Ni / zr / zn functional hierarchical gradient structure for laser welding of aluminum-copper dissimilar metals and welding method

Abstract

This invention discloses a Ni / Zr / Zn functional graded gradient structure and welding method for laser welding of aluminum and copper dissimilar metals, belonging to the field of dissimilar metal laser welding technology. The gradient structure consists of a Ni bonding layer, a Zr intermediate barrier strengthening layer, and a Zn barrier layer, which are combined at room temperature through rolling to form a metallurgically bonded integral structure. During welding, the Zn barrier layer preferentially melts to form a Zn-Al solid solution to block Al diffusion, the Ni bonding layer forms a Ni-Cu solid solution to consume Cu atoms, and the Zr layer provides physical barrier and mechanical strengthening in the form of solid particles. This invention fundamentally avoids direct contact between Al and Cu, controlling the total thickness of the brittle intermetallic compound layer at the joint interface to within 5 micrometers, eliminating continuous layered brittle phases, and achieving a joint tensile strength of over 85% of the aluminum base material. It also balances corrosion resistance and cost, with a simple and controllable process, suitable for high-quality joining of aluminum and copper dissimilar materials in fields such as electric vehicle batteries and power electronics.

Description

Technical Field

[0001] This invention relates to the field of dissimilar metal laser welding technology, specifically to a Ni / Zr / Zn functional graded gradient structure and welding method for aluminum-copper dissimilar metal laser welding, which is applicable to high-quality connection of aluminum-copper dissimilar materials in fields such as electric vehicle battery tab-bus connection, heat dissipation substrate of power electronic device, and aerospace cable connector. Background Technology

[0002] The joining of dissimilar metals such as aluminum (Al) and copper (Cu) has irreplaceable application value in modern industry. Aluminum has advantages such as low density, good electrical conductivity, and low cost, while copper has higher electrical and thermal conductivity. The composite joining of the two can achieve complementary advantages of material properties and is widely used in electric vehicle batteries, power electronics, and aerospace fields. Laser welding, due to its high energy density, precise heat input control, small welding deformation, and good automation compatibility, has become one of the most promising technologies for aluminum-copper dissimilar joining.

[0003] However, the significant differences in physical and chemical properties between aluminum and copper pose serious challenges to laser welding. Aluminum has a melting point of 660℃, while copper has a melting point as high as 1085℃. Their thermal conductivity differs by nearly double (Al 237 W / m·K vs Cu 401 W / m·K), and their coefficients of linear expansion also differ considerably. These differences in physical properties result in an extremely uneven temperature field in the molten pool during welding, easily leading to defects such as incomplete fusion, cracks, and porosity. More critically, the Al-Cu binary system has extremely low solid solubility. Under the thermal cycling of welding, a series of brittle intermetallic compounds (IMCs) such as θ-Al2Cu, η-AlCu, and γ-Al4Cu9 readily form at the weld interface. These IMC phases have high hardness and poor plasticity. When they are distributed in continuous layers at the interface, they become weak points in the joint, severely degrading the mechanical and electrical properties of the joint, and even causing brittle fracture during service.

[0004] To address these issues, scholars both domestically and internationally have conducted systematic research from multiple perspectives: 1. Process Parameter Optimization and Control: By adjusting parameters such as laser power, welding speed, and pulse waveform, heat input can be controlled, thereby influencing the growth behavior of IMC. Studies have shown that the IMC layer thickness increases with increasing laser power, and there exists an optimal heat input window that maximizes joint strength. The preheating stage in the pulse waveform can improve laser absorption efficiency and reduce the degree of dissimilar metal mixing. However, simply relying on process parameter optimization can only control the IMC thickness to a certain extent and cannot fundamentally change the interfacial reaction path of direct Al-Cu contact, making it difficult to completely suppress the formation of brittle IMC.

[0005] 2. Beam Modulation Techniques: These techniques employ beam oscillation, dual-beam configurations, and beam shaping to improve the flow state and elemental mixing uniformity of the molten pool. For example, a core-ring dual-beam combination with circular oscillation technology can ensure melt depth through the core beam and expand the molten pool through the ring beam, resulting in a more uniform IMC distribution. Beam oscillation can also regulate the fluid flow pattern within the molten pool, reducing elemental segregation. However, these techniques still cannot completely prevent direct contact between Al and Cu, and a continuous, brittle IMC layer will still form at the interface.

[0006] 3. Intermediate Layer Intervention Regulation: Introducing filler materials to alter the interfacial metallurgical reaction pathway is currently the most promising regulation strategy. Existing research mainly focuses on single-element intermediate layers and simple composite intermediate layers. Single-element interlayers: Ni, Ag, and Zn are the three most widely studied elements. Ni can dissolve into the Al-Cu IMC lattice to produce a solid solution strengthening effect, increasing the joint strength by 49%, but it is difficult to completely prevent direct Al-Cu contact. Ag interlayers can form Ag3Al and Al2Cu phases, suppressing the formation of brittle IMC, and the tensile strength of the joint can reach 78.5% of the base material, but the high cost of Ag severely limits its industrial application. Zn interlayers can improve wettability and increase the melt nucleus size by forming Zn-Al low-melting eutectic, but the introduction of Zn will significantly increase the corrosion sensitivity of the joint and affect long-term service performance.

