Aluminum alloy low-temperature high-strength diffusion welding method based on composite interlayer

Abstract

The invention discloses an aluminum alloy low-temperature high-strength diffusion welding method based on a composite interlayer. According to the method, Zn and Ge elements are used for coordinated control, the melting point of the composite intermediate layer is effectively reduced, the welding temperature is effectively reduced, Mg2Ge strengthening phase precipitation is induced, the joint strength is remarkably improved, the SPS diffusion welding process is applied, the welding period is greatly shortened, and the high-pressure acting time is shortened. According to the low-temperature, low-deformation and high-strength diffusion welding method, through deep fusion of materials and the technology, the problem that after-welding low-deformation-rate control and high-strength connection of the 6061 aluminum alloy obtained through an existing connection technology are cooperatively regulated and controlled is effectively solved, and low-temperature, low-deformation and high-strength diffusion welding with the joint metallurgical bonding strength exceeding the after-welding base metal intrinsic strength and the after-welding deformation rate being only 2.23% is achieved.

Description

Technical Field

[0001] This invention belongs to the field of welding materials technology, and more specifically, relates to a low-temperature high-strength diffusion welding method for aluminum alloys based on a composite interlayer. Background Technology

[0002] As aerospace aluminum alloy components increasingly move towards functional integration, structural complexity, and precise forming, ensuring high-strength welding quality while meeting high dimensional accuracy and geometric tolerance requirements is one of the core challenges facing the welding process of high-performance aluminum alloy components, particularly in aerospace electronic enclosures. Currently, these components are primarily joined using vacuum brazing, but the high melting point of existing brazing filler metals makes it difficult to control the overall deformation of the aluminum alloy structure. Compared to brazing, diffusion welding can achieve solid-state bonding at lower temperatures, which is beneficial for suppressing overall component deformation. However, in the traditional vacuum diffusion welding process for 6061 aluminum alloy, the temperature reduction significantly deteriorates its metallurgical bonding performance; simultaneously, the aluminum alloy components must be kept in a high-pressure, heat-preserving environment for extended periods, making it difficult to achieve low-temperature, low-deformation, and high-strength welding of aluminum alloy components.

[0003] The continuous updates to diffusion welding processes and the diversification of auxiliary methods have prompted us to rethink the diffusion welding mechanism of aluminum alloys. Currently, researchers have developed sandwich-structured diffusion weld joints using a low-melting-point interlayer, creating an elemental concentration gradient at the joint interface to promote elemental diffusion and induce the precipitation of strengthening phases, thereby achieving high-strength diffusion bonding at lower temperatures. Meanwhile, research indicates that spark plasma sintering (SPS) technology, utilizing pulsed current to induce a Joule thermal gradient field and couple it with plasma excitation effects to enhance rapid elemental diffusion, can significantly shorten welding time and facilitate efficient bonding. Summary of the Invention

[0004] Purpose of the invention: The problem to be solved by this invention is the technical dilemma of synergistic control of low deformation rate and high strength connection after welding of 6061 aluminum alloy avionics chassis. Specifically, this invention provides a method that can significantly shorten the high-pressure action time by using the intermediate layer material Al-20Zn-15Ge to construct an element concentration gradient with the aluminum alloy base material, inducing the precipitation of strengthening phases at the connection interface to improve the bonding strength, and supplementing it with the SPS thermo-electric-mechanical multi-field coupling effect to optimize the diffusion dynamics process, so as to achieve low-temperature, low-deformation, and high-strength diffusion connection of 6061 aluminum alloy components.

[0005] Technical Solution: To solve the above problems, this invention provides a low-temperature, high-strength diffusion welding method for aluminum alloys based on a composite interlayer, comprising the following steps: S1: The surfaces of the aluminum alloy base material and composite material to be welded are polished with sandpaper, then polished with diamond suspension polishing liquid, then rinsed with alcohol, and finally chemically cleaned to obtain the base material and composite material to be welded. S2: Add composite material between two aluminum alloy base materials to be welded to obtain a sandwich structure welded part based on a composite intermediate layer; S3: The sandwich structure workpiece based on the composite intermediate layer is placed in a discharge plasma sintering equipment for diffusion welding. A multi-physical energy field is applied in the diffusion welding equipment. After welding, the workpiece is naturally cooled with the furnace to obtain an aluminum alloy diffusion welded joint.

[0006] In step S1, the aluminum alloy base material is 6061-T6 aluminum alloy.

[0007] In step S1, the sandpaper is 400-3000 mesh sandpaper.

