Formation Of Welded Joints Research Articles

Microstructures and properties of 7075 aluminum alloy and CP780 steel resistance spot welded joint assisted by magnetic field

Joining steel and aluminum is vital for lightweight automobile but still challenging due to their different physical properties. Herein, resistance spot welding tests were performed on CP780 high-strength steel (thickness 1 mm) and 7075 aluminum alloy (thickness 1.5 mm) dissimilar metals under steady-state magnetic field. The influences of magnetic field (B = 40 mT) on the structure of welded joints, the phase composition/content of intermetallic compounds, and tensile properties of welded joints were analyzed under different welding current conditions (I = 9 kA,10 kA, 11 kA, and 12 kA). At the same welding current, the Lorentz force generated by the additional magnetic field promoted the outward circumferential movement of the molten metal in the weld along the horizontal surface , as well as increased the diameter of the Fe/Al contact interface in the weld nugget along the horizontal direction, conducive to the effective utilization of heat of the resistance spot welding. Except under (11 kA-0 mT) and (11 kA-40 mT), welded joints under other welding parameters displayed a few welding defects, such as incomplete fusion and shrinkage cavity formed at the cross-section of the welded joints. Therefore, the synergism between the magnetic field and appropriate welding current held important roles in the formation of welded joints without obvious welding defects. The intermetallic compounds of all the welds were mainly composed of (Fe, Si)Al2 and (Fe, Si)Al5. Meanwhile, the thickness and content of the intermetallic compounds layer reduced under a magnetic field at the same welding current, significantly improving the tensile properties of the welded joints. The comprehensive properties of welded joints were the best under 11 kA-40 mT, with an average shear force increase from 3.02 kN to 3.49 kN (15.56%) and an average displacement increase from 1.01 mm to 1.22 mm (20.79%). Overall, the proposed dissimilar aluminum/steel resistance spot welded joint assisted by magnetic field looks promising for lightweight automobile use.

Development of Polyhydroxybutyrate-Based Packaging Films and Methods to Their Ultrasonic Welding.

This study developed a technical task associated with the formation of welded joints based on biodegradable polymers and their subsequent physicochemical characterization. The primary objective was to establish the effect of the welding process and modification of natural poly(3-hydroxybutyrate) (PHB) with N,N-dibutylundecenoylamide (DBUA) as a plasticizing agent on the structure and properties of PHB-based biopolymer materials as well as the process and structure of welded joints formation using ultrasonic welding technique. The weldability of biodegradable layers based on PHB and PHB/DBUA mixture was ultrasonically welded and optimized using a standard Branson press-type installation. The effect of the DBUA plasticizer and welding process on the structure of PHB-based biodegradable material was investigated using scanning electron microscopy, X-ray diffraction, FT-IR spectroscopy, differential scanning calorimetry, and thermomechanical analysis. The results confirmed that the DBUA acted as an effective plasticizer of PHB, contributing to lower crystallinity of the PHB/DBUA mixture (63%) in relation to the crystallinity degree of pure PHB film (69%). Ultrasonic welding resulted in an additional increase (approximately 8.5%) in the degree of crystallinity in the PHB/DBUA in relation to the initial PHB/DBUA mixture. The significant shift toward lower temperatures of the crystallization and melting peaks of PHB modified with DBUA were observed using DSC concerning pure PHB. The melt crystallization process of PHB was affected by welding treatment, and a shift toward higher temperature was observed compared with the unwelded PHB/DBUA sample. The butt-welded joints of biodegradable PHB/DBUA materials made using the ultrasonic method tested for tensile strength have damaged the area immediately outside the joining surface.