[0007] Composite / Multi-element Intermediate Layers: To address the limitations of single intermediate layers, researchers have developed composite filler materials such as Ag-Cu-Zn ternary alloys and Cu-Ni binary coatings. Ag-18Cu-10Zn ternary alloys can replace the brittle Al2Cu phase by forming Ag2Al and Cu5Zn8 solid solutions, achieving a synergistic improvement in mechanical and electrical properties. Cu-Ni binary coatings can form toughening compounds at the interface, improving joint shear strength. However, existing composite intermediate layers are mostly binary or ternary homogeneous alloys, lacking a systematic design of multi-element "gradient structures," making it impossible to achieve hierarchical control of element diffusion and interfacial reactions. Furthermore, current research lacks sufficient understanding of the interactions between layers in the gradient structure, element diffusion paths, and interfacial reaction priorities, making it difficult to fully leverage the synergistic control effect of multiple elements.

[0008] In summary, existing aluminum-copper dissimilar metal laser welding technology still suffers from problems such as difficulty in effectively suppressing brittle intermetallic structures (IMCs), inability to simultaneously achieve optimal joint mechanical properties and corrosion resistance, and high intermediate layer costs. There is an urgent need to develop a novel intermediate layer structure and welding method to fundamentally solve the problem of brittle IMC formation at the Al-Cu interface, while improving the overall performance of the joint. Summary of the Invention

[0009] To address the shortcomings of existing technologies, this invention provides a Ni / Zr / Zn functional hierarchical gradient structure and welding method for laser welding of aluminum-copper dissimilar metals. The aim is to solve the problem of poor joint mechanical properties and insufficient overall service performance caused by the easy formation of continuous thick layers of brittle aluminum-copper intermetallic compounds at the interface during existing aluminum-copper dissimilar metal laser welding processes. This invention, by designing a Ni / Zr / Zn functional hierarchical gradient structure, utilizes the differences in the physical and metallurgical properties of each layer at different locations to achieve hierarchical control of the interfacial reaction during welding. This fundamentally blocks the direct diffusion reaction path between aluminum and copper, inhibits the formation of brittle intermetallic compounds, and simultaneously ensures both joint mechanical properties and corrosion resistance. The cost is controllable, making it suitable for industrial applications.

[0010] To achieve the above objectives, the technical solution of the present invention is as follows: A Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals is characterized by being composed of a Ni bonding layer, a Zr intermediate barrier strengthening layer, and a Zn barrier layer, which are then composited at room temperature to form a metallurgically bonded integral structure. The Ni bonding layer is a Ni foil, the Zr intermediate barrier strengthening layer is formed by rolling and compacting Zr powder, and the Zn barrier layer is a Zn foil.

[0011] Furthermore, the Ni bonding layer has a thickness of 5 to 20 micrometers, the Zr intermediate barrier reinforcement layer has a thickness of 10 to 30 micrometers, the Zn barrier layer has a thickness of 5 to 20 micrometers, and the overall total thickness is 20 to 70 micrometers.

[0012] Furthermore, the thickness ratio of the Ni bonding layer, the Zr intermediate barrier reinforcement layer, and the Zn barrier layer is 1:1.2 to 2.5:1, and the overall density is not less than 95%.

[0013] Furthermore, the Zr powder has a particle size of 1 to 10 micrometers, a purity of not less than 99.9%, and an interfacial bonding strength of not less than 15 MPa.

[0014] Based on the above structure, this invention also discloses a welding method using a Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals, the key of which includes the following steps: S1. Prepare the Ni / Zr / Zn functional hierarchical gradient structure for laser welding of aluminum and copper dissimilar metals; S2. Pre-treat the aluminum base material to be welded surface, the copper base material to be welded surface, and the upper and lower surfaces of the gradient structure to remove oxide film and oil stains; place the pre-treated gradient structure between the aluminum base material and the copper base material to be welded interface, so that the Zn barrier layer is in close contact with the aluminum base material to be welded surface without gaps, and the Ni bonding layer is in close contact with the copper base material to be welded surface without gaps. After assembly, use tooling to clamp and fix it. S3. Continuous laser is used to scan and weld the assembled area to be welded. During the welding process, the interface reaction is controlled by the hierarchical regulation of the three-layer structure.

[0015] Furthermore, the method for preparing the gradient structure in step S1 specifically includes the following steps: S101. Zr powder is evenly spread on the upper surface of Ni foil to form a Zr powder layer of uniform thickness; S102. Smoothly cover the Zn foil on the upper surface of the Zr powder layer, so that the edges of the three layers of materials are aligned without offset; S103. A composite structure is obtained by performing 1 to 3 passes of room temperature rolling at a rolling pressure of 50 to 150 MPa and a rolling speed of 0.5 to 2 m / min.

