A method of pulse magnetic field assisted aluminum copper metal diffusion

Abstract

The application provides a method for pulse magnetic field assisted aluminum copper metal diffusion, and belongs to the field of diffusion connection. The application provides a method for pulse magnetic field assisted aluminum copper metal diffusion, which comprises the following steps: bonding the connecting surface of an aluminum workpiece with the connecting surface of a copper workpiece, and performing heat treatment in a pulse magnetic field; the temperature of the heat treatment is 550 DEG C, and the holding time is 6h; the pulse magnetic field is applied every 15min, and the total application time of the pulse magnetic field is 3h. The application improves the traditional high-energy consumption mode of 'ultra-high temperature and ultra-long holding time', relies on the efficient enabling characteristics of a low-energy pulse external physical field, and can realize the preparation of an ultra-thick high-quality diffusion layer under the condition of medium temperature and short cycle, thereby greatly shortening the production cycle and reducing the energy consumption cost; meanwhile, the low-energy short-time external field does not damage the matrix organization, and completely avoids the problems of matrix grain coarsening and mechanical property attenuation caused by high-temperature long-term heat treatment.

Description

Technical Field

[0001] This invention relates to the field of diffusion bonding, specifically to a method for diffusion of aluminum and copper metal assisted by a pulsed magnetic field. Background Technology

[0002] Aluminum and copper each possess excellent material properties. Copper has excellent electrical and thermal conductivity and corrosion resistance, but it has a high density and high cost. Aluminum is lightweight, inexpensive, and has good plasticity, but its electrical and thermal conductivity is weaker than that of copper. Aluminum-copper dissimilar metal composite components can combine the advantages of lightweight, high electrical and thermal conductivity, and low cost, and are widely used in new energy battery terminals, power busbars, precision electronic devices, and lightweight aerospace components.

[0003] Diffusion bonding is a common method for joining dissimilar metals like aluminum and copper. Its principle is based on the interdiffusion of atoms at the interface under certain temperature and pressure conditions, forming a metallurgical bonding interface. Compared to fusion welding and brazing, diffusion bonding produces no molten pool, no inclusions, and a uniform interface, effectively avoiding defects such as excessive growth of brittle intermetallic compounds and cracks that are prone to occur in aluminum-copper welding.

[0004] However, existing traditional aluminum-copper diffusion bonding methods have significant technical drawbacks: First, the atomic diffusion activation energy is high, requiring high temperature and long-term heat preservation to achieve effective diffusion, resulting in high energy consumption and low production efficiency; Second, high temperature and long-term heat preservation easily lead to coarse grains in the aluminum and copper matrix, reducing the mechanical properties of the workpiece matrix, while the interface easily generates a large number of brittle intermetallic compounds such as Al2Cu and AlCu, causing joint embrittlement; Third, the uneven atomic diffusion at the interface during the diffusion process easily generates micropores and microgap defects, and the residual stress in the joint is large, resulting in poor tensile strength and fatigue resistance of the aluminum-copper joint, and severe attenuation of electrical and thermal conductivity, which restricts the high-end and large-scale application of aluminum-copper composite components.

[0005] Existing improvement technologies mostly focus on optimizing single thermal processing parameters such as temperature, holding time, and mechanical pressure. These technologies can only slightly improve the interface state and cannot fundamentally reduce the atomic diffusion activation energy or actively regulate atomic migration behavior and the evolution of interface compounds, resulting in limited performance improvements. To address these industry pain points, there is a need to develop a highly efficient, low-energy-consumption, and high-performance aluminum-copper dissimilar metal diffusion bonding method. Summary of the Invention

[0006] This invention provides a method for aluminum-copper metal diffusion assisted by a pulsed magnetic field. This method can efficiently and with low energy consumption prepare high-performance aluminum-copper dissimilar metal diffusion connections.

[0007] This invention provides a method for pulsed magnetic field-assisted diffusion of aluminum and copper metals, comprising the following steps: The surfaces of the aluminum workpieces to be joined are brought together with the surfaces of the copper workpieces to be joined, and then heat-treated in a pulsed magnetic field. The heat treatment temperature is 550 ℃ and the holding time is 6 h; The pulsed magnetic field is applied once every 15 minutes, and the total application time of the pulsed magnetic field is 3 hours.

[0008] Preferably, the bonding process further includes grinding, polishing, cleaning, and drying the surfaces of the aluminum workpiece and the copper workpiece to be bonded, respectively.

