New energy automobile liquid-cooled battery box and vacuum diffusion welding manufacturing method

Abstract

The present application relates to a new energy automobile liquid-cooled battery box and a vacuum diffusion welding manufacturing method, comprising a battery module and a battery box outside the battery module, the box is composed of a connecting side plate, a U-shaped surrounding plate and a bottom plate, the connecting side plate is composed of an outer plate, a middle concave plate etched with a fluid guide groove and an inner cover plate, and is integrally pressed by vacuum diffusion welding, so that the guide groove is closed to form an embedded liquid cooling flow channel, the horizontal flange edge of the lower edge of the connecting side plate is directly fused with the overlapping step of the outer edge of the bottom plate through vacuum diffusion welding, and the connecting side plate, the U-shaped surrounding plate and the bottom plate are welded and fixed through vacuum diffusion welding to form an integrated box without sealing ring and bolt fastening, the manufacturing method comprises the steps of pretreatment, stacking and molding, vacuum heating, segmented pressure diffusion and cooling forming, small pressure is applied for pre-sticking in the heating stage, high pressure is applied for atomic deep diffusion in the constant temperature stage, and the residual stress is eliminated after pressure maintaining, so that the integrated liquid-cooled battery box with high sealing performance and no thermal deformation is manufactured.

Description

Technical Field

[0001] This invention relates to the field of power battery manufacturing technology for new energy vehicles, and particularly to a liquid-cooled battery box for new energy vehicles and a vacuum diffusion welding manufacturing method. Background Technology

[0002] Traditional liquid-cooled battery boxes often require separate cooling water pipes to be hung on the outside of the side panels or the bottom of the box, and then fixed with glue or screws. This not only adds a lot of extra weight to the parts, but also the sealant is prone to aging after long-term vibration, leading to coolant leakage and causing safety accidents. In addition, traditional welding such as laser welding and argon arc welding can easily "deform" the aluminum alloy box because the high temperature is concentrated on one line, making it impossible to put the battery cells in.

[0003] Patent No. CN202311152888.6 discloses a highly reliable fluid-sealed through-type modular liquid cooling rack, in which the liquid cooling channels are set on the substrate by vacuum diffusion welding. This welding method does not add flux, avoiding the problems of welding corrosion and blockage of the liquid cooling channels. Moreover, the coolant enters all through-type liquid cooling modules sequentially through the second channel hole, the filter module of the liquid supply health management unit, and the first channel hole, and is discharged through the first channel hole after exchanging heat with the through-type liquid cooling modules. This coolant flow does not interfere with the first and second electrical connectors, which is conducive to achieving electro-hydraulic separation. However, this invention has the following problems: firstly, the sealing effect is not good, and micro gaps are easily generated; secondly, the welding stress problem cannot be solved, and deformation is easy. Summary of the Invention

[0004] The purpose of this invention is to address the shortcomings of existing technologies by designing the connecting side plate of the battery box as a three-layer metal plate structure, etching fluid guide grooves on the middle grooved plate, and using vacuum diffusion welding to integrally press the three-layer metal plates together, thus sealing the fluid guide grooves to form an internal liquid cooling channel. Simultaneously, the horizontal flange edge of the lower edge of the connecting side plate and the overlapping step of the outer edge of the base plate are directly fused together using vacuum diffusion welding. This, combined with vacuum diffusion welding between the connecting side plate, U-shaped enclosure, and base plate, forms an integrated, fully welded battery box structure without sealing rings or bolt fastening. Furthermore, the vacuum diffusion welding manufacturing process... The process employs a segmented voltage transformation technique. During the heating stage, a small initial pressure is applied to pre-bond the plates. After entering the constant temperature stage, the pressure is increased to the target high pressure for atomic deep diffusion. The pressure is then released in the later stage to eliminate residual stress inside the welding interface. This effectively solves the technical problems of traditional liquid-cooled battery boxes, such as the heavy weight of components due to external cooling water pipes, coolant leakage caused by aging of sealant, and the inability to assemble battery cells due to thermal deformation of the aluminum alloy box caused by high temperature concentration in traditional welding methods such as laser welding and argon arc welding. At the same time, the existing vacuum diffusion welding technology has poor sealing effect, is prone to micro gaps, and cannot eliminate welding stress.

[0005] To achieve the above objectives, the present invention provides the following technical solution:

[0006] A liquid-cooled battery box for new energy vehicles includes battery modules arranged side by side. A battery box body is provided on the outside of the battery modules. The battery box body includes a connecting side plate. U-shaped enclosures are connected to both sides of the connecting side plate. A bottom plate is fixedly connected to the lower end of the connecting side plate and the U-shaped enclosures. The outer edge of the bottom plate has an upwardly folded and outwardly extending overlapping step. The lower edge of the connecting side plate has an outwardly bent horizontal flange edge. The horizontal flange edge covers and fits onto the overlapping step. The entire annular overlapping surface of the horizontal flange edge and the overlapping step is directly fused together by vacuum diffusion welding.

