Welding Of Copper Research Articles

Effect of Tool Geometry on the Microstructure of Friction Stir Welding of Copper and 316L Stainless Steel

The microstructure evolution during dissimilar friction stir welding of copper with stainless steel 316L is studied. The welding is performed in transparence configuration using tools of two different geometries. The joints are characterized by optical microscopy, scanning and transmission electron microscopy, electron backscattered diffraction, and microhardness. The microstructure and crystallographic texture of base metals are significantly affected. The joint produced using a shoulder of 8 mm in diameter is characterized by a copper nugget with refined grains. The texture of copper is dominated by component of the shear texture. The steel beneath the tool shows a grain refinement with grains of sub‐micron size and a texture which is close to the ideal simple shear texture. For the joint produced by the 16 mm diameter tool shoulder, the nugget consists of large grains of copper, while the steel beneath the tool shows small recrystallized grains of micrometer size. The texture in the steel is dominated by the component of the shear texture. The Cu/316L interface in both types of joint is of very good quality. In a detailed study of the interface, it is revealed that the welding of metals is achieved by mutual intense mechanical interlocking without formation of any intermetallic compounds.

Experimental Investigation on the Effect of Nickel-plating Thickness on Continuous-wave Laser Welding of Copper and Steel Tab Joints for Battery Manufacturing

The welding of dissimilar materials, such as copper and steel, holds significant industrial significance in the production of electric vehicle batteries. These materials are commonly used in the case of connections between busbars and cylindrical cells inside a battery pack. To optimize welding and guarantee protection against corrosion, nickel is commonly used in the form of a coating. In this paper, the effect of nickel plating thickness on copper-to-steel welds made with laser technology is investigated. The initial phase consists of a statistical characterization of the nickel plating thickness of the busbar in order to identify the thickness ranges. Experiments were conducted using two different fiber laser sources (a single-mode laser source and a beam-shaping laser source) equipped with a Galvo scanner head; the fluence value and the thickness of nickel plating varied during the experiments. The study conducted has revealed that the thickness of nickel plating plays a crucial role in the weld bead interface, particularly when using a single-mode source. Furthermore, when using the beam-shaping laser source, the fluence employed can have a significant impact on both the depth of penetration and the interface width.

Tailored laser beam shapes for welding of copper using green laser radiation

AbstractThe rapid development of laser beam sources and adapted welding technologies in recent years lead to an increased use of laser welding techniques in automated production nowadays. Especially its precision and local energy input are key features for joining applications in electric vehicle components, where joints have to meet both mechanical and electrical requirements as current-carrying connections. However, the copper materials used are difficult to weld due to their physical properties, making a stable process with fewest seam imperfections only feasible within a limited process window. Recently available beam sources emitting visible laser radiation have proven to overcome the low absorptivity at process start, but spattering is still a prone defect significantly affecting process efficiency and quality. Literature approaches for modifying the energy input point to laser beam shaping as a method for reducing process imperfections, which, however, has not been extensively researched in copper processing using green laser radiation.Thus, this study investigates the influence of a shaped intensity profile for visible laser radiation created with a reflective diffractive optical element in laser beam welding with laser powers up to 3 kW. A characterization of the process dynamics is performed by use of high-speed imaging, and metallographic analysis is used to elaborate benefits of the applied beam shapes. With beam shaping, an enlarged heat conduction welding regime and an advantageous seam shape are found. Furthermore, a decrease in spatter formation during deep penetration welding is detected for the elliptical beam profile, which correlates with an oscillation movement of the capillary.

Suppression of spiking defects in deep penetration electron beam welded ETP copper

The electron beam is an appropriate tool to weld pure copper due to its high absorptivity on the copper surface, a high power density and inert vacuum environment. However, deep penetration electron beam welding of pure copper often produces the spiking defect. In this work bead on plate electron beam welding was done on Cu-ETP. A critical welding speed was determined for the distinction between a conduction-determined (at lower welding speed) and a non-conduction-determined welding speed range (at higher welding speed). The influence of high preheating temperatures was shown. The welds were investigated by light optical microscopy, electron backscatter diffraction measurements, ultrasonic testing, in situ thermal imaging, electrical resistance measurements and tensile tests. It was shown that in the conduction-determined welding speed regime without preheating, full and partial penetration welds exhibited root porosity. This effect was related to the overheating of the weld pool in combination with the phenomena causing spiking. Low defect root formation was achieved by using welding speeds greater than the critical value or by applying high preheating temperatures. The joints reached up to 98% of the international annealed copper standard in terms of specific electrical conductivity. Rupture took place within the joints during tensile tests. The joints exhibited up to 77% of the ultimate tensile strength of the base metal. Welds carried out with preheating exceeded the base metal regarding the fracture strain.