[0009] Preferably, the pulse voltage of the pulsed magnetic field is 200~400 V, the current is 150~250 A, the duty cycle is 20~50%, and the frequency is 10~40 Hz.

[0010] Preferably, the heat treatment is performed in a pulsed magnetic field tube furnace; The pulsed magnetic field tube furnace includes a control power supply, a furnace tube, an insulation layer covering the furnace tube, a heating element wrapping the insulation layer, a heat insulation tile wrapping the heating element, and an excitation coil wrapping the heat insulation tile.

[0011] Preferably, the excitation coil is a three-layer concentric copper excitation coil.

[0012] Preferably, the furnace tube is made of quartz.

[0013] The present invention has the following advantages over the prior art: (1) By applying a pulsed magnetic field every 15 minutes, combined with a medium-temperature holding of 550 ℃, the traditional thermal diffusion method relies entirely on high-temperature thermal energy to excite atomic transitions. Aluminum and copper lattice atoms have high potential barriers and large diffusion activation energy, so atoms can only undergo short-range weak diffusion. Effective diffusion can only be achieved with an ultra-long holding period of more than 30 hours. Compared with traditional strong magnetic fields and strong pulsed magnetic fields, this method reduces energy consumption and improves production efficiency. Moreover, as a non-contact external physical field control method, unlike pulsed current which relies on electrodes to directly contact the workpiece and the current needs to flow through the workpiece, and the main effects are Joule heating and electromigration, this external physical field control method can independently provide a stable additional driving force for atomic migration, significantly improving the vacancy diffusion, grain boundary diffusion, and dislocation diffusion rate. This allows atoms to achieve the long-range atomic migration effect that traditional inventions can only achieve in 30 hours under a medium-temperature holding period of 550 ℃ and a short period of 6 hours, thus completely breaking through the efficiency bottleneck of traditional thermal diffusion from a physical mechanism perspective.

[0014] (2) It solves the industry pain points of traditional aluminum-copper diffusion, such as "slow rate, thin layer, many defects and poor bonding". It does not require high temperature and long time heat preservation, has low energy consumption, strong invention stability and high repeatability, and provides an ideal way to obtain green and efficient preparation method.

[0015] (3) Non-contact external field uniform energy application densifies interface defects and solves the pain point of poor bonding in traditional diffusion: The pulsed electromagnetic field is a uniform non-contact physical field that can cover the aluminum-copper interface, avoiding problems such as uneven force, workpiece wear, and secondary pollution caused by contact processing. Under the effect of intermittent pulse oscillation, the aluminum-copper interface continuously generates micro-amplitude elastic oscillation and controllable micro-plastic rheology, which can effectively reduce the micro-uneven gaps in the interface and the micro-pores, micro-voids, and micro-gap defects generated by traditional thermal diffusion, and continuously optimize the interface bonding density. The uniform energy application characteristics of the external pulsed magnetic field can improve the problem of uneven atomic migration, making the interface diffusion reaction more complete and uniform, solving the industry pain points of "slow rate, thin layer thickness, many defects, and poor bonding" in traditional aluminum-copper diffusion, and greatly improving the continuity and stability of the interface metallurgical bonding.

[0016] (4) This invention employs pulsed electromagnetic field external loading, which differs from the pulsed current (pulse electric field) connection scheme disclosed in the prior art. Pulsed current relies on electrodes directly contacting the workpiece, with the current flowing through the joint interface, mainly generating Joule heating and electromigration effects, with the effect concentrated in the energized interface region. In contrast, this invention uses non-contact pulsed magnetic field loading, inducing eddy currents inside the aluminum-copper component through a time-varying magnetic field, simultaneously generating Lorentz force and magnetostrictive effect, achieving synergistic effects of multiple physical fields. In addition to activation energy, the effects of the magnetic field, such as matrix grain refinement, second-phase regulation, and accelerated atomic diffusion at the solid-solid interface, are unattainable by pulsed current technology, which is an important innovation point that distinguishes this invention from the prior art.

