A method of welding copper and its alloys

Abstract

The application provides a welding method of copper and its alloy, which comprises the following steps: obtaining a substrate, the material of the substrate is copper or copper alloy, and cleaning and drying one side of the substrate as a cladding surface; preparing an FeCoCrNi high-entropy alloy cladding layer on the cladding surface through a powder feeding laser cladding technology, the FeCoCrNi high-entropy alloy cladding layer comprises a first layer and a second layer which are stacked on the cladding surface in sequence, and the laser power of the first layer is higher than that of the second layer; cutting a composite sample with the FeCoCrNi high-entropy alloy cladding layer from the cladded substrate, and adopting a laser oscillation welding technology to butt weld the FeCoCrNi high-entropy alloy cladding layers of two composite samples. The application can provide an innovative technical solution for obtaining a copper and its alloy welding joint with high performance and high reliability.

Description

Technical Field

[0001] This invention relates to the field of welding technology, and in particular to a welding method for copper and its alloys. Background Technology

[0002] Copper and copper alloys play an irreplaceable role in fields such as power electronics, new energy vehicles, aerospace, chemical machinery, and transportation due to their excellent electrical and thermal conductivity, corrosion resistance, and good machinability. Particularly in the automotive manufacturing sector, copper and copper alloys are widely used in critical components such as motor windings, battery connectors, sensor terminals, high-voltage wiring harness connectors, and electronic control unit (ECU) circuit connections. The quality of these connections directly affects the overall electrical performance, safety, reliability, and service life of the vehicle.

[0003] However, welding copper and copper alloys, especially laser welding, has always faced significant technical challenges. These challenges are particularly pronounced in automobile manufacturing, as automotive parts often require highly efficient and automated welding processes, and the welds must meet extremely high mechanical strength and electrical conductivity requirements. The primary difficulty lies in copper's extremely high reflectivity to most commonly used industrial high-power near-infrared lasers (wavelengths typically around 1 μm), while its absorption rate at room temperature is extremely low, usually less than 5%. This makes it difficult for laser energy to be effectively coupled into the workpiece, resulting in exceptionally difficult initial melting. Although the absorption rate of near-infrared lasers increases significantly once copper melts and forms a molten pool, its extremely high thermal conductivity (almost five times that of pure iron) rapidly dissipates the input heat, leading to poor molten pool stability and difficulty in achieving ideal penetration depth and weld formation. To overcome the problems of high reflectivity and high thermal conductivity, traditional methods often require extremely high laser power, but this not only increases energy consumption but also exacerbates the uncontrollability of the welding process, easily producing defects such as spatter and undercut, which is unacceptable for precision, mass-produced automotive parts.

[0004] During welding, copper and copper alloys are prone to various metallurgical defects. Their high coefficient of thermal expansion and solidification shrinkage lead to high welding stress. Furthermore, impurities in the molten pool (such as lead, bismuth, sulfur, and oxygen) easily form low-melting-point eutectics, making the weld seam highly susceptible to hot cracking. In addition, liquid copper can dissolve a large amount of hydrogen, but the solubility of hydrogen decreases sharply during solidification. If the hydrogen does not escape in time, hydrogen pores will form. Hydrogen can also react with cuprous oxide in the molten pool to generate water vapor, forming water vapor pores, making copper welds far more susceptible to porosity than steel. In the welding of copper busbars in automotive battery packs, any pores or cracks can lead to increased resistance, localized overheating, and even serious malfunctions.

[0005] To address the aforementioned challenges, existing technologies have been explored in the automotive manufacturing field. For example, attempts have been made to use blue or green lasers for welding, as copper exhibits significantly increased absorption of these short-wavelength lasers in its solid state (e.g., copper absorbs up to 40% of 515nm green light, approximately eight times that of infrared lasers). Blue lasers (~450nm) reportedly consume 84% less energy than infrared lasers when welding copper, which is significant for reducing energy costs in automotive production lines. However, current high-power colored lasers are expensive, and their penetration ability in thick materials is still insufficient when used alone, potentially limiting their application in welding thick copper windings for electric vehicle motors. Another proposed solution is a combination of near-infrared and blue lasers, using blue light for initial melting and then leveraging the high absorption rate of near-infrared light in the molten pool to increase the weld depth. This composite light technology has been tested for welding components such as hairpins and battery tabs in new energy vehicles. However, simple beam combining still struggles to effectively control the dynamic behavior of the molten pool. The concentrated energy input of near-infrared lasers easily leads to violent fluctuations in the molten pool, causing spatter and poor forming. Furthermore, some methods propose using low-power lasers to roughen the area to be welded before welding to increase surface roughness and improve the absorption rate of subsequent welding lasers. While this method has some effect, it increases the number of process steps, placing higher demands on process coordination and equipment precision for the fast-paced automated automotive production lines.

[0006] In welding highly reflective metals, beam oscillation (or beam swinging) technology has been applied to welding alloys such as aluminum and titanium. This technology stabilizes the molten pool and reduces defects by increasing the interaction area between the laser beam and the material. However, effectively applying it to welding copper and copper alloys, which have extremely high laser reflection and rapid thermal conductivity, still faces the challenge of optimizing the oscillation mode, frequency, and trajectory to precisely control heat input and molten pool flow, thereby suppressing spatter, porosity, and ensuring uniform weld formation. For thin copper sheets (such as circuit boards) and small structural components commonly used in the automotive industry, single-mode lasers combined with oscillation welding have proven effective, but their process window is narrow and requires precise control.

