A copper-plated cold-rolled steel sheet for a battery pack liquid cooling plate, a liquid cooling plate, and a manufacturing method thereof

Abstract

The application discloses a copper-plated cold-rolled steel plate for a battery pack liquid cooling plate, which comprises a cold-rolled base plate and a copper-plated layer plated on the cold-rolled base plate, and the cold-rolled base plate comprises the following chemical elements in the following mass percentages: C: 0.05-0.10%, Si: 0.3-0.5%, Mn: 1.0-2.2%, Al: 0.02-0.05%, B: 0.0005-0.001%, P: less than or equal to 0.02%, S: less than or equal to 0.005%, N: less than or equal to 0.005%, and the balance of Fe and other inevitable impurities. The application further discloses a liquid cooling plate prepared from the copper-plated cold-rolled steel plate and a manufacturing method of the liquid cooling plate, which comprises the following steps: smelting and casting; hot rolling; pickling; cold rolling; continuous annealing; flattening; copper electroplating; forming a cooling medium channel on the copper-plated cold-rolled steel plate; butt jointing two copper-plated cold-rolled steel plates through brazing to form a liquid cooling plate with a cooling medium cavity; and controlling the brazing process to reach a maximum temperature of 1080-1150 DEG C and last for 10-20 s.

Description

Technical Field

[0001] This invention relates to a cold-rolled steel sheet and its manufacturing method, and more particularly to a copper-plated cold-rolled steel sheet and its manufacturing method. Background Technology

[0002] In battery manufacturing technology, especially in the manufacture of electric vehicle battery packs, liquid cooling plates are crucial components. Their primary function is to dissipate the heat generated during battery operation through the flow of liquid, ensuring the battery maintains its normal operating temperature. In battery pack cooling systems, aluminum alloys are often chosen for liquid cooling plates, mainly due to their superior corrosion resistance and excellent thermal conductivity.

[0003] However, aluminum alloy liquid cooling plates also have drawbacks. First, the design of the channels in stamped aluminum plates reduces the effective heat dissipation area, affecting the overall heat exchange efficiency of the liquid cooling plate. Secondly, aluminum alloy liquid cooling plates have certain weaknesses in terms of safety. Due to the low structural strength of welded aluminum alloys, with a yield strength typically below 100 MPa, the liquid cooling plate may be damaged during vehicle impacts, causing coolant leakage. This can damage battery cells and potentially lead to corrosion. Furthermore, aluminum has a low melting point (approximately 600°C), insufficient to meet the safety standards for battery pack protection against external fire. Finally, aluminum alloys are more expensive than steel, and the joining technology between aluminum and steel is not yet fully developed, resulting in complex joining processes and high processing costs.

[0004] Existing patent literature already relates to liquid cooling plates:

[0005] For example, Chinese patent document CN217641548U, published on October 21, 2022, entitled "A Liquid Cooling Plate for Steel Battery Packs", discloses a liquid cooling plate for steel battery packs. This patent document proposes the design concept of a liquid cooling plate and tray for steel battery packs, and proposes that the designed battery pack tray is obtained by hot stamping and its material is hot-formed steel coated with aluminum alloy; the designed water cooling plate is obtained by cold stamping and its material is low-carbon steel coated with aluminum alloy.

[0006] For example, Chinese patent document CN113594579B, published on September 5, 2023, entitled "Battery Pack Liquid Cooling Plate and Manufacturing Method Thereof, Battery Pack", discloses a battery pack liquid cooling plate and its manufacturing method, and a battery pack. This patent document provides a structural design and manufacturing method for a battery pack liquid cooling plate. In terms of design, it uniformly considers the design of the bottom box, irregular corrugated fins, sealing ring, top cover plate and bottom plate, and proposes that all structures are uniformly made of 304 stainless steel plate, which can avoid problems such as difficult steel-aluminum welding, electrochemical corrosion, poor sealing performance, poor fire and explosion resistance, and difficulty in recycling. Summary of the Invention

[0007] One of the objectives of this invention is to provide a copper-plated cold-rolled steel sheet for a battery pack liquid cooling plate. This copper-plated cold-rolled steel sheet can be used to manufacture the liquid cooling plate for the battery pack, which can improve the structural strength and corrosion resistance of the liquid cooling plate.

