Method for testing filamentous corrosion of vehicle body coating

Abstract

The invention provides a vehicle body coating filamentous corrosion testing method which comprises the following steps: destroying a coating on the surface of a test piece, exposing a metal matrix, and cleaning chips on the surface of the test piece; introducing an electrolyte solution on the metal matrix at the damaged part of the coating; placing a cover plate at the damaged part of the coating; transferring the test piece with the cover plate into an environmental test box, and setting temperature, humidity and test time; the test piece is moved out of the environment test box, washed, dried and photographed, the filiform corrosion length is measured, and the filiform corrosion risk of the plated steel is judged according to the filiform corrosion length. The method provided by the embodiment of the invention can shorten the test time.

Description

Technical Field

[0001] The invention relates to the technical field of corrosion testing, and in particular to a method for testing filamentary corrosion of a vehicle body coating. Background Art

[0002] Filiform corrosion, also known as sub-film corrosion, is a corrosion phenomenon that occurs under a metal surface coating. When the coating of the plated steel contains relatively active Mg, once the surface coating is damaged, filiform corrosion may occur, affecting the appearance of the vehicle body and even destroying the structural safety. Tests on plated steel under the vehicle body coating are generally conducted on the plated steel body, and the test cycle is long. It is impossible to predict the risk of filiform corrosion of the plated steel under the vehicle body coating in the actual service environment in a short period of time. Summary of the invention

[0003] The embodiment of the present invention provides a method for testing filamentary corrosion of vehicle body coatings to at least solve some of the above technical problems existing in the prior art.

[0004] In a first aspect, an embodiment of the present invention provides a method for testing filiform corrosion of a vehicle body coating, comprising:

[0005] Destroy the coating on the surface of the test piece to expose the metal matrix and clean the debris on the surface of the test piece;

[0006] introducing an electrolyte solution onto the metal substrate at the location where the coating is damaged;

[0007] Place a cover plate where the coating is damaged;

[0008] Move the test piece with the cover into the environmental test chamber and set the temperature, humidity and test time;

[0009] The test piece is removed from the environmental test chamber, rinsed, dried, photographed, and the length of the filiform corrosion is measured. The risk of filiform corrosion of the coated steel is determined by the length of the filiform corrosion.

[0010] In an optional embodiment, it also includes:

[0011] The coated steel plate is cut into sheets and painted together with the body-in-white in a painting line to obtain test pieces.

[0012] In an optional embodiment, the coated steel is cut into sheets and the coating process is completed in a coating production line together with the body in white, including:

[0013] A through hole is opened on the top of the sheet, a conductive metal wire is passed through the through hole, and the sheet is mounted on the white vehicle body for painting.

[0014] In an optional embodiment, the steel plates with different coatings are cut into sheets respectively, and the sheets with different coatings are subjected to coating treatment together with the body-in-white in a coating production line.

[0015] In an optional embodiment, destroying the surface coating of the test piece includes:

[0016] Use a scriber to mechanically damage the surface of the test piece to scratch a target width and depth directly to the steel plate substrate; or

[0017] A stone striking device is used to spray particles to impact the surface of the test piece, thereby forming damaged spots on the surface of the test piece.

[0018] In an optional embodiment, introducing an electrolyte solution onto the metal substrate at the damaged portion of the coating comprises:

[0019] If the coating on the surface of the test piece is damaged by a scriber, the electrolyte solution is introduced into the damaged part of the coating by a micro-injector;

[0020] If the surface coating of the test piece is damaged by stone-impact coating, the electrolyte solution is introduced into the damaged part of the coating by spraying in a salt spray environment test box.

[0021] In an optional embodiment, the stone striking device comprises:

[0022] An injection pipe, one end of which is closed and the other end is open, the open end forms an injection port, the injection pipe is provided with a feed port and an air inlet, the feed port is closer to the injection port than the air inlet;

[0023] A feeding assembly connected to the feeding port and used for feeding impact particles into the injection pipe;

[0024] An air inlet pipe connected to the air inlet and used to provide high-pressure gas;

[0025] The sample chamber is used for placing the sample, and the injection port extends into the sample chamber.