Influence of flux agent composition on the ionization potential in A-TIG welding of the electrolytic tough pitch copper (Cu-ETP) sheets

Due to its high thermal expansion coefficient and high thermal conductivity, welding of copper and copper alloys is considered difficult and demanding. Activated TIG welding (A-TIG) welding has been widely researched as a welding method for obtaining deeper penetration on various metals. However, A-TIG welding of copper remains unexplored without guidelines on the influence of flux agents and the influence of the applied parameters and achieved mechanical properties in produced welds. In this paper three agents were used as single component fluxes: calcium oxide (CaO), silicon dioxide (SiO2) and sodium carbonate (Na2CO3) for A-TIG welding Cu-ETP sheets. Welds were characterized by visual inspection and macrostructural analysis, also bend testing and tensile strength testing were conducted. Microstructure of the weld with optimal mechanical properties was analyzed by means of Field Emission Gun-Scanning Electron Microscope (FEG-SEM) and also the chemical characterization of the weld was made by means of Energy Dispersive Spectroscopy (EDS). The results showed that the most effective flux used was silicon dioxide. Welds welded with SiO2 showed good results in visual inspection, macrostructure analysis and band test and also have acceptable values of tensile strength. However, oxide inclusions have been found in weld metal in significant percentage which could indicate the possible degradation of electrical conductivity of the material.

Experimental study on magnetic field-assisted laser scanning welding of T2 copper

The study employed laser scanning welding technology for butt welding experiments on red copper, investigating the behavior of metal vapor plumes, plasma, and metal spatter during the welding process, as well as the quality and electrical conductivity of the resulting joints by varying the polarity and strength of the applied magnetic field. The results showed that the polarity of the magnetic field had a minor effect on welding performance, with the main influencing factor being the strength of the magnetic field. As the magnetic field strength increased, the formation volume and ejection intensity of metal vapor plumes and plasma exhibited an initial decrease followed by an increase, similarly affecting the weld seam morphology, mechanical properties, and electrical conductivity. At 120 mT magnetic strength, metal vapor and plasma formation are minimized, and metal spattering is eliminated, thereby enhancing welding stability; the weld seam was uniformly formed with no significant defects; the cross-sectional weld was even without obvious undulations; on one side of the weld zone, columnar crystals were extremely fine, and the center of the weld consisted of numerous equiaxed crystals with a few columnar crystals perpendicular to the horizontal direction, while the equiaxed crystals on the other side of the weld zone were denser; the sample joints achieved peak hardness and tensile strength at 70.9 HV and 202 MPa, showing increases of 17.2% and 14.8%, respectively, over nonmagnetic conditions; the weldment’s conductivity peaked at 79.58 mS/m, 36.5% higher than without a magnetic field, reaching 97.9% of the parent material’s.

Combined experimental and theoretical approach to improve measurement accuracy of temperature-dependent reflectance of copper for near-infrared lasers

AbstractThe low process stability of laser welding of copper with near-infrared lasers requires precise input data for process control and meaningful simulations. But meanwhile, available datasets of temperature-dependent reflectance or absorptance for near-infrared lasers on copper do not show good agreement between the different sources and often do not include the fusion process, which is of crucial importance for realistic laser welding simulations. Additionally, most of the datasets are only calculated. Therefore, in a previous study, temperature-dependent reflectance measurements were performed on electro tough-pitch copper using a near-infrared laser. The measurements revealed a reflectance drift, which was induced by the setup behavior during heating, and the time-dependence of chemical reactions like the redox-reaction as possible error sources. In this study, experiments on laser melting as the fundamental process of laser welding were performed, together with corresponding simulations using the measured reflectance values for oxide-reduced and for untreated copper from the previous study. Then, the simulations were compared with the experiments to estimate the accuracy of the reflectance measurements. To provide context, the same simulations were also conducted using reflectance datasets from other authors. In a second step, the reflectance data were corrected with respect to the reflectance drift and the effects of redox reactions were adapted to the conditions of the laser melting experiments. Using the resulting reflectance curves, an improved agreement of simulation results and the experiments was achieved over a range of different test cases, without the necessity of correction factors in the simulation model.

