Aluminum substrate grid mesh belt low-defect composite coating and preparation method thereof

Abstract

The invention discloses a low-defect composite coating of an aluminum substrate grid mesh belt and a preparation method of the low-defect composite coating, and relates to the technical field of metal composite boards. According to the method, gradient passivation, bimetal spraying, ultrasonic-mechanical cooperative pressing, intelligent dynamic repairing and other methods are introduced, the porosity of the coating is successfully controlled to be 0.15% or below through comprehensive cooperative application, the sand hole density is lower than 0.01 / cm < 2 >, and compared with a traditional technology, the defect rate is reduced by 99% or above. More importantly, the problem of dynamic quality control in the continuous production process is successfully solved, so that the defect rate in continuous production is controlled to be below 0.01 / cm < 2 >, the omission ratio is lower than 0.5%, and the stability and reliability of the production process are ensured.

Description

Technical Field

[0001] This invention relates to the field of metal composite sheet technology, specifically to a low-defect composite coating for an aluminum substrate grid strip and its preparation method. Background Technology

[0002] Traditional lead-acid battery grid manufacturing uses lead alloy technology; however, this method has significant drawbacks such as excessive density, insufficient mechanical strength, and high cost. Although aluminum substrate grids have advantages in terms of lightweighting, as a reactive metal, they are prone to reacting with electrolytes (such as dilute sulfuric acid). Patent application CN112428634A discloses an aluminum-based bimetallic composite plate and its preparation method. The aluminum-based bimetallic composite plate consists of a copper layer, an intermediate layer, and an aluminum layer connected in sequence, with a corrosion-resistant protective layer disposed on the surface of the aluminum layer.

[0003] In addition, the spraying process is prone to defects such as pinholes and microcracks during use. These problems can lead to acid penetration and thus cause the protective layer to fail.

[0004] Traditional lead-acid battery grids use lead alloy casting technology, which has the following main problems: High density: Lead alloys have a density as high as 11.3 g / cm³. 3 This results in excessively heavy batteries, making it difficult to meet the urgent need for lightweight design in modern devices. For example, lead alloy grids account for more than 30% of the mass of automotive starting batteries, directly leading to increased energy consumption in the vehicle.

[0005] High cost: Although the price of raw materials for lead is lower than that for aluminum, the cost per unit volume may actually be higher due to the high density of lead alloys. Furthermore, lead processing is energy-intensive, and recycling costs are relatively high, increasing the total life-cycle cost of the battery. Data shows that lead accounts for 40% of the total production cost of lead-acid batteries, while processing energy consumption accounts for 30%.

[0006] Insufficient mechanical strength: Pure lead is soft and easily deformed, so elements such as antimony and calcium are usually added to improve its strength. However, these additives may increase the risk of gas evolution during charging and discharging, affecting battery performance. For example, lead-calcium alloy grids produce 40% more gas during 2C charging than pure lead systems, leading to a faster electrolyte drying rate. In contrast, aluminum has higher mechanical strength and can be made into thinner structures, thus saving material and increasing the volumetric energy density of the battery.

[0007] Process discreteness: Existing technologies, such as the method described in patent application CN112345678A, mainly rely on manual inspection for quality control. This approach is difficult to achieve real-time and accurate quality control in high-speed continuous production, affecting production efficiency and product quality. For example, mold temperature fluctuations exceeding ±5℃ can lead to differences in grain size, while the defect identification rate of manual inspection is only 75%, resulting in a high rate of missed detections.

[0008] In summary, traditional lead-acid battery grid manufacturing technology faces comprehensive challenges in terms of material performance, process precision, and cost control, and needs to overcome existing limitations through material substitution, process innovation, and intelligent detection technology. Summary of the Invention

[0009] This invention addresses the core problems encountered in the continuous production of aluminum substrate gates, aiming to solve the following two major challenges: 1. Reaction of aluminum with dilute sulfuric acid electrolyte: As an active metal, aluminum readily undergoes a chemical reaction upon contact with dilute sulfuric acid electrolyte, leading to a shortened battery life. Therefore, it is essential to ensure that the aluminum substrate grid does not come into contact with dilute sulfuric acid.

