Copper-chromium alloy plate strip with low surface hardness, high strength and high conductivity and preparation method thereof

Abstract

The invention provides a copper-chromium alloy plate strip with low surface hardness, high strength and high conductivity, which contains 0.2-1.5 wt% of Cr and 0.02-0.5 wt% of Zr or one or more elements of Ag, Ti, Al, Si, Zn and Ce according to needs, and the total content of the copper-chromium alloy plate strip is 0.01-0.25 wt%. The balance is substantially Cu and unavoidable impurities. The tensile strength of the alloy ranges from 480 MPa to 650 MPa, the hardness ranges from 130 HV to 180 HV, the electric conductivity ranges from 80% IACS to 90% IACS, and the ratio of the tensile strength to the hardness ranges from 3.4 to 4.0. The alloy plate strip has crystal orientation of a pure copper type rolling texture, and the texture strength meets the formula that I {112} / I0 {112} is larger than or equal to 3.0. According to the prepared copper-chromium-zirconium alloy plate strip, the hardness is remarkably reduced while high strength and electric conductivity are kept. Compared with a traditional multi-stage rolling and aging process, higher tensile strength and lower hardness are obtained under the conditions of lower energy consumption and shorter process. The deformation heat treatment method is short in period, low in energy consumption and remarkable in strengthening, and has great application value in industrial production.

Description

Technical Field

[0001] The present invention belongs to the cross-field of advanced metal materials and their preparation technologies, and is particularly aimed at the research, development and application of high-performance copper-based alloy materials. The present invention relates to the development of an innovative copper-chromium alloy plate and strip and an efficient preparation method thereof. The alloy integrates the advantages of high conductivity, high strength and good bendability of copper. The exploration in this technical field aims to provide new high-performance material solutions for multiple key industries such as electronic information, power transmission, new energy vehicles, aerospace, and precision manufacturing, to meet their urgent needs for lightweight, high strength and high conductivity. The present invention covers the optimization of the entire preparation process from hot rolling, heat treatment, cold rolling, annealing to the final product, forming a complete and efficient production technology system. Technical Background

[0002] At present, the copper alloy strips used in lead frames, connectors and other components are mainly Cu-Cr series copper alloys, such as C18400, C18150, C18080, etc., with a conductivity range of 70% to 90% IACS. Their tensile strength is between 480 and 580 MPa, their conductivity exceeds 80% IACS, and their hardness is 150 to 180 HV. Cu-Cr series alloys, with their unique performance advantages, are widely used in key components such as lead frames and connector terminals, and have become mainstream products on the market.

[0003] In recent years, with the rapid development of electric vehicles and hybrid vehicles, lightweight, electrification, heat resistance and environmental protection have become core demands. In addition, with the evolution of copper alloy terminal connectors towards high current carrying and substrate-based trends, these application scenarios have put forward more stringent requirements on the performance of copper alloy plates and strips. On the one hand, in order to ensure stable and reliable conductive contact between terminals and avoid safety hazards caused by poor contact, the alloy must have sufficient mechanical strength and excellent conductive properties. Mechanical strength ensures the integrity of the structure under external forces, while high conductivity ensures smooth transmission of current. As the trend of lightweight products intensifies, the mechanical strength of the alloy is posed with higher challenges.

[0004] On the other hand, the pins of the lead frame and the terminals of the connector need to go through a complex bending process, especially the increasingly complex shape of the female terminals, which puts higher requirements on the bending performance of the alloy. These put forward more stringent requirements on the comprehensive performance of the Cu-Cr series copper alloys, including tensile strength exceeding 600MPa, conductivity not less than 80%IACS, heat resistance temperature exceeding 500℃, and excellent bending performance. Therefore, improving the comprehensive performance of Cu-Cr series alloy strips has become the key to promoting the development of the industry.

[0005] However, the three key performance indicators of mechanical strength, electrical conductivity and bending formability often restrict each other, making it a huge challenge for Cu-Cr alloys to comprehensively improve these three aspects of performance. For example, the highly respected "MZC1" in the market has a tensile strength of 598MPa in the H state, a conductivity of about 82%IACS, and a hardness of 181HV, but its H state bending performance is only 3.75 (BW), and the higher strength SH state conductivity is only about 74%IACS, and the bending performance is only 6.25 (BW). Its bending formability still needs to be improved, which limits its application range. Therefore, overcoming this technical difficulty will not only promote the innovative development of high-strength and high-conductivity copper alloy technology, but will also better meet the urgent needs of electronic products for high-performance materials.

