A high thermal stability Cu-Zr alloy with a core-shell structure formed by Ni micro-alloying

Abstract

This invention discloses a high thermal stability Cu-Zr alloy with a core-shell structure formed by Ni microalloying and its preparation method, belonging to the field of non-ferrous metal materials technology. The alloy composition by weight percentage is: Zr: 0.18~0.23%, Ni: 0.30~0.50%, with the balance being Cu and unavoidable impurities. The preparation method includes: vacuum casting, solution treatment, hot extrusion, large deformation cold drawing, and aging treatment. This invention, through Ni microalloying and a suitable cold deformation-aging process, forms a nanoscale core-shell precipitate structure in a copper matrix, with a Cu₅Zr phase as the core and a Ni-rich atomic layer as the shell. This structure significantly suppresses the coarsening of the precipitate at high temperatures, allowing the alloy to maintain high conductivity (>80% IACS) while significantly increasing its softening temperature from approximately 500℃ in traditional Cu-Zr alloys to over 580℃. This makes it suitable for electrical and electronic components and high-temperature structural parts with stringent requirements for strength, conductivity, and high-temperature stability.

Description

Technical Field

[0001] This invention relates to the field of non-ferrous metal materials technology, specifically to a high-strength, high-conductivity, and high-thermal-stability copper alloy and its preparation method, and particularly to a technique for strengthening the copper matrix by forming a distinctive core-shell structure precipitate phase through microalloying and process control. Background Technology

[0002] Copper and copper alloys are widely used in electrical and electronic, transportation, and aerospace fields due to their excellent electrical and thermal conductivity. However, pure copper has low strength and poor softening temperature (usually below 300°C), making it difficult to meet the comprehensive performance requirements of high-end equipment.

[0003] Precipitation strengthening by adding alloying elements (such as Zr, Cr, Ag, etc.) is an effective way to improve the strength of copper alloys. Among them, Cu-Zr alloys have attracted attention due to their good combination of strength and conductivity. However, the main strengthening phase Cu5Zr in traditional Cu-Zr alloys is prone to coarsening and dissolving at high temperatures (>500℃), resulting in rapid softening of the alloy. Its strength and thermal stability cannot meet the requirements of higher temperature service environments, such as high-power motor rotors, high-temperature welding electrodes, and high-speed rail contact lines.

[0004] Therefore, developing a new type of copper alloy material that maintains high conductivity while also possessing high strength and, in particular, high resistance to softening temperature, has significant industrial application value. Summary of the Invention

[0005] The technical problem this invention aims to solve is to address the insufficient high-temperature softening resistance of existing Cu-Zr alloys by providing a novel copper alloy and its preparation method. This method introduces trace amounts of Ni into the Cu-Zr alloy and, in conjunction with appropriate thermomechanical treatment processes, forms a core-shell structured nanoprecipitate phase with high thermal stability in the matrix. This significantly improves the alloy's strength and softening resistance temperature with almost no loss of conductivity. To achieve the above-mentioned objective, this invention adopts the following technical solution: This invention relates to a high thermal stability Cu-Zr alloy with a core-shell structure formed by Ni microalloying, characterized in that the copper alloy is composed of the following components by weight percentage (wt.%): Zr: 0.18~0.23%, Ni: 0.25~0.50%, with the balance being Cu and unavoidable impurities; the microstructure of the copper alloy contains a core-shell structured nanoprecipitate phase with Cu5Zr phase as the core and Ni-rich atom segregation layer as the shell.

[0006] In a preferred embodiment of the present invention, the average size of the core-shell structured nanoprecipitates is 2-5 nm. Another aspect of the present invention relates to a method for preparing the above-mentioned Cu-Zr alloy, characterized by comprising the following steps: S1. Melting and casting: According to the above composition ratio, the alloy ingot is obtained by melting and casting in a vacuum induction furnace; S2. Solution treatment: The alloy ingot is subjected to solution heat treatment at 920~960℃ for 4 hours to fully dissolve the alloying elements in the copper matrix; S3. Hot extrusion: After the solution-treated ingot is machined to the specified size, it is hot extruded and deformed at a temperature of 750~850℃ to obtain extruded bars; S4. Cold drawing: The hot-extruded bar is subjected to multiple cold drawing deformations, with a total deformation of not less than 90%, to obtain cold-drawn wire or bar. S5. Aging treatment: The cold-drawn material is aged in a resistance furnace at 450~550℃ for 0.5-1.5 hours to promote the precipitation of Cu5Zr phase, while Ni atoms diffuse and agglomerate on the surface of Cu5Zr phase to form the core-shell structured nanoprecipitated phase.

[0007] Preferably, the solution treatment temperature in step S2 is 950°C, and the holding time is 4 hours.