[0010] 2. Integrity of the protective layer on the aluminum substrate gate surface: The protective layer on the aluminum substrate gate surface must be free of any pinholes to ensure its protective performance.

[0011] To overcome these challenges, this invention introduces a series of advanced technologies, including gradient passivation, bimetallic spraying, ultrasonic-mechanical synergistic pressing, and intelligent dynamic repair. The combined application of these technologies successfully controls the coating porosity to below 0.15% and the pinhole density to below 0.01 per cm³. 2 Compared with traditional processes, the defect rate is reduced by more than 99%. More importantly, this invention also successfully solves the problem of dynamic quality control in continuous production processes.

[0012] The specific technical solution of the present invention is as follows: This invention provides a method for preparing a low-defect composite coating for a grid strip on an aluminum substrate, comprising the following steps: (a) Pretreatment of aluminum substrate: The aluminum alloy substrate is formed by continuous casting and rolling process, and the surface oxide layer is removed by laser cleaning; (b) Gradient passivation treatment: a two-stage passivation treatment is carried out by sequentially using a high-concentration inorganic acid passivation solution and an acidic solution containing a sealing agent, so that a passivation film is formed on the surface of the aluminum alloy substrate; (c) Bimetallic spraying: A pure tin bonding layer and a lead-tin alloy functional layer containing rare earth elements are sequentially sprayed onto the surface of the passivation film to form a spray coating. (d) Synergistic densification treatment: Combining ultrasonic vibration and mechanical rolling to seal the pores of the sprayed coating; (e) Dynamic defect repair: Based on machine vision online detection of coating defects after step (d), real-time repair is achieved through laser remelting.

[0013] Specifically, in step (a): the process temperature of the continuous casting and rolling is 680-700℃, the rolling speed is 15-20 m / min, and the thickness tolerance of the substrate is ≤0.02 mm; to ensure the dimensional accuracy and surface flatness of the substrate. The laser cleaning uses a fiber laser with a wavelength of 1000-1100 nm and a power of 1.5 kW to remove the surface oxide layer at a scanning speed of 2 m / s. The residual oxide layer thickness is ≤0.1 μm, which lays the foundation for improving the adhesion of the coating in the future.

[0014] Preferably, the aluminum substrate is made of 5052-H32 aluminum-magnesium alloy or 6061-T6 aluminum alloy. It has a tensile strength ≥230MPa and an elongation ≥12%, making it suitable for wire mesh forming and subsequent coating bonding.

[0015] As needed, the present invention uses a stamping machine to stamp the required aluminum plate grid battery mesh belt.

[0016] The grid undergoes surface passivation treatment to form a protective layer, preventing it from reacting with dilute sulfuric acid.

[0017] In some embodiments of the present invention, in step (b): the high-concentration inorganic acid passivation solution is a 90%-95% sulfuric acid solution, the treatment temperature is 20-30℃, and an Al2O3 underlayer with a thickness of 1.0-1.5 μm is formed; The acidic solution containing the blocking agent is a 50%-60% phosphoric acid solution with 3%-5% polyethylene glycol of molecular weight 900-1100 Da added. The total thickness of the passivation film formed is 2.0-2.5 μm, and the porosity is ≤5%.

[0018] Specifically, the two-stage etching film formation process: Stage 1 (Bottom Densification): The mesh belt enters the concentrated sulfuric acid passivation solution immersion tank, maintaining the temperature at 20℃~30℃, and the immersion time in the tank is 5 min, forming a dense passivated Al2O3 layer with a thickness of 1.0 μm; Stage 2 (Pore Sealing Stage): The mesh is placed in the second passivation tank and immersed for 2 minutes in a passivation tank containing 50%~60% phosphoric acid aqueous solution + (3%~5% PEG-1000). The phosphate ions react with the Al... 3+ The reaction generates AlPO4 to seal the residual pores, ensuring the quality and performance of the passivation film.

[0019] After the grid exits the second passivation groove, it is dried by blowing hot air at 100℃~120℃ to remove the liquid from the grid surface.

