High-adhesion hot galvanizing process

Abstract

The invention relates to the technical field of hot dip coating processes, in particular to a high-adhesion hot dip coating process which comprises the following steps: filling a base material and sodium bicarbonate into a tubular furnace, and carrying out high-temperature oxidation treatment to obtain a pre-oxidized base material; performing acid and alkali washing on the pre-oxidized base material to obtain a pre-treated base material; the pretreated base material is immersed in the modified plating assistant agent, and a film coating base material is obtained; the preparation method comprises the following steps: firstly, immersing a coating substrate in Zn-Ce alloy liquid for primary coating, then immersing the coating substrate in Zn-Al-Mg-Nano-CeO2 alloy liquid for secondary coating, taking out the coating substrate, and cooling the coating substrate to room temperature. According to the method, Si on the surface of the base material is oxidized into SiO2 in a selective oxidation mode, impurities such as SiO2 are peeled off so as to reduce the content of Si on the surface of the base material, the thickness of an alloy coating can be reduced in cooperation with a modified plating assistant and a double-coating process, a zeta phase layer can be more compact, and therefore the binding force between the coating and the base material is improved, and the service life of the coating is prolonged. And the corrosion resistance of the plating layer is improved.

Description

Technical Field

[0001] This invention relates to the field of hot-dip galvanizing technology, specifically a high-adhesion hot-dip galvanizing process. Background Technology

[0002] Hot-dip galvanizing is a corrosion protection process that involves immersing steel materials in molten zinc or zinc alloy to form a metallic coating. Hot-dip galvanized products have seen rapid development due to their advantages such as good corrosion resistance, simple process, and low cost. Traditional hot-dip galvanizing processes typically include water washing, alkaline washing, acid pickling, fluxing, and zinc plating. For steels with low silicon content, this type of hot-dip galvanizing treatment is sufficient. However, for steels with high silicon content, the high silicon content promotes the iron-zinc reaction, leading to increased coating thickness, a darker coating surface, and a discontinuous granular ζ phase, resulting in a looser coating structure and poorer adhesion between the coating and the steel. Therefore, a high-adhesion hot-dip galvanizing process is proposed. Summary of the Invention

[0003] To address the shortcomings of existing technologies, this invention provides a high-adhesion hot-dip galvanizing process. It employs selective oxidation to reduce the Si content on the substrate surface, and combines this with modified flux and a double-film coating process. This not only reduces the thickness of the alloy coating but also makes the ζ-phase layer more compact, thereby improving the adhesion between the coating and the substrate, as well as the corrosion resistance of the coating itself.

[0004] To achieve the above objectives, the present invention provides the following technical solution: a high-adhesion hot-dip galvanizing process, comprising the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 300-400℃ for 8-10h to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux, and remove and dry it after the fluxing is completed to obtain the coated substrate; (4) First, immerse the coating substrate in Zn-Ce alloy liquid for a first coating, and then immerse it in Zn-Al-Mg-Nano-CeO2 alloy liquid for a second coating. After the hot immersion zinc is finished, take it out and cool it to room temperature.

[0005] Preferably, in step (1), the substrate comprises the following components by mass percentage: C 3.6%, Si 2.9%, Mn 0.2%, Mg 0.044%, Re 0.035%, P ≤0.06%, S ≤0.025%, with the balance being Fe.

[0006] Preferably, in step (3), the plating temperature is 70-75℃ and the plating time is 3-4 min.

[0007] Preferably, in step (3), the modified plating flux is prepared as follows: ZnCl2 (zinc chloride), NH4Cl (ammonium chloride), NaF (sodium fluoride), surfactant and BiCl3 (bismuth chloride) are added to deionized water, and the modified plating flux is obtained after being thoroughly stirred and dissolved.

[0008] Preferably, in the modified flux, the amount of ZnCl2 added is 80 g / L, the amount of NH4Cl added is 20 g / L, the amount of NaF added is 5 g / L, the amount of surfactant added is 2 g / L, and the amount of BiCl3 added is 0.5 g / L.

[0009] Preferably, the surfactant is selected from fatty alcohol polyoxyethylene ether and fatty alcohol polyoxyethylene ether sodium sulfate.

[0010] Preferably, in step (4), the mass percentage of Ce in the Zn-Ce alloy liquid is 0.1%.

[0011] Preferably, in step (4), the mass percentage of Al in the Zn-Al-Mg-Nano-CeO2 alloy liquid is 5%, the mass percentage of Mg is 1%, and the mass percentage of Nano-CeO2 is 0.5%.

[0012] Preferably, the particle size of the Nano-CeO2 is 20-30 nm.

[0013] Preferably, in step (4), the temperature of the first coating is 455-465℃ and the coating time is 15-20s; the temperature of the second coating is 470-480℃ and the coating time is 60-70s.

