Corrosion resistance evaluation method for formed plated thin steel plate

Abstract

The invention relates to a method for evaluating the corrosion resistance of a formed plated thin steel plate, which comprises the following steps of: performing a drawing test on a disc-shaped sample of the formed plated thin steel plate to form a cup-shaped sample; calculating a deformation factor of the cup-shaped sample after the drawing test; cleaning, drying and weighing the cup-shaped sample subjected to the drawing test for the first time; performing a neutral salt spray test on the cup-shaped sample cleaned for the first time; cleaning, drying and weighing the cup-shaped sample subjected to the neutral salt spray test for the second time; respectively calculating the weight variation of the N cup-shaped samples after the first cleaning and the second cleaning, and calculating the average weight loss of the N samples; and comparing the average weight loss of different types of formed coating thin steel plate samples with the same coating thickness under the same deformation factor or the average weight loss of the same formed coating thin steel plate sample under different deformation factors, and when the average weight loss of the sample is smaller, the corrosion resistance of the formed coating thin steel plate under the same condition is stronger.

Description

Technical Field

[0001] The present invention belongs to the field of corrosion resistance of coated thin steel plates, and relates to a method for evaluating the corrosion resistance of coated thin steel plates after forming. Background Art

[0002] With the continuous improvement of the requirements for automobiles in terms of energy conservation, environmental protection, and safety, it is necessary to ensure that the steel materials are not severely corroded during their service life. Coated plates with excellent corrosion resistance account for an increasing proportion of the body materials. Most coated steel plates need to be cold-formed before corresponding parts can be formed. During the cold-forming process, internal stresses are generated between the coating and the substrate due to different plastic deformation degrees. Under different deformation amounts and deformation methods, different degrees and types of cracks are likely to occur in the coating, causing the coating to powder or peel off, thereby reducing the corrosion resistance and paintability of the coating. The mechanical stress generated by deformation leads to a reduction in the coating thickness and the appearance of internal cracks in the coating, thus reducing the protection ability of the coating for the substrate.

[0003] Currently, for the corrosion resistance test of automotive coated thin steel plates, most directly conduct neutral salt spray tests on the coated thin steel plates. However, it can only characterize the corrosion resistance of the coated thin steel plates in their original state and cannot characterize the corrosion resistance under the actual conditions after stamping. Moreover, there is no research on the method of neutral salt spray test for automotive coated thin steel plates after cold forming. Therefore, to solve this problem, a method for evaluating the corrosion resistance of cold-formed automotive coated thin steel plates is urgently needed. Summary of the Invention

[0004] In order to solve the problem that the existing corrosion resistance tests of materials are based on the original plates and cannot accurately characterize the actual service conditions of automotive coated thin plate materials, the technical solution adopted by the present invention is: a method for evaluating the corrosion resistance of coated thin steel plates after forming, including the following steps:

[0005] Obtain circular sheet specimens of N pieces of to-be-tested coated thin steel plates after forming;

[0006] Conduct a drawing test on the circular sheet specimens of the coated thin steel plates after forming to form cup-shaped specimens;

[0007] Calculate the deformation factor of the cup-shaped specimens after the drawing test;

[0008] Conduct the first cleaning, drying, and weighing on the cup-shaped specimens after the drawing test;

[0009] Conduct a neutral salt spray test on the cup-shaped specimens after the first cleaning;

[0010] Conduct the second cleaning, drying, and weighing on the cup-shaped specimens after the neutral salt spray test;

[0011] Calculate the weight change of N cup-shaped specimens after the first cleaning and the second cleaning respectively, and calculate the average weight loss of the N specimens;

[0012] Compare the average weight loss of coated steel sheet specimens with the same coating thickness and different types of forming under the same deformation factor, or the average weight loss of the same formed coated steel sheet specimens under different deformation factors. The smaller the average weight loss of the specimens, the stronger the corrosion resistance of the formed coated steel sheet under the same conditions.

[0013] Furthermore: The calculation formula for the deformation factor T is as follows:

[0014]

[0015] Where: D0 represents the diameter of the specimen; h represents the drawing depth of the specimen; d p represents the diameter of the drawing punch of the specimen; r p represents the fillet radius of the punch.

[0016] Furthermore: The drawing test is carried out according to the method of "GB / T15825.3-2008 Metallic materials - Sheet and strip - Determination of formability - Part 3: Drawing and drawing load tests".

[0017] Furthermore: During the operation of the neutral salt spray test on the specimens after the drawing test, N specimens of the coated steel sheet after the drawing test are placed with the openings facing down at different positions in the corrosion chamber for the neutral salt spray test.

