High-conductivity low-cost copper-iron composite powder and full-coating preparation method thereof

Abstract

The invention relates to the technical field of metal composite materials, in particular to high-conductivity low-cost copper-iron composite powder and a full-coating preparation method thereof.The two steps of chemical copper plating and 450-600 DEG C heat treatment are combined, micro-pores in an initial copper layer are diffused and healed by atoms, a compact copper shell is formed, the surface of the composite powder is free of red rust after a test, and the copper-iron composite powder is high in conductivity and low in cost. The corrosion resistance is improved compared with that of a non-heat-treated sample; a 0.5-3 m mutual diffusion layer is formed on the copper-iron interface through heat treatment, metallurgical bonding is achieved, the interface shear strength is improved to be larger than or equal to 25 MPa from less than 10 MPa of traditional physical bonding, and the problem that a coating layer is prone to stripping in the subsequent pressing, sintering or using process is solved.

Description

Technical Field

[0001] This invention relates to the field of metal composite materials technology, and in particular to a high-conductivity, low-cost copper-iron composite powder and its fully coated preparation method. Background Technology

[0002] Copper-iron composite powder, possessing both the high strength and low cost of iron and the excellent electrical and thermal conductivity of copper, has broad application prospects in powder metallurgy, conductive pastes, and microwave absorption. To optimize performance, the key lies in achieving a complete and dense coating of copper onto the iron powder.

[0003] Existing technologies mainly employ chemical plating or displacement methods to achieve copper coating, but both have inherent defects. For example, patent CN110899692A discloses a displacement-chemical plating combined method, which is environmentally friendly but relies on displacement reactions. The initial copper layer grows in an island-like pattern, resulting in poor coating integrity (typically below 85%). The interface is physically attached, making it prone to detachment and exhibiting numerous pores, leading to weak corrosion resistance. Patent CN118374795A uses a multi-step chemical plating process to improve coating uniformity, but its coating suffers from the inherent "hydrogen embrittlement" and microporosity (microporosity approximately 3-5%) of chemical plating. Furthermore, subsequent low-temperature (<200℃) drying treatment cannot eliminate these intrinsic defects, resulting in insufficient long-term stability.

[0004] Ultimately, existing technologies have failed to address two key issues: first, the failure of the anti-corrosion barrier due to the microscopic pores in the chemical plating layer; and second, the weak bonding at the copper-iron interface, which is easily peeled off under thermal or mechanical stress. Conventional low-temperature treatments can only remove moisture and cannot drive atomic diffusion to heal defects and strengthen the interface.

[0005] Therefore, developing a preparation method that can achieve complete densification of the copper layer and form a strong metallurgical bond with the iron core is the key to improving the overall performance and reliability of copper-iron composite powder. Summary of the Invention

[0006] The purpose of this invention is to provide a high-conductivity, low-cost copper-iron composite powder and its fully coated preparation method, aiming to solve the problems of non-dense coating, weak interfacial bonding, and easy corrosion of copper-iron composite powder in the prior art.

[0007] To achieve the above objectives, in a first aspect, the present invention provides a method for preparing a fully coated copper-iron composite powder with high conductivity and low cost, comprising the following steps: Iron powder is pretreated to obtain clean and activated iron powder; The activated iron powder was placed in a chemical copper plating solution to react and obtain a primary copper-iron composite powder with an initial copper layer deposited on the surface. The primary copper-iron composite powder is heat-treated in a reducing atmosphere or vacuum to obtain the composite powder.

[0008] The heat treatment employs a two-stage heating process: first, the temperature is raised to 250-350℃ at a rate of 5-10℃ / min and held for 10-30 minutes, and then the temperature is raised to the target temperature at a rate of 2-5℃ / min.

[0009] The reducing atmosphere is a nitrogen-hydrogen mixture containing 3%-10% hydrogen by volume.

[0010] The target temperature is 500-550℃.

[0011] In a second aspect, a high-conductivity, low-cost copper-iron composite powder is prepared using the high-conductivity, low-cost copper-iron composite powder full-coating preparation method described in the first aspect, comprising an iron core and a copper shell, wherein the copper shell and the iron core are connected by a metallurgical bond. The metallurgical bonding is manifested in the presence of a copper-iron interdiffusion layer at the interface between the copper shell and the iron core, the thickness of which is 0.5-3 μm.

[0012] The interfacial shear strength between the copper shell and the iron core is greater than 25 MPa.

