جستجوی مقالات مرتبط با کلیدواژه « جوشکاری اصطکاکی اغتشاشی » در نشریات گروه « مکانیک »

In this paper, the effect of including SiC nanoparticles in the weld zone on the maximum shear strength of friction stir lap welded 7075 aluminum alloy is investigated, both experimentally and numerically. This objective is carried out by studying the effects of rotational and transverse speeds, tilt angle, the shape of the tool and the penetration depth. The numerical investigation is based on developing an FE model by means of Deform and ABAQUS to simulate the welding procedure, which results are verified by the experimental findings. Experimental procedure is designed based on Taguchi method. The verification of the developed FE model shows that the simulation results are in proper agreement with the experimental findings. In general, including SiC nanoparticles in the weld zone can increase the maximum shear strength up to 24%, compared to the case of where the specimens are welded without SiC. Furthermore, applying the threaded tapered tool leads to higher shear strength in comparison with the squared shape tool, i.e., the strength of the specimens welded by threaded tapered tool are 4 to 5% higher without SiC inclusion and 4 to 7.5% higher with SiC, compared to the same case welded by squared tool. In addition, while the rotational speed has the highest influence on the findings, the tilt angle does not affect the results that much.

Additive manufacturing is a set of modern manufacturing technologies with a novel revolutionary point of view that addresses most of limitations that were around due to using conventional manufacturing methods. Due to the lack of references for additive friction stir manufacturing, in the present paper the new developments in friction stir additive manufacturing of metals, alloys, and metal matrix composites are presented and summarized. Friction stir additive manufacturing is a solid-state process that yields a dense and homogeneous structure with a significant microstructural refinement with no fusion defects such as shrinkage cavities, porosity, and cracks. The rest of the paper was arranged as follows: friction stir welding is discussed as the base technology. Then, the two additive manufacturing methods that are based on friction stir welding, i.e. additive friction stir manufacturing and additive friction stir deposition are presented.

In the present study, a rigid viscoplastic finite element model based on Lagrangian and remeshing methods was developed to simulate the dissimilar friction stir welding of AA5083-O and AA6061-T6 aluminum alloys. Then, a combination of Cellular Automata (CA) and Laasraoui Jonas (LJ) methods was used to investigate the microstructural evolutions of materials with regard to the thermo-mechanical conditions engaged in the process. Moreover, the point tracking method was used to evaluate the flow pattern of the material around the tool and the results were compared with experiment which the elongation and movement of the material towards the upper part of the advancing side was observed for the stirring and mixing of the material. By studying the dynamic recrystallization in the simulation, the simultaneous effect of temperature and severe plastic deformation on grain refining was investigated. The results of microstructural changes showed that with increasing Zener-Hollomon (Z) parameter, grain size decreases and changes the hardness and strength of the alloys used. Also in the mechanical test, the decrease in strength at the advancing side caused the samples become fractured from this side in the tensile test.

Solid-state welding and processing methods will be an alternative to joining lightweight metals that cannot be welded using conventional fusion welding processes. After three decades after its invention, FSW is the first choice in joining high-strength aluminum alloys with an application in automotive and aerospace. The process is also capable of joining other alloys too. Due to the success of FSW, it was considered for more complicated applications and joining high-strength alloys. It should be noted that FSW is not the only successful rotary friction-based solid-state welding process. In recent years, friction hydro-pillar processing (FHPP) which is successful in repairing surface and body cracks and defects of different steel grades is also very interesting. In the present study, main rotary friction-based welding and processing methods are introduced and discussed in two major classes including friction stir welding and friction hydro-pillar processing.