[0008] The chemical cleaning step in step S1 is as follows: the aluminum alloy base material is immersed in NaOH solution for alkaline washing, then placed in acetone for ultrasonic cleaning, then immersed in HNO3 solution for acid washing, and then placed in acetone for ultrasonic cleaning to obtain a clean and flat aluminum alloy base material to be welded.

[0009] The concentration of the NaOH solution is 20%, the alkaline washing time is 3 min, the concentration of the HNO3 solution is 5%, the acid washing time is 3 min, and the surface roughness of the base material to be welded is ≤1 μm.

[0010] In step S1, the composite material is an Al-xZn-yGe composite material, where x = 0~30, y = 0~10, and the elemental mass ratio of the Al-20Zn-15Ge composite intermediate layer is Al-65wt.%, Zn-20wt.%, Ge-15wt.%, with a thickness of 120 μm.

[0011] Preferably, the Al-xZn-yGe composite material is an Al-20Zn-15Ge composite material.

[0012] Specifically, step S2 includes: before assembling and welding the sample, immersing the composite material in acetone for 5 minutes, and then ultrasonically cleaning it in alcohol for 30 seconds to obtain a clean composite material.

[0013] In step S3, the diffusion welding equipment is an electro-plasma sintering equipment with a vacuum degree of 10Pa-40Pa. A multi-physical energy field is applied in the diffusion welding equipment to make the heating rate of the workpiece to be welded 30-50℃ / min and the welding holding time 20min.

[0014] Specifically, step S3 includes: a welding temperature of 460℃, which is 0.83 times the liquidus temperature of the Al-20Zn-15Ge composite intermediate layer, and a welding pressure of 5MPa.

[0015] The present invention also includes the aluminum alloy diffusion welded joint obtained by the method.

[0016] Beneficial Effects: Compared with existing technologies, this invention has the following advantages: Through a deep integration of material innovation and process control, this invention proposes an Al-20Zn-15Ge ternary composite intermediate layer. By introducing Zn and Ge elements to construct an Al-Zn-Ge ternary eutectic phase, the melting point temperature of the intermediate layer is significantly reduced, ensuring high-quality diffusion welding at a low temperature of 460℃. Furthermore, the addition of Ge element induces the precipitation of the Mg2Ge strengthening phase at the interface, thereby enhancing the joint performance. Simultaneously, the SPS diffusion welding process utilizes the multi-physics energy field effect of discharge plasma sintering technology to achieve rapid heating and high-flux diffusion of the material. This enables efficient diffusion welding of 6061 aluminum alloy under process conditions of a heating rate of 30~50℃ / min and a welding holding time of 20min, effectively shortening the pressure application time and significantly reducing the deformation rate of the diffusion-welded joint. Finally, by using an Al-20Zn-15Ge interlayer to induce SPS diffusion welding of 6061 aluminum alloy, under welding process parameters of 460℃ welding temperature, 20min holding time, and 5MPa welding pressure, low-temperature, low-deformation, high-strength diffusion welding of 6061 aluminum alloy can be achieved, with the joint metallurgical bond strength exceeding the intrinsic strength of the base material after welding (tensile fracture on the base material side, strength reaching 154.42 MPa) and the post-weld deformation rate being only 2.23%. Attached Figure Description

[0017] Figure 1 Figures showing the tensile strength and post-weld deformation rate of 6061 aluminum alloy SPS diffusion welded joints in different embodiments; Figure 2 The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-20Zn-15Ge interlayer in Example 1; Figure 3 In Example 2, the Al-20Zn-0Ge interlayer induced the microstructure of the 6061 aluminum alloy SPS diffusion weld joint. Figure 4 The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-20Zn-5Ge intermediate layer in Example 3; Figure 5 The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-20Zn-10Ge interlayer in Example 4; Figure 6The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-0Zn-10Ge intermediate layer in Example 5; Figure 7 The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-10Zn-10Ge intermediate layer in Example 6; Figure 8 The microstructure of the 6061 aluminum alloy SPS diffusion weld joint induced by the Al-30Zn-10Ge intermediate layer in Example 7. Detailed Implementation

[0018] To make the above-mentioned objects, features, and advantages of the present invention more apparent and understandable, specific embodiments of the present invention are described in detail below. However, it should be understood that the present invention can be implemented in various forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided to provide a more thorough and complete understanding of the invention. It should be understood that the accompanying drawings and embodiments of the present invention are for illustrative purposes only and are not intended to limit the scope of protection of the present invention.

