A corrosive agent and its corrosion method and use

Abstract

The application provides a kind of etchant and its corrosion method and use, the etchant includes sulfate hydrate and solvent;The mass-volume ratio of sulfate hydrate and solvent is (0.125-0.2):1g / mL.The corrosion method includes the following steps: (1) mixing and heating sulfate hydrate and solvent, to obtain etching liquid;(2) sample is immersed in etching liquid and is stationary, after sample is removed, to obtain the sample to be observed by grinding.The etchant of the application does not use non-explosive dangerous chemicals and strong corrosive dangerous chemicals, is low in cost, convenient to configure, safe and reliable, and has the advantages of short corrosion time, excellent corrosion effect and the like.

Description

Technical Field

[0001] This invention belongs to the field of materials testing technology, and in particular relates to a corrosive agent, its corrosion method, and its applications. Background Technology

[0002] Currently, the main methods for connecting steel plates in automobile bodies are spot welding and laser welding, while the main method for connecting chassis plates is arc welding. However, regardless of whether it is spot welding, laser welding, or arc welding, the welding strength between the steel plates directly affects the vehicle's collision and durability safety performance. Therefore, during the development of body and chassis steel plate materials and during the quality analysis of mass-produced vehicles, it is necessary to confirm the morphology of the weld points and weld seams, respectively.

[0003] The streamlines of an automotive component's cross-section are a low-magnification microstructure formed during the forging process by the continuous linear distribution of inclusions, carbides, and other precipitates along the deformation direction. This microstructure exhibits a clear directionality, resulting in directional mechanical properties. Tensile strength is high along the streamline direction, while shear strength perpendicular to the streamline direction is high. A well-distributed streamline structure can improve the product's mechanical properties. Conversely, significant defects in the streamlines, such as turbulence, irregular flow, or cross-flow, can severely impact the product's mechanical properties and final performance. Therefore, it is essential to verify the morphology of the streamlines in the cross-section of automotive components.

[0004] Currently, commonly used metallographic etchants contain picric acid, hydrochloric acid, or sulfuric acid, and are applicable to various steel grades, such as martensitic stainless steel. Using the immersion etching method, they offer advantages such as short corrosion time, uniform corrosion, and good corrosion effect. CN109355661A discloses a etchant for welded areas of steel plates, a corrosion method, and its application. The etchant comprises a saturated picric acid aqueous solution, glacial acetic acid, and sodium dodecylbenzenesulfonate. Based on the total volume of the saturated picric acid aqueous solution and glacial acetic acid, the volume percentage of the saturated picric acid aqueous solution is 85%-97%, with the balance being glacial acetic acid. Based on every 100 ml of the mixture of saturated picric acid aqueous solution and glacial acetic acid, the amount of sodium dodecylbenzenesulfonate is 0.25-5 g.

[0005] However, picric acid is a precursor chemical and is subject to strict control, making it difficult to purchase on the market. Therefore, developing a corrosion agent formulation that can replace picric acid, hydrochloric acid, or sulfuric acid is a problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0006] The purpose of this invention is to provide a corrosive agent, its corrosion method, and its uses. The corrosive agent does not require the use of non-explosive hazardous chemicals or highly corrosive hazardous chemicals, is low in cost, easy to prepare, safe and reliable, and has the advantages of short corrosion time and excellent corrosion effect.

[0007] To achieve this objective, the present invention adopts the following technical solution:

[0008] In a first aspect, the present invention provides a corrosive agent comprising a sulfate hydrate and a solvent;

[0009] The mass-to-volume ratio of the sulfate hydrate to the solvent is (0.125-0.2):1 g / mL, for example, it can be 0.13:1 g / mL, 0.14:1 g / mL, 0.15:1 g / mL, 0.16:1 g / mL, 0.17:1 g / mL, 0.18:1 g / mL or 0.19:1 g / mL, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0010] The corrosive agent of this invention comprises sulfate salt hydrate and a solvent. Because sulfate salt hydrate is easily hydrolyzed, releasing hydrogen ions in water, and the system also contains sulfate ions, it essentially forms sulfuric acid. Sulfuric acid is corrosive to the cross-section of forgings or welded areas of steel. Furthermore, this corrosive agent eliminates the need for non-explosive and highly corrosive hazardous chemicals, and can replace corrosive agents containing picric acid, hydrochloric acid, or sulfuric acid. It offers advantages such as low cost, no pollution, no need for special storage, and high safety.

