High-wear-resistance and corrosion-resistance treatment process for surface of automobile part die-casting die

Abstract

The invention belongs to the technical field of automobile die-casting dies, and discloses an automobile part die-casting die surface high-wear-resistance and corrosion-resistance treatment process which comprises the steps that a die is cleaned; polishing the surface; mold defects are recognized, and corresponding repairing measures are taken according to different defects; carrying out nitriding treatment on the cleaned and polished die subjected to defect repair; the mold is subjected to gas nitriding treatment, and then key parts and components are subjected to ion nitriding treatment; hard chromium plating treatment; chemical hole sealing and organic coating hole sealing treatment: multi-point detection is carried out, and it is ensured that the hardness of the nitriding layer and the hardness of the chromium plating layer meet the requirement. According to the method, fine defects of the mold can be found, and the wear resistance and corrosion resistance are improved through combination of gas nitriding treatment and key part ion nitriding treatment; through hard chromium plating treatment, surface performance strengthening, double hole sealing treatment, protection effect strengthening and adoption of the nano-powder addition amount and a pulsed electric field directional arrangement method, a plating layer is more uniform and compact, and the hardness and wear resistance of the plating layer are improved.

Description

Technical Field

[0001] The present application relates to the technical field of automobile die-casting molds, and more specifically, to a high-wear-resistant and corrosion-resistant surface treatment process for automobile parts die-casting molds. Background Art

[0002] The most common failure mode for die-casting molds for automotive parts is failure of the mold's working surface. Proper surface treatment of die-casting molds can significantly improve their corrosion and thermal fatigue resistance, thereby enhancing mold quality and extending their service life.

[0003] The document with the prior art publication number CN107868956B provides a corrosion-resistant and wear-resistant process for the surface of an automobile die-casting mold, including the steps of mold pretreatment, preparation of a wear-resistant coating, coating of a wear-resistant molten layer, coating of a deposition reinforcement layer, and application of lubricating oil. The wear-resistant molten layer uses PEEK resin as the main raw material. The resin has the advantages of high temperature resistance, wear resistance, and good self-lubricating properties. High-strength glass fiber is added to enhance wear resistance and mechanical properties. The mold surface is treated with material deposition by electrospark deposition. This method has high coating bonding strength, small heat-affected zone, and high deposition efficiency. The deposition material is a mixture of solid powder of Cr, ZnO, Co, and nano-TiO2, which has excellent corrosion resistance. Perfluoropolyether lubricant is applied to the surface of the coating to play a role of lubrication and protection. The treatment process is simple and easy to operate, with high execution efficiency. The treated automobile die-casting mold has excellent corrosion resistance and wear resistance.

[0004] Although the above-mentioned existing technical solutions can achieve relevant beneficial effects through the structure of existing technology, they still have the following defects: 1. It is impossible to detect subtle defects in the mold in time, which makes it difficult to guarantee the quality of the mold, and then causes a high scrap rate of castings due to mold defects. 2. In terms of improving the wear and corrosion resistance of the mold, the previous gas nitriding or ion nitriding treatment is relatively simple, which makes the key parts of the mold easy to wear and corrode, and the accuracy of the die-casting products is difficult to guarantee. 3. The existing hard chromium plating treatment effect is poor, and the corrosion resistance of the mold is also weak in complex die-casting environments. It is unable to effectively prevent the intrusion of corrosive media, and lacks the further protection of the organic coating, making it difficult to significantly enhance the protective performance of the mold.

[0005] In view of this, we propose a high wear-resistant and corrosion-resistant treatment process for the surface of die-casting molds for automotive parts. Summary of the Invention

[0006] 1. Technical problems to be solved

[0007] The purpose of this application is to provide a high wear-resistant and corrosion-resistant treatment process and method for the surface of die-casting molds for automotive parts, which solves the technical problems raised in the above-mentioned background technology, and realizes timely detection of subtle defects in the mold through precise image analysis to ensure the quality of the mold; improves the wear resistance and corrosion resistance by combining gas nitriding treatment and ion nitriding treatment of key parts; strengthens the surface performance through hard chromium plating treatment, further improves the surface hardness and wear resistance of the mold, reduces the surface friction coefficient, makes the casting easier to demold, and at the same time enhances the corrosion resistance of the mold and improves the corrosion resistance of the mold in complex die-casting environments; enhances the protection effect through double sealing treatment, effectively prevents the invasion of corrosive media, and improves the corrosion resistance of the mold; adopts the method of nano-powder addition and pulse electric field directional arrangement to make the coating more uniform and dense, and significantly improve the hardness and wear resistance of the coating.

[0008] 2. Technical solution

[0009] The technical solution of this application provides a high wear-resistant and corrosion-resistant treatment process for the surface of a die-casting mold for an automotive component, comprising the following steps:

[0010] S1. Mold Cleaning: Place the mold in a dedicated cleaning tank and soak it in an alkaline detergent at 50-60°C for 30-40 minutes to remove oil, release agent residue, and other impurities from the mold surface. Subsequently, flush the mold with a high-pressure water gun at a pressure of 15-20 MPa, using cavitation jet technology (cavitation collapse pressure to concentrate pore cleaning) to ensure that no contaminants remain on the surface.

[0011] S2. Surface grinding: Use 80-120 grit sandpaper to perform preliminary grinding on the mold surface to remove minor scratches and unevenness. Then, use 200-300 grit sandpaper for fine grinding to reduce the mold surface roughness to Ra0.8-1.6μm.

[0012] S3. Image Analysis and Defect Repair: After surface polishing, the mold is transferred to an inspection station equipped with high-definition image acquisition equipment. Multiple industrial-grade high-definition cameras capture comprehensive images of the mold surface from various angles. Defect analysis is performed on these high-definition images to promptly identify mold defects (such as scratches, pinholes, and pores). Appropriate repair measures are implemented for each defect type, ensuring that the mold surface quality meets the requirements of subsequent processing.

[0013] S4. Nitriding treatment: Nitriding treatment is performed on the mold after cleaning, polishing and defect repair; including gas nitriding and ion nitriding;

[0014] S41. Gas Nitriding: The cleaned, polished, and defect-repaired mold is placed in a nitriding furnace and ammonia (NH3) is introduced as the nitriding medium. The furnace is maintained at a temperature of 500-550°C, with a pressure of 1-2 kPa, for 8-10 hours. Ammonia decomposes at high temperatures to produce active nitrogen atoms, which react chemically with the metal atoms on the mold surface, forming a nitrided layer with high hardness and excellent wear resistance. The thickness of the nitrided layer can generally reach 0.02-0.05 mm.

[0015] S42. Ion Nitriding: Ion nitriding is performed on key mold parts. The mold serves as the cathode and is placed in an ion nitriding furnace, where a mixture of nitrogen (N2) and hydrogen (H2) is introduced. At a temperature of 450-500°C and a voltage of 500-800V, glow discharge is applied to ionize the gas. Nitrogen ions bombard the mold surface at high speeds under the action of the electric field, completing the nitriding process. Ion nitriding is suitable for situations where the performance requirements for key mold parts are extremely high, such as the core and cavity of die-casting molds, which are prone to wear and corrosion, as well as for precision molds that require high mold precision and do not require significant deformation. The ratio of nitrogen (N2) to hydrogen (H2) ranges from 3:1 to 1:1. The ratio depends on factors such as the mold material, specific usage requirements, and the characteristics of the ion nitriding equipment. During the gas ionization process, nitrogen molecules are ionized under the action of an electric field. Accelerated by the electric field, the nitrogen ions bombard the mold surface and react with metal atoms to form a nitride layer. Ion nitriding can make the nitride layer denser and harder.

