Solid-state Welding Technique Research Articles

A review of microstructural changes occurring during FSW in aluminium alloys and their modelling

Friction stir welding (FSW) process is currently considered as a promising alternative to join aluminium alloys. Indeed, this solid-state welding technique is particularly recommended for the assembly of these materials. Since parts are not heated above their melting temperature, FSW process may prevent solidification defects encountered in joining aluminium alloys and known as limitations to the dissemination of these materials in industries. During the past years, large literature has been devoted to the modelling of microstructural evolution in aluminium alloys during FSW processes and mainly dedicated to the analysis of precipitate evolutions and grain recrystallization mechanisms. Precipitate size distribution models have aroused widespread interest in recent years demonstrating their relevance to follow precipitation process in multicomponent alloys and multiphase systems. Efficient recrystallization models are also available and based on various grain growth mechanisms. In addition, multi-scale coupling strategies have recently emerged considering thermal, mechanical and metallurgical solutions. Consequently, the effect of FSW process parameters on weld properties is now investigated to determine optimized welding strategies regarding microstructure evolution. This research is based on reliable models reported in the literature enhancing the estimation of final weld state and associated properties as an answer to industrial needs. Validations of proposed modelling strategies have been reported based on in-depth analyses of experimental observations. This present work proposes a review of recent models dedicated to microstructural evolutions in aluminium alloys during FSW process. The interest and efficiency of current approaches will be discussed to highlight their limitations. Guidelines will propose new routes toward enhanced modelling strategies for future developments.

Effects of tool offset, pin offset, and alloys position on maximum temperature in dissimilar FSW of AA6061 and AA5086

Friction stir welding (FSW) is a solid-state welding technique, which two workpieces join by pressure and large plastic deformation near their melting points. The tool offset, pin offset, and position of dissimilar alloys can highly affect the maximum temperature and heat distribution in FSW process. In current research, the effects of three mentioned variables on the maximum temperature of FSW of AA6061 and AA5086 alloys have been investigated. In this manner, Response Surface Methodology (RSM) as an auxiliary method has been used. The results show that pin offset is the most effective parameter affecting maximum achieved temperature. In all pin and tool offsettings, placing the harder alloy (AA6061) at advancing side results in more maximum temperature increment compared to the case which the harder alloy is at the retreating side.

Tribiological investigation and optimization of friction stir spot welding of dissimilar metals by LSSM-ANN method

In manufacturing firms, welding technology plays a supreme role in joining purposes. The joining of dissimilar metals is complex in several conventional type welding. Friction stir spot welding (FSSW) is a solid-state welding technique and it is a derivative of conventional friction stir welding (FSW) to join the metals. The recent demands of advanced engineering materials such as aluminum alloys and stainless steel in the automobile sectors are forced to facilitate this research work, at the same time, the joining of such materials is quite complex because of its different welding characteristics. The main contribution of this work is to optimize and predict the microhardness and tensile failure properties of dissimilar metals by hybrid lightning search algorithm-simplex method (LSA-SM) and ANN algorithm. The dissimilarly joined metals namely, duplex stainless steel 32760 and aluminum 7075-T6 are utilized in this work and the experimentation is performed for six different test runs. Besides, the predicted values from the proposed algorithm are compared with the existing support vector machine (SVM) method. The predicted values of 314 Hv microhardness and 4967 N tensile shear failure load are optimized by the ANN-LSA-SM method at 1900 rpm. From the test results, it shows that the proposed model is efficient to predict the mechanical properties of the dissimilar welded materials than the experimental and SVM method.

Parametric study on joint quality in friction stir welding of polycarbonate

Now-a-days the use of thermoplastics is vastly popular in advanced industrial sectors due to unique mechanical properties. Friction stir welding is found to be unique of the major joining technologies to overcome heat induced fusion welding inadequacies. This friction stirred solid state welding technique can be magnificently used to join various challenging to weld materials. In this paper, the probability of friction stir butt welding has been scrutinized using a cylindrical tool on poor thermal conductive polycarbonate thermoplastic. The response of tool rotational speed and tool traverse speed on joint strength along with micro-hardness deviation along the centerline of weld has been studied. The maximum joint efficiency was found to be 37.01% at an intermediate tool rotational speed and a welding speed of 1800 rpm and 20 mm/min respectively, keeping tool tilt angle constant at 1°. The average joint strength was found to be poor at low tool rotational speed and high tool traverse speed although both process variables were significant over joint quality. The advancing side of the weld zone was found to be weaker in comparison to the number of failures during tensile test. The stress elongation profile specified a brittle failure in the heat induced weld interface welds similar to base polycarbonate. However, the joint efficiency was found to be reduced drastically due to predominant material scooping from advancing to rear side along with significant hardness variation from stirred weld zone to heat influenced zone interface as per the hardness deviation graph.