[0007] The connecting side plate has a liquid cooling channel on its inner side, and the connecting side plate is made of three metal plates integrally pressed together by vacuum diffusion welding, and a liquid cooling channel for the circulation of coolant is formed between each metal plate.

[0008] As a preferred embodiment, the connecting side plate includes an outer plate, a middle grooved plate, and an inner cover plate. Fluid guide grooves are etched on the middle grooved plate. The outer plate and the inner cover plate are respectively attached to both sides of the middle grooved plate, and the three are welded into a whole by vacuum diffusion welding, so that the fluid guide grooves are closed to form the liquid cooling channel.

[0009] As a preferred embodiment, the connecting side plate, U-shaped enclosure plate, and bottom plate are directly welded and fixed by vacuum diffusion welding to form a battery box without sealing rings or bolt fastening. A busbar is provided on the end face of the connecting side plate facing the battery module. The right side of the busbar is threadedly fixed to an electrical wiring fixing bracket, and the other end of the electrical wiring fixing bracket is threadedly fixed to the battery module.

[0010] As a preferred embodiment, the battery module is provided with a limiting U-shaped block at the upper end, and a partition plate is provided on the left side of the battery module. The partition plate has a C-shaped structure, and the lower end of the partition plate is fixedly connected to the base plate. The limiting U-shaped block is fixedly connected to the center position of the upper end of the partition plate.

[0011] As a preferred embodiment, the busbar includes a chip board, with connecting posts evenly fixedly connected to the upper and lower ends of the chip board, a connecting side plate fixedly connected to the other side of the connecting posts, and a heat dissipation partition plate fixedly connected to the left side of the chip board, the heat dissipation partition plate being a uniformly arranged rectangular block.

[0012] As a preferred embodiment, the U-shaped enclosure has a structural reinforcement layer inside, which is a closed hexagonal honeycomb cavity structure, and the structural reinforcement layer and the liquid cooling channel are set independently of each other.

[0013] A vacuum diffusion welding manufacturing method for liquid-cooled battery boxes in new energy vehicles, characterized by comprising the following steps:

[0014] Step S1: Pretreatment, the multi-layer metal plates that make up the connecting side plates and the base plate to be welded are degreased, cleaned and passivated to remove the surface oxide film.

[0015] Step S2: Stacking and mold closing, stacking and combining multiple layers of metal plates according to the preset flow channel shape, and positioning and clamping the combined connecting side plate, bottom plate, and U-shaped side plate in the fixture to ensure that all mating surfaces are completely fitted.

[0016] Step S3: Vacuum heating. Place the assembled fixture into a vacuum diffusion welding furnace, evacuate to a preset low-pressure vacuum level, below 10⁻³Pa, and heat at a predetermined heating rate of 5-10℃ per minute to a welding temperature of 520℃-560℃, which is below but close to the melting point of the metal material.

[0017] Step S4: Pressure diffusion. While maintaining the temperature of step S3, a constant diffusion pressure of 3-10 MPa is applied to the metal plate lamination surface through a fixture, and this pressure and temperature are maintained for 2-6 hours to allow the metal atoms at the bonding surface to diffuse into each other and form a metallurgical bond.

[0018] Step S5: After cooling and molding, and pressure holding, the battery is slowly cooled to room temperature in a vacuum environment. The fixture is then removed to obtain an integrated liquid-cooled battery box with sealed internal flow channels and no thermal deformation during welding.

[0019] As a preferred embodiment, in step S2, when the connecting side plate is spliced ​​from aluminum alloy extruded profiles, a layer of low-melting-point active diffusion agent is pre-coated at the joint of adjacent profiles, and during the pressure diffusion process in step S4, the instantaneous liquefaction of the agent promotes large-area atomic fusion at the joint interface.

[0020] As a preferred embodiment, in step S2, a transition metal foil is provided between the connecting side plate and the bottom plate and the U-shaped enclosure. During the heating and pressurization process in steps S3 and S4, the transition metal foil completely melts and diffuses into the aluminum substrates on both sides, eliminating the micro gaps that may be generated when splicing dissimilar materials or complex cross sections.

[0021] As another preferred option, in the pressurization diffusion process of step S4, a segmented pressure variation process is adopted, that is, a small initial pressure of 1-3 MPa is applied during the heating stage to pre-bond each plate; after entering the isothermal stage, the pressure gradient is increased to the target high pressure of 5-10 MPa to carry out atomic depth diffusion; in the later stage of pressure holding, the pressure is released to eliminate the residual stress inside the welding interface.

[0022] The beneficial effects of this invention are:

[0023] (1) In this invention, the connecting side plate is designed as a three-layer metal plate structure, and the fluid guide groove is etched on the middle groove plate. The outer plate, the middle groove plate and the inner cover plate are pressed together by vacuum diffusion welding, so that the fluid guide groove is closed to form a built-in liquid cooling channel. Thus, the coolant circulation channel is directly integrated into the inside of the side plate of the box, eliminating the need for traditional external cooling water pipes and additional parts such as sealant and bolts, greatly reducing the overall weight of the battery box. At the same time, it fundamentally eliminates the risk of coolant leakage caused by sealant aging or vibration loosening, and improves the safety and reliability of the battery box.