[0026] In an optional embodiment, the feeding assembly includes:

[0027] A feed hopper, which is used to contain impact particles, and a feed adjustment switch is provided at the bottom of the feed hopper;

[0028] A conveying assembly is arranged below the feed hopper, the conveying assembly comprises a conveyor belt and a conveying motor, the conveying motor drives the conveyor belt to rotate, and the conveyor belt receives and conveys the particles dropped from the feed hopper;

[0029] The material dropping channel is located below the output end of the transmission belt, and the material dropping channel is connected to the feed port.

[0030] In an optional embodiment, in the environmental test box, the temperature is set to 50±2° C., the humidity is set to 95±2%, and the test time is 150 hours.

[0031] In an optional embodiment, judging the risk of filiform corrosion of the coated steel by the filiform corrosion length includes:

[0032] When the maximum length of filiform corrosion is ≥1.0 mm, the corresponding coated steel plate is at risk of filiform corrosion under actual service conditions;

[0033] When the maximum filiform corrosion length is less than 1.0 mm, there is no risk of filiform corrosion for the coated steel plate under actual service conditions.

[0034] An embodiment of the present invention has the following advantages or beneficial effects:

[0035] In the filigree corrosion test method for vehicle body coating of the embodiment of the present invention, the coating on the surface of the test piece is destroyed to expose the metal substrate, and the debris on the surface of the test piece is cleaned; an electrolyte solution is introduced on the metal substrate at the damaged coating to corrode the metal substrate; a cover plate is placed at the damaged coating; the test piece with the cover plate is moved into an environmental test chamber, and the temperature, humidity, and test time are set; the test piece is moved out of the environmental test chamber, rinsed, dried, photographed, and the length of the filigree corrosion is measured, and the risk of filigree corrosion of the coated steel is determined by the length of the filigree corrosion. By placing a cover plate at the damaged coating, the embodiment of the present invention can avoid the concentration of the electrolyte solution in the environmental test chamber being affected by the humidification liquid, and can shorten the test time. BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The above and other features and advantages of the present invention will become more apparent by describing in detail exemplary embodiments thereof with reference to the attached drawings.

[0037] Figure 1 is a schematic flow chart of a method for testing filiform corrosion of a vehicle body coating according to an exemplary embodiment;

[0038] Figure 2 It is a schematic structural diagram of a stone impact device in a method for testing filamentary corrosion of a vehicle body coating according to an exemplary embodiment.

[0039] Among them, the figure numbers are explained as follows: 201-feed hopper, 202-feed adjustment switch, 203-transmission pipeline, 204-conveyor belt, 205-transmission motor, 206-feeding channel, 207-injection pipe, 208-air pressure valve, 209-intake pipe, 210-sample chamber, 211-sample rack, 213-collection tray, 214-particles. DETAILED DESCRIPTION

[0040] Example embodiments will now be described more fully with reference to the accompanying drawings. However, example embodiments can be implemented in a variety of forms and should not be construed as limited to the embodiments set forth herein; rather, these embodiments are provided so that the present invention will be comprehensive and complete and fully convey the concepts of the example embodiments to those skilled in the art. The same reference numerals in the figures represent the same or similar structures, and thus their detailed description will be omitted.

[0041] The terms "a", "an", "the", and "said" are used to indicate the presence of one or more elements / components / etc.; the terms "comprising" and "having" are used to express an open-ended inclusive meaning and mean that additional elements / components / etc. may be present in addition to the listed elements / components / etc.

[0042] See also Figure 1 The embodiment of the present invention provides a method for testing filiform corrosion of a vehicle body coating, comprising:

[0043] S10, destroy the coating on the surface of the test piece to expose the metal substrate, and clean the debris on the surface of the test piece;

[0044] S20, introducing an electrolyte solution onto the metal substrate at the damaged portion of the coating;

[0045] S30, placing a cover plate at the damaged part of the coating;

[0046] S40, moving the test piece with the cover into the environmental test box, and setting the temperature, humidity, and test time;

[0047] S50. Remove the test piece from the environmental test chamber, rinse, dry, take photos, and measure the length of filiform corrosion. The risk of filiform corrosion of the coated steel is determined by the length of filiform corrosion.