Investigation of shear failure load in ultrasonic additive manufacturing of 3D CFRP/Ti structures

Abstract Carbon fiber reinforced plastic (CFRP) is an extremely beneficial composite material in the aerospace and automobile industries owing to its high-strength-to-weight ratio, high stiffness, lightweight, and corrosion resistance. However, CFRP material alone is limited in its weight-bearing capabilities. A thin layer material such as Titanium (Ti) is often used along with CFRP laminates to address these issues. Traditional techniques used to join CFRP/Ti stacks include the use of adhesives, glues, or rivets, and bolts. These techniques have several limitations including weight addition, stress cracking, delamination, and limited operating temperatures. These limitations can be readily addressed by the use of solid-state welding techniques based on ultrasonic energy. One such technique is the Ultrasonic Additive Manufacturing (UAM) process, which is capable of fabricating 3D structures of CFRP/Ti laminar composites. Preliminary experimental studies proved the feasibility of using the UAM process to join CFRP/Ti stacks. Further development of this process needs a detailed investigation of the process parameters. This study aims to study the effect of critical process parameters including the ultrasonic energy and pre-surface roughness on the shear strength of the fabricated CFRP/Ti stacks using the UAM process. The study found that both ultrasonic energy and surface roughness have a positive impact on the resulting shear strengths of the UAM fabricated structures.

Mechanical Properties of Friction Stir Welded AA1050-H14 and AA5083-H111 Joint: Sampling Aspect

Welding of dissimilar aluminium alloys has been a challenge for a long period until the discovery of the solid-state welding technique called friction stir welding (FSW). The discovery of this technique encouraged different research interests revolving around the optimization of this technique. This involves the welding parameters optimization and this optimization is categorized into two classes, i.e., similar alloys and dissimilar alloys. This paper reports about the mechanical properties of the friction stir welded dissimilar AA1050-H14 and AA5083-H111 joint. The main focus is to compare the mechanical properties of specimens extracted from different locations of the welds, i.e., the beginning, middle, and the end of the weld. The specimen extracted at the beginning of the weld showed low tensile properties compared to specimens extracted from different locations of the weld. There was no certain trend noted through the bending results. All three specimens showed dimpled fracture, which is the characterization of the ductile fracture.

A Short Review on Welding and Joining of High Entropy Alloys

High entropy alloys are one of the most exciting developments conceived in the materials science field in the last years. These novel advanced engineering alloys exhibit a unique set of properties, which include, among others, good mechanical performance under severe conditions in a wide temperature range and high microstructural stability over long time periods. Owing to the remarkable properties of these alloys, they can become expedite solutions for multiple structural and functional applications. Nevertheless, like any other key engineering alloy, their capacity to be welded, and thus become a permanent feature of a component or structure, is a fundamental issue that needs to be addressed to further expand these alloys’ potential applications. In fact, welding of high entropy alloys has attracted some interest recently. Therefore, it is important to compile the available knowledge on the current state of the art on this topic in order to establish a starting point for the further development of these alloys. In this article, an effort is made to acquire a comprehensive knowledge on the overall progress on welding of different high entropy alloy systems through a systematic review of both fusion-based and solid-state welding techniques. From the current literature review, it can be perceived that welding of high entropy alloys is currently gaining more interest. Several high entropy alloy systems have already been successfully welded. However, most research works focus on the well-known CoCrFeMnNi. For this specific system, both fusion and solid-state welding have been used, with no significant degradation of the joints’ mechanical properties. Among the different welding techniques already employed, laser welding is predominant, potentially due to the small size of its heat source. Overall, welding of high entropy alloys is still in its infancy, though good perspectives are foreseen for the use of welded joints based on these materials in structural applications.

A Review paper on Friction Stir Welding (FSW)

Friction Stir Welding (FSW) is a new solid-state welding technique which finds application in various industries.It involves the joining of metals without any help of fusion or filler material. The joint between two metals can be formed through the combined action of frictional heating and mechanical deformation which is developed due to a rotating tool. The material that flows around the tool undergoes an extreme level of plastic deformation. Rotation generates enough friction and the friction generates sufficient heat to plastify the material. Friction Stir Welding (FSW) is handy for welding aluminum alloys. However, interest is growing in utilizing the process in a wider range of applications that also employ non aero engine metallic materials. Therefore, it is the objective of this report to provide a broad view of the capabilities of the FSW process for joining metals. This review paper will cover the various work performed on friction stir welding, and the basics of the process and the fundamental aspects of operating an FSW. This includes a description of the different parameters that have been involved in this process. And also studied the material flow, forces, and other output responses, including defects, and strain rates that is produced.