[0018] Furthermore: The operation process of the second cleaning of the specimens after the neutral salt spray test is as follows:

[0019] S61: Rinse the sodium chloride on the surface of the specimen after the neutral salt spray test with water;

[0020] S62: Immerse the specimen in hydrochloric acid solution and hexamethylenetetramine to remove the corrosion products;

[0021] S63: Wash the specimen from which the corrosion products have been removed with distilled water or deionized water;

[0022] S64: Finally, wash the specimen with ethanol.

[0023] Furthermore: The calculation formula for the average weight loss ΔM 平均 is as follows:

[0024]

[0025] Where: N represents the number of specimens, ΔM1 represents the mass of the first specimen, and ΔM n represents the mass of the nth specimen.

[0026] A method for evaluating the corrosion resistance of a plated thin steel sheet after forming provided by the present invention is a method for more accurately characterizing the corrosion resistance service performance of a plated thin steel sheet after stamping forming; the present invention uses a drawing test to preprocess the specimen for forming and then conducts a corrosion test to more accurately characterize the corrosion resistance service performance of the plated thin steel sheet after stamping forming, and provides a method for evaluating the corrosion resistance of a cold-formed plated thin steel sheet for automobiles, providing guidance for the popularization and application of the plated thin steel sheet for automobiles in automobiles. BRIEF DESCRIPTION OF THE DRAWINGS

[0027] In order to more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the following will briefly introduce the drawings required for the description of the embodiments or the prior art. Obviously, the drawings in the following description are some embodiments of the present invention. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative labor.

[0028] Figure 1 Flow chart of the method of the present application;

[0029] Figure 2 Schematic diagram of a circular sheet specimen of a plated thin steel sheet after forming;

[0030] Figure 3 Side view of a cup-shaped specimen after drawing. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0031] It should be noted that, without conflict, the embodiments in the present invention and the features in the embodiments can be combined with each other. The following will refer to the drawings and combine the embodiments to detail the present invention.

[0032] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the following will clearly and completely describe the technical solutions in the embodiments of the present invention with reference to the drawings in the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, rather than all embodiments. The following description of at least one exemplary embodiment is actually only illustrative and in no way limits the present invention and its application or use. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without creative labor belong to the scope of protection of the present invention.

[0033] Figure 1 Flow chart of the method of the present application;

[0034] A method for evaluating the corrosion resistance of a plated thin steel sheet after forming includes the following steps:

[0035] S1: Obtain circular sheet specimens of N formed coated steel sheets to be tested; the circular sheet specimens are processed by wire cutting based on the coated steel sheets, and it is necessary to ensure that there are no burrs and cracks on the edges of the specimens;

[0036] Figure 2 is a schematic diagram of a circular sheet specimen of a formed coated steel sheet;

[0037] S2: Conduct a drawing test on the circular sheet specimens of the formed coated steel sheets to form cup-shaped specimens; Figure 3 is a side view of the cup-shaped specimen after drawing;

[0038] S3: Calculate the deformation factor of the cup-shaped specimens after the drawing test;

[0039] S4: Conduct the first cleaning, drying, and weighing on the cup-shaped specimens after the drawing test;

[0040] S5: Conduct a neutral salt spray test on the cup-shaped specimens after the drawing test;

[0041] S6: Conduct the second cleaning, drying, and weighing on the cup-shaped specimens after the neutral salt spray test;

[0042] S7: Calculate the weight change of N cup-shaped specimens before the first cleaning and after the second cleaning respectively, and calculate the average weight loss of N specimens;

[0043] S8: Compare the average weight loss of specimens of formed coated steel sheets with the same coating thickness but different types under the same deformation factor or the average weight loss of specimens of the same formed coated steel sheet under different deformation factors. When the average weight loss of the specimens is smaller, the corrosion resistance of the formed coated steel sheet under the same conditions is stronger.

[0044] The same conditions mentioned above are: evaluating the corrosion resistance of specimens of formed coated steel sheets of different types or evaluating the corrosion resistance of specimens of the same formed coated steel sheet after drawing deformation under different deformation factors;

[0045] Specimens of formed coated steel sheets of different types: include galvanized steel sheets, galvanized aluminum steel sheets, galvanized aluminum magnesium steel sheets, etc.;

[0046] The steps S1 / S2 / S3 / S4 / S5 / S6 / S7 / S8 are executed in sequence;

[0047] Furthermore: The calculation formula for the deformation factor T is as follows:

[0048]

[0049] Among them: D0 represents the diameter of the specimen; h represents the drawing depth of the specimen; d pDenote the diameter of the drawing punch of the specimen; r p Denote the fillet radius of the punch. The deformation factor characterizes the degree of deformation of the coated thin sheet after drawing and bending. The larger the T, the greater the deformation of the material;

