Figure 6 - available via license: Creative Commons Attribution 4.0 International
Content may be subject to copyright.
Optical micrographs of cross-sections at the weld interface: (a-c) microasperities; ( d-f) locations with attached Al fragments.
Source publication
Ultrasonic metal welding (USMW) is widely used in assembling lithium-ion (Li-ion) battery packs due to its advantages in joining dissimilar and conductive materials in the solid state. However, the welding process and mechanisms are not yet clearly understood. In this study, dissimilar joints of aluminum alloy EN AW 1050 to copper alloy EN CW 008A...
Contexts in source publication
Context 1
... optical micrographs of cross-section I at different welding times in Stage I are shown in Figure 6. To learn the weld formation process, we focused on two characteristic regions: the microasperities (a-c) and the locations with attached Al fragments (d-f) on the Cu surface, which were mainly localized under the indentation of the sonotrode. ...
Context 2
... shown in Figure 6a,d, a gap was located at the weld interface in both regions when the welding time was shorter than 75 ms. Nevertheless, the attached Al fragments were discovered on the copper surface in the unbonded regions, which indicated that a metallurgical bonding between Al and Cu was already achieved at this time. ...
Context 3
... the attached Al fragments were discovered on the copper surface in the unbonded regions, which indicated that a metallurgical bonding between Al and Cu was already achieved at this time. Furthermore, Figure 6d shows that the Al surface fits the outline of the Al fragments. It is suggested that the initial bonding between Al and Cu fractured on the Al side under the shear stress, resulting in the formation of attached Al fragments on the Cu surface. ...
Context 4
... gap between Al and Cu was clearly reduced, and the microasperity of Cu penetrated into Al at a welding duration of 100 ms. As shown in Figure 6b, a strong bonding was formed on the top of the microasperity. Simultaneously, local bonding between the Al and Al fragments can be observed in Figure 6e, which was characterized by bonding with some inside cracks. ...
Context 5
... shown in Figure 6b, a strong bonding was formed on the top of the microasperity. Simultaneously, local bonding between the Al and Al fragments can be observed in Figure 6e, which was characterized by bonding with some inside cracks. Additionally, more and more unbonded regions on the Cu surface were covered by attached Al fragments, which could have promoted the formation of the bonding between the Al and Al fragments. ...
Context 6
... a result, a continuous weld line was observed at the weld interface. As shown in Figure 6c, the microasperity penetrated completely into the Al, where mechanical interlocking could be generated and enhance the joint strength. Nevertheless, there were still a few microcracks that appeared on the Al side, which further confirmed the bonding formed between the Al and attached Al fragments. ...
Context 7
... the welding time was 75 ms, minimal residual Al remained on the surface, and traces of Al oriented in line with the RD. Because no actual joint was form at this time, this residual Al should have been the attached Al fragments shown in Figu 6. This suggests that the initial Al/Cu bonding mainly concentrated on the microasperiti As the welding duration increased, the microwelds grew in the OD, and large continuo welded areas were formed. ...
Context 8
... the welding time was 75 ms, minimal residual Al remained on the Cu surface, and traces of Al oriented in line with the RD. Because no actual joint was formed at this time, this residual Al should have been the attached Al fragments shown in Figure 6. This suggests that the initial Al/Cu bonding mainly concentrated on the microasperities. ...
Similar publications
In this paper, we propose a novel method for planning grinding trajectories on curved surfaces to improve the grinding efficiency of large aluminum alloy surfaces with welds and defect areas. Our method consists of three parts. Firstly, we introduce a deficiency positioning method based on a two-dimensional image and three-dimensional point cloud,...
Citations
... In the context of wiring harnesses, the substitution of copper wires with aluminum serves dual purposes-lowering costs and minimizing fuel consumption. 2 of 10 For such reasons, a reliable joining technique is essential to ensure a robust mechanical and electrical connection between Al and Cu [7]. This raises unique challenges for conventional joining processes due to their distinct chemical and mechanical properties. ...