[0006] This patent aims to provide a new Cu-Cr series alloy and its preparation process, which can improve the ratio of alloy strength to hardness while ensuring high conductivity (≥80% IACS), increase strength and reduce hardness, so as to achieve the optimal balance between mechanical strength, conductivity and bending forming performance, thereby meeting increasingly stringent application requirements. Summary of the invention

[0007] The technical problem to be solved by the present invention is to optimize the production process based on the existing Cu-Cr alloy in response to the current connector and lead frame performance requirements of high current, light weight, high strength, high machinability, etc., in order to ensure that the conductivity of the alloy reaches 80% IACS while further improving its tensile strength and ensuring that the alloy has high bendability.

[0008] Highly processed alloys are prone to cracking when bent. This is because dislocations will continue to multiply and slip during the bending and deformation process, and the dislocation density of the highly processed alloy itself is very high, which makes it difficult for dislocations to slip during the bending process, leading to fracture. One of the macroscopic manifestations of high dislocation density is hardness. Therefore, the size of the microscopic Vickers hardness can reflect the bending performance of the alloy to a certain extent. The higher the hardness, the poorer the bending performance, and vice versa. The hardness and strength of the alloy are both manifestations of the alloy's ability to resist deformation. Therefore, hardness and strength have a certain proportional relationship. Generally, the ratio of tensile strength to hardness of Cu-Cr alloys is 3 to 3.3. This means that if you want better bending performance, you must sacrifice strength (hardness).

[0009] Although hardness and strength both reflect the alloy's ability to resist deformation to a certain extent, there is a certain proportional relationship between the two. It is unrealistic to adjust one side alone while keeping the other unchanged. However, copper alloys are crystals with significant anisotropy, that is, the strength and hardness in the three directions of rolling surface, rolling direction and perpendicular directions (usually referred to as ND, RD and TD directions) are different. As copper alloy sheets and strips for electrical and electronic components, what is required is the strength and hardness in the direction of the plate body (RD and TD), not the plate surface (ND direction). On the contrary, the higher the hardness of the plate surface (ND direction), the easier it is to crack during bending. Therefore, this patent adjusts the strength and hardness in different directions by regulating the texture of the alloy sheet and strip, and improves the ratio of the strength in the direction of alloy use and the hardness in the direction of the plate surface. Thereby achieving a perfect combination of high strength, high conductivity and excellent bending performance. The sheet and strip material is particularly suitable for electronic components such as connectors and lead frames.

[0010] To this end, the present invention provides the following technical solutions.

[0011] [Alloy composition]: The alloy composition of the present invention includes three compositions, namely, Cu-Cr alloy containing 0.2-1.5wt% Cr, and the rest being Cu and inevitable impurities. Or Cu-Cr-Zr alloy, containing 0.2-1.5wt% Cr, 0.02wt%-0.25wt% Zr, and the rest being Cu and inevitable impurities. Or Cu-Cr-X alloy, which contains 0.2-1.5wt% Cr, X includes one or more elements of Ag, Ti, Al, Si, Zn, Ce, and the total amount thereof is more than 0.01wt% and less than 0.25wt%. The rest is Cu and inevitable impurities.

[0012] In the present invention, Cr is used as the main alloy element and is dissolved into the copper matrix through solid solution treatment to form a supersaturated solid solution, and then the solid solution is decomposed into dispersed precipitate phases during heat treatment. The strength of the alloy is greatly improved. If the Cr content is too high, the size of the precipitate phase will increase and enrichment will occur, which will not only sharply reduce the electrical conductivity of the alloy, but also deteriorate the cold working performance of the alloy; if the Cr content is too low, the precipitation strengthening effect cannot be achieved. Therefore, the Cr content in the copper-chromium alloy plate and strip of the present invention is controlled within the range of 0.2wt% to 1.5wt%.

[0013] An appropriate amount of Zr element can greatly reduce the grain boundary energy, and produce solute drag and second phase pinning of grain boundaries, thereby improving heat resistance and strength; and the solubility of Zr in the Cu matrix is ​​very low, and the low-solubility alloy element Zr has a very limited effect on the overall electrical conductivity of the alloy, which can ensure the good electrical conductivity of the alloy. Therefore, the Zr content in the copper-chromium-zirconium alloy plate and strip of the present invention is controlled in the range of 0.02wt% to 0.25wt%.