Evaluation of pore formation during welding of copper using different laser sources

In the recent years laser beam welding has become an established joining technology especially for copper components. Therefore, the combination of process efficiency, process reliability and the quality of the resulting welds has been improved significantly. However, in many cases the resulting welds show a high amount of weld defects, such as pore formation. As these weld defects degrade both, the mechanical and electrical properties of the weld seam, it is from great interest to understand the cause effect relations of pore formation to develop process strategies and new system technologies to minimize or avoid such defects especially for industrial applications.Recent investigations by Bosch at the electron-synchrotron DESY enabled in-situ observation of the pore formation during welding. The cause effect relations of pore formation were analyzed for different laser wavelengths. This is the first time worldwide, that beside the formation of process pores a further pore formation mechanism at welding copper, the formation of gas pores, is observed and discussed using in-situ X-ray process observation. In addition, another pore formation, the so-called needle pore formation, was observed when welding copper in edge weld configuration. In this contribution, two different types of pore formation mechanisms, gas pore formation and needle pore formation, at welding copper are presented and discussed.

Tailored beamshape sequences for welding using a Dynamic Beam Laser

The industry requires high efficiency and superior quality in welding metals, particularly for complex geometries and hard-to-weld materials. In the past decades the laser has proven to be the right tool for fast and reliable welding. Especially superimposed beam oscillations in the kHz-domain enhance welding results by distributing heat over a wider area, reducing distortion and spatter. Another recent approach is to create multiple spots, lines, squares as well as intensity modulation between center and ring. Due to technological restrictions, these two common approaches are limited to rather static beamshapes. They lack the ability to be truly dynamic in the MHz-domain and therefore are unable to reach fine dynamic control over the melt pool. This paper presents the unique possibilities of coherent beam combining to create dynamic beamshape sequences for melt pool control tailored to copper and aluminum welding.

Investigation on indirect laser welding of copper to aluminum

Laser beam welding of aluminum (Al) to copper (Cu) is challenging due to the formation of intermetallic compounds that are brittle and have high resistivities. However, the Cu/Al phase diagram shows a region were solubility of Cu in Al is present and, on the other hand, a region with the formation of a eutectic phase between α-Al and Al2Cu is present as well. Targeting this area turned to be advantageous for solid state welding, as shown for probeless Friction-Stir-Spot-Welding realizing ductile joints between Al and Cu.In this paper an approach based on indirect laser welding of Cu with Al will be presented and discussed. A green laser was used in order to join Cu to Al in lap joint configuration. The laser beam irradiates the Cu surface, whereby the formation of a common melt pool between Cu and Al is avoided. The heat input and the temperature gradient are assumed to support diffusion at the interface between Cu and Al forming a near eutectic layer. Indeed, a melting layer is formed at the interface between Cu and Al supporting joint formation based on a firmly bonding between both materials. The solidified layer presents a copper rich area towards the copper sheet with plate-like structures of Al2Cu, a region with α-Al crystals on the aluminum side and a eutectic layer of lamellar Al2Cu and α-Al in between. The described morphology is very similar to investigations on probeless Friction-Stir-Spot-Welding, whereas a very low pressure is adopted in indirect laser welding and Al-oxide layer seems not to act as a barrier for joint formation.

Characterizations of laser transmission welding of glass and copper using nanosecond pulsed laser

Characterizations of laser transmission welding of glass and copper using nanosecond pulsed laser

Temperature-Dependent Reflectance of Copper with Different Surface Conditions Measured at 1064 nm

AbstractIn order to fully understand and to eventually overcome the instabilities in laser welding of copper using 1064 nm wavelength lasers, it is important to get a deeper understanding about the interaction of the incident beam with the copper surface during the process. One of the main parameters determining this behavior is the temperature-dependent absorptance. However, the existing datasets only show little consistency between the different sources, do often not include the important absorptance step at melt temperature, or they are only calculated. This article thus presents an experimental approach to measure the reflectance of electro tough-pitch copper (Cu-ETP) from room temperature until beyond the melting point with an integrating sphere setup. The setup was developed with particular attention to measurement accuracy up to high temperatures. The reflectance using a 1064 nm laser under an incident angle of 12° has been measured for four different sample groups, which are untreated rolled copper, mechanically polished copper, oxide reduced copper and resolidified copper. The measurement results reveal significant differences in the temperature-dependent reflectance between the sample types and, for some types, also between the samples of the same type. This study investigates the origins of the most significant features in the reflectance curves and their potential impact on processing copper using NIR lasers.