[0016] S5. Hard chromium plating: Use a mixed plating solution of chromic acid (H2CrO4) and sulfuric acid (H2SO4), where the chromic acid concentration is 250-300g / L and the sulfuric acid concentration is 2.5-3g / L. In order to improve the quality of the coating, add an appropriate amount of additives, such as rare earth element compounds, and the addition amount is generally 0.1-0.3g / L. The additive can also be an organic sulfonic acid (such as methanesulfonic acid, ethylsulfonic acid, etc.), and the amount is 1-5g / L. The mold that has been nitrided is used as the cathode and the lead-antimony alloy is used as the anode and placed in the plating solution. At a temperature of 50-60°C, control the current density to 30-50A / dm 2 The electroplating time is 2-3 hours. During the electroplating process, chromium ions obtain electrons on the cathode surface and deposit to form a hard and smooth chromium plating layer with a thickness of 0.02-0.03mm.

[0017] S6. Sealing treatment:

[0018] S61. Chemical Sealing: Immerse the hard chrome-plated mold in a sealing solution containing nickel salt and fluoride. Maintain the solution temperature at 80-90°C for 15-20 minutes. Nickel ions and fluoride ions react chemically on the mold surface, forming an insoluble nickel fluoride that fills the tiny pores in the chrome plating and improves the mold's surface corrosion resistance.

[0019] S62. Organic Coating Sealing: To further enhance the sealing effect, apply an organic coating after chemical sealing. Choose an organic coating with excellent corrosion and wear resistance, such as polytetrafluoroethylene (PTFE). Apply the coating evenly to the mold surface using a spray coating, maintaining a thickness of 0.05-0.1mm. Then, cure at 180-200°C for 1-2 hours to firmly bond the organic coating to the mold surface.

[0020] S7. Quality Inspection: Use a Vickers hardness tester to conduct multiple inspections at different locations on the mold surface to ensure that the hardness of the nitride layer and the chrome plating layer meet the requirements. The hardness of the nitride layer should reach HV900-1200, and the hardness of the chrome plating layer should reach HV800-1000.

[0021] Furthermore, the alkaline cleaning agent is a compound alkaline cleaning agent, which is composed of sodium hydroxide (10-15 g / L), trisodium phosphate (5-10 g / L), and sodium silicate (1-5 g / L).

[0022] As an optional solution of the present invention, image defect analysis accurately identifies various defects on the mold surface, such as scratches, pinholes, and pores, and includes the following steps:

[0023] 1. Image preprocessing: Multiple industrial-grade high-definition cameras are used to simultaneously capture the mold surface from different angles, ensuring complete coverage of all areas of the mold and obtaining comprehensive mold surface image information. The captured images are preprocessed, including grayscale conversion, noise reduction, and image enhancement.

[0024] 2. Scratch recognition:

[0025] 2.1. Edge Detection: Use edge detection algorithms, such as the Canny edge detection algorithm, to process the preprocessed image to highlight edge information. Scratches typically appear as continuous lines in an image. Edge detection can enhance the contrast between these lines and the surrounding area, making scratches easier to identify.

[0026] 2.2 Line Continuity Analysis: Line tracing is performed on the edge-detected image to determine line continuity. Scratches are generally characterized by long continuous lines. By setting a minimum continuous line length threshold, lines that may be scratches can be screened out.

[0027] 2.3 Width Measurement: For the initially identified scratch line, calculate its width in the image. By analyzing the distribution of pixels around the line, the line boundary is determined, and the scratch width is measured.

[0028] 2.4 Grayscale Change Analysis: Analyze the grayscale value changes of pixels along the scratch line. While the grayscale value distribution on a normal mold surface is relatively uniform, the grayscale value at the scratch site typically differs from the surrounding area. By calculating the rate of change in grayscale value, the software can further confirm the presence of a scratch and infer its depth based on the magnitude of the grayscale change.

[0029] 3. Identification of sand holes and pores:

[0030] 3.1. Binarization: The software binarizes the preprocessed image. Based on the grayscale difference between the mold surface and the defective area, an appropriate threshold is set to divide the image into the foreground (defective area) and the background (normal mold surface area). Sand holes and pores typically appear as black holes in the binary image (assuming the foreground is black and the background is white).

[0031] 3.2 Morphological Processing: Use morphological operations, such as erosion and dilation, to optimize the binary image. Erosion can remove isolated noise points and minor interference areas in the image, while dilation can restore defect areas that have been reduced by erosion, making the shapes of sand holes and pores clearer and more complete, facilitating subsequent feature extraction and recognition.

[0032] 3.3. Shape Feature Extraction: Shape feature extraction is performed on the morphologically processed image, calculating the area, perimeter, circularity, and other shape parameters of each black area (potential pores or air holes). Porphyry and air holes typically have circular or nearly circular shape characteristics. By comparing these shape parameters with the preset pore and air hole shape model parameters, a preliminary judgment can be made as to whether the black area is a pore or air hole.

[0033] 3.4 Edge Clarity Analysis: For the initially identified pores and air holes, analyze their edge clarity. The edges of pores and air holes are relatively clear, with distinct boundaries from the surrounding area. By calculating the edge gradient or edge sharpness index, we can further confirm whether these areas are true pores and air holes. A higher edge gradient or sharpness index indicates a clear edge, consistent with the characteristics of pores and air holes.

[0034] 3.5. Contrast Analysis: Calculate the grayscale contrast between the pinhole and pore areas and the surrounding normal mold surface areas. The grayscale values of pinhole and pore areas often differ significantly from those of the surrounding areas. Contrast analysis can quantify this difference, enabling more accurate identification of pinholes and pores. For example, a contrast threshold can be set. When the contrast between a region and its surroundings exceeds this threshold, the region is identified as a possible pinhole or pore.

[0035] 4. Defect Report Generation: Identified defects such as scratches, pinholes, and pores are marked on the original mold image, clearly displaying their locations using specific colors and symbols (e.g., red circles for pinholes and pores, red lines for scratches). For each defect, the software records its type (scratch, pinhole, or pore) and the analyzed dimensions. The software then summarizes the location, type, and dimensions of all defects to generate a detailed defect report.

[0036] As an optional solution of the present invention, the electroplating treatment is performed using a 0.5 g / L nanopowder addition + pulse electric field directional arrangement method, including the following steps:

[0037] 1. Nanopowder pretreatment:

[0038] 1.1. Powder screening and activation:

[0039] 1.1.1 Select 4-6nm single crystal diamond powder (purity ≥ 99.9%, SEM test confirms no agglomeration);

[0040] 1.1.2. Activate in a vacuum plasma treatment device (power 500W, Ar gas atmosphere) for 30 minutes to enhance surface wettability;

[0041] 1.2. Prepare the suspension: 0.5 g nanopowder + 100 mL deionized water. First, magnetically stir for 1 hour (1200 rpm), then ultrasonicate for 30 minutes (40 kHz, 200 W), and then continue magnetic stirring for another 30 minutes. This should be performed in a dust-free environment or on a clean bench.

[0042] 2. Dispersion stability control:

[0043] 2.1. Add 0.1% by mass of sodium dodecyl sulfate (SDS) as a dispersant;

[0044] 2.2. Use an ultrasonic cell disruptor (20kHz, 300W power, 5s on / 2s off pulse mode). Monitor the temperature using a temperature sensor. If the temperature exceeds 30°C, pause the treatment for 10 minutes and resume after the temperature drops. Check the instrument's working status regularly during the treatment process.

[0045] 2.3. Dynamic light scattering (DLS) was used to detect the particle size distribution. The measurements were repeated three times with an interval of 5 minutes between each measurement and the average value was taken. The requirements were D50 = 6.2 nm and PDI < 0.2.

[0046] 3. Constructing the plating solution system:

[0047] 3.1. Slowly add 280±5g / L of chromic acid (H2CrO4) into the plating solution container. Pre-add an appropriate amount of deionized water (about 1 / 3 of the final plating solution volume) into the container. During the addition, turn on the stirring device and set the stirring speed to a low level (such as a magnetic stirrer at 300-400 rpm) to allow the chromic acid to gradually dissolve.

[0048] 3.2. Slowly add 2.8±0.1g / L sulfuric acid to the solution containing dissolved chromic acid, stirring while adding. Do not add too quickly (control the rate to 1-2 drops per second) to prevent splashing of the solution and a violent chemical reaction. Increase the stirring speed to 400-500 rpm to ensure uniform dispersion of the sulfuric acid and thorough mixing with the solution.