[0008] To achieve the above objectives, the present invention provides a copper-plated cold-rolled steel sheet for a battery pack liquid cooling plate, comprising a cold-rolled substrate and a copper-plated layer coated on the cold-rolled substrate, wherein the mass percentage of each chemical element in the cold-rolled substrate is as follows:

[0009] C: 0.05-0.10%, Si: 0.3-0.5%, Mn: 1.0-2.2%, Al: 0.02-0.05%, B: 0.0005-0.001%, P≤0.02%, S≤0.005%, N≤0.005%, balance is Fe and other unavoidable impurities.

[0010] The design principles of each chemical element in the copper-plated cold-rolled steel sheet of this invention are as follows:

[0011] C: In the copper-plated cold-rolled steel sheet described in this invention, carbon (C) is dissolved in the steel matrix as interstitial atoms or precipitated as cementite. It enhances the yield strength of the steel sheet through solid solution strengthening and precipitation strengthening. With other components remaining constant, a higher C content results in a stronger strengthening effect on the steel sheet. Due to the need to form closed coolant channels, the formed liquid-cooled sheet requires rapid high-temperature brazing (processing temperature 1080–1150°C). Although the brazing process reduces the initial strength of the strip, due to genetic influence, the C content still directly affects the grain phase, morphology, and size formed by the slow cooling after brazing austenitization of the substrate. Adding a higher C content can still ensure the tensile strength after brazing. When the mass percentage of C is too low, the strength after brazing decreases significantly, with a yield strength of less than 200 MPa, making it difficult to guarantee safety in impact. When the mass percentage of C is too high, it easily leads to a decrease in material plasticity, which has an adverse effect on the product elongation. Therefore, in the copper-plated cold-rolled steel sheet of the present invention, the mass percentage content of element C is controlled between 0.05% and 0.10%.

[0012] Si: In the copper-plated cold-rolled steel sheet of this invention, Si can dissolve in ferrite and austenite to improve the strength of the steel. Its effect is second only to C and P, and stronger than Mn, Cr, Ti, and Ni. Si can also inhibit the precipitation of carbides in ferrite, allowing dissolved C atoms to fully accumulate in austenite, thereby improving its stability. When the mass percentage content of Si is too low, it is difficult to obtain retained austenite at room temperature. When the mass percentage content of Si is too high, the surface iron oxide scale formed by Si in the heating furnace is also difficult to remove, increasing the difficulty of descaling and seriously affecting the surface quality of the steel sheet. Therefore, in the copper-plated cold-rolled steel sheet of this invention, in order to match the other components, the mass percentage content of Si is controlled between 0.3% and 0.5%.

[0013] Mn: In the copper-plated cold-rolled steel sheet of this invention, the addition of Mn element reduces the austenite-ferrite transformation temperature range of the multiphase steel. Simultaneously, Mn element can improve hardenability within the cooling capacity range of a conventional continuous annealing production line. Furthermore, Mn element readily combines with S element to form the high-melting-point compound MnS, thereby eliminating or weakening the hot brittleness caused by FeS and improving the hot working properties of the steel. Mn element is also a commonly used solid solution strengthening element in steel. Mn element can combine with C element to form various carbides, playing a precipitation strengthening role, and can also dissolve in the matrix to enhance the solid solution strengthening effect. When the mass percentage content of Mn element is too high, it will affect the elongation of the material. Therefore, in the copper-plated cold-rolled steel sheet of this invention, the mass percentage content of Mn element is controlled between 1.0% and 2.2%.

[0014] Al: In the copper-plated cold-rolled steel sheet of this invention, Al can react with free N to form aluminum nitride, thereby fixing a portion of the N atoms and reducing the amount of dissolved N atoms, which is beneficial to improving the aging resistance of the steel sheet. However, when the mass percentage content of Al is too high, it will increase the alloy cost and also form too many deoxidation products, Al2O3 inclusions, which are detrimental to the fatigue resistance of the material. Therefore, in the copper-plated cold-rolled steel sheet of this invention, the mass percentage content of Al is controlled between 0.02% and 0.05%.