[0011] As a preferred embodiment of the present invention, the sulfate hydrate comprises potassium aluminum sulfate dodecahydrate (alum).

[0012] Preferably, the purity of the sulfate hydrate is ≥99%, for example, it can be 99.2%, 99.4%, 99.5%, 99.6%, 99.8% or 99.9%, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0013] Preferably, the solvent includes water.

[0014] As a preferred embodiment of the present invention, the corrosive agent further includes an acid reagent.

[0015] As a preferred embodiment of the present invention, the mass ratio of the sulfate hydrate to the acid reagent includes the following:

[0016] (A) The etchant is used for flowline corrosion of the longitudinal section of the forging, wherein the mass ratio of the sulfate hydrate to the acid reagent is (20-25):1; or

[0017] (B) The corrosive agent is used for corrosion of the spot weld area of ​​the steel plate, wherein the mass ratio of the sulfate hydrate to the acid reagent is (0.5-3):1.

[0018] It is worth noting that when the etchant is used for the flow line corrosion of the longitudinal section of the forging, the acid reagent may not be added. If the acid reagent is added, the mass ratio of sulfate salt hydrate to acid reagent should be controlled at (20-25):1. If too much acid reagent is added, a clear flow line morphology will not be obtained.

[0019] It is worth noting that when the etchant is used to etch the spot weld area of ​​the steel plate, the mass ratio of sulfate hydrate to acid reagent should be controlled at (0.5-3):1. For example, it can be 1:1, 1.5:1, 2:1, 2.5:1 or 2.8:1, but it is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0020] Preferably, the acid reagent includes citric acid and / or acetic acid.

[0021] Secondly, the present invention provides a corrosion method using a corrosive agent, wherein the corrosion is performed using the corrosive agent described in the first aspect, and the corrosion method includes the following steps:

[0022] (1) Mix the sulfate hydrate and solvent and heat them to obtain a corrosive solution;

[0023] (2) Immerse the sample in the corrosive solution and let it stand. After taking out the sample, grind it to obtain the sample to be observed.

[0024] The corrosion method described in this invention can be achieved by immersion etching, without the need for electrolytic corrosion. This corrosion method can produce a morphology with clear streamline structure that is easy to measure and observe, which can meet the requirements for morphological observation of welded areas and longitudinal sections of forgings in mass-produced automobiles with quality defects.

[0025] In this invention, the volume of the corrosive liquid is not specifically limited, as long as it can completely immerse the sample.

[0026] As a preferred technical solution of the present invention, step (1) further includes: mixing the acid reagent with the sulfate hydrate and solvent and heating.

[0027] Preferably, the heating temperature in step (1) is 50-70℃, for example, it can be 52℃, 54℃, 56℃, 58℃, 60℃, 62℃, 64℃, 66℃ or 68℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0028] Preferably, the heating time in step (1) is 5-10 min, for example, it can be 6 min, 6.5 min, 7 min, 7.5 min, 8 min, 8.5 min or 9 min, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0029] As a preferred technical solution of the present invention, the sample in step (2) includes forgings or steel plates.

[0030] Preferably, the forging includes a drive shaft or a bolt.

[0031] As a preferred technical solution of the present invention, the temperature for standing in step (2) is 65-75℃, for example, it can be 66℃, 67℃, 68℃, 69℃, 70℃, 71℃, 72℃, 73℃ or 74℃, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0032] Preferably, the settling time in step (2) is 3-7 minutes, for example, it can be 3.5 minutes, 4 minutes, 4.5 minutes, 5 minutes, 5.5 minutes, 6 minutes or 6.5 minutes, but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0033] Preferably, the grinding fluid used in step (2) is OPS fluid.

[0034] In this invention, the OPS solution (silicon oxide polishing solution) comprises 5% OPS solution. The grinding process removes the black substance from the sample surface to expose the forging flow lines or spot weld nugget.

[0035] As a preferred technical solution of the present invention, the observation method of the sample to be observed in step (2) includes visual observation or microscopy.