[0024] (2) In this invention, the horizontal flange edge of the lower edge of the connecting side plate and the overlapping step of the outer edge of the bottom plate are directly fused together by vacuum diffusion welding. Combined with vacuum diffusion welding between the connecting side plate, U-shaped enclosure and bottom plate, an integrated fully welded battery box structure without sealing rings or bolt fastening is formed, so that the various components of the box can achieve metallurgical bonding, the sealing performance of the joint surface is excellent, there are no micro gaps caused by traditional bolt connection or adhesive bonding, and the overall structural rigidity and vibration resistance are significantly enhanced, effectively meeting the long-term use requirements of new energy vehicles under complex working conditions.

[0025] (3) In the vacuum diffusion welding manufacturing method of the present invention, a segmented pressure transformation process is adopted. That is, a small initial pressure is applied during the heating stage to pre-fit the metal plates. After entering the constant temperature stage, the pressure is increased to the target high pressure for atomic depth diffusion. The pressure is then released in the later stage of pressure holding to eliminate the residual stress inside the welding interface. Combined with uniform heating in a vacuum environment and slow cooling with the furnace, the problem of thermal deformation of aluminum alloy box caused by high temperature concentration in traditional laser welding and argon arc welding is effectively avoided. The dimensional accuracy of the box after welding meets the requirements of cell assembly. At the same time, the high sealing of the liquid cooling channel and the absence of flux contamination are achieved, which significantly improves the product yield and consistency.

[0026] In summary, the manufacturing method of the battery box and vacuum diffusion welding has the advantages of high safety factor, high reliability, strong structural rigidity and vibration resistance, high yield, good sealing performance and no flux pollution, and is especially suitable for the field of power battery manufacturing technology for new energy vehicles. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0028] Figure 1 This is a schematic diagram of the overall structure of the present invention.

[0029] Figure 2 This is a schematic diagram of the battery module in this invention.

[0030] Figure 3 This is a schematic diagram of the outer layer plate in this invention.

[0031] Figure 4 This is a schematic diagram of the busbar structure in this invention.

[0032] Figure 5 This is a schematic diagram of the chip board structure in this invention. Detailed Implementation

[0033] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0034] Example 1

[0035] like Figures 1 to 5 As shown, the present invention provides a liquid-cooled battery box for new energy vehicles, including battery modules 1 arranged side by side. A battery box body 2 is provided on the outside of the battery module 1. The battery box body 2 includes a connecting side plate 3. U-shaped enclosures 4 are connected to both sides of the connecting side plate 3. A bottom plate 5 is fixedly connected to the lower end of the connecting side plate 3 and the U-shaped enclosures 4. The outer edge of the bottom plate 5 is provided with an upwardly folded and outwardly extending overlapping step. The lower edge of the connecting side plate 3 is provided with an outwardly bent horizontal flange edge. The horizontal flange edge covers and fits onto the overlapping step. The entire annular overlapping surface of the horizontal flange edge and the overlapping step is directly fused together by vacuum diffusion welding.

[0036] The connecting side plate 3 has a liquid cooling channel 31 on its inner side, and the connecting side plate 3 is made of three metal plates integrally pressed together by vacuum diffusion welding, and a liquid cooling channel 31 for the circulation of coolant is formed between each metal plate.

[0037] Furthermore, the connecting side plate 3 includes an outer plate 32, a middle grooved plate 33, and an inner cover plate 34. The middle grooved plate 33 has fluid guide grooves 35 etched on it. The outer plate 32 and the inner cover plate 34 are respectively attached to both sides of the middle grooved plate 33 and welded together as a whole by vacuum diffusion welding, so that the fluid guide grooves 35 are closed to form the liquid cooling channel 31. The connecting side plate 3 is composed of three metal plates: an outer plate 32, a middle grooved plate 33, and an inner cover plate 34. The middle grooved plate 33 has fluid guide grooves 35 etched on it. The outer plate 32 and the inner cover plate 34 are respectively attached to both sides of the middle grooved plate 33, and the three are welded together by vacuum diffusion welding, so that the fluid guide grooves 35 are closed to form the liquid cooling channel 31. The outer plate 32 serves as the outer support of the side plate. The core layer provides overall structural strength and impact resistance for the battery box. The guide grooves 35 on the middle groove plate 33 precisely define the flow direction and distribution path of the coolant, allowing the coolant to flow evenly across the entire side plate surface for efficient heat exchange. The inner cover plate 34 serves as the heat-conducting interface directly facing the battery module, rapidly transferring battery heat to the flow channel area. The vacuum diffusion welding process, under high temperature and pressure, causes the atoms at the interface of the three metal plates to diffuse into each other, forming a metallurgical bond without interface defects. This achieves complete sealing of the flow channel without any flux, avoiding corrosion and blockage of the liquid cooling flow channel by traditional welding residues, and eliminating the risk of coolant leakage caused by aging of the sealing ring or loosening of bolts. At the same time, the integrated flow channel eliminates the need for external pipes and fasteners, significantly reducing the weight of the box and improving the reliability under long-term vibration.