[0015] B: In the copper-plated cold-rolled steel sheet of this invention, element B can form partial compounds with free nitrogen in the steel to dissolve the nitrogen, thereby reducing the content of free nitrogen and improving the material's resistance to aging. However, when the mass percentage content of element B is too high, a network-distributed precipitate phase that makes the steel brittle will precipitate at the austenite grain boundaries, leading to high-temperature "boron embrittlement," which is detrimental to high-temperature thermoplasticity. Therefore, in the copper-plated cold-rolled steel sheet of this invention, the mass percentage content of element B is controlled between 0.0005% and 0.001%.

[0016] In this invention, P, S, and N are all unavoidable impurity elements in steel. Where technical conditions permit, the content of these impurity elements in the steel should be reduced as much as possible to obtain strip steel with better performance and superior quality. Specifically:

[0017] P and S: In the copper-plated cold-rolled steel sheet of this invention, both phosphorus (P) and sulfur (S) are harmful elements in steel. In cold-rolled low-carbon steel, it is desirable to control these two elements at low levels to improve the formability of the product. Therefore, considering practical process control capabilities, in the copper-plated cold-rolled steel sheet of this invention, the mass percentage content of phosphorus can be controlled to P ≤ 0.02%, and the mass percentage content of sulfur can be controlled to S ≤ 0.005%.

[0018] N: In the copper-plated cold-rolled steel sheet of this invention, nitrogen (N) will dissolve in the steel and affect its aging properties. Due to rapid cooling after high-temperature brazing, C and N atoms will inevitably precipitate from the supersaturated α-solid solution, leading to an increase in steel strength, i.e., aging. Since the C content of this invention is relatively high, it is desirable to strictly control the N content in the strip to mitigate the effects of aging. However, considering practical process control capabilities, the mass percentage of N in the copper-plated cold-rolled steel sheet of this invention can be controlled to N ≤ 0.005%.

[0019] Furthermore, in the copper-plated cold-rolled steel sheet of the present invention, the cold-rolled substrate further contains at least one of Ti, Nb, Cr, Mo, and V, wherein Ti ≤ 0.001%, Nb ≤ 0.001%, and Cr+Mo+V ≤ 0.003%.

[0020] In the copper-plated cold-rolled steel sheet of the present invention, the design principles of the above-mentioned chemical elements are specifically described as follows:

[0021] Ti and Nb: In the copper-plated cold-rolled steel sheet of this invention, although Ti and Nb elements can combine with C and N atoms to form carbonitridium compounds of Ti and Nb, thus fixing free C and N atoms, Ti and Nb are also strengthening elements. In steel sheets with high C content, they significantly increase the strength of the steel sheet, which can cause certain difficulties in processing and forming. If the C content is reduced, the steel sheet can achieve ideal strength before brazing due to the strengthening effect of Ti and Nb, but after high-temperature brazing above 1080°C, the strength of the steel sheet will be significantly reduced compared to before brazing. Therefore, in the copper-plated cold-rolled steel sheet of this invention, the mass percentage content of Ti can be controlled to Ti≤0.001%, and the mass percentage content of Nb can be controlled to Nb≤0.001%.

[0022] Cr, Mo, and V: In the copper-plated cold-rolled steel sheet described in this invention, the microalloying strengthening effects of Cr, Mo, and V are similar to those of Ti and Nb, and they can also play a certain strengthening role. However, the material properties are also prone to fluctuation after high-temperature brazing. Therefore, in order to improve the stability of the structural strength of the brazed parts, the total mass percentage content of Cr+Mo+V in the copper-plated cold-rolled steel sheet described in this invention can be controlled to Cr+Mo+V ≤ 0.003%.

[0023] Furthermore, in the copper-plated cold-rolled steel sheet of the present invention, the thickness of the copper plating layer is 3.0 to 6.0 μm.

