Method for plating nickel-zinc double-layer protective film on steel plate

Abstract

The invention relates to the technical field of metal surface treatment, in particular to a method for plating a nickel-zinc double-layer protective film on a steel plate. A steel plate is polished to be smooth, degreased, etched, cleaned and dried to obtain a steel plate substrate; the steel plate substrate is placed in a nickel plating solution to be electroplated, the electroplating temperature ranges from 70 DEG C to 80 DEG C, the electroplating time ranges from 20 min to 30 min, the pH value of the nickel plating solution ranges from 4.5 to 5, and a nickel-plated steel plate is obtained after distilled water washing; the nickel-plated steel plate is subjected to surface roughening treatment and then placed in a zinc solution for hot dipping, the hot dipping temperature is 390-410 DEG C, and the hot dipping time is 20-30 seconds. According to the method provided by the invention, the nickel element is dispersed between the steel plate substrate and the zinc coating, and the adhesion between the steel plate and the nickel-zinc double-layer protective film is improved due to the existence of nickel, so that the corrosion-resistant effect is improved.

Description

Technical Field

[0001] The invention relates to the technical field of metal surface treatment, and in particular to a method for plating a nickel-zinc double-layer protective film on a steel plate. Background Art

[0002] Steel materials are widely used in many fields such as construction, chemical industry, and transportation due to their excellent mechanical properties and relatively low cost. However, they face serious corrosion problems during their use, which not only reduces the structural strength and service life of steel materials, but may also cause safety hazards and economic losses. Galvanizing on the surface of steel materials is a relatively common and widely used anti-corrosion method. The protective layer formed by galvanizing can isolate the steel material from the external corrosive medium to a certain extent, and use the electrochemical activity of zinc to provide cathodic protection for the steel material, thereby slowing down the corrosion rate. However, in actual applications, the anti-corrosion effect of the galvanized layer is gradually unable to meet the increasingly stringent requirements of the use environment. For example, in some harsh environments with high humidity and high salinity, the protective life of the galvanized layer will be greatly shortened, and it will not be able to provide long-term and reliable protection for the steel material.

[0003] In order to further improve the corrosion resistance of steel materials, researchers will add a certain proportion of Al, Mg, Si and other alloy elements to the galvanizing solution to form an alloy coating on the surface of the steel material. The addition of these elements has changed the organizational structure and electrochemical properties of the coating to a certain extent, and improved the corrosion resistance effect, but the adhesion performance of many alloy coatings is unstable in harsh environments, resulting in the problem of local corrosion. Summary of the invention

[0004] In view of the technical problem in the prior art that the alloy coating on the surface of the steel plate has unstable adhesion performance in a high-salinity environment, resulting in poor corrosion resistance, the present invention provides a method for plating a nickel-zinc double-layer protective film on a steel plate, wherein the nickel element is dispersed between the steel plate base and the zinc coating layer. The presence of nickel improves the adhesion between the steel plate and the nickel-zinc double-layer protective film, thereby improving the corrosion resistance.

[0005] The technical solution of the present invention is as follows: A method for plating a nickel-zinc double-layer protective film on a steel plate comprises the following steps: grinding the steel plate to be smooth, degreasing, etching, cleaning and drying to obtain a steel plate substrate; electroplating the steel plate substrate in a nickel plating solution, wherein the electroplating temperature is 75-85°C, the electroplating time is 25-35 minutes, the pH value of the nickel plating solution is 4.5-5, and the nickel-plated steel plate is obtained after rinsing with distilled water; and the surface of the nickel-plated steel plate is roughened and then hot-dip plated in a zinc solution, wherein the hot-dip plating temperature is 390-410°C, and the hot-dip plating time is 20-30 seconds.

[0006] Further, the steel plate was polished on sandpapers of 80 mesh, 100 mesh, 120 mesh and 200 mesh in sequence.

[0007] Further, degreasing was performed using 5% sodium hydroxide solution.

[0008] Further, etching was performed using an 8% hydrochloric acid solution.

[0009] Furthermore, the solute of the nickel plating solution includes nickel nitrate, sodium hypophosphite and succinic acid.

[0010] Furthermore, the nickel nitrate concentration in the nickel plating solution is 30 g / L, the sodium hypophosphite concentration is 25 g / L, and the succinic acid concentration is 15 g / L.

[0011] Furthermore, the electroplating temperature is 80° C., the electroplating time is 30 minutes, and the pH value of the nickel plating solution is 4.5.

[0012] Furthermore, the nickel-plated steel plate was roughened using 80-200 grit sandpaper.

[0013] Furthermore, after hot-dip coating, hot air is used to blow away the zinc that has not been firmly hot-dip coated on the surface.