The friction stir welding method was first developed in 1991 at the British Welding Institute as a solid-state bonding method and employed for welding aluminum alloys. This method has high energy efficiency and good compatibility with the environment. In general, the frictional stir welding process is suitable for metals with a low melting point, whose melting welding is not of good quality. In this research, multi-objective optimization of the mechanical properties in the friction welding of AH12 1050 aluminum alloy has been performed experimentally using a combination of response surface methods and multi-objective particle swarm optimization. The Taguchi method has also been utilized to design experiments with two types of threaded cylindrical and simple tapered pins. Pin diameter, shoulder diameter, tool rotational speed, tool feed, and tool deviation angle are selected as the process variables. Specimen strength, toughness, and hardness are considered as objective functions. The optimization results and a prediction accuracy of more than 93%, show a good agreement between the surface prediction model and the experiments despite the complexity of the process.

Friction stir welding is a solid-state bonding technique based on two factors, a pressure greater than the material yield stress and large plastic deformation. The final joint between parts takes place in different welding geometries by using these two factors. The grain sizes in the weld areas are influenced by recovery, recrystallization, and grain growth. In the current research, using an analytical-numerical method based on finite element simulation of friction stir welding of AA6061-T6 alloy, the grain sizes in various welded areas have been predicted. The finite element simulation has been performed based on the coupled Eulerian-Lagrangian approach using ABAQUS software and the results have been verified by experiments. The predicted results were in good agreement with the experimental results. Due to the concentration of heat and plastic flow in the central region of the weld, the stirring region had the most microstructural changes and the grain size in this region decreased more sharply than other different areas of the weld. As the rotational welding speed increases, recrystallization phenomena in the central weld area increases. With increasing the translational welding speed, grain size increased in different welding areas. This increase occurred more severely in the central area of the welded joint.

The main aim of this experiment is to determine the mechanical and microstructural of using Nano powder of Al2O3 besides stir welding of Al2024-T6 in multi-pass welding. Nanoparticles welded nine specimens and one particle-free in 1400 rpm rotational speed and 16 mm/min traveling speed. A combination of volume percentage of powder (3%, 5%, and 7%) and three different multi continuous passes (1, 2, and 4) is applied for Nano-rich specimens. The microstructure of joint, micro hardness and ultimate tensile strength (UTS) of the welded joint has been studied. It was observed that by increasing the particle volume from 3% to 7% average grain size increased extremely to 37% and UTS to 10%, and in the staid situation of welding passes, average micro hardness has 10% increase in shoulder affected zone. The result showed that the specimen with 7% of Nanoparticles in two passes has the highest mechanical and metallurgical properties and has a significant decrease (55%) in average grain size compared with a particle-free specimen. Meanwhile, UTS and average micro hardness of the same specimen was about 11% and 48% more than particle free.

The thermal cycles involved in friction stir welding process cause softening in the joint of heat-treatable aluminum alloys. To overcome this limitation, submerged friction stir welding process has been developed. In this study, firstly, the butt joints were produced from Al7075-T6 alloy using friction stir welding process. To this end, the response surface methodology was selected as the experiment design technique. So, the factors such as tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were identified as the input variables. Then, a statistical analysis of variables affecting the tensile strength of joints was performed. Afterward, the butt joints were produced using submerged friction stir welding process based on the optimal values of tool feed rate and tool tilt angle. The obtained results from analysis of variance and regression analysis of experimental data confirmed the accuracy of regression equations. Furthermore, it is shown that the linear, interactional and quadratic terms of the tool rotational speed and tool shoulder diameter are effective on the ultimate tensile strength of the underwater welded joints. Also, the optimal condition of input variables was determined using the desirability method. In addition, the optimal condition has been confirmed by implementing the verification test.

In this study, aluminum-to-copper welding was performed by friction stir welding (FSW) process and then the mechanical properties of the joints were evaluated and compared with the ones rolled to reductions of 30 and 60 percent. Tensile strengths (UTS) of the joints were 99 MPa, 143 MPa, and 132 MPa, for the initial weld, 30% rolling reduction, and 60% rolling reduction, respectively and in the non-rolled weld specimen, fracture occurred from the aluminum base material but in rolled welds, the fracture occurred precisely from the weld interface. Microstructural studies of the weld region and fracture surface of the specimens showed that the Al4Cu9 and Al3Cu intermetallic compounds, which are the most common intermetallic compounds in this type of dissimilar joining, formed in these areas. The presence of these compounds at the weld interface and propagation cracking during rolling has been one of the important factors in the failure of the weld interface in the rolled specimens. Results of the hardness test also confirmed the existence of these intermetallic compounds. By increasing the percentage of rolling reduction from 30% to 60%, the welding strength decreased due to the increase in the number of micro-cracks of the intermetallic compounds. Finally, it can be said that by choosing the optimal percentage reduction in the rolling process (30%), can be significantly increased (about 43%).  the ultimate tensile strength of dissimilar Al/Cu joints produced by friction stir welding (FSW).