[0020] Process advantages: Compared with traditional chromate passivation, it avoids the use of toxic substances, and achieves high density and corrosion resistance of the passivation film through a two-stage reaction. In some embodiments of the present invention, in step (c): The pure tin bonding layer is prepared by arc spraying. The parameters of arc spraying are: spraying voltage 28-32 V, current 140-160 A, spraying distance 150 mm, and spraying thickness 18-22 μm. The pure tin wire with a purity ≥99.99% (wire diameter 1.2 mm, melting point 232℃) is used for arc spraying. This pure tin bonding layer serves as an anti-permeation barrier. The lead-tin alloy functional layer is prepared by plasma spraying with a plasma power of 38-42 kW; the lead-tin alloy contains 0.3-0.7 wt% cerium and the spraying thickness is 27-33 μm; the lead-tin alloy is a Pb-1.5%Sn-0.5%Ce alloy wire, and the rare earth element Ce inhibits grain boundary corrosion and enhances the acid resistance of the coating.

[0021] In some embodiments of the present invention, in step (d): The ultrasonic vibration frequency is 18-22 kHz, and the amplitude is 40-60 μm (to eliminate air bubbles in the coating). The mechanical rolling pressure is 10±0.5 MPa (to enhance coating density). The treated coating has a porosity of ≤0.2% and a surface roughness Ra of ≤0.5 μm.

[0022] Process steps: Pre-compression: The mesh is compressed by two or more ultrasonic vibrating rollers to eliminate internal stress. Main pressure: Pressed by two or more 10 MPa rollers to densify the surface; Results: Porosity can be reduced from 0.5% to 0.15%, and surface roughness Ra can be reduced from 1.5 μm to 0.4 μm, improving the mechanical properties of the coating.

[0023] In some embodiments of the present invention, in step (e): The machine vision system uses a Basler ace 2 series camera (Basler ace 2 a2A2448-210cm, project number: 109270). The algorithm used for detection is a defect recognition model based on YOLOv5 (the model is constructed with reference to patent publication number CN114663346A, and the training dataset contains 100,000 images of pinholes). The online detection accuracy is ≤50 μm, and the recognition accuracy is ≥99.5%. The laser remelting uses a fiber laser with a wavelength of 1050-1080 nm and a power of 200 W, with an energy density of 4-6 J / mm², which increases the hardness of the repaired area by 8%-12%.

[0024] The present invention also provides an aluminum substrate grid strip prepared by the method, wherein the composite coating porosity is <0.15% and the pinhole density is ≤0.01 pinholes / cm². 2 .

[0025] This invention demonstrates significant advantages over traditional processes in several key dimensions, including lightweighting, corrosion resistance, dynamic production stability, and economy. Lightweight advantage: The density of aluminum substrate grid is only 24% of that of lead alloy, achieving a weight reduction of up to 76%.

[0026] Defect control: By combining gradient passivation with bimetallic spraying technology, the density of pinholes is reduced by 98% compared with traditional aluminum-based processes, significantly improving product quality.

[0027] Dynamic stability: The application of the intelligent repair system enables the defect rate in continuous production to be controlled at 0.01 defects / cm. 2 The detection rate is below 0.5%, ensuring the stability and reliability of the production process.

[0028] Economic efficiency: The total life cycle cost is 19% lower than that of lead alloying processes, while the amount of rare earth added is reduced by 40%, which reduces production costs and environmental burden.

[0029] These significant advantages stem from process innovations across the entire workflow, particularly the integrated application of gradient passivation, bimetallic spraying, ultrasonic pressing, and intelligent repair technologies. These innovative technologies not only solve the challenges of high defect rates and dynamic quality control faced by aluminum substrate grids during production but also provide solid technical support for the development of new lead-acid batteries.

[0030] The core advantage of this invention lies in the synergistic optimization and intelligent control of the process chain, which not only improves production efficiency but also ensures the stability of product quality. In the field of power batteries, this technology provides an efficient and feasible solution for the requirements of lightweighting and high corrosion resistance, while leading the field of metal surface treatment towards a more efficient and environmentally friendly direction.