[0036] In this invention, the magnification of the microscope is 20-50 times, for example, it can be 25 times, 30 times, 35 times, 40 times or 45 times, etc., but is not limited to the listed values. Other unlisted values ​​within the range are also applicable.

[0037] Thirdly, the present invention provides a use of the corrosive agent as described in the first aspect, said corrosive agent for flowline corrosion of longitudinal sections of forgings or corrosion of spot weld areas of steel plates.

[0038] The numerical range described in this invention includes not only the point values ​​listed above, but also any point values ​​within the numerical ranges not listed above. Due to space limitations and for the sake of brevity, this invention will not exhaustively list all the specific point values ​​included in the range.

[0039] Compared with the prior art, the present invention has the following beneficial effects:

[0040] (1) The corrosive agent provided by the present invention does not use non-explosive hazardous chemicals or highly corrosive hazardous chemicals. Compared with existing corrosive agents containing picric acid, hydrochloric acid or sulfuric acid, it is low in cost, easy to prepare, safe and reliable, and has the advantages of short corrosion time and excellent corrosion effect.

[0041] (2) Compared with electrolytic corrosion, the corrosion method provided by the present invention is simple to operate, less time-consuming, and produces clear grain boundaries or flow lines that can be observed with the naked eye. The corrosive agent has less interference with the structure and the corrosion effect is good. Attached Figure Description

[0042] Figure 1 This is a streamline morphology diagram of the longitudinal section of an automotive bolt after corrosion in Embodiment 1 of the present invention;

[0043] Figure 2 This is a streamline morphology diagram of the longitudinal section of an automotive bolt after corrosion, as shown in Embodiment 2 of the present invention.

[0044] Figure 3 This is a microstructure image of the spot welded area of ​​the automotive steel sheet in Embodiment 3 of the present invention.

[0045] Figure 4 This is a streamline morphology diagram of the longitudinal section of an automotive bolt after corrosion in Embodiment 5 of the present invention;

[0046] Figure 5 This is a microstructure image of the spot welded area of ​​the automotive steel sheet in Embodiment 8 of the present invention.

[0047] Figure 6 This is a streamline morphology diagram of the longitudinal section of an automotive bolt after corrosion, as shown in Comparative Example 1 of this invention. Detailed Implementation

[0048] The technical solution of the present invention will be further illustrated below through specific embodiments. Those skilled in the art should understand that the embodiments described are merely illustrative of the present invention and should not be construed as limiting the invention.

[0049] Example 1

[0050] This embodiment provides a corrosive agent and a corrosion method. The corrosive agent is potassium aluminum sulfate dodecahydrate and water, wherein the mass-to-volume ratio of potassium aluminum sulfate dodecahydrate to water is 0.2:1 g / mL, and the purity of potassium aluminum sulfate dodecahydrate is 99.5%.

[0051] The corrosion method includes the following steps:

[0052] (1) Mix potassium aluminum sulfate dodecahydrate with water and heat at 60°C for 6 min to obtain a corrosion solution;

[0053] (2) Immerse the car bolt in the corrosion solution, ensuring that the corrosion solution covers the longitudinal section of the car bolt. Then let it stand at 65°C for 5 minutes. After that, take out the car bolt and use 5% OPS solution to grind the car bolt on the abrasive cloth until the forging flow lines are exposed. Observe the flow lines of the longitudinal section of the car bolt after corrosion with the naked eye.

[0054] Figure 1This embodiment shows the streamline morphology of the longitudinal section of the automotive bolt after corrosion. Figure 1 As can be seen, clear streamlines can be obtained, and the metal streamlines can be observed to show that after the forging of automotive bolts, the plastic impurities are distributed in a band-like pattern along the main elongation direction as the metal deforms.

[0055] Example 2

[0056] This embodiment provides a corrosive agent and a corrosion method. The corrosive agent is potassium aluminum sulfate dodecahydrate, citric acid, and water. The mass-to-volume ratio of potassium aluminum sulfate dodecahydrate to water is 0.17:1 g / mL, the mass ratio of potassium aluminum sulfate dodecahydrate to citric acid is 23:1, and the purity of potassium aluminum sulfate dodecahydrate is 99.5%.

