Cold-rolled composite copper steel used below electronic equipment screen and preparation method of cold-rolled composite copper steel

Abstract

The invention discloses cold-rolled composite copper steel used below an electronic equipment screen and a preparation method of the cold-rolled composite copper steel. The preparation method comprises the following steps: carrying out surface treatment on a copper strip to form a selected surface with nano-micron roughness; plating a nickel transition layer; the copper strip and the stainless steel strip are attached and subjected to cold rolling treatment, and a cold-rolled complex is obtained; performing segmented heat treatment on the cold-rolled complex to obtain a heat-treated complex; and gradient cooling treatment is conducted on the heat treatment complex, and the cold-rolled composite copper steel used below the electronic equipment screen is obtained. Through innovative raw material pretreatment, cold rolling and heat treatment processes, the thicknesses of the copper layer and the stainless steel layer are accurately controlled, and the yield strength of the prepared composite material is YSgt; the thickness of the copper layer and the thickness of the stainless steel layer are accurately controlled at the same time, and the requirements for heat dissipation, rigidity and light weight are effectively balanced.

Description

Technical Field

[0001] This invention relates to the field of metal composite materials technology, and in particular to a cold-rolled composite copper steel for use under electronic device screens and its preparation method. Specifically, it relates to a method for preparing a cold-rolled composite copper steel for use under electronic device screens that combines high rigidity, excellent heat dissipation and lightweight properties. Background Technology

[0002] As electronic devices become thinner, lighter, and more high-performance, the support and heat dissipation materials under the screen need to possess high strength, efficient heat dissipation, and lightweight characteristics. While pure copper has good thermal conductivity, its rigidity is insufficient for support requirements, and its density is relatively high. Although 316SUS stainless steel is rigid and has good corrosion resistance, its poor thermal conductivity and heavy weight cannot meet the comprehensive performance requirements of electronic devices.

[0003] Existing copper-steel composite material manufacturing processes are difficult to precisely control the thickness of each layer. They cannot achieve high strength indicators such as yield strength YS>1200Mpa(MD) and Young's modulus≥180GPa while ensuring that the copper layer thickness is about 20um to meet heat dissipation requirements and the 316SUS layer thickness is 80-100um to achieve lightweighting. Therefore, there is an urgent need to develop a new manufacturing process to meet the higher requirements of electronic products for under-screen support and heat dissipation materials. Summary of the Invention

[0004] To address the shortcomings of existing technologies, the present invention aims to provide a cold-rolled composite copper steel for use under the screen of electronic devices and its preparation method.

[0005] To achieve the aforementioned objectives, the technical solution adopted by this invention includes:

[0006] In a first aspect, the present invention provides a method for preparing cold-rolled composite copper steel for use under the screen of electronic devices, comprising:

[0007] The copper strip undergoes surface treatment to form a selected surface with a roughness at the nanometer to micrometer level;

[0008] A nickel transition layer is plated onto the selected surface;

[0009] The copper strip and stainless steel strip are bonded together and then cold-rolled to obtain a cold-rolled composite, wherein the nickel transition layer is located between the copper strip and the stainless steel strip, the cold rolling oil temperature is 15-25℃, and the cold rolling process is carried out in a protective atmosphere throughout.

[0010] The cold-rolled composite is subjected to segmented heat treatment to obtain a heat-treated composite, including a first heat treatment stage and a second heat treatment stage. The first heat treatment stage performs stress-relieving annealing at a first temperature, and the second heat treatment stage performs aging strengthening at a second temperature. The first temperature is lower than the second temperature.

[0011] The heat-treated composite is subjected to gradient cooling treatment to obtain cold-rolled composite copper steel for use under the screen of electronic devices.

[0012] Secondly, the present invention also provides a cold-rolled composite copper steel prepared by the above preparation method, which includes a stainless steel layer, a nickel transition layer and a copper layer sequentially stacked along a specified direction, wherein a copper-nickel solid solution is formed at the interface between the nickel transition layer and the copper layer, and an intermetallic compound is formed at the interface between the stainless steel layer and the nickel transition layer.