[0019] Unless otherwise defined, all technical and scientific terms used in this application have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains; the terminology used in the description of this application is for the purpose of describing particular embodiments only and is not intended to limit this application.

[0020] In the relevant technology, the 6061 aluminum alloy was purchased from Southwest Aluminum (Group) Co., Ltd. It is an Al-Mg-Si series aluminum alloy, which has the advantages of being lightweight, corrosion resistant, and having high electromagnetic compatibility. It is often used in the manufacture of aerospace electronic enclosures.

[0021] The SPS (Spark Plasma Sintering System) was purchased from Sinter Land Corporation of Japan. The Labox-350 diffusion welding equipment is a highly efficient welding method that utilizes pulsed current to induce a Joule thermal gradient field and couple it with plasma excitation effect to enhance the rapid diffusion of elements, which can significantly shorten the welding time. It has the advantages of fast heating rate, short connection time and high degree of element diffusion.

[0022] This invention employs an Al-20Zn-15Ge ternary composite interlayer system. By introducing Ge element, an Al-Zn-Ge ternary low-temperature eutectic phase is constructed, reducing the element diffusion activation energy and meeting the low-temperature welding process conditions. It induces the precipitation of the Mg2Ge strengthening phase, whose semi-coherent interface with the matrix can effectively hinder dislocation movement and enhance joint performance. Through the Al-20Zn-15Ge alloy design, the excellent plasticity of Zn is used to compensate for the high brittleness of Ge, while controlling the Zn content to inhibit the dissolution of the base material, so that the composite interlayer has both low-temperature characteristics and machinability.

[0023] Therefore, this invention uses Al-20Zn-15Ge as-cast alloy as an intermediate layer to reduce the welding temperature and suppress post-weld deformation, construct an interfacial atomic concentration gradient to promote diffusion, induce the precipitation of Mg2Ge strengthening phase at the joint interface, and achieve joint performance enhancement. In addition, the SPS multi-physics energy field coupling effect promotes efficient diffusion welding and significantly shortens the high-pressure action time, in order to achieve low-temperature, low-deformation, and high-strength diffusion welding of 6061 aluminum alloy.

[0024] This invention provides a welding method for low-temperature, high-efficiency, low-deformation diffusion bonding of aluminum alloys, comprising the following steps: S1: Use sandpaper to grind the surfaces of the aluminum alloy base material and intermediate layer to be welded, then use diamond suspension polishing liquid to polish the surfaces to be welded, then use alcohol to rinse the polished sample, and finally chemically clean the surface of the base material to be welded to obtain the base material and intermediate layer to be welded. S2: Add an Al-20Zn-15Ge composite intermediate layer between two 6061 aluminum alloy base materials to be welded to obtain a 6061Al / Al-20Zn-15Ge / 6061 Al sandwich structure to be welded. S3: The workpiece to be welded is placed in a discharge plasma sintering equipment for diffusion welding. A multi-physical energy field is applied in the diffusion welding equipment, the welding temperature is 460 ℃, the welding holding time is 20 min, the welding pressure is 5 MPa, and the workpiece is naturally cooled with the furnace after welding to obtain an aluminum alloy diffusion welded joint.

[0025] In this embodiment, an Al-20Zn-15Ge composite intermediate layer is introduced between the two base materials to be welded. Utilizing the low-temperature eutectic reaction of Al-Zn-Ge, the diffusion welding temperature is reduced to 460 ℃, avoiding severe plastic deformation of the 6061 aluminum alloy diffusion joint caused by high welding temperatures. The uniform precipitation of a large amount of Mg2Ge phase at the interface ensures the joint bonding strength. Simultaneously, the multi-physics energy field effect of discharge plasma sintering technology is utilized to achieve rapid heating and high-flux diffusion of the material. Efficient diffusion welding of 6061 aluminum alloy can be achieved under process conditions of a heating rate of 30-50℃ / min and a welding holding time of 20min. This effectively shortens the pressure application time and further reduces the deformation rate of the diffusion welded joint. Ultimately, a low-temperature, low-deformation, high-strength diffusion weld of 6061 aluminum alloy is obtained, with a joint metallurgical bonding strength exceeding the intrinsic strength of the base material after welding (tensile fracture on the base material side, strength reaching 154.42 MPa) and a post-weld deformation rate of only 2.23%.

[0026] Optionally, step S1 specifically includes: grinding and polishing the surface of the aluminum alloy base material to be welded, and then performing chemical cleaning—immersing the aluminum alloy base material in NaOH solution for alkaline washing, then immersing it in acetone for ultrasonic cleaning, then immersing it in HNO3 solution for acid washing, and then immersing it in acetone for ultrasonic cleaning, so that the surface of the aluminum alloy base material to be welded is clean and flat.