[0007] In summary, high-quality, high-efficiency, and high-reliability laser welding of copper and copper alloys remains a critical technological bottleneck in the automotive manufacturing industry. Especially with the rapid development of the new energy vehicle industry, higher demands are placed on the welding of copper components within power battery systems and electric drive systems. These welds not only require excellent appearance and no defects, but also superior conductivity and long-term reliability. Therefore, there is an urgent need in this field for a laser welding method for copper and copper alloys that is particularly suitable for the automotive manufacturing environment, effectively overcomes the adverse effects of copper's high reflectivity and thermal conductivity on lasers, stably controls the welding process, significantly reduces defects such as porosity, spatter, and hot cracking, and ultimately obtains high-quality welds. Summary of the Invention

[0008] The purpose of this invention is to provide a welding method for copper and its alloys, which aims to solve the problem of poor welding effect in traditional laser welding methods for copper and copper alloys.

[0009] In a first aspect, the present invention provides a method for welding copper and its alloys, the method comprising:

[0010] Obtain a substrate, the substrate being made of copper or a copper alloy, and clean and dry one side of the substrate as the cladding surface;

[0011] A FeCoCrNi high-entropy alloy cladding layer is prepared on the cladding surface by powder feeding laser cladding technology. The FeCoCrNi high-entropy alloy cladding layer includes a first layer and a second layer stacked sequentially on the cladding surface. The laser power of the first layer is higher than that of the second layer.

[0012] Composite samples with FeCoCrNi high-entropy alloy cladding layers were cut from the clad substrate, and the FeCoCrNi high-entropy alloy cladding layers of the two composite samples were butt welded together using laser oscillating welding technology.

[0013] In some embodiments, the substrate is made of brass, comprising 61.46 wt.% Cu, 0.0069 wt.% Pb, 0.026 wt.% Fe, with the balance being Zn.

[0014] In some embodiments, the powder used for cladding is FeCoCrNi high-entropy alloy powder, wherein the particle size of the FeCoCrNi high-entropy alloy powder is 45-105μm, and the FeCoCrNi high-entropy alloy powder contains 23.2wt.%Fe, 24.4wt.%Co, 26.0wt.%Cr, and 26.4wt.%Ni.

[0015] In some embodiments, the laser power of the first layer is 1500W, the laser power of the second layer is 750W, and the laser scanning speed of each layer is 10mm / s.

[0016] In some embodiments, the parameters of the powder-feeding laser cladding technology include: a laser wavelength of 1064 nm, a focused spot diameter of 2 mm, a powder feeding rate of 25 g / min, and the use of argon gas with a flow rate of 5 L / min as the powder feeding gas.

[0017] In some embodiments, the FeCoCrNi high-entropy alloy powder is dried at 80°C for 30 minutes before cladding.

[0018] In some embodiments, the thickness of both the first layer and the second layer is 1 mm.

[0019] In some embodiments, the process parameters of the laser oscillation welding include: laser power of 750W, welding scanning speed of 10mm / s, oscillation pattern of a straight line, oscillation amplitude of 1mm, and oscillation frequency of 50Hz.

[0020] In some embodiments, before welding, the upper surface of the FeCoCrNi high-entropy alloy cladding layer in the composite sample is ground flat, then the composite sample is cleaned with an ultrasonic cleaner, and the surface is wiped dry with anhydrous ethanol.

[0021] In some embodiments, pure argon is used as a shielding gas during the butt welding process, and the gas flow rate is 20 L / min.

[0022] In summary, this invention first utilizes laser cladding technology to deposit a layer of FeCoCrNi high-entropy alloy onto H62 brass. This high-entropy alloy layer is then used as an intermediate layer for laser welding of H62 brass to H62 brass. This successfully achieves a perfect metallurgical bonding zone with a clear, defect-free interface and uniform microstructure at the microscopic level, and also demonstrates significant advancements in mechanical properties. From the nanometer to the micrometer scale, this method effectively solves the core challenges in welding copper and its alloys. Attached Figure Description

[0023] Figure 1 This is a schematic diagram of FeCoCrNi high-entropy alloy powder clad onto an H62 copper substrate.

[0024] Figure 2 This is a schematic diagram of laser welding.

[0025] Figure 3 This is a diagram comparing the welding results, in which... Figure 3 (a) to Figure 3 (d) in the figure are schematic diagrams of the welding effect of H62–FeCoCrNi–H62 joint, H62–H62 joint, H62–6061 joint and H62–QP1180 joint respectively.

[0026] Figure 4 This is a schematic diagram of a three-dimensional topography representation, in which, Figure 4 (a) to Figure 4 (d) in the figure are schematic diagrams of the three-dimensional morphology of H62–FeCoCrNi–H62 joint, H62–H62 joint, H62–6061 joint and H62–QP1180 joint, respectively.

[0027] Figure 5 This is a schematic diagram of scanning electron microscopy characterization, where, Figure 5 (a) to Figure 5(d) in the figure are scanning electron microscope characterization schematic diagrams of the H62–FeCoCrNi–H62 interface, H62–H62 interface, H62–6061 interface and H62–QP1180 interface, respectively.

[0028] Figure 6 This is a schematic diagram of the microstructure of the weld interface where the FeCoCrNi high-entropy alloy is used as the intermediate layer. Figure 6 (a) to Figure 6 (d) in the figure are schematic diagrams of the microstructure of the weld interface magnified 1000 times, 2000 times, 4000 times, and 8000 times, respectively.

[0029] Figure 7 This is a schematic diagram illustrating the microstructure of the weld, where... Figure 7 (a) to Figure 7 (c) in the figure represents the first, second, and third microstructure characterization images of the H62-H62 weld, respectively. Figure 7 (d) to Figure 7 Images (f) in the diagram represent the first, second, and third microstructures of the H62-6061 weld. Figure 7 (g) to Figure 7 (i) in the figure represents the first, second and third microstructure characterization images of the H62-QP1180 weld, respectively.