[0014] Preferably, the mass percentage composition of the copper-chromium-zirconium alloy plate and strip also includes a total amount of 0.01wt% to 0.25wt% of X, and X is selected from at least one of Ag, Ti, Al, Si, Zn, and Ce.

[0015] The X element can play a certain degree of strengthening effect. In the melting and casting process, the X element can play the role of a deoxidizer, or serve as a nucleation center to increase the nucleation rate of the alloy, thereby achieving the purpose of purifying the melt and refining the grains. When the content of the optional element X is lower than 0.01wt%, the effect of purifying the melt and refining the grains is not obvious; when its content is higher than 0.25wt%, the excessive X element will have a greater negative impact on the electrical conductivity of the alloy. Therefore, the present invention controls the total content of the X element to 0.01wt% to 0.25wt%, preferably between 0.01wt% and 0.1wt%.

[0016] [Characteristics] The tensile strength of the copper-chromium alloy plate and strip in the rolling direction of the present invention is 480-650MPa; the conductivity is above 80%IACS, the softening temperature is ≥500℃, the surface hardness is 130-180HV, and the ratio of tensile strength to plate surface hardness is between 3.4 and 4.0.

[0017] [Texture] In order to achieve the same requirements for strength (hardness) and bending processability in use, first look at the distribution of Schmidt factors in each crystal orientation (see Appendix Figure 1 ). The larger the Schmidt factor, the easier it is to deform in that direction and the lower the hardness (strength); conversely, the smaller the Schmidt factor, the greater the hardness and strength.

[0018] That is to say, if we want the bending workability of the plate and strip to be better, the orientation in the plate surface (ND) direction should be closer to the center of the Schmidt factor distribution triangle; on the contrary, if we want the tensile strength to be higher, the orientation in the RD (and TD) direction should be closer to the corner of the Schmidt factor distribution triangle, especially <111> direction.

[0019] As is known to all, copper and copper alloys have two typical rolling textures, namely pure copper rolling texture (Copper texture, or C texture) and alloy rolling texture (also known as brass rolling texture, Brass texture, B texture). C texture {112} <111> (ie, the ND direction is <112> ,RD direction is <111> ); B texture {110} <112> (ie, the ND direction is <110> ,RD direction is <112> Compared with the B texture, the Schmidt factor of the C texture in the ND direction is similar, but the Schmidt factor of the B texture in the RD direction is <111> The Schmidt factor is much smaller than <112> That is to say, the tensile strength on the C-orientation RD is much higher at the same ND surface hardness. Quantitatively, it is hoped that the strength of the texture is close to that of the C texture, satisfying I{112} / I0{112}≥3.0. The X-ray diffraction intensity on the {112} crystal plane on the copper alloy plate surface is I{112}, and the X-ray diffraction intensity on the {112} crystal plane of the pure copper standard powder is I0{112}. It can ensure that the ratio of tensile strength to plate surface hardness is between 3.4 and 4.0, while the ratio of tensile strength to plate surface hardness obtained under conventional processes is only about 3.0 to 3.3 for the texture close to B.

[0020] [Manufacturing method] The second technical problem to be solved by the present invention is to provide a method for preparing the above alloy plate and strip. The process includes the following steps: melting and casting → hot rolling → rough rolling → aging heat treatment → intermediate rolling (finishing rolling);

[0021] After the melting and casting is completed, the copper-chromium series alloy ingot is subjected to insulation treatment, wherein the heating and insulation temperature is 1000-1050°C and the insulation time is 3-5h to ensure that the alloy elements are fully dissolved into the copper matrix. The present invention performs multiple hot rolling on the alloy ingot after the heating and insulation is completed, and ensures that the final rolling temperature is not less than 700°C, and then sprays water to quickly cool it to room temperature to prevent the precipitation of elements such as chromium and zirconium in this step, so that the alloy elements are in a solid solution state. The conductivity of the alloy after hot rolling should be maintained at 35-45% IACS to ensure that there are sufficient precipitation phases to provide strengthening effects in the future. When the initial temperature of hot rolling is lower than 1000°C, the temperature of the metal drops too fast during hot rolling, resulting in a final rolling temperature lower than 700°C, and the precipitation of alloy elements makes the conductivity after hot rolling higher; when the initial temperature of hot rolling is higher than 1050°C, it will cause oxidation or excessive burning of the alloy elements, resulting in serious impact on the quality of the hot-rolled billet. The deformation amount (rolling rate) of the hot rolling process is between 10% and 45%, and the rolling rate of the last three passes is between 30% and 45%, so as to provide sufficient distortion energy to promote the transformation of the copper-type texture in the hot-rolled billet, so as to control the copper-type texture strength in the finished product to meet the requirements.

