Solid State Welding Process Research Articles

Optimization of friction stir welding process parameters using MCDM method

Friction Stir Welding (FSW) is categorized into a solid-state welding process which is preferred to join aluminum-based materials effectively. Generally, aluminum-based materials are welded using solid state welding than fusion-based welding due to the chance of hot cracking, loss of elements and porosity. Process parameters and its selection in FSW process are important and it leads to efficient of weld quality. Taguchi concept is a standard optimization procedure but it has a limitation of not capable to solve multi objective problems simultaneously. Multi Criteria Decision Making (MCDM) method can be used for solving multiple objectives simultaneous effectively. Al-6061 T6 alloy is used as workpiece and carbon steel, H13 tool steel and high carbon high chromium steel is used as tool materials. The important process parameters considered are rotational speed of tool and welding speed. Response parameters selected are tensile strength and microhardness of welded joints. Process parameters are optimized using MCDM method and the optimum values obtained are rotational speed of 700 rpm and welding speed of 35 mm/min. It is understood that better tensile strength and microhardness of FSW joints at optimized condition due to adequate material flow, fine grain size and pulsating action. MCDM method has simple calculation procedure and easier solving methodology for machining parameters optimization.

Optimization of Friction Stir Welded Dissimilar Aluminum Alloys EN AW-5083-H111 and EN AW-6082-T651 using Hybrid Taguchi-Based Grey Relation Analysis

Friction Stir Welding (FSW) which is a kind of solid state welding process used essentially for joining nonferrous metals and their alloys. Involving pollution free and no filler material are the advantages of FSW when compared to other welding methods. The present work was focused on the multi objective optimization of friction stir welded EN AW-6082-T651 and EN AW-5083-H111 aluminum alloys using Taguchi based Grey relational analysis (GRA) method under different parameters of shoulder diameter (SD, mm), tool rotation (TR, rpm) and welding speed (WS, mm/min) on tensile strength (TS, MPa), percent elongation (E, %) and joint efficiency (JE). Taguchi related experiments were performed using L27 Orthogonal Array. The grey relational analysis which relates between the FSW parameters and the responses applied to find the optimum condition. Additionally, the Analysis of Variance (ANOVA) approach was used to identify the most important factor and its impact on the multiple response. The results of the obtained tests were then verified using the confirmation test.

Perspectives of the Low Force Friction Welding Process

The conventional solid-state friction welding process involves imparting a movement to one of them, bringing them closer together so that there is friction from the clamping force. By overcoming the frictional resistance on the surface of the workpieces, work converted into heat is generated. The obtained heat heats the elements to a temperature close to the melting point but not exceeding it. After stopping the movement in relation to each other, the process of pressing the elements with the force P with a greater force causes plasticization of the material and the formation of a flash. In low pressure friction welding, most of the heat required for the joining process comes from the induction coil. This means that two key process parameters such as friction time and contact force are significantly reduce. This affects the course of the process and the end result of the process of joining materials. The shape and size of the flash as well as the size of the heat-affected zone in the weld will change. Among the many advantages of this method of joining metals, one should mention the possibility of welding smaller parts, thin-walled, with complicated geometry, which the friction butt welding process would not be able to cope with. Additionally, there is a possibility of heat treatment. In order to verify the feasibility of the friction welding process with low pressure in industrial conditions, a number of tests presented in this study were carried out, together with the analysis of the results. A number of proposals for the optimization of low-force friction welding with the use of artificial intelligence have also been developed has also been developed. A simpler but less effective solution is application of neural networks. It is possible due to multiple digital recording and process automation parameters with digital recording and process automation This solution approach is not as productive as the proposed hybrid algorithm combining neural networks, fuzzy logic and genetic algorithmsThe hybrid method enables you to take advantages of all three algorithms in the position optimization.