Технологические особенности ультразвуковой сварки разнородных пластмасс

The paper considers technological features of heterogeneous plastics ultrasonic welding, which specificity is manifested in the volumetric interaction nature. Results of studying the mechanism of a welded joint formation showed that micro-volumes mixing, polymer molecules mutual diffusion in the contacting surfaces and emergence of the new chemical bonds with the block copolymers formation were the simultaneous processes. Their common feature was that all these processes proceeded in the temperature range corresponding to the polymer viscous-flow state. It was experimentally confirmed that one of the criteria for weldability of the heterogeneous plastics was their compatibility in terms of acoustic properties being estimated by the melt density and viscosity. Technological methods were proposed making it possible to compensate for differences in the welded materials acoustic properties, and thereby obtain the high-quality welded joints. Four stages of the welded joints formation mechanism were determined during ultrasonic welding of the heterogeneous plastics. It was established that physical and mechanical properties of the heterogeneous plastics were playing a decisive role in the mechanism of heat generation during the ultrasonic welding. An ultrasonic welding unit for welding the heterogeneous plastics in vacuum was developed.

Investigation of Magnesium and Chromium Fillers FSW Dissimilar Joint of AA6063 and AA 5154

Friction stir welding (FSW) is a solid-state metal joining process. There is no melting and recasting of metal while welding is used. Some of the defects commonly encountered in FSW are tunnel defect, bond, cracks, pin holes, and pipping defects. The defects occur because of improper metal mixing and less heat input in the weld nugget zone. In the fusion welding process, a filler rod is employed to form a quality weld with superior mechanical properties. In this work magnesium and chromium powders are used as filler materials. The purpose of this study is to ascertain whether filler materials and manufacturing processes have an impact on the weld nugget zone spot weld joint formation as well as the mechanical and abrasive properties of welded joints. This study's FSW filler materials mixing ratio and process parameters were improved by using the Central Composite Design (CCD) idea, which is discussed in more detail below Response Surface Methodology (RSM). The best empirical relationship between the parameters was provided by the CCD. The mathematical relationships were established to forecast the maximum tensile strength, maximum weld nugget hardness, and minimum corrosion rate by incorporating filler materials with process parameters. The optimal processing factors combination is predicted by conducting the validation test. The optimum parameters were the tool rotatory speed 600–1000 revolution per minute, welding speed 60 to 180 mm/min, plunge depth of 0.05 to 0.25 mm, center distance between the sample is 0–4 mm, as well as powder mixing ratio of 90 : 10, 92.5 : 7.5, 95 : 5, 97.5 : 2.5, and 100 : 0, the tensile test, microhardness, and corrosion rate analysis were conducted on the weld specimen. The welded test specimen provides better joint strength, weld nugget hardness, and enhanced corrosion resistance properties. The microstructure analysis shows the fine grain structure and homogeneous distribution of filler material with the base metal in the welded area.

Termička barijera u zavarenim spojevima ugljeničnih čelika

When welding carbon steels, a part of the metal of the heat affected zone directly next to the weld bath undergoes austenitic transformation, which is characterized by a combination of minimal thermal conductivity and high thermal capacity. This zone represents a thermal barrier and prevents heat transfer from the weld bath to the base metal. In addition, this zone is able to accumulate and retain a significant amount of heat for a certain period of time. In the heating phase, this barrier has a positive effect on the formation of welded joints, and in the cooling phase it causes a negative effect - the formation of hot or cold cracks, overheating and brittleness of the metal. The negative influence of the thermal barrier on the metal of welded joints increases with the increase of carbon content and alloying elements in steel, and also with the increase of heat input into the welded joint. Currently, an effective means of reducing the negative impact of the thermal barrier on the metal of welded joints is to reduce the heat input to the welded joints and their periodic cooling. Maximum efficiency is achieved in the case of a combination of these two techniques.