[0014] This invention provides a high-adhesion hot-dip galvanizing process, which has the following advantages compared with the prior art: This invention employs selective oxidation to oxidize Si on the substrate surface into SiO2, and then removes impurities such as SiO2 through acid-base washing to reduce the Si content on the substrate surface. Combined with modified flux and a double-coating process, this not only reduces the thickness of the alloy coating but also makes the ζ-phase layer denser, thereby improving the adhesion between the coating and the substrate, as well as the coating's corrosion resistance. Specifically, sodium bicarbonate is decomposed at temperatures above 300°C, generating a large amount of CO2 gas, which reduces the oxygen partial pressure inside the tube. This allows the substrate surface to undergo selective oxidation primarily to generate SiO2, with only a small amount of Fe oxides, ensuring precise reduction of the Si content and increasing the adhesion between the coating and the substrate.

[0015] This invention uses BiCl3 and NaF together in a modified flux. BiCl3 forms a protective film on the substrate surface by physically covering it, while NaF stabilizes the plating solution components by complexing them, thus achieving uniformity, adhesion, and corrosion resistance of the coating.

[0016] This invention employs a dual-coating process. Because the salt film formed by the flux reacts with Al in the alloy solution, the Al content in the alloy solution gradually decreases, which in turn affects the stability of the subsequent film quality. The single-coating process avoids the consumption of Al in the Zn-Al-Mg-Nano-CeO2 alloy solution during the second coating, ensuring that the coating always maintains high quality. In addition, adding Ce to the alloy solution in the first coating and adding Nano-CeO2 to the alloy solution in the second coating can reduce the thickness of the coating and improve the overall density of the coating. Attached Figure Description

[0017] The accompanying drawings, which are included to provide a further understanding of this application and form part of this application, illustrate exemplary embodiments and are used to explain this application, but do not constitute an undue limitation of this application. In the drawings: Figure 1 These are images showing the interface morphology of the coatings on the products in Embodiment 3, Comparative Examples 1, 5, and 6 of the present invention. Figure 2 These are surface morphology diagrams of the substrate and pre-oxidized substrate in Embodiment 3 of the present invention. Detailed Implementation

[0018] The following embodiments are provided to illustrate the implementation of this application in detail, so that the process of how this application uses technical means to solve technical problems and achieve technical effects can be fully understood and implemented accordingly.

[0019] The specific composition of the substrate used in this invention is shown in Table 1.

[0020] Table 1 Substrate Composition In this invention, Zn-0.1Ce alloy liquid means that the mass percentage of Ce in the alloy liquid is 0.1%.

[0021] In this invention, the Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid means that in the alloy liquid, the mass percentage of Al is 5%, the mass percentage of Mg is 1%, and the mass percentage of Nano-CeO2 is 0.5%.

[0022] Example 1 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 300°C for 10 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 70°C for 4 minutes. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 455℃ for 20s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 470℃ for 70s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0023] Example 2 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 400°C for 8 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3 minutes. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (sodium fatty alcohol polyoxyethylene ether sulfate) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 465℃ for 15s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 480℃ for 60s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0024] Example 3 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0025] Comparative Example 1 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain a pretreated substrate; (2) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (3) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0026] Comparative Example 2 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the amount of ZnCl2 added is 80 g / L, the amount of NH4Cl added is 20 g / L, the amount of surfactant (fatty alcohol polyoxyethylene ether) added is 2 g / L, and the amount of BiCl3 added is 0.5 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0027] Comparative Example 3 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the amount of ZnCl2 added is 80 g / L, the amount of NH4Cl added is 20 g / L, the amount of NaF added is 5 g / L, and the amount of surfactant (fatty alcohol polyoxyethylene ether) added is 2 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0028] Comparative Example 4 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) Immerse the coating substrate in Zn-5Al-1Mg-0.5Nano-CeO2 alloy liquid and coat it at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature; wherein the particle size of Nano-CeO2 is 20-30nm.

[0029] Comparative Example 5 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) First, immerse the coating substrate in pure Zn solution and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5Nano-CeO2 alloy solution and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of Nano-CeO2 is 20-30nm.

[0030] Comparative Example 6 A high-adhesion hot-dip galvanizing process includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 350°C for 8.5 hours to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux and perform fluxing at 75°C for 3.5 min. After the fluxing is completed, remove the substrate and dry it to obtain the coated substrate. The preparation method of the above modified flux is as follows: using deionized water as solvent, the addition amount of ZnCl2 is 80 g / L, the addition amount of NH4Cl is 20 g / L, the addition amount of NaF is 5 g / L, the addition amount of surfactant (fatty alcohol polyoxyethylene ether) is 2 g / L, and the addition amount of BiCl3 is 0.5 g / L. (4) First, immerse the coating substrate in Zn-0.1Ce alloy liquid and coat it once at 460℃ for 18s. Then immerse it in Zn-5Al-1Mg-0.5CeO2 alloy liquid and coat it a second time at 475℃ for 65s. After the hot zinc dipping is completed, take it out and cool it to room temperature. The particle size of CeO2 (cerium oxide) is 2-3μm.