[0016] Furthermore, the preprocessing described in step S2 specifically includes the following steps: S201. Use 800 to 1200 grit sandpaper to polish the aluminum base material to be welded surface, the copper base material to be welded surface, and the upper and lower surfaces of the gradient structure until a uniform metallic luster is achieved; S202. Place the polished base material and gradient structure into acetone and anhydrous ethanol respectively for ultrasonic cleaning for 5 to 10 minutes. S203. After removing it, dry it with cold air and immediately assemble and clamp it.

[0017] Furthermore, the graded control of the welding process described in step S3 specifically includes the following steps: S301. The Zn barrier layer melts preferentially and reacts with aluminum elements at the interface of the aluminum matrix to form a continuous and dense Zn-Al solid solution layer, which physically prevents aluminum elements from diffusing to the copper side. The S302.Ni bonding layer remains semi-solid and reacts with the copper elements at the interface of the copper substrate to form an infinitely miscible Ni-Cu solid solution layer, consuming free copper atoms at the interface. The S303.Zr intermediate barrier strengthening layer remains in a solid particle state throughout the entire process, dispersed in the central area of ​​the weld. At the same time, it acts as a physical barrier layer to block the direct diffusion channels between aluminum and copper, thereby improving the mechanical properties of the joint through the synergistic effect of dispersion strengthening and grain refinement strengthening.

[0018] Furthermore, the laser welding described in step S3 uses a fiber continuous laser with a laser power controlled at 700 to 1200 watts, a welding speed of 5 to 15 millimeters per second, a defocusing amount of -1 to +1 millimeters, and a laser spot diameter of 0.2 to 0.5 millimeters. During the welding process, argon gas with a purity of not less than 99.99% is used as a side-blown protective gas with a gas flow rate of 12 to 18 liters per minute. The protective gas nozzle is at an angle of 30 to 45 degrees to the welding direction, and the protective range covers the molten pool and the high-temperature area within 50 millimeters behind it.

[0019] Furthermore, the aluminum base material is industrial pure aluminum, 5052 aluminum alloy, or 6061 aluminum alloy, with a thickness of 0.3 to 2 mm; the copper base material is industrial pure copper, red copper, or brass, with a thickness of 0.3 to 2 mm; the joint type is a lap joint, with an overlap of 5 to 15 mm; after welding, the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface does not exceed 5 micrometers, and there are no continuously layered θ-Al2Cu, η-AlCu, and γ-Al4Cu9 phases.

[0020] Compared with the prior art, the significant advantages of the present invention are: Compared with the prior art, the present invention has the following advantages: 1. Effectively suppresses the formation of brittle IMC: This invention employs a functionally graded three-layer structure. A Zn barrier layer reacts with Al to form a Zn-Al solid solution layer, physically preventing Al diffusion to the copper side. A Ni bonding layer reacts with Cu to form a Ni-Cu solid solution layer, consuming free Cu atoms at the interface. The Zr intermediate layer acts as a physical barrier layer, further blocking the direct diffusion channels between Al and Cu. This synergistic effect of the three layers fundamentally avoids direct contact between Al and Cu, controlling the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface to within 5 micrometers, and eliminating the presence of continuously layered brittle phases. This significantly improves the mechanical and electrical properties of the joint.

[0021] 2. Achieving Synergistic Improvement of Mechanical Properties: The Zr intermediate barrier strengthening layer remains in a solid-phase particle state throughout the welding process, dispersed in the central region of the weld. Through the synergistic effect of dispersion strengthening and fine-grain strengthening, the strength and toughness of the joint are further improved. Experiments show that the aluminum-copper welded joint prepared using the gradient structure and welding method of this invention can achieve a tensile strength of over 85% of that of the aluminum base material, and an elongation that is more than 60% higher than that of joints without an intermediate layer.

[0022] 3. Balancing corrosion resistance and cost: This invention avoids the corrosion sensitivity problem caused by a single Zn interlayer, and at the same time uses relatively inexpensive Ni, Zr, and Zn elements to replace expensive Ag elements, which greatly reduces the cost of the interlayer and has good prospects for industrial application.

[0023] 4. Simple and controllable preparation process: The gradient structure of this invention is prepared using a room temperature rolling composite process, which is simple, efficient, and low-cost, making it easy to achieve industrial-scale mass production. By controlling the thickness ratio of each layer, rolling pressure, and rolling speed, the density and interfacial bonding strength of the gradient structure can be precisely controlled, ensuring the stability of product quality. Detailed Implementation

[0024] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. Additional aspects and advantages of this invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. It should be understood that the following description is merely illustrative and not intended to limit the invention.

[0025] The terms “comprising,” “including,” “having,” “containing,” or any other variations thereof, as used herein, are intended to cover a non-exclusive inclusion. For example, a composition, step, method, article, or apparatus that includes the listed elements is not necessarily limited to those elements, but may include other elements not expressly listed or elements inherent to such composition, step, method, article, or apparatus.