Влияние параметров питающей сети на стабильность фазового регулирования при контактной сварке

Resistance welding in large-scale manufacturing is carried out with a significant number of disturbances, the cumulative effect of which may exceed the capabilities of modern control equipment. Most resistance welding control systems used in industry to compensate for existing disturbances provide welding current phase control depending on the measured parameters characterizing the process of welded joint formation. The efficiency of such controllers is largely determined by the accuracy of measuring and setting the phase control parameters, which include the opening and conduction angles of welding thyristors. The paper shows that when switching on a contact machine, a phase shift of the mains voltage occurs in the load mode relative to the mains voltage in the idle mode. Using a simplified electric equivalent circuit of a contact welding machine, the paper describes the nature of the phase shift of the mains voltage. Circuit active resistance and inductance are selected as parasitic parameters of the mains. The authors simulated the electrical processes in the contact machine according to the three-loop equivalent circuit. The study shows the influence of mains parasitic parameters on the phase regulation stability, the features of the obtained current and voltage oscillograms. Depending on the mains and contact welding machine parameters, the phase shift magnitude ranges from fractions to units of an electrical degree. With welding current parametric stabilization by the mains voltage, the influence of mains parasitic parameters can be neglected. When the regulator operates in the mode of maintaining the secondary current numerical value, a decrease in the generated current relative to the specified one is observed. The authors proposed and tested a technique for determining the parasitic parameters of the supply mains based on the results of a short circuit test.

Planning and experimental studies of selection the optimal welding mode by the friction of fitting rods

The methods of friction welding of various materials have been studied, as well as the design and capabilities of the device for friction welding have been determined. The design of the device for friction welding on the basis of a lathe has been developed taking into account the established requirements and recommendations of machine building enterprises. To study the influence of technological factors on the quality of welded joint formation, a full factorial experiment (FFE) of type 22 was set up according to the plan. The adequacy of the planned experiment was confirmed by calculations (Fcalcul. = 1.1 < Ftabl. = 4.46.) on the basis of which a full-scale experiment was carried out. According to the results of the experimental plan, it was found that the heating time of the work pieces being welded has the most significant effect on the total length of the seam upsetting. The optimal mode with the correct formation of the burr has been chosen. The convergence of the full-scale test results with the planning of the Type 22 full factor experiment has been identified, resulting in the determination of the optimal mode.

Prerequisites for developing an advanced welding technology for repair of worn elements of steam-conducting systems

The main disadvantage of standard technologies of welding steam pipelines of thermal power plants is that they can allow the presence of defective structures close to the defective ones in the metal of the seam and in the sections of the HAZ. In this regard, the question arises about the development of a new technology that will provide the appropriate structure and properties that will increase the service life of steam pipelines and get a significant economic effect. Goal. The goal is improvement of the technology of welding pipelines of thermal power plants based on the study of the features of the formation of welded joints operating in Creep conditions. Methodology. The level of wear of the elements of the Steam-conducting path was estimated taking into account the provisions of the regulatory documentation of metallographic analysis, determination of chemical composition and properties, as well as the degree of their deformation. Results. It is revealed that welded joints are characterized by initial structural heterogeneity, which is closely related to long-term strength, ductility and impact strength. For example, at different sections of a welded joint, there is a different intensity of transition of alloying elements and, accordingly, a different type of structural component can be formed. The proposed technology of welding repair of damaged elements of steam pipelines using mechanized welding in CO2+Ar provides for the production of welded joints with a higher level of uniformity of structure, chemical composition and properties. Scientific novelty and practical significance. The welding technology has been improved, which includes developing the modes for performing repair work by mechanized welding in an Ar + CO2 environment of steam pipeline samples with a depth of ≥ 20 mm and a width of ≥ 30 mm, and differs from the known ones by using linear energy welding of 1.2–1.5 MJ/m.

The process of forming welded joints by high-voltage capacitor welding

The article substantiates the relevance of obtaining welded joints from dissimilar alloys with minimizing the processes responsible for the formation of intermetallic joints by using high-voltage capacitor welding with an induction-dynamic drive. A schematic diagram of high-voltage capacitor welding is given, the physical nature of the work is described. The parts to be welded are connected in series to an electric circuit and an inductor, which is a feature of this method. The physical processes and stages of high-voltage capacitor welding with an induction-dynamic drive are described. Comparison and analysis of high-speed photographic recording with oscillograms of current and voltage is carried out. The presence of an inductive resistance in the discharge circuit shifts the discharge current relative to the voltage. Confirmation of the hypothesis of formation of welded joints in the solid phase is based on the analysis of welded joints by scanning electron microscopy. Energy dispersive analysis of the welded joint zone did not reveal the diffusion of zinc into the AlMg2.5 alloy and magnesium into the B63 alloy. Energy dispersive analysis confirmed the assumption about the formation of a welded joint under conditions of wetting of molten metal by a pulsed electric arc, followed by displacement from the joint zone and plastic deformation of the heated metal. Recommendations are given for taking into account the polarity in high-voltage capacitor welding, depending on the thickness of the thinnest element.