The thermal cycles involved in friction stir welding (FSW) cause softening in the joint. This phenomenon generally occurs in heat-treatable aluminum alloys leading to decrease in mechanical properties. Submerged friction stir welding (SFSW) has been developed to overcome this limitation. In this study, firstly, the butt joints were produced from Al7075-T6 alloy using FSW process. To this end, the RSM was selected as the experiment design technique. So, the factors such as: tool rotational speed, tool feed rate, tool shoulder diameter, and tool tilt angle were identified as the input variables. Then, statistical analysis and optimization of variables affecting the hardness of cross-sections was performed. In attention to the high value of desirability function (0.976), it could be found that the procedure of optimization has well fulfilled the pre-determined target. In addition, the optimal condition has been confirmed by implementing the verification test. Afterward, the butt joints were produced using SFSW based on the optimal values of tool feed rate and tool tilt angle. The obtained results from analysis of experimental data, confirmed the accuracy of regression equation. Furthermore, it is shown that the final model can predict the MHD parameter with an error less than 5%. Also, the linear terms of the tool shoulder diameter and tool rotational speed are effective on the hardness of cross-sections of the underwater welded joints.

Metal sandwiches are a new class of ultra-lightweight materials made from a porous metal core and two outer metal plates. High strength and high energy absorption capacity, resistance to heat, and also fast and inexpensive recyclability make these materials ideal for use in many industries including automotive, aerospace, oil, energy and construction industries. Considering the advantages of friction stir welding, the connection of these plates using this welding technology can be used industries for welding of bimetal sandwiches. In this research, feasibility of using frictional stir welding to prepare metal sandwiches with a core of aluminum foams and copper covers was investigated. The investigated parameters were tool rotational speed, in three levels of 2000, 2500 and 3000 rpm, and tilt angle in two levels of 5 and 7 degree. The cross-sections of the joints were investigated for weld quality which confirmed a successful joining. Tensile tests were carried out to evaluate the joint strength. It was concluded that the effect of tool rotational speed on the weld strength is much higher than the effect of tilt angle and has a reverse relation with tensile strength. The best strength which was 18.8 MPa was obtained with a tool rotational speed of 2000 rpm and a tilt angle of 5 degree.

The friction stir welding is a suitable substitute for gas metal arc welding for joining aluminum alloys in aerospace and shipbuilding industries. Recently a new friction stir welding method named floating bobbin tool friction stir welding has been introduced, that enables the implementation of this process with almost zero vertical force. Another advantage of this technique is the simultaneous double sided welding and the symmetry of the stirred region along the thickness. This paper focuses on the use of double sided friction stir welding technology with a floating bobbin tool for joining pure commercial aluminum. The tool used in this process was made from hot working steel with a hardness of 52 HRC. This tool has two shoulders and a threaded cylindrical pin. After performing the welding process, in order to assess the quality of the connection, non-destructive tests of visual inspection, radiography, as well as destructive tests of tensile, bending, hardness and metallography performed on a welded sample. Non-destructive tests confirmed the perfection of a welded sample with optimal parameters. The results of the tensile test showed that the connection efficiency was very significant and reached about 80%. In addition, the fracture strain of the welded sample was 80% higher than that of the base metal. Accordingly, the development and exploitation of this method provides the potential for the development of a low cost, solid state and reliable technology, and the feasibility of designing inexpensive equipment for mobile friction stir welding.