[0013] Based on the above technical solution, compared with the prior art, the beneficial effects of the present invention include at least the following:

[0014] This invention utilizes innovative raw material pretreatment, cold rolling, and heat treatment processes to precisely control the thickness of the copper and stainless steel layers. The resulting composite material exhibits a yield strength YS > 1200 MPa (MD) and a Young's modulus ≥ 180 GPa. Simultaneously, it achieves precise thickness control of the copper layer (approximately 20 μm) and the stainless steel layer (80-100 μm), effectively balancing the requirements for heat dissipation, rigidity, and lightweighting.

[0015] Through dual heat treatment and surface treatment processes, the strength, wear resistance, oxidation resistance and heat dissipation performance of the material are significantly improved. The nickel transition layer enhances the interfacial bonding force between the copper layer and the stainless steel layer. The good chemical compatibility and diffusion performance between nickel, copper and steel ensure the long-term stable operation of the material in the complex working environment of electronic equipment.

[0016] The cold-rolled composite copper steel provided by this invention is highly compatible with the requirements of precision manufacturing processes for electronic equipment, which is conducive to achieving automated and large-scale production, improving production efficiency and product quality consistency.

[0017] The above description is merely an overview of the technical solution of the present invention. In order to enable those skilled in the art to better understand the technical means of this application and to implement it in accordance with the contents of the specification, the preferred embodiments of the present invention are described below. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the cold rolling process provided in a typical embodiment of the present invention. Detailed Implementation

[0019] In view of the shortcomings of the prior art, the inventors of this invention, through long-term research and extensive practice, have proposed the technical solution of this invention. The following will further explain and illustrate this technical solution, its implementation process, and its principles.

[0020] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and therefore the scope of protection of the invention is not limited to the specific embodiments disclosed below.

[0021] Moreover, relational terms such as “first” and “second” are used merely to distinguish one component or method step from another that has the same name, and do not necessarily require or imply any such actual relationship or order between these components or method steps.

[0022] This invention aims to provide a method for preparing cold-rolled composite copper steel for use under electronic device screens. By optimizing raw material processing, cold rolling process, and heat treatment process, a method is used to prepare a product with a yield strength YS > 1200 MPa (MD), Young's modulus ≥ 180 GPa, and a copper layer thickness of approximately 20 mm. u m, 316SUS layer thickness 80-100 u m's high rigidity, efficient heat dissipation, and lightweight composite material solves the shortcomings of existing technologies in terms of performance and thickness control.

[0023] To achieve the above objectives, embodiments of the present invention provide a method for preparing cold-rolled composite copper steel for use under the screen of electronic devices, comprising the following steps:

[0024] The copper strip undergoes surface treatment to form a selected surface with a roughness at the nanometer to micrometer level;

[0025] A nickel transition layer is plated onto the selected surface;

[0026] The copper strip and stainless steel strip are bonded together and then cold-rolled to obtain a cold-rolled composite, wherein a nickel transition layer is located between the copper strip and the stainless steel strip. The cold rolling oil temperature is 15-25°C, and the entire cold rolling process is carried out in a protective atmosphere. The specific cold rolling process is as follows: Figure 1 As shown;

[0027] The cold-rolled composite is subjected to segmented heat treatment to obtain a heat-treated composite, including a first heat treatment stage and a second heat treatment stage. The first heat treatment stage performs stress-relieving annealing at a first temperature, and the second heat treatment stage performs aging strengthening at a second temperature. The first temperature is lower than the second temperature.

[0028] The heat-treated composite is subjected to gradient cooling treatment to obtain cold-rolled composite copper steel for use under the screen of electronic devices.