[0026] The Ni / Zr / Zn functionally graded gradient structure for laser welding of dissimilar metals (aluminum and copper) provided by this invention adopts a "functionally graded" design concept. The three layers each perform different functions: the Zn barrier layer bonds with the aluminum substrate and blocks Al diffusion; the Ni bonding layer bonds with the copper substrate and consumes Cu; and the Zr intermediate barrier and strengthening layer provides physical barrier and mechanical strengthening. The three layers are metallurgically bonded together through room temperature rolling, ensuring that delamination does not occur during welding.

[0027] In the preparation of gradient structures, the particle size and purity of Zr powder have a significant impact on the performance of the gradient structure. Excessively large Zr powder particle size leads to reduced density after rolling and decreased interfacial bonding strength; insufficient purity introduces impurities, affecting the performance of the welded joint. Therefore, this invention selects Zr powder with a particle size of 1 to 10 micrometers and a purity of not less than 99.9%.

[0028] The thickness ratio of each layer is a key parameter affecting the performance of the gradient structure. If the Ni bonding layer is too thin, Cu cannot be fully consumed; if it is too thick, the joint resistance will increase. If the Zn barrier layer is too thin, Al diffusion cannot be effectively blocked; if it is too thick, the Zn content in the weld will increase, potentially causing corrosion. If the Zr intermediate layer is too thin, physical barrier and strengthening effects will be insufficient; if it is too thick, the metallurgical bond between the three layers will be affected. Therefore, this invention controls the thickness ratio of the Ni bonding layer, Zr intermediate barrier strengthening layer, and Zn barrier layer to be between 1:1.2 and 2.5:1.

[0029] The parameters of room temperature rolling composite processes directly affect the density and interfacial bonding strength of the gradient structure. Too low a rolling pressure will prevent the formation of a good metallurgical bond between the three layers, while too high a rolling pressure will cause excessive deformation or even cracking of the material. Too high a rolling speed will result in insufficient rolling, while too low a speed will reduce production efficiency. Increasing the number of rolling passes can improve density and interfacial bonding strength, but too many passes will increase production costs. Therefore, this invention uses a rolling pressure of 50 to 150 MPa and a rolling speed of 0.5 to 2 m / min for 1 to 3 passes to obtain a gradient structure with a density of not less than 95% and an interfacial bonding strength of not less than 15 MPa.

[0030] During the welding process, laser power and welding speed are key parameters affecting weld quality. Insufficient laser power leads to insufficient penetration and failure to form an effective metallurgical bond; excessive laser power results in excessive heat input and increased IMC layer thickness. Conversely, excessively slow welding speed leads to excessive heat input, while excessively fast welding speed results in incomplete fusion defects. Therefore, this invention controls the laser power to 700 to 1200 watts and the welding speed to 5 to 15 millimeters per second.

[0031] The purpose of the shielding gas is to prevent oxidation of the molten pool and the high-temperature heat-affected zone during welding. Argon gas with a purity of not less than 99.99% is used as the shielding gas, with a gas flow rate of 12 to 18 liters per minute. The shielding gas nozzle is at an angle of 30 to 45 degrees to the welding direction, which can effectively cover the molten pool and the high-temperature area within 50 mm behind it, preventing the generation of oxidation defects.

[0032] Example 1 This embodiment provides a Ni / Zr / Zn functional graded structure for laser welding of dissimilar metals such as aluminum and copper, with the following specific parameters: Ni bonding layer: 10-micron thick Ni foil Zr intermediate barrier reinforcement layer: rolled from Zr powder with a particle size of 5 micrometers and a purity of 99.9%, with a thickness of 15 micrometers. Zn barrier layer: Zn foil with a thickness of 10 micrometers Thickness ratio of the three layers: 1:1.5:1 Overall thickness: 35 micrometers Overall density: 96% Interfacial bonding strength of each layer: 18 MPa The gradient structure is prepared as follows: S101. Zr powder with a particle size of 5 micrometers and a purity of 99.9% is uniformly spread on the surface of a Ni foil with a thickness of 10 micrometers to form a Zr powder layer with a thickness of 15 micrometers. S102. Smoothly cover the upper surface of the Zr powder layer with a Zn foil of 10 micrometers thickness, so that the edges of the three layers of materials are aligned without offset; S103. A composite integral gradient structure is obtained by performing two passes of room temperature rolling at a rolling pressure of 100 MPa and a rolling speed of 1 m / min.