[0050] Furthermore, the drawing test is carried out according to the method of "GB / T 15825.3-2008 Metallic sheet--Forming properties and test methods--Part 3: Drawing and drawing load tests". The drawing specimen is drawn to a certain depth h (drawing stroke), the diameter of the punch is d p , and the fillet radius of the punch is r p Ensure that no cracking, wrinkling or obvious asymmetry in shape occurs to the cup body after drawing;

[0051] Furthermore, the first cleaning process for the cup-shaped specimen after the drawing test is as follows:

[0052] Use a clean soft brush, soft cloth or ultrasonic cleaning device to thoroughly clean with an appropriate organic solution (hydrocarbon with a boiling point between 60°C and 120°C), remove the oil stains and dust on the surface, and then dry;

[0053] After cleaning, blow-dry and weigh the cup-shaped specimen to obtain the weight M of N specimens i (i = 1, 2... N), accurate to ±1 mg;

[0054] After the first cleaning, protect the edges and back of the specimen with a removable covering layer. Before weighing after the second cleaning, remove the covering layer on the edges and back of the specimen;

[0055] Furthermore, the operation process of the neutral salt spray test for the specimen after the drawing test is as follows:

[0056] Place the N specimens of the coated thin steel sheet after the tensile test with the opening facing down at different positions in the corrosion chamber;

[0057] The spray solution is prepared by dissolving sodium chloride in distilled water or deionized water with a conductivity not higher than 20 μS / cm to a concentration of 50 g / L ± 5 g / L;

[0058] During the test, the pH value of the spray solution collected in the salt spray chamber is between 7 ± 0.5.

[0059] The test cycle of the neutral salt spray test is 2 h, 6 h, 24 h, 48 h, 72 h, 96 h, 144 h, 168 h, 240 h, 480 h, 720 h, 1000 h or other agreed time cycles.

[0060] Furthermore: The operation process of the second cleaning for the specimen after the neutral salt spray test is as follows:

[0061] S61: After the neutral salt spray test, rinse the sodium chloride on the surface of the specimen with water;

[0062] S62: Immerse the specimen in a hydrochloric acid solution with a volume fraction of 50% added with 3 g / L of hexamethylenetetramine to remove the corrosion products;

[0063] S63: Wash the specimen with distilled water or deionized water to remove the corrosion products;

[0064] S64: Then finally wash the specimen with alcohol, and weigh the specimen as M after cleaning and drying i ’(i = 1, 2…N).

[0065] Furthermore: The average weight loss ΔM 平均 is calculated as follows:

[0066]

[0067] where: N represents the number of specimens, ΔM1 represents the mass of the first specimen, and ΔM n represents the mass of the nth specimen.

[0068] Example 1:

[0069] S1. Sampling and processing of specimens:

[0070] Take specimens of two plating sheets 1 and 2 with the same plating thickness but different plating types, and process the specimens by wire cutting. Each plating sheet is processed into 6 circular specimens with a diameter of D0 = 100 mm, ensuring that there are no burrs or cracks at the edges of the specimens;

[0071] S2. Deep drawing test: According to the method of "GB / T15825.3-2008 Metallic materials - Sheet and strip -- Determination of formability -- Part 3: Deep drawing and deep drawing load test", the same deep drawing test is carried out on plating sheets 1 and 2. Deep draw the specimen to a depth of h = 29 mm, with a punch diameter d p = 50 mm and a punch fillet radius r p = 5 mm; ensure that no cracking, wrinkling or obvious asymmetry in shape occurs on the drawn cup;

[0072] S3. The deformation factor T calculation formula for plating sheets 1 and 2 is as shown in formula (1), and the deformation factor is used to characterize the degree of deformation of the plated thin sheet after drawing and bending.

[0073]

[0074] S4: Carefully conduct the first cleaning on the cup-shaped specimens of plating sheets 1 and 2, dry them and weigh them. The results are shown in Table 1, accurate to ±1 mg,

[0075] S5: Neutral salt spray test: Conduct a neutral salt spray test on the coated sheets 1 and 2 after the first cleaning. Note that the open ends of the cup-shaped specimens are placed downward at six different positions in the corrosion chamber. The pH value of the spray solution is between 7 ± 0.5, the collected salt fog concentration is 50 g / L ± 5 g / L, and the time is 168 hours.

[0076] Table 1 Weights of the 6 cup-shaped specimens before corrosion (unit: g)

[0077] Specimen label <![CDATA[M1]]> <![CDATA[M2]]> <![CDATA[M3]]> <![CDATA[M4]]> <![CDATA[M5]]> <![CDATA[M6]]> Coated sheet 1 61.623 61.585 61.587 61.650 61.662 61.638 Coated sheet 2 61.658 61.678 61.532 61.485 61.688 61.552

[0078] S6: After the salt spray test, conduct a second cleaning on the specimens. The specific process is as follows:

[0079] Immerse the specimens in a hydrochloric acid solution with a volume fraction of 50% + hexamethylenetetramine at 3 g / L, then clean the specimens with distilled water or deionized water, and weigh them after cleaning and drying with alcohol as shown in Table 2.

