Aluminum alloy solid phase diffusion welding method with small deformation and high strength

Abstract

This invention relates to the field of material joining technology, and particularly to a solid-state diffusion welding method for aluminum alloys with small deformation and high strength, comprising the following steps: Step S1: Grinding and cleaning the surfaces of two aluminum alloy plates to be welded; Step S2: Shot peening; Step S3: Cleaning the two aluminum alloy plates and the intermediate layer; Step S4: Placing an inner core inside the inner flow channel of the two aluminum alloy plates, stacking the two aluminum alloy plates in a mirror image, with an intermediate layer placed in the middle to form a block structure to be welded; Step S5: Placing the block structure to be welded as a whole between the upper and lower pressure heads in a vacuum diffusion welding furnace, and isolating it with upper and lower weld resist layers, and performing welding to obtain an aluminum alloy composite component; Step S6: Removing the inner core and intermediate layer from the inner flow channel; Step S7: Performing heat treatment. This invention, through multi-level control, simultaneously optimizes the interface bonding quality and residual stress distribution under low deformation, resulting in a significant improvement in the mechanical properties of the joint.

Description

Technical Field

[0001] This invention relates to the field of material joining technology, and in particular to a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength. Background Technology

[0002] For the joining requirements of precision aluminum alloy components with complex internal flow channels and micropores, solid-state diffusion welding, with its non-fusion bonding characteristics, exhibits unique advantages in suppressing structural deformation and avoiding flow channel blockage, and is considered an effective method for achieving precision welding of aluminum alloys. However, traditional diffusion welding processes rely on high-temperature and high-pressure conditions to promote inter-diffusion of interfacial elements. This intense thermo-coupling effect easily leads to significant joint deformation, making it difficult to meet the micro-deformation requirements of precision components. More importantly, in extreme operating conditions, it is also necessary to ensure that the joint has sufficient structural strength to maintain long-term stability. How to achieve a diffusion weld joint with "micro-deformation-high strength" synergistic optimization while ensuring interfacial metallurgical bonding and airtightness has become a key bottleneck restricting the engineering application of this technology.

[0003] The literature “Influence of Al foil interlayer on performance of vacuum diffusion bonding joint of 6061 aluminum alloy, DS Liu, JH Xu, XH Li, et al., Journal of iron and steel research international, 2024, 31(10): 2404-2412” discloses a method for diffusion bonding of 6061 aluminum alloy by adding an aluminum foil interlayer. The obtained joint has a strength of 79 MPa and a bonding rate of 95.91%. Compared with the joint without aluminum foil, its deformation rate is reduced by 1.58% to 8.05%. However, the equipment cost is high and it is limited by the size of the workpiece, making it difficult to achieve large-scale application.

[0004] The invention patent application CN202310735100.8 discloses a low-temperature, low-pressure joining method for aluminum alloys based on liquid-solid co-diffusion, which removes the gas film and oxide film on the material surface through mechanical means such as mutual friction or ultrasonic waves. However, for some workpieces with special structures, the mechanical implementation process can cause structural failure, and the liquid metal poses a risk of clogging micropores.

[0005] The paper "Surface modification of pure aluminum via Ar ion bombardment for Al / Al solid-state diffusion bonding, CN Niu, WL Zhou, XG Song, et al., Materials Characterization, 2022, 187" discloses a method for surface modification of pure aluminum via Ar ion bombardment to assist diffusion bonding of aluminum alloys. This method achieves a joint with a shear strength of 45.9 MPa at lower than conventional welding parameters. However, considering the high cost of Ar ion bombardment equipment and limitations on workpiece size, this method is not adopted in practical applications.

[0006] Therefore, in order to meet the engineering needs of precision aluminum alloy components, there is an urgent need to develop a new process method that is low-cost, simple to operate, and practical to improve the performance of aluminum alloy joints and provide a new solution for the reliable connection of precision aluminum alloy components. Summary of the Invention

[0007] To address the problems of large deformation, insufficient strength, poor adaptability, and high cost in existing diffusion welding of aluminum alloy precision components, the purpose of this invention is to provide a solid-state diffusion welding method for aluminum alloys with small deformation and high strength. This method employs surface shot peening pretreatment to pre-stress the aluminum alloys and uses an interface migration-driven diffusion welding connection method. Simultaneously, post-weld heat treatment further enhances the joint strength. This composite process solves the problem of achieving "small deformation, high strength" connections in aluminum alloy precision instruments, which is difficult to achieve synergistically.

[0008] To achieve the above objectives, the present invention adopts the following technical solution:

[0009] This invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, characterized by comprising the following steps:

[0010] Step S1: Select two aluminum alloy plates with the same internal flow channel, and grind and clean the surfaces of the two aluminum alloy plates to be welded.

[0011] Step S2: The surfaces of the two aluminum alloy plates that have been polished and cleaned are shot peened. The nanocrystalline layer formed by shot peening provides a fast channel for atomic diffusion through a large number of grain boundaries.