[0049] 3.3. Place 0.5g / L of the measured nanodiamond suspension into another container and slowly heat it to 40°C using a heating device (such as a constant temperature water bath). During the heating process, the suspension must be continuously stirred (a magnetic stirrer can be used at about 300 rpm) to prevent local overheating from causing nanoparticle agglomeration. The suspension temperature can be monitored in real time using a thermometer. When the temperature of the nanodiamond suspension reaches 40°C, slowly add it to the plating solution container, turn on the stirring device and appropriately increase the stirring speed to 500-600 rpm so that the nanodiamond suspension can be quickly and evenly dispersed into the plating solution. The addition process needs to be stirred continuously for 15-20 minutes to ensure its uniformity.

[0050] 3.4. Slowly add 3.5g / L of methanesulfonic acid to the plating solution, stirring at 500-600 rpm to ensure rapid and uniform dispersion of the methanesulfonic acid. Continue stirring for 10-15 minutes after addition.

[0051] 3.5. Slowly add 0.2g / L of rare earth cerium nitrate to the plating solution while stirring continuously at a speed of 500-600 rpm to ensure that it is fully dissolved and evenly dispersed in the plating solution. After the addition is complete, stir for another 10-15 minutes.

[0052] 3.6. After all components have been added, add deionized water to the plating solution container to adjust the plating solution volume to the target total volume. Stir continuously during the water addition process to ensure more uniform mixing of the plating solution. Use heating and thermostat equipment to adjust the plating solution temperature to 55±1°C. Monitor temperature changes in real time using a high-precision thermometer. Adjust the stirring speed appropriately during this process to promote uniform temperature distribution. Once the temperature stabilizes within the target range, the plating solution system is complete and can be prepared for subsequent electroplating operations.

[0053] 4. Set pulse plating process parameters:

[0054] 4.1. Magnetic field-assisted positioning: Apply a 0.5 T horizontal magnetic field (NdFeB permanent magnet array) to orient the nanoparticles along the magnetic field lines; monitor the conductivity of the plating solution in real time (maintain 120-150 mS / cm); check the cleanliness and stability of the electrodes every 2 hours.

[0055] 4.2. Flow field optimization design: Use a turbulence promoter (Reynolds number Re>4000) to ensure uniform particle distribution; regularly check its working status; the cathode movement speed is 15 times / minute (stroke 50mm), and an automatic control system is used to ensure its stability and eliminate concentration polarization.

[0056] 5. Pre-plating treatment:

[0057] 5.1. Cathode activation of mold: Place the anode graphite electrode and the cathode connected to the mold into the 10% H2SO4 solution of the electrolytic cell. Adjust the electrode position so that the mold surface can be evenly contacted with the solution, and keep an appropriate distance between the cathode and the anode to avoid short circuit between the electrodes. Turn on the DC power supply and adjust the current to meet the mold surface area corresponding to 10A / dm 2 Current density. The current adjustment process needs to be carried out slowly, and the current value displayed by the power supply should be observed to ensure that the set value is reached accurately. Time for 30 seconds. During this period, closely observe the reaction in the electrolytic cell. Small bubbles should be evenly generated on the surface of the mold, indicating that the activation reaction is in progress. If no bubbles are generated locally on the surface of the mold or the bubbles are abnormal, it may be that the electrode contact is poor or there is an uncleaned area on the surface of the mold. Stop the operation immediately, check and reprocess it. After 30 seconds, turn off the DC power supply, quickly remove the mold from the electrolytic cell, and rinse the mold surface with plenty of clean water to remove the residual sulfuric acid solution. After rinsing, place the mold on clean filter paper to drain the surface moisture.

[0058] 5.2. Pre-plating base layer: Place the pure chromium anode plate and the cathode hanger with the mold installed into the plating solution of the electroplating tank, adjust the electrode position to keep the appropriate distance and relative position between the anode and cathode. Generally, the distance between the cathode and cathode is controlled at 10-15cm, and the mold surface is parallel to the anode plate to ensure uniform current distribution in the plating solution. Turn on the stirring device and set the appropriate stirring speed to make the plating solution form a uniform flow state in the tank, avoid uneven concentration of the plating solution, and ensure the uniformity of the coating thickness. Turn on the DC power supply and adjust the current density to 50A / dm 2 During the adjustment process, closely monitor the current and voltage displayed on the power supply to ensure that the current remains stable near the set value. During the pre-plating process, continuously monitor the plating tank for 5 minutes. Bubbles should form evenly in the plating solution, and the mold surface should gradually be covered with a bright base layer of chromium. Simultaneously, measure the plating solution temperature every 1-2 minutes to ensure it remains within the 50-55°C range. If the temperature exceeds this range, adjust it using the heating or cooling devices. After the 5-minute period, turn off the DC power supply and stop the stirring device. Remove the mold from the cathode hanger and rinse the mold surface with clean water to remove any residual plating solution. After rinsing, briefly soak the mold in a dilute hydrochloric acid solution (approximately 5% concentration) for approximately 10-15 seconds to remove any surface oxide film. Rinse thoroughly with clean water and finally place the mold in a clean drying oven at 60-70°C for 5-10 minutes. The dried mold is ready for the subsequent nanocomposite plating process.

[0059] 6. Nanocomposite plating:

[0060] 6.1, 0.5A / dm 2 / min rate from 30A / dm 2 Increased to 55A / dm 2 , cell voltage ≤ 4.2V, 0-30min;

[0061] 6.2. Steady-state pulse deposition, temperature fluctuation ±0.5°C, using high-precision temperature sensors and heating and cooling systems for real-time control, time 30-120 minutes;

[0062] 6.3. Reverse pulse refinement (15A / dm 2 ), thickness growth rate 0.17μm / min, measure the coating thickness every 10 minutes, adjust the pulse parameters according to the measurement results, time 120-150min;

[0063] 7. Post-plating treatment:

[0064] 7.1. Three-stage countercurrent rinsing: pure water conductivity <5μS / cm, each rinsing time 5 minutes, water flow rate 10L / min;

[0065] 7.2 Vacuum drying (-0.08MPa, 80℃×2h). Install vacuum sensor and temperature sensor for real-time monitoring to ensure the stability of vacuum and temperature.

[0066] 3. Beneficial effects

[0067] One or more technical solutions provided in the technical solution of this application have at least the following technical effects or advantages:

[0068] 1. Through precise image analysis, the present invention can promptly detect minor defects in the mold and ensure mold quality. Corresponding repair measures are taken for different defects, such as sanding minor scratches with sandpaper and repairing sand holes and air holes with argon arc welding, to ensure that the mold surface quality meets the requirements of subsequent processing, greatly improve the reliability and service life of the mold, and reduce the scrap rate of castings caused by mold defects.

[0069] 2. Improve wear and corrosion resistance by combining gas nitriding treatment with ion nitriding treatment of key parts. Ion nitriding makes the nitrided layer of key parts denser and harder, meeting the stringent performance and precision requirements of mold cores, cavities, and other parts prone to wear and corrosion, as well as precision molds. This reduces wear and corrosion in key parts of the mold and ensures the accuracy of die-cast products.

[0070] 3. Through hard chrome plating treatment, the surface performance is enhanced, the surface hardness and wear resistance of the mold are further improved, the surface friction coefficient is reduced, the casting is easier to demold, and the corrosion resistance of the mold is enhanced, and the corrosion resistance of the mold is improved in complex die-casting environments.

[0071] 4. Double sealing treatment enhances the protective effect, effectively preventing the intrusion of corrosive media and improving the corrosion resistance of the mold. The organic coating further isolates the mold from external erosion, and its excellent corrosion resistance and wear resistance can significantly enhance the protective performance of the mold and extend its service life.

