Batch hot galvanizing zinc-aluminum-magnesium plating assistant and galvanizing process

Abstract

The invention discloses a batch hot-dip galvanizing zinc-aluminum-magnesium auxiliary agent and a galvanizing process, and belongs to the technical field of batch hot-dip galvanizing. In order to overcome the defects that a traditional plating assistant is narrow in alloy component adaptation range of zinc-aluminum-magnesium multi-element alloy, limited in base material applicability and the like, the universal plating assistant is provided and comprises ZnCl2 (100-400 g / L), SnCl2 (5-30 g / L), CeCl3 (5-20 g / L), K2ZrF6 (20-40 g / L) and Bi2O3 (5-20 g / L). The problems of segregation of a multi-component alloy coating, galvanization leakage of a structural part and the like are effectively solved by optimizing the ratio of a plating assistant and combining a batch hot galvanizing process. The plating assistant does not need an organic surfactant, avoids high-temperature decomposition residues, is suitable for batch hot galvanizing of zinc-aluminum alloy (0.2-1.0 wt.% of Al) and zinc-aluminum magnesium alloy (0.2-1.0 wt.% of Al and 0.1-0.5 wt.% of Mg), remarkably widens the application range of a base material, reduces the production cost, and is uniform and compact in obtained plating, free of skip plating defects and capable of meeting the long-acting anti-corrosion requirement of structural parts.

Description

Technical Field

[0001] The present invention belongs to the technical field of batch hot-dip galvanizing, and particularly relates to a batch hot-dip zinc-aluminum-magnesium flux with certain universality and a galvanizing process Background Art

[0002] Due to the excellent corrosion resistance and mechanical properties of the coating, the hot-dip galvanized alloy technology is widely used in the field of steel structure protection. Industrially, the hot-dip galvanized alloy technology is divided into continuous hot-dip galvanizing and batch hot-dip galvanizing. Continuous hot-dip galvanizing is good at efficiently processing thin plates and strips. The coating is thin, uniform and smooth, and is suitable for subsequent painting or precision machining of large quantities of standardized products. Compared with continuous hot-dip galvanizing, the core advantage of batch hot-dip galvanizing lies in its thicker coating and full-wrap protection, which can meet the overall anti-corrosion requirements of complex workpieces. It forms a zinc-iron alloy layer with strong adhesion through metallurgical bonding, providing long-term protection for decades in harsh environments, and does not rely on a continuous production line, flexibly supporting small-batch or customized production, especially suitable for infrastructure fields with extremely high requirements for corrosion resistance and durability.

[0003] In the batch hot-dip galvanizing process, the flux, as a key pretreatment material, directly affects the coating quality, uniformity and bonding strength. This composite salt solution usually consists of components such as zinc chloride and ammonium chloride, forming a protective film to prevent secondary oxidation of the substrate, removing residual oxides, and enhancing the wettability of the molten metal to ensure uniform adhesion of the coating. The traditional batch hot-dip galvanizing flux system is mainly designed for a specific alloy composition ratio and is difficult to have the ability to prepare different alloy compositions at the same time. In addition, the traditional batch hot-dip galvanizing flux system generally uses plates as the substrate, and when using standard structural parts for galvanizing, there are often problems such as missing plating and uneven coating at the porous and concave parts of the structural parts.

[0004] Therefore, it is of great research significance to develop a batch hot-dip zinc-aluminum-magnesium flux with certain universality and a galvanizing process to solve the defects such as narrow alloy composition adaptation range and limited substrate applicability. Summary of the Invention

[0005] The present invention aims to provide a batch hot-dip zinc-aluminum-magnesium flux with certain universality and a galvanizing process to address the defects of the traditional batch hot-dip galvanizing flux, such as narrow alloy composition adaptation range and limited substrate applicability.

[0006] To solve the above problems, the flux adopted by the present invention can be simultaneously applicable to the batch hot-dip galvanizing requirements of Zn-Al and Zn-Al-Mg alloys, and can also meet the batch hot-dip galvanizing requirements of structural parts. The composition of the flux is as follows: 100-400 g / L ZnCl2, 5-30 g / L SnCl2, 5-20 g / L CeCl3, 20-40 g / L K2ZrF6, 5-20 g / L Bi2O3, and the rest is water.

[0007] The flux for batch hot-dip galvanizing of the present invention contains 100-300 g / L ZnCl2, and is further preferably 250-260 g / L ZnCl2.