[0012] Step S3: Select the intermediate layer and clean the two aluminum alloy plates and the intermediate layer;

[0013] Step S4: Place two inner cores in the inner flow channels of the two aluminum alloy plates respectively, stack the two aluminum alloy plates in a mirror image, and place an intermediate layer between the two aluminum alloy plates to form a block structure to be welded.

[0014] Step S5: Place the block structure to be welded between the upper and lower pressure heads in the vacuum diffusion welding furnace. Place the upper and lower resistance welding layers between the upper and lower pressure heads and the block structure to be welded, respectively, and perform the welding process to obtain the aluminum alloy composite component.

[0015] Step S6: Remove the inner core and intermediate layer from the inner channels of the two aluminum alloy plates;

[0016] Step S7: Heat treat the aluminum alloy composite component.

[0017] In step S2, the surface of the aluminum alloy plate to be welded after grinding is shot peened using a shot peening machine. The shot peening medium is glass pellets with a diameter of 0.3 mm, the shot peening pressure is 0.4 MPa, and the shot peening time is 3-5 min.

[0018] In step S3, the aluminum alloy sheet and intermediate layer after shot peening are sequentially subjected to ultrasonic cleaning, chemical cleaning with NaOH and HNO3 solution, and ultrasonic cleaning with anhydrous ethanol to remove the surface oxide film.

[0019] The intermediate layer is made of aluminum foil;

[0020] The compositional difference between the intermediate layer and the aluminum alloy sheet creates a concentration gradient, which can accelerate the migration of interface elements.

[0021] In step S4, the block structure to be welded is placed inside the outer graphite sleeve, and an upper graphite pressure plate is placed on top of the block structure to be welded, with the edge of the upper graphite pressure plate fitting against the inner wall of the outer graphite sleeve.

[0022] In step S5, the welding process is as follows: apply a pre-pressure of 0.5~1MPa, evacuate to 3~6×10⁻³Pa; heat up at a rate of 10℃ / min, hold at 400℃ for 30min; continue heating to 480~520℃, apply pressure of 4~6MPa, hold for 120min; after holding, cool with the furnace to 100℃, maintain pressure during cooling, and obtain an aluminum alloy composite component.

[0023] In step S5, after heating to 480~520℃, pressurizing to 4~6MPa, and holding for 120min, the following additional steps are added: heating the furnace temperature to 540~560℃, pressurizing to 1~2MPa, holding for 90min, and then cooling with the furnace.

[0024] In step S6, strong acid and ultrasonic waves are used to corrode the inner core inside the flow channels of the two aluminum alloy plates; abrasive flow is used to polish the inner flow channels of the two aluminum alloy plates, thereby grinding away the intermediate layer.

[0025] The inner core is made of 45# steel.

[0026] In step S7, the composite component is placed in a heat treatment device and solution treated at 530°C for 50 min to 1 h, with water cooling or air cooling as the cooling method; then it is aged at 175°C for 8 h, air cooled, and welding is completed.

[0027] The advantages and beneficial effects of this invention are:

[0028] This invention innovatively proposes a solid-state diffusion welding method for aluminum alloys that synergistically achieves small deformation and high strength through shot peening pretreatment and an intermediate layer. By constructing a gradient nanocrystalline layer and strain energy field on both sides of the joint interface through surface shot peening pretreatment, it overcomes the technical bottleneck of aluminum alloy welding. The nanocrystalline layer formed by shot peening provides rapid atomic diffusion channels through numerous grain boundaries, while the high strain energy accumulated by the dislocation network significantly reduces the diffusion activation energy. The introduction of the intermediate layer improves the interfacial contact state and increases the concentration gradient at the interface, accelerating element diffusion and void closure. During welding, the strain energy difference on both sides of the interface triggers a strain-induced grain boundary migration mechanism, causing grain boundaries to bulge at the interface. Post-weld heat treatment of the joint further enhances the joint strength by relieving stress, optimizing interfacial bonding, and regulating the microstructure. This method, through multi-level regulation, simultaneously optimizes the interfacial bonding quality and residual stress distribution under low deformation, resulting in a significant improvement in the mechanical properties of the joint.

[0029] This invention uses an outer graphite sleeve to achieve triaxial compressive stress diffusion welding, rather than the uniaxial compressive stress diffusion welding of the prior art. Triaxial compressive stress diffusion welding is more conducive to the uniformity of micro-grain arrangement, which is beneficial to providing fatigue resistance under thermal cycling loads and extending crack initiation life.

[0030] Other features and advantages of the invention will be set forth in the following description, and will be apparent in part from the description, or may be learned by practicing the invention. The objects and other advantages of the invention may be realized and obtained by means of the structures particularly pointed out in the written description and the accompanying drawings.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0032] The accompanying drawings are provided to further illustrate the invention and form part of the specification. They are used in conjunction with embodiments of the invention to explain the invention and do not constitute a limitation thereof. In the drawings:

[0033] Figure 1 This is a schematic diagram of a clamping structure for diffusion welding of aluminum alloy workpieces according to the present invention;

[0034] Figure 2 This is a schematic diagram of shot peening treatment on the surface of aluminum alloy sheet in this invention;

[0035] Figure 3 This is a schematic diagram of another clamping structure for diffusion welding of aluminum alloy workpieces according to the present invention;

[0036] Figure 4 This is an isometric view of another clamping structure for diffusion-welded aluminum alloy workpieces according to the present invention;

[0037] Figure 5 This is a schematic diagram of the structure of the outer graphite sleeve in this invention;

[0038] Figure 6 This is a schematic diagram of the structure of the lower aluminum alloy sheet in this invention;

[0039] Figure 7 This is a schematic diagram of the lower core structure in this invention.