Blue diode lasers – Understanding and influencing melt pool dynamics in copper

Within the last years an increasing demand of copper components was observed, especially in the fields of energy transition, e-mobility, or digitalization. For joining those components, laser welding has become more and more popular. Infrared lasers are commonly used for metal welding. They are characterized by a low absorptivity in solid copper at room temperature. In contrast, lasers in the blue wavelength spectrum are characterized by a significantly higher absorptivity. This facilitates the initial energy input into the material and makes the welding process more efficient. Further, in the liquid state, the absorptivity change in copper is much smaller for the blue wavelength. This results in a continuous heating of the material, a more stable melt pool and a lower amount of spatter. One supplier of lasers in the visible wavelength spectrum is Laserline. In 2023, they launched a 4 kW blue diode laser, the currently highest available power for this wavelength. It makes accessible a broad variety of applications. But the scientific investigations for the blue wavelength at a power of several kilowatt are still limited. It is the paper’s purpose to extend them by analysing welding of copper and its alloys with a blue diode laser. One the one hand, synchrotron trials were performed allowing a look into the material during welding. A special focus was on the transition between heat conduction and deep penetration welding as well as the keyhole behaviour. On the other hand, conventional welding trials were performed analysing the impact of beam shaping on the melt pool dynamics.

Effect of different pulse shapes on the laser welding of aluminum and copper

The Nd: YAG laser is utilized to weld 1060 aluminum (Al) and 110 copper (Cu) with a thickness of 0.4 mm. The effect of different pulse shapes on the microstructure, mechanical and electrical properties of Al-Cu lap joints are investigated by using of the optical microscopy, scanning electron microscope (SEM), tensile test device and micro-resistance tester, respectively. This investigation provided a detailed understanding of how the different pulse shapes influence the metal mixing and the formation of intermetallic compounds (IMCs). The results indicate that the pulse shape with an initial preheating phase improved the laser absorption efficiency. Additionally, this pulse shape resulted in less dissimilar metal mixing compared to the pulse shape that maintained the maximum power throughout. Furthermore, the pulse shape in which the laser power was linearly increased and then maintained at maximum power reduced the formation of IMCs at the joint interface. As a result, the joint exhibited mechanical strengths up to 92 % of the Al base material and similar electrical conductivity. The study provides theoretical guidance on how to utilize pulse shape modulation in laser welding to achieve optimal mechanical and electrical properties in typical joints between Al tabs and Cu busbars.

A molecular dynamic simulation-based study on nanoscale friction stir welding between copper and aluminium

ABSTRACT The primary aim of this study is to enhance our understanding of friction stir welding (FSW) at the atomic level. To accomplish this, we utilised molecular dynamics simulations to examine the nanoscale fusion welding of dissimilar metals, i.e. aluminium and copper, through the FSW method. Our particular focus was on how the rotation speed of the tool affects structural changes and defect evolution during the nanoscale FSW process. Our research findings revealed that the region subjected to frictional stirring undergoes a phase change as a result of extensive plastic deformation during the FSW operation. Notably, stacking faults and similar defects were predominantly observed on the advancing side as the tool rotated and moved into the friction stir zone. Further, investigation of atomic shear strain snapshots indicated that higher rotational speeds resulted in a broader and more scattered friction stir zone, requiring a longer recovery time compared to slower rotational speeds. Additionally, the changes in atomic concentration during FSW have been studied using displacement vectors, concentration profiles and diffusion coefficient parameters. We also conducted simulation-based tensile and shear deformation tests, which revealed that higher tool rotational speeds led to enhanced material interlocking, consequently improving the mechanical strength of the FSW joints.

Effect of the tool rotation direction on the joint properties of the pinless friction stir spot welding of pure copper

The main goal of this work is to explore the effect of the tool rotation direction with spiral groove on the joint properties of the pinless friction stir spot welding (PFSSW) of thin pure copper sheet. For this purpose, the surface appearance, cross-sectional morphology, microhardness, welding temperature and joint strength of the welded joints under the tool rotation conditions of clockwise and anticlockwise were studied comparatively at different rotation speeds. The fracture modes of welded joints under different tool rotation directions were also analyzed. The results show that the tool clockwise rotation has higher welding strength than anticlockwise rotation at lower rotation speeds, while the opposite is true at higher rotation speeds. Under the clockwise rotation of the tool, the fracture modes of the welded joints are shear fracture and plug shear fracture. When the tool rotates anticlockwise, the fracture modes of the welded joints are shear fracture and plug shear-pullout fracture. Furthermore, the depth of the stir zone produced by anticlockwise rotation of the tool is higher than that produced by clockwise rotation. Overall, the microhardness with anticlockwise rotation of the tool is higher than that with clockwise rotation. In addition, the tool rotation direction has little effect on the welding temperature. The research content can provide a reference for the selection of the tool rotation direction of the PFSSW.