[0008] The flux for batch hot-dip galvanizing of the present invention contains 5-30 g / L SnCl2, and is further preferably 10-15 g / L SnCl2.

[0009] The flux for batch hot-dip galvanizing of the present invention contains 5-20 g / L CeCl3, and is further preferably 5-10 g / L CeCl3.

[0010] The flux for batch hot-dip galvanizing of the present invention contains 20-40 g / L K2ZrF6, and is further preferably 30-40 g / L K2ZrF6.

[0011] The flux for batch hot-dip galvanizing of the present invention contains 5-20 g / L Bi2O3, and is further preferably 10-20 g / L Bi2O3.

[0012] The usage method of the flux of this patent is as follows:

[0013] (1) Material preparation: Select Q235 and national standard angle codes as the substrates, with dimensions of 50 mm×30 mm×1 mm and 30 mm×30 mm×3 mm respectively;

[0014] (2) Material pretreatment: Use #280 sandpaper to polish the surface of the substrate to be bright, flat, without obvious rust and other oxide films or impurities.

[0015] (3) Alkaline washing and acid washing: Use a 10 wt.% NaOH solution at 40-60 °C for ultrasonic cleaning for 5-10 min, and rinse with water for 1 min; then use a 10 wt.% HCl solution at 40-60 °C for ultrasonic cleaning for 2-4 min, and rinse with water for 1 min.

[0016] (4) Fluxing: Immerse the substrate treated in step (3) into the flux for fluxing, the fluxing temperature is 40-60 °C, and the fluxing time is 3-5 min.

[0017] (5) Drying: The substrate after fluxing is dried. The drying temperature is 100 - 150 °C, and the drying time is 1 - 3 min.

[0018] (6) Hot dip galvanizing: The dried substrate is put into the alloy liquid for hot dip galvanizing. The hot dip galvanizing temperature is 470 - 500 °C, and the hot dip galvanizing time is about 30 - 120 s; after hot galvanizing, it is air-cooled at 15 - 30 °C.

[0019] Furthermore, in step (3), it is preferred to ultrasonically clean with a 10 wt.% NaOH solution at 50 °C for 8 min, and preferably ultrasonically clean with a 10 wt.% HCl solution at 60 °C for 3 min.

[0020] Furthermore, before fluxing in step (4), it is preferred to adjust the pH value of the flux to 2 - 4; the reagent for adjusting the pH is preferably hydrochloric acid, and the mass fraction is preferably 95 - 97%.

[0021] Furthermore, in step (4), the fluxing temperature is preferably 50 °C, and the fluxing time is preferably 3 min.

[0022] Furthermore, in step (5), the drying temperature is preferably 110 °C, and the drying time is preferably 2 min.

[0023] Furthermore, in step (6), the hot dip galvanizing temperature is preferably 490 °C, the hot dip galvanizing time is preferably 60 s, and the air-cooling temperature is 20 °C.

[0024] Furthermore, when the structural part is hot dip galvanized in step (6), after being taken out from the alloy bath, it needs to be shaken immediately for 5 - 10 s.

[0025] Furthermore, the composition of the zinc-aluminum alloy liquid in step (6) is: 0.2 - 1.0 wt.% Al, and the rest is zinc; the composition of the zinc-aluminum-magnesium alloy liquid is: 0.2 - 1.0 wt.% Al, 0.1 - 0.5 wt.% Mg.

[0026] The flux adopted in the present invention can simultaneously meet the batch hot-dip galvanizing requirements of zinc-aluminum-magnesium alloy and zinc-aluminum alloy, can meet the needs of producing different types of alloys, thereby effectively reducing costs; this flux can be applied to the batch hot-dip galvanizing of zinc-aluminum-magnesium alloy for structural parts, significantly broadening the applicable substrate range of batch hot-dip galvanizing of zinc-aluminum-magnesium alloy; this flux does not use conventional organic surface activators, and can effectively prevent problems such as the reduction of the binding force of the flux and the emission of harmful gases caused by the decomposition and residue of the surface activator at high temperature. Description of the Drawings

[0027] Figure 1 is the process flow chart of the batch hot-dip galvanizing process of this patent;

[0028] Figure 2It is the surface diagram of the 0.4wt.% Al - 0.2wt.% Mg - Zn coating in Example 1;

[0029] Figure 3 It is the surface diagram of the 0.4wt.% Al - Zn coating in Example 1;

[0030] Figure 4 It is the surface SEM diagram of the 0.4wt.% Al - 0.2wt.% Mg - Zn coating in Example 1;