[0033] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 1 mm thick 6061 aluminum alloy base material to be welded, the 1 mm thick copper base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1000 grit sandpaper until a uniform metallic luster is achieved, then immerse in acetone and anhydrous ethanol for ultrasonic cleaning for 8 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the aluminum alloy and copper to be welded interfaces, ensuring that the Zn barrier layer is seamlessly bonded to the aluminum alloy to be welded surface and the Ni bonding layer is seamlessly bonded to the copper to be welded surface, with an overlap of 10 mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 900 watts, the welding speed is 10 mm / s, the defocusing amount is 0 mm, and the laser spot diameter is 0.3 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 15 liters per minute. The protective gas nozzle is at a 40-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0034] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.2 micrometers, with no continuous layered distribution of θ-Al2Cu, η-AlCu, and γ-Al4Cu9 phases; the tensile strength of the joint was 112 MPa, reaching 86% of that of the 6061 aluminum alloy base material; the elongation of the joint was 8.2%; the resistivity of the joint was 2.6 micro ohms·cm; after immersing the joint in 3.5% NaCl solution for 72 hours, the corrosion rate was 0.02 mm / year, which is much lower than that of the joint using a single Zn intermediate layer.

[0035] Example 2 This embodiment provides a Ni / Zr / Zn functional graded structure for laser welding of dissimilar metals such as aluminum and copper, with the following specific parameters: Ni bonding layer: Ni foil with a thickness of 5 micrometers Zr intermediate barrier reinforcement layer: rolled from Zr powder with a particle size of 1 micrometer and a purity of 99.95%, with a thickness of 10 micrometers. Zn barrier layer: Zn foil with a thickness of 5 micrometers Thickness ratio of three layers: 1:2:1 Overall thickness: 20 micrometers Overall density: 95% Interfacial bonding strength of each layer: 15 MPa The gradient structure is prepared as follows: S101. Zr powder with a particle size of 1 micrometer and a purity of 99.95% is uniformly spread on the surface of a Ni foil with a thickness of 5 micrometers to form a Zr powder layer with a thickness of 10 micrometers. S102. Smoothly cover the upper surface of the Zr powder layer with a Zn foil of 5 micrometers thickness, so that the edges of the three layers of materials are aligned without offset; S103. A single pass of room temperature rolling was performed at a rolling pressure of 50 MPa and a rolling speed of 0.5 m / min to obtain an integral gradient structure.

[0036] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 0.3 mm thick industrial pure aluminum base material to be welded, the 0.3 mm thick brass base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 800 grit sandpaper until a uniform metallic luster is achieved, then ultrasonically clean in acetone and anhydrous ethanol for 5 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the pure aluminum and brass interfaces to be welded, so that the Zn barrier layer is seamlessly bonded to the pure aluminum surface to be welded, and the Ni bonding layer is seamlessly bonded to the brass surface to be welded, with an overlap of 5 mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 700 watts, the welding speed is 5 mm / s, the defocusing amount is -1 mm, and the laser spot diameter is 0.2 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 12 liters per minute. The protective gas nozzle is at a 30-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0037] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 2.8 micrometers, with no continuously layered brittle phases; the tensile strength of the joint was 78 MPa, reaching 82% of that of industrial pure aluminum base material; the elongation of the joint was 9.5%; and the resistivity of the joint was 2.3 micro ohms-cm.

[0038] Example 3 This embodiment provides a Ni / Zr / Zn functional graded structure for laser welding of dissimilar metals such as aluminum and copper, with the following specific parameters: Ni bonding layer: 20-micron thick Ni foil Zr intermediate barrier reinforcement layer: rolled from Zr powder with a particle size of 10 micrometers and a purity of 99.9%, with a thickness of 30 micrometers. Zn barrier layer: Zn foil with a thickness of 20 micrometers Thickness ratio of the three layers: 1:1.5:1 Overall thickness: 70 micrometers Overall density: 97% Interfacial bonding strength of each layer: 22 MPa The gradient structure is prepared as follows: S101. Zr powder with a particle size of 10 micrometers and a purity of 99.9% is uniformly spread on the surface of a Ni foil with a thickness of 20 micrometers to form a Zr powder layer with a thickness of 30 micrometers. S102. Smoothly cover the upper surface of the Zr powder layer with a Zn foil of 20 micrometers thickness, so that the edges of the three layers of materials are aligned without offset; S103. A three-pass room temperature rolling composite process was performed at a rolling pressure of 150 MPa and a rolling speed of 2 m / min to obtain an integral gradient structure.

[0039] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 2mm thick 5052 aluminum alloy base material to be welded, the 2mm thick industrial pure copper base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1200 grit sandpaper until a uniform metallic luster is achieved, then immerse in acetone and anhydrous ethanol for ultrasonic cleaning for 10 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the 5052 aluminum alloy and pure copper to be welded interfaces, so that the Zn barrier layer is seamlessly bonded to the aluminum alloy to be welded surface, and the Ni bonding layer is seamlessly bonded to the pure copper to be welded surface, with an overlap of 15mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 1200 watts, the welding speed is 15 mm / s, the defocusing amount is +1 mm, and the laser spot diameter is 0.5 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 18 liters per minute. The protective gas nozzle is at a 45-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0040] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 4.5 micrometers, with no continuous layered brittle phases; the tensile strength of the joint was 105 MPa, reaching 84% of that of the 5052 aluminum alloy base material; the elongation of the joint was 7.8%; and the resistivity of the joint was 2.8 micro ohms-cm.