[0014] The beneficial effects of the present invention are: The present invention provides a method for plating a nickel-zinc double-layer protective film on a steel plate. Electroplating a certain amount of nickel on the steel plate first can promote further diffusion of zinc during subsequent hot-dip plating. The nickel-zinc double-layer protective film becomes a denser internal alloy phase, thereby enhancing its adhesion to the steel plate and improving the corrosion resistance. DETAILED DESCRIPTION

[0015] In order to enable those skilled in the art to better understand the technical solutions in the present invention, the technical solutions in the embodiments of the present invention are described clearly and completely below. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work should fall within the scope of protection of the present invention.

[0016] Example 1 A method for plating a nickel-zinc double-layer protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) Prepare nickel plating solution: nickel nitrate is 30 g / L, sodium hypophosphite is 25 g / L, succinic acid is 15 g / L, and ammonium hydroxide is used to adjust the pH to 4.5 for later use; (3) Nickel electroplating: The steel plate substrate is directly placed in a nickel plating solution for electroplating at a temperature of 80°C for 30 minutes. After the electroplating is completed, it is rinsed with distilled water to obtain a nickel-plated steel plate. (4) Hot-dip galvanizing: Use 80-mesh sandpaper to grind the surface of the nickel-plated steel plate to roughen its surface, and then immerse it in a zinc solution for hot-dip galvanizing. The hot-dip galvanizing temperature is 400°C and the hot-dip galvanizing time is 20 seconds. After the hot-dip galvanizing is completed, use hot air to blow off the excess zinc on the surface.

[0017] Example 2 A method for plating a nickel-zinc double-layer protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) Prepare nickel plating solution: nickel nitrate is 30 g / L, sodium hypophosphite is 25 g / L, succinic acid is 15 g / L, and ammonium hydroxide is used to adjust the pH to 4.5 for later use; (3) Nickel electroplating: The steel plate substrate is directly placed in a nickel plating solution for electroplating at a temperature of 80°C for 30 minutes. After the electroplating is completed, it is rinsed with distilled water to obtain a nickel-plated steel plate. (4) Hot-dip galvanizing: Use 200-mesh sandpaper to grind the surface of the nickel-plated steel plate to roughen its surface, and then immerse it in a zinc solution for hot-dip galvanizing. The hot-dip galvanizing temperature is 410°C and the hot-dip galvanizing time is 30 seconds. After the hot-dip galvanizing is completed, use hot air to blow off the excess zinc on the surface.

[0018] Comparative Example 1 A method for coating a galvanized protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) Hot-dip galvanizing: Use 80-mesh sandpaper to grind the steel plate base to roughen its surface, and then immerse it in a zinc solution for hot-dip galvanizing. The hot-dip galvanizing temperature is 400°C and the hot-dip galvanizing time is 1 minute. After the hot-dip galvanizing is completed, use hot air to blow off the excess zinc on the surface.

[0019] Comparative Example 2 A method for plating a nickel protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) Prepare nickel plating solution: nickel nitrate is 30 g / L, sodium hypophosphite is 25 g / L, succinic acid is 15 g / L, and ammonium hydroxide is used to adjust the pH to 4.5 for later use; (3) Nickel electroplating: Place the steel plate substrate directly in the nickel plating solution for electroplating at a temperature of 80°C for 30 minutes. Rinse with distilled water after electroplating.

[0020] Comparative Example 3 A method for plating a nickel-zinc double-layer protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) preparing nickel plating solution: nickel nitrate is 10 g / L, sodium hypophosphite is 25 g / L, succinic acid is 15 g / L, and ammonium hydroxide is used to adjust the pH to 4.5 for later use; (3) Nickel electroplating: The steel plate substrate is directly placed in a nickel plating solution for electroplating at a temperature of 80°C for 30 minutes. After the electroplating is completed, it is rinsed with distilled water to obtain a nickel-plated steel plate. (4) Hot-dip galvanizing: Use 80-mesh sandpaper to grind the surface of the nickel-plated steel plate to roughen its surface, and then immerse it in a zinc solution for hot-dip galvanizing. The hot-dip galvanizing temperature is 400°C and the hot-dip galvanizing time is 20 seconds. After the hot-dip galvanizing is completed, use hot air to blow off the excess zinc on the surface.

[0021] Comparative Example 4 A method for coating a zinc-nickel double-layer protective film on a steel plate comprises the following steps: (1) Prepare a steel plate substrate; grind the steel plate on 80-mesh, 100-mesh, 120-mesh and 200-mesh sandpapers in sequence and clean it with clean water until the surface is smooth, then degrease it in a 5% sodium hydroxide solution at 60°C, etch it in an 8% hydrochloric acid solution to ensure that there is no oxide on the surface, then wash it with distilled water and dry it to obtain a steel plate substrate for later use; (2) Hot-dip galvanizing: Use 80-grit sandpaper to grind the surface of the steel plate base to roughen its surface, and then immerse it in a zinc solution for hot-dip galvanizing. The hot-dip galvanizing temperature is 400°C and the hot-dip galvanizing time is 20 seconds. After the hot-dip galvanizing is completed, use hot air to blow off the excess zinc on the surface to obtain a galvanized steel plate; (3) preparing nickel plating solution: nickel nitrate is 30 g / L, sodium hypophosphite is 25 g / L, succinic acid is 15 g / L, and ammonium hydroxide is used to adjust the pH to 4.5 for later use; (4) Nickel electroplating: Place the galvanized steel sheet directly in the nickel plating solution for electroplating at a temperature of 80°C for 30 minutes. Rinse with distilled water after electroplating.