[0022] The hot-rolled alloy is milled and then subjected to multiple room temperature rolling deformations to break and elongate the grains. The total deformation (rolling rate) is greater than 70%, and is generally controlled at 88-98% according to the thickness of the finished product, of which the deformation per pass (rolling rate) is 20-30%, which can promote the formation of a pure copper-type rolling texture inside the alloy.

[0023] Preferably, the rolled copper-chromium series alloy obtained after rolling is subjected to aging treatment, wherein the aging temperature is 400-500°C, the holding time is 4-8h, and then cooled to room temperature. The key is to make the alloy in an over-aged state and fully recover, which can make the alloy hardness lower than the peak aging hardness, prevent the alloy hardness from being too high after aging, and at the same time improve the conductivity of the alloy after aging. The conductivity of the over-aged alloy is about 88-90% IACS. The entire process flow has only one aging treatment, and single aging is beneficial to reducing hardness.

[0024] Due to the softening caused by the alloy recovery after over-aging, the strength and hardness of the aged alloy are at a low level. Therefore, the copper-chromium alloy after aging is rolled to control the total deformation (rolling rate) to be greater than 20%, and the single-pass deformation (rolling rate) to be 20-30%, and further enhance the copper texture orientation in the rolling direction of the alloy to improve the strength of the alloy in the rolling direction. At the same time, the hardness normal to the rolling surface is only increased by 5-10HV. The strength of the alloy after finished rolling is 480-650MPa, the hardness is 130-180HV, the conductivity is 80-90%IACS, and due to the copper texture orientation, the ratio of alloy strength to hardness is between 3.4 and 4.0.

[0025] Compared with the prior art, the technical solution of the present invention has the following advantages:

[0026] 1. The present invention utilizes a hot rolling process to treat the copper-chromium-zirconium alloy for solid solution treatment, completing the hot rolling recrystallization and solid solution treatment of the alloy ingot in one step, eliminating the solid solution treatment process required for the subsequent copper-chromium-zirconium alloy plate, shortening the process flow, improving production efficiency, and greatly reducing energy consumption.

[0027] 2. A larger total rolling process volume ensures that the alloy particles can be sufficiently crushed. The total rolling process volume is controlled at more than 70% and the single-pass process volume is controlled at 20-30%. This can effectively produce a copper-type texture inside the alloy, giving the alloy obvious anisotropy, and can significantly improve the tensile strength of the copper-chromium alloy plate in the rolling direction and reduce the hardness of the alloy in the normal direction of the rolling surface.

[0028] 3. Aging annealing does not require strict control of the copper-chromium alloy to reach the peak aging state, but rather over-aging the copper-chromium alloy, which broadens the aging temperature range of the alloy, reduces the temperature control requirements of the heat treatment furnace, and reduces the dependence on high-end annealing equipment in the production process of the copper-chromium alloy. In addition, the hardness of the over-aged copper-chromium alloy is reduced, making the alloy less likely to crack on the surface when bent, and improving the bending performance of the alloy.

[0029] 4. Since the copper texture strength will be weakened and the hardness will be low after aging annealing, a large deformation (rolling rate) rolling process is added after aging. The rolling process needs to control the total deformation (rolling rate) to be greater than 20%, generally between 20 and 70%, in order to further improve the strength of the copper texture inside the alloy, thereby improving the tensile strength of the alloy. Since the copper texture will reduce the hardness in the normal direction of the rolling surface, the hardness of the alloy will not be significantly improved after rolling, but too high a total rolling amount will also reduce the bending performance. Compared with the manufacturing process of traditional copper-chromium alloys, the present invention adopts a method of controlling texture to improve the tensile strength of the alloy, rather than achieving the target strength through precipitation strengthening of elements such as Zr and Cr. The former can improve the strength alone, while the latter can only improve the strength and hardness at the same time. Therefore, the copper-chromium-zirconium alloy manufactured by the process of the present invention has lower hardness and excellent bending performance.