[0030] Figure 8 The room temperature tensile stress-strain curves of Example 1 and three comparative welded joints are shown.

[0031] Figure 9 The image shows the macroscopic fracture morphology of the welded joint after tensile testing. Figure 9 (a) to Figure 9 (d) in the figure represents the macroscopic fracture morphology of the H62–FeCoCrNi–H62 joint, H62–H62 joint, H62–6061 joint, and H62–QP1180 joint, respectively.

[0032] Figure 10 Microstructure of the tensile fracture surface containing a FeCoCrNi high-entropy alloy cladding layer;

[0033] Figure 11 The image shows a transmission electron microscope (TEM) micro-area analysis of the interface of the H62 / FeCoCrNi high-entropy alloy weld joint. Figure 11 In the diagram, (a) represents the interface region between the high-entropy alloy phase and the H62 phase. Figure 11 (b) in the diagram represents the diffraction spots in the interface region. Figure 11 (c) in the diagram is one of the magnified schematic diagrams of the diffraction spots. Figure 11 (d) in the diagram is the second magnified schematic of the diffraction spot.

[0034] The following detailed description, in conjunction with the accompanying drawings, will further illustrate the present invention. Detailed Implementation

[0035] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention. Unless otherwise defined, the technical or scientific terms used herein should have the ordinary meaning understood by those skilled in the art. The terms "comprising" and similar expressions used herein mean that the element or object preceding the word covers the element or object listed after the word and its equivalents, but does not exclude other elements or objects.

[0036] Example 1

[0037] (1) Raw material description: The materials used in this embodiment are brass (H62) and FeCoCrNi high entropy alloy (HEAs) powder, wherein the brass substrate is 10 mm thick and the high entropy alloy powder has a particle size of 45-105 μm. The chemical composition of the high entropy alloy is shown in Table 1, and the chemical composition of H62 is shown in Table 2.

[0038] Table 1: Chemical composition of high-entropy alloys

[0039]

[0040] Table 2: Chemical composition of H62

[0041]

[0042] (2) Description of cladding equipment: In this embodiment, a laser cladding system consisting of a Kepler Optoelectronics BFL-CW3000 fiber laser and a ZF-CH001A off-axis laser cladding head is used for single-pass multi-layer powder feeding laser cladding. The fiber laser has a wavelength of 1064nm and a maximum power of 3000W. The focused spot is 2mm. The CNC four-axis linkage machine tool has a stroke of X=63cm, Y=42cm, Z=43cm. The double-cylinder powder feeder has a powder feeding repeatability of ±2%, can transport particles with a size of 20~200μm, and a powder feeding range of 10-150g / min.

[0043] (3) Welding equipment description: IPG YLS-UK laser, fiber laser (wavelength 1070nm, maximum power 15000W), RAYTOOLS BF3306 oscillating laser welding head (scanning welding supports circular, straight, C-shaped and S-shaped), FANUC Robot operating system are used to weld the sample.

[0044] (4) Welding process:

[0045] Step 1: Obtain a brass substrate and clean and dry one side of the brass substrate as the cladding surface. Specifically, first use an industrial steel wire brush to remove dirt from the cladding surface, then clean the substrate with alcohol and dry it with a hair dryer.

[0046] Step 2: Place the FeCoCrNi high-entropy alloy powder in a ventilated dryer, dry at 80℃ for 30 min;

[0047] Step 3, as follows Figure 1 A FeCoCrNi high-entropy alloy cladding layer was prepared on the cladding surface using powder-feeding laser cladding technology. The FeCoCrNi high-entropy alloy cladding layer includes a first layer and a second layer stacked sequentially on the cladding surface. When cladding the first layer of high-entropy alloy powder on the cladding surface, a laser power of 1500W and a laser scanning speed of 10mm / s were used. After the first layer was cladding, a laser power of 750W and a laser scanning speed of 10mm / s were used to continue cladding the second layer. During powder-feeding laser cladding, argon gas (Ar) was introduced into the powder feeder to blow the FeCoCrNi high-entropy alloy powder evenly onto the substrate surface through the powder feeding tube. The argon gas (Ar) flow rate was 5L / min, the powder feeding nozzle was 4mm away from the substrate end face, and the powder feeding amount was 25g / min. The thickness of the first and second layers was 1mm. Due to the large difference in physical properties between the cladding layer and the substrate, if a large amount of powder is claddinged on it at once, cracks may be caused at the interface. Therefore, the cladding was performed in two stages.

[0048] Step 4, as follows Figure 2 Composite samples with FeCoCrNi high-entropy alloy cladding layers were cut from the clad substrate using an electrical discharge wire cutting machine. The composite sample dimensions were 60mm × 12mm × 1.5mm. The FeCoCrNi high-entropy alloy cladding layers of the two composite samples were butt-welded using laser oscillation welding technology. Before butt welding, the upper surface of the FeCoCrNi high-entropy alloy cladding layer in the composite sample was ground flat. The composite sample was then cleaned with an ultrasonic cleaner and wiped and dried with anhydrous ethanol. During butt welding, the welding power was 750W, the welding scanning speed was 10mm / s, the laser oscillation pattern was a straight line of 1mm to ensure that the laser scanning range was always on the high-entropy alloy cladding layer, the oscillation frequency was 50Hz, and pure argon was used as the shielding gas at a flow rate of 20 L / min during the welding process.