[0031] Quality Inspection 1. Using the products from Examples 1-3 and Comparative Examples 1-6 as test samples, the adhesion between the substrate and the coating in the products was tested using a WS-2005 automatic coating adhesion scratch tester. The specific test results are shown in Table 2.

[0032] Table 2 Bonding Force 2. Using the products from Example 3 and Comparative Examples 1-6 as test samples, corrosion resistance tests were conducted according to the standard GB / T 10125-2021. The specific test results are shown in Table 3.

[0033] Table 3 Corrosion Resistance From Table 2 and Table 3, and in combination Figure 1It can be seen that: in Example 3, the adhesion between the coating and the substrate and the corrosion resistance of the coating are better, and the ζ phase layer is relatively dense as shown in the figure; compared with Example 3, in Comparative Example 1, the substrate was not pre-oxidized, and the excessive Si content on the surface will significantly reduce the adhesion between the coating and the substrate, and the corrosion resistance will also be worse, as shown in the figure; the ζ phase layer is relatively loose as shown in the figure; compared with Example 3, in Comparative Example 2 and Comparative Example 3, BiCl3 or NaF was used alone in the flux, and the adhesion between the coating and the substrate and the corrosion resistance of the coating will be reduced; compared with Example 3, pure zinc liquid was used in Comparative Example 5, and micron-sized CeO2 was used in the alloy liquid in Comparative Example 6. The adhesion between the coating and the substrate and the corrosion resistance of the coating of the resulting products are reduced, and the ζ phase layer in Comparative Example 5 is slightly loose, while the ζ phase layer in Comparative Example 6 is slightly denser as shown in the figure.

[0034] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and variations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A high-adhesion hot-dip galvanizing process, characterized in that, Includes the following steps: (1) The substrate and sodium bicarbonate are placed in a tube furnace without contact and treated at 300-400℃ for 8-10h to oxidize the Si on the surface of the substrate and obtain a pre-oxidized substrate. (2) The pre-oxidized substrate is subjected to alkali washing, water washing, acid washing, water washing and drying in sequence to remove impurities on the surface of the substrate and obtain the pre-treated substrate; (3) Immerse the pretreated substrate in the modified flux, and remove and dry it after the fluxing is completed to obtain the coated substrate; (4) First, immerse the coating substrate in Zn-Ce alloy liquid for a first coating, and then immerse it in Zn-Al-Mg-Nano-CeO2 alloy liquid for a second coating. After the hot immersion zinc is finished, take it out and cool it to room temperature.

2. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (1), the substrate comprises the following components by mass percentage: C 3.6%, Si 2.9%, Mn 0.2%, Mg 0.044%, Re 0.035%, P ≤0.06%, S≤0.025%, with the balance being Fe.

3. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (3), the fluxing temperature is 70-75℃ and the fluxing time is 3-4 min.

4. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (3), the modified flux is prepared as follows: ZnCl2, NH4Cl, NaF, surfactant and BiCl3 are added to deionized water and dissolved by stirring to obtain the modified flux.

5. The high-adhesion hot-dip galvanizing process according to claim 4, characterized in that, In the modified flux, the amount of ZnCl2 added is 80 g / L, the amount of NH4Cl added is 20 g / L, the amount of NaF added is 5 g / L, the amount of surfactant added is 2 g / L, and the amount of BiCl3 added is 0.5 g / L.

6. The high-adhesion hot-dip galvanizing process according to claim 4, characterized in that, The surfactant is selected from fatty alcohol polyoxyethylene ether and fatty alcohol polyoxyethylene ether sodium sulfate.

7. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (4), the mass percentage of Ce in the Zn-Ce alloy liquid is 0.1%.

8. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (4), the mass percentage of Al in the Zn-Al-Mg-Nano-CeO2 alloy liquid is 5%, the mass percentage of Mg is 1%, and the mass percentage of Nano-CeO2 is 0.5%.

9. The high-adhesion hot-dip galvanizing process according to claim 8, characterized in that, The particle size of the Nano-CeO2 is 20-30 nm.

10. The high-adhesion hot-dip galvanizing process according to claim 1, characterized in that, In step (4), the temperature of the first coating is 455-465℃ and the coating time is 15-20s; the temperature of the second coating is 470-480℃ and the coating time is 60-70s.

Images