[0013] This invention discloses a high-conductivity, low-cost copper-iron composite powder and its fully coated preparation method. The invention employs a two-step combination of "chemical copper plating + heat treatment at 450-600℃," which heals the micropores in the initial copper layer through atomic diffusion, forming a dense copper shell with a porosity of <0.1%. The composite powder exhibits no red rust on its surface after 72 hours of neutral salt spray testing, and its corrosion resistance is at least three times higher than that of the untreated sample. Simultaneously, the heat treatment forms a 0.5-3µm interdiffusion layer at the copper-iron interface, achieving metallurgical bonding and increasing the interfacial shear strength. The pressure of physical bonding is increased from <10MPa to ≥25MPa, solving the problem of easy peeling of the coating layer during subsequent pressing, sintering or use; the dense copper shell and strong interface work together to make the volume resistivity of the composite powder as low as 2.3µΩ·cm, while maintaining the high strength of the iron core. The overall performance is better than commercially available mechanically mixed powders and samples dried at low temperature; the process steps are simple, the heat treatment window of 450-600℃ is compatible with conventional reducing atmospheres, and existing continuous reduction furnaces can be used directly, making it suitable for large-scale stable production. Attached Figure Description

[0014] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0015] Figure 1This is a SEM image of the copper-iron composite powder of the present invention.

[0016] Figure 2 This is a flowchart of a method for preparing a fully coated copper-iron composite powder with high conductivity and low cost, as provided by the present invention. Detailed Implementation

[0017] Embodiments of the present invention are described in detail below, examples of which are illustrated in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0018] Please see Figures 1 to 2 In a first aspect, the present invention provides a method for preparing a fully coated copper-iron composite powder with high conductivity and low cost, comprising the following steps: S1 pre-treats the iron powder to obtain clean and activated iron powder; S2 places the activated iron powder into a chemical copper plating solution for reaction, and obtains primary copper-iron composite powder with an initial copper layer deposited on the surface. S3 heat-treats the primary copper-iron composite powder in a reducing atmosphere or vacuum to obtain composite powder.

[0019] The heat treatment employs a two-stage heating program: first, the temperature is raised to 250-350℃ at a rate of 5-10℃ / min and held for 10-30 minutes, and then raised to the target temperature at a rate of 2-5℃ / min.

[0020] The reducing atmosphere is a nitrogen-hydrogen mixture containing 3%-10% hydrogen by volume.

[0021] The target temperature is 500-550℃.

[0022] In a second aspect, a high-conductivity, low-cost copper-iron composite powder is prepared using the high-conductivity, low-cost copper-iron composite powder full-coating preparation method described in the first aspect, comprising an iron core and a copper shell, wherein the copper shell and the iron core are connected by a metallurgical bond. The metallurgical bonding is manifested in the presence of a copper-iron interdiffusion layer at the interface between the copper shell and the iron core, the thickness of which is 0.5-3 μm. Example

[0023] Raw material: 100g of reduced iron powder with an average particle size of 45μm.

[0024] step: Pretreatment: Iron powder is activated with dilute acid for 2 minutes, then washed and dried.

[0025] Chemical copper plating: The primary composite powder is obtained by reacting in a copper plating solution (CuSO4·5H2O 40g / L, complexing agent EDTA-2Na 40g / L) at 60℃ and pH=12.8 for 10 minutes.

[0026] High-temperature heat treatment: Place the primary composite powder in a tube furnace and introduce a mixture of 5% H2 and 95% N2. First, raise the temperature to 300℃ at 8℃ / min and hold for 20 minutes, then raise the temperature to 520℃ at 3℃ / min and hold for 1.5 hours, and then cool with the furnace.

[0027] Test results: The surface of the iron powder is completely covered by a continuous, dense copper layer. A diffusion layer exists at the interface, with a gradient transition between copper and iron elements.

[0028] Bond strength: The average interfacial shear strength is 28.5 MPa.

[0029] Corrosion resistance: After 72 hours of neutral salt spray test (5% NaCl, 35℃), no red rust appeared on the sample surface.

[0030] Comparative Example 1 (simulating a process similar to CN118374795A) The steps are the same as in Example 1, but the high-temperature heat treatment step is omitted, and drying is only carried out in argon at 80°C for 2 hours.

[0031] Test results: The copper layer shows obvious micropores and cracks, with a clear and straight interface and no signs of diffusion.

[0032] There are obvious pores at the microscopic level.

[0033] Corrosion resistance: After 24 hours of the same salt spray test, pitted red rust appeared on the surface.

[0034] Comparative Example 2 (simulating a process similar to CN110899692A) The coating is performed using a chemical plating system with glucose as a reducing agent, without high-temperature heat treatment.

[0035] Test results: The coating is incomplete; the iron surface is not covered by copper, resulting in extremely poor corrosion resistance.