[0049] Comparative Example 1

[0050] The brass material and welding equipment used in this comparative example are exactly the same as those in Example 1.

[0051] (1) Welding process:

[0052] Step 1: Obtain a brass substrate and clean and dry one side of the brass substrate as the welding surface. Specifically, first use an industrial steel wire brush to remove dirt from the welding surface, then clean the substrate with alcohol and dry it with a hair dryer.

[0053] Step 2: Cut a sample from the brass substrate using an electrical discharge wire cutter. The sample size is 60mm × 12mm × 1.5mm. Then, use laser oscillation welding technology to butt weld the two samples together. Before butt welding, grind the upper surface of the sample flat, clean the sample with an ultrasonic cleaner, wipe the surface with anhydrous ethanol and blow dry. During butt welding, the welding power is 750W, the welding scanning speed is 10mm / s, the laser oscillation pattern is a straight line of 1mm, the oscillation frequency is 50Hz, and pure argon is used as the shielding gas at a flow rate of 20 L / min during the welding process.

[0054] Comparative Example 2

[0055] The brass substrate used in this comparative example is exactly the same as that in Example 1, the aluminum alloy substrate used is made of 6061 aluminum alloy, and the welding equipment used is exactly the same as that in Example 1.

[0056] Welding process:

[0057] Step 1: Obtain a brass substrate and an aluminum alloy substrate respectively, and use one side of the brass substrate as the first welding surface and one side of the 6061 aluminum alloy substrate as the second welding surface. Clean and dry the first and second welding surfaces. Specifically, first use an industrial wire brush to remove dirt from the welding surface, then clean the substrate with alcohol and dry it with a hair dryer. The dimensions of the two substrates are 60mm×12mm×1.5mm.

[0058] Step 2: The first and second welding surfaces are butt welded using laser oscillation welding technology. Before butt welding, both welding surfaces are ground flat. The sample is then cleaned with an ultrasonic cleaner and wiped dry with anhydrous ethanol. During butt welding, the welding power is 750W, the welding scanning speed is 10mm / s, the laser oscillation pattern is a straight line of 1mm, the oscillation frequency is 50Hz, and pure argon is used as the protective gas at a flow rate of 20 L / min during the welding process.

[0059] Comparative Example 3

[0060] This comparative example is basically the same as Comparative Example 2, except that the aluminum alloy substrate is replaced with a steel plate made of QP1180 material.

[0061] Results analysis; such as Figure 3 As shown, a comparative analysis of actual welding results is presented, specifically, Figure 3 (a) in the example is the H62–FeCoCrNi–H62 joint involved in Embodiment 1 of the present invention. Its weld formation is uniform and continuous, the trajectory is straight and regular, the width is consistent, the surface is smooth and flat, and no obvious pores, cracks or large spatter are seen. Figure 3 (b) in Comparative Example 1 shows the H62–H62 welded joint of the same material. Even though the materials are the same, the weld surface still has a large number of black spots and impurities, the overall color is dull, and the roughness is high, reflecting the inherent difficulties of laser welding of copper alloys. Figure 3 (c) in Comparative Example 2 shows the H62–6061 dissimilar material welded joint. The weld morphology quality is poor, with obvious surface depressions, irregular undulations and uneven color. The color difference between the two sides is significant (one side is silvery white and the other side is dark), indicating poor material fusion and defects such as incomplete fusion or component segregation. Figure 3 (d) in Comparative Example 3 shows the H62–QP1180 dissimilar material weld joint, with a rough, black, striped weld seam and an extremely uneven surface, revealing a large amount of residual oxides. In summary, the above comparative experiments demonstrate that copper alloys are prone to various process challenges during laser welding. This invention, by pre-coating the copper alloy surface with a high-entropy alloy coating before butt welding, significantly improves weld formation quality and effectively suppresses the generation of welding defects.

[0062] To quantitatively evaluate weld formation quality, a super depth-of-field microscope was used to characterize the three-dimensional morphology of four types of joints. For example... Figure 4 As shown in (a), the FeCoCrNi high-entropy alloy used as the intermediate layer weld in this invention exhibits extremely high flatness and uniformity in its three-dimensional morphology, with a continuous and smooth weld trajectory and a clear outline. Quantitative analysis of the three-dimensional height data reveals that the surface undulation height difference is 315.38 μm. Figure 4 (b) to Figure 4 As shown in (d), the weld height differences obtained in Comparative Examples 1 to 3 are 505.34 μm, 461.53 μm, and 870.03 μm, respectively. In other words, the height difference of the present invention is much smaller than that of the comparative examples, which geometrically demonstrates that the weld obtained by the welding method of the present invention has the advantages of low residual stress and stable formation.

[0063] Furthermore, to more clearly observe the morphology of the weld, the welded products obtained in the embodiments and comparative examples of the present invention were characterized by scanning electron microscopy. Figure 5As can be seen from the H62-FeCoCrNi interface characterized in (a) of this invention, the interface is clear, flat, and continuous. The interface between the FeCoCrNi high-entropy alloy cladding layer and the H62 brass on the right is very clear, flat, and continuous. This indicates that the material achieves uniform and stable melting and solidification during laser welding, resulting in a dense interface bond. No obvious cracks, pores, inclusions, or lack of fusion were observed throughout the interface area. This clean and complete interface is a basic requirement for high-performance welded joints, meaning that the joint has high strength and good sealing performance. This proves that the process parameters (laser power, speed, etc.) used in this invention can precisely control the molten pool, enabling the intermediate layer to melt uniformly and achieve good metallurgical bonding with the base material, successfully suppressing stress concentration and cracking tendency caused by differences in material physical properties (such as the coefficient of thermal expansion). It should be noted that... Figure 5 In example (a), cracks appeared at both the upper and lower portions of the weld. This is mainly because after welding, the weld melts instantly to form liquid metal. During solidification, the liquid metal cannot solidify completely smoothly. Therefore, the surface and bottom of the weld are inevitably uneven. When a sample is taken to observe the cross-section, cracks can be seen at the upper and lower portions of the weld. This situation is also observed in the comparative examples. This is a natural phenomenon that occurs during metal solidification and cannot be avoided.