[0072] 5. Adopting a method of nanopowder addition and pulsed electric field directional alignment, through a series of operations such as nanopowder pretreatment, dispersion stability control, plating solution construction, and setting pulse electroplating process parameters, the coating can be made more uniform and dense. The addition of nanopowders, such as single-crystal diamond powder, can significantly improve the hardness and wear resistance of the coating. Pulsed electric field directional alignment can orderly distribute the nanoparticles in the coating, further optimizing the coating performance and meeting the high-performance surface requirements of automotive die-casting molds. BRIEF DESCRIPTION OF THE DRAWINGS

[0073] Figure 1 This is a schematic diagram of the high wear-resistant and corrosion-resistant treatment process for the surface of the die-casting mold for automobile parts disclosed in this application. DETAILED DESCRIPTION

[0074] The present application is further described in detail below with reference to the accompanying drawings.

[0075] Reference Figure 1 The present invention provides a process for treating the surface of a die-casting mold for an automotive component to achieve high wear resistance and corrosion resistance, including the following steps:

[0076] S1. Mold Cleaning: Place the mold in a dedicated cleaning tank and soak it in an alkaline detergent at 50-60°C for 30-40 minutes to remove oil, release agent residue, and other impurities from the mold surface. Subsequently, flush the mold with a high-pressure water gun at a pressure of 15-20 MPa, using cavitation jet technology (cavitation collapse pressure to concentrate pore cleaning) to ensure that no contaminants remain on the surface.

[0077] S2. Surface grinding: Use 80-120 grit sandpaper to perform preliminary grinding on the mold surface to remove minor scratches and unevenness. Then, use 200-300 grit sandpaper for fine grinding to reduce the mold surface roughness to Ra0.8-1.6μm, providing a good base surface for subsequent processing.

[0078] S3. Image analysis and defect repair: After the surface polishing is completed, the mold is transferred to the inspection station equipped with high-definition image acquisition equipment. By setting up multiple industrial-grade high-definition cameras, all-round image acquisition of the mold surface is carried out from different angles. Defect analysis is performed on the collected high-definition images to promptly identify defects in the mold (such as scratches, sand holes, air holes, etc.). Once defects are detected on the mold surface, the system will automatically generate a detailed defect report, clearly indicating information such as the defect location, type, and size. According to the content of the report, the staff will take corresponding repair measures for different types of defects. For minor scratches, use finer-grained sandpaper for local fine polishing until the scratches disappear; for sand holes and air holes, use argon arc welding and other methods to fill and repair, and then polish again to make the repair area consistent with the overall surface flatness of the mold, ensuring that the mold surface quality meets the requirements of subsequent processing processes.

[0079] S4. Nitriding treatment: Nitriding treatment is performed on the mold after cleaning, polishing and defect repair; including gas nitriding and ion nitriding;

[0080] S41. Gas Nitriding: The cleaned, polished, and defect-repaired mold is placed in a nitriding furnace and ammonia (NH3) is introduced as the nitriding medium. The furnace is maintained at a temperature of 500-550°C, with a pressure of 1-2 kPa, for 8-10 hours. Ammonia decomposes at high temperatures to produce active nitrogen atoms, which react chemically with the metal atoms on the mold surface, forming a nitrided layer with high hardness and excellent wear resistance. The thickness of the nitrided layer can generally reach 0.02-0.05 mm.

[0081] S42. Ion nitriding: Ion nitriding treatment is performed on key parts of the mold. The mold is used as the cathode and placed in an ion nitriding furnace, and a mixture of nitrogen (N2) and hydrogen (H2) is introduced. At a temperature of 450-500°C, a voltage of 500-800V is applied, and the gas is ionized by glow discharge. Nitrogen ions bombard the mold surface at high speed under the action of the electric field to realize the nitriding process. Ion nitriding is suitable for situations where the performance requirements of key parts of the mold are extremely high, such as the core and cavity of the die-casting mold, which are prone to wear and corrosion, as well as precision molds with high requirements for mold precision and do not want large deformation. The ratio of nitrogen (N2) and hydrogen (H2) is between 3:1 and 1:1. The ratio depends on factors such as the material of the mold, the specific usage requirements, and the characteristics of the ion nitriding equipment.

[0082] During the ion nitriding process, the ion nitriding treatment is carried out according to the following model:

[0083] h=k×T a ×t b ×P c ×V d ×F e ×∏ n i＝1 α iWhere h represents the thickness of the nitride layer, measured in millimeters (mm), reflecting the size of the nitride layer formed on the mold surface perpendicular to the mold surface after nitriding. k represents a comprehensive constant, whose value is related to factors such as the mold material, gas type, and nitriding equipment characteristics. Different mold materials (such as mold steel and aluminum alloy) have different chemical properties and crystal structures, which affect the diffusion and reactivity of nitrogen atoms in them. Different gas types (such as ammonia, nitrogen, and hydrogen mixtures) also affect the mechanism and efficiency of the nitriding reaction. Equipment characteristics (such as the heating method and thermal insulation performance of the nitriding furnace) also affect the nitriding process. k needs to be determined through basic experiments for specific materials and equipment. T is the temperature, measured in absolute temperature (K). Temperature is one of the key factors affecting the nitriding process because it directly affects the diffusion rate of nitrogen atoms. According to the Arrhenius equation, increased temperature intensifies the thermal motion of atoms, thereby accelerating the diffusion rate of nitrogen atoms in the mold material, which in turn affects the growth rate of the nitride layer. The higher the temperature, the faster the nitride layer grows. However, excessively high temperatures may cause changes in the microstructure and properties of the mold material, affecting the overall mold quality. a is the temperature index, which reflects the degree of temperature's influence on the growth of the nitride layer. The effect of temperature on the thickness of the nitride layer varies depending on the material and nitriding process, and the value of a will also vary. t is the nitriding time, measured in hours (h). b is the time index, which reflects the growth pattern of the nitride layer thickness over time. Due to the variable growth rate of the nitride layer, b is less than 1. P is the furnace pressure, measured in Pascals (Pa). Pressure affects the collision frequency and reactivity of gas molecules. During the nitriding process, an appropriate pressure helps the nitriding medium (such as the reactive nitrogen atoms produced by the decomposition of ammonia) more effectively contact and react with the mold surface. Excessive or insufficient pressure can adversely affect the nitriding effect. For example, too low a pressure may lead to an incomplete reaction, while too high a pressure may cause abnormalities on the mold surface. c is the pressure index, which reflects the degree of influence of the furnace pressure on the growth of the nitride layer. Different nitriding processes and mold materials have different pressure sensitivities, and the value of c will vary accordingly. In some ion nitriding processes, the value of c is between 0.2-0.5, and the specific value needs to be determined through experiments. V is voltage, measured in volts (V). During the ion nitriding process, voltage is used to accelerate ions so that nitrogen ions can bombard the mold surface with higher energy, thereby promoting the injection of nitrogen atoms and the nitriding reaction. The magnitude of the voltage will affect the bombardment energy and injection depth of the ions, thereby affecting the thickness and performance of the nitride layer. d is the voltage index, which reflects the degree of influence of the voltage on the growth of the nitride layer. A suitable voltage range is crucial to obtaining an ideal nitriding effect. Too high a voltage may cause problems such as overheating and sputtering on the mold surface, affecting the quality of the nitride layer; too low a voltage may result in insufficient ion bombardment energy, resulting in slow growth of the nitride layer.The value of d is usually small, between 0.1-0.3, depending on the characteristics of the mold material and the ion nitriding equipment. F is the gas flow rate, measured in liters per hour (L / h). The gas flow rate affects the renewal rate and concentration distribution of the nitriding medium in the furnace. A suitable gas flow rate can ensure that there is always an adequate supply of nitriding medium on the mold surface, promoting the continuous progress of the nitriding reaction. If the gas flow rate is too small, it may lead to insufficient supply of nitriding medium, affecting the growth of the nitriding layer; if the gas flow rate is too large, it may cause problems such as excessive heat loss and too short a gas residence time in the furnace, which is also not conducive to the nitriding process. e is the gas flow index, which reflects the degree of influence of gas flow on the growth of the nitriding layer. Under different nitriding process and equipment conditions, the value of e varies, generally between 0.3-0.6. The specific e value needs to be determined through experiments to optimize the gas flow parameters and obtain the best nitriding effect. ∏ n i＝1 α i is a series of correction factors α i The product of n and n represents the number of correction factors, and the specific value depends on the number of influencing factors that need to be considered. Different nitriding scenarios may require different numbers and types of correction factors. i is the i-th correction factor. Common correction factors include mold material microstructure correction factor, mold geometry correction factor, gas purity correction factor, etc. The value of each correction factor is determined according to the specific influencing factors. For example, when a certain influencing factor promotes the growth of the nitride layer, α i The value of is greater than 1; when there is an inhibitory effect, α i The value of is less than 1; if this factor has little effect on the growth of the nitride layer, then α i The value of is close to 1. By introducing these correction factors, the formula can have better accuracy and adaptability in a wider range of practical application scenarios.