[0038] Furthermore, the connecting side plate 3, U-shaped enclosure 4, and bottom plate 5 are directly welded together using vacuum diffusion welding to form a battery box 2 without sealing rings or bolt fastening. A busbar 6 is provided on the end face of the connecting side plate 3 facing the battery module 1. The right side of the busbar 6 is threadedly connected to an electrical wiring fixing bracket 61, and the other end of the electrical wiring fixing bracket 61 is threadedly connected to the battery module 1. The connecting side plate 3, U-shaped enclosure 4, and bottom plate 5 are directly welded together using vacuum diffusion welding to form an integrated battery box 2 that requires no sealing rings or bolt fastening. This fully welded structure enables atomic-level metallurgical bonding at the joint surfaces of each component, eliminating the micro-gaps and aging leakage risks associated with traditional bolted or glued connections, and significantly improving the overall rigidity and vibration resistance of the box. A busbar 6 is provided on the end face of the side panel 3 facing the battery module 1. The busbar 6 serves as a transfer hub for electrical connection and heat dissipation, collecting the current of the battery module 1 and leading it outward through the electrical wiring fixing bracket 61 fixed by threads on its right side. At the same time, the busbar 6 itself has a heat dissipation structure, which can help dissipate heat from the battery tabs. One end of the electrical wiring fixing bracket 61 is fixedly connected to the busbar 6, and the other end is fixedly connected to the battery module 1 by threads. This provides a stable and reliable conductive path and mechanical support, and makes the installation positioning between the battery module 1 and the side panel of the box more precise, which facilitates the quick assembly and maintenance of the module in the box. At the same time, it avoids the electrical lines from directly contacting the high-temperature flow channel area, realizing the physical isolation between the electrical and liquid cooling systems, and improving the safety and maintenance convenience of the entire package.

[0039] Furthermore, the upper end of the battery module 1 is provided with a limiting U-shaped block 11, and the left side of the battery module 1 is provided with a partition plate 12. The partition plate 12 has a C-shaped structure, and the lower end of the partition plate 12 is fixedly connected to the base plate 5. The limiting U-shaped block 11 is fixedly connected to the center position of the upper end of the partition plate 12. As the core unit of energy storage, the battery module 1 is connected to the electrical wiring fixing bracket 61 through its own tabs and mounting holes to realize the input and output of electrical energy, while maintaining a predetermined gap with the inner wall of the box to prevent vibration and collision. The limiting U-shaped block 11 is set at the upper end of the battery module 1, and uses the U-shaped opening structure to clamp and press the top of the battery module 1, restricting the battery module 1 from above. The U-shaped structure provides uniform surface contact clamping force during vehicle bumps, avoiding stress concentration caused by point contact. It also facilitates quick assembly, disassembly, and maintenance. The partition plate 12 is a C-shaped structure, located on the left side of the battery module 1. Its lower end is fixedly connected to the base plate 5, and its upper center is fixedly connected to the limiting U-shaped block 11. The C-shaped structure serves as a lateral support column to physically isolate the battery module 1 from the adjacent area, effectively preventing the spread of thermal runaway or electrical short circuits. It also forms a closed force transmission path through the fixed upper and lower ends, directly transmitting the clamping force and vibration load on the limiting U-shaped block 11 to the base plate 5, thereby enhancing the torsional and bending stiffness of the overall frame.

[0040] The base plate 5 serves as the basic support for the enclosure, bearing the installation load of the battery module 1 and the partition plate 12. By welding and fixing it with the connecting side plate 3 and the U-shaped enclosure plate 4, the force of each component is evenly distributed to the entire bottom surface of the enclosure, thereby ensuring that the battery module 1 maintains a stable position in three-dimensional space for a long time and improving the safety and reliability of the battery pack under complex working conditions such as vibration and impact.

[0041] Furthermore, the busbar 6 includes a chip board 64, with connecting posts 62 uniformly fixedly connected to the upper and lower ends of the chip board 64. A side plate 3 is fixedly connected to the other side of the connecting posts 62. A heat dissipation partition plate 63 is fixedly connected to the left side of the chip board 64. The heat dissipation partition plate 63 is a uniformly arranged rectangular block. The busbar 6 serves as a current collection and heat management transfer hub between the battery module 1 and the external electrical circuit. Its core component, the chip board 64, is made of highly conductive and thermally conductive material. It undertakes the task of collecting and conducting the electrical energy output by the battery module 1 to the external electrical wiring fixing bracket 61. At the same time, it has a certain heat capacity to buffer the temperature rise caused by instantaneous large current.

