Solid-state Joining Method Research Articles

Effect of Friction Pressure on the Mechanical Properties of CDFW Dissimilar Aluminium 6061-T6 and Stainless steel 304 Welding Joints

Welding technology has significantly developed in the industrial sector along with advances in manufacturing technology. The demand for joining methods combining dissimilar metals is increasing in the industrial sector. However, joining dissimilar metals is challenging because of differences in physical and mechanical properties. Continuous drive friction welding is a solid-state joining method widely used to join dissimilar metals. The research aimed to determine the effect of variations in friction pressure on the mechanical properties of continuous drive friction welding joints with dissimilar materials, Aluminum 6061 T6 and Stainless Steel 304. The process parameters used in this welding were the friction pressures used were 30 MPa, 35 MPa, and 45 MPa. The friction time is 2 seconds, the rotation speed is 1000 rpm, and the upset pressure is 50 MPa. Then, welded joints were evaluated for Vickers microhardness and microstructure observations. Based on the research results, it shows that the temperature distribution and microstructure results show that there is a change in the hardness value of the aluminum material. In contrast, the 304 stainless steel material experiences an insignificant change in the hardness value.

Direct spot joining of thin gauge aluminum alloy to stainless steel and joint performance in a corrosion environment

Direct joining of aluminum alloy and steel sheets offers a great potential for achieving effective structural lightweighting for transportation systems. The major challenge is how to avoid the formation of brittle intermetallic compounds (IMCs), which can be detrimental to joint load capacity and corrosion resistance. This paper presents a friction-based direct solid-state joining method for welding thin aluminum alloy (AA6061-T6) to stainless steel (316). Using a flat head friction heating tool, high quality interfacial bonding was achieved under a spot time of 20s and 1000 rpm without detrimental IMCs. The effects of an automotive-relevant corrosion environment condition on joint strengths were then examined through mechanical testing. The test results show that aluminum and stainless-steel spot joints produced by the proposed method exhibit no corrosion-induced damage or cracking nor any noticeable reduction in strengths, resulting in dominantly ductile failure mode.

Cavity growth – or lack thereof – in imperfectly roll bonded sheet metal

Roll bonding is a well-established solid-state joining method that has also found commercial use. In current industrial practice, a near-perfectly bonded interface is commonly aimed for, achieved by optimizing surface preparation and rolling parameters. On the other hand, an intriguing recent study has shown that roll bonding scrap metal has the potential to provide significant environmental benefits while not jeopardizing performance, despite the resulting imperfect interface with a distribution of cavities. This present work focuses on the mechanical aspects of this observation, aiming to provide a deeper understanding of the influence (or lack thereof) of the cavity content on the mechanical behavior of a roll bonded stainless steel, and a roll bonded mild steel. Imperfectly bonded samples of both steels are studied using mechanical tests and microstructure characterization, which both revealed that the interface cavities exhibit limited growth and no crack nucleation or propagation into the interface. A numerical finite element model of the imperfectly bonded sheet confirmed a tendency for low cavity growth by showing that opening stresses on the interface cavity remain low for various geometries and loading conditions, in line with linear elastic fracture mechanics calculations. Overall, this experimental-numerical study provides insights regarding the unexpected formability (and thus the wide applicability) of imperfectly roll bonded sheets.

Cold spot joining of high-strength steel sheets

A novel solid-state joining method, called cold spot joining (CSJ), has been successfully developed. In this method, the material near the joining interface undergoes plastic deformation under high pressure, forming a joining interface, while oxide layers at the interface are fragmented and expelled to the exterior. High-strength steel sheets (HSS) with strengths of 780 MPa were joined under various conditions. The joining temperature can be adjusted by applying pressure during CSJ. Applying suitable pressure results in solid-state joining, and microstructural observations, alongside fracture morphology, indicate that the formation of a brittle structure was effectively prevented. Furthermore, cross-tensile strength measurements were conducted on steel sheets of varying strength grades, ranging from 270 to 1180 MPa and exhibited that the cross-tensile strength increased with increasing tensile strength.