[0084] During the gas ionization process, nitrogen molecules are ionized under the action of an electric field. Nitrogen ions bombard the mold surface under the acceleration of the electric field and react with metal atoms to form a nitride layer. Ion nitriding can make the nitride layer denser and harder.

[0085] S5. Hard chromium plating: Use a mixed plating solution of chromic acid (H2CrO4) and sulfuric acid (H2SO4), where the chromic acid concentration is 250-300g / L and the sulfuric acid concentration is 2.5-3g / L. In order to improve the quality of the coating, add an appropriate amount of additives, such as rare earth element compounds, and the addition amount is generally 0.1-0.3g / L. The additive can also be an organic sulfonic acid (such as methanesulfonic acid, ethylsulfonic acid, etc.), and the amount is 1-5g / L. The mold that has been nitrided is used as the cathode and the lead-antimony alloy is used as the anode and placed in the plating solution. At a temperature of 50-60°C, control the current density to 30-50A / dm2 The electroplating time is 2-3 hours. During the electroplating process, chromium ions obtain electrons on the cathode surface and deposit to form a hard and smooth chromium plating layer with a thickness of 0.02-0.03mm.

[0086] S6. Sealing treatment:

[0087] S61. Chemical Sealing: Immerse the hard chrome-plated mold in a sealing solution containing nickel salt and fluoride. Maintain the solution temperature at 80-90°C for 15-20 minutes. Nickel ions and fluoride ions react chemically on the mold surface, forming an insoluble nickel fluoride that fills the tiny pores in the chrome plating and improves the mold's surface corrosion resistance.

[0088] S62. Organic Coating Sealing: To further enhance the sealing effect, apply an organic coating after chemical sealing. Choose an organic coating with excellent corrosion and wear resistance, such as polytetrafluoroethylene (PTFE). Apply the coating evenly to the mold surface using a spray coating, maintaining a thickness of 0.05-0.1mm. Then, cure at 180-200°C for 1-2 hours to firmly bond the organic coating to the mold surface.

[0089] S7. Quality Inspection: Use a Vickers hardness tester to perform multiple inspections at different locations on the mold surface to ensure that the hardness of the nitride and chrome plating layers meets the requirements. The hardness of the nitride layer should reach HV900-1200, and the hardness of the chrome plating layer should reach HV800-1000. Use an eddy current thickness gauge to measure the thickness of the nitride and chrome plating layers, ensuring that the nitride layer thickness is within the range of 0.02-0.05mm, and the chrome plating layer thickness is within the range of 0.02-0.03mm. A friction and wear tester is used to simulate the wear conditions during the aluminum die-casting process. Under a certain load and friction number, the wear volume of the mold surface is measured, and the wear volume is required to be kept within an extremely small range to ensure the mold has good wear resistance. A salt spray test is used to test the corrosion resistance of the mold surface. The mold is placed in a salt spray test chamber and tested continuously for 48-72 hours according to standard salt spray test methods under specific temperature, humidity, and salt spray concentration conditions. After the test, observe whether there is corrosion on the mold surface, such as rust, peeling, etc., to evaluate its corrosion resistance.

[0090] Furthermore, the alkaline cleaning agent is a compound alkaline cleaning agent, which is composed of sodium hydroxide (10-15 g / L), trisodium phosphate (5-10 g / L), and sodium silicate (1-5 g / L).

[0091] Furthermore, image defect analysis accurately identifies various defects on the mold surface, such as scratches, pinholes, and pores, and includes the following steps:

[0092] 1. Image preprocessing: Multiple industrial-grade high-definition cameras are used to simultaneously capture the mold surface from different angles, ensuring complete coverage of all areas of the mold and obtaining comprehensive mold surface image information. The captured images are preprocessed, including grayscale conversion, noise reduction, and image enhancement.

[0093] Image grayscale processing: Convert the acquired color image into a grayscale image. In a grayscale image, the brightness information of each pixel can be represented by a single value, which simplifies subsequent analysis and calculations while retaining key information related to defects in the image.

[0094] Image noise reduction: Filtering algorithms, such as Gaussian filtering, are used to reduce noise in grayscale images. Mold surfaces may contain noise due to factors such as uneven light reflection and camera noise. Noise reduction can smooth the image, remove these irrelevant interferences, and improve image quality, laying the foundation for accurate defect identification.

[0095] 2. Scratch recognition:

[0096] 2.1. Edge Detection: Use edge detection algorithms, such as the Canny edge detection algorithm, to process the preprocessed image to highlight edge information. Scratches typically appear as continuous lines in an image. Edge detection can enhance the contrast between these lines and the surrounding area, making scratches easier to identify.

[0097] 2.2 Line Continuity Analysis: Lines are traced in the edge-detected image to determine their continuity. Scratches are generally characterized by long, continuous lines. By setting a minimum continuous line length threshold, lines that may be scratches are screened out. For example, if the continuous length of a line exceeds a set threshold (e.g., 5 pixels), it is preliminarily identified as a possible scratch line.

[0098] 2.3 Width Measurement: For the initially identified scratch line, calculate its width in the image. By analyzing the distribution of pixels surrounding the line, the line boundary is determined, and the scratch width is measured. Width measurement can help determine the severity of the scratch; wider scratches may have a greater impact on mold performance.

[0099] 2.4 Grayscale Change Analysis: Analyzes the grayscale value changes of pixels along the scratch line. While the grayscale value distribution on a normal mold surface is relatively uniform, the grayscale value at a scratch typically differs from the surrounding area. By calculating the rate of change in grayscale value, the software can further confirm the presence of a scratch and infer its depth based on the magnitude of the grayscale change. For example, a larger grayscale change rate may indicate a deeper scratch.

[0100] 3. Identification of sand holes and pores:

[0101] 3.1. Binarization: The software binarizes the preprocessed image. Based on the grayscale difference between the mold surface and the defective area, an appropriate threshold is set to divide the image into the foreground (defective area) and the background (normal mold surface area). Sand holes and pores typically appear as black holes in the binary image (assuming the foreground is black and the background is white).

[0102] 3.2 Morphological Processing: Use morphological operations, such as erosion and dilation, to optimize the binary image. Erosion can remove isolated noise points and minor interference areas in the image, while dilation can restore defect areas that have been reduced by erosion, making the shapes of sand holes and pores clearer and more complete, facilitating subsequent feature extraction and recognition.

[0103] 3.3. Shape Feature Extraction: Shape feature extraction is performed on the morphologically processed image, calculating the area, perimeter, circularity, and other shape parameters of each black area (potential pores or air holes). Porphyry and air holes typically have circular or nearly circular shape characteristics. By comparing these shape parameters with the preset pore and air hole shape model parameters, a preliminary judgment can be made as to whether the black area is a pore or air hole.

[0104] 3.4 Edge Clarity Analysis: For the initially identified pores and air holes, analyze their edge clarity. The edges of pores and air holes are relatively clear, with distinct boundaries from the surrounding area. By calculating the edge gradient or edge sharpness index, we can further confirm whether these areas are true pores and air holes. A higher edge gradient or sharpness index indicates a clear edge, consistent with the characteristics of pores and air holes.