[0031] Figure 5 It is the surface diagram of the zinc - aluminum - magnesium coating on the structural part in Example 6;

[0032] Figure 6 It is the surface diagram of the 0.4wt.% Al - Zn and 0.4wt.% Al - 0.2wt.% Mg - Zn coatings obtained in Comparative Example 1; Specific embodiments

[0033] The present invention will be further described below in conjunction with examples

[0034] Example 1

[0035] Composition and ratio of the flux:

[0036] 250g / L ZnCl2, 10g / L SnCl2, 10g / L CeCl3, 30g / L K2ZrF6, 10g / L Bi2O3, and the rest is water.

[0037] The base material is Q235, and the alloy solutions used are Zn - 0.4wt.% Al - 0.2wt.% Mg and Zn - 0.2wt.% Al.

[0038] The base material is polished, and then alkali - washed and pickled; then the pH of the flux is adjusted to 4, and the base material is fluxed at 50°C for 3 min; the base material is taken out and dried at 110°C for 2 min, immersed in the alloy solution at 490°C for 60 s, and then the base material is taken out for air - cooling treatment to obtain the zinc - aluminum - magnesium alloy coating and the zinc - aluminum alloy coating.

[0039] Example 2

[0040] Composition and ratio of the flux:

[0041] 100g / L ZnCl2, 10g / L SnCl2, 20g / L CeCl3, 10g / L K2ZrF6, 10g / L Bi2O3, and the rest is water.

[0042] The base material is Q235, and the alloy solutions used are Zn - 0.4wt.% Al - 0.2wt.% Mg and Zn - 0.2wt.% Al.

[0043] The substrate is polished, and then undergoes alkaline cleaning and pickling treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, and then the substrate is taken out and air-cooled to obtain a zinc-aluminum-magnesium alloy coating and a zinc-aluminum alloy coating.

[0044] Example 3

[0045] Composition and ratio of the flux:

[0046] 300 g / L ZnCl2, 10 g / L SnCl2, 10 g / L CeCl3, 20 g / L K2ZrF6, 30 g / L Bi2O3, and the rest is water.

[0047] The substrate selected is Q235, and the alloy solutions used are Zn-0.4 wt.% Al-0.2 wt.% Mg and Zn-0.2 wt.% Al.

[0048] The substrate is polished, and then undergoes alkaline cleaning and pickling treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, and then the substrate is taken out and air-cooled to obtain a zinc-aluminum-magnesium alloy coating and a zinc-aluminum alloy coating.

[0049] Example 4

[0050] Composition and ratio of the flux:

[0051] 250 g / L ZnCl2, 10 g / L SnCl2, 10 g / L CeCl3, 30 g / L K2ZrF6, 10 g / L Bi2O3, and the rest is water.

[0052] The substrate selected is Q235, and the alloy solutions used are Zn-0.4 wt.% Al-0.2 wt.% Mg and Zn-0.2 wt.% Al.

[0053] The substrate is polished, and then undergoes alkaline cleaning and pickling treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, and then the substrate is taken out and air-cooled to obtain a zinc-aluminum-magnesium alloy coating and a zinc-aluminum alloy coating.

[0054] Example 5

[0055] Composition and ratio of the flux:

[0056] 250 g / L ZnCl2, 10 g / L SnCl2, 10 g / L CeCl3, 30 g / L K2ZrF6, 10 g / L Bi2O3, the balance being water.

[0057] The base material is Q235, and the alloy liquid used is Zn - 0.8 wt.% Al - 0.4 wt.% Mg and Zn - 0.4 wt.% Al.

[0058] The base material is polished, and then undergoes alkaline cleaning and pickling treatments; then the pH of the flux is adjusted to 4, and the base material is fluxed at 50 °C for 3 min; the base material is taken out and dried at 110 °C for 2 min, immersed in the alloy liquid at 490 °C for 60 s, taken out and air-cooled to obtain zinc-aluminum-magnesium alloy coating and zinc-aluminum alloy coating.

[0059] Example 6

[0060] Composition and ratio of the flux:

[0061] 250 g / L ZnCl2, 10 g / L SnCl2, 10 g / L CeCl3, 30 g / L K2ZrF6, 10 g / L Bi2O3, the balance being water.

