Fusion Joining Research Articles

Influence of laser texturing on the properties of fusion joints between aluminum alloys and carbon fiber reinforced thermoplastic composites

Laser texturing is an effective method to enhance the fusion joining of aluminum alloy (Al) to carbon fiber reinforced thermoplastics composite (CFRTP). The enhancement effect is related to the morphology and spacing of the microstructures on Al surface. However, because of the correlation between the morphology and the spacing of the microstructures, excessive dense microstructures change the morphology, leading to a reduction in the enhancement effect, while sparse microstructures are also difficult to significantly enhance the joint. To this end, this paper proposes an improved laser texturing process to enhance fusion joints, through the investigation of the recast layer formation process during laser texturing on the Al surface, which comprehensively reveals the synergistic effects of microstructural morphology and spacing on joint properties. The results indicated that the increase of the number of laser processes and the microstructure spacing increased the height of the recast layer, with the difference that the microstructure spacing had less effect after increasing to a certain value. With the increase of microstructure spacing, the morphology of the microstructure on the Al surface transformed from the serrated microstructure to the double-scale microstructure, and finally to the independent microstructure, affected by the recast layer on sides of the microstructure. Once the dual-scale microstructures were formed on the Al surface, the shear strength of the Al/CFRTP fusion joint was the highest with a value of 25.05 MPa. The findings could provide a basis for laser texturing pretreatment for fusion joining.

Abstract We006: Metabolic Reprogramming to Increase Mitochodnrial Mass, Fusion and Energetics Represents an Important Rate Limiting Step in Direct Cardiac Reprogramming

Direct reprogramming of cardiac fibroblasts (CFs) into induced cardiomyocytes (iCMs) shows promise for treating myocardial infarction (MI). However, low conversion efficiency and relative immaturity of iCMs have so far precluded its clinical translation. Native CM maturation and cell cycle exit is associated with a switch from glycolytic metabolism to mitochondrial fatty acid oxidation (FAO), accompanied by a shift in the dynamic balance of mitochondrial fission (dividing) and fusion (joining) toward fusion. Because CFs lack the energy requirements of CMs, we hypothesized that transdifferentiation of CFs to iCMs requires a similar switch. Combining confocal microscopy with metabolic flux assays, we directly compared native CF and CM mitochondrial morphology and energetics. CMs showed significantly higher mitochondrial mass, fusion and energetics, all metrics relevant for increased reliance on mitochondrial FAO. Applying these techniques to study reprogramming, we found that at later reprogramming time points key metrics move significantly toward the phenotypes of native CMs. We then hypothesized that facilitating metabolic reprogramming by inhibiting fission and/or promoting fusion could improve iCM conversion. A loss of function screen identified certain fission genes, particularly the little studied mitochondrial fission regulator 1-like protein (Mtfr1l), as potent barriers to iCM conversion and maturation. In contrast, the core fusion genes were necessary for successful generation of iCMs, particularly the key fusion effector optical atrophy 1 (Opa1). Mtfr1l has been shown to promote cleavage of Opa1, and indeed concurrent knockdown of Opa1 ablated improvements to reprogramming efficiency. In conclusion, we showed both that iCMs are associated with increased mitochondrial mass, fusion and energetics approaching those of native CMs and that inducing CM-like mitochondria by knocking down Mtfr1l dramatically improved reprogramming, potentially through increased fusion activity of Opa1. By incorporating metabolic reprogramming into traditional direct cardiac reprogramming strategies, we may be able to move the field closer to clinical application to improve outcomes after MI.