DEVELOPMENT OF TECHNOLOGY AND CREATION OF TEST EQUIPMENT FOR PRESSURE WELDING OF HIGH-LOAD THIN-WALLED HETEROGENEOUS STEEL TUBULAR PARTS

Introduction. Magnetically impelled arc butt welding (MIAB) method differs from the existing arc methods by high productivity, stable quality of welded joints, high degree of mechanization and automation of the technological process and so on. Welding is performed automatically, which significantly reduces the influence of theoperator-welder on the quality of welded joints. The optimal values of the magnetic field induction components for thin-walled tubular parts with a diameter of 212 mm are determined. The basic technological parameters on welding of tubular details in stationary conditions are defined, it is: qualitative preparation of end faces of pipes;optimal distribution of induction of the control magnetic field (CMF); arc voltage; the magnitude and order of programming the welding current; the rate of closure of the arc gap in the process of upset. The influence of liquid metal melt in the arc gap during upset on the formation of welded joints of pipes is determined. Metallographicstudies showed no defects in the weld line and a relatively small area of thermal impact. Mechanical properties of welded joints at the level of mechanical properties of the base metal. Studies have been conducted to determine theparameters that affect the stable movement of the arc along the thin-walled edges of tubular parts and the influence of liquid metal melt in the arc gap during heating on the formation of welded joints.Problem Statement. Pipes of small diameters (up to 220 mm) are used in various industrial enterprises and construction of pipelines. The work requires high-performance automatic welding methods that allow obtaining stable and reliable welded joints.Purpose. The purpose is to raise labor productivity and to save materials by using equipment and technology for press welding of magnetically controlled arc of thin-walled tubular parts.Materials and Methods. Steel thin-walled tubular parts with a diameter of 42mm and 212 mm, with a wall thickness of 2.5… 3 mm were used for research on press welding. To create a control magnetic field, magnetic systems for tubular parts with a diameter of 212 mm were developed. Experimental welding was performed andsamples of welded joints of pipes with a diameter of 212 mm with a wall thickness of 3 mm were investigated. In the course of the research, the main parameters are recorded and the welding process is controlled by computer. Results. The main technological parameters: preparation of pipe ends; magnitude and distribution of control magnetic field induction; the arc voltage; the magnitude and order of programming the welding current; the rateof closure of the arc gap during upset, which affects the formation of welds have been determined. The experimental industrial technology for welding of thin-walled tubular details with a diameter up to 212 mm for thepurpose of its industrial use and the concept of the welding equipment has been developed, patents for the invention have been received.Conclusions. The mechanical and metallographic tests have shown that the properties of welded joints are at the level of the properties of the base metal. The use of press welding technology for tubular parts increases productivity and automates the welding process. The influence of the bandwidth of the liquid molten metal in the arc gap, while heating, on the formation of welded joints of pipes has been experimentally established. The main technological parameters and their influence on the quality of welded joints in the process of heating, the ends, and the upset of thin-walled tubular parts have been determined. Experimental industrial technology for press welding of thin-walled tubular parts has been developed and industrial tests have been conducted, in accordance with the customer's requirements.

Contact welding of palladium foil with stainless steel

ABSTRACT The features of the welded joint formation of palladium foil with stainless steel by using nickel foil as an intermediate layer at resistance welding are considered. It is shown that through the choice the optimal welding parameters, it is possible to obtain the equal strength connection of the specified materials, while the core of the welding point will be shifted to a thicker part.