[0029] One of the main technical means of this invention is that a thin nickel (Ni) transition layer is plated on the surface of the copper strip. Nickel has good chemical activity and diffusion properties. During subsequent cold rolling and heat treatment, the nickel layer can form a solid solution with copper, and at the same time, it can undergo diffusion reactions with elements such as iron and chromium in stainless steel to form stable intermetallic compounds, such as Ni-Cu solid solutions and Ni-Fe intermetallic compounds, thereby effectively enhancing the interfacial bonding force between copper and stainless steel.

[0030] Some existing technologies for preparing composite copper-steel do not employ this method of strengthening the interface through an electroplated nickel transition layer. Instead, the copper and steel are bonded solely through cold rolling and atomic diffusion during heat treatment, resulting in relatively weak interfacial bonding strength. In practical applications, the interface enhancement method of this invention enables the composite material to maintain good interfacial stability even under complex conditions such as significant external forces and temperature changes, effectively preventing delamination and significantly improving the material's reliability and service life.

[0031] Some existing technologies improve the bonding between steel and copper by plating an alloy coating on both the copper and steel surfaces, but these are used in hot rolling processes, which are fundamentally different from the cold rolling processes used in this invention. The specific differences are as follows:

[0032] The process systems differ: This invention employs a cold-rolling composite process, where cold rolling is carried out at room temperature or lower. During this process, the material undergoes significant work hardening. By precisely controlling parameters such as the reduction and rolling speed in multiple rolling passes, and utilizing ultra-low temperature rolling, the grain size can be effectively refined, improving the material's strength and hardness. Simultaneously, the cold rolling process better maintains the material's surface quality, avoiding the negative impact on material properties caused by high-temperature oxidation during hot rolling. In contrast, some existing copper-steel composite technologies use hot rolling. While hot rolling provides good plasticity and ease of deformation at high temperatures, it also leads to severe surface oxidation and coarse grains, negatively affecting the material's surface quality and mechanical properties. In subsequent processing and applications, the cold-rolling composite process used in this invention produces products with higher dimensional accuracy and surface quality, making it more suitable for fields such as electronic equipment where material precision and surface quality are critical.

[0033] Secondly, there are differences in coating design and mechanism of action: This invention electroplats only a nickel transition layer on the copper surface, utilizing the good chemical compatibility and diffusion properties between nickel and copper / steel to enhance interfacial bonding. During cold rolling and heat treatment, the nickel layer forms a stable bonding phase with copper / steel through atomic diffusion, improving interfacial bonding strength at the microscopic level. In contrast, the existing technology coats both copper and steel with an alloy coating, the composition and mechanism of which differ from the nickel transition layer of this invention. This alloy coating is primarily designed to withstand the high temperature and large deformation conditions of hot rolling. During hot rolling, the alloy coating undergoes complex physicochemical reactions with copper and steel to achieve interfacial bonding. However, this coating design is not suitable for cold rolling because the lower temperatures prevent the alloy coating from fully utilizing its high-temperature reactivity and bonding effect. The nickel transition layer designed for the characteristics of cold rolling in this invention can more effectively achieve a strong bond between copper and stainless steel in a cold rolling system, improving the overall performance of the composite material.

[0034] Furthermore, this invention focuses on preparing composite materials that meet the requirements of the area beneath electronic device screens, with a particular emphasis on optimizing the material's rigidity, heat dissipation, and lightweight properties. By precisely controlling the thickness of each layer and process parameters, the copper layer thickness is controlled to approximately 20µm to ensure good heat dissipation, while the 316SUS steel layer thickness is 80-100µm to achieve lightweighting. Simultaneously, the material's yield strength YS > 1200 MPa (MD) and Young's modulus ≥ 180 GPa exhibit high rigidity. In contrast, some existing technologies, employing hot rolling processes, prioritize the characteristics of hot rolling, such as overall material plasticity and processing performance. They fail to specifically optimize and design for the high rigidity, precise heat dissipation, and lightweight balance required for the area beneath electronic device screens, resulting in a significant difference in material performance focus and application direction compared to this invention.