[0008] Preferably, the hot extrusion temperature in step S3 is 800°C.

[0009] Preferably, the final deformation of the cold drawing in step S4 is to draw the diameter from 14 mm to 4 mm.

[0010] Preferably, the aging treatment temperature in step S5 is 500°C. Beneficial effects

[0011] Unique reinforced phase structure This invention successfully constructed a core-shell structured nanoprecipitate phase with a Cu5Zr core and a Ni atom-enriched layer as the shell in a copper matrix through microalloying of Ni and cold deformation-aging process. This structure is the microscopic basis for the high performance of this alloy.

[0012] Excellent overall performance ① High conductivity retention: Ni atoms mainly agglomerate at the precipitation phase interface, which greatly reduces the content of Ni dissolved in the matrix, thereby minimizing the scattering of electrons by alloy atoms. This allows the alloy to maintain high conductivity (conductivity can reach over 80% IACS) while achieving high strength.

[0013] ② Significantly improved thermal stability: The slow diffusion rate of Ni atoms enriched at the interface effectively hinders the coarsening kinetics of Cu5Zr precipitates at high temperatures, allowing them to maintain high number density and fine size even after prolonged exposure to high temperatures. This significantly increases the alloy's softening resistance temperature from approximately 500℃ for traditional Cu-Zr alloys to over 580℃.

[0014] ③ High strength: The high-density, fine core-shell structure precipitates and the dislocation structure introduced by cold deformation work together to produce a strong pinning effect on dislocation movement, giving the alloy high room temperature strength and high temperature strength.

[0015] The process is controllable and suitable for industrialization. The vacuum melting, hot extrusion, cold drawing and aging treatment used in this invention are all mature industrial production methods with clear process flow, controllable parameters, and easy to achieve large-scale production. Attached Figure Description

[0016] Figure 1 The image shows a bright-field transmission electron microscope (TEM) image and a corresponding high-resolution spectrum of the Cu-0.2Zr-0.3Ni alloy prepared in Example 1 of this invention after aging at 500℃. The image shows a diffusely distributed nano-precipitated phase.

[0017] Figure 2 for Figure 1 The 3DAP image of the precipitated phase and the corresponding elemental distribution diagram clearly show the spatial distribution of Zr (core) and Ni (shell), confirming the existence of the core-shell structure.

[0018] Figure 3 The hardness change curves of alloys in Examples 1-3 and Comparative Example 1 (Cu-0.2Zr) after holding at different temperatures for 1 hour are shown, demonstrating the significant improvement in the softening resistance temperature of the alloys of the present invention. Detailed Implementation

[0019] The present invention will be further described in detail below with reference to the embodiments and accompanying drawings, but the scope of protection of the present invention is not limited thereto.

[0020] Example 1: A high thermal stability Cu-Zr alloy with a core-shell structure formed by Ni microalloying and its preparation method, the composition of which is: Cu-0.2wt.%Zr-0.3wt.%Ni.

[0021] Preparation method: 1. The raw materials used are high-purity oxygen-free copper (Cu content greater than 99.999 wt.%), Cu-40 wt.% Zr master alloy and pure nickel particles (Ni content greater than 99.999 wt.%), which are melted in a vacuum induction furnace and cast into ingots with a diameter of 81 mm.

[0022] 2. The ingot is solution treated at 920℃ for 4 hours.

[0023] 3. Machining removes the surface oxide scale, yielding a blank with a diameter of 80mm.

[0024] 4. The billet is hot-extruded at 800℃ to obtain a bar with a diameter of 14mm.

[0025] 5. The Φ14mm bar was cold-drawn in multiple passes to finally obtain the Φ4mm wire, with a total deformation of about 92%.

[0026] 6. The cold-drawn wire is aged in a resistance furnace at 500℃ for 1 hour.

[0027] Example 2: The difference from Example 1 is that the alloy composition is: Cu-0.18wt.%Zr-0.4wt.%Ni. The remaining steps are the same as in Example 1.

[0028] Example 3: The difference from Example 1 is that the alloy composition is: Cu-0.23wt.%Zr-0.5wt.%Ni. The remaining steps are the same as in Example 1.

[0029] A traditional Cu-Zr alloy with the composition of Cu-0.2wt.%Zr. Its preparation method is the same as that in Example 1, except that Ni is not added. The processes of melting and casting, solution treatment (950℃×4h), hot extrusion (800℃), cold drawing (to Φ4mm), and aging (450℃×1h) are the same.

[0030] Microstructure observation: TEM and 3DAP analyses were performed on the aged sample from Example 1. The results are as follows... Figure 1 , Figure 2 As shown, the presence of a dispersed precipitate phase with a size of 2-5 nm was confirmed, and Ni atoms were segregated around the Cu5Zr phase, forming a clear core-shell structure.