[0040] In the diagram: 1. Shot peening medium; 2. Aluminum alloy sheet; 201. Lower aluminum alloy sheet; 202. Upper aluminum alloy sheet; 203. Inner flow channel; 3. Upper pressure head; 4. Upper solder resist layer; 5. Intermediate layer; 6. Lower pressure head; 7. Upper graphite pressure plate; 8. Outer graphite sleeve; 9. Upper core; 10. Lower core; 11. Lower solder resist layer. Detailed Implementation

[0041] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0042] The preferred embodiments of the present invention will be described below with reference to the accompanying drawings. It should be understood that the preferred embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0043] One embodiment of the present invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength. By constructing a nanocrystalline layer through surface shot peening, ensuring uniform pressure through a special clamping structure, and optimizing the microstructure through post-weld heat treatment, the method achieves a synergy of "small deformation and high strength" for precision aluminum alloy components, while reducing costs and improving the ability to be applied on a large scale.

[0044] See Figures 1 to 7As shown, the present invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, comprising the following steps:

[0045] Step S1: Select two aluminum alloy plates 2 with the same inner flow channel 203, and grind and clean the surfaces of the two aluminum alloy plates 2 to be welded.

[0046] Step S2: Perform shot peening on the surfaces of the two aluminum alloy plates 2 that have already been ground and cleaned. Use shot peening medium 1 to refine the nanocrystals on the surfaces of the aluminum alloy plates 2 that will be diffused and welded. See [link to relevant documentation]. Figure 2 As shown, the nanocrystalline layer formed by shot peening constructs rapid atomic diffusion channels through numerous grain boundaries, while accumulating high strain energy, significantly reducing the diffusion activation energy.

[0047] Step S3: Select intermediate layer 5, perform ultrasonic cleaning on the two aluminum alloy plates 2 and intermediate layer 5, and perform chemical cleaning to remove oxide film before welding;

[0048] Step S4: Place two inner cores in the inner flow channels 203 of the two aluminum alloy plates 2 respectively, stack the two aluminum alloy plates 2 in a mirror image, and place an intermediate layer 5 between the two aluminum alloy plates 2 to form a block structure to be welded.

[0049] Step S5: Place the block structure to be welded between the upper pressure head 3 and the lower pressure head 6 in the vacuum diffusion welding furnace. Place the upper welding resist layer 4 and the lower welding resist layer 11 between the upper pressure head 3 and the lower pressure head 6 and the block structure to be welded, respectively, and perform the welding process to obtain the aluminum alloy composite component.

[0050] Step S6: Remove the inner core and intermediate layer 5 from the inner flow channel 203 of the two aluminum alloy plates 2 to restore the smooth flow of the internal flow channel of the aluminum alloy composite component;

[0051] Step S7: Heat treat the aluminum alloy composite component to further improve the joint strength.

[0052] Specifically, for ease of understanding, the two aluminum alloy plates 2 are defined as the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202, respectively. Both the lower and upper aluminum alloy plates 201 and 202 are machined with internal flow channels 203 of the same structure. The internal flow channels 203 have a complex structure and have inlets and outlets. Because of the complex structure of the internal flow channels 203, if diffusion welding is used with existing technology, the different stiffness in the direction of the diffusion welding surface will lead to different pressures in the diffusion welding, resulting in uneven diffusion welding strength. By adding inner cores (upper core 9 and lower core 10), the uniformity of welding strength in the direction of the diffusion welding surface is improved. The upper core 9 and lower core 10 are preferably made of 45# steel. The inner cores solve the problem of theoretical mechanical failure of the pressure bar structure due to the excessively high internal cavity ratio of the aluminum alloy plate 2 in special applications, which would prevent the aluminum alloy plate 2 from reaching the bonding pressure for diffusion welding, thus ensuring uniform pressure on the welding surface.

[0053] In an embodiment of the present invention, in step S2, the surfaces to be welded after grinding of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 are shot peened using a shot peening machine. The shot peening medium 1 is glass pellets with a diameter of 0.3 mm, the shot peening pressure is 0.4 MPa, and the shot peening time is 3-5 min. See [link to relevant documentation]. Figure 2 As shown.

[0054] In an embodiment of the present invention, in step S3, the lower aluminum alloy plate 201, the upper aluminum alloy plate 202, and the intermediate layer 5 after shot peening are first ultrasonically cleaned, and then chemically cleaned with NaOH and HNO3 solution before welding to completely remove the surface oxide film; after cleaning, they are immediately placed in anhydrous ethanol for ultrasonic cleaning again to avoid secondary oxidation.