[0022] Experimental Example 1 The performance tests were conducted on the steel plates coated with protective films prepared in Example 1 and Comparative Examples 1-4, and the test results are shown in Table 1. The steel plates coated with the nickel-zinc double-layer protective films prepared in Example 1 were cut to prepare samples, and the size of the nickel-zinc double-layer protective films on each sample was 10 cm×1 cm; the samples of Comparative Examples 1-4 were prepared in the same manner.

[0023] Hardness test: The Vickers hardness test was performed on the specimens using a Shimadzu HMV-2000 instrument according to ASTM E 384-899, with a test load of 50 gf, an indentation time of 12 s, and a temperature of 22.9 °C.

[0024] Thickness test: The thickness of the protective film is measured according to ASTM standard A 525-93.

[0025] Adhesion Test: To determine the adhesion of the protective film to the steel plate, the specimen was bent until both ends became parallel and then restored to its original texture, and the surface of the specimen was visually inspected using a magnifying lens to find out if there were any cracks or defects.

[0026] Corrosion resistance test: Use 5% NaCl to conduct immersion test. NaCl solution contains chloride ions, which easily react with the galvanized layer and accelerate the corrosion of zinc. The time point when rust spots appear on the sample is used as the evaluation standard. Take out the sample every 24 hours, and use a magnifying lens to visually inspect the surface of the sample. Put it back after observation and recording, and compare the initial corrosion time of different samples.

[0027] Table 1 Performance test results

[0028] As can be seen from Table 1, the hardness, adhesion and corrosion resistance of Comparative Examples 1 and 2 coated with a single-layer protective film are not as good as those of Example 1, Comparative Example 3 and Comparative Example 4 coated with a double-layer protective film. However, when the nickel element in the double-layer protective film is insufficient, or the order of the double-layer protective film is changed, its adhesion and corrosion resistance will be greatly reduced. The reason for this may be that a certain amount of nickel is first electroplated on the steel plate to promote the further diffusion of subsequent zinc during hot dip plating, and the nickel-zinc double-layer protective film becomes a denser internal alloy phase, that is, nickel is between iron and zinc, which can better promote the alloying reaction of iron and zinc, enhance the adhesion between the steel plate and the nickel-zinc double-layer protective film, and improve its corrosion resistance.

[0029] Although the present invention has been described in detail by way of preferred embodiments, the present invention is not limited thereto. Without departing from the spirit and essence of the present invention, a person of ordinary skill in the art may make various equivalent modifications or substitutions to the embodiments of the present invention, and such modifications or substitutions shall be within the scope of the present invention. Any person of ordinary skill in the art may easily conceive of changes or substitutions within the technical scope disclosed by the present invention, and such changes or substitutions shall be within the scope of protection of the present invention.

Claims

1. A method for plating a nickel-zinc double-layer protective film on a steel plate, characterized in that: The steel plate is polished to be smooth, degreased, etched, cleaned and dried to obtain a steel plate base; the steel plate base is placed in a nickel plating solution for electroplating, the electroplating temperature is 75-85°C, the electroplating time is 25-35 minutes, the pH value of the nickel plating solution is 4.5-5, and the nickel-plated steel plate is obtained after rinsing with distilled water; the surface of the nickel-plated steel plate is roughened and then placed in a zinc solution for hot-dip plating, the hot-dip plating temperature is 390-410°C, and the hot-dip plating time is 20-30 seconds.

2. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: The steel plate was polished on 80-grit, 100-grit, 120-grit and 200-grit sandpapers in sequence.

3. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: For degreasing, use 5% sodium hydroxide solution.

4. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: Etching uses 8% hydrochloric acid solution.

5. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: The solutes of the nickel plating solution include nickel nitrate, sodium hypophosphite and succinic acid.

6. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 5, characterized in that: The nickel nitrate concentration in the nickel plating solution is 30 g / L, the sodium hypophosphite concentration is 25 g / L, and the succinic acid concentration is 15 g / L.

7. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: The electroplating temperature is 80°C, the electroplating time is 30 minutes, and the pH value of the nickel plating solution is 4.

5.

8. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: The nickel-plated steel plate was roughened using 80-200 grit sandpaper.

9. A method for plating a nickel-zinc double-layer protective film on a steel plate as claimed in claim 1, characterized in that: After hot-dip coating, use hot air to blow away the zinc that has not been firmly hot-dip coated on the surface.

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