[0064] from Figure 5 As shown in (b) of the diagram, the H62-H62 interface exhibits a small number of irregular defects despite being welded from the same material. These are typically manifestations of oxides, impurities, or pores. This indicates that even in laser welding of H62 brass from the same material, improper process control (such as poor shielding gas performance, inadequate surface cleaning, or unreasonable parameters) can introduce defects at the interface, deteriorating joint performance. This underscores the superior purity control capability of the welding process proposed in this invention. Figure 5 As can be seen in (c), there are obvious cracks and pores at the interface between H62 and 6061 aluminum alloys. Figure 5 As can be seen in (d), the interface between H62 and QP1180 steel is significantly irregular, exhibiting an uneven and discontinuous morphology. Large defects are also observed. The root cause of these defects lies in the significant differences in the physicochemical properties between H62 brass and 6061 aluminum alloy or QP1180 high-strength steel. Direct welding easily leads to the formation of hard and brittle intermetallic compounds, generating enormous thermal stress during rapid heating and cooling, ultimately resulting in interface cracking, void formation, and other failures.

[0065] Furthermore, to further reveal the microscopic mechanism of this invention, the microstructure of the weld interface with FeCoCrNi high-entropy alloy as the intermediate layer was systematically observed using scanning electron microscopy (SEM) at magnifications ranging from 1000x to 8000x. For example... Figure 6 (a) to Figure 6 As shown in (d), a clear, flat, and clean interface morphology was observed at all magnifications, fully demonstrating that the present invention successfully achieved high-quality metallurgical bonding of dissimilar materials. Specifically, across the entire observation scale, a distinct, continuous, and uninterrupted interface was formed between the gray-contrast FeCoCrNi high-entropy alloy cladding layer and the white-contrast H62 brass base material. Even... Figure 6 Even at a magnification of up to 8000x (d), the interface lines remain clear and sharp, with no common welding defects such as cracks, holes, lack of fusion, or impurity segregation observed. This phenomenon is direct evidence of precise control of welding heat input and sufficient metallurgical reaction. It indicates that the laser welding process parameters used in this invention are perfectly matched, enabling uniform and stable melting and solidification of the two materials at the interface. More importantly, no intermetallic compound phases were observed to form between Cu or Zn atoms and any of the elements Fe, Co, Cr, or Ni in the interface region. This phenomenon fundamentally avoids the risk of interface cracking caused by brittle phases and also highlights a fundamental difference from existing technologies in the field: in existing technologies, at least Cu reacts with Fe, Co, and Cr to form intermetallic compounds such as Cu9Fe4, Cu3Co, and CuCr2O4, respectively, while no such third phase was found in the scanning electron microscope results of this invention. This is a significant advancement of this invention compared to traditional dissimilar material welding methods.

[0066] In summary, from the overall morphology at low magnification (1000x) to the fine local structure at high magnification (8000x), the interface quality and microstructure exhibit a high degree of consistency. The flatness and continuity of the interface at low magnification corroborate the sharp, defect-free characteristics of the interface at high magnification. This consistency in multi-scale observation strongly demonstrates the excellent stability and reproducibility of the welding process described in this invention. It is not an isolated, accidental good result, but rather a universally excellent structure produced by a reliable and controllable process.

[0067] In addition, to objectively evaluate the technical effects of the embodiments of the present invention, the weld microstructure of the comparative examples was also characterized, such as... Figure 7 (a) to Figure 7 In section (i), through systematic comparison, it can be clearly observed that regardless of whether the materials are the same or dissimilar, direct welding results in insurmountable microscopic defects at the interface. However, the embodiments of this invention exhibit almost none of these defects, demonstrating their fundamental advantage. Specifically, for the welding of H62 to H62, by… Figure 7 (a) to Figure 7As shown in (c), although the materials are the same and the interface is relatively flat, scattered black dots or dark contrast areas can be observed in the interface region at different magnifications. These black features are usually manifestations of impurities such as oxides and sulfides, or micropores. This indicates that even with the same base material, welding can still introduce impurities or generate porosity in the molten pool, deteriorating the joint performance.

[0068] For welding dissimilar materials H62-6061, by Figure 7 (d) to Figure 7 As shown in (f), this resulted in the worst interface quality among these experimental groups. The interface exhibited an extremely irregular, jagged, and even discontinuous morphology. The colors of the materials on both sides were sharply contrasting, and there may have been a transition layer of uneven thickness, accompanied by obvious black cracks and pores. This is a typical consequence of metallurgical incompatibility. H62 brass (Cu-Zn) and 6061 aluminum alloy (Al-Mg-Si) undergo intense interdiffusion at high temperatures, generating various hard and brittle Cu-Al series intermetallic compounds (such as CuAl2). These brittle phases are extremely prone to cracking under welding stress, forming macroscopic cracks and microscopic pores, leading to extremely low joint strength and complete failure. This strongly demonstrates, from the opposite perspective, the necessity of introducing a FeCoCrNi high-entropy alloy cladding layer.