[0055] In an embodiment of the present invention, the intermediate layer 5 is made of aluminum foil; the compositional difference between the intermediate layer 5 and the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 forms a concentration gradient, which can accelerate the migration of interface elements.

[0056] Further, in step S4, the block structure to be welded is placed inside the outer graphite sleeve 8, and an upper graphite pressure plate 7 is placed above the block structure to be welded. The edge of the upper graphite pressure plate 7 is fitted against the inner wall of the outer graphite sleeve 8. See [link to relevant documentation]. Figure 3 and Figure 4 As shown, the outer graphite sleeve 8 creates a triaxial compressive stress environment for welding, rather than the traditional uniaxial compressive stress. The outer graphite sleeve 8 can restrict the lateral movement of the internally stacked components, ensure the overall stability of the clamping structure, and provide support for the formation of the triaxial compressive stress welding environment.

[0057] In an embodiment of the present invention, the welding process in step S5 is as follows: applying a pre-pressure of 0.5~1MPa, evacuating to 3~6×10⁻³Pa; heating at a rate of 10℃ / min, holding at 400℃ for 30min; continuing to heat to 480~520℃, applying pressure of 4~6MPa, and holding for 120min; after holding, cooling to 100℃ in the furnace, maintaining pressure during cooling, to obtain an aluminum alloy composite component. This stage solves the problems of uneven welding pressure and instability in complex structural parts through a special clamping structure and vacuum welding parameter control, thus completing solid-phase diffusion welding.

[0058] In an embodiment of the present invention, in step S5, after the room temperature is raised to 480~520℃, pressurized to 4~6MPa, and held for 120min, the following additional step is added: the furnace temperature is raised to 540~560℃, pressurized to 1~2MPa, held for 90min, and then cooled with the furnace.

[0059] In an embodiment of the present invention, in step S6, strong acid and ultrasonic waves are used to corrode the inner core inside the inner flow channel 203 of the two aluminum alloy plates 2; abrasive flow is used to polish the inner flow channel 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202, thereby grinding away the intermediate layer 5.

[0060] In an embodiment of the present invention, in step S7, the composite component is placed in a heat treatment device and subjected to solution treatment at 530°C for 50 min to 1 h, with water cooling or air cooling as the cooling method; subsequently, it is aged at 175°C for 8 h, air-cooled, and then welded.

[0061] See Figure 5 As shown, the outer graphite sleeve 8 is a ring structure. The triaxial compressive stress environment constructed by the outer graphite sleeve 8 is conducive to the uniform distribution of micro-grains during the welding process, significantly improving the fatigue resistance of the joint under thermal cycling load and extending the crack initiation life. In addition, the optimization effect of post-weld heat treatment on the microstructure makes the joint not only have high strength, but also excellent long-term service stability, which is suitable for fields with extremely high reliability requirements such as aerospace and semiconductor equipment.

[0062] For aluminum alloy sheet 2 containing complex internal flow channels 203, uneven stiffness is prone to occur on the surface to be welded due to structural differences. The upper graphite pressure plate 7, through its own flatness and strength, assists the upper core 9 and lower core 10 in further balancing the pressure on the welding surface, ensuring that effective welding pressure is achieved in different areas such as around the flow channels and the edges of the sheet, thus solving the problem of "uneven strength of joints in complex structures" in traditional processes. The upper graphite pressure plate 7 evenly distributes the concentrated pressure applied by the pressure head 3 of the diffusion welding equipment to the area to be welded of the aluminum alloy sheet 2, avoiding the problems of excessive local pressure (causing excessive deformation) or insufficient local pressure (leading to low weld rate) caused by pressure concentration.

[0063] The inner flow channel 203 is a channel structure pre-machined inside the aluminum alloy sheet 2. It is ultimately formed by diffusion welding of the lower aluminum alloy sheet 201 and the upper aluminum alloy sheet 202 to create a closed flow channel. The entire closed flow channel is located inside the aluminum alloy composite component and must meet the precision requirements of no external opening leakage and unobstructed internal passages, adapting to the functional requirements of media transmission (such as coolant and gas) in fields such as semiconductor equipment and aerospace. The shape of the closed flow channel must adapt to the customized needs of precision components and may include multiple bends, diameter changes, or local fine hole structures. See [reference needed]. Figure 6 As shown. This further highlights the necessity of the support structure for the upper core 9 and the lower core 10. The structure of the upper core 9 and the lower core 10 is adapted to the shape of the inner flow channel 203, see [reference]. Figure 7 As shown.

[0064] Aluminum alloy surfaces readily form dense oxide films with high chemical stability, which can hinder atomic diffusion and metallurgical bonding at the welding interface. Intermediate layer 5 overcomes this challenge through the following methods:

[0065] The intermediate layer 5 (such as 4104 aluminum foil or Al-Mg-Si-Zr-Ti self-made aluminum foil) serves as a transition layer, which can physically isolate the oxide film of the upper and lower aluminum alloy plates, reducing the bonding obstacles caused by direct contact of the original oxide film; at the same time, the intermediate layer material is easy to undergo diffusion reaction with the oxide film at the welding temperature (480~560℃), gradually dissolving or breaking the oxide film, opening up channels for interdiffusion of matrix atoms.

