Method for characterizing corrosion resistance and adhesive force of surface coating of hot-dip galvanized steel plate

Abstract

The invention discloses a characterization method for corrosion resistance and adhesive force of a coating on the surface of a hot-dip galvanized steel sheet, which comprises the following steps: using a 15% hydrochloric acid aqueous solution as a corrosive agent, adjusting the flow of the corrosive agent, and controlling the rising speed of the liquid level to be 2.5-3.5 mm / min; after a sample is corroded, four parts including a surface zinc layer, a zinc layer part corrosion layer, an inhibition layer and an iron base layer appear, the length of each part after corrosion is measured, the corrosion resistance time of the zinc layer and the inhibition layer is respectively calculated according to the proportion of the length of each part in the total length, and finally the corrosion resistance and the adhesive force of the coating are represented by the corrosion time. According to the method, comprehensive detection of the quality of the zinc layer is achieved, special equipment is not needed, and the universality is high; the detection stability is good, chemical reagents are easy to obtain, and the reagents have low harm to human bodies; the performance of the material coating can be reflected, the morphology of the inhibition layer can be observed under a scanning electron microscope, and more information can be provided for research and development of products and process adjustment.

Description

Technical Field

[0001] The invention belongs to the technical field of steel material detection, and specifically relates to a method for characterizing the corrosion resistance and adhesion of a surface coating of a hot-dip galvanized steel plate. Background Art

[0002] Hot-dip galvanized steel sheets form a protective film on the surface of steel by coating a layer of zinc on the surface. In the atmosphere, an oxide layer is formed on the surface of the zinc layer to prevent further oxidation and prevent rust. In a strong corrosive environment, the zinc layer has a lower electrode potential during corrosion, and the zinc layer is corroded first, thus protecting the iron base and achieving an anti-corrosion effect.

[0003] During the production and process adjustment of hot-dip galvanized products, it is necessary to understand the corrosion resistance and adhesion of the zinc layer. The current tests for zinc layer adhesion and corrosion resistance include adhesion test and salt spray test. These experimental methods are complex and require specific equipment, and the final test results cannot serve as an effective reference for product production and research. Therefore, some simple and practical detection methods are needed to feedback the information of the coating, so as to assist in production and research.

[0004] In the prior art, such as the patent with publication number CN106092709A, "A preparation method and corresponding preparation device for testing the characteristics of the interface inhibition layer of hot-dip galvanized sheet", this detection method requires special devices, including a corrosion reaction device and a constant speed descending device for the sample, which slowly and continuously immerses the galvanized sheet strip sample into the corrosive liquid at a constant speed μ for corrosion until the head of the sample is excessively corroded and the metallic luster of the substrate is clearly revealed; therefore, the detection process requires special auxiliary equipment, which is difficult to implement and the measurement plan is difficult to implement. The utility model patent with announcement number CN219935588U discloses "an online detection system for the quality of hot-dip galvanized zinc layer", and the front and rear of the galvanizing system are respectively equipped with a front surface size detector and a rear surface size detector for detecting the surface size of the workpiece; it mainly monitors the stability of the zinc layer thickness and macroscopic morphology online, which is inconsistent with the objectives of the present invention. Summary of the invention

[0005] In order to overcome the defects of the above-mentioned prior art, the purpose of the present invention is to form a testing method, by which the corrosion resistance of the zinc layer of the hot-dip galvanized steel sheet and the adhesion ability of the coating can be simply and conveniently characterized.

[0006] The main factors that affect the corrosion performance and adhesion of the surface zinc layer are: the quality and thickness of the zinc layer, the quality and thickness of the inhibition layer. The so-called inhibition layer is formed between the zinc layer and the steel substrate by adding 0.15% to 0.2% aluminum to the zinc liquid during the hot-dip galvanizing process. The morphology of the inhibition layer affects the adhesion of the zinc layer. At the same time, the corrosion resistance of the inhibition layer is different with different morphologies. Generally speaking, the denser the morphology of the inhibition layer, the stronger its adhesion and corrosion resistance. Therefore, the corrosion resistance and adhesion performance of the material can be fed back by the performance of the surface coating in acid solution, and the corrosion resistance time of the zinc layer and the inhibition layer in acid can be used to characterize the corrosion resistance and adhesion performance of the material.