[0042] The upper and lower ends of the chip board 64 are fixedly connected to the connecting side plate 3 through evenly arranged connecting fixing posts 62. This structure with evenly distributed multiple posts ensures the installation stability of the busbar 6 under vibration conditions and disperses the mechanical load transmitted during vehicle operation through multi-point support, avoiding deformation or breakage caused by stress concentration at a single connection point. At the same time, the specific length of the connecting fixing posts 62 creates a reasonable gap between the chip board 64 and the connecting side plate 3, which is conducive to airflow and heat dissipation. A heat dissipation partition plate 63 is fixedly connected to the left side of the chip board 64. The heat dissipation partition plate 63 is composed of evenly arranged rectangular blocks. These rectangular blocks increase the heat dissipation area, allowing the heat conducted from the chip board 64 to be quickly dissipated into the surrounding environment through convection and radiation, effectively reducing the operating temperature of the busbar area. On the other hand, the gaps between the rectangular blocks facilitate airflow to enhance convective heat transfer and form a physical isolation barrier between adjacent electrical terminals, preventing short circuit risks caused by accidental contact or condensate dripping. This improves heat dissipation efficiency while enhancing the electrical safety performance of the system.

[0043] further, like Figure 3 As shown,The U-shaped enclosure 4 has a structural reinforcement layer inside, which is a closed hexagonal honeycomb cavity structure. The structural reinforcement layer and the liquid cooling channel 31 are set independently of each other. The structural reinforcement layer inside the U-shaped enclosure 4 has a closed hexagonal honeycomb cavity structure. Its operating principle is to use the hexagonal honeycomb geometry to provide the highest compressive strength and bending stiffness per unit area. When the U-shaped enclosure 4 is subjected to external impact or extrusion load, the hexagonal honeycomb wall will distribute the force along the honeycomb wall surface to the adjacent units, so that the local impact energy is absorbed and dissipated by a large number of closed cavities, thereby significantly improving the impact resistance and structural stability of the enclosure side. At the same time, the honeycomb cavity is a closed structure, which not only prevents moisture or dust from entering the cavity and causing corrosion, but also avoids the cavity from forming convection with the outside air and increasing heat exchange, thus playing a certain role in sound insulation and heat insulation.

[0044] More importantly, the structural reinforcement layer and the liquid cooling channel 31 are set independently, that is, the honeycomb cavity and the coolant channel are completely isolated in space and perform their respective functions. Even if the honeycomb structure is deformed or damaged during long-term bumps or collisions, it will not cause squeezing damage or coolant leakage to the adjacent liquid cooling channel 31. This ensures that the sealing integrity of the liquid cooling system is not affected by structural stress. At the same time, this independent layout allows the honeycomb design of the structural reinforcement layer to be independently optimized in terms of thickness and cell size to meet different strength requirements. The depth and path of the guide channel of the liquid cooling channel 31 do not need to be compromised due to the consideration of structural stress. The two achieve the dual goals of lightweight structural reinforcement and efficient thermal management without interference.

[0045] A vacuum diffusion welding manufacturing method for liquid-cooled battery boxes in new energy vehicles, characterized by comprising the following steps:

[0046] Step S1: Pretreatment, the multi-layer metal plates constituting the connecting side plate 3 and the base plate 5 to be welded are subjected to surface degreasing, cleaning and passivation treatment to remove the surface oxide film;

[0047] Step S2: Stacking and mold closing, stacking and combining multiple metal plates according to the preset flow channel shape, and positioning and clamping the combined connecting side plate 3, bottom plate 5, and U-shaped side plate 4 in the fixture to ensure that all joint surfaces are completely fitted.

[0048] Step S3: Vacuum heating. Place the assembled fixture into a vacuum diffusion welding furnace, evacuate to a preset low-pressure vacuum level, below 10⁻³Pa, and heat at a predetermined heating rate of 5-10℃ per minute to a welding temperature of 520℃-560℃, which is below but close to the melting point of the metal material.

[0049] Step S4: Pressure diffusion. While maintaining the temperature of step S3, a constant diffusion pressure of 3-10 MPa is applied to the metal plate lamination surface through a fixture, and this pressure and temperature are maintained for 2-6 hours to allow the metal atoms at the bonding surface to diffuse into each other and form a metallurgical bond.

[0050] Step S5: After cooling and molding, and pressure holding, the battery is slowly cooled to room temperature in a vacuum environment. The fixture is then removed to obtain an integrated liquid-cooled battery box with sealed internal flow channels and no thermal deformation during welding.