[0027] Optionally, a 20% NaOH solution is used for alkaline washing for 3 minutes, and a 5% HNO3 solution is used for acid washing for 3 minutes to obtain a base material with a surface roughness ≤1 μm.

[0028] Specifically, before chemical cleaning, the surface of the aluminum alloy base material and the intermediate layer is polished with 400-grit, 800-grit, 1500-grit, and 3000-grit sandpaper. Then, W2.5 diamond polishing paste and woolen polishing cloth are used for rough polishing to remove scratches. Subsequently, W1 diamond polishing paste and cashmere polishing cloth are used for fine polishing until the polished surface is as bright as a mirror. Finally, an alcohol solution is used for ultrasonic cleaning and drying.

[0029] In this optional embodiment, alkaline washing removes oil stains and oxide films (such as Al2O3) from the surface of the aluminum alloy substrate, and acid washing removes residual reactants after alkaline washing.

[0030] Optionally, step S2 specifically includes: before assembling and welding the sample, immersing the Al-20Zn-15Ge composite intermediate layer in acetone for 5 minutes, and then ultrasonically cleaning it in alcohol for 30 seconds to obtain a clean composite material.

[0031] Optionally, step S3 specifically includes: sealing the middle layer of the sample with high-temperature copper foil tape, utilizing the zinc-copper oxide chemical reaction (Zn+CuO=ZnO+Cu) under heating conditions to generate ZnO and prevent Zn vapor from escaping. The diffusion welding equipment is a discharge plasma sintering equipment with a vacuum degree of 10Pa-40Pa. A multi-physical energy field is applied in the diffusion welding equipment to make the heating rate of the workpiece to be welded 30-50℃ / min and the welding holding time 20min.

[0032] Optionally, the welding temperature is 460 ℃, the welding pressure is 5 MPa, and the holding time is 20 min.

[0033] Optionally, the aluminum alloy base material is 6061-T6 aluminum alloy, and the welding sample size is φ20×7 mm.

[0034] Al-xZn-yGe series alloy intermediate layer materials were prepared by melt casting. The specific preparation process is as follows: First, high-purity Al (99.99%), Zn (99.95%), and Ge (99.9%) metal powders were accurately weighed according to the preset mass fractions and pretreated by vacuum drying at 120 °C. A KAlF4-based fluoride salt protective layer was pre-laid in an alumina-coated graphite crucible, followed by the addition of Al powder and heating under an Ar atmosphere to form a liquid Al molten pool. After the melt stabilized, an Ar-0.5%SF6 (vol%) mixed protective gas was continuously introduced, and Zn powder was added in batches using a vibrating feeder, utilizing the density difference between the molten salt and the liquid metal to achieve interfacial layering and isolation. After the Zn powder was completely alloyed, Ge powder was pressed into the bottom of the melt, and diffusion was promoted by electromagnetic stirring. Ar gas rotary refining was carried out immediately after melting, and unmelted particles were removed using a porous alumina ceramic filter. Finally, the melt was poured into a preheated copper mold at 250 °C under dynamic Ar gas protection to achieve rapid solidification, thus preparing Al-Zn-Ge alloy intermediate layer materials with different Zn / Ge ratios.

[0035] Optionally, the intermediate layer is an Al-20Zn-15Ge as-cast composite material with a welding specification of 20 mm in diameter, 120 μm in thickness, and 99.999% purity.

[0036] In this embodiment of the invention, the change in joint thickness is selected as an indicator to measure the post-weld deformation rate of the joint. A micrometer is used to randomly measure the sample to be welded, and the arithmetic mean of the measurements at 10 locations is taken as the initial thickness. Similarly, the post-weld thickness of the sample is measured. The post-weld deformation of the joint is calculated based on the following formula:

[0037] In the formula: —Deformation rate of the welded joint; — Length of the sample in the thickness direction before welding; — Length of the sample in the thickness direction before welding.