[0017] Therefore, this invention improves upon the high-energy-consumption mode of traditional "ultra-high temperature, ultra-long-term heat preservation" methods. Relying on the highly efficient energizing characteristics of low-energy pulsed external physical fields, ultra-thick, high-quality diffusion layers can be prepared under medium-temperature conditions of 550 ℃ and a short cycle of 6 hours, significantly shortening the production cycle and reducing energy consumption costs. Simultaneously, the low-energy, short-duration external field does not damage the substrate structure, completely avoiding the problems of coarse substrate grains and mechanical property degradation caused by long-term high-temperature heat treatment. The non-contact external field processing method is consumable-free, pollution-free, and environmentally friendly. The equipment has a simple structure, adjustable parameters, and high flexibility, adaptable to the diffusion connection processing of aluminum and copper components of different specifications, exhibiting extremely high industrial adaptability and engineering application value. Attached Figure Description

[0018] Figure 1 SEM morphology and elemental line scan results of Al / Cu composite interface after being held at 550 ℃ in a vacuum tube furnace for different times; Figure 2 SEM & EDS of the Al / Cu diffusion interface after 30 h of heat treatment; Figure 3To determine the microstructure of the Al / Cu diffusion interface under different pulse currents, with a holding temperature of 550 °C for 6 h, a pulse voltage of 250 V, a duty cycle of 20%, and a frequency of 20 Hz. Figure 4 SEM & EDS of the Al / Cu diffusion interface under different current parameters in Example 1; Figure 5 EPMA & ZAF for Al / Cu diffusion interface at 225 A current; Figure 6 EPMA & ZAF for Al / Cu diffusion interface at 250 A current; Figure 7 Statistical results of infiltration layer thickness under different currents; Figure 8 The morphology of the Al-Cu diffusion interface was determined by holding the material at 550 ℃ for 6 h with a pulse current of 200 A, a duty cycle of 20%, a frequency of 20 Hz, and different voltages. Figure 9 Statistical results of infiltration layer thickness under different voltages; Figure 10 SEM images of the Al / Cu diffusion interface under different frequency parameters; Figure 11 SEM images of the Al / Cu diffusion interface under different duty cycle parameters; Figure 12 Image of the pulsed magnetic field tube furnace used in the embodiment. Detailed Implementation

[0019] This invention provides a method for pulsed magnetic field-assisted diffusion of aluminum and copper metals, comprising the following steps: The surfaces of the aluminum workpieces to be joined are brought together with the surfaces of the copper workpieces to be joined, and then heat-treated in a pulsed magnetic field. The heat treatment temperature is 550 ℃ and the holding time is 6 h; The pulsed magnetic field is applied once every 15 minutes, and the total application time of the pulsed magnetic field is 3 hours.

[0020] Before bonding, the present invention preferably further includes grinding, polishing, cleaning and drying the surfaces of the aluminum workpiece and the copper workpiece to be bonded, respectively.

[0021] In this invention, there are no special limitations on the grinding and polishing. Any method known to those skilled in the art can be used to remove interface oxide scale, processing scratches, burrs and surface stress defects.

[0022] In this invention, the cleaning preferably includes ultrasonic cleaning; the detergent used for cleaning preferably includes ethanol. Cleaning thoroughly removes oil, dust, and impurities from the interface, maximizing the interfacial adhesion and atomic contact activity, and providing the necessary conditions for interfacial atomic interdiffusion.

[0023] In this invention, the pulse voltage of the pulsed magnetic field is preferably 200-400 V, the current is preferably 150-250 A, the duty cycle is preferably 20-50%, and the frequency is preferably 10-40 Hz. In specific embodiments of this invention, the pulse voltage can be 210V, 220V, 230V, 240V, 250V, 260V, 270V, 280V, 290V, 300V, 310V, 320V, 330V, 340V, 350V, 360V, 370V, 380V, or 390V; the current can be 160A, 170A, 180A, 190A, 200A, 210A, 220A, 230A, or 240A; and the duty cycle can be 21%, 22%, 23%, 24%, 25%, 26%, 27%, 28%, 29%, 30%, 31%, or 30%. 2%, 33%, 34%, 35%, 36%, 37%, 38%, 39%, 40%, 41%, 42%, 43%, 44%, 45%, 46%, 47%, 48%, 49%, or 50%, with frequencies of 11Hz, 12Hz, 13Hz, 14Hz, 15Hz, 16Hz, 17Hz, 18Hz, 19Hz, 20Hz, 21Hz, 22Hz, 23Hz, 24Hz, 25Hz, 26Hz, 27Hz, 28Hz, 29Hz, 30Hz, 31Hz, 32Hz, 33Hz, 34Hz, 35Hz, 36Hz, 37Hz, 38Hz, or 39Hz.