[0066] The compositional difference between the intermediate layer 5 and the aluminum alloy substrate (such as the presence of elements like Mg and Si) can form a concentration gradient. According to the diffusion law, the greater the concentration gradient, the stronger the driving force for atomic diffusion, which can accelerate the migration of interface elements, shorten the heat preservation time required to achieve metallurgical bonding, and indirectly reduce workpiece deformation at high temperatures.

[0067] Compared to mechanical cutting to remove the inner core (which may cause deformation of the aluminum alloy joint or damage to the internal flow channel due to external force), strong acid corrosion is a "stress-free removal" method, which can avoid introducing additional stress in subsequent processing stages and ensure the stability of the joint deformation rate (as in the examples, the deformation rate is 0.81%). The corrosion removal of the 45# steel inner core does not affect the already formed aluminum alloy welded joint, ensuring that the high-strength metallurgical bond formed in the previous welding process is not destroyed, and ultimately achieving an aluminum alloy composite component with "structural integrity and performance compliance".

[0068] In embodiments of the present invention, the removal of the intermediate layer 5 is achieved through the Smanker abrasive flow principle:

[0069] Smank's abrasive flow principle is based on the synergistic effect of fluid dynamics and particle collisions. High pressure drives semi-solid abrasive particles to flow at high speed within the complex surface or internal structure of a workpiece, achieving deburring, polishing, and surface leveling. The core principle is: abrasive flow uses high pressure (3-15 MPa) to inject a semi-fluid medium mixed with high-hardness abrasives such as silicon carbide and alumina into a pipe or workpiece. During the flow, the abrasive particles generate high-frequency collisions and friction with the workpiece surface through extrusion motion, while the shear force generated by the velocity difference in the fluid layers further enhances the grinding effect. This "micro-sandpaper" style grinding method can penetrate deep into tiny pores and complex structures, achieving efficient deburring and surface polishing.

[0070] The technological features include:

[0071] Environmental friendliness: The abrasive is recyclable and produces no dust, high heat or dangerous gases.

[0072] Applicability: Suitable for fields with high precision requirements such as automobiles, aerospace, and precision molds, especially good at handling complex structures such as internal holes, intersecting holes, and micro holes.

[0073] Efficiency and Precision: High-precision surface treatment (Ra≤0.2μm) can be achieved by improving finishing efficiency through tooling assistance.

[0074] Multi-objective synergy: Simultaneously removes burrs and oxide layers and smooths the surface, reducing subsequent processing steps.

[0075] Flexibility: It can handle different materials (such as aluminum alloy and stainless steel) and adapt to the needs of mass production.

[0076] Specifically, the process of removing intermediate layer 5 can be divided into the following three stages:

[0077] (a) Abrasive media filling stage

[0078] The abrasive flow equipment injects semi-fluid abrasive (composed of abrasive grains, binder, lubricant, etc. mixed in proportion) into the inlet of the inner flow channel of the aluminum alloy composite component through a pressure system (usually hydraulically driven). Since the inner flow channel is a closed structure (formed by welding the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202), and the intermediate layer 5 is located at the interface of the two plates and partially exposed on the surface of the inner flow channel, the abrasive medium will fully fill all the passages of the inner flow channel under pressure, including complex areas such as flow channel bends and diameter changes, ensuring complete contact between the abrasive grains and the part to be removed in the intermediate layer 5.

[0079] (ii) Abrasive cutting removal stage

[0080] When the abrasive medium flows at high speed along the inner channel under pressure, the hard abrasive grains in the abrasive will continuously produce "micro-cutting", "scraping" and "grinding" effects on the surface of the intermediate layer 5:

[0081] Micro-cutting action: The edges of high-hardness abrasive grains (usually harder than the aluminum foil material of the intermediate layer 5) cut into the aluminum foil matrix of the intermediate layer 5, cutting the aluminum foil material into tiny fragments.

[0082] Scraping action: The abrasive grains moving with the fluid will slide along the surface of the intermediate layer 5, scraping off the oxide layer and incompletely welded aluminum foil residues.

[0083] Grinding effect: The dense movement of a large number of abrasive grains can finely grind the remaining part of the intermediate layer 5, making the surface of the aluminum alloy substrate at the interface smooth.

[0084] Since the intermediate layer 5 is made of aluminum foil, its hardness (about 20-30 HV) is much lower than that of abrasive grains (such as silicon carbide abrasive grains with a hardness of about 2300 HV). It also has a certain hardness difference with the upper and lower aluminum alloy plates (the substrate hardness is usually higher than 50 HV). The abrasive grains will preferentially cut the intermediate layer 5 with lower hardness, while causing minimal damage to the aluminum alloy substrate, thus achieving "selective removal".