[0038] The present invention will be further described below with reference to specific embodiments. Example 1

[0039] (1) Preparation of Al-20Zn-15Ge as-cast composite material: First, high-purity Al (99.99%), Zn (99.95%), and Ge (99.9%) metal powders were accurately weighed according to the preset mass fractions (20wt.%Zn, 15wt.%Ge, 65wt.%Al), and then pretreated by vacuum drying at 120 ℃ for later use. A KAlF4-based fluoride salt protective layer was pre-laid in an alumina-coated graphite crucible, and then Al powder was added and heated under Ar atmosphere to form a liquid Al molten pool. After the melt stabilized, Ar-0.5%SF6 (vol%) mixed protective gas was continuously introduced, and Zn powder was added in batches through a vibrating feeder, using the density difference between the molten salt and the liquid metal to achieve interfacial layering and isolation. After the Zn powder was completely alloyed, Ge powder was pressed into the bottom of the melt, and diffusion was promoted by electromagnetic stirring. Immediately after melting, Ar gas rotary refining is carried out, and a porous alumina ceramic filter is used to remove unmelted particles. Finally, under dynamic Ar gas protection, the melt is poured into a preheated copper mold at 250 °C to achieve rapid solidification and prepare Al-20Zn-15Ge alloy intermediate layer material.

[0040] (2) The surface of the 6061-T6 aluminum alloy base material and the Al-20Zn-15Ge cast composite material was polished by sandpaper with 400 grit, 800 grit, 1500 grit and 3000 grit respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the grinding marks. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (3) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 minutes for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 minutes to obtain a base material with a surface roughness ≤1 μm. Blow it dry and set it aside. (4) The Al-20Zn-15Ge composite intermediate layer was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-20Zn-15Ge composite material. (5) A 120μm thick Al-20Zn-15Ge composite material (20mm diameter, 120μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy pieces (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 30Pa. The heating rate during welding was 40℃ / min, the welding temperature was 460℃, the holding time was 20min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was taken out, and a 6061-T6 aluminum alloy welded joint with low temperature, small deformation, and high strength was finally obtained, as shown in the figure. Figure 2 As shown, the joint interface achieves fully densified diffusion welding, forming a continuous diffusion gradient structure; the tensile strength of the diffusion welded joint was measured to be 154.42 MPa (the interfacial metallurgical bond strength exceeds the load-bearing capacity of the base material after welding, and tensile fracture occurs in the base material region), and the post-weld deformation rate was 2.23%. Figure 1 As shown. Example 2

[0041] (1) The Al-20Zn-0Ge composite material was prepared according to the preset mass fraction (20wt.%Zn, 80wt.%Al), and the method was the same as in Example 1; (2) The surface of the 6061-T6 aluminum alloy base material and the Al-20Zn-0Ge cast composite material was polished by sandpaper with 400 grit, 800 grit, 1500 grit and 3000 grit respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the grinding marks. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (3) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 minutes for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 minutes to obtain a base material with a surface roughness ≤1 μm. Blow it dry and set it aside. (4) The Al-20Zn-0Ge composite material was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-20Zn-0Ge composite material. (5) A 120 μm thick Al-20Zn-0Ge composite material (20 mm diameter, 120 μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 30 Pa. The heating rate during welding was 40 °C / min, the welding temperature was 530 °C, the holding time was 20 min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 3 As shown, the high melting point of the intermediate layer led to a welding temperature of 530℃, which exacerbated the oxidation at the interface. This large-area oxidation hindered atomic interdiffusion, resulting in a clear, straight metallurgical boundary line. Furthermore, the excessively high welding temperature caused excessive Al-Zn metallurgical reaction on both sides of the interface, generating ferrous intermetallic compounds. The tensile strength of the diffusion weld was measured at 97.42 MPa (insufficient interfacial metallurgical bond strength, tensile fracture in the weld zone), and the post-weld deformation rate was 7.93%. Figure 1 As shown. Example 3

[0042] (1) The Al-20Zn-5Ge composite material was prepared according to the preset mass fraction (20wt.%Zn, 5wt.%Ge, 75wt.%Al), and the method was the same as in Example 1; (2) The surface of the 6061-T6 aluminum alloy base material and the Al-20Zn-5Ge cast composite material were polished by using 400 grit, 800 grit, 1500 grit and 3000 grit sandpaper respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the grinding marks. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (3) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 minutes for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 minutes to obtain a base material with a surface roughness ≤1 μm. Blow it dry and set it aside. (4) The Al-20Zn-5Ge composite material was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-20Zn-5Ge composite material. (5) A 120μm thick Al-20Zn-5Ge composite material (20mm diameter, 120μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 20Pa-40Pa. The heating rate during welding was 40℃ / min, the welding temperature was 500℃, the holding time was 20min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 4 As shown, the welding temperature was 500℃. Oxidation at the joint interface resulted in poor atomic interdiffusion, leading to a straight metallurgical boundary line at the joint interface and localized presence of ferrous intermetallic compounds. The tensile strength of the diffusion-welded joint was measured to be 120.52 MPa (insufficient interfacial metallurgical bond strength, tensile fracture occurred in the weld zone), and the post-weld deformation rate was 4.84%. Figure 1 As shown. Example 4