Friction Stir Welding: A Comprehensive Review of Non-Metallic Particle Reinforcement in Joints

Friction Stir Welding (FSW), a solid-state joining technique, has demonstrated superior efficiency in welding metal-matrix-reinforced composite joints. FSW has garnered significant attention in recent years as a viable technique for joining similar and dissimilar materials, particularly those reinforced with non-metallic particles. By utilizing diverse mixture of reinforcement particles and base matrices, FSW outperforms traditional fusion joining methods in terms of effectiveness and reliability. Despite significant progress, challenges persist in achieving a homogeneous distribution of Non-metallic particles in the weld zone, which directly impacts macrostructural and microstructural characteristics. Moreover, the mechanical properties of these welds are intricately linked to process parameters, influencing grain enhancement and reinforcement particle distribution. This review critically evaluates these aspects, providing insights into the current understanding and highlighting areas for future research.

Review of High Voltage Pulsed Power Supplies and Power Electronics in Pulse Power Generation

Recently, pulse-shaped power supplies have become more popular. Pulsed power is versatile and useful as a supply method since it can take several shapes and has many pulse characteristics. The release of electrons, protons, and neutrons from an atom and the synthesis of molecules to generate ions or other molecules require a lot of immediate energy. Pulsed power is needed for decomposition, molecular fusion and material joining, radiation generation (e.g., electrons, lasers, radar), explosive processes for concrete recycling, wastewater and exhaust gas treatment, and material surface treatments. Industrial and environmental applications require pulsed power, which requires efficient and adaptive pulse modulators. Higher-quality repeating pulses are needed for plasma fusion and laser weapons. Marx Generators, Magnetic Pulse Compressors, Pulse Forming Networks, and Multistage Blumlein Lines have several uses. Pulse modulators use spark gap and hydrogen thyratron gas/magnetic switching technologies for their high voltage tolerance and low-rise times. These creatures are inefficient, unreliable, repetitious, and short-lived. These devices are heavy, bulky, and expensive. Solid-state switching technology can replace conventional devices, improving pulse supply. High-frequency switching repeats the pulsed power supply. These items are compact, efficient, affordable, reliable, and durable. Solid-state transistor applications may not meet switch voltage ratings and rise time constraints. Various power electronics configurations can produce solid-state high-voltage pulses.

Force reduction of friction stir welding and processing of steel

Friction stir welding and processing (FSW&P) is considered as a new fabrication method for canisters and repair of existing dry cask storage system canisters (generally made of austenitic stainless steel). Low heat input compared to fusion joining processes and grain refinement associated with low-temperature FSW&P result in a material with improved mechanical properties and equivalent generalized corrosion performance relative to the base metal. But FSW&P of austenitic stainless steel requires significant tool forge axis force to produce a weld (or a run). Exploratory runs utilizing forge axis force control were conducted to investigate the minimum force required to achieve defect-free runs. The correlation between forge axis force and resultant plunge depth was also investigated. Furthermore, detailed microstructural characterization was conducted to display the microstructural variation within the nugget zone.

Fusion joining of thermoplastic composites with a carbon fabric heating element modified by multiwalled carbon nanotube sheets

Fusion joining of thermoplastic composites with a carbon fabric heating element modified by multiwalled carbon nanotube sheets

Lipid acyl chain protrusion induced by the influenza virus hemagglutinin fusion peptide detected by NMR paramagnetic relaxation enhancement

The glycoprotein spikes of membrane-enveloped viruses include a subunit that catalyzes fusion (joining) of the viral and target cell membranes. For influenza virus, this is subunit 2 of hemagglutinin which has a ∼ 20-residue N-terminal fusion peptide (Fp) region that binds target membrane. An outstanding question is whether there are associated membrane changes important for fusion. Several computational studies have found increased “protrusion” of lipid acyl chains near Fp, i.e. one or more chain carbons are closer to the aqueous region than the headgroup phosphorus. Protrusion may accelerate initial joining of outer leaflets of the two membranes into a stalk intermediate. In this study, higher protrusion probability in membrane with vs. without Fp is convincingly detected by larger Mn2+-associated increases in chain 13C NMR transverse relaxation rates (Γ2's). Data analysis provides a ratio Γ2,neighbor/Γ2,distant for lipids neighboring vs. more distant from the Fp. The calculated ratio depends on the number of Fp-neighboring lipids and the experimentally-derived range of 4 to 24 matches the range of increased protrusion probabilities from different simulations. For samples either with or without Fp, the Γ2 values are well-fitted by an exponential decay as the 13C site moves closer to the chain terminus. The decays correlate with free-energy of protrusion proportional to the number of protruded -CH2 groups, with free energy per -CH2 of ∼0.25 kBT. The NMR data support one major fusion role of the Fp to be much greater protrusion of lipid chains, with highest protrusion probability for chain regions closest to the headgroups.