Modal Analysis of Ultrasonic Spot Welding for Lightweight Metals Joining

Ultrasonic spot welding (USW) represents one of the unique solid-state joining methods for lightweight materials such as magnesium alloy and aluminum alloy. However, the sonotrode vibration may have a detrimental impact on the sheet material and the existing welds, depending on the component geometry and vibration frequency. In this study, a modal analysis tool based on steady-state dynamics was developed for ultrasonic spot welding which features a cyclic load applied to the sheets during the joining process. Through predicting relative motion and shear stress at the faying surfaces, coupon geometry and weld spacing are identified as two major factors that affect the welding reliability and joint quality in USW. The model was validated via welding experiments on aluminum alloy and magnesium alloy and relevant characterization of temperature distribution, joint strength as well as fracture location.

Development of a cold spot joining method that enables sound joining of carbon steel below the A1 temperature

A novel solid-state joining method, which we call cold spot joining (CSJ), was successfully developed. In this joining concept, the material in the vicinity of the interface is plastically deformed using high pressure to form the joining interface, and impurities at the interface are expelled to the outside. Medium-carbon steel sheets were joined using the CSJ method under various process conditions. The joining temperature can be modified by the pressure applied during CSJ. Microstructural observations and hardness distributions revealed that proper pressurisation led to a joining temperature below the A1 point and prevented the formation of brittle martensitic phase. A sound S45C joint showing plug rupture at the base metal under both tensile shear and cross-tension tests was successfully fabricated by providing appropriate applied pressure and energising conditions.

Investigation on the mechanical properties of AA5052/AZ61A by ultrasonic welded joints

In this research, Ultrasonic spot welding (USW) was used as a solid-state joining method to strengthen the joints. Magnesium-alloy (AZ61A) and aluminum-alloy (AA5052) welded structures are commonly found in lightweight vehicles. Under this process, plastic deformation was observed in the weld joint at an energy level of 1550 J, with increasing welding energies beyond 1550 J, and a reaction layer of intermetallic compounds (IMCs) forms, with a thickness of about 17 µm. The γ-Mg17Al12 + β-Mg2-Al3 phase comprises the majority of the IMCs; the β-Mg2-Al3 phase exhibits a hardness of 6.7 GPa and a classic pop-in phenomenon, while the γ-Mg17Al12 cubic structure phase has an average hardness of 3.5 GPa. For welding energies exceeding 1550 J, the rapid formation of these phases can negatively impact the joint's performance. The observed fractures feature multiple secondary cracks, which could indicate a cleavage fracture, although further analysis would be necessary to confirm this.

Modelling, Temperature Analysis, and Mechanical Properties of Friction Stir Welding of Al-Cu Joints with Hardened OHNS Steel Tools

Friction stir welding (FSW) is a nearly modern welding method with vital advantages over the conventional welding process, such as lower distortion, enhanced mechanical properties, and eco- friendly. In FSW, the joint characteristics mainly depend on heat development during the joining process due to its solid-state joining method. The basic principles of thermomechanical methods during FSW are unknown since it is a new metal joining method. In this investigation, the 2D and 3D models of the tools with different pin forms were designed using SOLIDWORKS. The ANSYS software was used to investigate the temperature distributions near the weld zones. The fixture was designed and made according to the machine conditions. The base plates used were AA6101 and C11000; the tool material used was the Hardened OHNS steel tool with square and circular pin form. The temperature values were measured in each trial while joining of Al-Cu base plates along the weld line. The results reveal that in the joint area, a trial with high temperature leads to high ultimate tensile strength (UTS) and Charpy impact strength (CIS). Made at tool rotation speed 1200 rpm and feed velocity 20 mm/min of Hardened OHNS steel tool with circular pin form. The obtained UTS value at joints was less than that of Al and Cu base plates. The microhardness value detected at the joint area was higher than the Al and Cu base plates, providing high strength, and irregularly dispersed.

Optimization of friction stir blind riveting process parameters for non-ferrous sheet metal alloys

Friction Stir Blind Riveting (FSBR) is a modern successful solid-state joining method used to join different combinations of dissimilar and similar alloy sheets. The most critical elements that influence the Ultimate Tensile Strength (UTS) of joints produced by the friction stir blind riveting technique were determined using the Design of Experiments (DOE). In this proposed research study, the effect of process parameters such as rivet material, rivet diameter, sheet material 1 (top sheet), sheet material 2 (bottom sheet), and spindle speed was determined using the Taguchi experimental design approach with the L36 orthogonal array. The percentage contribution of each element to the tensile strength of FSBR riveted joints was determined using an ANOVA analysis. The tensile strength of riveted joints increased with an increase in rotational speed from 1150 rpm to 1750 rpm but a further increase in the rotational speed from 1750 rpm to 2750 rpm decreased the tensile strength of the joints. In addition, this study revealed that the most important process parameter on the joint strength is the rivet material followed by rivet diameter, sheet material 2, spindle speed, and sheet material 1.