[0041] Example 4 (Verification of Three-Pass Rolling Process) This embodiment provides a Ni / Zr / Zn functional graded structure for laser welding of dissimilar metals such as aluminum and copper, with the following specific parameters: Ni bonding layer: 15-micron thick Ni foil Zr intermediate barrier reinforcement layer: rolled from Zr powder with a particle size of 7 micrometers and a purity of 99.92%, with a thickness of 20 micrometers. Zn barrier layer: 15-micron thick Zn foil Thickness ratio of the three layers: 1:1.33:1 Overall thickness: 50 micrometers Overall density: 96.5% Interfacial bonding strength of each layer: 20 MPa The gradient structure is prepared as follows: S101. Zr powder with a particle size of 7 micrometers and a purity of 99.92% is uniformly spread on the surface of a Ni foil with a thickness of 15 micrometers to form a Zr powder layer with a thickness of 20 micrometers. S102. Smoothly cover the upper surface of the Zr powder layer with a Zn foil of 15 micrometers thickness, so that the edges of the three layers of materials are aligned without offset; S103. Three passes of room temperature rolling were performed at a rolling pressure of 120 MPa and a rolling speed of 1.5 m / min, with a reduction rate of approximately 15% per pass, to obtain an integral gradient structure.

[0042] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 1.5 mm thick 6061 aluminum alloy base material to be welded, the 1.5 mm thick copper base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1000 grit sandpaper until a uniform metallic luster is achieved, then ultrasonically clean in acetone and anhydrous ethanol for 9 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the aluminum alloy and copper to be welded interfaces, so that the Zn barrier layer is in close contact with the aluminum alloy to be welded surface without gaps, and the Ni bonding layer is in close contact with the copper to be welded surface without gaps, with an overlap of 12 mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 1000 watts, the welding speed is 12 mm per second, the defocusing amount is 0 mm, and the laser spot diameter is 0.4 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 16 liters per minute. The protective gas nozzle is at a 35-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0043] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.6 micrometers, with no continuously layered brittle phases; the tensile strength of the joint was 115 MPa, reaching 88% of that of the 6061 aluminum alloy base material; the elongation of the joint was 8.5%; the resistivity of the joint was 2.5 micro ohms·cm; after immersing the joint in 3.5% NaCl solution for 72 hours, the corrosion rate was 0.018 mm / year.

[0044] Example 5 (Verification of the mating joint type) This embodiment provides a Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals, with parameters exactly the same as in Embodiment 1.

[0045] The specific steps for aluminum-copper laser butt welding using the above gradient structure are as follows: S2. Pre-treat the 1 mm thick 5052 aluminum alloy base material to be welded, the 1 mm thick copper base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1000 grit sandpaper until a uniform metallic luster is achieved, then ultrasonically clean in acetone and anhydrous ethanol for 8 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the butt joint bevels of the aluminum alloy and copper, with a bevel angle of 30 degrees and an assembly gap of 0.1 mm, so that the Zn barrier layer is in close contact with the aluminum alloy base material to be welded and the Ni bonding layer is in close contact with the copper base material to be welded, and clamp and fix it with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 950 watts, the welding speed is 8 mm / s, the defocusing amount is 0 mm, and the laser spot diameter is 0.3 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 15 liters per minute. The protective gas nozzle is at a 40-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0046] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.4 micrometers, with no continuous layered brittle phases; the tensile strength of the joint was 108 MPa, reaching 86% of that of the 5052 aluminum alloy base material; the joint bending angle reached 120 degrees without cracks; and the resistivity of the joint was 2.7 micro ohms·cm.

[0047] Example 6 (Verification of Low-Power Slow-Speed ​​Process) This embodiment provides a Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals, with parameters exactly the same as in Embodiment 1.

[0048] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 1 mm thick 6061 aluminum alloy base material to be welded, the 1 mm thick copper base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1000 grit sandpaper until a uniform metallic luster is achieved, then immerse in acetone and anhydrous ethanol for ultrasonic cleaning for 8 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the aluminum alloy and copper to be welded interfaces, ensuring that the Zn barrier layer is seamlessly bonded to the aluminum alloy to be welded surface and the Ni bonding layer is seamlessly bonded to the copper to be welded surface, with an overlap of 10 mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 800 watts, the welding speed is 6 mm / s, the defocusing amount is -0.5 mm, and the laser spot diameter is 0.3 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 15 liters per minute. The protective gas nozzle is at a 40-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0049] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.8 micrometers, with no continuous layered brittle phases; the tensile strength of the joint was 109 MPa, reaching 84% of that of the 6061 aluminum alloy base material; the elongation of the joint was 7.9%; and the resistivity of the joint was 2.6 micro ohms-cm.

