the effect of rotational speed at constant welding speed, in the butt joint of pure commercial aluminum, was investigated. The results of the study showed that, increasing the rotational speed due to increases the amount of material transfer in the weld zone. The welded zone was investigated by appearance weld zone experiments and using radiography tests. Also weld zone was investigated in macro and microstructure by using cross section. Then the micro hardness testing has been used by cross section at welded zone. In order to investigate the mechanism of materials transfer during the process, the electrical resistivity test has been used to analyses the amount of materials transfer in the weld zone. Results shows that, increasing rotational speed due to increasing the amount of materials transfer in the weld zone and decreasing the amount of defects in the weld zone.