Ultrasonic metal welding (USMW) finds widespread utilization in automotive industries, where it is used for connecting the wire harness of the vehicle, consisting of stranded wires, to the terminals. However, the behavior of the strands during the compaction process is still understudied and often overlooked. Therefore, this work focuses on the investigation of the wire compaction behavior from a morphological point of view. A newly developed method for investigating cross-sections of such joints is introduced, facilitating area quantification of the strands for a microscale examination of compaction variations for every single strand as a function of welding time. It is shown that the deformation in the wire is not homogenous throughout the wire cross-section; instead, the formation of distinct zones is observed. Three distinct regimes dominating the welding process were observed: (i) linear reduction in nugget height with primary compaction of the nugget and sealing of the interstitial spaces between the strands for weld times from 0 s up to 1.3 s; (ii) accelerated loss of nugget height due to strong plastic deformation of the strands for weld times between 1.3 s and 1.7 s; and (iii) comprehensive welding of the individual strands and strong loss of nugget height. Furthermore, it was demonstrated that the deformation of the wire during the USMW process originates in the coupling area of the horn and the wire and not in the interface of the wire and the terminal. Therefore, it can be assumed that the temperature of the interface between the horn and the wire must be significantly higher than that of the interface between the wire and the terminal. The presented approach and new insights into the behavior of ultrasonically welded joints of stranded wires and terminals provide guidance for improving the welding process.
... Li et al. studied the relationship between the tensile strength of Cu and Al cables that were ultrasonically welded. The welding energy revealed that the tensile strength would first increase with increasing energy and when it reached a peak, it would then decrease with further increase in welding energy [23]. Andreas et al. studied the ultrasonic welding of EN AW-1070 cables with EN CW004A substrate and investigated that the strength of the welded joint increases with welding time [3]. ...
Ultrasonic wire welding is considered a method of choice for creating reliable interconnects in electronics industry including
aerospace, batteries and electric vehicles. In this paper, ultrasonic welding tests between EVR252 copper wire and substrate
are carried out. Novel pattern morphologies are machined on substrates to explore its infuence on mechanical properties of
welded joint. Patterns are divided into three diferent categories e.g., original surface, vertical and horizontal shapes. Cracks,
microstructure strength and tensile properties of welded joint are studied and its joining mechanism is analysed. Compared
with the reference substrate (S1), the welded joint performance of the longitudinal patterns (S2, S3, S4) has been improved,
among which the longitudinal pattern (S4) has the most signifcant improvement (+15%). Likewise, the performance of
transverse pattern (S5) welded joints is relatively poor (−16%). The microstructural analysis using SEM has revealed pre�dominant joint strength on Cu wire surface while maintaining rock-like and compact properties of S4 substrate. Upper side
of wire-harness compactness is frequently observed due to vertical direction of patterns on substrate and also increases the
strength of welded joint. Values of failure load, failure displacement and failure energy absorption were increased by 7.9%,
72% and 35% for S2, 6.1%, 75% and 42% for S3 and 15%, 87% and 113% for S4 compared to S1. Failure modes of welded
joints are mainly characterized into: 1-poor ductility or rupture (no deformation) failure in vertical 3-line pattern joints
2-cylindrical deep holes failure in vertical 3-line zigzag pattern joints and 3-bulging efect failure in horizontal 3-line zigzag
pattern joints. Point and line scans EDS measurement were performed to investigate weaker and stable trends of diferent
locations in welded joints. In S4 substrate, 17.9% carbon content at the position of welded joint was investigated, leading
to content of less oxides and fraction impurities. However, S1 weld zone contains 38.7% carbon content which can weaken
welded joint and reduce durability
... Therefore, this property makes it the perfect choice for manufacturing [4,[34][35][36]. The aerospace industry relies heavily on alloy 7075 which is one of the highest strength lightweight aluminum alloys [37][38][39][40][41][42]. Likewise, alloy 2024 has a strength-to-weight ratio that is its outstanding feature and is used in many manufacturing parts that will be subjected to high levels of stress [43,44]. ...
... The relation between copper and aluminum cross-sections under optimized parameters (a) associated with Al cross-sections (b) associated with Al cross-sections under different locations and (c) associated with Al and Cu cross-sections. Reproduced with permission from IOP-MDPI publisher[39,128]. ...
... Therefore, this property makes it the perfect choice for manufacturing [4,[34][35][36]. The aerospace industry relies heavily on alloy 7075 which is one of the highest strength lightweight aluminum alloys [37][38][39][40][41][42]. Likewise, alloy 2024 has a strength-to-weight ratio that is its outstanding feature and is used in many manufacturing parts that will be subjected to high levels of stress [43,44]. ...