Linear friction welding of Ti60 near-α titanium alloy: Investigating phase transformations and dynamic recrystallization mechanisms

Linear friction welding (LFW) is a solid-state welding process used primarily in manufacturing of aeroengine blisks. Ti60 near-α titanium alloy was developed for blisks operating at 600 °C, and shows excellent thermal stability and high-temperature oxidation resistance. In order to promote the wider use of such blisks, the mechanisms of microstructure evolution including phase transformation and dynamic recrystallization of welded Ti60 joint were studied. The effects of phase transformation and dynamic recrystallization on microhardness and tensile strength were investigated as well. Results show that the microstructure of the thermo-mechanically affected zone (TMAZ) deforms severely along the friction direction, forming {0001}[11 2 ¯ 0] α texture. β → metastable β then → α + β transformations occur, leading to lamellar α precipitating from the deformed β. Sufficient continuous dynamic recrystallization makes the WZ almost composed of fine equiaxed grains of 10 μm size. In addition, α → β with the subsequent αˊ transformation occurs in the weld zone (WZ), producing extensive distribution of acicular αˊmartensite inside the recrystallized grains. Under the effects of strain hardening, precipitation strengthening and fine grain strengthening, the hardness in WZ increases significantly (i.e., 381 HV) compared to base metal (BM) (335 HV), with the tensile strength of the joint (943 MPa) also increasing over that of the BM (914 MPa). However, because of inhomogeneous deformation, the elongation of the joint (13.3%) is slightly lower than that of BM (14.1%). • β → metastable β then → α + β transformations occur in TMAZ, leading to lamellar α precipitating from deformed β; α → β with the subsequent αˊ transformation occurs in WZ, producing extensive distribution of acicular αˊmartensite. • Adequate continuous dynamic recrystallization occurs in weld zone, accompanying by violent dislocation motion and formation of many subgrains and low-angle grain boundaries. • The tensile strength of the joint (943 MPa) increases to that of the base metal (914 MPa), but the elongation of the joint (13.3%) is slightly lower than that of the base metal (14.1%) because of inhomogeneous deformation.

Effect of rotational speed on the microstructure and mechanical properties of rotary friction welded AISI 1018/AISI 1020 asymmetrical joints

Abstract Asymmetrical joints (joining of the plate with rod) were joined using traditional fusion welding processes. However, the usage of unsuitable filler wire tends to lower weld penetration over the material surface, which also results in the attainment of hot or solidification cracks over the weld surface. To overcome these issues, solid-state welding processes are preferable. This study investigates the rotary friction welding (RFW) of AISI 1018 low carbon steel plate with AISI 1020 low carbon steel rod of asymmetrical joints. The friction welding process parameters such as rotational speed were taken as variable, and other parameters like friction pressure, forging pressure, friction time, and forging time were kept constant in this investigation. The impact of rotational speed on macrostructure, microstructure, and mechanical characteristics of joints such as microhardness, tensile strength, and fractography studies was analyzed. The fractured surface of the tensile specimen was examined through a scanning electron microscope (SEM). The maximum tensile strength of the joint about 452 MPa was observed. Maximum hardness at the weld interface was perceived at about 252Hv. Increasing rotational speed tends to increase the strength of the asymmetrical steel joints in rotary friction welding.

Mechanical behavior of friction stir butt welded joints under different loading and temperature conditions

Friction Stir Welding is a process that has led to increasing usage of aluminum and its alloys in different industries, since it is an autogenous and a solid-state welding process. The work developed in this paper was focused on the analysis of the mechanical behavior of AA7075-T651 friction stir butt welded joints, of 4 mm of thickness, under different loading and temperature conditions. A selection process was applied to assure the appropriate welding parameters. The welds from which the investigated specimens were manufactured from were submitted to nondestructive testing to assess the presence of welding defects. Fatigue tests were carried out, under a constant amplitude loading regime, at stress ratios of 0.05 and 0.5 and at temperatures of 23 °C and 150 °C. The results obtained by the fatigue tests point to a higher fatigue life of the specimens when the highest stress ratio, R = 0.5, was used (for the maximum stress applied), for both loading temperatures. For the stress range, the contrary was found to be true. Room temperature was also found to result in a significantly better fatigue performance. A Scanning Electron Microscope was used to characterize the fatigue fracture surfaces.

The Joining of Copper to Stainless Steel by Solid-State Welding Processes: A Review.