[0036] Example 2 (Influence of different heat treatment temperatures) The target heat treatment temperature in step 3 of Example 1 was changed to 400℃, 480℃, 560℃, and 620℃, respectively, while the other conditions remained unchanged.

[0037] Test results: 400℃: There are obvious pores and slight diffusion; the bonding strength is 15MPa.

[0038] 480℃: No obvious pores were observed, the diffusion layer was about 0.8μm, and the bonding strength was 24MPa.

[0039] 560℃: No obvious pores were observed, the diffusion layer was about 1.8μm, and the bonding strength was 29MPa.

[0040] 620℃: The diffusion layer is too thick (>4μm), and some iron powder surfaces show sintering and adhesion.

[0041] Conclusion: 450-600℃, especially 500-550℃, is the optimal temperature window, which can achieve a balance between efficient pore healing and moderate diffusion.

[0042] Example 3 (Comprehensive Performance Comparison) The performance of the product of Example 1 was compared with that of commercially available mechanically mixed powder and the product of Comparative Example 1.

[0043]

[0044] Beneficial effects: A groundbreaking "plating-diffusion" synergistic process: Unlike existing technologies (such as the simple plating + low-temperature drying in CN118374795A, and the displacement + plating in CN110899692A), this invention creatively introduces a specific high-temperature heat treatment as a key post-processing step. This step is not simply drying or impurity removal, but rather utilizes the significant diffusion ability of copper and iron atoms at 450-600℃ to actively heal defects in the chemical plating layer and construct a metallurgical interface, achieving a qualitative leap in technical effectiveness.

[0045] A dense barrier layer is obtained: Through high-temperature thermally driven surface diffusion and grain boundary diffusion, the inherent micropores and cracks in the chemical plating layer are effectively eliminated, reducing the porosity of the coating layer and improving the composite powder's resistance to moisture oxidation and electrochemical corrosion by orders of magnitude.

[0046] Achieving a robust metallurgical bonding interface: Heat treatment promotes the interdiffusion of copper and iron atoms at the interface, forming an interdiffusion layer with gradually changing composition. This increases the interfacial bonding strength from <10MPa in traditional physical bonding to >25MPa, solving the industry problem of easy peeling of the coating layer during subsequent processing (such as pressing, sintering) or use.

[0047] Optimized overall performance: The dense copper layer and strong metallurgical bonding interface enable the composite powder to maintain high conductivity (low resistivity) while possessing excellent long-term stability and mechanical reliability, with overall performance far exceeding that of existing technology products.

[0048] The process is controllable and suitable for industrialization: the method and process are simple, the parameters are clearly controlled, and it is easy to achieve large-scale and stable production.

[0049] The above description is merely a preferred embodiment of the present invention of a high-conductivity, low-cost copper-iron composite powder and its fully coated preparation method. It should not be construed as limiting the scope of the present invention. Those skilled in the art can understand that all or part of the above embodiments can be implemented, and equivalent changes made in accordance with the claims of the present invention are still within the scope of the invention.

Claims

1. A high-conductivity, low-cost copper-iron composite powder and its fully coated preparation method, characterized in that, Includes the following steps: Iron powder is pretreated to obtain clean and activated iron powder; The activated iron powder was placed in a chemical copper plating solution to react and obtain a primary copper-iron composite powder with an initial copper layer deposited on the surface. The primary copper-iron composite powder is heat-treated in a reducing atmosphere or vacuum to obtain the composite powder.

2. The method for preparing a fully coated copper-iron composite powder with high conductivity and low cost as described in claim 1, characterized in that, The heat treatment employs a two-stage heating program: first, the temperature is raised to 250-350℃ at a rate of 5-10℃ / min and held for 10-30 minutes, and then raised to the target temperature at a rate of 2-5℃ / min.

3. The method for preparing a fully coated copper-iron composite powder with high conductivity and low cost as described in claim 1, characterized in that, The reducing atmosphere is a nitrogen-hydrogen mixture containing 3%-10% hydrogen by volume.

4. The method for preparing a fully coated copper-iron composite powder with high conductivity and low cost as described in claim 2, characterized in that, The target temperature is 500-550℃.

5. A high-conductivity, low-cost copper-iron composite powder, prepared by the full-coating preparation method of the high-conductivity, low-cost copper-iron composite powder according to any one of claims 1-4, characterized in that, It includes an iron core and a copper shell, wherein the copper shell and the iron core are connected by a metallurgical bonding. The metallurgical bonding is manifested in the presence of a copper-iron interdiffusion layer at the interface between the copper shell and the iron core, the thickness of which is 0.5-3 μm.

6. The high-conductivity, low-cost copper-iron composite powder as described in claim 5, characterized in that, The interfacial shear strength between the copper shell and the iron core is greater than 25 MPa.

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