[0048] In the filigree corrosion test method for vehicle body coating of the embodiment of the present invention, the coating on the surface of the test piece is destroyed to expose the metal substrate, and the debris on the surface of the test piece is cleaned; an electrolyte solution is introduced on the metal substrate at the damaged coating to corrode the metal substrate; a cover plate is placed at the damaged coating; the test piece with the cover plate is moved into the environmental test chamber, and the temperature, humidity, and test time are set; the test piece is moved out of the environmental test chamber, rinsed, dried, photographed, and the length of the filigree corrosion is measured, and the risk of filigree corrosion of the coated steel is determined by the length of the filigree corrosion. The embodiment of the present invention can reduce the volatilization of the electrolyte solution by placing a cover plate at the damaged coating, and can. It can avoid being washed away by accumulated water droplets in the environmental test chamber, reduce the impact on corrosion, and shorten the test time.

[0049] In the embodiment of the present invention, a test piece is used to perform a filiform corrosion test on a vehicle body coating, and there is no need to perform a test on the coated steel body. The test piece is used for the test, which can shorten the test time.

[0050] In some embodiments, the method of the embodiment of the present invention further includes: cutting the coated steel plate into sheets, and completing the coating process together with the body-in-white in a coating production line to obtain a test piece. By coating the cut sheets together with the body-in-white in a coating production line, the surface coating of the test piece can be made consistent with that of the body, so that the surface state of the test piece is close to the actual service state, thereby improving the accuracy of the test result.

[0051] In the embodiment of the present invention, the size of the cut sheet can be determined according to the specific situation. In a specific implementation, the size of the test piece can be, for example, 75 mm×150 mm×2 mm.

[0052] In some embodiments, the coated steel is cut into sheets and the coating process is completed in the coating production line together with the body in white, including: a through hole is opened on the top of the sheet, a conductive metal wire is passed through the through hole, and the sheet is mounted on the body in white for coating. By opening a through hole on the top of the sheet, the sheet can be hung on the body in white through the conductive metal wire for coating, so that the coating of the obtained test piece is consistent with the body. The size of the through hole can be determined according to the situation. The size of the through hole should ensure the passing of the conductive metal wire. In a specific implementation, the diameter of the through hole can be 5 mm.

[0053] In some embodiments, steel plates with different coatings are cut into sheets respectively, and the sheets with different coatings are coated together with the body-in-white in a coating production line. By cutting steel plates with different coatings, the obtained test pieces can simulate different body types, thereby testing different body types.

[0054] In some embodiments, damaging the coating on the surface of the test piece includes: using a scriber to mechanically scratch the surface of the test piece with a target width and depth reaching the steel plate substrate. Using a scriber to perform scratching can simulate the situation where filiform corrosion extends from the edge of the sheet metal blanking.

[0055] In some embodiments, a stone striking device is used to spray particles to impact the surface of the test piece, forming damaged spots on the surface of the test piece. The use of stone striking can simulate the expansion of steel wire-like corrosion of the coating after the coating is damaged by sand and stone during the driving process of the car.

[0056] In the embodiment of the present invention, the debris on the surface of the test piece can be cleaned by at least one of a brush and an adhesive tape, or other methods can be adopted to clean it.

[0057] In the embodiment of the present invention, the electrolyte solution includes a neutral electrolyte solution, an alkaline electrolyte solution and an acidic electrolyte solution. In a specific implementation, the electrolyte solution includes but is not limited to a sodium chloride solution, an acetic acid solution and a hydrochloric acid solution.

[0058] In some embodiments, the electrolyte solution is introduced onto the metal substrate at the damaged portion of the coating, including: if a scriber is used to damage the coating on the surface of the test piece, a microinjector is used to introduce the electrolyte solution at the damaged portion of the coating.

[0059] In some embodiments, an electrolyte solution is introduced onto the metal substrate at the damaged portion of the coating, including: if the coating on the surface of the test piece is damaged by stone impact coating, an electrolyte solution is introduced into the damaged portion of the coating by spraying in a salt spray environment test chamber.

[0060] In some embodiments, see Figure 2 The stone striking device includes a jet pipe, a feeding assembly, an air inlet pipe and a sample bin. One end of the jet pipe is closed and the other end is open. The open end forms a jet port. A feeding port and an air inlet are provided on the jet pipe. The feeding port is closer to the jet port than the air inlet. The feeding assembly is connected to the feeding port and is used to transport impact particles into the jet pipe. The air inlet pipe is connected to the air inlet and is used to provide high-pressure gas. The sample bin is used to place samples, and the jet port extends into the sample bin. The feeding assembly inputs the impact particles from the feeding port into the jet pipe. The high-pressure gas provided by the air inlet pipe flows at a high speed in the jet pipe, and drives the particles to be ejected from the jet port to impact the sample, thereby forming damage spots on the surface of the sample.