Joining immiscible materials such as copper and stainless steel together is a significant concern due to distinct mechanical and metallurgical properties across the joint line, such as melting points, the coefficient of linear thermal expansion, and thermal conductivity. The joint properties of copper to stainless steel welds are in great demand for various mechanical components of the international thermonuclear experimental reactor, ultra-high vacuum system, plan wave linear-accelerator or linac structure, and heat exchanger. These dissimilar-metals joints offer excellent flexibility in design and production, leading to a robust structure for many cutting-edge applications. Hence, the present article reviews the copper to stainless steel joining mechanism under different solid-state processing conditions. The present understanding says that defect-free strong joints between the dissimilar metals are systematically possible. Apart from this understanding, the authors have identified and highlighted the gaps in the research exploration to date. Moreover, a sustainable methodology to achieve a desirable weld of copper to stainless steel depends on favorable processing conditions.

Parametric Optimisation of Friction-Stir-Spot-Welded Al 6061-T6 Incorporated with Silicon Carbide Using a Hybrid WASPAS-Taguchi Technique.

Friction stir spot welding (FSSW) is one of the most popular fusion joining processes. The process is a solid-state welding process that allows welding of weldable as well as non-weldable materials. As a part of this investigation, weld samples of Al6061-T6 were reinforced with silicon carbide (SiC) powder with an average particle size of 45 µm. Initially, a Taguchi L9 orthogonal array was developed with three factors, i.e., rotational speed of the tool, pre-dwelling time, and diameter of the hole that was filled with SiC before welding. The effects of the SiC particles and process parameters were investigated as tensile–shear load and micro-hardness. The optimisation of parameters in order to maximise the output responses—i.e., strength and hardness of the welded joints—was performed using a hybrid WASPAS–Taguchi method. The optimised process parameters obtained were a 3.5 mm guiding hole diameter, 1700 rpm tool rotation speed, and 14 s of pre-dwelling time.

Optimization of friction stir welding AA6082-T6 parameters using analysis of variance and grey relational analysis

Friction stir welding (FSW) is a solid-state welding process, which has a significant role in solid-state welding processes for nonferrous alloys. Conventional arc welding processes for aluminum alloys such as metal inert gas (MIG) and tungsten inert gas (TIG) are replaced by FSW. The effect of FSW parameters such as rotational and traverse speeds, tool geometry, plunge depth, tilt angle, etc., on weld quality were considered in several optimization studies. Hence, the effect of fixture position is included in this study. Multi-criteria decision-making (MDCM) techniques such as grey relational analysis (GRA) were used to determine the optimal condition among experimental runs designed by response surface methodology (RSM). The Taguchi method was widely applied with MCDM techniques. Therefore, the experiments were conducted according to response surface methodology. Input parameters were (14, 16 and 18) mm for shoulder diameter (SD), (0.0, 0.2 and 0.4) mm for plunge depth (PD), and (30, 60 and 90) mm for fixture position (FP), which is the distance between fixture bolts used to fix the welded plate. The results obtained by GRA were similar to the ANOVA optimizer, and the optimum process conditions are shoulder diameter of 14 mm, plunge depth of 0.2 mm, and fixture position of 60 mm.

Novel Correlations Between Process Forces and Void Morphology for Effective Detection and Minimization of Voids During Friction Stir Welding

Abstract Sub-surface voids and material heterogeneities resulting from the friction stir welding (FSW) process often necessitate post-weld inspection to ensure the quality of weld obtained from this solid-state welding process. In this context, in-process void detection techniques can potentially help in optimizing the process conditions and thereby reduce expensive and time-consuming post-process inspection of welds. Current in-process void detection techniques rely on approaches that try to directly correlate the part-scale welding quality to void formation, without a fundamental understanding of the underlying mechanics and materials physics that modulate void evolution. In this work, we demonstrate an effective in-process numerical technique that uses process force signals to detect volumetric void formation and connect the variations in the force signals to interactions between the tool probe and the underlying material voids. Our approach relies on a high-fidelity finite element analysis simulation of the FSW process and on correlation of numerically obtained process force signals with the corresponding void structures. This correlation is obtained in the phase-space relating in-plane reaction forces on the tool to the tool rotation angle. We focus on the interactions of the tool geometry and tool motion with the surrounding material undergoing plastic deformation and deduce novel insights into various correlations of tool motion and void formation. Through this approach, we can identify tool-related process conditions that can be optimized to minimize void formation and demonstrate a potential in situ force-based void monitoring method that links to the underlying plastic flow and void structures during the FSW process.