[0050] Example 7 (Verification of different Zr powder particle sizes) This embodiment provides a Ni / Zr / Zn functional graded structure for laser welding of dissimilar metals such as aluminum and copper, with the following specific parameters: Ni bonding layer: 10-micron thick Ni foil Zr intermediate barrier reinforcement layer: rolled from Zr powder with a particle size of 3 micrometers and a purity of 99.9%, with a thickness of 15 micrometers. Zn barrier layer: Zn foil with a thickness of 10 micrometers Thickness ratio of the three layers: 1:1.5:1 Overall thickness: 35 micrometers Overall density: 96.2% Interfacial bonding strength of each layer: 19 MPa The preparation method and welding process parameters of this gradient structure are exactly the same as those in Example 1.

[0051] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.0 micrometers, with no continuously layered brittle phases; the tensile strength of the joint was 114 MPa, reaching 87% of that of the 6061 aluminum alloy base material; the elongation of the joint was 8.4%; and the resistivity of the joint was 2.5 micro ohms-cm.

[0052] Example 8 (Verification of 5052 aluminum alloy combined with brass base material) This embodiment provides a Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals, with parameters exactly the same as in Embodiment 1.

[0053] The specific steps for aluminum-copper laser welding using the above gradient structure are as follows: S2. Pre-treat the 1 mm thick 5052 aluminum alloy base material to be welded, the 1 mm thick brass base material to be welded, and the upper and lower surfaces of the gradient structure: polish with 1000 grit sandpaper until a uniform metallic luster is achieved, then immerse in acetone and anhydrous ethanol for ultrasonic cleaning for 8 minutes each, remove and dry with cold air, and assemble immediately; place the pre-treated gradient structure between the aluminum alloy and brass interfaces to be welded, so that the Zn barrier layer is seamlessly bonded to the aluminum alloy surface to be welded, and the Ni bonding layer is seamlessly bonded to the brass surface to be welded, with an overlap of 10 mm, and clamp and fix with tooling after assembly; S3. A fiber continuous laser is used to scan and weld the assembled area to be welded. The laser power is 900 watts, the welding speed is 10 mm / s, the defocusing amount is 0 mm, and the laser spot diameter is 0.3 mm. During the welding process, 99.99% pure argon gas is used as the side-blowing protective gas with a gas flow rate of 15 liters per minute. The protective gas nozzle is at a 40-degree angle to the welding direction, and the protection range covers the molten pool and the high-temperature area within 50 mm behind it.

[0054] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 3.3 micrometers, with no continuously layered brittle phases; the tensile strength of the joint was 106 MPa, reaching 85% of that of the 5052 aluminum alloy base material; the elongation of the joint was 8.0%; and the resistivity of the joint was 2.7 micro ohms·cm.

[0055] Comparative Example 1 (without intermediate layer) Using the same base material and welding process parameters as in Example 1, aluminum-copper laser welding was performed without adding any intermediate layer.

[0056] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 12.5 micrometers, with continuous layered distribution of θ-Al2Cu and γ-Al4Cu9 phases; the tensile strength of the joint was 52 MPa, only 40% of that of the 6061 aluminum alloy base material; the elongation of the joint was 2.1%; and the resistivity of the joint was 4.2 micro ohms·cm.

[0057] Comparative Example 2 (Single Ni Interlayer) A single Ni foil with a thickness of 35 micrometers was used as the intermediate layer, and aluminum-copper laser welding was performed using the same base material and welding process parameters as in Example 1.

[0058] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 8.7 micrometers, with locally continuous layered θ-Al2Cu phases; the tensile strength of the joint was 76 MPa, which was 58% of that of the 6061 aluminum alloy base material; the elongation of the joint was 4.3%; and the resistivity of the joint was 3.5 micro ohms·cm.

[0059] Comparative Example 3 (Single Zn Intermediate Layer) A single Zn foil with a thickness of 35 micrometers was used as the intermediate layer, and aluminum-copper laser welding was performed using the same base material and welding process parameters as in Example 1.

[0060] After welding, the joint was subjected to performance tests: the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface was 6.2 micrometers, with no continuously layered brittle phases; the tensile strength of the joint was 89 MPa, which was 68% of that of the 6061 aluminum alloy base material; the elongation of the joint was 5.7%; the resistivity of the joint was 2.9 micro ohms per centimeter; however, after the joint was immersed in 3.5% NaCl solution for 72 hours, the corrosion rate was 0.15 mm / year, which was 7.5 times that of Example 1 of the present invention.

[0061] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A Ni / Zr / Zn functional graded structure for laser welding of aluminum and copper dissimilar metals, characterized in that, It consists of a Ni bonding layer, a Zr intermediate barrier strengthening layer and a Zn barrier layer, which are combined by room temperature rolling to form a metallurgically bonded integral structure. The Ni bonding layer is a Ni foil, the Zr intermediate barrier strengthening layer is formed by rolling and compacting Zr powder, and the Zn barrier layer is a Zn foil.