[0057] The corrosion method includes the following steps:

[0058] (1) Mix potassium aluminum sulfate dodecahydrate, citric acid and water and heat at 65°C for 10 min to obtain a corrosion solution;

[0059] (2) Immerse the car bolt in the corrosion solution, ensuring that the corrosion solution covers the longitudinal section of the car bolt. Then let it stand at 70°C for 3 minutes. After that, take out the car bolt and use 5% OPS solution to grind the car bolt on the abrasive cloth until the forging flow lines are exposed. Observe the flow lines of the longitudinal section of the corroded car bolt under a microscope.

[0060] Figure 2 This embodiment shows the streamline morphology of the longitudinal section of the automotive bolt after corrosion. Figure 2 As can be seen, clear streamlines can be obtained, and the metal streamlines can be observed to show that after the forging of automotive bolts, the plastic impurities are distributed in a band-like pattern along the main elongation direction as the metal deforms.

[0061] Example 3

[0062] This embodiment provides a corrosive agent and a corrosion method. The corrosive agent is potassium aluminum sulfate dodecahydrate, citric acid, and water. The mass-to-volume ratio of potassium aluminum sulfate dodecahydrate to water is 0.17:1 g / mL, the mass ratio of potassium aluminum sulfate dodecahydrate to citric acid is 0.5:1, and the purity of potassium aluminum sulfate dodecahydrate is 99.5%.

[0063] The corrosion method includes the following steps:

[0064] (1) Mix potassium aluminum sulfate dodecahydrate, citric acid and water and heat at 65°C for 8 min to obtain a corrosion solution;

[0065] (2) Immerse the car steel sheet in the corrosion solution, ensuring that the corrosion solution covers the welding area of ​​the car steel sheet, and then let it stand at 70°C for 5 minutes. After that, take out the car steel sheet and use 5% OPS solution to grind the car steel sheet on the abrasive cloth until the spot weld nugget is exposed. Observe the structure of the car steel sheet after corrosion with a microscope.

[0066] The welding area of ​​the automotive steel sheet is formed by spot welding.

[0067] Figure 3 This is the microstructure of the spot welded joint of the automotive steel sheet in this embodiment. Figure 3 As can be seen, the weld nugget boundary is clearly visible, the boundary is clear, and the surface is free of contamination.

[0068] Example 4

[0069] This embodiment provides a corrosive agent and a corrosion method. Except that the mass-to-volume ratio of potassium aluminum sulfate dodecahydrate to water is 0.25:1 g / mL, all other conditions are the same as in Example 1.

[0070] In this embodiment, when the alum concentration is too high, heating for only 6 minutes is insufficient to achieve complete hydrolysis of the alum. A longer heating time is required to achieve a better corrosion effect, which reduces efficiency.

[0071] Example 5

[0072] This embodiment provides a corrosive agent and a corrosion method. Except that the mass-to-volume ratio of potassium aluminum sulfate dodecahydrate to water is 0.1:1 g / mL, all other conditions are the same as in Example 1.

[0073] Figure 4 This embodiment shows the streamline morphology of the longitudinal section of the automotive bolt after corrosion. Figure 4 It can be seen that when the alum concentration is too low, the resulting corrosive solution is weakly acidic. After corroding the longitudinal section of the car bolt, the metal flow lines are shallow, and the morphology of the longitudinal section flow lines of the car bolt cannot be clearly and accurately observed.

[0074] Example 6

[0075] This embodiment provides a corrosive agent and a corrosion method. Under the condition that the amount of potassium aluminum sulfate dodecahydrate remains unchanged, except that the mass ratio of potassium aluminum sulfate dodecahydrate to citric acid is adjusted to 15:1, all other conditions are the same as in Example 2.

[0076] In this embodiment, an excessive amount of citric acid was added. When citric acid comes into contact with the metal, some chemical reactions occur. The negative ions in citric acid can react with the metal surface through electron transfer to form metal ions and citrate salts. While a high concentration of citric acid may enhance its corrosive effect on the metal surface, it cannot corrode the unique internal flow lines of the forged metal, making it impossible to observe the forging flow lines on the longitudinal section of the automotive bolts.

[0077] Example 7

[0078] This embodiment provides a corrosive agent and a corrosion method. Except that citric acid is not added to the corrosive agent, all other conditions are the same as in Example 3.