[0043] (1) The Al-20Zn-10Ge composite material was prepared according to the preset mass fraction (20wt.%Zn, 10wt.%Ge, 70wt.%Al), and the method was the same as in Example 1; (2) The surface of the 6061-T6 aluminum alloy base material and the Al-20Zn-10Ge cast composite material was polished by sandpaper with 400 grit, 800 grit, 1500 grit and 3000 grit respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the grinding marks. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (3) Immerse the aluminum alloy base material in a 20% NaOH solution for 3 min for alkaline washing, then put it in acetone for ultrasonic cleaning, then immerse it in HNO3 solution for acid washing, and then put it in acetone for ultrasonic cleaning for 2 min to obtain a base material with a surface roughness ≤1 μm. Dry it and set it aside. (4) The Al-20Zn-10Ge composite material was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-20Zn-10Ge composite material. (5) A 120μm thick Al-20Zn-10Ge composite material (20mm diameter, 120μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 20Pa-40Pa. The heating rate during welding was 40℃ / min, the welding temperature was 480℃, the holding time was 20min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 5 As shown, the welding temperature was 480 ℃, and the joint interface achieved complete densification, forming a clear diffusion transition zone. The joint interface line disappeared and formed a continuous diffusion gradient structure. The tensile strength of the diffusion welded joint was measured to be 147.87 MPa (the interfacial metallurgical bond strength exceeded the load-bearing capacity of the base material after welding, and tensile fracture occurred in the base material region). The post-weld deformation rate was 3.32%. Figure 1 As shown. Example 5

[0044] (1) The Al-0Zn-10Ge composite material was prepared according to the preset mass fraction (10wt.%Ge, 90wt.%Al), and the method was the same as in Example 1; (2) The surface of the 6061-T6 aluminum alloy base material and Al-0Zn-10Ge composite material was polished by sandpaper with 400 grit, 800 grit, 1500 grit and 3000 grit respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the scratches. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (3) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 minutes for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 minutes to obtain a base material with a surface roughness ≤1 μm. Blow it dry and set it aside. (4) The Al-0Zn-10Ge composite material was soaked in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-0Zn-10Ge composite material. (5) A 120 μm thick Al-0Zn-10Ge composite material (20 mm diameter, 120 μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 20 Pa-40 Pa. The heating rate during welding was 40 °C / min, the welding temperature was 523 °C, the holding time was 20 min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 6 As shown, the intermediate Ge element, due to the lack of Zn solute decomposition effect, forms a significant Ge-rich agglomeration zone (black area) on the left side of the joint interface, greatly increasing the joint's brittle and hard tendency. Simultaneously, the high-temperature welding at 523 ℃ intensifies the interfacial oxidation reaction, resulting in a straight metallurgical boundary line. The tensile strength of the diffusion weld joint was measured at 112.13 MPa (insufficient interfacial metallurgical bond strength, tensile fracture in the weld zone), and the post-weld deformation rate was 6.94%. Figure 8 As shown. Example 6

[0045] (1) The Al-10Zn-10Ge composite material was prepared according to the preset mass fractions (10wt.%Zn, 10wt.%Ge, 80wt.%Al), and the method was the same as in Example 1; (1) The surface of the aluminum alloy base material 6061-T6 aluminum alloy and Al-10Zn-10Ge composite material was polished by sandpaper with 400 grit, 800 grit, 1500 grit and 3000 grit respectively. Then, the sample was rough polished with W2.5 diamond polishing paste and woolen polishing cloth to remove the scratches. Then, W1 diamond polishing paste and cashmere polishing cloth were used for fine polishing until the polished surface was as bright as a mirror. (2) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 min for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 min to obtain a base material with a surface roughness ≤1 μm. Dry it and set it aside. (3) The Al-10Zn-10Ge composite material was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-10Zn-10Ge composite material. (4) A 120 μm thick Al-10Zn-10Ge composite material (20 mm diameter, 120 μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 20 Pa-40 Pa. The heating rate during welding was 40 °C / min, the welding temperature was 503 °C, the holding time was 20 min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 7 As shown, with the appropriate addition of Zn (10 wt.%), the intermediate β-Ge phase amplitude modulation decomposition was triggered, causing the disappearance of the black Ge-rich phase defect structure at the joint interface. Simultaneously, the interface oxidation effect was suppressed as the welding temperature decreased, and the degree of interface element diffusion gradually improved. The tensile strength of the diffusion-welded joint was measured to be 138.81 MPa (the interfacial metallurgical bond strength exceeded the load-bearing capacity of the base material after welding, and tensile fracture occurred in the base material region), and the post-weld deformation rate was 4.83%. Figure 1 As shown. Example 7