Force enhanced wire laser additive manufacturing of aluminum and titanium alloys

Brittle intermetallic compound formation is typically difficult to avoid during fusion joining of dissimilar metals. In this paper, a new approach called force enhanced wire laser additive manufacturing is proposed to join aluminum and titanium alloys. Ti6Al4V titanium alloy single track was additively fabricated on AA7075 plate successfully, through two liquid pools of the wire and the substrate, separated by a buckled unmelted part of the wire, leading to a mechanically interlocked interface. The effects of manufacturing parameters including laser power, wire feeding speed, scanning speed and initial contact force between wire and substrate on the surface morphology, internal interface microstructure and formation of intermetallic compounds were investigated through high-speed camera, spectrometer, laser topography, optical imaging, SEM imaging, XRD characterizations along with numerical simulations at different scales. And the maximum tensile strength reached 380 MPa in the tensile test. The experimental and numerical results indicate that the thermal modulation approach can effectively control the formation of brittle compounds between titanium and aluminum alloys and that the initial contact force ensures a good bond between the two metals.

Особенности формирования сварного соединения сплава ВТ14 сваркой трением с перемешиванием с использованием жаропрочного инструмента из сплава ЖС6У

Introduction. The technological process of fabrication products from titanium alloys is often complicated by low quality of welded joints during electric arc or gas-flame welding operations due to high residual stresses and deformations. An example of a successful solution to this problem is the development and implementation of such high-tech processes of metal joining as friction stir welding, which does not refer to the methods of fusion joining. Friction stir welding as an advanced technology is used to obtain joints of “soft” metallic materials, such as aluminum. For “hard” metallic materials, friction stir welding has been limited due to the high demands on welding tools. The aim of this work is investigation of the possibility of using a tool made of the nickel-based heat-resistant alloy ZhS6U in friction stir welding of the titanium alloy Ti-5Al-3Mo-1V. Results and discussion. Optical and scanning electron microscopy results revealed that the structure of the weld is typical of this type of welding, gradient, consisting of a heat-affected zone, thermo-mechanical affected zone and a stir zone with a fragmented structure. When varying welding parameters, it is shown that the defectiveness of the weld is affected to a greater extent by the axial load on the tool, which is caused by a significant difference in the thermal effect on the material. Metallographic analysis methods revealed dissolution of welding tool material fragments in the stir zone of the non-detachable joint. Fractographic analysis of the fracture surface shows that the fracture in the weld zone is ductile, although in this case there are brittle bridges. Varying the parameters of friction stir welding made it possible to obtain an indissoluble joint with at least 90 % of the strength of the base metal.

Friction stir welding of SS 316 LN and Nitronic 50 jacket sections for application in superconducting fusion magnet systems

This study explored the possibility of using friction stir welding (FSW) to join jacket web sections of two nitrogen-containing stainless steels for housing internally cooled superconducting cables which are utilized to generate magnetic fields in tokamak type fusion reactor systems. The two candidate materials chosen for the jacket are SS 316 LN and Nitronic – 50 owing to their desirable mechanical and physical properties at cryogenic service temperature. The current manufacturing techniques to fabricate the jackets or conduits include fusion butt welding. There are some inherent disadvantages of utilizing the fusion joining process such as the possibility of sensitization and the evolution of undesirable phases detrimental to the application. An attempt has been made to fabricate the jackets with FSW to evaluate its feasibility to obtain the desired mechanical and physical properties critical to the application. The welding parameters optimization, workpiece clamping approach, microstructure evolution, hardness line profiles, tensile properties, and magnetic properties of the jacket welds corresponding to both the materials have been discussed in the paper. It has been shown that the FSW fabricated SS 316 LN jackets possessed the required strength and magnetic properties critical to this application.