[0105] 3.5. Contrast Analysis: Calculate the grayscale contrast between the pore and air hole areas and the surrounding normal mold surface areas. The grayscale values of pore and air hole areas are usually significantly different from those of the surrounding areas. Contrast analysis can quantify this difference, thereby more accurately identifying pores and air holes. For example, a contrast threshold is set. When the contrast between a certain area and the surrounding area exceeds this threshold, the area is identified as a possible pore or air hole. Perform pore and air hole analysis according to the following formula:

[0106] ó 2 b (t)=w0[ln(u0+e)-ln(u T +e)] 2 +w1[(u1 / u T )-1]; where ó 2 b(t) is the inter-class variance, which represents the separation between the trachoma / pore defect area and the normal area. The larger the value, the clearer the defect recognition. w0 is the pixel weight of the defect area, which is the area ratio of the trachoma or pore in the image. w1 is the pixel weight of the normal area. u0 is the grayscale mean of the defect area, and u1 is the grayscale mean of the normal area, which is the uniform grayscale value of the defect-free aluminum substrate and is related to the material density and thickness. T is the global grayscale mean, the average grayscale of the entire X-ray image, reflecting the overall density of the casting; e is a small constant (e = 0.01) to prevent overflow of values in defect-free areas or fully defective areas.

[0107] 4. Defect Report Generation: Identified defects such as scratches, pinholes, and pores are marked on the original mold image, clearly displaying their locations using specific colors and symbols (e.g., red circles mark pinholes and pores, and red lines outline scratches). For each defect, the software records its type (scratch, pinhole, or pore) and dimensional information obtained through analysis, such as the length and depth of scratches, and the diameter or area of pinholes and pores. The location, type, and size of all defects are summarized to generate a detailed defect report. The report can be presented in the form of a text file, spreadsheet, or visual chart, making it convenient for staff to review and subsequently process.

[0108] As an optional solution of the present invention, the electroplating treatment is performed using a 0.5 g / L nanopowder addition + pulse electric field directional arrangement method, including the following steps:

[0109] 1. Nanopowder pretreatment:

[0110] 1.1. Powder screening and activation:

[0111] 1.1.1 Select 4-6nm single crystal diamond powder (purity ≥ 99.9%, SEM test confirms no agglomeration);

[0112] 1.1.2. Activate in a vacuum plasma treatment device (power 500W, Ar gas atmosphere) for 30 minutes to enhance surface wettability;

[0113] 1.2. Prepare the suspension: 0.5 g nanopowder + 100 mL deionized water. First, magnetically stir for 1 hour (1200 rpm), then ultrasonicate for 30 minutes (40 kHz, 200 W), and then continue magnetic stirring for another 30 minutes. This should be performed in a dust-free environment or on a clean bench.

[0114] 2. Dispersion stability control:

[0115] 2.1. Add 0.1% by mass of sodium dodecyl sulfate (SDS) as a dispersant;

[0116] 2.2. Use an ultrasonic cell disruptor (20kHz, 300W power, 5s on / 2s off pulse mode). Monitor the temperature using a temperature sensor. If the temperature exceeds 30°C, pause the treatment for 10 minutes and resume after the temperature drops. Check the instrument's working status regularly during the treatment process.

[0117] 2.3. Dynamic light scattering (DLS) was used to detect the particle size distribution. The measurements were repeated three times with an interval of 5 minutes between each measurement and the average value was taken. The requirements were D50 = 6.2 nm and PDI < 0.2.

[0118] 3. Constructing the plating solution system:

[0119] 3.1. Slowly add 280±5g / L of chromic acid (H2CrO4) into the plating solution container. Pre-add an appropriate amount of deionized water (about 1 / 3 of the final plating solution volume) into the container. During the addition, turn on the stirring device and set the stirring speed to a low level (such as a magnetic stirrer at 300-400 rpm) to allow the chromic acid to gradually dissolve.

[0120] 3.2. Slowly add 2.8±0.1g / L sulfuric acid to the solution containing dissolved chromic acid, stirring while adding. Do not add too quickly (control the rate to 1-2 drops per second) to prevent splashing of the solution and a violent chemical reaction. Increase the stirring speed to 400-500 rpm to ensure uniform dispersion of the sulfuric acid and thorough mixing with the solution.

[0121] 3.3. Place 0.5g / L of the measured nanodiamond suspension into another container and slowly heat it to 40°C using a heating device (such as a constant temperature water bath). During the heating process, the suspension must be continuously stirred (a magnetic stirrer can be used at about 300 rpm) to prevent local overheating from causing nanoparticle agglomeration. The suspension temperature can be monitored in real time using a thermometer. When the temperature of the nanodiamond suspension reaches 40°C, slowly add it to the plating solution container, turn on the stirring device and appropriately increase the stirring speed to 500-600 rpm so that the nanodiamond suspension can be quickly and evenly dispersed into the plating solution. The addition process needs to be stirred continuously for 15-20 minutes to ensure its uniformity.

[0122] 3.4. Slowly add 3.5g / L of methanesulfonic acid to the plating solution, stirring at 500-600 rpm to ensure rapid and uniform dispersion of the methanesulfonic acid. Continue stirring for 10-15 minutes after addition.

[0123] 3.5. Slowly add 0.2g / L of rare earth cerium nitrate to the plating solution while stirring continuously at a speed of 500-600 rpm to ensure that it is fully dissolved and evenly dispersed in the plating solution. After the addition is complete, stir for another 10-15 minutes.

[0124] 3.6. After all components have been added, add deionized water to the plating solution container to adjust the plating solution volume to the target total volume. Stir continuously during the water addition process to ensure more uniform mixing of the plating solution. Use heating and thermostat equipment to adjust the plating solution temperature to 55±1°C. Monitor temperature changes in real time using a high-precision thermometer. Adjust the stirring speed appropriately during this process to promote uniform temperature distribution. Once the temperature stabilizes within the target range, the plating solution system is complete and can be prepared for subsequent electroplating operations.

[0125] 4. Set pulse plating process parameters:

[0126] 4.1. Magnetic field-assisted positioning: Apply a 0.5 T horizontal magnetic field (NdFeB permanent magnet array) to orient the nanoparticles along the magnetic field lines; monitor the conductivity of the plating solution in real time (maintain 120-150 mS / cm); check the cleanliness and stability of the electrodes every 2 hours.

[0127] 4.2. Flow field optimization design: Use a turbulence promoter (Reynolds number Re>4000) to ensure uniform particle distribution; regularly check its working status; the cathode movement speed is 15 times / minute (stroke 50mm), and an automatic control system is used to ensure its stability and eliminate concentration polarization.

[0128] 5. Pre-plating treatment:

[0129] 5.1. Cathode activation of mold: Fix the mold to be processed on the cathode electrode rod to ensure a firm connection and good conductivity. The mold surface should be cleaned in advance to remove oil, impurities, etc. It can be wiped with an organic solvent such as acetone, then rinsed with clean water and dried. Place the anode graphite electrode and the cathode connected to the mold into the 10% H2SO4 solution of the electrolytic cell, adjust the electrode position so that the mold surface can be evenly in contact with the solution, and maintain an appropriate distance between the anode and cathode (generally 5-10cm) to avoid short circuits between the electrodes. Turn on the DC power supply and adjust the current to 10A / dm2 corresponding to the mold surface area. 2 Current density. The current adjustment process needs to be carried out slowly, and the current value displayed by the power supply should be observed to ensure that the set value is reached accurately. Time for 30 seconds. During this period, closely observe the reaction in the electrolytic cell. Small bubbles should be evenly generated on the surface of the mold, indicating that the activation reaction is in progress. If no bubbles are generated locally on the surface of the mold or the bubbles are abnormal, it may be that the electrode contact is poor or there are uncleaned areas on the surface of the mold. The operation must be stopped immediately, checked and reprocessed. After 30 seconds, turn off the DC power supply, quickly remove the mold from the electrolytic cell, rinse the mold surface with plenty of water, and remove residual sulfuric acid solution. The rinsing time should be no less than 1 minute to ensure that there is no sulfuric acid residue on the surface of the mold to prevent it from affecting the subsequent plating process. After rinsing, place the mold on a clean filter paper to drain the surface moisture.