[0046] (1) The Al-30Zn-10Ge composite material was prepared according to the preset mass fraction (30wt.%Zn, 10wt.%Ge, 60wt.%Al), and the method was the same as in Example 1; (1) Use 400 grit, 800 grit, 1500 grit and 3000 grit sandpaper to polish the surface of the aluminum alloy base material 6061-T6 aluminum alloy and Al-30Zn-10Ge composite material. Then use W2.5 diamond polishing paste and woolen polishing cloth to rough polish the sample to remove the scratches. Then use W1 diamond polishing paste and cashmere polishing cloth to fine polish until the polished surface is as bright as a mirror. (2) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 min for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 min to obtain a base material with a surface roughness ≤1 μm. Dry it and set it aside. (3) The Al-30Zn-10Ge composite material was immersed in acetone for 5 minutes, and then ultrasonically cleaned in alcohol for 30 seconds to obtain a clean Al-30Zn-10Ge composite material. (4) A 120μm thick Al-30Zn-10Ge composite material (20mm diameter, 120μm thickness, 99.999% purity) was placed between two chemically cleaned 6061-T6 aluminum alloy sheets (φ20×7 mm). The middle layer of the sample was sealed with high-temperature copper foil tape and then placed in an SPS diffusion welding machine for welding. The vacuum degree of the SPS diffusion welding machine was 20Pa-40Pa. The heating rate during welding was 40℃ / min, the welding temperature was 465℃, the holding time was 20min, and a constant pressure of 5 MPa was applied. The welded part was then cooled with the furnace. After cooling, it was removed. Figure 8 As shown, the Zn content in the intermediate layer increased to 30 wt.%, resulting in an excessively high Zn content in the diffusion weld joint. At a welding temperature of 465 ℃ (far exceeding the Al-Zn eutectic temperature), this triggered an explosive overflow of molten Zn. Excessive reaction between the base material and the intermediate layer produced a large amount of ferrous intermetallic compounds. The Al-Zn liquid phase was squeezed out, forming numerous voids, which deteriorated interfacial element diffusion and forced the reappearance of a distinct metallurgical boundary. The tensile strength of the diffusion weld joint was measured at 60.72 MPa (insufficient interfacial metallurgical bond strength, tensile fracture in the weld zone), and the post-weld deformation rate was 2.38%. Figure 1 As shown.

[0047] Comparative Example 1 (1) Use 400 grit, 800 grit, 1500 grit and 3000 grit sandpaper to polish the surface of the 6061-T6 aluminum alloy base material in sequence. Then use W2.5 diamond polishing paste and woolen polishing cloth to rough polish the sample to remove the scratches. Then use W1 diamond polishing paste and cashmere polishing cloth to fine polish until the polished surface is as bright as a mirror. (2) Immerse the 6061-T6 aluminum alloy base material in a 20% NaOH solution for 3 min for alkaline washing. After alkaline washing, place it in acetone for ultrasonic cleaning. Then immerse it in HNO3 solution for acid washing. After acid washing, place it in acetone for ultrasonic cleaning for 2 min to obtain a base material with a surface roughness ≤1 μm. Dry it and set it aside. (3) Place two pieces of 6061-T6 aluminum alloy (φ20×7 mm) into the diffusion welding equipment, close the vent valve, turn on the rotary vane pump and molecular pump to start evacuating the vacuum until the vacuum degree reaches 10. -3 At a pressure of 4 MPa, the diffusion welding test was initiated. During welding, the heating rate was 5℃ / min, the welding temperature was 540℃, the holding time was 120 min, and a constant pressure of 4 MPa was applied. The welded parts were then cooled in the furnace. After cooling, the welded parts were removed, resulting in a well-connected 6061 aluminum alloy welded joint. The post-weld deformation rate of the joint was measured to be 22%.