[0024] In this invention, the pulsed magnetic field is applied once every 15 minutes, and the total application time of the pulsed magnetic field is 3 hours.

[0025] In this invention, the heat treatment temperature is 550 °C and the holding time is 6 h.

[0026] The mechanism by which pulsed magnetic fields promote diffusion at the aluminum-copper interface in this invention is as follows: Atomic diffusion is essentially the migration of interfacial atomic vacancies, lattice mutual solubility, and nucleation and growth of intermetallic compounds. Low-energy pulsed magnetic fields couple with high-temperature fields from five dimensions—electron motion, lattice defects, vacancy migration, interfacial stress, and phase precipitation—to synergistically enhance diffusion. (1) The Lorentz force perturbs the charge carriers and lowers the atomic migration barrier. Aluminum and copper metals contain a large number of free electrons. When a pulsed alternating magnetic field passes through a diffusion couple, the free electrons continuously generate alternating Lorentz forces under the influence of the time-varying magnetic field. Electrons reciprocate in a directed manner, impacting lattice atoms and transferring kinetic energy to the aluminum and copper matrix lattice. This weakens the interatomic metallic bonds and reduces the activation energy required for atoms to escape their original lattice positions. Al and Cu atoms, which are normally difficult to transition at high temperatures, can more easily overcome diffusion barriers with the aid of magnetic perturbation, thus increasing the inter-diffusion rate of interatomic atoms at the interface.

[0027] (2) Alternating magnetostriction induces lattice micro-vibrations, opening up diffusion channels. The periodic changes in the strength of the pulsed magnetic field cause a reversible magnetostrictive effect in aluminum and copper polycrystals, triggering micron-level periodic elastic micro-vibrations in the lattice. These vibrations continuously impact the aluminum-copper interface, breaking the original dense oxide barrier layer (Al2O3 film) and eliminating the atomic diffusion barrier. (3) Magnetic field regulates vacancy concentration and accelerates vacancy-assisted diffusion. Metal atom diffusion mainly relies on vacancy migration mechanisms: The pulsed alternating magnetic field changes the distribution of electron cloud inside the metal, induces local energy fluctuations in the lattice, and promotes the generation of a large number of vacancies inside the matrix. The magnetic field drives the vacancies to migrate to the aluminum-copper interface, and the high concentration of vacancies at the interface provides sufficient migration sites for the mutual solubility of Al and Cu atoms. The vacancy-atom exchange frequency is significantly increased, which is macroscopically manifested as a rapid increase in the thickness of the diffusion layer.

[0028] In this invention, the heat treatment is preferably carried out in a pulsed magnetic field tube furnace.

[0029] In this invention, the pulsed magnetic field tube furnace preferably includes a control power supply; the control power supply is used to generate a controllable low-frequency pulse current to power the external coil and precisely control the pulse amplitude, frequency, pulse width, and magnetic field strength.

[0030] In this invention, the pulsed magnetic field tube furnace preferably includes a furnace tube, and the material of the furnace tube is preferably quartz. The furnace tube is used to isolate air and protect the aluminum-copper diffusion connectors, while providing no magnetic shielding, allowing the magnetic field to penetrate the tube wall without loss and act on the sample.

[0031] In this invention, the pulsed magnetic field tube furnace preferably includes an insulation layer covering the furnace tube.

[0032] In this invention, the pulsed magnetic field tube furnace preferably includes a heating element that wraps around the insulation layer.

[0033] In this invention, the pulsed magnetic field tube furnace preferably includes heat-insulating tiles that wrap around the heating element.

[0034] In this invention, the pulsed magnetic field tube furnace preferably includes an excitation coil surrounding the heat insulation tile, and the excitation coil is preferably a three-layer concentric copper excitation coil. According to Ampere's circuital law of electromagnetic induction, the internal space of the energized copper coil will generate a pulsed alternating magnetic field that changes synchronously with the pulsed current; the three layers of copper coils are arranged in the same direction and the magnetic fields are superimposed, which greatly improves the uniformity of the magnetic field and the effective magnetic induction intensity in the central region of the furnace tube, and the uniform magnetic field eliminates diffusion inhomogeneity; the magnetic field gradient at both ends of a conventional single-layer coil furnace tube is large, and the difference in diffusion thickness before and after the sample is obvious, while the magnetic fields of the three-layer external copper coils are superimposed, the magnetic field distribution in the isothermal zone of the quartz tube is uniform, all parts of the diffusion connector are subjected to equal magnetic effects, the thickness of the diffusion layer and the size of the precipitated phase at the aluminum-copper interface are uniform, and the repeatability of the experiment is significantly improved.