[0031] Softening resistance test: The final state samples of Examples 1-3 and Comparative Example 1 were kept at different temperatures (400℃, 420℃, 440℃, 460℃, 480℃, 500℃, 520℃, 540℃, 560℃, 580℃, 600℃, 620℃) for 1 hour, and then air-cooled before measuring their Vickers hardness. The results are as follows: Figure 3 As shown, Comparative Example 1 (Cu-0.2Zr) experienced a sharp decrease in hardness after holding at 500℃, indicating that its softening resistance temperature was approximately 500℃. In contrast, all alloys in the embodiments of this invention maintained more than 80% of their initial hardness after holding at 580℃, and their softening resistance temperatures were all higher than 580℃.

[0032] The electrical conductivity of the wire was tested according to GB / T 3048.2 standard (expressed as %IACS). The conductivity of alloys in Examples 1-3 was 80.3-81.4% IACS, and the conductivity of alloy in Comparative Example 1 was 88.9% IACS. This shows that the addition of 0.3-0.5 wt.% Ni only slightly decreased the conductivity, but it remained at a very high level.

[0033] Table 1. Conductivity test data of Φ4mm wires prepared by the comparative examples and embodiments of the present invention after aging treatment.

[0034] This invention, through compositional design and process innovation, successfully developed a novel Cu-Zr alloy with a core-shell structure strengthening phase exhibiting high thermal stability. This alloy perfectly balances high strength, high electrical conductivity, and extremely high softening temperature, overcoming the bottleneck problem of insufficient high-temperature performance in traditional precipitation-strengthened copper alloys. It has broad application prospects in high-end electrical engineering, electronics, and high-temperature service fields.

[0035] It should be understood that those skilled in the art can make improvements or modifications based on the above description, and all such improvements and modifications should fall within the protection scope of the appended claims.

Claims

1. A high thermal stability core-shell structure reinforced Cu-Zr alloy, characterized in that, The Cu-Zr alloy is composed of the following components by weight percentage: Zr: 0.18~0.23%, Ni: 0.3~0.5%, with the balance being Cu and unavoidable impurities; the microstructure of the Cu-Zr alloy contains a core-shell structure of nanoprecipitates with a Cu5Zr phase as the core and a Ni-rich atomic layer as the shell, and the Cu-Zr alloy is prepared by the following steps: S1. Melting and casting: According to the composition ratio, the alloy ingot is obtained by melting and casting in a vacuum induction furnace; S2. Solution treatment: The alloy ingot is subjected to solution heat treatment at 920~980℃ for 2~6 hours; S3. Hot extrusion: The solution-treated ingot is machined and then hot-extruded at a temperature of 750~850℃ to obtain hot-extruded bars; S4. Cold drawing: The hot-extruded bar is subjected to multiple cold drawing deformations, with a total deformation of not less than 90%, to obtain the cold-drawn material; S5. Aging treatment: The cold-drawn material is aged at 400~550℃ for 0.5-1.5 hours.

2. The high thermal stability core-shell structure reinforced Cu-Zr alloy according to claim 1, characterized in that, The average size of the core-shell structured nanoprecipitates is 2-5 nm.

3. A method for preparing a high thermal stability core-shell structure reinforced Cu-Zr alloy as described in claim 1 or 2, characterized in that, Includes the following steps: S1. Melting and casting: According to the composition ratio, the alloy ingot is obtained by melting and casting in a vacuum induction furnace; S2. Solution treatment: The alloy ingot is subjected to solution heat treatment at 920~980℃ for 2~6 hours; S3. Hot extrusion: The solution-treated ingot is machined and then hot-extruded at a temperature of 750~850℃ to obtain hot-extruded bars; S4. Cold drawing: The hot-extruded bar is subjected to multiple cold drawing deformations, with a total deformation of not less than 90%, to obtain the cold-drawn material; S5. Aging treatment: The cold-drawn material is aged at 400~550℃ for 0.5-1.5 hours.

4. The preparation method according to claim 3, characterized in that, The solution treatment conditions in step S2 are: heat treatment at 950°C for 4 hours.

5. The preparation method according to claim 3, characterized in that, The temperature of the hot extrusion in step S3 is 800°C.

6. The preparation method according to claim 3, characterized in that, The cold drawing deformation described in step S4 is to draw a 14mm diameter bar into a 4mm diameter wire.

7. The preparation method according to claim 3, characterized in that, The aging treatment temperature in step S5 is 450~500℃.

8. The preparation method according to claim 3, characterized in that, After the aging treatment, the alloy's resistance to softening is not lower than 580℃.

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