[0024] In this invention, the copper plating layer thickness is controlled to be 3.0 to 6.0 μm, which ensures that the copper plating layer can play a role in corrosion resistance of the internal flow channel, and at the same time play a role in brazing, so that the two opposite surfaces of the parts can be brazed together.

[0025] Furthermore, in the copper-plated cold-rolled steel sheet of the present invention, the ferrite grain size in the cold-rolled substrate is ≤20μm.

[0026] Furthermore, the copper-plated cold-rolled steel sheet of the present invention has a yield strength of 250-400 MPa, a tensile strength of 350-650 MPa, and an elongation of ≥20%.

[0027] Another object of the present invention is to provide a liquid cooling plate with good structural strength and corrosion resistance.

[0028] To achieve the above objectives, the present invention provides a liquid cooling plate made of the aforementioned copper-plated cold-rolled steel plate.

[0029] Furthermore, in the liquid cooling plate described in this invention, its yield strength is ≥240MPa, its tensile strength is ≥350MPa, and its elongation is ≥20%.

[0030] Another object of the present invention is to provide a method for manufacturing a liquid cooling plate, which can simplify the manufacturing process of the liquid cooling plate and reduce the manufacturing cost.

[0031] To achieve the above objectives, the present invention provides a method for manufacturing a liquid-cooled plate, comprising the following steps:

[0032] Smelting and casting;

[0033] Hot-rolled;

[0034] Pickling;

[0035] Cold rolling;

[0036] Continuous annealing;

[0037] smooth;

[0038] Electroplating with copper to obtain copper-plated cold-rolled steel sheet;

[0039] Cooling medium channels are formed in copper-plated cold-rolled steel sheets;

[0040] Two copper-plated cold-rolled steel sheets are brazed together to form a liquid-cooled plate with a cooling medium cavity: the maximum temperature is controlled to reach 1080-1150℃ during the brazing process and is maintained for 10-20 seconds.

[0041] In this invention, after the forming process, the resulting copper-plated cold-rolled steel sheet needs to be processed by brazing technology. In this step, two opposing steel sheet surfaces are precisely butted and pressed together. Induction heating can be used to control the maximum temperature range of 1080–1150°C, with the duration of the maximum temperature controlled to 10–20 seconds. Utilizing the excellent thermal conductivity and self-brazing properties of the copper plating layer, a strong bond is achieved between the upper and lower liquid cooling plates, forming a closed coolant channel with high-strength sealing performance. Subsequently, the water-cooled plate assembly is sprayed with water to room temperature before being removed from the furnace. Producing this liquid cooling plate through the above process maintains excellent heat dissipation performance and ensures the structural integrity and corrosion resistance of the liquid cooling plate during long-term operation.

[0042] In this invention, if the maximum temperature reached during brazing is too low, the melting point cannot be reached, and the self-brazing of the molten metal cannot be completed. Therefore, the maximum temperature reached during brazing is controlled between 1080 and 1150°C. However, if the high temperature is maintained for too long, on the one hand, the Cu layer on the surface of the liquid cooling channel will flow under gravity, which is detrimental to the corrosion protection of the cold-rolled substrate by the Cu layer; on the other hand, prolonged exposure to high temperatures will severely damage the structural strength of the steel plate. Therefore, in this invention, the duration of the high temperature is controlled to be between 10 and 20 seconds.

[0043] Furthermore, in the hot rolling step of the manufacturing method described in this invention, the heating temperature is controlled at 1180–1250°C, the final rolling temperature is controlled at 860–930°C, and the coiling temperature is controlled at 580–620°C.

[0044] In this invention, when hot-rolled slabs are prepared using continuous casting, the slabs need to be reheated. However, if the heating temperature is too high, the slab will overheat, resulting in a severe thickening of the oxide scale and defects such as surface peeling. Conversely, if the heating temperature is too low, the deformation resistance of the slab will be excessive. Therefore, in this invention, the heating temperature can be controlled between 1180 and 1250°C.