[0069] For welding of dissimilar materials H62 - QP1180, by Figure 7 (g) to Figure 7 As shown in (i), a large number of black spots appear on the interface. This is mainly because the carbon element in QP118 steel may react with oxygen in the atmosphere or contaminants on the surface of the base material at high temperatures to generate CO or CO2 gas. At the same time, the solidification rate of the molten pool is too fast, and the gas does not have time to escape. After the laser energy stops, the molten pool solidifies rapidly and forms pores.

[0070] Furthermore, in order to illustrate the practical effects of the method of the present invention, Figure 8 The invention and three comparative welded joints are shown, along with room temperature tensile engineering stress-strain curves. Figure 8As can be seen, the H62 / FeCoCrNi / H62 welded joint using FeCoCrNi high-entropy alloy as the intermediate layer exhibits significantly superior comprehensive mechanical properties compared to all other comparative examples, demonstrating the core advantages of this invention. Specifically, the H62 / FeCoCrNi / H62 sample demonstrates the highest tensile strength, with a peak engineering stress reaching approximately 450 MPa. This indicates that the joint can withstand enormous loads. Furthermore, the curves clearly show an elastic stage, a yield plateau, a continuous plastic deformation (work hardening) stage, and finally, fracture. The engineering strain before fracture is close to 25%, indicating that the joint possesses good deformation capacity while bearing load, i.e., a good combination of strength and toughness. This is a typical fracture curve for ductile metals. It should be noted that even the base material (H62) itself, according to existing technology, has a tensile strength of only 400-500 MPa. This demonstrates that through the method of this invention, the strength of the welded joint is consistent with that of the base material, representing a significant performance improvement from a welding perspective.

[0071] For the H62-H62 tensile sample in Comparative Example 1, although its plasticity is approximately 37%, its peak stress is approximately 300 MPa, far lower than the strength of this invention and its own inherent strength. In practical engineering applications, this could very likely lead to failure due to insufficient strength. This indicates that even when welding from the same material, the joint performance is often lower than that of the base material due to potential impurities, porosity, and other defects, becoming a weak point in the entire component. This invention, through its innovative intermediate layer design, achieves a significant improvement in joint performance.

[0072] The curves for H62 / 6061 and H62 / QP1180 in Comparative Examples 2 and 3 are the most unique and convincing. Their curves show rapid fracture at very low stress levels (approximately 200 MPa for H62 / QP1180 and approximately 100 MPa for H62 / 6061), with a plasticity of only about 1.5%. This curve morphology is typical of brittle fracture. It indicates the existence of an extremely fragile region at the joint interface (i.e., the cracks and black spots observed in the previous SEM), preventing it from undergoing plastic deformation along with the base material. Under very low loads, cracks propagate rapidly from the fragile interface, leading to early joint failure. Its strength is even significantly lower than that of the weaker of the two base materials.

[0073] Furthermore, to demonstrate the generality of the experiment, an investigation of several existing technologies for laser welding of dissimilar metals such as copper with steel, iron, nickel, aluminum, and titanium revealed that the joint strength is generally low and highly volatile, with the tensile strength of most copper dissimilar metal welded joints concentrated below 200 MPa. Even with process optimization, the strength exhibits significant fluctuations, indicating a narrow process window and poor stability. The fundamental reason lies in the easy formation of continuous brittle intermetallic compound layers (such as Cu-Fe, Cu-Ti, and Cu-Al series compounds) between dissimilar materials.

[0074] also, Figure 9 The image clearly shows the macroscopic fracture morphology of the four welded joints after tensile testing. For the H62-FeCoCrNi-H62 joint, [the following is a description of the fracture morphology]. Figure 9 As shown in (a), the fracture occurred in the H62 brass base material, not at the weld interface. Obvious necking (local thinning) and fibrous tearing morphology are visible. This represents the highest quality of the welded joint. It indicates that the strength of the weld zone (including interfacial bonding strength) is higher than the strength of the H62 base material itself. Therefore, under external force, the component fractures at its weakest point—the base material. This proves that the weld obtained by this invention achieves a "super-strong" connection, with sufficient interfacial bonding force to ensure effective load transfer and causing fracture to occur in the more ductile base material region—an ideal failure mode.

[0075] For H62 - H62 connectors, by Figure 9 As shown in (b), the fracture occurred in the weld area. The fracture surface was relatively smooth with minimal necking. Theoretically, brass is mainly composed of the FCC phase; however, the lack of significant necking indicates that even when welding the same material, the weld area's performance deteriorates due to potential grain coarsening, impurities, or porosity (as described in the preceding analysis), becoming the weakest link in the joint. Its strength is lower than that of the base material, highlighting the superior weld quality achieved by this invention through the FeCoCrNi high-entropy alloy cladding layer and optimized process compared to traditional welding of the same material. Figure 9 (c) and Figure 9 As shown in (d), the fractures of both the H62-6061 and H62-QP1180 joints occurred strictly along the interface between the dissimilar materials. The fracture surfaces were very smooth, with no signs of necking, exhibiting typical brittle fracture morphology. This directly demonstrates the extremely poor metallurgical bonding between H62 and QP1180 steel, and between H62 and 6061 aluminum. Hard and brittle intermetallic compound layers (such as Fe-Cu and Al-Cu compounds) formed at the interface, resulting in extremely low interfacial bonding strength, making it unable to withstand loads and causing early brittle failure under slight stress.