Influence of technological and metallurgical factors on copper welded joint formation in electron beam welding

Influence of technological and metallurgical factors on copper welded joint formation in electron beam welding

ВЛИЯНИЕ ПОСЛЕСВАРОЧНОГО ОТПУСКА НА МЕХАНИЧЕСКОЕ ПОВЕДЕНИЕ ФРИКЦИОННЫХ СВАРНЫХ СОЕДИНЕНИЙ СТАЛЕЙ 32Г2 И 40ХН В УСЛОВИЯХ МНОГОЦИКЛОВОЙ УСТАЛОСТИ

At modern mechanical facilities, the friction-welded joints are getting widespread as the most advanced production technique characterized by high efficiency, processability, cost-effectiveness, and safety. Moreover, it allows producing high-quality joints of a large number of different analogous and opposite metals and alloys. Despite all these advantages, one should consider that metal, in the process of welded joint formation, suffers a local thermo-deformational effect, which causes the gradient nature of the structure and residual strains of a welded joint. These factors directly influence the structure’s working ability and durability under fatigue loads, which are the most common cause for parts failure. The paper contains the assessment of the post-weld tempering influence on the cyclic life of welded joints of 32G2 and 40HN steels produced using the rotational friction welding technique. The authors tested laboratory specimens with welded joints under the high-cycle fatigue using the simulation machine with the two-point fastening of a revolving specimen under the action of even twisting moment. The study involved the statistical processing of the obtained results of cyclic life. Based on the metallographic analysis, the authors identified the weak points in welded points where the fatigue cracks initiation and progress occurred in the initial state and after tempering. The paper presents the fractographs illustrating the fracture mechanism of specimens under the study. The authors identified the influence of different tempering temperature modes on the cyclic life of the studied welded joints and the nature of their fracture. The study shows that tempering at the temperature over 400 °C promotes fracture acceleration under the effect of fatigue loads due to the development of return and polygonization processes in the vulnerable area of the thermomechanical action zone.

Research Progress on Numerical Simulation of Welded Joints Microstructure

Since the integrity and mechanical properties of welded joints mainly depend on the solidification behavior of the weld pool and the microstructure characteristics of the welding heat affected zone, it is crucial for engineers and scientists to reveal the solidification behavior of the weld pool and the structural transformation of the welding heat-affected zone. With the dramatical improve of material calculation methods, the formation mechanism of the microstructure of some metal welded joints has been continuously revealed. In this article, the application of computer simulation in the study of welded joint microstructure is comprehensively analyzed. It focuses on the difficulties of simulating each area of welded joints, the advanced simulation methods applicable to each area and the current research status. Based on the characteristics of welded joint formation and simulation methods, some hot issues in research are proposed, aiming to provide effective help for researchers in related fields and open up new research ideas.

Effect of tool geometry in dissimilar Al-Steel Friction Stir Welding

Aluminum-Steel joining is an example of a multi-material design. An amalgamation of both the material is very beneficial, yet they pose their set of difficulties in joining due to a significant difference in properties. Solid-state joining processes such as friction stir welding are beneficial in avoiding fusion and formation of a thick intermetallic layer in the Al-steel joint. Critical control of process parameters and tool geometry is essential in friction stir welding to attain a reasonably sound joint. In present work, butt welding of low carbon steel with Aluminum 5052 alloy is performed with the use of three different tools. Progressive refinement in the geometry of tools was done to achieve the optimized dimensions of the tool. The weld joints obtained from various tools were compared based on heat generation. The joints were characterized based on peak temperature achieved, tensile strength, and the number of steel fragments in the Al matrix through micrographs. The weld joint was observed under an optical microscope and Field emission scanning electron microscope (FESEM) for quantification of intermetallic compounds (IMC) layer. Energy-dispersive X-ray spectroscopy (EDX) and XRD analysis were performed to investigate the phase and composition of the IMC layer. The fractured surface under tensile loading was observed under high magnification scanning electron microscope. The tool with a shoulder diameter of 13 mm and a cylindrical pin was found to be optimized for its minimum heat generation and strongest weld joint formation with a minimum number of void-causing steel fragments.