Investigation of interface microstructure and properties of copper/304 stainless steel fabricated by explosive welding

Explosive welding is a solid state welding process that is used for the metallurgical joining of two or more dissimilar metals. This paper presented a systematic study of microstructure and properties of copper/304 stainless steel fabricated by explosive welding. The microstructure and chemical composition were evaluated using Scanning Electron Microscope (SEM) and Transmission Electron Microscope (TEM). The properties were performed by the nanoindentation tests and bending experiments of the microcantilevers, and the microcantilevers were milled out using the Focused Ion Beam (FIB) system. The results showed that the interface between this couple metals presents a typical wavy structure. There are some vortex regions in front of the crest, which are strong intermixing of this couple metals. The diffusion layer and melting layer are two typical layers at the interface. The diffusion layers are formed by strongly collision points, while the melting layers only appear on the stainless steel side. The average nanohardnesses of diffusion layer and melting layer are between that of copper and 304 stainless steel. The nanohardness of this couple metals exhibits increasing trend from 0° to 60°, while decreasing trend from 60° to 90°. The nanohardness in Area 4 of the vortex region is highest, where is the highest temperature. The average flexural strength of micro-cantilevers shows the same change rules with the nanohardness.

Projection-capacitor discharge resistance welding of 430 stainless steel and 14YWT

Efforts to advance structural materials with improved properties and service life in support of next generation designs for nuclear reactor components have recently led to development of nano-ferritic alloys (NFAs) containing nano-oxides such as 14YWT. A key enabling technology to realizing the useful properties of NFAs during service involves preservation of the oxide dispersions during joining. Solid-state welding processes, such as projection-capacitor discharge resistance welding (P-CDRW) used here, are well suited for joining NFAs while retaining the oxides. Due to limitations in the supply of 14YWT NFA material, initial experiments were conducted using 430 stainless steel as an inexpensive surrogate material. The goal of the surrogate experiments was to scale suitable parameters from 430 welds to 14YWT using ratios of key properties for the two materials including flow stress at temperatures and strain rates relevant to hot working. Results indicated that weld displacement increased with increasing weld force and increasing weld energy for all other variables held constant. Weld energy appeared to have a larger effect on displacement than weld force for the sample geometry used here. Appropriate process parameters (no melting) were established for the two materials. The process window for the 430 material extended from 350 J to 600 J of energy for weld forces of 2.2 kN and 3.1 kN. Suitable parameters for 14YWT were similar in terms of energy but for force levels of 3.1 kN and 4.0 kN. Displacement for both materials ranged from 150 μm to 300 μm for welds that did not experience melting. Simple heat flow analysis confirmed that the extent of displacement was limited by the characteristic thermal distance determined from thermo-physical properties and the weld current rise time. The higher flow stresses of 14YWT relative to 430 were apparently offset by greater heating due to higher electrical resistivity near the projection tip and lesser heat conduction from the projection tip owing to lower thermal conductivity. Based on the results presented here and in our companion paper. The P-CDRW process appears capable of successfully joining the 14YWT NFA while retaining the microstructures and properties of the original material.

Interface Structure in Friction Welded Joints between Stainless Steel 304 and Mild Carbon Steel

Friction welding is a solid-state welding process using heat generated through friction. Dissimilar materials can be joined properly with friction welding. This study is a continuation of the previous study and aimed to determine the interface structure occurred on stainless steel and carbon steel joints. Stainless steel 304 and mild carbon steel are joined with this method at 2000 rpm rotation for 15 seconds and forging time of 5 seconds with a pressure of 5 MPa. The results of a micro-observation using a scanning electron microscope show good bonding in the interface area. The carbon steel is more welded to the stainless steel in the periphery than in the center. The spectrum results of Energy Dispersive X-Ray of the interface show Fe, C and Cr elements content. This is what causes the strong welding bond.