[0007] In order to achieve the above-mentioned purpose of the invention, the present invention provides a method for characterizing the corrosion resistance and adhesion of the surface coating of a hot-dip galvanized steel plate, which can measure the corrosion resistance time of the zinc layer and the inhibition layer of the steel plate under a specific corrosive agent, and characterize the corrosion resistance and adhesion of the coating by measuring the corrosion resistance time parameters of each layer; the longer the corrosion time of the zinc layer and the inhibition layer, the more corrosion resistant they are; the longer the corrosion time of the inhibition layer, the denser and more complete the structure of the inhibition layer is, and the stronger the adhesion of the zinc layer is; the characterization method comprises the following steps:

[0008] ① Sample cutting: Cut the hot-dip galvanized steel sheet into long strip samples;

[0009] ② Preparation of the corrosive agent: Measure 250-260 ml of pure water and put it into a large beaker. Then measure 40-50 ml of analytical pure hydrochloric acid solution and add it to the beaker containing pure water. Mix well to form a 15% volume content of hydrochloric acid aqueous solution, which is the corrosive agent.

[0010] ③ Use a clamp to hold the long strip sample and hang it vertically in a 200 ml beaker, with the sample piece standing vertically at the bottom of the sample.

[0011] ④ Pour the corrosive agent into the infusion bottle, place the infusion bottle above the beaker at a height of 50 cm from the bottom of the beaker, place the water outlet of the infusion tube of the infusion bottle at the bottom of the beaker, open the control valve of the infusion tube, and slowly inject the corrosive agent in the infusion bottle into the bottom of the beaker, adjust the flow rate of the corrosive agent, and control the rising speed of the liquid level to 2.5-3.5 mm / min.

[0012] ⑤ With the slow injection of the corrosive agent, the liquid level of the corrosive agent in the beaker gradually rises; when the corrosive agent contacts the bottom of the sample, start timing with a stopwatch; as the liquid level of the corrosive agent rises, it corrodes the surface of the sample. The part that contacts the corrosive agent first is corroded deeply, while the part that contacts the corrosive agent later is corroded less deeply. As the liquid level rises, the corrosion time of each part is linearly distributed.

[0013] ⑥ After the sample is corroded, four parts will appear: surface zinc layer (original surface of uncorroded steel plate), zinc layer partial corrosion layer (zinc layer corrosion part), inhibition layer (inhibition layer corrosion part), steel plate iron base (steel plate iron base part). After the sample is corroded to the steel plate iron base, take out the sample, stop timing, and get the total corrosion time; rinse off the corrosion products on the surface of the sample, blow dry the sample with a hair dryer, and the different parts of the steel plate surface can be seen with the naked eye.

[0014] ⑦Coating performance test characterization

[0015] The lengths of the four parts of the sample after corrosion (surface zinc layer, partial corrosion layer of the zinc layer, inhibition layer, and iron base layer of the steel plate) were measured. The steel plate coatings under different process conditions have different corrosion resistance and adhesion properties. The lengths of the zinc layer and inhibition layer at each level will show obvious differences under this corrosion state.

[0016] Measuring the total length of the zinc layer corrosion area and the inhibition layer corrosion area reflects the corrosion resistance of the material. The longer the length, the stronger the corrosion resistance.

[0017] Measuring the length of the corrosion inhibition layer reflects the adhesion performance of the material. The longer the length, the stronger the adhesion of the material.

[0018] The total length of the sample corrosion was measured, and the time from the bottom of the sample contacting the corrosive solution to the sample being taken out was counted. The corrosion time of the sample was linearly distributed. The corrosion resistance time of the zinc layer and the inhibition layer in the hydrochloric acid aqueous solution (corrosive agent) could be calculated separately through the proportion of the length of each part to the total length.

[0019] Finally, the corrosion time is used to characterize the corrosion resistance and adhesion of the coating.