[0130] 5.2. Pre-plating base layer: Place the pure chromium anode plate and the cathode hanger with the mold installed into the plating solution of the electroplating tank, adjust the electrode position to keep the appropriate distance and relative position between the anode and cathode. Generally, the distance between the cathode and cathode is controlled at 10-15cm, and the mold surface is parallel to the anode plate to ensure uniform current distribution in the plating solution. Turn on the stirring device and set the appropriate stirring speed (generally 100-150 rpm) to form a uniform flow state of the plating solution in the tank, avoid uneven concentration of the plating solution, and ensure the uniformity of the coating thickness. Turn on the DC power supply and adjust the current density to 50A / dm 2 During the adjustment process, the current and voltage values displayed by the power supply must be closely observed to ensure that the current is stable near the set value. If the current fluctuates, it is necessary to promptly check the electrode connection, plating solution status, etc. to eliminate the fault. Timing is 5 minutes. During the pre-plating process, continue to observe the situation in the electroplating tank. Bubbles should be evenly generated in the plating solution, and the mold surface is gradually covered with a bright base chromium layer. At the same time, measure the plating solution temperature every 1-2 minutes to ensure that the temperature is maintained within the range of 50-55°C. If the temperature is out of range, it can be adjusted by heating or cooling devices. After 5 minutes, turn off the DC power supply and stop the stirring device. Remove the mold from the cathode hanger and rinse the mold surface with clean water to remove the residual plating solution on the surface. When rinsing, the water flow should not be too large to avoid washing away the base chromium layer that has just been plated. After rinsing, place the mold in a dilute hydrochloric acid solution (concentration of about 5%) for a short soak (about 10-15s) to remove any oxide film that may exist on the surface, then rinse it with clean water. Finally, place the mold in a clean drying oven and dry it at 60-70°C for 5-10 minutes. After drying, the mold can proceed to the subsequent nano-composite plating process.

[0131] 6. Nanocomposite plating:

[0132] 6.1, 0.5A / dm 2 / min rate from 30A / dm 2 Increased to 55A / dm 2 , cell voltage ≤ 4.2V, 0-30min;

[0133] 6.2. Steady-state pulse deposition, temperature fluctuation ±0.5°C, using high-precision temperature sensors and heating and cooling systems for real-time control, time 30-120 minutes;

[0134] 6.3. Reverse pulse refinement (15A / dm 2 ), thickness growth rate 0.17μm / min, measure the coating thickness every 10 minutes, adjust the pulse parameters according to the measurement results, time 120-150min;

[0135] 7. Post-plating treatment:

[0136] 7.1. Three-stage countercurrent rinsing: Pure water conductivity <5μS / cm, 5-minute rinse time per rinse, and a water flow rate of 10L / min. A three-stage countercurrent rinsing process efficiently removes residual plating solution and impurities from the surface of the plated parts to ensure the cleanliness and quality of the plated parts. The conductivity of the pure water used for rinsing must be strictly controlled to <5μS / cm, which is a key water quality indicator for ensuring effective rinsing. Each rinse time is set at 5 minutes, during which time the plated parts are fully exposed to the pure water, effectively dissolving the plating solution and impurities and removing them from the surface. The water flow rate is maintained at 10L / min. The stable and appropriate water flow continuously refreshes the rinse water around the plated parts, further improving rinsing efficiency and making the rinsing process more uniform and comprehensive.

[0137] 7.2 Vacuum Drying: Place the plated parts in a vacuum drying device, set the vacuum to -0.08MPa, the temperature to 80℃, and the duration to 2 hours. This vacuum and temperature condition can accelerate the vaporization of moisture on the surface of the plated parts, achieving efficient drying, while also preventing damage to the plated parts caused by excessively high temperatures.

[0138] To precisely control the drying process, vacuum and temperature sensors are installed within the equipment. The vacuum sensor monitors the vacuum environment within the equipment in real time. If the vacuum level fluctuates, the system responds promptly by adjusting the vacuum pump's operating state to ensure a stable vacuum level of -0.08 MPa. The temperature sensor constantly monitors the drying temperature. If the temperature deviates from 80°C, the heating or cooling device activates immediately to adjust the temperature back to the set value, ensuring a smooth and orderly vacuum drying process and ensuring that the dried plated parts meet the requirements for subsequent processing or storage.

[0139] This invention uses precise image analysis to promptly detect subtle mold defects and ensure mold quality. Appropriate repair measures are implemented for each defect, such as sanding minor scratches and using argon arc welding to repair pinholes and pores. This ensures that the mold surface quality meets subsequent processing requirements, significantly improving the mold's reliability and service life and reducing the scrap rate of castings due to mold defects. The invention combines gas nitriding with ion nitriding of key areas to enhance wear and corrosion resistance. Ion nitriding creates a denser and harder nitride layer in key areas, meeting the stringent performance and precision requirements of wear- and corrosion-prone areas like the mold core and cavity, as well as precision molds. This reduces wear and corrosion in key areas and ensures the precision of die-cast products. Hard chromium plating enhances surface properties, further improving mold surface hardness and wear resistance, and reducing surface friction, making castings easier to demold. It also enhances the mold's corrosion resistance, improving its ability to withstand complex die-casting environments. Double sealing enhances protection, effectively preventing the intrusion of corrosive media and improving the mold's corrosion resistance. The organic coating further isolates the mold from environmental corrosion, and its inherent excellent corrosion and wear resistance can significantly enhance the mold's protective properties and extend its service life. By combining nanopowder addition with pulsed electric field directional alignment, a series of operations, including nanopowder pretreatment, dispersion stability control, plating solution construction, and pulse electroplating process parameter setting, can achieve a more uniform and dense coating. The addition of nanopowders, such as single-crystal diamond powder, can significantly improve the coating's hardness and wear resistance. Pulsed electric field directional alignment allows the nanoparticles to be distributed orderly throughout the coating, further optimizing the coating's performance and meeting the high-performance surface requirements of automotive die-casting molds.

[0140] As described above, the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit the same. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions described in the above embodiments can still be modified, or some of the technical features thereof can be replaced by equivalents. However, these modifications or replacements do not deviate the essence of the corresponding technical solutions from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A high wear-resistant and corrosion-resistant treatment process for the surface of a die-casting mold for automobile parts, characterized in that: The following steps are involved: S1. Mold cleaning: Place the mold in a cleaning tank, use an alkaline cleaning agent, soak it at 50-60°C for 30-40 minutes, and rinse the mold with a high-pressure water gun; S2. Surface grinding: Use 80-120 grit sandpaper to grind the mold surface initially, and then use 200-300 grit sandpaper for fine grinding; S3. Image analysis and defect repair: Collect all-round mold images, analyze the images for defects, identify mold defects, and take appropriate repair measures for different defects; S4. Nitriding treatment: Nitriding treatment is performed on the mold after cleaning, polishing and defect repair; S5, hard chromium plating treatment: use a mixed plating solution of chromic acid and sulfuric acid, add appropriate additives, control the current density to 30-50A / dm at a temperature of 50-60℃ 2 , electroplating time 2-3 hours; S6. Sealing treatment: S61, chemical sealing: immerse the mold in a sealing solution containing nickel salt and fluoride, maintain the solution temperature at 80-90°C, and seal for 15-20 minutes; S62, organic coating sealing: Use polytetrafluoroethylene coating, spray the coating evenly on the mold surface, and cure it at 180-200℃ for 1-2 hours; S7. Quality inspection: Perform multi-point inspection to ensure that the hardness of the nitride layer and chrome plating layer meets the requirements.

2. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 1, characterized in that: Step S4 includes the following steps: S41. Gas nitriding: Place the cleaned, polished and defect-repaired mold into a nitriding furnace, introduce ammonia as the nitriding medium, maintain the furnace pressure at 1-2 kPa at a temperature of 500-550°C, and nitriding for 8-10 hours; S42. Ion nitriding: Ion nitriding treatment is performed on key parts of the mold. The mold is used as the cathode and placed in an ion nitriding furnace. A mixed gas of nitrogen and hydrogen is introduced. At a temperature of 450-500°C, a voltage of 500-800V is applied. The gas is ionized by glow discharge. Nitrogen ions bombard the mold surface at high speed under the action of the electric field to realize the nitriding process. The ratio of nitrogen to hydrogen is between 3:1 and 1:

1.

3. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 2, characterized in that: In step S42, during the ion nitriding process, the ion nitriding treatment is performed according to the following model: h=k×T a ×t b ×P c ×V d ×F e ×∏ n i＝1 α i ; In the formula, h represents the thickness of the nitride layer; k represents the comprehensive constant; T is temperature; a is the temperature index; t is the nitriding time; b is the time index; P is the pressure in the furnace; c is the pressure index; V is the voltage; d is the voltage index; F is the gas flow rate; e is the gas flow rate index; ∏ n i＝1 α i is a series of correction factors α i The product of n represents the number of correction factors. α i is the i-th correction factor, including the mold material microstructure correction factor, mold geometry correction factor, and gas purity correction factor.

4. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 1, characterized in that: Step S3 includes the following steps: S31, image preprocessing: preprocessing the collected images, including grayscale conversion, noise reduction and image enhancement; S32, scratch recognition: S32.

1. Edge detection: Use the Canny edge detection algorithm to process the preprocessed image and highlight the edge information in the image; S32.2 Line Continuity Analysis: Tracing lines in the image to determine their continuity; by setting a minimum continuous length threshold for lines, lines that may be scratches are screened out; S32.

3. Width measurement: For the scratch lines initially identified, calculate their width in the image; S32.

4. Grayscale change analysis: Analyze the grayscale value changes of pixels along the scratch line. Calculate the grayscale value change rate to confirm the presence of a scratch and estimate the scratch depth based on the grayscale change amplitude. S33, identification of sand holes and pores: S33.

1. Binarization: performing binarization on the preprocessed image; S33.

2. Morphological processing: Use morphological operations to optimize the binary image; S33.

3. Shape feature extraction: Perform shape feature extraction on the morphologically processed image, calculating the area, perimeter, and circularity parameters of each black region; and preliminarily determine whether there are trachoma or pores. S33.

4. Edge clarity analysis: For the initially identified trachoma and pore areas, analyze their edge clarity; S33.

5. Contrast Analysis: Calculate the grayscale contrast between the pores and air holes and the surrounding normal mold surface area; accurately identify pores and air holes through contrast analysis; S34. Defect report generation: The identified defects are marked on the original mold image. For each defect, its type and size information are recorded, and a detailed defect report is generated.

5. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 4, characterized in that: In step S3.5, the analysis of pinholes and pores is performed according to the following formula: ó 2 b (t)=w0[ln(u0+e)-ln(u T +e)] 2 +w1[(u1 / u T )-1]; where ó 2 b (t) is the inter-class variance, which represents the separation between the sand hole / pore defect area and the normal area; w0 is the pixel weight of the defect area; w1 is the normal area pixel weight; u0 is the grayscale mean of the defective area, and u1 is the grayscale mean of the normal area; T is the global grayscale mean; e is a small constant.

6. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 1, characterized in that: In step S5, the electroplating process is performed using a 0.5 g / L nanopowder addition + pulsed electric field oriented arrangement method, including the following steps: S51, nano powder pretreatment: S51.

1. Powder screening and activation: Select 4-6nm single crystal diamond powder and activate it in a vacuum plasma treatment equipment with a power of 500W and an Ar gas atmosphere for 30 minutes; S51.

2. Prepare the suspension: 0.5 g nanopowder + 100 mL deionized water. First, magnetically stir for 1 hour, then sonicate for 30 minutes, and then continue magnetic stirring for another 30 minutes. S52, dispersion stability control: add 0.1% by mass of sodium dodecyl sulfate (SDS) as a dispersant; use ultrasonic cell disruptor for treatment; S53, constructing a plating solution system; S54. Set pulse plating process parameters: 4.

1. Magnetic field-assisted positioning: Apply a 0.5T horizontal magnetic field to orient the nanoparticles along the magnetic field lines; 4.

2. Flow field optimization design: Use turbulence promoters to ensure uniform particle distribution; S55, pre-plating treatment: 5.

1. Cathode activation of mold: Place the anode graphite electrode and the cathode connected to the mold into an electrolytic cell containing 10% sulfuric acid solution, and slowly adjust the current to 10A / dm2 corresponding to the mold surface area. 2 Current density; after 30 seconds, turn off the power, remove the mold and rinse with plenty of water to remove the residual sulfuric acid solution; drain the mold; 5.

2. Pre-plating base layer: Place the pure chromium anode plate and the cathode hanger with the mold into the plating bath, turn on the stirring device and set the appropriate speed to allow the plating solution to flow evenly; adjust the current density to 50A / dm 2 , after 5 minutes, turn off the power and stirring device, remove the mold and rinse with clean water, then soak it in 5% dilute hydrochloric acid solution for 10-15 seconds to remove the oxide film, rinse with clean water and dry it in a 60-70℃ drying oven for 5-10 minutes; S56, nanocomposite plating; S57, post-plating treatment: S57.

1. Three-stage countercurrent rinsing: A three-stage countercurrent rinsing process is used to remove residual plating solution and impurities on the surface of the plated parts. The conductivity of the pure water used for rinsing must be strictly controlled to <5μS / cm. The rinsing time is set to 5 minutes each time, and the water flow rate is maintained at 10L / min. S57.2 Vacuum drying: Place the plated parts in a vacuum drying device, set the vacuum degree to -0.08 MPa, the temperature to 80°C, and the duration for 2 hours.

7. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 6, characterized in that: In step S57.2, a vacuum sensor and a temperature sensor are provided in the vacuum drying equipment. The vacuum sensor monitors the vacuum environment inside the equipment in real time. Once the vacuum degree fluctuates, the working state of the vacuum pump is adjusted to ensure that the vacuum degree is stably maintained at -0.08MPa; the temperature sensor monitors the drying temperature at all times. When the temperature deviates from 80°C, the heating or cooling device is quickly started to adjust the temperature back to the set value to ensure that the entire vacuum drying process is carried out smoothly and orderly.

8. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 6, characterized in that: Step S53 includes the following steps: S53.

1. Slowly add 280 ± 5 g / L of chromic acid to the plating solution container. Pre-add an appropriate amount of deionized water to the container. Turn on the stirring device during the addition to allow the chromic acid to gradually dissolve. S53.

2. Slowly add 2.8 ± 0.1 g / L sulfuric acid dropwise to the solution containing dissolved chromic acid, stirring to ensure uniform dispersion and thorough mixing of the sulfuric acid. S53.

3. Place 0.5 g / L of the nanodiamond suspension in another container and slowly heat it to 40°C using a heating device. Then, activate the stirring device and increase the stirring speed to 500-600 rpm to ensure that the nanodiamond suspension is quickly and evenly dispersed into the plating solution. S53.

4. Slowly add 3.5 g / L methanesulfonic acid to the plating solution while stirring to ensure rapid and uniform dispersion of the methanesulfonic acid. S53.

5. Slowly add 0.2 g / L rare earth cerium nitrate to the plating solution while continuously stirring; S53.

6. After all components are added, add deionized water to the plating solution container, adjust the plating solution volume to the target total volume, and adjust the plating solution temperature to 55±1°C. After the temperature stabilizes within the target range, the plating solution system is completed.

9. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 6, characterized in that: Step S56 includes the following steps: S56.1, at 0.5A / dm 2 / min rate from 30A / dm 2 Increased to 55A / dm 2 , cell voltage ≤ 4.2V, 0-30min; S56.2, steady-state pulse deposition, temperature fluctuation ±0.5°C, using high-precision temperature sensors and a heating and cooling system for real-time control, time 30-120 minutes; S56.3, reverse pulse refinement 15A / dm 2 , thickness growth rate is 0.17μm / min, the coating thickness is measured every 10 minutes, and the pulse parameters are adjusted according to the measurement results. The time is 120-150min.

10. The process for treating the surface of a die-casting mold for automobile parts with high wear resistance and corrosion resistance according to claim 1, characterized in that: In step S1, the alkaline cleaning agent is a compound alkaline cleaning agent, which is 10-15g / L sodium hydroxide, trisodium phosphate A compound alkaline cleaning agent composed of 5-10g / L of sodium silicate and 1-5g / L of sodium silicate.

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