[0035] Regarding the specific process, in some implementations, the surface treatment includes mechanical polishing and chemical etching.

[0036] In some embodiments, the surface roughness Ra of the mating surface between the stainless steel strip and the nickel transition layer is ≤0.08 μm. Furthermore, unless otherwise specified, all roughnesses mentioned in this invention refer to Ra.

[0037] In some embodiments, the preparation method may specifically include: chemical polishing and electrochemical polishing of the bonding surface of the stainless steel strip to achieve the above-mentioned roughness index.

[0038] Regarding specific process parameters, in some implementations, the thickness of the nickel transition layer is 0.3-0.5 μm.

[0039] In some embodiments, the nickel transition layer is applied to the selected surface by electroplating.

[0040] In some embodiments, the total reduction of the cold rolling process is 55%-65%, the total number of rolling passes is 6-8, and the rolling speed is 0.2-0.4 m / min.

[0041] In some embodiments, the initial reduction in the cold rolling process is 12%-14%, with the reduction in subsequent passes decreasing sequentially. Specifically, this reduction can be linear or proportional, with the reduction rate determined by ensuring the final total reduction meets the aforementioned requirements.

[0042] In some embodiments, the copper strip has a thickness of 30-40 μm and the stainless steel strip has a thickness of 100-120 μm before the composite material is formed.

[0043] In some implementations, the thickness of the copper layer in the formed cold-rolled composite copper steel is 18-22 μm, and the thickness of the stainless steel layer is 80-100 μm.

[0044] In some implementations, the first temperature is 180-220°C, the duration of the first heat treatment stage is 30-60 min, the second temperature is 480-520°C, and the duration of the second heat treatment stage is 90-120 min.

[0045] In some implementations, the attitude cooling process specifically includes: cooling to 300°C at a rate of 10-15°C / s, and then cooling to room temperature at a rate of 3-5°C / s.

[0046] This invention precisely controls process parameters in all stages, including raw material selection and pretreatment, cold rolling composite and thinning, and heat treatment strengthening. For example, in the raw material pretreatment stage, the stainless steel strip undergoes chemical polishing combined with electrochemical polishing to reduce the surface roughness to Ra≤0.08um. This high-precision surface treatment lays the foundation for good interfacial bonding and uniform rolling deformation in the subsequent process. During cold rolling composite, the total reduction is controlled at 55%-65%, rolled in 6-8 passes, with the first pass having a reduction of 12%-14%, and subsequent passes proceeding in a decreasing gradient. The rolling speed is controlled at 0.2-0.4m / min, and an ultra-low temperature rolling process is adopted, maintaining the rolling oil temperature at 15-25℃ and introducing high-purity argon gas for protection. By precisely controlling every process parameter, the stainless steel layer thickness is reduced to 80-100um, the copper layer to about 20um, and the internal quality of the material is guaranteed to be uniform and defect-free. Many existing technologies have relatively broad control over process parameters, making it difficult to precisely control the thickness of each layer within the range required by this invention. They also do not employ advanced processes such as cryogenic rolling and argon protection. This invention has significant advantages in terms of product dimensional accuracy and performance stability, and can better meet the stringent requirements for high precision and high performance of materials under electronic device screens.

[0047] Furthermore, the raw materials used in this invention, such as stainless steel strip and copper strip, can generally be selected from SUS316 steel base strip or other stainless steel strip with similar properties, as well as high-purity electrolytic copper strip (purity ≥99.99%). Of course, they can also be appropriately adjusted, such as copper alloys with similar thermal conductivity.

[0048] As some typical application examples of the above technical solutions, the process of the preparation method provided by the present invention is as follows:

[0049] 1. Raw material selection and pretreatment

[0050] 316SUS steel base strip: High-precision 316SUS stainless steel strip is selected, with an initial thickness controlled at 100-120um. A combination of chemical and electrochemical polishing processes is used to reduce the surface roughness to Ra≤0.08um. Subsequently, solution treatment is performed in a vacuum environment at a temperature of 1050-1100℃ for 15-25 minutes, followed by rapid water cooling to room temperature to eliminate work hardening, improve the material's plasticity and toughness, and facilitate subsequent rolling thinning.