[0035] In this invention, the component to be connected after fixing is preferably placed in the constant temperature zone at the center of the furnace tube. During heat treatment, the component to be connected is simultaneously subjected to the dual effects of a high-temperature thermal diffusion field and a pulsed magnetic field.

[0036] Pulsed magnetic field generation method in a pulsed magnetic field tube furnace: The pulse control power supply periodically outputs intermittent low-energy pulse current, which is fed into a three-layer superimposed copper excitation coil outside the furnace tube. According to Ampere's circuital law of electromagnetic induction, the internal space of the energized copper coil will generate a pulsed alternating magnetic field that changes synchronously with the pulse current. The three layers of copper coils are arranged in the same direction and the magnetic fields are superimposed, which greatly improves the uniformity of the magnetic field and the effective magnetic induction intensity in the central area of ​​the furnace tube. The magnetic field penetrates the non-magnetic quartz tube wall and acts completely on the interface of the aluminum-copper diffusion connector inside the tube.

[0037] The following detailed description of the pulsed magnetic field-assisted aluminum-copper metal diffusion method provided by the present invention, with reference to specific embodiments, should not be construed as limiting the scope of protection of the present invention.

[0038] Figure 12 This is a schematic diagram of the pulsed magnetic field tube furnace used in the embodiment.

[0039] Comparative Example 1 Microstructural evolution of the Al / Cu interface under conventional heat preservation treatment Sample loading and sealing: The aluminum-copper diffusion connector is placed in the quartz furnace tube, and a vacuum is drawn / a protective atmosphere is introduced to prevent oxidation; Heating and heat preservation: The heating element inside the furnace is heated to the target diffusion temperature.

[0040] Diffusion process: High temperature provides the basis for thermal activation of atoms; Experiment completed: After furnace cooling, the sample was removed to characterize the diffusion layer and microstructure; Experimental parameters: temperature 550℃, time 6 h, 12 h, 24 h and 30 h respectively.

[0041] Figure 1The SEM morphology and elemental line scan results of the Al / Cu composite interface after being held at 550 °C in a vacuum tube furnace for different times are shown. Figure 1 (a) shows the SEM morphology and elemental line scan results of the Al / Cu composite interface after being held at 550 °C in a vacuum tube furnace for 6 h. Figure 1 (b) shows the SEM morphology and elemental line scan results of the Al / Cu composite interface after being held at 550 ℃ in a vacuum tube furnace for 12 h. Figure 1 (c) shows the SEM morphology and elemental line scan results of the Al / Cu composite interface after being held at 550 ℃ in a vacuum tube furnace for 24 h. Figure 1 The middle (d) shows the SEM morphology and elemental line scan results of the Al / Cu composite interface after being held at 550 ℃ in a vacuum tube furnace for 30 h.

[0042] Depend on Figure 1 As shown in (a), when the holding time is 6 h, only a small amount of discontinuous reaction products appear at the interface. This indicates that the atomic diffusion is limited at this time, and a continuous and stable diffusion reaction layer has not yet been formed. As the holding time is extended to 12 h, as... Figure 1 As shown in (b), a distinct diffusion reaction zone begins to appear at the interface, indicating that Al and Cu atoms have interdiffused and may have formed an Al-Cu intermetallic compound layer. A transition layer of a certain thickness forms between the Al and Cu sides. Figure 1 In Figure (c), when the holding time is extended by 24 h, the gradient changes of Al and Cu elements at the interface in the linear scan curve are more pronounced, indicating a further enhancement of the diffusion reaction. At this point, a relatively complete intermetallic compound layer of approximately 53.76 µm, such as Al₂Cu, has formed at the interface. Figure 1 (d) indicates that the thickness of the aluminum-copper diffusion layer has increased to 82.34 µm after 30 h of heat preservation.

[0043] Figure 2 SEM & EDS of the Al / Cu diffusion interface during 30 h of heat treatment for Comparative Example 1.