The effect of laser impingement angle on the optimization of melt pool geometry to improve process stability during high-speed laser welding of thin-gauge automotive steels

Automated laser welding is a popular fusion joining method used for numerous applications involving the joining of similar and dissimilar materials of varying thicknesses. Laser welding offers several advantages over other fusion joining methods such as: high reliability and consistency in the quality of the welds, high production rates, ease of process optimization, higher power density and lower heat input, significantly reduced heat affected zone due to the ability to effectively deliver energy to a highly localized area, and most importantly, improved joint efficiency. However, without proper optimization, the laser welded joints can have significant external and internal defects such as porosity, humping, concavity, and undercut which are widely known to adversely affect the mechanical performance of the joint. The laser welding process is most commonly optimized by adjusting the laser power and the welding speed, but this usually increases the processing time which can be costly in an industrial setting. This work explores the optimization of high-speed laser welding of thin-gauge automotive steels by changing the laser impingement angle during open-keyhole mode welding. The numerical simulations and the experimental results presented in this study clearly show that by optimizing the laser impingement angle, the melt pool geometry can be effectively controlled which eliminates surface defects such as weld concavity and undercut when welding thin-gauge steels at high-speeds without the need for expensive consumables and tighter setups needed for wire-feeding capabilities. The findings presented in this paper hold a major relevance to industries that employ fiber laser systems in welding and additive manufacturing applications which can benefit from improved process efficiencies while minimizing defects.

Multi-objective optimisation of ultrasonically welded dissimilar joints through machine learning

The use of composite materials is increasing in industry sectors such as renewable energy generation and storage, transport (including automotive, aerospace and agri-machinery) and construction. This is a result of the various advantages of composite materials over their monolithic counterparts, such as high strength-to-weight ratio, corrosion resistance, and superior fatigue performance. However, there is a lack of detailed knowledge in relation to fusion joining techniques for composite materials. In this work, ultrasonic welding is carried out on a carbon fibre/PEKK composite material bonded to carbon fibre/epoxy composite to investigate the influence of weld process parameters on the joint’s lap shear strength (LSS), the process repeatability, and the process induced defects. A 33 parametric study is carried out and a robust machine learning model is developed using a hybrid genetic algorithm–artificial neural network (GA–ANN) trained on the experimental data. Bayesian optimisation is employed to determine the most suitable GA–ANN hyperparameters and the resulting GA–ANN surrogate model is exploited to optimise the welding process, where the process performance metrics are LSS, repeatability and joint visual quality. The prediction for the optimal LSS was subsequently validated through a further set of experiments, which resulted in a prediction error of just 3%.

Mitigation of cracks in laser welding of titanium and stainless steel by in-situ nickel interlayer deposition

• Fusion joining of SS-Ti by directed energy deposition of Ni interlayer demonstrated. • Ni interlayer restricted brittle intermetallic formation of Fe and Ti. • Ni between SS and Ti formed joint with graded thermal expansion coefficient. • Thus, Ni interlayer eliminated longitudinal and transverse cracks in SS-Ti joint. • Directed energy deposition of Ni interlayer improved the weld strength. In-situ laser deposition of Ni powder as an interlayer has been exploited to join dissimilar metals, titanium and stainless steel. Direct fusion joining of these materials often suffers from longitudinal cracks due to the formation of hard and brittle intermetallics of Ti and Fe, and also transverse cracks because of large difference in their thermal expansion coefficients. The Ni-interlayer mitigated the longitudinal cracks by acting as an effective barrier to elemental diffusion, thus restricting the growth of brittle intermetallics. As the thermal expansion coefficient of Ni lies between that of SS and Ti, this acted as a functionally graded layer to reduce the thermal residual stresses, thus preventing the formation of transverse cracks across the joint. Maximum ultimate tensile strength of the weld joints obtained was 375 MPa. Results were analyzed by performing various microstructural characterizations using scanning electron microscopy, x-ray diffraction, and energy-dispersive X-ray spectroscopy. The novelty of this method is its easy adaptability in three dimensions contour welding any dissimilar metals using an interlayer of a compatible material.