[0061] In some embodiments, see Figure 2 A sample holder may be provided in the sample chamber, and the sample is fixed on the sample holder. In a specific implementation, the sample holder may include a clamping mechanism, and the clamping mechanism is used to clamp and fix the sample.

[0062] In some embodiments, see Figure 2 The feeding assembly includes a feed hopper, a transmission assembly, and a drop channel. The feed hopper is used to hold impact particles. A feed adjustment switch is provided at the bottom of the feed hopper. The drop speed of the feed hopper can be adjusted by adjusting the switch, thereby adjusting the supply of particles.

[0063] The conveying assembly is arranged below the feed hopper, and the conveying assembly includes a conveyor belt and a conveying motor. The conveying motor drives the conveyor belt to rotate, and the conveying belt receives and conveys the particles falling from the feed hopper. The particles falling from the feed hopper fall onto the conveying belt. When the conveying motor drives the conveyor belt to rotate, the particles are carried and moved, and fall from the output end of the conveyor belt, thereby realizing the transmission of the particles. The conveying assembly may also include a conveying pipe, which is connected to the bottom of the feed hopper, and the conveyor belt and the conveying motor may be arranged in the conveying pipe.

[0064] The material dropping channel is located below the output end of the transmission belt, and is connected to the feed port. The material dropping channel can be connected to the conveying pipeline, and the particles carried by the conveying belt fall into the material dropping channel and fall into the injection pipe along the material dropping channel.

[0065] In some embodiments, see Figure 2The stone striking device also includes a collecting tray, which is arranged at the bottom of the sample bin and is used to collect particles after injection.

[0066] In the embodiment of the present invention, the impact particles may be gravel or steel balls. In a specific implementation, the steel balls may have edges and corners.

[0067] In the embodiment of the present invention, the stone striking device can perform stone striking destruction according to the following steps:

[0068] 1. Place the sample on the sample holder; 2. Pour the steel balls into the feed hopper; 3. Introduce compressed air into the injection pipe and adjust the pressure valve to the set value; 4. Turn on the conveying motor and adjust the motor speed to the set value; 5. Turn on the feed adjustment switch; 6. Spray the steel balls to impact the sample for the set time; 7. After the injection is completed, turn off all switches and recover the steel balls from the collection box.

[0069] In some embodiments, in the environmental test box, the temperature is set to 50±2°C, the humidity is set to 95±2%, and the test time is 150 hours. In the embodiment of the present invention, the sample time is about 150 hours to complete the filamentary corrosion experiment, and the test time is short. The experimental temperature and humidity can be adjusted according to the specific situation. In the specific implementation, the experimental temperature and humidity can be adjusted according to the electrolyte solution used.

[0070] In some embodiments, the risk of filiform corrosion of coated steel is determined by the length of filiform corrosion, including: when the maximum filiform corrosion length is ≥1.0 mm, the corresponding coated steel plate has the risk of filiform corrosion under actual service conditions; when the maximum filiform corrosion length is <1.0 mm, there is no risk of filiform corrosion for the coated steel plate under actual service conditions.

[0071] The method and effects of the embodiments of the present invention are described below through specific examples.

[0072] Example 1

[0073] Step 1: Use laser cutting to cut the galvanized sheet into sheets of 75mm×150mm×2mm, and cut a circular hole with a diameter of 5mm on the top of the sheet. Use iron wire to pass through the circular hole and mount it on the body in white. Follow the body in white in the production line to undergo degreasing, surface conditioning, phosphating, electrophoresis, drying, intermediate coating, topcoat, varnish and other processes to form a complete body coating on the surface of the sheet to obtain a test piece.

[0074] Step 2: Use a scriber to form a scratch with a length of 60 mm and a width of 1 mm on the test piece. The scratch penetrates the electro-coating layer and the metal plating layer to reach the surface of the metal substrate. Use a soft brush to clean the debris on the surface of the test piece.

[0075] Step 3: Use a microinjector to evenly inject 10 μL of a 1.5 mol / L CH3COOH solution (pH≈2) onto the scratch.