[0044] Depend on Figure 2 It can be seen that without the action of a pulsed magnetic field, a continuous intermetallic compound diffusion layer is formed at the interface; EDS surface scanning can intuitively reflect the distribution of Al and Cu elements in the interface region. Al diffuses from the aluminum side to the copper side, and Cu diffuses in the opposite direction from the copper side to the aluminum side. The two interdiffusion occur at the interface and form intermetallic compounds.

[0045] Example 1 Sample loading and sealing: The aluminum-copper diffusion connector is placed in the quartz furnace tube, and a vacuum is drawn / a protective atmosphere is introduced to prevent oxidation; Heating and heat preservation: The heating element inside the furnace is heated to the target diffusion temperature.

[0046] Applying a pulsed magnetic field: During the isothermal stage, the pulsed power supply is started, and the three-layer copper excitation coil generates a low-energy alternating pulsed magnetic field that penetrates the quartz tube and continuously acts on the aluminum-copper interface. Diffusion process: High temperature provides the basis for thermal activation of atoms, and pulsed magnetic field assists atomic migration through multiple mechanisms such as Lorentz force, lattice vibration and vacancy regulation. The two work together to greatly improve Al / Cu interdiffusion efficiency. Experiment completed: Stop the magnetic field output, allow the furnace to cool, and remove the sample to characterize the diffusion layer and microstructure.

[0047] Experimental parameters The heat treatment parameters were set uniformly. The parameters for the following experiments were: holding temperature 550 ℃ and total holding time 6 h. During the entire 6 h holding period, a pulsed magnetic field was applied every 15 min (the actual magnetization time was 3 h).

[0048] The pulse magnetic field parameters are adjusted by different pulse currents (150A, 200A, 225A, 240A, 250A), with a fixed pulse voltage of 250V, duty cycle of 20%, and frequency of 20Hz.

[0049] Figure 3 To determine the microstructure of the Al / Cu diffusion interface under different pulse currents (0 A, 150 A, 200 A, 225 A, 240 A, 250 A) under the conditions of holding at 550 ℃ for 6 h with a pulse voltage of 250 V, a duty cycle of 20%, and a frequency of 20 Hz.

[0050] Figure 4 SEM & EDS of the Al / Cu diffusion interface under different current parameters.

[0051] Depend on Figure 4 It can be seen from the SEM morphology and elemental distribution under pulsed current conditions of 225A and 250A that, with the increase of pulsed current, the interdiffusion of Al and Cu elements intensifies, the interpenetration range of Al and Cu elements at the interface expands, and the thickness of the intermetallic compound diffusion layer increases significantly. Under the 250A condition, a network-structured reaction layer appears at the interface, indicating more complete elemental diffusion.

[0052] Figure 3 In (a), no obvious Al / Cu diffusion layer was observed at the 0 A interface without current. However, when the pulse current was 150 A, as shown in (a), no significant Al / Cu diffusion layer was observed. Figure 3 In the middle (b) interface, a certain degree of interdiffusion of Al and Cu elements has occurred, but a continuous and stable diffusion layer has not yet formed, with a thickness of approximately 14.02 μm. The current is increased to 200 A ( Figure 3 In the middle (c), the diffusion layer thickness increased to 41.33 μm, and the interface continuity was significantly improved. Figure 3 In the diagram, (d) indicates that the thickness of the diffusion layer reaches 48.55 μm at a current of 225 A. When the current increases to 240 A ( Figure 3 In (e), the diffusion layer rapidly thickens to 88.34 μm, indicating that the pulsed magnetic field further enhances the promoting effect on atomic migration. Figure 3 Figure (f) shows that when the magnetic field parameter current increases to 250 A, the thickness of the diffusion layer increases to 202.17 µm, and a continuous and dense network structure reaction layer appears.

[0053] Figure 5 The Al / Cu diffusion interface EPMA & ZAF is used at a current of 225 A.