Increase of strength and development of aerial structures has long been of interest to researchers. In this study, to investigate the T-joint T6-6061 aluminum alloy using friction stir welding process, laboratory samples were made, and also the software simulations were performed to find out the appropriate amounts of tools dynamic effects. Fluent commercial software has been used to better understand heat generation and distribution in the welding process. For this purpose, the T6-6061 aluminum joint with different linear and rotational tools speeds was studied. Depending on the selected parameters in the process, the strongest connection was produced in the 1600 rpm rotational speed and 68 mm/min linear velocity. The failure place of all tensile samples was located on the aluminum T appendage. Tunnel void was the major defect in the joints which disappeared with increasing heat input and simultaneous cooling rate to the joint. The maximum strength produced in these experiments is 188 MPa which is close to the strength of the aluminum base metal.

In this study, the effect of tool pin geometry on the mechanical and microstructural changes in the weld region and near it was investigated in the Friction Stir Welding process of butt joint of GOST 4784-97 aluminum alloy, using two types of threaded conical and cylindrical tool pins. To study the microstructure, a metallographic analysis using optical microscope and scanning electron microscope was used, and a tensile and micro hardness tests were used to investigate the effect of pin rotation on the mechanical properties of the joint. The results of the metallographic survey show a smooth and polished surface of the welded specimens with fine threaded cylindrical pin. The EDS analysis indicates the precipitates of aluminum, magnesium, manganese and iron in bright colors and the precipitates of oxygen, magnesium, aluminum, and silicon in the dark colors in the images. The micro-hardness analysis has shown that the highest degree of hardness in the weld region is obtained by coarse threaded cylindrical tool; and its reason was hard mechanical work and high temperature during the welding process, which led to the formation of very fine grains by the dynamic recrystallization mechanism, in the stir region. The tensile strength of all welded specimens was greater than the tensile strength of the base metal; and indicates that there are no imperfections in the welds, as well as an appropriate microstructure in frictional stir welding that improves the mechanical properties of the welded area.

The purpose of this study is to investigate the effect of using bobbin tool on the mechanical properties of aluminum alloy 6061-T6 in friction stir welding. The friction stir welding method is one of the suitable process to welding aluminum alloys to reducing welding defects and increase joint strength. In this process, the welding parameters such as the rotational speed of tools and travel speed, beside the type and geometry of the tool also has a great effect on the quality and strength of the weld. In this study by using the typical tool and bobbin tool the effect of welding parameters on the mechanical strength of the welded joint are investigated. The results of this study show that the bobbin tool has a higher performance and capability in connection with this type of alloy. The main advantage of the bobbin tool is welding the both sides of the weld zone at one stage of the welding process compared to the typical tool. Also in terms of mechanical strength of connection, the use of bobbin tool has resulted in improving the tensile strength of the connection and resistance to a better impact. The effects of welding parameters show that by increasing the rotational speed of the device from 900 to 1100 rpm as well as increasing the travel speed of the tool from 25 to 32 mm/min of the joints shear strength has increased.

Due to higher demands for tailor welded blanks (TWBs) applications in the transportation industry, it is important to understand their forming characteristics in manufacturing processes, especially the deep drawing, in order to produce products with higher qualities. Due to differences between the base materials strength as well as the existence of the welding zone, the formability of TWBs is frequently less than the base metals. The aim of this study is the comparison of weld line displacement and drawing depth in TWBs designed and produced by laser welding and friction stir welding. Laser welding is more appropriate for TWBs production comparing to the other welding processes because of the creation of limited heat affected zone and suitable keyhole. The parameters of the friction stir welding process are very important due to having a high influence on complicated plastic zone variation, the material flow pattern and temperature distribution in TWBs sheets. In this paper, by design experiments, the effect of blank holder force and linear welding velocity on drawing depth and weld line displacement of TWBs have been investigated. Moreover, the harnesses of the weld zone in both processes have been examined. Results show that by increasing the linear velocity of laser welding, the amount of weld line displacement and drawing depth will be increased. Furthermore, the higher linear velocity of friction stir welding will result in the higher weld line displacement and drawing depth. Likewise, the harnesses of the laser welding zone are higher than those ones for friction stir welding zone.