[0030] The low-hardness, high-strength, high-conductivity copper-chromium-zirconium alloy of the present invention has no separate solid solution process, only one aging annealing treatment and two cold rolling processes, and has low requirements for heat treatment equipment. It has the advantages of short process flow and high yield rate. In addition, the hot rolling and cold rolling processes with large deformation (rolling rate) are the key to obtaining high strength and low hardness of the alloy. Compared with existing similar products, under the premise of ensuring the same 80-90% IACS conductivity and 480-650MPa tensile strength, it has a lower hardness (130-180HV), which is much lower than the 150-210HV of similar products, so that the strength-hardness ratio of the alloy is significantly improved, which makes the copper-chromium alloy produced by the process of the present invention have excellent bending performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The distribution diagram of Schmidt factor with different orientations.

[0032] Figure 2 The copper-chromium alloy with low surface hardness, high strength and high conductivity of the present invention is formed by rolling after aging. <111> Directional copper-type texture inverse pole figure (Example 3).

[0033] Figure 3 The comparative example is the {110} formed by rolling the copper-chromium-zirconium alloy after aging. <112> Directional brass texture inverse pole figure (Comparative Example 3).

[0034] Figure 4The texture change of the alloy of the present invention during the rolling process. DETAILED DESCRIPTION

[0035] The following examples are provided for a better understanding of the present invention, but are not intended to limit the best mode of implementation, nor to limit the content and protection scope of the present invention. Any product identical or similar to the present invention obtained by anyone under the inspiration of the present invention or by combining the features of the present invention with other prior arts shall fall within the protection scope of the present invention.

[0036] If no specific experimental steps or conditions are specified in the examples, the experiments can be carried out according to the conventional experimental steps or conditions described in the literature in the field. If no manufacturer is specified for the instruments, they are all conventional products that can be purchased commercially.

[0037] Example

[0038] Two Cu-Cr alloy embodiments (Example 1, Example 2), two Cu-Cr-Zr alloy embodiments (Example 3, Example 4), three Cu-Cr-X alloy embodiments (Example 5, Example 6, Example 7) and three similar alloy comparison examples commonly found on the market were selected, and the seven embodiments were processed into finished strips. The process flow for preparing the high-strength and high-conductivity copper-chromium alloy strip of the present invention is: batching → melting and casting → sawing → hot rolling → milling → primary cold rolling → secondary aging treatment → secondary cold rolling → straightening, specifically including the following steps:

[0039] Melting and casting: Raw materials are prepared and proportioned according to the chemical composition of copper-chromium alloy. First, the raw materials are dried to remove moisture, and then smelted in an electric furnace. Cu is first added to melt, and then intermediate alloys such as CuCr, CuZr, and CuX are added for melting and casting.

[0040] Sawing: Sawing the two end faces of the ingot to obtain an ingot with a specification of 220x420mm

[0041] Hot rolling: the ingot is heated at 1020°C and kept warm for 3 hours to homogenize the structure and composition of the ingot, and then hot rolled. According to the rolling method required by the present invention, after 9 rolling passes, the total processing rate is 92%, and the hot-rolled billet with a specification of 17x450mm is obtained by final rolling.

[0042] Solution treatment: The hot rolled billet is subjected to online quenching, i.e. solution treatment, and the surface is milled after quenching to obtain a plate with a specification of 12.6x450mm.

[0043] Cold rolling: The milled plate is subjected to secondary cold rolling, and according to the rolling method required by the present invention, 12.6 mm is rolled through 13 passes to obtain a 0.5 mm bottom material.

[0044] Aging treatment: The cold-rolled plate and strip are aged. Different aging temperatures are set according to the thickness of the bottom plate and strip, generally between 430℃ and 450℃, and the insulation time is 6 to 8 hours. Hydrogen protection is used. If the conductivity is low after aging, the conductivity of the finished product will be reduced. On the contrary, it means that the alloy has recrystallized, resulting in rapid softening of the alloy and reduced texture strength. Generally, the conductivity of the alloy after aging is guaranteed to be in the range of 88 to 90% IACS. Here, 440℃ is selected for insulation for 7 hours. After aging, the alloy is cooled with the furnace, and the conductivity of the alloy after it is taken out of the furnace is measured, which is 90% IACS.

[0045] Cold rolling: The strip after aging treatment is subjected to secondary cold rolling, and the thickness is rolled from the bottom thickness to the finished product. Different total processing rates are set within 20% to 70% according to the thickness of the finished product.