Friction stir welding of dissimilar alloy combinations—A Review

Friction stir welding (FSW) is one among solid-state welding processes that can be employed for producing joints between dissimilar combinations with more ease than that of fusion welding processes. Several high coupled physical phenomena have addressed FSW as an extremely complex process. It is around three decades of invention, optimization of the parameters have been carried out even today by many researchers all over the world to obtain sound joints. This article focuses mainly on the research developments in the dissimilar FSW (DFSW), with the factors that are involved in joint fabrication between dissimilar materials. From the literature, it is found that the most influential factors in deciding the quality of the joints are pin profile, shoulder shape, welding speed and tool rotational speed. In addition, all other parameters will provide incremental support to it. The study on microstructure in different zones and the mechanical properties of welded specimens are elaborated from the available literature. Special attention is given to the reinforcement of micro- and nano- sized solid particles in the DFSW process. Future studies of DFSW are discussed based on the untracked studies that are not available in the literature.

Joining of aluminium matrix composites using friction stir welding: A review

Aluminium matrix composites are one of the most important classes of materials and have become a major focus of attention in aerospace, aeronautical, defense, and automotive industries. Aluminium matrix composites when compared to conventional alloys offer various promising properties like excellent strength-to-weight ratio, higher stiffness, lower coefficient of thermal expansion, better dimensional stability, and tribological behavior. The properties of aluminium matrix composites are highly influenced by the appropriate selection of metal matrix, processing routes, and reinforcement. Various ceramic particles (oxides, carbides, nitrides, borides, etc.) are used as reinforcements for aluminium matrix composites. Significantly different properties may be obtained using various reinforced particles and matrix material, which makes it difficult for the traditional fusion welding techniques to meet the joining requirements of these composites and is restricted to certain grades of materials. Solid-state welding process offers greater advantages over the conventional fusion welding. As a solid-state joining process, friction stir welding has proven to be a better and promising technique for joining aluminium matrix composites. However, it is still subjected to various challenges to join aluminium matrix composites even with considerable progress has been made in recent years. The current review provides an overview of state-of-the-art of friction stir welding of aluminium matrix composite materials. Specific attention and critical assessment have been given to weldability, the macrostructure and microstructure of aluminium matrix composite joints, mechanical properties of joints, fractography, and the wear of friction stir welding tool during welding of aluminium matrix composite. Furthermore, the various existing challenges of friction stir welding of aluminium matrix composites are summarized and the recommendations for future research are proposed.

The role of thermal contribution in the design of AA2024 friction stir welded butt and lap joints: mechanical properties and energy demand

Although in recent times the use of solid-state welding processes as friction stir welding (FSW) has become increasingly widespread, for some joint morphologies, as lap joints, there are still significantly less data available on both process parameters optimization and energy consumption. In the present paper, the authors investigated the possibility of enhancing the joint quality in two different configurations, i.e. lap and butt joints, taking into account specific thermal contribution (STC) conferred to the weld. Strength, micro-hardness and microstructure were evaluated on the produced AA2024 aluminum alloys butt and lap joints. The surface response method (RSM) was used to investigate the effects of the main process parameters and to identify optimal technological parameters in terms of joint resistance, while the specific energy consumption (SEC) of the entire process was acquired with the aim to provide design guidelines taking into account, at the same time, mechanical performance and environmental impact. It was found that the same optimal range of revolutionary pitch can be identified for both the configurations. Additionally, maximizing welding speed, for a given revolutionary pitch, contributes to significantly reduce the environmental impact of the process with no detrimental effect on the joint performance.

Effect of Grade 5 titanium interlayer on microstructure and pitting corrosion behaviour of AA1100/A36 explosion welds

Explosion welding is a solid-state welding process that is used for the metallurgical joining of similar and dissimilar combinations of metals and alloys with varying physical and mechanical properties. In this process the metal surfaces are brought into sufficiently close contact, the valence electrons overcome the repulsive forces and result in sharing of their orbits. In recent years ocean acidification is the main problem due to a variety of pollutants. In naval applications A36 steel is used for making ship hulls that are very poor in corrosion. The present study is aimed to improve the corrosion resistance of the A36 steel by cladding aluminium alloy (AA110) using the explosion welding technique. Grade 5 titanium alloy has been used as an inter-layer between AA110 and A36 plates. The presence of Ti-6Al-4V inter-layer facilitated good bonding between aluminium and steel dissimilar weld joint with smooth bond line. The microhardness values were measured at various points start from the weld interface and towards both base metal regions. Higher hardness values were observed in the bond region and the Inter-layer regions, owing to the inherent higher hardness of Titanium and the formation of Martensitic structure near the bond region, as a result of higher and sudden impact energies. Potentiodynamic polarization tests were made in 3.5% NaCl solution. Corrosion resistance in AA1100 is higher than A36. All the observed results were correlated with microstructural features as evidenced by SEM studies.