Review on joining of aluminum alloy by solid-state welding technique

FSW is a solid-state welding technique in which no filler material is used to join two similar or dissimilar materials. Welding is performed by a rotating tool, rotation of tool results in a huge amount of friction between shoulder and base material which plays a major role in the joining process. For the welding of 2000, 6000, and 7000 series of aluminium alloys mostly FSW have been preferred over other conventional welding technique such as ARC, TIG, and MIG. Process parameters such as Tool dimension, transverse speed, inclined angle, tool rotation, longitudinal tool force plays a major role in the tailoring of desired mechanical and Microstructural properties, Further investigation on the influence of tool pin profile of these properties are needed. This review paper provides an in-depth discussion about tool profile, microstructure and rotational speed. Also provides existing issues related to welding of metal matrix composite (MMC) and their remedies.

Optimization of Friction Stir Welding of AA6062-T6 Alloy

Friction stir welding (FSW) process is solid state welding technique used to weld soft alloys. It is the solid state welding in which a rotating tool in plunged into the plates and joint is made by passing the tool across the adjoining edges of the pates. The increasing use of aluminum alloys in aviation, marine and transport industries gives raise the development of new solid state joining process. The prime objective of this paper is to optimize the process parameters in order to obtained better mechanical properties. The process parameters considered are tool tilt angle, tool rotation speed and welding speed. Taguchi L9 orthogonal design of experiments is used to reduce the number of experiments. A statistical tool (ANOVA) has been used to analyze results. ANOVA tools clearly indicate the percentage contribution of each parameter. Analysis of variance revealed that the tool rotation speed effect more 57.95 % followed by welding speed has the contribution of 23.22 % and tool tilt angle has lesser contribution 3.12 % for deciding soundness of the joint

Condition monitoring of FSW tool using vibration analysis – A machine learning approach

Friction stir welding (FSW) is a new kind of solid state welding technique. Rigid and reliable joints in intricate shapes are possible with FSW. Mutual transfer of material occurs between two work pieces when heat is generated by continuous stirring of the welding tool. This type of welding process is frequently used in many commercial applications like automobile, ship building, aerospace and many more. In this scenario, monitoring the FSW tool condition is essential in order to avoid the early defects and breakdown of the machine. The FSW tool condition monitoring offers numerous benefits in the fabrication of aluminium products with less weld defects. Condition monitoring of friction stir welding tool is an advanced predictive maintenance technique for collecting real time data from the operating machine through sensors. The collected data can be analyzed using a machine learning approaches. In this study Al alloy was used for experimentation by using vibration analysis techniques signals were captured for good and faulty conditions of the tool. Statistical information was extracted from the raw vibration signatures and selection of feature was carried out. The selected features were then classified using Best first tree (BFT) classifier. The post pruned best first tree produced 93.07% as the classification accuracy.

Process parameters optimization of friction stir welding for optimum tensile strength in Al 6061-T6 alloy butt welded joints

Friction stir welding is a creative solid-state welding technique broadly used for the joining of different metals and their alloys mostly aluminium and its alloys for several applications in aerospace and automotive industries. Friction stir welding of Aluminium 6061-T6 alloy of 3 mm thickness is performed using H13 tool steel pin. The friction stir welding is carried out by taking the process parameters such as rotational speed, tilt angle and feed to identify the individual as well as simultaneous effects of process parameters on the tensile properties of the welded joints. The Taguchi L9 approach is used to construct the numbers of welding experiments to identify the optimized levels of process parameters to achieve the maximum tensile strength. The tensile strength and elongation of friction stir butt welded joints of Al 6061-T6 alloy sheets is experimentally measured. The highest tensile strength 191 MPa is obtained when the rotational speed 1400RPM, tilt angle 0° and feed 100 mm/min. The percentage elongation 10% is expresses that the weld joint is ductile in nature.