[0085] (III) Debris Removal and Surface Finishing Stage

[0086] The aluminum foil debris generated during cutting is carried by the flowing abrasive medium and discharged from the inner channel with the abrasive circulation system. At the same time, the continuous action of the abrasive flow will simultaneously repair the surface of the inner channel of the aluminum alloy substrate, remove burrs, weld beads and other defects that may exist in the inner channel, reduce the roughness of the inner wall of the inner channel, and thus complete the removal of the intermediate layer 5 and optimize the flow performance of the inner channel.

[0087] Example 1

[0088] This invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, specifically employing the following steps:

[0089] Step S1: Select lower aluminum alloy plate 201 and upper aluminum alloy plate 202 of appropriate thickness, and clean the surface of the sample to be welded by mechanical grinding to keep the surface flat and clean, so as to ensure the effect of shot peening pretreatment.

[0090] Step S2: Use a shot peening machine to shot peen the polished surfaces of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202, ensuring a uniform surface finish. Use 0.3 mm glass pellets as the peening medium, a shot peening pressure of 0.4 MPa, and a shot peening time of 3-5 minutes. This refinement of the crystal structure on the surfaces to be welded effectively improves the bonding strength of the diffusion weld.

[0091] Step S3: Perform ultrasonic cleaning on the surface-treated lower aluminum alloy plate 201, upper aluminum alloy plate 202 and intermediate layer 5; before welding, use NaOH and HNO3 solution to chemically clean the surface of the sample to be welded and the intermediate layer 5 to remove the surface oxide film; after cleaning, immediately place them in anhydrous ethanol and perform ultrasonic cleaning on the surface of the sample to be welded and the intermediate layer 5.

[0092] Step S4: Place the lower core 10 and the upper core 9 in the inner flow channels 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 respectively; stack the processed lower aluminum alloy plate 201, the intermediate layer 5 and the upper aluminum alloy plate 202 in sequence to form a block structure to be welded.

[0093] When stacking, the longitudinal section of the middle layer 5 must be equal to the welding surface area of ​​the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202. The inner flow channels 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 are arranged face to face, thereby forming a closed inner flow channel.

[0094] Step S5: Place the block structure to be welded between the upper pressure head 3 and the lower pressure head 6 in the vacuum diffusion welding furnace, and place the upper welding resist layer 4 and the lower welding resist layer 11 between the upper pressure head 3 and the lower pressure head 6 and the block structure to be welded, respectively, and then perform welding.

[0095] During welding, a pre-pressure of 0.5~1 MPa is applied to the structure to be welded; the vacuum diffusion welding furnace is evacuated to 3~6×10⁻⁶ MPa. - 3 Pa; The vacuum diffusion welding furnace is heated at a rate of 10 °C / min, and the furnace temperature is raised from room temperature to 400 °C and held for 30 min; The furnace temperature is raised to 480~520 °C, pressure is applied at 4~6 MPa, and the temperature is held for 120 min. After the holding period, the furnace is cooled to 100 °C; the pressure is maintained during the cooling process; the aluminum alloy composite component is obtained.

[0096] Step S6: Use strong acid and ultrasonic waves to etch the upper core 9 and the lower core 10;

[0097] Step S7: The closed inner flow channel of the aluminum alloy composite component is polished by abrasive flow polishing, and the intermediate layer 5 is also polished away.

[0098] Step S8: The aluminum alloy composite component is heat-treated using heat treatment equipment. The solution treatment temperature is 530℃ for 1 hour, followed by water cooling; the aging temperature is 175℃ for 8 hours, followed by air cooling.

[0099] The test results showed that the deformation rate of the joint was 0.81% and the welding rate was 97.5%, which met the deformation and strength requirements of precision instruments.

[0100] Example 2

[0101] This invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, specifically employing the following steps:

[0102] Step S1: Select lower aluminum alloy sheet 201 and upper aluminum alloy sheet 202 of appropriate thickness, and clean the sheets by mechanical grinding to keep the surface flat and clean, so as to ensure the effect of shot peening pretreatment.

[0103] Step S2: Use a shot peening machine to perform surface shot peening treatment on the sample surfaces of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202. The surface treatment should be uniform. Select glass pellets with a shot diameter of 0.3 mm as the shot peening medium, the shot peening pressure is 0.4 MPa, and the shot peening time is 3-5 min.

[0104] Step S3: Select 4104 aluminum foil as intermediate layer 5. Intermediate layer 5 improves the surface contact state and increases the concentration gradient at the interface, which accelerates the diffusion of elements and the closure of voids. Perform ultrasonic cleaning on the surface-treated lower aluminum alloy plate 201, upper aluminum alloy plate 202 and intermediate layer 5.

[0105] Before welding, the surface of the sample to be welded and the intermediate layer 5 were chemically cleaned with NaOH and HNO3 solution to remove the surface oxide film; after cleaning, the sample was immediately placed in anhydrous ethanol and ultrasonically cleaned.

[0106] Step S4: Place the lower core 10 and the upper core 9 in the inner flow channels 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 respectively; stack the processed lower aluminum alloy plate 201, the intermediate layer 5 and the upper aluminum alloy plate 202 in sequence to form a block structure to be welded; when stacking, the longitudinal section of the intermediate layer 5 must be equal to the area of ​​the surface to be welded of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202.