[0020] Compared with the prior art, the present invention has the following beneficial effects:

[0021] The present invention can realize comprehensive detection of zinc layer quality; it does not require special equipment and has the characteristics of strong popularization; the detection stability is good; the chemical reagents are easy to obtain, the chemical reagents are less harmful to human body, and are easy to operate. In addition to reflecting the material coating performance, the detection method can also observe the morphology of the inhibition layer under a scanning electron microscope, which is conducive to providing more information for product development and process adjustment. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] Figure 1 It is a schematic diagram of the arrangement of the experimental apparatus and the detection method of the present invention;

[0023] Figure 2 This is a schematic diagram of the distribution of various regions of the sample after corrosion in the embodiment;

[0024] Figure 3This is a picture of the morphology of the DC51D+Z sample after corrosion in the embodiment. DETAILED DESCRIPTION

[0025] The present invention is further described below in conjunction with specific examples, but the present invention is not limited in any way. To avoid redundant description, the raw materials in the following examples are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0026] A method for characterizing the corrosion resistance and adhesion of a coating on a hot-dip galvanized steel plate surface, the method comprising the following steps:

[0027] ① Sample cutting: Cut the hot-dip galvanized steel sheet into long strip samples;

[0028] ② Preparation of the corrosive agent: Measure analytical pure hydrochloric acid solution, add it to pure water, and mix well to form a 15% volume content of hydrochloric acid aqueous solution;

[0029] ③ Use a clamp to hold the long strip sample and hang it vertically in a 200ml beaker;

[0030] ④ Pour the corrosive agent into the infusion bottle, place the infusion bottle above the beaker at a height of 50 cm from the bottom of the beaker, place the water outlet of the infusion tube of the infusion bottle at the bottom of the beaker, open the control valve of the infusion tube, inject the corrosive agent in the infusion bottle into the bottom of the beaker, adjust the flow rate of the corrosive agent, and control the rising speed of the liquid level to 2.5-3.5 mm / min;

[0031] ⑤ As the corrosive agent is injected, the level of the corrosive agent in the beaker rises. When the corrosive agent contacts the bottom of the sample, start timing with a stopwatch;

[0032] ⑥ After the sample is corroded, four parts appear. When the steel plate iron base appears, take out the sample, stop timing, and obtain the total corrosion time; wash off the corrosion products on the surface of the sample, and blow dry the sample;

[0033] ⑦ Characterization of coating performance detection: The lengths of the four parts of the sample after corrosion are measured, and the corrosion resistance time of the zinc layer and the inhibition layer are calculated respectively by the ratio of the length of each part to the total length. Finally, the corrosion resistance and adhesion of the coating are characterized by the corrosion time.

[0034] The matters not described in the following embodiments are the same as the description of the above specific implementation methods.

[0035] Example

[0036] A method for characterizing the corrosion resistance and adhesion of the coating on the surface of a hot-dip galvanized steel plate. The specific test process takes the corrosion of a DC51D+Z hot-dip galvanized steel plate sample as an example. The specific test steps are as follows:

[0037] Testing equipment: 1 200ml beaker, 500ml infusion bottle and matching infusion tube;

[0038] Chemical reagent: 15% hydrochloric acid aqueous solution.

[0039] ① Sample cutting: Cut the hot-dip galvanized steel sheet into 25×60mm long strip samples;

[0040] ② Preparation of the corrosive agent: Measure 255 ml of pure water and put it into a large beaker. Then measure 45 ml of analytical pure hydrochloric acid solution and add it to the beaker containing pure water. Mix well to form a 15% hydrochloric acid aqueous solution, which is the corrosive agent.

[0041] ③ Use a fixture to hold the long strip sample and hang it vertically in a 200ml beaker, with the sample piece perpendicular to the bottom of the sample (such as Figure 1 shown).

[0042] ④ Pour the corrosive agent into the infusion bottle, place the infusion bottle at a height of 50 cm from the bottom of the beaker, place the water outlet of the infusion tube of the infusion bottle at the bottom of the beaker, open the control valve of the infusion tube, and slowly inject the corrosive agent in the infusion bottle into the bottom of the beaker. Adjust the flow rate of the corrosive agent to control the rising speed of the liquid level to 3.0 mm / min.

[0043] ⑤ As the level of the corrosive agent in the beaker rises, when the corrosive agent contacts the bottom of the sample, start timing with a stopwatch; as the level of the corrosive agent rises, it corrodes the surface of the sample. The part that contacts the corrosive agent first is corroded deeply, while the part that contacts the corrosive agent later is corroded less deeply. As the level of the agent rises, the corrosion time of each part is linearly distributed.