[0031] The beneficial effects of this invention are: 1. Performance Improvement: The coating defect rate has been significantly reduced; Improved quality stability under dynamic production environments makes it suitable for applications with stringent requirements for lightweighting and corrosion resistance, such as power batteries and energy storage systems.

[0032] 2. Environmental protection and economic efficiency: Using aluminum-based materials to replace lead alloys achieves the requirement of lightweight batteries and reduces the total life cycle cost. The introduction of rare earth element Ce reduces the amount of precious metals used while improving coating life. Detailed Implementation

[0033] Example 1: Full-process implementation 1. Substrate preparation 5052-H32 aluminum-magnesium alloy strip (Mg content 2.5%, Cr 0.25%) was selected and produced into aluminum strip with a thickness of 0.5±0.02 mm by continuous casting and rolling process (temperature 690℃, rolling speed 18 m / min), and then stamped into a plate grid strip with a mesh size of 3×5 mm.

[0034] 2. Gradient passivation processing First stage: Immersion in 95% concentrated sulfuric acid (30℃, 5 min) to form a dense Al2O3 layer of 1.2 μm; Second stage: Immersion in 50% H3PO4 + 3% PEG-1000 solution (2 min) to generate a 1.0 μm AlPO4 blocking layer; After hot air drying (110℃), the total thickness of the passivation film was 2.3 μm, and the porosity was 4.2% (measured by mercury porosimetry).

[0035] 3. Bimetallic spraying Base coat: pure tin (purity ≥99.99% tin wire, wire diameter 1.2 mm, melting point 232℃) arc spraying (voltage 30V, current 150 A) to form a 22 μm bonding layer; Surface coating: Pb-1.5% Sn-0.5% Ce plasma spraying (power 40 kW) to generate a 32 μm functional layer with a porosity of 0.4%.

[0036] 4. Ultrasonic-mechanical compression Ultrasonic rolling (20 kHz, 50 μm amplitude) eliminates air bubbles; After hydraulic rolling (10 MPa), the porosity of the coating decreased to 0.12%, and Ra=0.38 μm.

[0037] 5. Intelligent detection and repair Online detection module: Hardware: Basler ace 2 series high-resolution industrial camera (Basler ace 2 a2A2448-210cm, project number: 109270). Algorithm: Defect recognition model based on YOLOv5 (model construction refers to patent publication number CN114663346A, training dataset contains 100,000 trachoma images). Three pinholes (60-80 μm in size) were identified during online detection. IPG fiber laser (wavelength 1070 nm, power 200 W) for remelting of sand-hole areas (energy density 5 J / mm²). 2 After laser repair, the pinholes disappeared, and the hardness of the repaired area reached HV 58 (the original coating was HV 52).

[0038] Example 2: Dynamic Continuous Production Validation 1. Substrate preparation 5052-H32 aluminum-magnesium alloy strip (Mg content 2.5%, Cr 0.2%) was selected and a thickness of 0.5±0.02 mm was prepared by continuous casting and rolling process (temperature 700℃, rolling speed 50 m / min), and then stamped into a plate grid strip with a mesh size of 3×5 mm.

[0039] 2. Gradient passivation processing Stage 1: Immersion in 95% concentrated sulfuric acid (35℃, 5 min) to form a dense Al2O3 layer of 1.2 μm; Second stage: Immersion in 50% H3PO4 + 5% PEG-1000 solution (2 min) to generate a 1.0 μm AlPO4 blocking layer; After hot air drying (110℃), the total thickness of the passivation film was 2.2~2.4 μm, and the porosity was 4.2% (measured by mercury porosimetry).

[0040] 3. Bimetallic spraying Base coat: Pure tin (purity ≥99.99% tin wire, wire diameter 1.2 mm, melting point 232℃) arc spraying (voltage 30V, current 150 A) to form a 20 μm bonding layer; Surface coating: Pb-1.5% Sn-0.5% Ce plasma spraying (power 40 kW) to generate a 32 μm functional layer with a porosity of 0.1~0.25%.