Investigation on microstructural features and tensile shear fracture properties of resistance spot welded advanced high strength dual phase steel sheets in lap joint configuration for automotive frame applications

Abstract The main objective of this research paper is to study the microstructural features and mechanical properties of resistance spot welded advanced high-strength steel of dual phase grade in lap joint configuration which is mainly employed in sheet form for fabrication of the automotive structure. Resistance spot welding (RSW) being a solid-state welding (SSW) process is used to overcome the problems in fusion welding of AHSS-DP steel such as heat affected zone (HAZ) softening, solidification cracking and distortion which significantly deteriorates the mechanical properties of AHSS-DP800 steel joints. The straight lap (SL-TSFL) and cross lap tensile shear fracture load (CL-TSFL) of spot joints were evaluated. Optical microscopy (OM), scanning electron microscopy (SEM), and transmission electron microscopy (TEM) techniques were used to characterize the weld nugget. The X-ray diffraction (XRD) results are also presented for phase identification in the weld nugget. The fracture surface of failed TSFL specimens was analyzed using SEM. The lap joints made using RSW disclosed superior SL-TSFL, CL-TSFL, and WNZH of 21.7 kN, 17.65 kN, and 589 HV0.5 The superior joint strength and hardness of the weld nugget zone are correlated to the evolution of lath martensite in the nugget zone.

Friction stir welding of two major pin contours of AA2024 and AA6061

The research work deals with to join two dissimilar aluminum alloys by solid state welding process compared to fusion welding processes and compared with fusion welding process, fusion welds tend to produce more defects while joining dissimilar materials. The major problem of the two dissimilar metals involve in welding process have different mechanical properties and microstructures which in turn may affect welding parameters like weld current, hold time, weld force etc. In order to overcome these issues, Friction Stir Welding (FSW) can be used to get rid of defects since it uses a non-consumable tool and also produces defect free welds compared to other welding processes. This thesis work aims to joining an aluminum alloy of 2024 and aluminum alloy of 6061. The plates are joined by means of octagon probe tool made of high carbon high chromium steel (D2 tool steel). Other issues while welding dissimilar aluminum alloys are phase transformation change and selection of welding parameters (rotational speed, transvers speed, pin diameter, shoulder diameter, D/d ratio and etc.) From conducted trail experiment aluminum alloy of 2024 and aluminum alloy of 6061 by using octagon probe tool made by HC-HCR tool it was observed that a lower welding speed 500 rpm at starting stage lack of filling took place and after thermo-mechanical heating took place that produce better weld while compared to weld at higher speeds (710 rpm, and 1000 rpm) with same transvers speed of 20 mm/min.

Multi-objective parametric optimization of FSW for mechanical properties of AA5083 joint

The solid-state joining process named Friction Stir Welding (FSW) overcomes the problems which were arose due to the diffusion of base material during conventional welding procedures. Basically the soft materials such as aluminium alloys were very difficult to join by the diffusion welding processes. The recasting of these alloys caused the unwanted grain growth along with others casting defects. The industries like aerospace require higher quality of welding joints of aluminium alloys. So, solid state welding process FSW is utilized for this purpose. The quality of FSW joints and the success of the process are depending on the combination of parameters. So, the optimization of process parameters is important for an efficient FSW process. The present study is an effort to optimize the process parameters i.e. tool Rotational speed (RS), transverse Welding Speed (WS), and pin diameter (PD). The weld joints were tested for tensile strength (TS) and tensile elongation (EL). ANOVA test was performed to check the significance of considered process parameters. All considered parameters were found significantly affected the responses. To optimize the parameters for multi-objective the Gray Relation Analysis (GRA) was used. The results revealed that all three process parameters significantly affected the responses. The combination of 1900 RPM of RS, 30 mm/min WS and 5 mm PD were suggested as a set of optimal parameters by GRA.