A multi-physics CFD study to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser welding of copper to steel for battery terminal-to-casing connections

This study aims to investigate the impact of laser beam shaping on metal mixing and molten pool dynamics during laser beam welding of Cu-to-steel for battery terminal-to-casing connections. Four beam shapes were tested during LBW of 300 µm Cu to 300 µm nickel-plated steel. Both experiments and simulations were used to study the underlying physics. A CFD model was firstly calibrated against experiments and then deployed to explore the effect of the increasing ring-to-core diameter, as well as a tandem laser spot configuration. The study showed that metal mixing is influenced by the keyhole dynamics and collapse events, but also there is an intricate interplay between keyhole geometry, fluid dynamics via Marangoni forces and buoyancy forces. Notably, the buoyance forces due to the different densities of steel and Cu, along with the recoil pressure contribute to the upward flow of steel towards Cu, and hence impact meaningfully the material mixing. The study pointed-out that the selection of a custom ring-to-core diameter and ring-to-core power is a decision with a trade-off between the need of stabilising the keyhole dynamics and the need to reduce the mixing. Findings indicated that 350 µm ring and 90 µm core with 30% of ring power (weld configuration C3) resulted in more stable dynamics of the keyhole, with significant reduction of collapse events, and ultimately controlled migration of steel towards Cu. Additionally, the pre-heating approach with the tandem beam only led to local fusion of Cu and no significant improvement in keyhole stability was observed.

Investigation of the Processes of Structure Formation during Explosion Welding of Copper and Molybdenum

This article examines the processes of structure formation occurring during joint plastic deformation by the explosion of copper and molybdenum. These components are dissimilar metals with very limited mutual solubility under normal conditions, and the circumstances allowing for their interaction, as well as the products of the mechanochemical reactions of such interactions, have not been sufficiently studied and require new approaches. A cluster approach was used to describe the processes of structure formation, which describes phase formation as the process transitioning of the polyhedron of the initial phase into the polyhedron of the final phase. This work shows that under the conditions under consideration, not only is the formation of solid solutions in the contact zone with smooth concentration transitions from one component to another possible, but also the formation of new structural states, which can be represented as localized icosahedral atomic configurations (amorphous metal clusters). Such a structure is capable of locally strengthening the composite, which is confirmed by microhardness studies.

Microstructure and mechanical properties of ultrasonic welded copper to aluminum cables joints

The experiments of ultrasonic welding were carried out for BVR2.0 copper (Cu) cables and BLV6.0 aluminum (Al) cables with different welding parameters. Scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), temperature measurement, microhardness evaluation and tensile tests were conducted to investigate the microstructure and mechanical properties of Cu−Al cables joints. The results show that the tensile load of Cu−Al joints reaches 355.6 N, while the welding parameters are set as follows: welding pressure of 0.21 MPa, amplitude of 31%, and time of 860 ms. The diffusion thickness of well-welded Cu−Al joint is only about 3 μm and the peak temperature is 212 °C, which avoids the formation of intermetallic (IMC) effectively. The joint fractures on the copper side rather than the interface of the Cu−Al with a ductile−brittle hybrid fracture mode, indicating that the joint has excellent properties.

Comparison of melting efficiency between blue, green, and IR lasers in pure copper welding

Pure copper parts are commonly used in many industrial products because of their low thermal resistance and high electrical conductivity. However, connecting high-quality and high-efficiency copper materials remains a challenge. This is because pure copper has low absorption of near-infrared light, making it difficult to weld stably with a near-infrared laser. Visible light lasers should realize high-efficiency laser welding of pure copper. However, there are few reports comparing the laser wavelength dependence of welding efficiency for pure copper. In this study, bead-on-plate welding was performed on pure copper plates of 2 mm thickness using a 1.5 kW blue diode laser (445 nm), a 16 kW IR disk laser (1030 nm), and a 3 kW green disk laser (515 nm). Bead-on-plate welding of pure copper was performed in the thermal conduction mode or the keyhole mode by varying the laser spot diameter and power, and the amount of melting was measured from cross-sectional observations. As a result, compared to the IR disk laser, blue and green lasers showed higher melting efficiency in both the thermal conduction and keyhole modes, and the melting behavior was more stable. In thermal conduction mode welding, the melting efficiency was 0.2% with the IR disk laser and 0.7% with the blue diode laser. In keyhole mode welding, the melting efficiency with the blue diode laser or green disk laser was about 7%, which is equivalent to that with the IR disk laser with 2.5 times the output power.