[0046] Tension straightening: The cold-rolled strip is straightened to obtain high-precision copper-chromium alloy strips. The performance of the finished product is shown in Table 1.

[0047] Electrical conductivity: measured according to the method specified in JIS H0505.

[0048] Hardness: Vickers hardness was measured with a load of 500g / 10s.

[0049] Bending performance: Plate specimens (10 mm in width) cut in the rolling direction GW and perpendicular to the rolling direction BW were bent according to the 90°W-type bending method specified in JIS H3110. The surface and cross section of the specimen after bending were observed with an optical microscope. The minimum bending radius R without cracks was obtained. The ratio R / t of the minimum bending radius R and the plate thickness t was used as an evaluation of the bending processability. The smaller the R / t value, the better the bending processability. Figure 1-4 The present invention is explained.

[0050] Obviously, the above embodiments are merely examples for the purpose of clear explanation, and are not intended to limit the implementation methods. For those skilled in the art, other different forms of changes or modifications can be made based on the above description. It is not necessary and impossible to list all the implementation methods here. The obvious changes or modifications derived from these are still within the scope of protection of the invention.

[0051] Table 1 Chemical composition of the embodiments and comparative examples

[0052]

[0053]

Claims

1. Low surface hardness, high strength and high conductivity copper-chromium alloy sheet and strip, characterized in that: It contains 0.2-1.5wt% Cr, the rest is Cu and inevitable impurities, the tensile strength is 480-650MPa, the hardness is 130-180HV, the softening temperature is ≥500°C, the conductivity is 80-90%IACS, and the ratio of tensile strength to hardness is between 3.4 and 4.

0.

2. The copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 1, characterized in that: It also contains 0.02wt% to 0.25wt% of Zr.

3. The copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 1, characterized in that: It also contains one or more elements of Ag, Ti, Si, Zn and Ce, and the total content is between 0.01wt% and 0.25wt%.

4. The copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 3, characterized in that: It contains one or more elements of Ag, Ti, Si, Zn and Ce, and the total content is between 0.01wt% and 0.1wt%.

5. The copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to any one of claims 1 to 4, characterized in that: The alloy plate and strip have a crystal orientation of a pure copper type rolling texture, and the texture strength satisfies I{112} / I0{112}≥3.0, wherein the X-ray diffraction intensity on the {112} crystal plane on the surface of the copper alloy plate is I{112}, and the X-ray diffraction intensity on the {112} crystal plane of the pure copper standard powder is I0{112}.

6. The method for manufacturing a copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to any one of claims 1 to 5, characterized in that: The process comprises the following steps, performed in sequence: S1, melt casting; S2, heat preservation treatment: heating at 1000-1050℃ for 3-5 hours; S3, hot rolling and quenching after hot rolling; S4, cold rolling treatment with a rolling rate greater than 70%; S5, aging treatment in the temperature range of 400-500°C; S6, cold rolling of finished products with a rolling rate greater than 20%.

7. The method for manufacturing a copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 6, characterized in that: In the S3 hot rolling process, multiple hot rolling passes are used, the hot rolling pass rolling rate is 10-45%, the rolling rate of the last three hot rolling passes is between 30-45%, the final rolling temperature is greater than 700°C, and the conductivity after hot rolling is maintained at 35-45% IACS.

8. The method for manufacturing a copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 6, characterized in that: S3 The alloy after hot rolling is subjected to milling treatment, and then subjected to multiple cold rolling treatments at room temperature to break and elongate the grains. The total rolling rate is controlled at 88-98% according to the thickness of the finished product, wherein the rolling rate of each pass is 20-30%.

9. The method for manufacturing a copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 6, characterized in that: In the S5 aging treatment process, the alloy is treated at 410°C to 440°C for 6 to 7 hours. The electrical conductivity of the alloy after aging treatment is 88 to 90% IACS.

10. The method for manufacturing a copper-chromium alloy sheet and strip with low surface hardness, high strength and high conductivity according to claim 6, characterized in that: The finished product of S6 is cold rolled in multiple passes, with a single-pass rolling rate of 20-30%, which further enhances the copper-type texture orientation in the alloy rolling direction to improve the strength of the alloy in the rolling direction, while increasing the hardness normal to the rolled surface by 5-10HV.

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