[0045] In this invention, if the hot rolling finishing temperature is too low, mixed crystals may occur during two-phase rolling. Therefore, it is necessary to ensure that rolling is carried out entirely in the austenitic region to avoid mixed crystals in the two-phase region. In addition, low-temperature rolling can also cause the sheet to have excessively high deformation resistance. Therefore, the finishing rolling temperature is controlled between 860 and 930°C.

[0046] In this invention, excessively high winding temperatures promote the continuous precipitation and coarsening of carbonitride two-phase particles during hot winding. Conversely, excessively high winding temperatures reduce element diffusion and grain boundary migration rates, thereby inhibiting ferrite grain growth. Therefore, controlling the winding temperature between 580 and 620°C in this invention can refine grains and improve microstructure uniformity.

[0047] Furthermore, in the cold rolling step of the manufacturing method described in this invention, the cold rolling reduction rate is controlled to be 60-80%.

[0048] Furthermore, in the continuous annealing step of the manufacturing method described in this invention, the annealing temperature is controlled at 760–800°C, and the soaking time is 30–60 seconds.

[0049] Furthermore, in the leveling step of the manufacturing method described in this invention, the leveling reduction rate is controlled to be 0.2% to 0.4%.

[0050] The copper-plated cold-rolled steel sheet, liquid cooling plate, and manufacturing method thereof for battery pack liquid cooling plates described in this invention have the following advantages and beneficial effects compared to the prior art:

[0051] The copper-plated cold-rolled steel sheet for battery pack liquid cooling plates described in this invention not only improves the structural strength of the liquid cooling plate, but also extends the product's service life through the corrosion resistance of the copper layer.

[0052] The copper-plated cold-rolled steel sheet for battery pack liquid cooling plates described in this invention has a cost advantage over aluminum alloys; by utilizing the self-brading property of the copper layer, the connection between the upper and lower plates can be achieved, avoiding the step of applying brazing filler metal when connecting aluminum alloy plates.

[0053] The liquid cooling plate described in this invention facilitates connection with the steel chassis and frame, avoiding welding problems between dissimilar materials and galvanic corrosion issues. This improves the overall quality and safety of the battery pack product.

[0054] The manufacturing method of the liquid cooling plate described in this invention simplifies the manufacturing process and reduces manufacturing costs. Attached Figure Description

[0055] Figure 1 The image shows a metallographic photograph of the copper-plated cold-rolled steel sheet used as a liquid cooling plate for a battery pack according to Embodiment 1 of the present invention.

[0056] Figure 2The image shows a cross-sectional metallographic photograph of a copper-plated cold-rolled steel sheet used as a liquid cooling plate for a battery pack according to Embodiment 1 of the present invention.

[0057] Figure 3 The image shows the metallographic structure of the liquid cooling plate after brazing according to Embodiment 1 of the present invention. Detailed Implementation

[0058] The copper-plated cold-rolled steel sheet, liquid cooling plate, and manufacturing method thereof for battery pack liquid cooling plates described in this invention will be further explained and described below with reference to specific embodiments and accompanying drawings. However, this explanation and description do not constitute an improper limitation on the technical solution of this invention.

[0059] Examples 1-8 and Comparative Examples 1-2

[0060] The liquid cooling plates in Examples 1-10 of this invention are all prepared using the following steps:

[0061] (1) Smelting and casting.

[0062] (2) Hot rolling: The final rolling temperature is controlled at 860-930℃, the coiling temperature is controlled at 580-620℃, and the heating temperature can be controlled at 1180-1250℃.

[0063] (3) Pickling: Pickling removes the iron oxide scale from the surface.

[0064] (4) Cold rolling: By performing cold rolling on a cold rolling mill with multiple stands, the cold rolling reduction rate can be controlled to 60-80%.

[0065] (5) Continuous annealing: After cold rolling, recrystallization continuous annealing is carried out. The annealing temperature can be controlled at 760-800℃, the annealing medium can be a non-oxidizing atmosphere of H2+N2, and the soaking time can be controlled at 30-60s.

[0066] (6) Flattening: The flattening reduction rate can be controlled to 0.2-0.4%, and then the cold-rolled substrate for the battery pack liquid cooling plate is obtained by winding.