[0041] 4. Ultrasonic-mechanical compression Ultrasonic rolling (20 kHz, 50 μm amplitude) eliminates air bubbles; After hydraulic rolling (10 MPa), the porosity of the coating decreased to 0.1~0.18%, and Ra=0.38 μm.

[0042] 5. Intelligent detection and repair Online detection module: Hardware: Basler ace 2 high-resolution industrial camera (Basler ace 2 a2A2448-210cm, project number: 109270) was used. Algorithm: YOLOv5-based defect identification model (training dataset contains 100,000 images of trachoma). Online detection identified 42 pinholes (60-80 μm in size); An IPG fiber laser (wavelength 1070 nm, power 200 W) was used to remelt the sand hole area (energy density 5 J / mm2). The sand hole repair rate after laser repair was 98.1%, and the hardness of the repaired area reached HV 58 (original coating HV 52).

[0043] Subsequent sampling tests (every 30 minutes) showed that the density of trachoma was <0.008 per cm³. 2 .

[0044] Example 3 (Boundary Parameter Verification) The preparation method is the same as in Example 1, except that: In step 2, the gradient passivation process, the first stage involves using 90% H2SO4 (20℃, 5 min) to form a passivation film with a thickness of 1.8 μm. Second stage: Immersed in 60% H3PO4 + 5% PEG-1000 solution (2 min), and after hot air drying (110℃), the passivation film has a total thickness of 2.4 μm and a porosity of 4.8%. The final test results showed that the coating porosity was 0.17% and the pinhole density was 0.011 pinholes / cm². 2 .

[0045] Example 4 (6061-T6 substrate) The substrate used was 6061-T6 aluminum alloy (Si 0.6%, Mg 1.0%), and the other steps were the same as in Example 1.

[0046] The measured film thickness after gradient passivation was 2.1 μm, and the porosity was 4.5%. The final test results showed that the coating porosity was 0.14% and the bonding strength was 26 MPa.

[0047] Comparative Example 1: Traditional lead alloy grid The grid is cast using a lead-antimony alloy containing 3% antimony, with an alloy density of 11.2 g / cm³. 3 The cast grid has a thickness of 1.2 mm. The grid was detected using a Basler ace 2 high-resolution industrial camera (Basler ace 2 a2A2448-210cm, project number: 109270) and an algorithm (a YOLOv5-based defect recognition model (training dataset containing 100,000 sand hole images)). The porosity was >5% (casting defect), and the sand hole density was 0.5 holes / cm². 2 .

[0048] Comparative Example 2: Ordinary Aluminum-based Spray Coating Process 1. Substrate preparation 5052-H32 aluminum-magnesium alloy strip (Mg content 2.5%, Cr 0.25%) was selected and produced into aluminum strip with a thickness of 0.5±0.02 mm by continuous casting and rolling process (temperature 690℃, rolling speed 18 m / min), and then stamped into a plate grid strip with a mesh size of 3×5 mm.

[0049] 2. Passivation treatment Immersion in 50% H3PO4 + 3% PEG-1000 solution (2 min) generates a 1.0 μm AlPO4 blocking layer; After hot air drying (110℃), the total thickness of the passivation film was 2.3 μm, and the porosity was 12% (measured by mercury porosimetry).

[0050] 3. Metal spraying Base coat: pure lead (purity ≥99.99% lead wire, wire diameter 1.2 mm) arc spraying (voltage 30 V, current 150 A) to form a 15 μm bonding layer; The coating was found to have a porosity of 1.2% and a pinhole density of 0.15 per cm³. 2 ; Manual sampling (once per hour) has a false negative rate of >30%.

[0051] Comparative Example 3: Single-segment passivation + traditional suppression 1. Substrate preparation 5052-H32 aluminum-magnesium alloy strip (Mg content 2.5%, Cr 0.25%) was selected and produced into aluminum strip with a thickness of 0.5±0.02 mm by continuous casting and rolling process (temperature 690℃, rolling speed 18 m / min), and then stamped into a plate grid strip with a mesh size of 3×5 mm.

[0052] 2. Passivation treatment Immersion in 50% H3PO4 solution (2 min) generates a 1.0 μm AlPO4 sealing layer; After hot air drying (110℃), the total thickness of the passivation film was 2.3 μm, and the porosity was 4.2% (measured by mercury porosimetry).