[0107] The block structure to be welded is then embedded into the outer graphite sleeve 8, and an upper graphite pressure plate 7 is placed on top of the block structure to be welded, with the edge of the upper graphite pressure plate 7 fitting against the inner wall of the outer graphite sleeve 8.

[0108] Step S5: Place the block structure to be welded between the upper pressure head 3 and the lower pressure head 6 in the vacuum diffusion welding furnace, and place the upper welding resist layer 4 and the lower welding resist layer 11 between the upper pressure head 3 and the lower pressure head 6 and the block structure to be welded, respectively, and then perform welding.

[0109] During welding, a pre-pressure of 0.5~1 MPa is applied to the structure to be welded; the vacuum diffusion welding furnace is evacuated to 3~6×10⁻⁶ MPa. - 3Pa; The vacuum diffusion welding furnace is heated at a rate of 10 °C / min, and the furnace temperature is raised from room temperature to 400 °C and held for 30 min; the furnace temperature is raised to 500~520 °C, pressure is applied at 4~6 MPa, and the temperature is held for 120 min; the furnace temperature is raised to 540~560 °C, pressure is applied at 1~2 MPa, and the temperature is held for 90 min; after the holding period, the furnace is cooled to 100 °C; pressure is maintained during the cooling process; an aluminum alloy composite component is obtained.

[0110] Step S6: Use strong acid and ultrasonic waves to etch the upper core 9 and the lower core 10.

[0111] Step S7: The closed inner flow channel of the aluminum alloy composite component is polished by abrasive flow, and the intermediate layer 5 is also ground away.

[0112] Step S8: The aluminum alloy composite component is heat-treated using heat treatment equipment. The solution treatment temperature is 530℃ for 1 hour, followed by air cooling; the aging temperature is 175℃ for 8 hours, followed by air cooling.

[0113] The test results showed that the shear strength of the joint was 105 MPa, the deformation rate was 0.81%, and the welding rate was 98.5%, which met the deformation and strength requirements of precision instruments.

[0114] Example 3

[0115] This invention provides a solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, specifically employing the following steps:

[0116] Step S1: Select lower aluminum alloy sheet 201 and upper aluminum alloy sheet 202 of appropriate thickness, and clean the sheets by mechanical grinding to keep the surface flat and clean, so as to ensure the effect of shot peening pretreatment.

[0117] Step S2: Use a shot peening machine to perform surface shot peening on the surfaces of the ground samples of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202. The surface treatment should be uniform. Select glass pellets with a diameter of 0.3 mm as the shot peening medium, the shot peening pressure is 0.4 MPa, and the shot peening time is 3-5 min.

[0118] Step S3: Use self-made Al-Mg-Si-Zr-Ti aluminum foil as intermediate layer 5 to improve the surface contact state and increase the concentration gradient at the interface, thereby accelerating element diffusion and void closure; perform ultrasonic cleaning on the surface-treated sample and intermediate layer 5; before welding, use NaOH and HNO3 solution to chemically clean the surface of the sample to be welded and intermediate layer 5 to remove the surface oxide film; immediately after cleaning, place it in anhydrous ethanol and perform ultrasonic cleaning on the surface of the sample to be welded and intermediate layer 5.

[0119] Step S4: Place the lower core 10 and the upper core 9 in the inner flow channels 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 respectively; stack the processed lower aluminum alloy plate 201, the intermediate layer 5 and the upper aluminum alloy plate 202 in sequence to form a block structure to be welded.

[0120] When stacking, the longitudinal section of the middle layer 5 must be equal to the welding surface area of ​​the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202. The inner flow channels 203 of the lower aluminum alloy plate 201 and the upper aluminum alloy plate 202 are arranged face to face, thereby forming a closed inner flow channel.

[0121] The block structure to be welded is then embedded into the outer graphite sleeve 8, and an upper graphite pressure plate 7 is placed on top of the block structure to be welded, with the edge of the upper graphite pressure plate 7 fitting against the inner wall of the outer graphite sleeve 8.

[0122] Step S5: Place the block structure to be welded between the upper pressure head 3 and the lower pressure head 6 in the vacuum diffusion welding furnace, and place the upper welding resist layer 4 and the lower welding resist layer 11 between the upper pressure head 3 and the lower pressure head 6 and the block structure to be welded, respectively, and then perform welding.

[0123] During welding, a pre-pressure of 0.5~1 MPa is applied to the structure to be welded; the vacuum diffusion welding furnace is evacuated to 3~6×10⁻⁶ MPa. - 3 Pa; The vacuum diffusion welding furnace is heated at a rate of 10 °C / min, and the furnace temperature is raised from room temperature to 400 °C and held for 30 min; the furnace temperature is raised to 500~520 °C, pressure is applied at 4~6 MPa, and the temperature is held for 120 min; the furnace temperature is raised to 540~560 °C, pressure is applied at 1~2 MPa, and the temperature is held for 90 min; after the holding period, the furnace is cooled to 100 °C; the pressure is maintained during the cooling process; and an aluminum alloy composite component is obtained.