[0076] also, Figure 10The microstructure of the tensile fracture surface containing a FeCoCrNi high-entropy alloy cladding layer is characterized by numerous pit-like structures of varying sizes and depths, known as "dimples." These dimples are the result of plastic deformation at the microscale of the material. Specifically, under tensile stress, plastic slip occurs at the crack tip, leading to the nucleation, growth, and eventual interconnection of micropores, thus forming dimples. It is noteworthy that the dimples in the image are widely distributed, exhibiting both deep, large dimples and relatively shallow ones. This indicates that plastic deformation occurs at multiple scales during fracture, demonstrating the material's good ductility. This dimple-dominated morphology is a typical criterion for micropore-aggregated ductile fracture. It clearly shows that the welded joint underwent significant plastic deformation before fracture, and its fracture mechanism is ductile fracture, not brittle fracture.

[0077] Figure 11 This invention utilizes transmission electron microscopy (TEM) micro-area analysis of the interface of the H62 / FeCoCrNi high-entropy alloy welded joint. Figure 11 (a) shows the interface region between the high-entropy alloy phase and the H62 phase in the analysis region. Figure 11 (b) in the diagram represents the diffraction spots in the interface region. This means that the diffraction spots of the high-entropy alloy phase and the H62 phase, or any intermetallic compound phase that may form, should all be located in... Figure 11 In (b) of the text. However, through the analysis of... Figure 11 After performing diffraction pattern calibration (using PDF card 70-0989-Ni, which represents the FCC crystal structure) in section (b), it was confirmed that all diffraction spots were of the FCC phase. Further magnification of individual points in the diffraction pattern, such as... Figure 11 In rectangle (c) in the image, it can be seen that there are actually two spots here, meaning that... Figure 11 (c) actually consists of two sets of spots, and the difference is only slightly noticeable at locations far from the transmission point. The locations closer to the transmission point, when magnified, appear as... Figure 11As shown in (d), the difference is almost imperceptible, meaning that the high-entropy alloy phase and the H62 phase completely overlap on the crystal plane near the transmission point. This indicates two points: First, the interface region contains only the high-entropy alloy phase of FCC and the H62 phase of FCC, confirming the absence of intermetallic compounds. Second, the high-entropy alloy phase and the H62 phase form a rare, completely coherent interface where diffraction spots completely overlap in multiple crystallographic directions. This indicates that the high-entropy alloy phase and the H62 phase have the same lattice type and very similar lattice constants, allowing for a one-to-one correspondence of atomic positions at the interface. The atoms at the interface belong to both crystal lattices simultaneously, resulting in a perfect, smooth transition with extremely low interface energy. These two points represent a significant advancement of this invention, completely different from existing technologies, and cannot be inspired by existing technologies. This is the direct reason for the superior mechanical properties of this invention.

[0078] In summary, this invention first utilizes laser cladding technology to deposit a layer of FeCoCrNi high-entropy alloy onto H62 brass. This high-entropy alloy layer is then used as an intermediate layer for laser welding H62 brass to H62 brass, successfully achieving a perfect metallurgical bonding zone with a clear, defect-free interface and uniform microstructure at the microscopic level, and demonstrating significant improvements in mechanical properties. From the nanometer to the micrometer scale, this innovative method effectively solves the core challenges in welding copper and its alloys. Specifically:

[0079] 1. By cladding a high-entropy alloy layer onto H62, the welding process of this invention becomes a butt weld of "high-entropy alloy cladding layer" + "high-entropy alloy cladding layer". This is actually welding between the same material (high-entropy alloy). This method cleverly addresses the most difficult and uncontrollable problem of the "Cu / high-entropy alloy" dissimilar material interface in advance during the cladding step. Furthermore, during cladding, the contact area is larger, and thermal stress is easier to control. Existing technologies generally involve directly adding an intermediate layer, which is a typical sandwich-style dissimilar material welding. During welding, the laser needs to simultaneously melt the H62 copper alloy and the physically different intermediate layer, requiring extremely high precision in process control (heat input, molten pool flow). Even slight differences in the melting order and quantity of the two materials can lead to defects.

[0080] 2. In traditional methods, the intermediate layer is placed directly in mechanical contact with the base material, and metallurgical bonding is only achieved at the moment of welding. The bonding quality heavily depends on the instantaneous welding parameters, and areas of incomplete fusion or insufficient bonding may exist at the interface. In this invention, the cladding process is an independent and controllable metallurgical process. By optimizing the cladding parameters, a robust interface with a compositional gradient, sufficient metallurgical bonding, and no defects can be formed between the copper substrate and the high-entropy alloy layer. This interface is pre-prepared, and its quality is far superior to that formed at the moment of welding. This provides an extremely stable and reliable foundation for subsequent welding. In addition, the absorption rate of high-entropy alloys for lasers is generally higher than that of copper alloys. The pre-clad high-entropy alloy layer serves as a ready-made surface with high laser energy absorption efficiency, making the subsequent butt welding process easier to initiate and the energy coupling more stable.

[0081] 3. Pure copper and copper alloys (such as H62) have extremely high reflectivity to infrared lasers, leading to difficulties in energy absorption and unstable welding. FeCoCrNi high-entropy alloy has a significantly higher absorption rate for common industrial lasers (such as fiber lasers) than copper alloys. As an intermediate layer, it can first efficiently absorb laser energy and melt, and then preheat and melt the H62 brass on both sides through heat conduction, acting like an "energy transfer station" and greatly improving the stability and efficiency of the welding process.

[0082] 4. When directly welding copper alloys or copper with dissimilar metals (such as steel or aluminum), brittle intermetallic compounds are easily formed due to metallurgical incompatibility (such as the reaction of Cu and Fe to form a brittle phase), resulting in low joint strength and easy cracking. FeCoCrNi high-entropy alloy contains multiple elements; however, it can be seen from the microstructure that the present invention does not produce intermetallic compounds, which is an unexpected effect.