Application of artificial neural network models to predict ultrasonic welding parameters for joining copper to aluminium sheet

Ultrasonic welding is a method of combining solid-state components that does not require the use of heat or flux and instead relies on vibration to hold the components together. When connecting copper wires to an equipment alternator in electrical and automotive applications, a solid-state joining method is utilized as the preferred connection method. This situation calls for the utilization of ultrasonic welding of metal. In businesses that use ultrasonic metal welding processes, issues with weld quality and strength appear to be the most frequently encountered difficulties. These issues are frequently the result of inadequate parameter selection, which may be traced back to the welding process. To produce ultrasonically welded joints with a thickness of 0.3 mm, the welding characteristics of copper to aluminum connections, such as welding pressure, weld duration, and vibration amplitude, are considered in this study. Compared to the size of this weld, alternative joint construction methods could potentially cause damage to the joint. To conduct the tests, a suitable experimental design was conceived and put into action by employing Taguchi's robust design process in a manner that was tailored to the specifics of the situation. With the help of a synthetic neural network, the answer was predicted, and its accuracy was checked using the mean square relative error, the Nash-Sutcliffe efficiency, and the mean absolute percentage error.

Microstructural and Mechanical Characteristics of Pure-Cu/brass Dissimilar Joints Welded by Friction Stir Welding Using Various Process Parameters

FSW (friction stir welding) is a solid-state joining method that attracts interest from all industries. The influence of various tool rotational speeds on the microstructure and mechanical characteristics of dissimilar pure Cu-brass joints has been investigated. The travel speed and vertical load were kept constant in the welding trials, at 40 mm/min and 10 kN, respectively, while the tool rotational speed varied from 1000 to 1400 rpm. The increase of the rotational speed to 1400 rpm resulted in degradation of the mechanical properties. The stir zone grain structure was refined; however, the grain size was irregular. Grain refining occurs due to a continuous and discontinuous dynamic recrystallization mechanism. In the grain interior, there were many large dislocations, identifying that incomplete recrystallization took part within the SZ. Instead, the lower rotational speed, i.e., 1000 rpm, led to more uniform grain refinement in the SZ. Moreover, in contrast to the welded zone where very fine grains exist, the base metal and thermomechanically heat-affected zone display coarser grains. Because of the microstructural modification, the stir zone’s mechanical characteristics were higher than the base materials, and the mechanical strength and plasticity were simultaneously upgraded. These results indicate that the size of the grains is independent of rotational speed. And mechanical properties like hardness and impact strength decreased as the rotational speed increased.

Comparison of process behavior, microstructure and mechanical properties of ultrasound enhanced friction stir welded titanium/titanium joints

AbstractTitanium as a high-performance material offers great potential for a wide range of applications with different aspects like lightweight-constructions, biocompatibility as well as design and is used in various industrial areas like the transportation sector or in medical and sports engineering. To exploit the full potential of titanium, there is still a need for innovative and efficient joining techniques compared to conventional methods. The process of friction stir welding as a solid-state joining method is able to produce high-quality similar joints of titanium. Nevertheless, there are still some challenging aspects when friction stir welding titanium like the formation of oxide layers that affect the mechanical properties especially in the field of fatigue negatively. The superposition of power ultrasound on the friction stir welding process can address this issue. Therefore, the hybrid process of ultrasound enhanced friction stir welding was applied on similar Ti6Al4V/Ti6Al4V joints in a butt joint configuration to reduce the amount of oxide layers and improve the fatigue lifetime of the joints. For the joint configuration, a positive impact of the power ultrasound could be identified by the breakup of oxide layers and an increase in the tensile strength of 16%. Also stepwise load increase tests revealed a higher estimated fatigue strength for ultrasound enhanced friction stir welded specimen in this butt joint configuration.