2. The Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals according to claim 1, characterized in that, The Ni bonding layer has a thickness of 5 to 20 micrometers, the Zr intermediate barrier reinforcement layer has a thickness of 10 to 30 micrometers, the Zn barrier layer has a thickness of 5 to 20 micrometers, and the overall total thickness is 20 to 70 micrometers.

3. The Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals according to claim 1, characterized in that, The thickness ratio of the Ni bonding layer, the Zr intermediate barrier reinforcement layer, and the Zn barrier layer is 1:1.2 to 2.5:1, and the overall density is not less than 95%.

4. The Ni / Zr / Zn functional graded structure for laser welding of aluminum and copper dissimilar metals according to any one of claims 1-3, characterized in that, The Zr powder has a particle size of 1 to 10 micrometers, a purity of not less than 99.9%, and an interfacial bonding strength of not less than 15 MPa.

5. A welding method employing the Ni / Zr / Zn functional graded gradient structure for laser welding of aluminum and copper dissimilar metals as described in any one of claims 1-4, characterized in that, Includes the following steps: S1. Prepare the Ni / Zr / Zn functional hierarchical gradient structure for laser welding of aluminum and copper dissimilar metals; S2. Pre-treat the aluminum base material to be welded surface, the copper base material to be welded surface, and the upper and lower surfaces of the gradient structure to remove oxide film and oil stains; place the pre-treated gradient structure between the aluminum base material and the copper base material to be welded interface, so that the Zn barrier layer is in close contact with the aluminum base material to be welded surface without gaps, and the Ni bonding layer is in close contact with the copper base material to be welded surface without gaps. After assembly, use tooling to clamp and fix it. S3. Continuous laser is used to scan and weld the assembled area to be welded. During the welding process, the interface reaction is controlled by the hierarchical regulation of the three-layer structure.

6. The welding method according to claim 5, characterized in that, The method for preparing the gradient structure in step S1 specifically includes the following steps: S101. Zr powder is evenly spread on the upper surface of Ni foil to form a Zr powder layer of uniform thickness; S102. Smoothly cover the Zn foil on the upper surface of the Zr powder layer, so that the edges of the three layers of materials are aligned without offset; S103. A composite structure is obtained by performing 1 to 3 passes of room temperature rolling at a rolling pressure of 50 to 150 MPa and a rolling speed of 0.5 to 2 m / min.

7. The welding method according to claim 5, characterized in that, The preprocessing described in step S2 specifically includes the following steps: S201. Use 800 to 1200 grit sandpaper to polish the aluminum base material to be welded surface, the copper base material to be welded surface, and the upper and lower surfaces of the gradient structure until a uniform metallic luster is achieved; S202. Place the polished base material and gradient structure into acetone and anhydrous ethanol respectively for ultrasonic cleaning for 5 to 10 minutes. S203. After removing it, dry it with cold air and immediately assemble and clamp it.

8. The welding method according to claim 5, characterized in that, The graded control of the welding process described in step S3 specifically includes the following steps: S301. The Zn barrier layer melts preferentially and reacts with aluminum elements at the interface of the aluminum matrix to form a continuous and dense Zn-Al solid solution layer, which physically prevents aluminum elements from diffusing to the copper side. The S302.Ni bonding layer remains semi-solid and reacts with the copper elements at the interface of the copper substrate to form an infinitely miscible Ni-Cu solid solution layer, consuming free copper atoms at the interface. The S303.Zr intermediate barrier strengthening layer remains in a solid particle state throughout the entire process, dispersed in the central area of ​​the weld. At the same time, it acts as a physical barrier layer to block the direct diffusion channels between aluminum and copper, thereby improving the mechanical properties of the joint through the synergistic effect of dispersion strengthening and grain refinement strengthening.

9. The welding method according to claim 5, characterized in that, The laser welding described in step S3 uses a fiber continuous laser with a laser power of 700 to 1200 watts, a welding speed of 5 to 15 millimeters per second, a defocusing amount of -1 to +1 millimeters, and a laser spot diameter of 0.2 to 0.5 millimeters. During the welding process, argon gas with a purity of not less than 99.99% is used as a side-blowing protective gas with a gas flow rate of 12 to 18 liters per minute. The protective gas nozzle is at an angle of 30 to 45 degrees to the welding direction, and the protective range covers the molten pool and the high-temperature area within 50 millimeters behind it.

10. The welding method according to any one of claims 5-9, characterized in that, The aluminum base material is industrial pure aluminum, 5052 aluminum alloy, or 6061 aluminum alloy, with a thickness of 0.3 to 2 mm; the copper base material is industrial pure copper, red copper, or brass, with a thickness of 0.3 to 2 mm; the joint type is a lap joint, with an overlap of 5 to 15 mm; after welding, the total thickness of the aluminum-copper brittle intermetallic compound layer at the joint interface does not exceed 5 micrometers, and there are no continuously layered θ-Al2Cu, η-AlCu, and γ-Al4Cu9 phases.