[0051] Copper layer material: High-purity electrolytic copper strip (purity ≥99.99%) with an initial thickness of 30-40 μm is selected. The surface of the copper strip is mechanically ground and chemically etched to form a micron-nano scale rough structure. Then, a nickel (Ni) transition layer with a thickness of approximately 0.3-0.5 μm is deposited using electroplating technology to enhance the interfacial bonding between copper and 316SUS steel. The nickel layer can form a solid solution with copper and simultaneously undergo diffusion reactions with elements such as iron and chromium in 316SUS steel to form stable intermetallic compounds, thereby effectively improving the interfacial bonding strength.

[0052] 2. Cold rolling composite and thinning

[0053] The pretreated copper strip is stacked with 316SUS steel base strip, with the copper strip facing the screen side. Multi-pass cold rolling composite processing is performed using an eight-roll high-precision cold rolling mill (e.g.,...). Figure 1 As shown), the total reduction is controlled at 55%-65%. Rolling is carried out in 6-8 passes, with the first pass having a reduction of 12%-14%, and subsequent passes being rolled in a decreasing gradient. The rolling speed is controlled at 0.2-0.4 m / min to ensure that the 316SUS steel layer thickness is reduced to 80-100 μm and the copper layer is reduced to about 20 μm.

[0054] During the rolling process, an ultra-low temperature rolling process is adopted, the rolling oil temperature is maintained at 15-25℃, and high-purity argon gas is introduced for protection to prevent oxidation of the material surface. At the same time, the friction coefficient and rolling force during the rolling process are reduced to avoid local deformation or cracks in the 316SUS steel layer.

[0055] 3. Heat treatment strengthening

[0056] The cold-rolled composite material undergoes a double heat treatment: first, stress-relief annealing is performed by heating at 180-220℃ in a vacuum furnace and holding for 30-60 minutes to eliminate rolling stress; then, aging strengthening treatment is performed by heating to 480-520℃ and holding for 90-120 minutes. Through the precipitation phase strengthening mechanism, fine carbides and intermetallic compounds are precipitated in the 316SUS steel matrix, thereby improving the yield strength and Young's modulus of the material.

[0057] After aging treatment, a gradient cooling process is adopted, first cooling to 300℃ at a rate of 10-15℃ / s, and then cooling to room temperature at a rate of 3-5℃ / s to further refine the grains and improve the comprehensive mechanical properties of the material.

[0058] 4. Surface treatment and finishing

[0059] High-precision laser cutting technology is used to cut composite boards to the required size for the bottom of electronic device screens. The cutting accuracy is controlled within ±0.02mm, and the cut edges are deburred by electrochemical treatment to meet the requirements of precision assembly of electronic devices.

[0060] This invention also provides a cold-rolled composite copper steel prepared by the above preparation method, which includes a stainless steel layer, a nickel transition layer and a copper layer sequentially stacked along a specified direction, wherein a copper-nickel solid solution is formed at the interface between the nickel transition layer and the copper layer, and an intermetallic compound is formed at the interface between the stainless steel layer and the nickel transition layer.

[0061] The technical solution of the present invention will be further described in detail below through several embodiments. However, the selected embodiments are only used to illustrate the present invention and do not limit the scope of the present invention.

[0062] Example 1

[0063] Raw material selection and pretreatment

[0064] 316SUS stainless steel strip with an initial thickness of 110um was selected. After chemical polishing and electrochemical polishing, the surface roughness Ra = 0.06um was obtained. The strip was then subjected to solution treatment at 1080℃, held at the temperature for 20 minutes, and then rapidly water-cooled.