Experimental investigation of friction stir spot welding of polymer-aluminum alloy weldments

The friction stir spot welding (FSSW) process is one of the main solid-state joining methods used widely for welding different materials and dissimilar metals. In this article, the welding of Polytetrafluoroethylene (PTFE) and aluminum alloy sheets by the FSSW process will be investigated experimentally. The joining of polymer (PTFE) and metal (AA1050 aluminum alloy) was done successfully. The effect of process parameters including tool rotational speed, penetration depth, initial holding time, dwell time, and tool shoulder diameter on the joint strength and elongation of the weldments will be studied using response surface methodology (RSM). The joint strength was increased by creating a threaded hole in the aluminum sheet. A mechanical lock was created between the softened PTFE and the edge of the threaded hole. The shear-tensile tests have been carried out for 32 designed experiments. The results show that the joint strength increased by increasing the initial holding time due to the better wettability of PTFE and aluminum sheet. The joint strength increased by increasing the tool rotational speed and tool diameter (better pouring of the hole and formation of the mechanical lock). Two different fracture modes have been observed in the samples: (1) fracture in the peripheral area of the joint (partial interfacial fracture mode) and (2) fracture in the mechanically locked area (pull-out mode with tearing).

Experimental investigation of mechanical and tribological properties of AA2024-T3 friction stir welded butt joint

Friction stir welding (FSW) is a solid-state joining method in which a non-melting tool is used to fix two same or different materials by the application of heat. The impact of different FSW tool shoulder sizes on the mechanical and tribological behavior of an AA2024 – T3 manufactured butt joint is investigated in this experiment. The heat generated in the nugget zone and material churning change the mechanical and tribological properties of the welded joint. The tensile strength of the welded samples improves as the shoulder diameter increases. Whereas, the hardness of the prepared samples decreases with increasing shoulder diameter. With increasing shoulder diameter, the wear rate is likewise observed to be higher. So, 6 mm shoulder diameter was the optimum pin diameter for friction stir welding of AA2024-T3.

Ti-6Al-4V/SUS316L dissimilar joints with ultrahigh joint efficiency fabricated by a novel pressure-controlled joule heat forge welding method

Ti-6Al-4V/SUS316L dissimilar joints were manufactured by a novel solid-state joining method named “pressure-controlled joule heat forge welding”. The microstructure and mechanical properties of the joints were systematically investigated. Both materials were homogeneously deformed by applying the pressure corresponding to the intersectional point of the temperature-dependent yield strength. Along the joint interface, the uniform hardness distributions in the center and periphery regions were obtained because the heat input generated by the joule heat was homogeneous from center to periphery. The welding temperature was able to be decreased to suppress the formation of the intermetallic compound (IMC) layers by applying the high pressure because the welding is accompanied and accomplished by the interfacial deformation and the high pressure affects the deformable temperature. As a result, when the applied pressure was increased from 300 MPa to 450 MPa, the width of the IMC layers was decreased to around 28 nm. As the upset increased, the interfacial area ratio to base material increased hence the interfacial defects were successfully suppressed, and the tensile strength increased by removing the ragged surface and the oxide layers existing on the surface of the base material. Eventually, the joint efficiency reached 98.5 % compared to the base material.

A novel pressure-controlled joule-heat forge welding method to fabricate sound carbon steel joints below the A1 point

A novel solid-state joining method, that we called Pressure-controlled Joule-heat Forge Welding (PJFW), in which electric resistance heat is utilized as the heat source, was successfully developed. Medium carbon steel, S45C, rods were joined using this PJFW method under various conditions. The welding temperature can be determined uniquely by the applied pressure in the PJFW. The fabricated joints show homogeneous temperature distribution and hence hardness distribution along the weld interfaces. A sound S45C joint showing superior tensile properties comparable with the base material was successfully fabricated by providing an appropriate high pressure to lower the welding temperature below the A 1 point in order to prevent the brittle martensitic transformation, and applying a sufficiently large faying-surface deformation, not only to introduce significant microstructural refinement and large strains to prevent the softening, but to also sufficiently fragment the oxide layers, generate fresh surfaces, promote their atomic bonding and eliminate weld interface defects. • A novel “Pressure-controlled Joule-heat Forge Welding (PJFW)” method was developed. • The welding temperature is determined uniquely by the applied pressure in PJFW. • Uniform temperature and hardness distributions are achieved over weld interfaces. • A sound S45C steel joint was successfully fabricated by PJFW under the A 1 point. • This method shows potential to well join carbon steel regardless of carbon content.