Friction stir welding parameters such as is rotational speed, traverse speed and axial tool offset play as the main roles in achieving joint properties. In this research the effect of axial tool offset and depth of tool shoulder on the quality and mechanical properties of joint resulted from friction stir welding of 2 mm thickness to 4 mm thickness and 2mm thickness to 6 mm thickness of 6061-T6 Al alloy was investigated. It was shown that tensile strength of joints differs by varying the axial tool offset. When tool offsets there are in the thicker part, large discontinues particles could be observed in the stir zone which caused some cracks at the weld surface and therefore reduced surface quality and mechanical properties of joint. The best surface quality and mechanical properties were resulted from the tool offsetting in thinner part. The depth of tool shoulder is an important factor in heat generation, material extrusion under the shoulder and material flow during friction stir welding. At lower depth of shoulder weaker mechanical properties were observed which may be resulted from lack of sufficient heat generation and material flow at this situation.

Al6061 alloy is widely used in the industry; so, its welding with reliable methods is of great importance. In the fusion welding of these alloys, imperfections such as cracks, cavities, and segregations of alloy element may occur that necessitates the application of solid state welding processes such as friction stir welding method. In spite of the many advantages of the friction stir welding, several attempts have been made to improve the properties of the resulting joints. In this study, the effect of increasing the cooling rate and the effect of vibration during the process on the microstructure and mechanical properties of Al6061 welds . Also, the simultaneous effect of water and vibration on the mechanical properties of the joints is evaluated The results showed that vibration due to increasing the strain  and water due to increasing the cooling rate reduced the size in the stir zone. Investigations revealed that cooling rate increment decreased the dissolution of Mg2 precipitates significantly. The results of the tensile test showed that the strength of the due to the grain refinement as was applied or when increased. Also, when the vibration and coolant were applied simultaneously, the strength increased dramatically due to significant grain refinement and presence of Mg2 precipitates. On the other hand, with grain refinement, the volume fraction of grain boundaries increases and, thus, the growth of the cracks decreases and correspondingly elongation enhances.

Friction stir welding (FSW) process is a method for joining the aluminum alloys. Nowadays, it is considered to form the blanks fabricated by this method. Single point incremental forming (SPIF) is used to manufacture complex shapes with high depth which is not possible with traditional methods. SPIF is a flexible method for low production or manufacturing a prototype model. In this paper, experiments are performed on the blanks fabricated by FSW process to study the effect of the SPIF parameters. The first step conducted to investigate the influence of rotational speed and feed rate of friction stir welding process on mechanical properties of AA 6061-T6. The output of this step is the appropriate samples for next step. In the next step, the effect of the lubrication, rotational speed, feed rate and tool trajectory has been studied on thickness reduction (thinning), surface roughness and formability. The results show the lubricant and tool trajectory increase the depth of formation up to 1.6 times. Also, these two parameters improve the effects of thickness reduction and surface quality.

Friction Stir welding (FSW) is a solid state technique that was invented to eliminate the limitations of welding of aluminum alloys. In the present study numerical simulation of friction stir welding and friction stir spot welding (FSSW) of AA6061-T6 aluminum alloy by pinless tool which has an embedded part with same material of the workpiece was performed in four different diameters. The temperature peak generated in the process was recorded for all simulation states and compared with previous experimental data for validation purposes. It has been found that in the FSSW process, the heat generation and temperature increase is higher than the FSW process, which is due to the Lack of transitional speed in this case and the increase in heat in a smaller volume section. Investigation of the vertical reaction force of tool was performed in FSSW, it was observed that if an embedded part in tool is used, the peak force is reduced and the amount of this decrease will increase with increasing the diameter of the embedded aluminum section. In the case of using d10 tool, the peak force compared to the d0 tool was about 10% lower.