[0083] 5. Tensile test data show that compared with the early brittle fracture (strength <150 MPa) of dissimilar materials such as H62 / QP1180 and H62 / 6061 through direct welding, the joint strength of the present invention is increased to 450 MPa, and it has an elongation at break of nearly 25%. This fully demonstrates that the introduction of the FeCoCrNi high-entropy alloy cladding layer transforms the previously difficult-to-weld copper and its alloy weld joints into high-performance joints with excellent strength and toughness. It should be noted that the strength of the joint of the present invention is significantly better than that of traditional H62 same-material weld joints and comparable to that of the H62 base material. This proves that this innovative method not only solves the problem of dissimilar material connection, but also establishes a completely new high-performance welding method, in which the joint is no longer a weak link in the component, but a reliable load-bearing part.

[0084] 6. In existing technologies, the strength of most dissimilar copper welded joints is around 200 MPa. However, the H62 / FeCoCrNi / H62 joint obtained by this invention has a tensile strength of approximately 450 MPa. This strength value significantly surpasses the performance of most copper-based dissimilar material joints reported in existing literature, achieving a qualitative leap.

[0085] 7. The fracture morphology shows that, unlike the inevitable brittle fracture along the weak interface in direct welding of dissimilar materials, the joint of the present invention exhibits ductile fracture with high plasticity. This directly confirms that the introduction of the FeCoCrNi high-entropy alloy cladding layer effectively inhibits the formation of continuous brittle intermetallic compounds at the interface between the FeCoCrNi high-entropy alloy cladding layer and copper and its alloys, thereby transferring the weak point of the joint from the brittle interface to the ductile matrix.

[0086] 8. Transmission electron microscopy analysis clearly confirmed the absence of intermetallic compounds at the phase boundary, and for the first time, a fully coherent interface between the high-entropy alloy FCC phase and the copper FCC phase was successfully constructed and observed. This discovery breaks through the traditional understanding that interfaces between dissimilar materials are usually semi-coherent or incoherent, and is revolutionary. It fundamentally eliminates the interface weakening effect, achieving a "perfect" metallurgical bond. Unlike the high dislocation density interface (dislocation, lattice distortion) caused by lattice mismatch in traditional dissimilar material welding, the coherent interface obtained by this invention has a continuous atomic arrangement and extremely low interface energy. This structure maximizes the interfacial bonding force, fundamentally preventing the interface from becoming the source of microcrack initiation and propagation. This is the fundamental atomic mechanism for the joint strength reaching 450 MPa and the fracture occurring in the base material.

[0087] While embodiments of the present invention have been described in detail above, it will be apparent to those skilled in the art that various modifications and variations can be made to these embodiments. However, it should be understood that such modifications and variations fall within the scope and spirit of the invention as set forth in the claims. Furthermore, the invention described herein may have other embodiments and can be implemented or carried out in various ways.

Claims

1. A welding method of copper and its alloys, characterized by, The method comprises: obtaining a substrate, the material of the substrate being copper or copper alloy, and cleaning and drying one side of the substrate as a cladding surface; preparing a FeCoCrNi high-entropy alloy cladding layer on the cladding surface by a powder feeding laser cladding technology, the FeCoCrNi high-entropy alloy cladding layer comprising a first layer and a second layer stacked on the cladding surface in sequence, the laser power of the first layer being higher than that of the second layer; cutting a composite sample with the FeCoCrNi high-entropy alloy cladding layer from the cladded substrate, and butt welding the FeCoCrNi high-entropy alloy cladding layers of two composite samples by a laser oscillation welding technology; the process parameters of the laser oscillation welding include: a laser power of 750 W, a welding scanning speed of 10 mm / s, a straight line as the oscillation pattern, an oscillation amplitude of 1 mm, and an oscillation frequency of 50 Hz.

2. The welding method of copper and its alloys according to claim 1, characterized by, The material of the substrate is brass, which comprises 61.46 wt.% Cu, 0.0069 wt.% Pb, 0.026 wt.% Fe, and the balance of Zn.

3. The welding method of copper and its alloys according to claim 1, characterized by, The powder selected for cladding is a FeCoCrNi high-entropy alloy powder, the particle size of the FeCoCrNi high-entropy alloy powder being 45-105 μm, and the FeCoCrNi high-entropy alloy powder comprising 23.2 wt.% Fe, 24.4 wt.% Co, 26.0 wt.% Cr, and 26.4 wt.% Ni.

4. The welding method of copper and its alloys according to claim 1, characterized by, The laser power of the first layer is 1500 W, the laser power of the second layer is 750 W, and the laser scanning speed of each layer is 10 mm / s.

5. The welding method of copper and its alloys according to claim 1, characterized by, The parameters of the powder feeding laser cladding technology include: a laser wavelength of 1064 nm, a focused spot diameter of 2 mm, a powder feeding amount of 25 g / min, and argon gas with a flow rate of 5 L / min as the powder feeding gas.

6. The welding method of copper and its alloys according to claim 3, characterized by, Before cladding, the FeCoCrNi high-entropy alloy powder is dried at 80℃ for 30 minutes.

7. The welding method of copper and its alloys according to claim 4, characterized by, The thickness of the first layer and the second layer is both 1 mm.

8. The welding method of copper and its alloys according to claim 1, characterized by, Before butt welding, the upper end surface of the FeCoCrNi high-entropy alloy cladding layer in the composite sample is polished, then the composite sample is cleaned by an ultrasonic cleaning machine, and the surface is wiped with anhydrous ethanol and dried.

9. The welding method of copper and its alloys according to claim 1, characterized in that, During the butt welding process, pure argon gas is used as the protective gas, and the gas flow rate is 20 L / min.

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