[0054] Figure 5 Image (a) shows the EPMA elemental surface scan, secondary electron morphology (SED), and backscattered electron morphology (BED-C) of the Al / Cu composite interface after treatment with a 225 A pulsed magnetic field current. Statistical analysis of the surface scan average composition reveals that the average atomic fraction of Al in the diffusion layer is 33 at.%, and the average atomic fraction of Cu is 38 at.%, indicating vigorous inter-elemental diffusion at the interface. The SED secondary electron morphology clearly shows the uneven surface of the diffusion layer, the formation of numerous pores and irregular intermetallic reactants at the interface. Figure 5 Image (b) shows a magnified view of the diffusion interface. ZAF quantitative elemental analysis was performed on the marked feature points in the image: the Al atomic fraction in this feature region was 70.74 at.%, and the Cu atomic fraction was 29.25 at.%. Figure 5 In the characteristic region (c), the Al atomic fraction is 52.35 at.% and the Cu atomic fraction is 47.40 at.%. Based on the Al-Cu binary phase diagram, it can be determined that intermetallic compounds such as Al2Cu and AlCu are formed at this location.

[0055] Figure 6 EPMA & ZAF are Al / Cu diffusion interfaces under a current of 250 A.

[0056] Figure 6 Image (a) shows the EPMA elemental surface scan, secondary electron scattering (SED), and backscattered electron scattering (BED-C) morphology of the Al / Cu composite interface after treatment with a 250 A pulsed magnetic field current. Statistical data from the surface scan indicate that the average atomic fraction of Al in the diffusion layer is only 23 at.%, while the average atomic fraction of Cu reaches 39 at.%. Compared to the 225 A sample, the enrichment of Cu in the diffusion layer and the interfacial reaction products exhibit a continuous network distribution. The SED secondary electron image below shows the formation of numerous continuous, interconnected irregular pores and bulky intermetallic reactants at the interface.

[0057] Figure 6(b) to (g) show the interface feature regions at different magnifications. Six typical locations were selected for quantitative elemental detection using the ZAF method, and the composition and tissue characteristics of each marker point were analyzed.

[0058] Figure 6 In section (b), a quantitative analysis of the infiltration layer in the Al-side matrix revealed an Al atomic fraction as high as 98.8 at.%, while the Cu element content was only 1.10 at.%. Figure 6 The quantitative results of ZAF in (c) show that the Al atomic fraction in this region is 72.72 at.% and the Cu atomic fraction is 27.27 at.%. Figure 6 In the middle (d) feature point, the Al and Cu atomic fractions are 71.54 at.% and 28.46 at.%, respectively, indicating that this region is dominated by Al-rich Al-Cu transition metal interphase. Figure 6(e) shows the diffusion layer region near the Cu matrix under medium magnification. Quantitative results show that the Al atomic fraction is 54.41 at.% and the Cu atomic fraction is 45.58 at.%, with an Al to Cu atomic ratio close to 1:1, corresponding to an AlCu intermediate metal interphase. Figure 6 The middle (g) sample was taken from the shallow region of the Cu matrix. The Al atom fraction was only 10.84 at.%, and the matrix was mainly composed of Cu. Only a small amount of Al atoms were diffused through solid solution in the surface layer, indicating that Al atoms could not penetrate into the interior of the Cu matrix over long distances. Figure 6 In the middle (f), the interfacial reaction layer immediately adjacent to the Cu matrix is ​​shown in a high-magnification fine field of view. At this point, the Al atomic fraction drops to 47.01 at.%, while the Cu atomic fraction increases to 52.99 at.%. Figure 6 (g) is taken from the shallow region of the Cu matrix.

[0059] The ZAF quantitative data from six characteristic sites show that, along the direction from the Al matrix to the Cu matrix, the Al atomic fraction monotonically decreases from 98.89 at.% to 10.84 at.%, while the Cu atomic fraction shows the opposite trend. The intermetallic phases at the interface simultaneously undergo a continuous evolution from an Al-rich transition phase to an AlCu intermediate phase, and finally to a brittle Al₂Cu-rich phase. The strong Lorentz force provided by the 250 A pulsed magnetic field significantly enhances the interdiffusion ability of Al and Cu atoms, generating a continuous network of brittle Al₂Cu phase while simultaneously forming a gradient diffusion layer. The pulsed electromagnetic field also improves the compactness and bonding performance of the Al / Cu composite interface.

[0060] Figure 7 Statistical results of infiltration layer thickness under different currents.

[0061] Effects of different magnetic field parameters and voltage on Al / Cu interface microstructure Figure 8The morphology of the Al-Cu diffusion interface (200 V, 250 V, 300 V, 400 V) was determined by holding the material at 550 ℃ for 6 h with a pulse current of 200 A, a duty cycle of 20%, a frequency of 20 Hz, and different voltages.