Managing Welded Joint Formation at Electron-Beam Welding of Aluminum Alloys of Increased Thicknesses

Abstract—The technology of electron beam welding of homogeneous and dissimilar welds of aluminum alloys 1561, 1560М, and 1980T1 has been developed. Beam scanning along the semielliptical trajectory has secured the quality of the welded parts with fine mechanical properties. The welding scheme and optimal modes have been determined. The results of mechanical and corrosion tests, as well as the results of the delayed failure tests, are presented. The technology is implemented for hydrofoil devices and for the manufacture of shipbuilding machinery components.

Electron Beam Welding of 2099-T83 Aluminium-lithium Alloy Thick Plates

The paper deals with the welding of AW 2099-T83 aluminium lithium alloy being used for construction of lower wing stringers. The thickness of AW 2099-T83 aluminium lithium alloy was 25.4 mm. Electron beam welding with the accelerating voltage of 55 kV was used for production of welded joints. Welded joints were inspected by computer tomography, macroscopic and microscopic analysis, tensile strength test and microhardness measurement. Welded joints exhibited good weld joint formation, typical to electron beam welding. Weld metal was structure was dendritic formed by α solid solution. Decrease of microhardness was observed mainly in the centre of weld metal due to dissolution of precipitates. The fracture occurred in the weld metal during tensile strength test. Further research will focus on post-heat treatment of welded joints in order to improve mechanical properties of weld metal.

The influence mechanism of variable polarity plasma arc pressure on flat keyhole welding stability

The variable polarity plasma arc (VPPA) welding process is well suited for the welding of aluminum alloy, but the stable welding process and good-quality weld bead are difficult to be obtained in the flat position. The purpose of this work is to study the characteristic of variable polarity plasma arc pressure with different polarity time and find the key fact to achieve welding process stability and good quality welding joint in the flat position. The arc shape variation, arc pressure evolution and the molten pool behavior were observed and measured to discover the relationship to the weld joint formation. It was found that the small plasma arc pressure in the center with a similar affected region and enough upward shear force of arc plasma are the necessary conditions to get a stable keyhole process, which could drive the liquid metal of the back side weld pool converges at the bottom of the keyhole and flows upward and form a high-quality weld bead. Comparing the welding stability and quality, adjusting polarity time is the good method for completing the necessary conditions. With the variable polarity time decreasing, the stable keyholes process and acceptable weld quality were obtained in the flat position.

Special features of the formation of welded joints in vertical laser-arc welding of low-alloy steels

ABSTRACTInvestigations were carried out into the special features of the technology of vertical laser-arc welding of large structures made of high-strength and low-alloy steels with a variable welding gap and a large root face.The parameters of the conditions of vertical laser-arc welding of root passes in the low-alloy steel 30–40 mm thick with a root face of 10 mm (welding speed, the amplitude and frequency of transverse oscillations, the intensity of welding current, arc voltage, laser radiation power) resulting in the formation of high-quality welded joints are determined. The experimental results show that the laser radiation power, required for producing continuous penetration of the root face, depends on the thickness of the parent metal: for the metal thickness of 14–30 mm the sufficient laser radiation power is 3.8 kW, for a thickness of 40 mm it is no less than 4.6 kW to penetrate a depth of 5 mm.The welded joints have a fine-dispersed acicular structure of the martensitic – bainitic type. The experimental results were used to develop a technology of welding of low-alloy steels of different thickness using robotic equipment.

EBW of aluminium alloys with application of electron beam oscillation

This article presents the investigation results of influence of electron beam oscillation on the formation of welded joints of aluminium alloys. It is shown that for EBW with longitudinal oscillation, at a certain frequency and amplitude of oscillation, a lifting force appears. It acts on the metal of welding pool and displaces it from the root of the weld. The maximum lifting effect of liquid metal corresponds to a frequency of 35 Hz at amplitude of 1 mm (for aluminium alloys 12 mm thick at a welding speed of 90 m/h). The detected effect can be used for EBW materials of large thickness with through penetration.