[0124] Step S6: Use strong acid and ultrasonic waves to etch the upper core 9 and the lower core 10.

[0125] Step S7: The closed inner flow channel of the aluminum alloy composite component is polished by abrasive flow polishing, and the intermediate layer 5 is also polished away.

[0126] Step S8: The aluminum alloy composite component is heat-treated using heat treatment equipment. The solution treatment temperature is 530℃ for 50 min, followed by water cooling; the aging temperature is 175℃ for 8 h, followed by air cooling.

[0127] The test results showed that the shear strength of the joint was 122 MPa, the deformation rate was 0.81%, and the welding rate was 98.8%, which met the deformation and strength requirements of precision instruments.

[0128] This invention employs a composite process of "shot peening-induced activation + post-weld heat treatment" for solid-state diffusion welding of aluminum alloys, involving shot peening machines, diffusion welding equipment, and muffle furnaces. Shot peening can prepare a nanocrystalline layer on the aluminum surface, effectively reducing the diffusion activation energy required for atoms during aluminum alloy diffusion welding. The welding process is carried out in a vacuum environment, minimizing the impact of oxide films on weld quality. Vacuum post-weld heat treatment in a muffle furnace further enhances joint strength.

[0129] Obviously, those skilled in the art can make various modifications and variations to this invention without departing from its spirit and scope. Therefore, if these modifications and variations fall within the scope of the claims of this invention and their equivalents, this invention also intends to include these modifications and variations.

Claims

1. A solid-phase diffusion welding method for aluminum alloys with small deformation and high strength, characterized in that, Includes the following steps: Step S1: Select two aluminum alloy plates with the same internal flow channel, and grind and clean the surfaces of the two aluminum alloy plates to be welded. Step S2: The surfaces of the two aluminum alloy plates that have been polished and cleaned are shot peened. The nanocrystalline layer formed by shot peening provides a fast channel for atomic diffusion through a large number of grain boundaries. Step S3: Select the intermediate layer and clean the two aluminum alloy plates and the intermediate layer; Step S4: Place two inner cores in the inner flow channels of the two aluminum alloy plates respectively, stack the two aluminum alloy plates in a mirror image, and place an intermediate layer between the two aluminum alloy plates to form a block structure to be welded. Step S5: Place the block structure to be welded between the upper and lower pressure heads in the vacuum diffusion welding furnace. Place the upper and lower resistance welding layers between the upper and lower pressure heads and the block structure to be welded, respectively, and perform the welding process to obtain the aluminum alloy composite component. Step S6: Remove the inner core and intermediate layer from the inner channels of the two aluminum alloy plates; Step S7: Heat treat the aluminum alloy composite component; In step S2, the surface to be welded of the aluminum alloy plate after grinding is shot peened using a shot peening machine. The shot peening medium is glass pellets with a diameter of 0.3 mm, the shot peening pressure is 0.4 MPa, and the shot peening time is 3-5 min. In step S3, the aluminum alloy sheet and intermediate layer after shot peening are sequentially subjected to ultrasonic cleaning, chemical cleaning with NaOH and HNO3 solution, and ultrasonic cleaning with anhydrous ethanol to remove the surface oxide film. The intermediate layer is made of aluminum foil; the difference in composition between the intermediate layer and the aluminum alloy sheet creates a concentration gradient, which can accelerate the migration of interface elements. In step S4, the block structure to be welded is placed inside the outer graphite sleeve, and an upper graphite pressure plate is placed on top of the block structure to be welded, with the edge of the upper graphite pressure plate fitting against the inner wall of the outer graphite sleeve. In step S6, strong acid and ultrasonic waves are used to corrode the inner core inside the flow channel of the two aluminum alloy plates; abrasive flow is used to polish the inner flow channel of the two aluminum alloy plates, thereby grinding away the intermediate layer. The inner core is made of 45# steel.

2. The solid-phase diffusion welding method for aluminum alloys with small deformation and high strength according to claim 1, characterized in that, In step S5, the welding process is as follows: apply a pre-pressure of 0.5~1MPa, evacuate to 3~6×10⁻³Pa; heat up at a rate of 10℃ / min, hold at 400℃ for 30min when the room temperature reaches 400℃; continue heating to 480~520℃, apply pressure of 4~6MPa, hold for 120min; after holding, cool with the furnace to 100℃, maintain pressure during cooling, and obtain an aluminum alloy composite component.

3. The solid-phase diffusion welding method for aluminum alloys with small deformation and high strength according to claim 1, characterized in that, In step S5, after heating to 480~520℃, pressurizing to 4~6MPa, and holding for 120min, the following additional steps are added: heating the furnace temperature to 540~560℃, pressurizing to 1~2MPa, holding for 90min, and then cooling with the furnace.

4. The solid-phase diffusion welding method for aluminum alloys with small deformation and high strength according to claim 1, characterized in that, In step S7, the composite component is placed in a heat treatment device and solution treated at 530°C for 50 min to 1 h, with water cooling or air cooling as the cooling method; then it is aged at 175°C for 8 h, air cooled, and welding is completed.

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