Investigation on the microstructure and mechanical properties of Ti6Al4V titanium alloy electron beam welding joint

Electron beam welding (EBW) is a fusion joining process particularly suitable for welding titanium plates. In the present work, 2.5 mm thickness Ti6Al4V titanium alloy plates were butt-welded together with backing plates by EBW. The detailed procedures of experiments were used to investigate the microstructure and mechanical properties of welded joints. The optimum welding speed was determined by microstructure examinations, microhardness tests, X-Ray diffraction tests, shear punch tests (SPT) and stress simulation calculations. The results showed that all microstructure of welded metal (WM) was martensite phase under the different welding speeds. In the heat-affected zone (HAZ), the martensite phase gradually evolved to be small and equiaxed. It can be seen that the microstructure of each region in welded joints did not change significantly. When the welding speed is between 8 mm/s and 14 mm/s, it can be seen from the macroscopic appearance of the joints that there was no utterly fused penetration between the butt plate and substrate. Finite element simulation was carried out for the no-penetration depth under different welding conditions, and it was found that the stress suffered by the small no-penetration depth was the smallest. Using different welding parameters shows that the engineering stress in WM was higher than other areas, and BM was the lowest. As welding speed increases from 8 mm/s to 14 mm/s, the variation of microhardness distribution was not evident.

Al-steel dissimilar joining: Challenges and opportunities

Al-steel joining has a lot of use in the automotive and aerospace industries since it saves a lot of weight. The materials' physical, thermal, and metallurgical qualities differed significantly, making connecting this combination difficult. This article provides a comprehensive overview of the Al-steel joining processes. The fundamental reason for the problem in fusion joining operations is the formation of a thick intermetallic compound (IMC) layer and additional difficulties related to solidification. The effects of heat input, wettability, and IMC layer on joint formation are summarised in this article. To achieve a good joint, numerous elements like heat generation, IMC formation, and process parameters must be critically balanced in solid-state joining processes. The effects of process parameters in friction stir welding (FSW) techniques on joint's mechanical and metallographic soundness are explored in this work. Because of the steel's higher strength, there have been various attempts to soften it and make it easier to deform in order to improve weld amalgamation. The use of tungsten inert gas (TIG) welding and electrical resistance heating to achieve heat-assisted hybrid friction stir welding has been documented in the literature. The hybrid joining processes are found to be improving the joint's tensile properties.

Investigations on laser welding of dissimilar joints of stainless steel and copper for hot crack prevention

Fusion joining of stainless steel to copper without a filler material for pipe processing proves itself to be challenging due to the very different material properties of the joining partners and very heterogeneous characteristics in the weld metal due to different mixing ratios. One of the most common weld defects in this material combination is solidification cracking in the weld metal due to liquid copper accumulation between the stainless steel grain boundaries, which cannot withstand the tensile tensions while cooling down. Consequently, these cracks can reduce the mechanical properties, lead to leakages or cause faster corrosion. To prevent cracking, a precise control of the melting and mixing ratio of stainless steel and copper is needed. Laser beam welding offers many capabilities to influence the resulting weld metal shape and size as well as the mixing ratios with different approaches such as parameter optimization, inline process control, or the use of different beam shapes. This work shows different weld configurations and applications using sheets with thicknesses in the area of 1 mm and pipe samples. The main focus is on different solutions to influence the copper dilution and the weld metal geometry for solidification crack prevention. Therefore, a design of experiment approach and inline weld depth control using optical coherence tomography (OCT) data is used for the lap weld configuration to limit the copper dilution below 10 wt. % in steel dominated weld metals. Moreover, the benefits of adjustable intensity profiles for the butt weld configuration to control the shape and dimensions of the weld metal and mixing behavior with different power distributions in the laser beam welding spot are shown. The overall results indicate that solidification cracking in steel-copper joints can be influenced by different process approaches.