... The relation between copper and aluminum cross-sections under optimized parameters (a) associated with Al cross-sections (b) associated with Al cross-sections under different locations and (c) associated with Al and Cu cross-sections. Reproduced with permission from IOP-MDPI publisher[39,128]. ...
The lightweight alloy sheet materials have been widely used in industries such as automobiles, aviation, and aerospace. However, there are huge challenges in the structural joining process. Likewise, industries are probing new technologies and are rapidly adapting to more complex light alloy materials. The ultrasonic metal welding is a reliable solid-phase joining technology, which has incomparable development prospects in the high-strength joining of lightweight alloy sheet materials. This article summarizes the research progress of ultrasonic welding of aluminum alloy, magnesium alloy, and titanium alloy thin plates in recent years. The key features of this review article are the ultrasonic welding process, advantages, applications, and limitations. It introduces the welding process parameters to explore the breakthroughs for straightforward direction. Furthermore, to strengthen the phenomena, the current state of the ultrasonic welding of lightweight alloys and their future perspectives are also reflected.
... Different properties of joining partners, e.g. significant hardness difference between Al and Cu, could have an influence on the weld formation process [8,36,37] as well as the system dynamics [34]. Second, due to the low sampling rate, the acquired measurement data has been analyzed almost exclusively in the time domain and the signal features in the frequency domain have not been thoroughly studied. ...
... The results of this study are in accordance with our previous investigation [37] regarding the bond evolution at the weld interface during USMW: The strong bonding appeared initially at the edge of the weld zone in the time span of 150-200 ms, which has 60-70 % of the mechanical performance as the base materials. After then, the weld area expanded gradually in the center of the weld zone and resulted in further enhancement of the mechanical propriety. ...
In recent years, ultrasonic metal welding (USMW) has gained considerable research attention due to the increasing application of lithium-ion batteries in electric vehicles. Although USMW is widely used in battery manufacturing, the fundamental understanding and monitoring of the welding process needs to be investigated to ensure the process robustness. Therefore, this work aims to establish in-situ observation of the bond formation process by using Laser-Doppler Vibrometry (LDV). The acquired velocity data was analyzed in the time and time- frequency domains. Based on the relative motion, a five-stage model was developed to describe the welding process. The changes in system dynamics led to the formation of sidebands in the frequency domain. Addi- tionally, the power consumption was recorded by the welding system, which had a good correlation with the system dynamics. The results provided the scientific understanding behind the bond formation process and suggested relevant signals for in-process monitoring.
... The latter is the simplest and most commonly used method. In order to optimize welding conditions, numerous attempts are made to establish the relationships between the process parameters (amplitude, compression (clamping) force, welding time, etc.) and the actual weld area (AWA) [8][9][10][11][12], linear weld density (LWD), and the average thickness of the top material after welding [8,13], since both the electrical conductivity and mechanical properties of joints depend on these characteristics [2,8]. ...
... An increase in both of these parameters to optimum values leads to an increase in the strength of joints [1][2][3][4][5][6]. However, long-term USW under the action of a large clamping force leads to excessive penetration of the ridges of the tip and anvil into the sheets to be joined and their thinning [8][9][10][11][12][13][20][21][22][23]. In such cases, the failure of joints occurs by the pull-out mode taking place in the thinnest, "weakest" section of a sheet under stress, which is less than the actual strength of the joint. ...
... In such cases, the failure of joints occurs by the pull-out mode taking place in the thinnest, "weakest" section of a sheet under stress, which is less than the actual strength of the joint. Therefore, the ridge penetration depth or vertical (i.e., normal to the interface) displacement of a sonotrode, as well as the amplitude of oscillations, clamping force (or normal pressure), welding time, and temperature in the contact zone, are often controlled [2,11,[23][24][25][26][27][28]. ...
Joints of copper sheets with a thickness of 0.8 mm were produced by ultrasonic welding. To assess the quality of the joints, tensile lap-shear strength, area fraction of bonding, distributions of normal strains in the cross sections of welded samples, linear weld density at a magnification of ×1000, and the microstructure and microhardness of welded samples were analyzed. It was proved that the arrangement of microbonds and length of gaps in joint zones significantly depended on the local normal strains of welded samples caused by the penetration of tool ridges under the clamping pressure. Joint regions with a linear weld density of more than 70% were observed if the local compression strains of the sample exceeded 15%. The appearance of local tensile strains was accompanied by a drop in the linear weld density of the joints in some regions, down to 5%. The distribution of normal strains depends on the mutual positions of the ridges of the welding tip and anvil. It is concluded that in order to improve the quality of joints obtained by ultrasonic welding and reduce the scatter of their strength values, welding tools should provide sufficiently high normal compression strains in the weld spot area.