[0079] In this embodiment, without the addition of citric acid, although alum hydrolysis is corrosive, it can only slightly corrode the general outline of the spot weld nugget, and cannot clearly obtain the microstructure of the spot weld joint of the automotive steel sheet.

[0080] Example 8

[0081] This embodiment provides a corrosive agent and a corrosion method. Under the condition that the amount of potassium aluminum sulfate dodecahydrate remains unchanged, the mass ratio of potassium aluminum sulfate dodecahydrate to citric acid is adjusted to 5:1, and all other conditions are the same as in Example 3.

[0082] Figure 5 This is the microstructure of the spot welded joint of the automotive steel sheet in this embodiment. Figure 5 As can be seen, when the amount of citric acid added is too small, it can only slightly corrode the general outline of the spot weld nugget, and cannot clearly observe the microstructure of the corrosion at the spot weld of the automotive steel plate.

[0083] Comparative Example 1

[0084] This comparative example provides an etchant and an etching method. A conventional etchant in the art (DL / T884-2019) is selected. The etchant is 5g of ferric chloride, 50ml of concentrated hydrochloric acid, and 100ml of water. All other conditions are the same as in Example 1.

[0085] Figure 6 To illustrate the streamlined morphology of the longitudinal section of the automotive bolt after corrosion in this comparative example, from... Figure 6 As can be seen, after etching with conventional etchants, the special flow lines inside the metal after forging cannot be clearly observed and cannot be clearly etched out.

[0086] The applicant declares that the detailed structural features of the present invention are illustrated through the above embodiments, but the present invention is not limited to the above detailed structural features, that is, it does not mean that the present invention must rely on the above detailed structural features to be implemented. Those skilled in the art should understand that any improvements to the present invention, equivalent substitutions for the components selected in the present invention, additions of auxiliary components, selection of specific methods, etc., all fall within the protection scope and disclosure scope of the present invention.

[0087] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0088] It should also be noted that the various specific technical features described in the above specific embodiments can be combined in any suitable manner without contradiction. In order to avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0089] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A corrosive agent, characterized in that, The corrosive agent is a sulfate hydrate, an acid reagent, and a solvent; the mass-to-volume ratio of the sulfate hydrate to the solvent is (0.125-0.2):1 g / mL; The sulfate hydrate is potassium aluminum sulfate dodecahydrate; the acid reagent is citric acid and / or acetic acid; the solvent is water; the mass ratio of the sulfate hydrate to the acid reagent includes the following: (A) When the etchant is used for flowline corrosion of the longitudinal section of a forging, the mass ratio of the sulfate hydrate to the acid reagent is (20-25):1; or (B) When the corrosive agent is used to corrode the spot weld area of ​​the steel plate, the mass ratio of the sulfate salt hydrate to the acid reagent is (0.5-3):

1.

2. The corrosive agent according to claim 1, characterized in that, The purity of the sulfate hydrate is ≥99%.

3. A corrosion method using a corrosive agent, characterized in that, The etching process employs the corrosive agent described in claim 1 or 2, and the etching method comprises the following steps: (1) The acid reagent is mixed with the sulfate hydrate and solvent and heated to obtain the corrosive solution; (2) Immerse the sample in the corrosive solution and let it stand. After taking out the sample, grind it to obtain the sample to be observed.

4. The corrosion method according to claim 3, characterized in that, The heating temperature in step (1) is 50-70℃.

5. The corrosion method according to claim 3, characterized in that, The heating time in step (1) is 5-10 minutes.

6. The corrosion method according to claim 3, characterized in that, The sample in step (2) includes forgings or steel plates.

7. The corrosion method according to claim 6, characterized in that, The forging includes a drive shaft or a bolt.

8. The corrosion method according to claim 3, characterized in that, The temperature for standing in step (2) is 65-75℃.

9. The corrosion method according to claim 3, characterized in that, The settling time in step (2) is 3-7 minutes.

10. The corrosion method according to claim 3, characterized in that, The grinding fluid used in step (2) is OPS fluid.

11. The corrosion method according to claim 3, characterized in that, The observation methods for the sample to be observed in step (2) include visual inspection or microscopy.

12. The use of a corrosive agent as described in claim 1 or 2, characterized in that, The corrosive agent is used for flowline corrosion of the longitudinal section of forgings or corrosion of spot weld areas of steel plates.

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