[0065] A 35µm thick high-purity electrolytic copper strip was selected, mechanically ground and chemically etched, followed by electroplating to deposit a 0.4µm nickel transition layer. The plating solution used was Watt's nickel plating solution, the plating temperature was 50℃, the current density was 2A / dm², and the plating time was precisely controlled according to the required nickel layer thickness.

[0066] Cold rolling composite and thinning

[0067] Argon gas was introduced for protection, and the rolling was carried out in 7 passes on an eight-roll cold rolling mill with a total reduction of 60%. The first pass had a reduction of 13%, and the rolling speed of the remaining passes decreased linearly by 0.3 m / min. The temperature of the cooling oil was controlled to fluctuate around 20℃. The final 316SUS steel layer thickness was 90 μm, and the copper layer thickness was 21 μm.

[0068] Heat treatment strengthening

[0069] First, stress-relief annealing was performed at 200℃ for 45 minutes, followed by aging strengthening treatment at 500℃ for 105 minutes. A gradient cooling process was adopted, first cooling to 300℃ at 12℃ / s, and then cooling to room temperature at 4℃ / s.

[0070] Surface treatment and finishing

[0071] High-precision laser cutting technology was used to cut the composite sheet to the target size, with the cutting accuracy controlled within ±0.02mm. Electrochemical deburring was then performed on the cut edges. Performance test results show that the composite copper-steel prepared in this embodiment has a yield strength YS = 1260 MPa (MD), a Young's modulus of 188 GPa, and a thermal conductivity of 200 W / (m·K), meeting the application requirements below electronic device screens.

[0072] Example 2

[0073] Raw material selection and pretreatment

[0074] The initial thickness of the 316SUS stainless steel strip is 105um, and the roughness Ra after polishing is 0.05um. It is then solution treated at 1060℃ for 18min.

[0075] After processing the 32µm electrolytic copper strip, a 0.35µm nickel transition layer was deposited by electroplating. The electroplating conditions were similar to those in Example 1, with the electroplating time adjusted according to the required thickness.

[0076] Cold rolling composite and thinning

[0077] Argon gas protection was introduced, and 8 rolling passes were used with a total reduction of 62%. The first pass had a reduction of 12.5%, and the reduction decreased linearly in the remaining passes. The rolling speed was 0.25 m / min, and the temperature of the cooling oil was controlled to fluctuate around 20℃. The final thickness of the 316SUS steel layer was 85 μm, and the thickness of the copper layer was 20 μm.

[0078] Heat treatment strengthening

[0079] Stress-relief annealing at 190℃ for 35 min, aging strengthening at 510℃ for 110 min, followed by gradient cooling.

[0080] Surface treatment and finishing

[0081] High-precision laser cutting technology is used to cut the composite sheet into the required dimensions, with cutting accuracy controlled within ±0.02mm. The cut edges are then subjected to electrochemical deburring treatment. Testing revealed that the material has a yield strength YS = 1240 MPa (MD), a Young's modulus of 183 GPa, and a thermal conductivity of 195 W / (m·K), meeting the requirements of electronic equipment for high rigidity, heat dissipation, and lightweight design.

[0082] Comparative Example 1

[0083] This comparative example is basically the same as Example 1, except that the nickel plating step on the copper strip surface is omitted.

[0084] Test results: The interfacial bonding strength was significantly reduced (only 85 MPa), and localized delamination occurred in the cold-rolled composite after heat treatment. Yield strength YS = 980 MPa (MD), Young's modulus 165 GPa, and thermal conductivity 190 W / (m·K). This indicates that the absence of the nickel transition layer led to insufficient interfacial bonding and a severe decline in mechanical properties.

[0085] Comparative Example 2

[0086] This comparative example is basically the same as Example 1, except that the temperature of the cold rolling oil was not controlled (it was naturally heated to 45-50℃).