[0048] Summary of Results of Examples 1-7 and Comparative Examples: In the Al-xZn-yGe interlayer, changes in Zn and Ge elements can lower the melting point temperature of the interlayer, thereby altering the welding temperature and inducing changes in the interfacial microstructure. This significantly affects the tensile strength and post-weld deformation rate of the diffusion-welded joint. By controlling the Zn and Ge content, the diffusion welding temperature can be lowered, suppressing post-weld deformation and base metal performance loss, reducing interfacial oxidation, and ensuring sufficient diffusion of interfacial elements. This also prevents the enrichment and growth of the brittle β-Ge phase and the escape of the Al-Zn liquid phase, as well as the formation of brittle phases, which would degrade the joint bonding strength. Based on the above component ratio control, the optimal ratio of the intermediate layer was determined, namely, using an Al-20Zn-15Ge intermediate layer to induce SPS diffusion welding of 6061 aluminum alloy. Under the welding process conditions of 460 ℃, 20 min holding time, and 5 MPa welding pressure, low-temperature, low-deformation, high-strength diffusion welding was achieved, with the joint metallurgical bond strength exceeding the intrinsic strength of the base material after welding (tensile fracture on the base material side, strength reaching 154.42 MPa) and the post-weld deformation rate only 2.23%. Compared to traditional vacuum diffusion welding of 6061 aluminum alloy, the introduction of the Al-20Zn-15Ge composite intermediate layer significantly reduced the welding temperature from 520℃ to 460℃. Ge promotes the precipitation of Mg2Ge phase, which strengthens the bonding strength and makes the joint bonding strength exceed that of the base material after welding. Based on spark plasma sintering technology, SPS diffusion welding was carried out, which shortened the holding time to 20 minutes and had a much higher heating efficiency than vacuum diffusion welding. This achieved a reduction in welding temperature and a shorter high-temperature and high-pressure treatment time, which significantly improved the low deformation of 6061 aluminum alloy components after welding.

Claims

1. A low-temperature, high-strength diffusion welding method for aluminum alloys based on a composite interlayer, characterized in that, Includes the following steps: S1: Use sandpaper to grind the surfaces of the aluminum alloy base material and composite material to be welded, then use diamond suspension polishing liquid to polish the surfaces to be welded, then use alcohol to rinse the polished sample, and finally chemically clean the surface of the base material to be welded to obtain the base material and composite material to be welded. S2: Add composite material between two aluminum alloy base materials to be welded to obtain a sandwich structure welded part based on a composite intermediate layer; S3: The sandwich structure workpiece based on the composite intermediate layer is placed in a discharge plasma sintering equipment for diffusion welding. A multi-physical energy field is applied in the diffusion welding equipment. After welding, the workpiece is naturally cooled with the furnace to obtain an aluminum alloy diffusion welded joint.

2. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, The aluminum alloy base material in step S1 is 6061-T6 aluminum alloy.

3. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, The sandpaper used in step S1 is 400-3000 grit sandpaper.

4. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, The chemical cleaning step in step S1 is as follows: the aluminum alloy base material is immersed in NaOH solution for alkaline washing, then placed in acetone for ultrasonic cleaning, then immersed in HNO3 solution for acid washing, and finally placed in acetone for ultrasonic cleaning, to obtain a clean and flat aluminum alloy base material to be welded.

5. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 2, characterized in that, The NaOH solution has a volume concentration of 20% and an alkaline washing time of 3 min; the HNO3 solution has a concentration of 5% and an acid washing time of 3 min; and the surface roughness of the base material to be welded is ≤1 μm.

6. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, The composite material in step S1 is an Al-xZn-yGe composite material, where x = 0~30, y = 0~10, and the elemental mass ratio of the Al-20Zn-15Ge composite intermediate layer is Al-65wt.%, Zn-20wt.%, Ge-15wt.%, with a thickness of 120 μm.

7. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, Step S2 specifically includes: before assembling and welding the sample, immersing the composite material in acetone for 5 minutes, and then ultrasonically cleaning it in alcohol for 30 seconds to obtain a clean composite material.

8. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, The diffusion welding equipment in step S3 is an electro-plasma sintering equipment with a vacuum degree of 10Pa-40Pa. A multi-physical energy field is applied in the diffusion welding equipment to make the heating rate of the workpiece to be welded 30-50℃ / min and the welding holding time 20min.

9. The welding method for low-temperature high-strength diffusion bonding of aluminum alloys based on a composite interlayer according to claim 1, characterized in that, Step S3 specifically includes: a welding temperature of 460℃, which is 0.83 times the liquidus temperature of the Al-20Zn-15Ge composite intermediate layer, and a welding pressure of 5MPa.

10. The aluminum alloy diffusion welded joint obtained by the method according to any one of claims 1 to 9.

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