[0067] (7) Electroplating with copper to obtain copper-plated cold-rolled steel sheet:

[0068] In some more specific implementations, the copper plating line speed can be controlled at 8.5 meters per minute, and the copper plating process can be as follows: uncoiling of cold-rolled substrate → splicing buffer zone → ultrasonic water washing → first-level alkaline washing → second-level alkaline washing → hot water rinsing → acid washing → water washing → pre-plating → electroplating copper → ultrasonic first-level water washing → ultrasonic second-level water washing → ultrasonic third-level water washing → passivation → oven drying → winding into coils → unwinding and inspection.

[0069] In some specific implementations, the thickness of the copper plating layer can be controlled to be 3.0–6.0 μm.

[0070] (8) Cooling medium channels are formed on copper-plated cold-rolled steel sheets:

[0071] In some specific implementations, computer-aided engineering (CAE) techniques, such as ANSYS software, can be used to simulate and optimize the design of coolant flow cavities to ensure the best performance of the thermal management system.

[0072] In some specific implementations, copper-plated cold-rolled steel sheets can be precisely processed into a predetermined shape using roll forming or stamping processes according to the design drawings optimized by CAE software, forming cavities for coolant flow.

[0073] (9) Two copper-plated cold-rolled steel plates are brazed together to form a liquid cooling plate with a cooling medium cavity: the brazing process is controlled to reach the maximum temperature of 1080~1150℃ and continue for 10s~20s to achieve a firm combination of the upper and lower liquid cooling plates, thereby forming a closed coolant channel with high strength sealing performance.

[0074] Table 1 lists the mass percentage of each chemical element in the copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 of the present invention and the comparative steel sheets in Comparative Examples 1-2.

[0075] Table 1. (wt%, balance Fe and other unavoidable impurities besides P, S and N)

[0076] serial number C Si Mn Al B Ti Nb Cr+Mo+V P S N Example 1 0.07 0.3 2.0 0.02 0.0005 0 0 0 0.015 0.003 0.003 Example 2 0.08 0.4 1.8 0.03 0.0006 0.0006 0.0004 0.003 0.01 0.003 0.004 Example 3 0.09 0.5 2.1 0.04 0.0008 0.0007 0.0008 0.003 0.02 0.004 0.002 Example 4 0.10 0.3 1.0 0.05 0.001 0.0008 0.0007 0.003 0.015 0.005 0.005 Example 5 0.06 0.45 1.3 0.025 0.0007 0.0009 0.0006 0.003 0.018 0.001 0.001 Example 6 0.09 0.35 1.5 0.045 0.0009 0.001 0.001 0.002 0.02 0.002 0.004 Example 7 0.05 0.5 2.2 0.02 0.0006 0.0006 0.0009 0.002 0.01 0.003 0.005 Example 8 0.10 0.4 1.2 0.03 0.0008 0.0007 0.0005 0.002 0.015 0.004 0.003 Comparative Example 1 0.15 0.6 2.3 0.04 0.0006 0.0015 0.0007 0.004 0.025 0.005 0.005 Comparative Example 2 0.02 0.45 0.8 0.03 0.007 0.039 0.005 0.002 0.02 0.004 0.005

[0077] Table 2 lists the process parameters for the liquid-cooled plates of Examples 1-8 of the present invention until the copper-plated cold-rolled steel plates are obtained, and the specific process parameters for the comparative steel plates of Comparative Examples 1-2.

[0078] Table 2.

[0079]

[0080] The copper-plated cold-rolled steel sheets for battery pack liquid cooling plates of Examples 1-8 of the present invention and the comparative steel sheets of Comparative Examples 1-2 were sampled and their microstructure was observed. The observation results are listed in Table 3.

[0081] Table 3 lists the microstructure observation results of the copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 of the present invention and the comparative steel sheets in Comparative Examples 1-2.

[0082] Table 3.