[0087] Test results: Edge cracks appeared in the stainless steel strip during rolling, and the composite thickness fluctuated by ±3 μm. Yield strength YS = 1100 MPa (MD), Young's modulus 172 GPa, thermal conductivity 185 W / (m·K). High-temperature rolling oil led to an increase in the coefficient of friction and uneven material deformation.

[0088] Comparative Example 3

[0089] This comparative example is basically the same as Example 1, except that: each rolling pass uses an equal reduction (8.6% per pass).

[0090] Test results: After the fourth pass, penetrating microcracks appeared in the copper layer, resulting in a final yield of only 68%. Yield strength YS = 1050 MPa (MD), Young's modulus 168 GPa. This demonstrates that the decreasing reduction design is crucial for protecting thin copper layers with poor ductility.

[0091] Comparative Example 4

[0092] This comparative example is basically the same as Example 1, except that the cold rolling process was not protected by argon gas (it was carried out in air).

[0093] Test results: A Cu2O oxide layer (thickness ≈ 200 nm) was detected at the interface, and the thermal conductivity decreased to 175 W / (m·K). The yield strength YS = 1020 MPa (MD), and interface corrosion occurred after 48 hours of damp heat testing (85℃ / 85%RH).

[0094] Comparative Example 5

[0095] This comparative example is basically the same as Example 1, except that stress-relief annealing is omitted and direct aging strengthening is performed.

[0096] Test results: The residual stress of the material reached 215 MPa, and the edge warping deviation during laser cutting was 0.12 mm. The yield strength YS = 1180 MPa (MD) but the dispersion reached ±8%, and the Young's modulus was 178 GPa. This indicates that stress concentration leads to unstable performance.

[0097] Comparative Example 6

[0098] This comparative example is basically the same as Example 1, except that the aging process is omitted.

[0099] Test results: Cr in the 316SUS layer 23 C6 carbides were not fully precipitated; the yield strength YS = 950 MPa (MD) and Young's modulus 155 GPa. This confirms the crucial role of aging treatment in precipitation strengthening.

[0100] Comparative Example 7

[0101] This comparative example is basically the same as Example 1, except that uniform cooling (cooling to room temperature at 4°C / s throughout the process) is used.

[0102] Test results: Metallographic findings show a 37% increase in grain size (average 12.4 μm), a yield strength YS = 1120 MPa (MD), and a 25% decrease in impact toughness. The grain refinement effect of gradient cooling was disrupted.

[0103] Detailed performance test data of the samples obtained from the above embodiments and comparative examples are shown in the table below.

[0104]

[0105]

[0106] System comparison confirms:

[0107] The nickel transition layer is the core of the interface strengthening in this invention (interface strength decreased by 60% in Comparative Example 1); ultra-low temperature rolling + argon protection effectively ensures deformation accuracy (oxidation and cracking occurred in 2 / 4 of Comparative Example 2); the use of decreasing reduction amount avoids damage to the thin copper layer (yield dropped sharply in Comparative Example 3); dual heat treatment is indispensable: stress-relief annealing eliminates cutting deformation (see Comparative Example 5); precipitation strengthening is achieved through aging treatment (e.g., strength loss of 24% in Comparative Example 6); grain refinement and strength improvement are achieved through gradient cooling (e.g., grain coarsening in Comparative Example 7 led to an 11% decrease in YS).

[0108] Based on the above embodiments and comparative examples, it is clear that the embodiments of the present invention, through innovative raw material pretreatment, cold rolling and heat treatment processes, precisely control the thickness of the copper layer and the stainless steel layer, and prepare a composite material with a yield strength YS>1200Mpa(MD) and a Young's modulus≥180GPa. At the same time, it achieves precise thickness control of the copper layer thickness of about 20um and the stainless steel layer thickness of 80-100um, effectively balancing the requirements of heat dissipation, rigidity and lightweight.