Mechanical and micro structural behaviour of flux coated GTAW and FSW joined AA6061 aluminium alloy

In the present paper, an attempt was made to experimentally investigate the mechanical properties of flux coated weld butt Joints of AA6061 aluminium alloy by considering two different welding processes namely GTAW and FSW. Gas Tungsten arc welding (GTAW) is preferred due to its comparatively simpler applicability and better economy. And the revolutionary solid-state welding technique, friction stir welding (FSW) is used due to its defect-free welds with good mechanical properties. Rolled plates of 3 mm thickness have been used as the base material for preparing single pass butt welded joints. The filler metal used to join the plates is AA4043 aluminium alloy. In this the investigation, tensile properties, Micro hardness, Microstructure and fracture surface morphology of the GTAW and FSW joints have been evaluated and the findings are contrasted. FSW Joint of Aluminium alloy AA6061 has shown superior mechanical properties compared to the GTAW Joint, this is mainly due to the formation of very fine, fully equally axed grain microstructures in the weld zone.

An Experimental Investigation on Joining of Copper and Stainless Steel by Induction Welding Technique

The Cu–SS welded structures are widely used in nuclear and power generation industries. Various solid state and fusion welding techniques have been experimented for welding Cu–SS with resultant phenomena of low joining strength in solid state and generation of crack in fusion. Of late application of induction heating as a joining technique is gaining momentum in view of its low maintenance, high production rate and cost effectiveness. In consideration of the above facts, in this study, induction heating for welding Cu–SS is experimented in ambient condition under varied settings of load and current. Although few micro-cracks were observed in SEM images, successful joining between copper and stainless steel was achieved. Some compounds like FeCu4, Cr3Fe, Cu(Fe2O4) and CrO were detected by XRD near the weld interface. The microhardness increased near the interface in comparison to the base metals. The interface microhardness was increased with current and load. Similarly, the tensile strength was also increased for higher values of process parameters. Highest strength of 220 MPa was obtained at 2 kg load and 650 A current. Failure of welded joint under tension took place by ductile–brittle fracture mode.

Microstructures and thermal properties of Ag-CNT/Cu composites fabricated by friction stir welding

Friction stir welding (FSW) is a novel solid-state welding technique. This process has many advantages, such as no consumable requirement, low distortion, low shrinkage, and excellent mechanical properties. Recently, FSW has been successfully used to fabricate metal matrix composites (MMCs), as the process overcomes environmental problems caused by other MMC fabrication processes. In previous studies, the goal was to reinforce the mechanical properties of base materials. In this study, the FSW technique and Ag-decorated carbon nanotubes (Ag-CNTs) were used to enhance the thermal properties of copper, and the microstructures of joints of Ag-CNT-reinforced copper fabricated by FSW were evaluated. The microstructures were analyzed using an optical microscope, and the presence of Ag-CNT in the joint was observed using a scanning electron microscope. Additionally, we confirmed the distribution of Ag-CNTs by electron probe microanalyzer, and the thermal properties of joints were evaluated by laser flash analysis. The Ag-CNT-reinforced Cu composites fabricated by FSW have improved thermal properties compared with conventional copper MMCs.

Influence of high temperature diffusion bonding process parameters on mechanical and metallurgical characteristics of nickel superalloy to martensitic stainless steel.

Welding of dissimilar metals is challenging because of the formation of microfissuring, strain age cracking and brittle intermetallic compounds. The above-said problems can be avoided by controlled heating and cooling rates and the formation of beneficial intermetallic layers in the joint interface using solid-state welding techniques such as diffusion bonding. This study investigates, the effect of diffusion bonding process parameters of dissimilar metals (AISI 410 martensitic stainless steel and nickel [Su 718] based superalloy). Fifteen joints were fabricated using different levels of bonding temperature (920-1,000°C), bonding pressure (10-18 MPa) and holding time (30-90 min). From this investigation, it is identified that joints fabricated at bonding temperature 980°C, bonding pressure 16 MPa and holding time 75 min yielded an extreme tensile strength (263 MPa) and hardness (450 HV) compared to the other joints. The tensile properties of the welded joints were assessed and associated with the microstructures. Optical Microscopy (OM), Scanning Electron Microscopy (SEM) and X-Ray Diffraction (XRD) analysis were used to estimate the metallurgical characteristics of the weldment. The EDS examination was supported out to analyses the interface composition and to decide the composition at the interface. Furthermore, a lot of δ phase precipitates were likewise found in the bonded region.