[0051] Furthermore, in step S2, when the connecting side plate 3 is spliced ​​from aluminum alloy extruded profiles, a layer of low-melting-point active diffusion additive is pre-coated at the joint of adjacent profiles. This additive is an aluminum-based brazing filler metal. During the pressure diffusion process in step S4, the instantaneous liquefaction of this additive promotes large-area atomic fusion at the joint interface. In step S2, when the connecting side plate 3 is spliced ​​from aluminum alloy extruded profiles, a layer of low-melting-point active diffusion additive is pre-coated at the joint of adjacent profiles. During the pressure diffusion process in step S4, the additive undergoes instantaneous liquefaction as the temperature rises to near the melting point of the aluminum alloy. The excellent fluidity and wettability of the liquid additive rapidly fill the micro-unevenness and capillary gaps at the joint interface. At the same time, its active ingredients can break down the dense alumina film remaining at the interface and inhibit the formation of new oxide layers. The formation of the liquefied additive layer provides a clean metal contact surface for the free diffusion of aluminum atoms. Under continuous high temperature and pressure, the liquefied additive layer gradually fuses with the base material through isothermal solidification and atomic interdiffusion, and finally completely transforms into a metallurgical bonding layer with the same composition as the base material. This avoids the presence of brittle phases or inclusions in the weld that would affect the mechanical properties of the joint, and also avoids the technical difficulties of solid-phase diffusion welding, which requires extremely high interface flatness and surface cleanliness, and the formation of local unwelded micropores due to poor contact during large-size splicing. Thus, without the need for machining to make the profile joints completely flush, it achieves large-area, highly reliable atomic-level fusion of the joint interface, significantly reducing the manufacturing difficulty and cost of large-size box side panels, while ensuring the continuous sealing of the liquid cooling channel in the splicing area and the overall structural strength.

[0052] Furthermore, in step S2, a transition metal foil is placed between the connecting side plate 3 and the bottom plate 5 and the U-shaped enclosure 4. During the heating and pressurization process in steps S3 and S4, the transition metal foil completely melts and diffuses into the aluminum substrates on both sides, eliminating the micro gaps that may be generated when splicing dissimilar materials or complex cross sections. The transition metal foil placed between the connecting side plate 3 and the bottom plate 5 and the U-shaped enclosure 4 in step S2 utilizes the fact that the foil material, such as copper or nickel, has a lower yield strength than the aluminum alloy base material, and undergoes plastic deformation first during the heating and pressurization process in steps S3 and S4. This deformation allows it to fully fill the micro-unevenness and capillary gaps on the joint surface due to processing precision limitations, establishing a completely tight physical contact.

[0053] Subsequently, driven by high temperature and pressure, intense atomic interdiffusion occurs between the foil and the aluminum substrates on both sides, eventually causing the transition metal foil to completely integrate into the base material, forming a metallurgical bond without pores or cracks.

[0054] By utilizing the plastic flow of the foil as a "mechanical bridge," the hardness and surface unevenness of the base material are compensated, thereby achieving a high-quality connection under conditions far lower than those required for direct diffusion welding. At the same time, its complete fusion and diffusion characteristics can eliminate micro-gaps that may occur when splicing complex cross-sections, significantly improving the joint sealing and mechanical properties. Furthermore, due to the lower welding pressure required, the dimensional accuracy of the components can be effectively maintained, preventing the box structure from deforming under high pressure.

[0055] Furthermore, in the pressurization diffusion process of step S4, a segmented pressure variation process is adopted. That is, a small initial pressure of 1-3 MPa is applied during the heating stage to pre-bond the plates; after entering the isothermal stage, the pressure gradient is increased to the target high pressure of 5-10 MPa for atomic depth diffusion; in the later stage of pressure holding, the pressure is released to eliminate the residual stress inside the welding interface. The segmented pressure variation process in the pressurization diffusion process of step S4 has fundamentally different requirements for driving force due to different atomic behaviors at different stages: a small initial pressure of 1 to 3 MPa is applied during the heating stage. This pressure is not enough to induce significant plastic deformation, but it is sufficient to overcome the relative slippage tendency caused by the difference in thermal expansion coefficients of the metal plates, ensuring that the lamination surface always maintains a tight fit during the temperature rise, and preventing thermal misalignment from causing micro-separation of the interface.

[0056] After entering the isothermal stage, the pressure gradient is increased to the target high pressure of 5 to 10 MPa. This high pressure crushes the micro protrusions at the interface and increases the actual contact area. At the same time, after the atoms obtain sufficient transition energy, the vacancy flow and dislocation channeling effect excited by the high pressure significantly enhance the diffusion rate of atoms across the interface barrier, realize the deep interdiffusion of aluminum atoms on both sides of the interface, and form a metallurgical bonding layer with uniform thickness.

[0057] The underlying principle of pressure relief in the later stage of pressure holding is that the elastoplastic strain energy accumulated near the interface due to lattice distortion and atomic misalignment at high temperature is released through short-range atomic rearrangement and grain boundary slip after the pressure is removed, thereby reducing the residual tensile stress level inside the joint and preventing stress concentration during cooling from inducing microcracks or interface peeling.

[0058] The characteristic of this segmented variable pressure process is that it decouples pressure control from temperature regime, precisely matches the physical requirements of different diffusion welding processes in stages, avoids the instability and deformation of thin-walled components caused by the simultaneous action of high temperature and high pressure, ensures diffusion efficiency, thereby shortening the holding time and refining the grains, and relieves pressure in the later stage to eliminate residual stress and eliminate the need for subsequent heat treatment processes. It comprehensively achieves the welding quality goals of high dimensional accuracy, high joint strength, and low stress state.