[0109] The embodiments of the present invention significantly improve the strength, wear resistance, oxidation resistance and heat dissipation performance of the material through dual heat treatment and surface treatment processes. The nickel transition layer enhances the interfacial bonding force between the copper layer and the stainless steel layer. The good chemical compatibility and diffusion performance between nickel and copper and steel ensure the long-term stable operation of the material in the complex working environment of electronic devices.

[0110] The cold-rolled composite copper steel provided in this invention is highly compatible with the requirements of precision manufacturing processes for electronic devices, which is conducive to achieving automated and large-scale production, improving production efficiency and product quality consistency.

[0111] It should be understood that the above embodiments are merely illustrative of the technical concept and features of the present invention, and are intended to enable those skilled in the art to understand the content of the present invention and implement it accordingly. They should not be construed as limiting the scope of protection of the present invention. All equivalent changes or modifications made in accordance with the spirit and essence of the present invention should be covered within the scope of protection of the present invention.

Claims

1. A method for preparing cold-rolled composite copper steel for use under the screen of electronic devices, characterized in that, include: The copper strip is surface treated to form a selected surface with a roughness at the nanometer to micrometer level; A nickel transition layer is plated onto the selected surface; The copper strip and stainless steel strip are bonded together and then cold-rolled to obtain a cold-rolled composite, wherein the nickel transition layer is located between the copper strip and the stainless steel strip, the cold rolling oil temperature is 15-25℃, and the cold rolling process is carried out in a protective atmosphere throughout. The cold-rolled composite is subjected to segmented heat treatment to obtain a heat-treated composite, including a first heat treatment stage and a second heat treatment stage. The first heat treatment stage performs stress-relieving annealing at a first temperature, and the second heat treatment stage performs aging strengthening at a second temperature. The first temperature is lower than the second temperature. The heat-treated composite is subjected to gradient cooling treatment to obtain cold-rolled composite copper steel for use under the screen of electronic devices.

2. The preparation method according to claim 1, characterized in that, The surface treatment includes mechanical polishing and chemical etching; And / or, the surface roughness Ra of the mating surface between the stainless steel strip and the nickel transition layer is ≤0.08 μm.

3. The preparation method according to claim 2, characterized in that, Specifically, it includes: The bonding surfaces of the stainless steel strip are subjected to chemical polishing and electrochemical polishing treatments.

4. The preparation method according to claim 1, characterized in that, The thickness of the nickel transition layer is 0.3-0.5 μm.

5. The preparation method according to claim 1 or 4, characterized in that, The nickel transition layer is applied to the selected surface by electroplating.

6. The preparation method according to claim 1, characterized in that, The total reduction of the cold rolling process is 55%-65%, the total number of rolling passes is 6-8, and the rolling speed is 0.2-0.4 m / min.

7. The preparation method according to claim 6, characterized in that, The initial reduction in the cold rolling process is 12%-14%, and the reduction in subsequent passes decreases sequentially.

8. The preparation method according to claim 1, characterized in that, The thickness of the copper strip is 30-40 μm, and the thickness of the stainless steel strip is 100-120 μm. And / or, in cold-rolled composite copper steel, the thickness of the copper layer is 18-22μm, and the thickness of the stainless steel layer is 80-100μm.

9. The preparation method according to claim 1, characterized in that, The first temperature is 180-220℃, and the duration of the first heat treatment stage is 30-60 min; the second temperature is 480-520℃, and the duration of the second heat treatment stage is 90-120 min. And / or, the process of the attitude cooling treatment specifically includes: cooling to 300°C at a rate of 10-15°C / s, and then cooling to room temperature at a rate of 3-5°C / s.

10. The cold-rolled composite copper steel prepared by the preparation method according to any one of claims 1-9, characterized in that, It includes a stainless steel layer, a nickel transition layer and a copper layer stacked sequentially along a specified direction, wherein a copper-nickel solid solution is formed at the interface between the nickel transition layer and the copper layer, and an intermetallic compound is formed at the interface between the stainless steel layer and the nickel transition layer.

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