[0062] Figure 8 In the middle (a), it means that at a voltage of 200 V, only a thin Al-Cu diffusion region with a thickness of 14.31 μm is formed at the interface. Figure 8 In (b), the diffusion layer thickness increases to 41.33 μm when the voltage is increased to 250 V. Figure 8 In (c), when the voltage is 300 V, the magnetic field strength is significantly increased, which accelerates the atomic diffusion rate and greatly deepens the degree of interfacial reaction. Figure 8 In the middle (d) experimental group, the thickness of the diffusion layer increased sharply to 415.97 μm, and the interface structure underwent a fundamental change. On the one hand, a large-area mixed structure of layered α-Al and Cu-rich precipitates appeared inside the Al matrix, and Cu atoms diffused into the aluminum matrix in large quantities over long distances; on the other hand, the intermetallic compounds at the interface were completely connected, forming a thick, continuous, brittle network structure that runs through the entire diffusion layer.

[0063] Figure 9 Statistical results of infiltration layer thickness under different voltages.

[0064] Influence of different magnetic field parameters frequency on Al / Cu interface microstructure Figure 10 SEM images of the Al / Cu diffusion interface at different frequency parameters (10 Hz, 20 Hz).

[0065] Figure 10 Backscattered SEM morphology of Al / Cu diffusion interface was obtained when the pulsed magnetic field current was fixed at 240 A, voltage at 250 V, duty cycle at 20%, and heat treatment at 550 ℃ for 6 h, with pulse frequencies of 10 Hz and 20 Hz, respectively. Figure 10 In (a), the pulse frequency is 10 Hz, the overall thickness of the interface diffusion layer is relatively small, the infiltration layer is distributed in a discontinuous blocky pattern, and there are a few isolated pores at the interface. Figure 10 In (b), increasing the pulse frequency to 20 Hz doubles the number of alternating magnetic field cycles per unit time, resulting in a significant increase in the width of the diffusion layer.

[0066] Influence of different magnetic field parameters duty cycle on Al / Cu interface microstructure Figure 11 SEM images of the Al / Cu diffusion interface under different duty cycle parameters (20%, 30%).

[0067] Figure 11In (a), the duty cycle is 20%, the pulse conduction time is moderate, the diffusion layer thickness is uniform, the interface IMCs are arranged in a fine and long strip, the pore defects are small in size and few in number, and the overall interface is relatively dense. Figure 11 In (b), the duty cycle is increased to 30%, the effective time of the magnetic field within a single cycle is extended, and the interface diffusion layer is further widened.

[0068] Comparing the two sets of variables, it can be seen that 20 Hz and 20% duty cycle are the optimal pulse parameters for this system, which can balance sufficient metallurgical bonding and low-defect interface. Too high a frequency and too large a duty cycle will induce thick continuous brittle intermetallic phases and a large number of pores, reducing the mechanical properties of the interface.

[0069] The above description is only a preferred embodiment of the present invention. It should be noted that for those skilled in the art, several improvements and modifications can be made without departing from the principle of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for pulsed magnetic field-assisted diffusion of aluminum and copper metals, characterized in that, Includes the following steps: The surfaces of the aluminum workpieces to be joined are brought together with the surfaces of the copper workpieces to be joined, and then heat-treated in a pulsed magnetic field. The heat treatment temperature is 550 ℃ and the holding time is 6 h; The pulsed magnetic field is applied once every 15 minutes, and the total application time of the pulsed magnetic field is 3 hours.

2. The method according to claim 1, characterized in that, Before bonding, the process also includes grinding, polishing, cleaning, and drying the surfaces of the aluminum workpiece and the copper workpiece to be bonded, respectively.

3. The method according to claim 1, characterized in that, The pulsed magnetic field has a pulse voltage of 200~400 V, a current of 150~250 A, a duty cycle of 20~50%, and a frequency of 10~40 Hz.

4. The method according to claim 1, characterized in that, The heat treatment is carried out in a pulsed magnetic field tube furnace; The pulsed magnetic field tube furnace includes a control power supply, a furnace tube, an insulation layer covering the furnace tube, a heating element wrapping the insulation layer, a heat insulation tile wrapping the heating element, and an excitation coil wrapping the heat insulation tile.

5. The method according to claim 4, characterized in that, The excitation coil is a three-layer concentric copper excitation coil.

6. The method according to claim 4, characterized in that, The furnace tube is made of quartz.

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