[0080] S7: Calculate the weight change ΔM of the specimens before and after corrosion, ΔM = M i -M i ’ where i = 1…6; the results are shown in Table 3.

[0081] Table 2 Weights of the 6 cup-shaped specimens after corrosion (unit: g)

[0082] Specimen label <![CDATA[M1’]]> <![CDATA[M2’]]> <![CDATA[M3’]]> <![CDATA[M4’]]> <![CDATA[M5’]]> <![CDATA[M6’]]> Coated sheet 1 55.708 55.573 56.055 55.284 56.437 56.310 Coated sheet 2 58.276 57.663 57.895 57.330 58.200 57.213

[0083] Table 3 Weight changes of the 6 cup-shaped specimens after corrosion (unit: g)

[0084] Specimen label <![CDATA[ΔM1]]> <![CDATA[ΔM2]]> <![CDATA[ΔM3]]> <![CDATA[ΔM4]]> <![CDATA[ΔM5]]> <![CDATA[ΔM6]]> Coated sheet 1 5.915 6.012 5.532 6.366 5.225 5.328 Coated sheet 2 3.382 4.015 3.637 4.155 3.488 4.339

[0085] Calculate that under the condition of the deformation factor T = 0.037, the average weight loss ΔM of the 6 specimens of the coated sheet 1 平均1 = 5.729 g, and the average weight loss ΔM of the 6 specimens of the coated sheet 2 under the condition of the deformation factor T = 0.037 平均2 = 3.836 g;

[0086] S8. Since under the test conditions of the same deformation factor of 0.037, the average weight loss value of the coated sheet 1 after the salt spray test is greater than that of the coated sheet 2, it is proved that the coated sheet 2 has better corrosion resistance after stamping than the coated sheet 1.

[0087] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that they can still modify the technical solutions described in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for evaluating the corrosion resistance of a thin steel sheet with a coating after forming, characterized in that: It includes the following steps: Obtain circular sheet specimens of N formed electroplated steel sheets to be tested; Conduct a drawing test on the circular sheet specimens of the formed electroplated steel sheets to form cup-shaped specimens; Calculate the deformation factor of the cup-shaped specimens after the drawing test; Conduct the first cleaning, drying and weighing on the cup-shaped specimens after the drawing test; Conduct a neutral salt spray test on the cup-shaped specimens after the first cleaning; Conduct the second cleaning, drying and weighing on the cup-shaped specimens after the neutral salt spray test; Calculate the weight change of each of the N cup-shaped specimens after the first cleaning and after the second cleaning respectively, and calculate the average weight loss of the N specimens; Compare the average weight loss of specimens of formed electroplated steel sheets with the same electroplating thickness but different types under the same deformation factor or the average weight loss of specimens of the same formed electroplated steel sheet under different deformation factors. The smaller the average weight loss of the specimens, the stronger the corrosion resistance of the formed electroplated steel sheet under equivalent conditions.

2. The method for evaluating the corrosion resistance of a thin steel sheet with a coating after forming according to claim 1, wherein: The calculation formula for the deformation factor T is as follows: Where: D0 represents the diameter of the specimen; h represents the drawing depth of the specimen; d p represents the diameter of the drawing punch of the specimen; r p represents the fillet radius of the punch.

3. The method for evaluating the corrosion resistance of a formed thin steel sheet with a coating according to claim 1, characterized in that: During the operation of conducting the neutral salt spray test on the specimens after the drawing test, place the N electroplated steel sheet specimens after the drawing test with their openings facing down at different positions in the corrosion chamber for the neutral salt spray test.

4. The method for evaluating the corrosion resistance of the formed thin steel sheet with a coating layer according to claim 1, wherein: The operation process of conducting the second cleaning on the specimens after the neutral salt spray test is as follows: S61: Rinse the specimens after the neutral salt spray test with water to wash off the sodium chloride on the specimen surface; S62: Immerse the specimens in a hydrochloric acid solution and hexamethylenetetramine to remove the corrosion products; S63: Wash the specimens with distilled water or deionized water to remove the corrosion substances; S64: Finally, clean the specimens with ethanol.

5. The method for evaluating the corrosion resistance of the formed thin steel sheet with a coating layer according to claim 1, characterized in that: The average weight loss ΔM 平均 is calculated as follows: Where: N represents the number of specimens, ΔM1 represents the mass of the first specimen, and ΔM n represents the mass of the nth specimen.

Images