Validation of a lightning protection system for a fusion-welded thermoplastic composite wind turbine blade tip

Fusion welding for thermoplastic composite wind turbine blades is being investigated as a replacement for adhesives in bond lines to reduce manufacturing time and cost and to promote ease of recyclability. Resistance welding uses an electrically conductive material, such as carbon fiber, embedded in the bond line to heat the joining surfaces and fuse them together under pressure. One main challenge with fusion joining for large wind blades is the ability to use this conductive heating element in the bond line while still protecting the blade from the catastrophic effects of a lightning strike. This paper outlines the design and manufacturing of a lightning protection system for a 5-m-long thermally welded blade tip. The outcomes of high voltage and high current lightning testing applied to the 5 m blade tip show that the proposed design was able to protect the fusion welded bond lines from significant lightning damage.

Mitochondrial transformations in the aging human placenta.

Mitochondria play a key role in homeostasis and are central to one of the leading hypotheses of aging, the free radical theory. Mitochondria function as a reticulated network, constantly adapting to the cellular environment through fusion (joining), biogenesis (formation of new mitochondria), and fission (separation). This adaptive response is particularly important in response to oxidative stress, cellular damage, and aging, when mitochondria are selectively removed through mitophagy, a mitochondrial equivalent of autophagy. During this complex process, mitochondria influence surrounding cell biology and organelles through the release of signaling molecules. Given that the human placenta is a unique organ having a transient and somewhat defined life span of ∼280 days, any adaption or dysfunction associated with mitochondrial physiology as a result of aging will have a dramatic impact on the health and function of both the placenta and the fetus. Additionally, a defective placenta during gestation, resulting in reduced fetal growth, has been shown to influence the development of chronic disease in later life. In this review we focus on the mitochondrial adaptions and transformations that accompany gestational length and share similarities with age-related diseases. In addition, we discuss the role of such changes in regulating placental function throughout gestation, the etiology of gestational complications, and the development of chronic diseases later in life.

Enhancing fatigue resistance of activated tungsten inert gas welded UNS S32750 super duplex stainless steel by optimizing its technological properties

In engineering industries and heavy manufacturing plants, fatigue life of joints plays a pivotal role in determining the overall life span of the welded joint. In this paper, an advanced fusion joining technique, namely activated tungsten inert gas welding, was used for joining UNS S32750 super duplex stainless steel, with ZnO as activation flux. For the enhancement of fatigue resistance of joints, important welding process parameters were fluctuated according to a developed central composite design model. Empirical relationships were developed between the process parameters and the fatigue strength of the joints, which was correlated with the number of cycles to failure (NCF). Using analysis of variance, the significance of the developed fatigue model was ascertained. Using response surface methodology, optimization of process parameters for enhancement of fatigue resistance was done. It was observed that at the optimized activated tungsten inert gas weld process parameters of travel speed of welding torch at 69.85 mm/min, weld current at 125.20 A, and shielding gas flow rate at 14.77 L/min, a high fatigue life of 7.66396 × 108 NCF was obtained and the model was validated to very high predictability. Microstructural variations in the fatigue-tested specimens were evaluated for identifying the grain modifications.

Research on Fusion Joining of Aluminum Alloy and Galvanized Steel Plates

Research on Fusion Joining of Aluminum Alloy and Galvanized Steel Plates