Dissolution of delta phase in Ni-based superalloy during linear friction welding: integrated multiphysics computational process modelling

Linear friction welding (LFW) is an increasingly popular solid-state joining method for challenging applications such as integrated blade disk of aero-engines. However, the influence of friction-generated heat on the material microstructural evolution, material deformation and resultant mechanical performance of the manufactured components is not well understood. A novel integrated multiphysics computational modelling is presented for predicting the component-scale microstructural evolution of IN718 alloy during LFW. A modified time-temperature equivalence formulation was implemented for predicting the evolution of the δ phase, which was coupled with thermomechanical modelling of the LFW process. There is reasonably good agreement between the computational modelling results of this paper and the experimental results from the literature in terms of δ phase volume fraction and weld temperature. The integrated multiphysics computational modelling predicts the influence of process parameters on thermomechanical and microstructural processes of IN718 LFW. By systematically analysing the influence of 10 different LFW process parameter configurations, the friction pressure was identified as the most influential process parameter determining the extent of δ phase dissolution and weld temperature during LFW.

Current advancements in friction stir welding of high density materials: A review

In today's industrial sector, welding seems to be a very essential procedure required for the manufacture and renovation of metal products. Scientists are continuously searching for the right forms of welding to be used for different joints. This growing interest will contribute to the use of dissimilar alloys that involve welding. Owing to energy efficiency and environmental friendliness, Friction stir welding (FSW), extremely efficient solid-state joining method, was being referred to as “green” technology. This is an emerging paradigm for joining metallic components, in specific compact high-strength alloys that have been known as non-weldable by conventional fusion welding. This is also recognized as being the most important breakthrough in the field of material integration over the last couple of decades. As in the current context, welding of metallic materials is substituted through FSW due to its special characteristics across fusion welding processes, i.e. lowered heat-affected zone (HAZ), significantly lower porous defect, eco-friendly, minimized distortion, no gas shielding requirement, etc. This review article provides a framework for engineers and designers to explore FSW for a broader variety of different materials. Applications, challenges as well as other factors relevant to FSW are also discussed to provide guidelines for the worldwide scientific community to undertake comprehensive research in this area. This review ends with suggestions for the future direction of study.

A literature review on friction stir welding of dissimilar materials

Friction stir welding (FSW) employs a tool that does not require any filler materials; frictional heat is produced and performs a solid-state joining method. Severe plastic deformation causes to join similar and dissimilar materials without melting the workpiece at the welding line. Friction stir welding is the most recent friction welded joining processes with the most surprising features when welding various metal alloys, including magnesium, aluminium, copper, and steel. FSW is victorious of all the other conventional welding methods implied in many industrial applications like automobile, aerospace, fabrication, shipping, marines and robotics. It gives high-quality welds, energy input, and distortion are lower, better retention of mechanical properties; it is eco-friendly and can be performed less operating cost. This research work aims at the FSW process in Al-Cu alloys, highlighting:(a) Optimizing the welding process parameters, welding feed rate, tool rotation speed, (b) Evaluation of Electrical Conductance properties of joints, (c) Mechanical properties and metallography characteristics of joints.

Preliminary Finite Element assessment of residual stresses in dissimilar AA6082-S355 butt welded joints produced with the Hybrid Metal Extrusion and Bonding (HYB) technique

Hybrid Metal Extrusion & Bonding (HYB) is a new solid-state joining method for metals and alloys that utilizes continuous extrusion as a technique to enable aluminum filler metal additions. Previous works showed that this method is well suitable for joining dissimilar metals such as steel and aluminum. In the present paper a Finite Element model for the thermal residual stresses were implemented employing the FE code WELDSIM. As a starting point, the results of a semi-analytical heat generation model previously implemented for HYB process of aluminum butt welds were used to estimate the net power input as a sum of contributions that are dependent on the welding parameters i.e. the welding speed, the rotational speed and the material properties. Subsequently, the thermal stresses occurring in the material and finally the residual stresses were determined. In the present work, predictions of the FE model for different sets of welding parameters are presented and discussed.