[0083] serial number Ferrite grain size (μm) in cold-rolled substrate Example 1 6.3 Example 2 8.2 Example 3 7.4 Example 4 13.9 Example 5 19.1 Example 6 10.5 Example 7 15.7 Example 8 17.1 Comparative Example 1 8.6 Comparative Example 2 13.3

[0084] As can be seen from Table 3 above, the ferrite grain size in the copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 of the present invention is all less than or equal to 20 μm.

[0085] Figure 1 The image shows a metallographic photograph of the copper-plated cold-rolled steel sheet used as a liquid cooling plate for a battery pack according to Embodiment 1 of the present invention.

[0086] like Figure 1 As shown, the cold-rolled substrate is composed of recrystallized ferrite grains and dispersed carbide particles.

[0087] Figure 2 The image shows a cross-sectional metallographic photograph of a copper-plated cold-rolled steel sheet used as a liquid cooling plate for a battery pack according to Embodiment 1 of the present invention.

[0088] like Figure 2 As shown, a relatively uniform copper layer with a thickness of 4.8 μm is plated on the cold-rolled substrate.

[0089] The copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 of the present invention and the comparative steel sheets in Comparative Examples 1-2 were sampled and their mechanical properties were tested. The test results are listed in Table 4. Wherein:

[0090] Mechanical property testing: The copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 were tested according to the requirements of GB / T228_1 Metallic materials, tensile testing - Part 1 - Room temperature test method, P5 specimen requirements.

[0091] Table 4 lists the mechanical property test results of the copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 and the comparative steel sheets in Comparative Examples 1-2.

[0092] Table 4.

[0093]

[0094] As can be seen from Table 4 above, the yield strength of the copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 of the present invention is all between 250 and 400 MPa, the tensile strength is all between 350 and 650 MPa, and the elongation is all greater than or equal to 20%.

[0095] Table 5 lists the brazing steps of the liquid cooling plates in Examples 1-8 of the present invention and the specific process parameters of the comparative steel in Comparative Examples 1-2.

[0096] Table 5.

[0097] serial number Brazing temperature (°C) Duration (s) Example 1 1084 20 Example 2 1091 10 Example 3 1122 15 Example 4 1137 12 Example 5 1141 18 Example 6 1150 19 Example 7 1129 16 Example 8 1145 20 Comparative Example 1 1184 50 Comparative Example 2 1195 20

[0098] Samples were taken from the liquid-cooled plates of Examples 1-8 of the present invention and the comparative steels of Comparative Examples 1-2, and their mechanical properties were tested. The test results are listed in Table 6. Wherein:

[0099] Mechanical property testing: The copper-plated cold-rolled steel sheets used for liquid cooling plates of battery packs in Examples 1-8 were tested according to the requirements of GB / T228_1 Metallic materials, tensile testing - Part 1 - Room temperature test method, P5 specimen requirements.

[0100] Table 6 lists the mechanical property test results of the liquid-cooled plates of Examples 1-8 of the present invention and the comparative steels of Comparative Examples 1-2.

[0101] Table 6.

[0102]

[0103]

[0104] As can be seen from Table 6 above, the yield strength of the liquid cooling plates of Examples 1-8 and the comparative steel of Comparative Examples 1-2 are all greater than 240 MPa, the tensile strength is all greater than 350 MPa, and the elongation is all greater than or equal to 20%.

[0105] Figure 3 The image shows the metallographic structure of the copper-plated cold-rolled steel sheet used for the liquid cooling plate of the battery pack according to Embodiment 1 of the present invention after brazing.

[0106] like Figure 3 As shown, after high-temperature brazing, the substrate microstructure is transformed into a relatively uniform and fine bainitic microstructure and a small amount of retained austenite.