[0053] 3. Mechanical pressing After hydraulic rolling (15 MPa), the coating porosity decreased to 8.7%, and the coating bonding strength was only 18 MPa. After 4 hours of continuous production, the density of trachoma increased to 0.12 per cm. 2 .

[0054] The specific data comparison and analysis of this invention are shown in Table 1.

[0055] Table 1

[0056] *Note: The corrosion resistance test conditions are 40℃ and immersion in 30% H2SO4 until the coating fails. The 1000-hour test is a cyclic corrosion test (drying (1h) - spraying (1h)).

Claims

1. A method for preparing a low-defect composite coating on an aluminum substrate grid strip, characterized in that, Includes the following steps: (a) Pretreatment of aluminum substrate: The aluminum alloy substrate is formed by continuous casting and rolling process, and the surface oxide layer is removed by laser cleaning; (b) Gradient passivation treatment: a two-stage passivation treatment is carried out by sequentially using a high-concentration inorganic acid passivation solution and an acidic solution containing a sealing agent, so that a passivation film is formed on the surface of the aluminum alloy substrate; (c) Bimetallic spraying: A pure tin bonding layer and a lead-tin alloy functional layer containing rare earth elements are sequentially sprayed onto the surface of the passivation film to form a spray coating. (d) Synergistic densification treatment: Combining ultrasonic vibration and mechanical rolling to seal the pores of the sprayed coating; (e) Dynamic defect repair: Based on the online detection of coating defects after step (d) by machine vision system, real-time repair is achieved by laser remelting.

2. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 1, characterized in that, In step (a): the process temperature of continuous casting and rolling is 680-700℃, the rolling speed is 15-20 m / min, and the thickness tolerance of the substrate is ≤0.02mm; The laser cleaning uses a fiber laser with a wavelength of 1000-1100 nm and a power of 1.5 kW, with a residual oxide layer thickness of ≤0.1 μm.

3. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 2, characterized in that, The aluminum substrate is made of 5052-H32 aluminum-magnesium alloy or 6061-T6 aluminum alloy.

4. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 1, characterized in that, In step (b): the high-concentration inorganic acid passivation solution is a 90%-95% sulfuric acid solution, the treatment temperature is 20-30℃, and an Al2O3 underlayer with a thickness of 1.0-1.5μm is formed; The acidic solution containing the blocking agent is a 50%-60% phosphoric acid solution with 3%-5% polyethylene glycol of molecular weight 900-1100 Da added. The total thickness of the passivation film formed is 2.0-2.5 μm, and the porosity is ≤5%.

5. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 1, characterized in that, In step (c): The pure tin bonding layer is prepared by arc spraying. The parameters of arc spraying are: spraying voltage 28-32 V, current 140-160 A, spraying distance 150 mm, and spraying thickness 18-22 μm. The lead-tin alloy functional layer is prepared by plasma spraying with a plasma power of 38-42 kW; the lead-tin alloy contains 0.3-0.7 wt% cerium and the spraying thickness is 27-33 μm.

6. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 1, characterized in that, In step (d): The ultrasonic vibration frequency is 18-22 kHz, and the amplitude is 40-60 μm; The mechanical roller pressing pressure is 10±0.5 MPa; The treated coating has a porosity of ≤0.2% and a surface roughness Ra of ≤0.5 μm.

7. The method for preparing a low-defect composite coating on an aluminum substrate grid strip according to claim 1, characterized in that, In step (e): The machine vision system uses a Basler Ace 2 high-resolution industrial camera, and the algorithm model used for inspection is a YOLOv5-based defect recognition model; the online inspection accuracy is ≤50 μm, and the recognition accuracy is ≥99.5%. The laser remelting process employs a fiber laser with a wavelength of 1050-1080 nm and a power of 200 W, achieving an energy density of 4-6 J / mm². 2 .

8. The aluminum substrate grid strip prepared by the method according to any one of claims 1-7, wherein the composite coating porosity is <0.15% and the pinhole density is ≤0.01 pinholes / cm². 2 .

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