[0059] Working process: First, the pretreatment step S1 is performed to degrease, clean and passivate the outer plate 32, middle groove plate 33 and inner cover plate 34 that make up the connecting side plate 3, as well as the bottom plate 5 to be welded, to completely remove the surface oxide film; then the stacking and molding step S2 is performed to place the middle groove plate 33 with the fluid guide groove 35 etched between the outer plate 32 and the inner cover plate 34, and stack them according to the preset flow channel shape to form the connecting side plate 3. When the connecting side plate 3 is spliced ​​from aluminum alloy extruded profiles, a layer of low melting point active diffusion agent is applied to the joint of adjacent profiles. The assembled connecting side plate 3, bottom plate 5 and U-shaped enclosure plate 4 are positioned and clamped in the fixture. At the same time, a transition metal foil is placed between the connecting side plate 3, bottom plate 5 and U-shaped enclosure plate 4 to ensure that all joint surfaces are completely fitted.

[0060] Next, perform step S3, vacuum heating, and place the assembled fixture into a vacuum diffusion welding furnace. Evacuate the furnace to a vacuum level below 10⁻³Pa and heat it to a welding temperature of 520 to 560 degrees Celsius at a heating rate of 5 to 10 degrees Celsius per minute.

[0061] Then, step S4, pressurized diffusion, is performed. A segmented pressure-changing process is used to first apply an initial pressure of 1 to 3 MPa during the heating stage to pre-bond each plate. After entering the constant temperature stage, the pressure gradient is increased to 5 to 10 MPa and maintained for 2 to 6 hours to allow the atoms to undergo deep interdiffusion and form a metallurgical bond. At the same time, during this process, the low-melting-point active diffusion aid is instantaneously liquefied to promote large-area atomic fusion at the profile joint interface. The transition metal foil is completely melted under heating and pressure and diffuses into the aluminum substrates on both sides to eliminate micro gaps. After the pressure is maintained, the pressure is released to eliminate the residual stress inside the welding interface.

[0062] Then, step S5 is performed to cool and form the battery. After being slowly cooled to room temperature in a vacuum environment, the fixture is removed to obtain an integrated fully welded battery box 2 with a sealed liquid cooling channel 31 inside and no thermal deformation during welding. The battery box 2 is formed by directly fixing the connecting side plate 3, U-shaped enclosure 4 and bottom plate 5 through vacuum diffusion welding to form an integral structure that does not require sealing rings and bolt fastening. The sealed hexagonal honeycomb structure reinforcement layer inside the U-shaped enclosure 4 is independently set with the liquid cooling channel 31.

[0063] Finally, the battery modules 1 arranged side by side are installed into the battery housing 2. The bottom plate 5 is fixedly connected to the lower end of the C-shaped partition plate 12 on the left side of the battery module 1, and the limiting U-shaped block 11 is fixedly connected to the center of the upper end. The limiting U-shaped block 11 clamps and presses the top of the battery module 1 from above to limit its vertical movement. At the same time, the busbar 6 opened on the end face of the connecting side plate 3 facing the battery module 1 is fixedly connected to the battery module 1 by the electrical wiring fixing bracket 61 on its right side. The chip board 64 of the busbar 6 is fixed to the connecting side plate 3 at the upper and lower ends by the connecting fixing post 62. The heat dissipation isolation plate 63 on the left side of the chip board 64 dissipates heat and provides electrical isolation for the busbar area. The coolant circulates in the liquid cooling channel 31 formed by three layers of metal plates inside the connecting side plate 3 to efficiently cool the battery module 1.

[0064] In the description of this invention, it should be understood that the terms "front and back", "left and right", etc., indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are only for the convenience of describing this invention and simplifying the description, and do not indicate or imply that the device or component referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention.

[0065] Of course, those skilled in the art should understand that the term "a" should be understood as "at least one" or "one or more". That is, in one embodiment, the number of an element can be one, while in another embodiment, the number of the element can be multiple. The term "a" should not be understood as a limitation on the quantity.

[0066] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art under the technical guidance of the present invention should be included within the scope of protection of the present invention. Therefore, the scope of protection of the present invention should be determined by the scope of the claims.

Claims

1. A liquid-cooled battery box for new energy vehicles, characterized in that: The battery module (1) is arranged side by side. A battery box (2) is provided on the outside of the battery module (1). The battery box (2) includes a connecting side plate (3). The connecting side plate (3) is connected to U-shaped enclosures (4) on both sides. The bottom plate (5) is fixedly connected to the lower end of the connecting side plate (3) and the U-shaped enclosures (4). The outer edge of the bottom plate (5) is provided with an upwardly folded and outwardly extending overlapping step. The lower edge of the connecting side plate (3) is provided with an outwardly bent horizontal flange edge. The horizontal flange edge covers and fits on the overlapping step. The horizontal flange edge and the entire annular overlapping surface of the overlapping step are directly fused together by vacuum diffusion welding. The connecting side plate (3) has a liquid cooling channel (31) on its inner side, and the connecting side plate (3) is made of three metal plates integrally pressed together by vacuum diffusion welding, and a liquid cooling channel (31) for circulating coolant is formed between each metal plate.