There are a lot of problems with the conventional fusion welding process, so ultrasonic welding has been used for about 20 years and has helped a lot of manufacturing industries, including aviation, medicine, and microelectronics. Ultrasonic welding takes less than one second, making it suitable for mass production. Poor weld quality and joint strength are common issues that industries encounter as a result of this process. Actually, the success and quality of the welding are determined by its control parameters. This research examines the impacts of weld time, vibrational amplitude, and weld pressure on the welding of 0.6 mm thick sheets of two different metals, specifically copper and aluminum (AA2024). Responses, including tensile shear stress, weld area, and T-peel stress, are acquired through experiments that follow a full factorial design including four replicas. The highest recorded tensile shear stress was 4.34 MPa, the maximum weld area measured was 63.6 mm², and the peak T-peel stress reached 1.22 MPa. A second-order non-linear regression model was constructed using all of these data points, which related the responses to the predictors. Due to the importance of quality in the production sector, the process parameters were determined by the combination of genetic algorithm (GA) and fuzzy logic (FL) approaches. The impact of the weld zone temperature on various quality characteristics has been investigated through experiments. It has been noted from the confirmatory test that FL produces superior output outcomes compared to the genetic algorithm, with FL achieving a fuzzy multi-performance index of 0.94 compared to 0.61 for GA. By conducting microstructural analysis, weld quality levels, including “under-weld,” “good weld,” and “over-weld,” were established.
The high weld quality of dissimilar aluminum (Al)/copper (Cu) joint is essential to improve the reliability of connecting components in secondary batteries. This study was aimed at enhancing the weld quality of dissimilar Alsingle bondCu joints to connect tab-to-busbar in secondary batteries. AA1050 and Ni-coated Cu (C1100) sheets were lap-welded using dual-beam laser welding with a continuous-wave (CW) laser for welding and a pulsed laser for preheating. Consequently, the weld quality was investigated by characterizing the morphology, microstructure, and mechanical and electrical properties of the joints. For comparison of the weld quality, single-beam welding was also performed. Soundly welded joints were achieved using a dual-beam at a CW laser power range of 1000–1400 W for fixed pulsed laser power and welding speed of 100 W and 80 mm/s, respectively. Microstructural analysis of the weld indicated that the upper weld metal (WM) comprised α-Al and Al-Cu eutectic phases, whereas the lower WM exhibited mixed morphology of different phases including Al2Cu, AlCu, Al3Cu4, and Al4Cu9. Further, the electrical resistance was linearly correlated with weld penetration depth, exhibiting a minimum of 352.3 μΩ against a penetration depth of 341.7 μm. In addition, The Vickers micro-hardness and lap shear tensile testing of soundly welded sample (A4) exhibited an average hardness value of 921.7 HV in the lower WM, and the average tensile load for the welded sample was 247.4 N. This study provides valuable insights for improving the weld quality of reliable Al-Cu dissimilar joints for connecting tab-to-busbar in secondary batteries.
The cold spot forge-welding method, recently developed to achieve high-productivity and high-strength dissimilar material joining, was applied to multiple solid-phase joining of aluminum (Al) foils simulating tab-lead electrodes. Fifty Al foils of 12-μm thickness were sandwiched between 0.5 and 0.8 mm A1050 Al alloy plates and pressurized with 6-mm diameter punch for 1 s. The effect of bonding temperature (330–420 °C) and the reduction ratio (R, 1.4–3) on the tensile shear load of the joint was investigated. A lower R value at a higher bonding temperature resulted in base metal fracture (i.e., plug fracture) of the Al alloy plate. The maximum load reached 410 N using a reduction ratio of higher than 2.1 and bonding temperature of 420 °C. The processed foils were properly stretched in the plane without breakage, and a total of 51 sound layered bonded interfaces were formed. The results also confirmed that the oxide film became more rarefied with increasing R. These results are expected to be applicable to high-throughput, high-reliability bonding of secondary battery electrodes.