[0044] ⑥ After the sample is corroded, four parts will appear; the four parts include: surface zinc layer, partial corrosion layer of zinc layer, inhibition layer, and steel plate matrix. After the sample is corroded to the appearance of steel plate iron base, take out the sample, stop timing, and get the total corrosion time; rinse off the corrosion products on the surface of the sample, blow dry the sample with a hair dryer, and the different parts of the steel plate surface can be seen with the naked eye.

[0045] ⑦Coating performance test characterization

[0046] The lengths of the four parts of the sample after corrosion (surface zinc layer, partial corrosion layer of the zinc layer, inhibition layer, and steel plate substrate) were measured. The steel plate coatings under different processes have different corrosion resistance and adhesion properties. The lengths of the zinc layer and inhibition layer at each level will show differences under this corrosion state.

[0047] The timing started when the bottom of the steel plate came into contact with the acid solution. After a period of corrosion, obvious stratification appeared on the sample surface and the timing was stopped. The total corrosion time was 9 minutes. The sample was taken out, rinsed, blown dry with a hair dryer, placed on a ruler, photographed, and then the length of each part was measured using measurement software. The total corrosion length was 28 mm, the zinc layer corrosion part was 6.9 mm long, and the inhibition layer corrosion part was 6.3 mm long.

[0048] Based on the length ratio, it is calculated that the corrosion time of the zinc layer of the steel plate under the corrosive agent is 2.2 minutes, and the corrosion resistance time of the inhibition layer is 2 minutes; then, the quality of the zinc layer is compared based on the length of the corrosion resistance time.

[0049] For any technician familiar with the art, without departing from the scope of the technical solution of the present invention, the technical content disclosed above can be used to make many possible changes and modifications to the technical solution of the present invention, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention should still fall within the scope of protection of the technical solution of the present invention.

Claims

1. A method for characterizing the corrosion resistance and adhesion of a hot-dip galvanized steel plate surface coating, characterized in that: The characterization method comprises the following steps: ① Sample cutting: Cut the hot-dip galvanized steel sheet into long strip samples; ② Preparation of the corrosive agent: Measure analytical pure hydrochloric acid solution, add it to pure water, and mix well to form a 15% volume content of hydrochloric acid aqueous solution; ③ Use a clamp to hold the long strip sample and hang it vertically in a 200ml beaker; ④ Pour the corrosive agent into the infusion bottle, place the infusion bottle above the beaker, place the water outlet of the infusion tube of the infusion bottle at the bottom of the beaker, open the control valve of the infusion tube, inject the corrosive agent in the infusion bottle into the bottom of the beaker, adjust the flow rate of the corrosive agent, and control the rising speed of the liquid level to 2.5-3.5 mm / min; ⑤ As the corrosive agent is injected, the level of the corrosive agent in the beaker rises. When the corrosive agent contacts the bottom of the sample, start timing with a stopwatch; ⑥ After the sample is corroded, four parts appear. When the steel plate iron base appears, take out the sample, stop timing, and obtain the total corrosion time; wash off the corrosion products on the surface of the sample, and blow dry the sample; ⑦ Characterization of coating performance detection: The lengths of the four parts of the sample after corrosion are measured, and the corrosion resistance time of the zinc layer and the inhibition layer are calculated respectively by the ratio of the length of each part to the total length. Finally, the corrosion resistance and adhesion of the coating are characterized by the corrosion time.

2. The characterization method according to claim 1, characterized in that The four parts described in step ⑥ include: the uncorroded original surface of the steel plate, the zinc layer corrosion part, the inhibition layer corrosion part, and the iron base part of the steel plate.

3. The characterization method according to claim 1, characterized in that The total length of the zinc layer corrosion area and the inhibition layer corrosion area measured in step ⑦ reflects the corrosion resistance of the material.

4. The characterization method according to claim 1, characterized in that The length of the corrosion inhibition layer measured in step ⑦ reflects the adhesion performance of the material.

5. The characterization method according to claim 1, characterized in that: In step ⑦, the corrosion time of the sample is linearly distributed.

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