2. The liquid-cooled battery box for new energy vehicles according to claim 1, characterized in that, The connecting side plate (3) includes an outer plate (32), a middle groove plate (33) and an inner cover plate (34). The middle groove plate (33) is etched with fluid guide grooves (35). The outer plate (32) and the inner cover plate (34) are respectively attached to the two sides of the middle groove plate (33) and welded into a whole by vacuum diffusion welding so that the fluid guide grooves (35) are closed to form the liquid cooling channel (31).

3. The liquid-cooled battery box for new energy vehicles according to claim 1, characterized in that, The connecting side plate (3), U-shaped enclosure (4) and bottom plate (5) are directly welded and fixed by vacuum diffusion welding to form a battery box (2) without sealing rings and bolt fastening. A busbar (6) is provided on the end face of the connecting side plate (3) facing the battery module (1). The right side of the busbar (6) is threadedly fixed to the electrical wiring fixing bracket (61), and the other end of the electrical wiring fixing bracket (61) is threadedly fixed to the battery module (1).

4. The liquid-cooled battery box for new energy vehicles according to claim 1, characterized in that, The battery module (1) is provided with a limiting U-shaped block (11) at the upper end, and a partition plate (12) is provided on the left side of the battery module (1). The partition plate (12) is a C-shaped structure, and the bottom plate (5) is fixedly connected to the lower end of the partition plate (12). The limiting U-shaped block (11) is fixedly connected to the center position of the upper end of the partition plate (12).

5. The liquid-cooled battery box for new energy vehicles according to claim 3, characterized in that, The busbar (6) includes a chip board (64), with connecting posts (62) uniformly fixedly connected to the upper and lower ends of the chip board (64), and a connecting side plate (3) fixedly connected to the other side of the connecting posts (62). A heat dissipation partition plate (63) is fixedly connected to the left side of the chip board (64), and the heat dissipation partition plate (63) is a rectangular block arranged uniformly.

6. The liquid-cooled battery box for new energy vehicles according to claim 1, characterized in that, The U-shaped enclosure (4) has a structural reinforcement layer inside. The structural reinforcement layer is a closed hexagonal honeycomb cavity structure, and the structural reinforcement layer and the liquid cooling channel (31) are set independently of each other.

7. A vacuum diffusion welding manufacturing method for a liquid-cooled battery box for new energy vehicles as described in any one of claims 1-6, characterized in that, Includes the following steps: Step S1: Pretreatment, the multilayer metal plates constituting the connecting side plate (3) and the base plate (5) to be welded are subjected to surface degreasing, cleaning and passivation treatment to remove the surface oxide film; Step S2: Stack and assemble the mold. Stack and combine the multi-layer metal plates according to the preset flow channel shape, and position and clamp the combined connecting side plate (3), bottom plate (5), and U-shaped side plate (4) in the fixture to ensure that each joint surface is completely fitted. Step S3: Vacuum heating. Place the assembled fixture into a vacuum diffusion welding furnace, evacuate to a preset low-pressure vacuum level, below 10⁻³Pa, and heat at a predetermined heating rate of 5-10℃ per minute to a welding temperature of 520℃-560℃, which is below but close to the melting point of the metal material. Step S4: Pressure diffusion. While maintaining the temperature of step S3, a constant diffusion pressure of 3-10 MPa is applied to the metal plate lamination surface through a fixture, and this pressure and temperature are maintained for 2-6 hours to allow the metal atoms at the bonding surface to diffuse into each other and form a metallurgical bond. Step S5: After cooling and molding, and pressure holding, the battery is slowly cooled to room temperature in a vacuum environment. The fixture is then removed to obtain an integrated liquid-cooled battery box with sealed internal flow channels and no thermal deformation during welding.

8. The vacuum diffusion welding manufacturing method for a liquid-cooled battery box for new energy vehicles according to claim 7, characterized in that, In step S2, when the connecting side plate (3) is spliced ​​from aluminum alloy extruded profiles, a layer of low melting point active diffusion agent is pre-coated at the joint of adjacent profiles, and during the pressure diffusion process in step S4, the instantaneous liquefaction of the agent promotes large-area atomic fusion of the joint interface.

9. The vacuum diffusion welding manufacturing method for a liquid-cooled battery box for new energy vehicles according to claim 7, characterized in that, In step S2, a transition metal foil is provided between the connecting side plate (3) and the bottom plate (5) and the U-shaped enclosure plate (4). During the heating and pressurization process in steps S3 and S4, the transition metal foil is completely melted and diffused into the aluminum substrates on both sides, eliminating the micro gaps that may be generated when splicing dissimilar materials or complex cross sections.

10. The vacuum diffusion welding manufacturing method for a liquid-cooled battery box for new energy vehicles according to claim 7, characterized in that, In the pressurization diffusion process of step S4, a segmented pressure variation process is adopted. That is, a small initial pressure of 1-3 MPa is applied during the heating stage to pre-bond the plates; after entering the isothermal stage, the pressure gradient is increased to the target high pressure of 5-10 MPa to carry out atomic depth diffusion; in the later stage of pressure holding, the pressure is released to eliminate the residual stress inside the welding interface.

Images