[0076] Step 4: Place a PP cover plate with a size of 62 mm × 3 mm × 0.3 mm on the scratch to cover the scratch.

[0077] Step 5, move the test piece into the test box, fix the test piece on the sample holder in the test box, make the scratch angle 75° with the horizontal plane. The test box temperature is set to 50±2℃, the humidity is set to 95±2%, the test time is 150 hours, and the test box is filled with deionized water with a conductivity of ≤20μs / cm to maintain the humidity.

[0078] Step 6: Rinse the surface of the test piece with deionized water with a conductivity of ≤20μs / cm, dry the test piece with hot air at 40±3°C, then use a high-definition camera to photograph the corrosion condition on the surface of the test piece, import the photograph into the image processing software to measure the length of the filiform corrosion, and record the maximum filiform corrosion length data. See Table 1 for details.

[0079] Table 1 Maximum filiform corrosion length of different specimens under scratching damage mode

[0080]

[0081] When test pieces 1 and 2 are in actual service, there is a risk of filiform corrosion when they are at the edge of the sheet metal; when test pieces 3 and 4 are in actual service, there is no risk of filiform corrosion when they are at the edge of the sheet metal.

[0082] Example 2

[0083] Step 1: Use laser cutting to cut the galvanized sheet into sheets of 75mm×150mm×2mm, and cut a circular hole with a diameter of 5mm on the top of the sheet. Use iron wire to pass through the circular hole and mount it on the body in white. Follow the body in white in the production line to undergo degreasing, surface conditioning, phosphating, electrophoresis, drying, intermediate coating, topcoat, varnish and other processes to form a complete body coating on the surface of the sheet to obtain a test piece.

[0084] Step 2: Use a stone striking device to destroy the surface coating of the sample. The diameter of the steel ball used is 3-4 mm. After surface quenching, the hardness can reach Rockwell hardness 60-63. Adjust the conveyor motor so that the conveyor belt speed is 1m / s. The pressure valve of the spray channel is set to 1.1±0.05bar, the distance between the fracture of the spray channel and the surface of the test piece is 20cm, and the impact time is 1min. After the impact, use a soft brush to clean the debris on the surface of the test piece.

[0085] Step 3, put the test piece into a salt spray test chamber, add a 1.5 mol / L CH3COOH solution as the medium in the salt spray test chamber, and take out the test piece after 1 hour.

[0086] Step 4: Place a 0.3mm thick PP cover plate on the impact damaged surface to cover all coating damage.

[0087] Step 5, move the test piece into the test box, fix the test piece on the sample holder in the test box, make the scratch angle 75° with the horizontal plane. The test box temperature is set to 50±2℃, the humidity is set to 95±2%, the test time is 150 hours, and the test box is filled with deionized water with a conductivity of ≤20μs / cm to maintain the humidity.

[0088] Step 6: Rinse the surface of the test piece with deionized water having a conductivity of ≤20μs / cm, dry the test piece with hot air at 40±3°C, then photograph the corrosion condition of the test piece surface with a high-definition camera, import the photograph into the image processing software to measure the length of the filiform corrosion, and record the maximum filiform corrosion length data. See Table 2 for details.

[0089] Table 2 Maximum filiform corrosion length of different specimens under simulated stone impact damage

[0090]

[0091] When test pieces 1 and 2 are in actual service, there is a risk of filiform corrosion when they are in the sand and gravel splashing area; when test pieces 3 and 4 are in actual service, there is no risk of filiform corrosion when they are in the sand and gravel splashing area.

[0092] In the embodiments of the present invention, the term "plurality" refers to two or more than two, unless otherwise clearly defined. The terms "installation", "connection", "fixation" and the like should be understood in a broad sense. For example, "connection" can be a fixed connection, a detachable connection, or an integral connection. For those of ordinary skill in the art, the specific meanings of the above terms in the embodiments of the present invention can be understood according to specific circumstances.

[0093] In the description of the embodiments of the present invention, it needs to be understood that the directions or positional relationships indicated by the terms "upper" and "lower" are based on the directions or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the embodiments of the present invention and simplifying the description, rather than indicating or implying that the device or unit referred to must have a specific direction, be constructed and operated in a specific orientation. Therefore, it cannot be understood as a limitation on the embodiments of the present invention.