[0107] Furthermore, to verify the corrosion resistance performance of the inner flow channel of the copper-plated cold-rolled steel sheet used for the liquid cooling plate of the battery pack described in this invention after brazing, this case also adopted a simulation evaluation method for the corrosion resistance performance of the inner flow channel:

[0108] Six parallel specimens (50×25mm) were cleaned and strung together for corrosion resistance testing. The specimens were separated by plastic gaskets and placed in a glass container filled with the mixed solution. The test temperature was 88±2℃, and the test period was 336±2h. The test solution consisted of 40% antifreeze and 60% corrosive water (volume ratio). The corrosive water was prepared by adding 148mg sodium sulfate, 1320mg sodium chloride, and 138mg sodium bicarbonate to 1L of distilled water and stirring until completely dissolved. Changes in the appearance of the solution and specimens after the test were recorded, including whether the solution became cloudy and the specimens rusted, whether the change in specimen mass was ≤3mg / specimen, and whether the pH change of the solution was ≤0.5. Table 7 lists the corrosion resistance results of the internal flow channels in Examples 1-8 and Comparative Examples 1-2.

[0109] Table 7.

[0110]

[0111] Therefore, the internal flow channel of the liquid cooling plate prepared by this invention has excellent corrosion resistance.

[0112] It should be noted that the combination of the technical features in this case is not limited to the combination methods described in the claims of this case or the combination methods described in the specific embodiments. All technical features described in this case can be freely combined or combined in any way, unless they contradict each other.

[0113] It should also be noted that the embodiments listed above are merely specific embodiments of the present invention. Obviously, the present invention is not limited to the above embodiments, and similar changes or modifications made thereto are those that can be directly derived or easily conceived by those skilled in the art from the content disclosed in the present invention, and should all fall within the protection scope of the present invention.

Claims

1. A copper-plated cold-rolled steel sheet for a battery pack liquid cooling plate, comprising a cold-rolled substrate and a copper-plated layer coated on the cold-rolled substrate, characterized in that, The mass percentage of each chemical element in the cold-rolled substrate is as follows: C: 0.05-0.10%, Si: 0.3-0.5%, Mn: 1.0-2.2%, Al: 0.02-0.05%, B: 0.0005-0.001%, P≤0.02%, S≤0.005%, N≤0.005%, balance is Fe and other unavoidable impurities.

2. The copper-plated cold-rolled steel sheet as described in claim 1, characterized in that, The cold-rolled substrate further contains at least one of Ti, Nb, Cr, Mo, and V, wherein Ti ≤ 0.001%, Nb ≤ 0.001%, and Cr+Mo+V ≤ 0.003%.

3. The copper-plated cold-rolled steel sheet as described in claim 1, characterized in that, The thickness of the copper plating layer is 3.0 to 6.0 μm.

4. The copper-plated cold-rolled steel sheet as described in claim 1, characterized in that, Its yield strength is 250–400 MPa, tensile strength is 350–650 MPa, and elongation is ≥20%.

5. A liquid-cooled plate, characterized in that, It is made from copper-plated cold-rolled steel sheet as described in any one of claims 1-4.

6. The liquid cooling plate as described in claim 5, characterized in that, Its yield strength is ≥240MPa, tensile strength is ≥350MPa, and elongation is ≥20%.

7. The method for manufacturing a liquid-cooled plate as described in claim 5 or 6, characterized in that, Including the following steps: Smelting and casting; Hot-rolled; Pickling; Cold rolling; Continuous annealing; smooth; Electroplating with copper to obtain copper-plated cold-rolled steel sheet; Cooling medium channels are formed in copper-plated cold-rolled steel sheets; Two copper-plated cold-rolled steel sheets are brazed together to form a liquid-cooled plate with a cooling medium cavity: the maximum temperature is controlled to reach 1080-1150℃ during the brazing process and is maintained for 10-20 seconds.

8. The manufacturing method as described in claim 7, characterized in that, In the hot rolling process, the heating temperature is controlled at 1180–1250℃, the final rolling temperature is controlled at 860–930℃, and the coiling temperature is controlled at 580–620℃.

9. The manufacturing method as described in claim 7, characterized in that, In the cold rolling process, the cold rolling reduction rate is controlled to be 60-80%.

10. The manufacturing method as described in claim 7, characterized in that, In the continuous annealing step, the annealing temperature is controlled at 760–800℃, and the soaking time is 30–60s; and / or in the leveling step, the leveling reduction rate is controlled at 0.2–0.4%.

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