Behaviour of explosively welded impedance-graded multi-metal composite plates under near-field blast loads

This paper presents a comprehensive analysis of the blast response of functionally graded composite metallic plates, fabricated using explosive welding. Explosive welding is a solid-state welding technique, which has previously shown capabilities in bonding metals that have different chemical and mechanical properties. Impedance, which is the product of volumetric mass density and wave propagation velocity for a given material, was chosen as the function when designing the graded composite plates. The performance of two composite plate configurations, namely, Steel-Titanium-Aluminium and Steel-Brass-Aluminium were compared with a monolithic steel configuration of equal overall plate dimensions. The plates were subjected to highly intensive blast loads produced by detonation of the 250 g cylindrical Composition-B charges at standoff distances between 20–65 mm and spherical 1 kg Nitromethane charges at standoff distances of 200 mm and 250 mm. Detailed numerical models of near-field loading of the monolithic and composite plates were developed using the non-linear finite element analysis software LS-DYNA and validated using the experimental deformation measurements. Experimental evaluation of the impedance-graded explosively- welded composite plates has been carried out for the first time and herein lies the novelty of the work presented in the paper. It was observed that the impedance graded composite plates, which were lighter in density than the monolithic plates, resisted the highly intensive blast loads through their enhanced ductility.

Generating Lap Joints Via Friction Stir Spot Welding on DP780 Steel.

Friction stir spot welding (FSSW), a derivative of friction stir welding (FSW), is a solid-state welding technique that was developed in 1991. An industry application was found in the automotive industry in 2003 for the aluminum alloy that was used in the rear doors of automobiles. Friction stir spot welding is mostly used in Al alloys to create lap joints. The benefits of friction stir spot welding include a nearly 80% melting temperature that lowers the thermal deformation welds without splashing compared to resistance spot welding. Friction stir spot welding includes 3 steps: plunging, stirring, and retraction. In the present study, other materials including high strength steel are also used in the friction stir welding method to create joints. DP780, whose traditional welding process involves the use of resistance spot welding, is one of several high strength steel materials used in the automotive industry. In this paper, DP780 was used for friction stir spot welding, and its microstructure and microhardness were measured. The microstructure data showed that there was a fusion zone with fine grain and a heat effect zone with island martensite. The microhardness results indicated that the center zone exhibited a greater degree of hardness compared with the base metal. All data indicated that the friction stir spot welding used in dual phase steel 780 can create a good lap joint. In the future, friction stir spot welding can be used in high-strength steel welding applied in industrial manufacturing processes.

Microstructure Evaluation on Friction Stir Welding of Cryorolled 2219 Aluminum Alloy

Abstract This article presents a study of friction stir welding (FSW) on cryorolled (CR) AA2219 alloy using a hexagonal pin tool with different set of process parameters. Normally, AA2219 alloy is difficult to weld, but it is possible to get a defect-free, sound weldment with a solid-state welding technique (FSW) compared to traditional welding methods. Here, among the 9 weld joints, the weld made on CR AA2219 by the hexagonal pin tool with 1,000 r/min tool rotational speed at 25 mm/min welding speed and 3° axis inclination exhibited better tensile strength, impact toughness, hardness, and corrosion resistance. It was confirmed by microscopy analysis that the ultrafine grains structure and dissolution of Al2Cu were present at the weld zone. The fine dimple morphology was found at the fracture surface area of weldment. Also, the X-ray Diffraction (XRD) and energy-dispersive X-ray results showed that the intensity of Al2Cu was decreased at the weld portion for the CR AA2219. Dissolution of precipitates resisted the flow of electrons and delivered good resistance against corrosion. Corroded portion surface topography was analyzed, and pit details were measured.

Microstructure and micro-hardness analysis of friction stir welded bi-layered laminated aluminum sheets

Friction Stir Welding (FSW) is an economical and environment friendly solid-state welding technique. Properties such as high specific strength, low crack propagation rate and high resistance to impact and fatigue loadings enhance the use of aluminum laminates in the modern aircraft and automotive industry. In this study, FSW process was employed for butt joining of bi-layered Al-1350 laminated sheet. Preliminary experimentation, microhardness and microstructure evolution of the FSWed laminates were examined. The microscopic investigations revealed that the FSW process parameters greatly affect the dissolution of strengthening particles, material mixing and formation of defects. The Scanning Electron Microscopy (SEM) revealed that increasing in the tool rotation rate led to increase in the grain size and the size of second phase particles. However, with increasing tool traverse speed a very small rise in the grain size was observed. The increase in the density of second phase particles promoted a small rise in the hardness. Moreover, the microhardness of bi-layered aluminum weldments decreased with increase in grain size hence, following the Hall–Petch relationship. A comparative analysis of FSW of multilayered and monolithic sheet was also performed. Finally, a set of best suited parameters was suggested for the welding of bi-layered laminated sheets of aluminum.