[0094] In the description of this specification, the description of the terms "one embodiment", "a preferred embodiment", etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the embodiment of the present invention. In this specification, the schematic representation of the above terms does not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any one or more embodiments or examples in a suitable manner.

[0095] The above are only preferred embodiments of the present invention and are not intended to limit the present invention. For those skilled in the art, the present invention may have various modifications and changes. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present invention should be included in the protection scope of the present invention.

Claims

1. A method for testing filamentary corrosion of a vehicle body coating, characterized in that: include: Destroy the coating on the surface of the test piece to expose the metal matrix and clean the debris on the surface of the test piece; introducing an electrolyte solution onto the metal substrate at the location where the coating is damaged; Place a cover plate where the coating is damaged; Move the test piece with the cover into the environmental test chamber and set the temperature, humidity and test time; The test piece is removed from the environmental test chamber, rinsed, dried, photographed, and the length of the filiform corrosion is measured. The risk of filiform corrosion of the coated steel is determined by the length of the filiform corrosion.

2. The method for testing the filiform corrosion of a vehicle body coating according to claim 1, characterized in that: Also includes: The coated steel plate is cut into sheets and painted together with the body-in-white in a painting line to obtain test pieces.

3. The method for testing the filiform corrosion of a vehicle body coating according to claim 2, characterized in that: The coated steel is cut into sheets and painted along with the body in white in the painting line, including: A through hole is opened on the top of the sheet, a conductive metal wire is passed through the through hole, and the sheet is mounted on the white vehicle body for painting.

4. The method for testing the filiform corrosion of a vehicle body coating according to claim 2, characterized in that: The steel plates with different coatings are cut into sheets respectively, and the sheets with different coatings are painted together with the body in white in the painting production line.

5. The method for testing the filiform corrosion of vehicle body coating according to claim 1, characterized in that: Destroy the surface coating of the test piece, including: Use a scriber to mechanically damage the surface of the test piece to scratch a target width and depth directly to the steel plate substrate; or A stone striking device is used to spray particles to impact the surface of the test piece, thereby forming damaged spots on the surface of the test piece.

6. The method for testing the filiform corrosion of vehicle body coating according to claim 5, characterized in that: Introducing an electrolyte solution onto the metal substrate where the coating is damaged, including: If the coating on the surface of the test piece is damaged by a scriber, the electrolyte solution is introduced into the damaged part of the coating by a micro-injector; If the surface coating of the test piece is damaged by stone-impact coating, the electrolyte solution is introduced into the damaged part of the coating by spraying in a salt spray environment test box.

7. The method for testing the filiform corrosion of a vehicle body coating according to claim 5, characterized in that: The stone striking device includes: An injection pipe, one end of which is closed and the other end is open, the open end forms an injection port, the injection pipe is provided with a feed port and an air inlet, the feed port is closer to the injection port than the air inlet; A material conveying assembly connected to the feed port and used for conveying impact particles into the injection pipe; An air inlet pipe connected to the air inlet and used to provide high-pressure gas; The sample chamber is used for placing the sample, and the injection port extends into the sample chamber.

8. The method for testing the filiform corrosion of vehicle body coating according to claim 7, characterized in that: The feeding assembly comprises: A feed hopper, which is used to contain impact particles, and a feed adjustment switch is provided at the bottom of the feed hopper; A conveying assembly is arranged below the feed hopper, the conveying assembly comprises a conveyor belt and a conveying motor, the conveying motor drives the conveyor belt to rotate, and the conveyor belt receives and conveys the particles dropped from the feed hopper; The material dropping channel is located below the output end of the transmission belt, and the material dropping channel is connected to the feed port.

9. The method for testing the filiform corrosion of vehicle body coating according to claim 1, characterized in that: In the environmental test box, the temperature is set to 50±2° C., the humidity is set to 95±2%, and the test time is 150 hours.

10. The method for testing the filiform corrosion of vehicle body coating according to claim 1, characterized in that: The risk of filiform corrosion of coated steel is determined by the length of filiform corrosion, including: When the maximum length of filiform corrosion is ≥1.0 mm, the corresponding coated steel plate is at risk of filiform corrosion under actual service conditions; When the maximum filiform corrosion length is less than 1.0 mm, there is no risk of filiform corrosion for the coated steel plate under actual service conditions.

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