[0062] The base material selected is a national standard galvanized angle code, and the alloy liquid used is Zn - 0.4 wt.% Al - 0.2 wt.% Mg;

[0063] The base material is polished until there is no galvanized layer and other oxide layers on the surface, and then undergoes alkaline cleaning and pickling treatments; then the pH of the flux is adjusted to 4, and the base material is fluxed at 50 °C for 3 min; the base material is taken out and dried at 110 °C for 2 min, immersed in the alloy liquid at 490 °C for 60 s, taken out and slightly shaken for 10 s, and then air-cooled to obtain zinc-aluminum-magnesium alloy coating.

[0064] Example 7

[0065] Composition and ratio of the flux:

[0066] 250 g / L ZnCl2, 10 g / L SnCl2, 10 g / L CeCl3, 30 g / L K2ZrF6, 10 g / L Bi2O3, the balance being water.

[0067] The base material selected is a national standard galvanized angle code, and the alloy liquid used is Zn - 0.6 wt.% Al - 0.3 wt.% Mg;

[0068] The substrate is polished until there is no galvanized layer and other oxide layers on the surface, and then it is subjected to alkali washing and acid washing treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, the substrate is taken out and gently shaken for 10 s, and then air cooling treatment is carried out to obtain a zinc-aluminum-magnesium alloy coating.

[0069] Comparative Example 1

[0070] Composition and ratio of the flux:

[0071] 250 g / L ZnCl2, 10 g / L NaF, 30 g / L CeCl2, 10 g / L SnCl2, 6% ethanol, 2% alkylphenol polyoxyethylene ether, and the rest is water.

[0072] The substrate is Q235, and the alloy solutions used are Zn-0.4 wt.% Al-0.2 wt.% Mg and Zn-0.2 wt.% Al;

[0073] The substrate is polished, and then subjected to alkali washing and acid washing treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, the substrate is taken out and air cooled to obtain a zinc-aluminum-magnesium alloy coating and a zinc-aluminum alloy coating.

[0074] Comparative Example 2

[0075] Composition and ratio of the flux:

[0076] 250 g / L ZnCl2, 10 g / L SnCl2, 40 g / L KCl, 10 g / L BiCl3, 0.4 - 1 g / L AEO9, and the rest is water;

[0077] The substrate is Q235, and the alloy solutions used are Zn-0.4 wt.% Al-0.2 wt.% Mg and Zn-0.2 wt.% Al;

[0078] The substrate is polished, and then subjected to alkali washing and acid washing treatments; then the pH of the flux is adjusted to 4, and the substrate is fluxed at 50 °C for 3 min; the substrate is taken out and dried at 110 °C for 2 min, immersed in the alloy solution at 490 °C for 60 s, the substrate is taken out and air cooled to obtain a zinc-aluminum-magnesium alloy coating and a zinc-aluminum alloy coating;

[0079] Comparative Example 3

[0080] Composition and ratio of the flux:

[0081] 150 g / L ZnCl2, 20 g / L SnCl4, 20 g / L NaCl, 10 g / L CaCl2, 5 g / L NiCl2, 1 g / L LaCl3, 25 ml / L HCl, the rest is water;

[0082] The base material is a national standard galvanized angle code, and the alloy liquid is Zn - 0.6 wt.% Al - 0.3 wt.% Mg;

[0083] Grind the base material until there is no galvanized layer and other oxide layers on the surface, and then carry out alkali washing and acid washing treatments; then adjust the pH of the flux to 4, and flux the base material at 50 °C for 3 min; take out the base material and dry it at 110 °C for 2 min, immerse it in the alloy liquid at 490 °C for 60 s, slightly shake the base material for 10 s after taking it out, and then carry out air cooling treatment to obtain a zinc - aluminum - magnesium alloy coating.

[0084] Comparative Example 4

[0085] The composition and ratio of the flux:

[0086] 50 g / L ZnSO4, 80 g / L (NH4)2SO4, 20 g / L Sn(SO4)2, 1 g / L Ce2(SO4)3, 2 g / L lauryl dimethyl betaine, the rest is water;

[0087] The base material is a national standard galvanized angle code, and the alloy liquid is Zn - 0.6 wt.% Al - 0.3 wt.% Mg;

[0088] Grind the base material until there is no galvanized layer and other oxide layers on the surface, and then carry out alkali washing and acid washing treatments; then adjust the pH of the flux to 4, and flux the base material at 50 °C for 3 min; take out the base material and dry it at 110 °C for 2 min, immerse it in the alloy liquid at 490 °C for 60 s, slightly shake the base material for 10 s after taking it out, and then carry out air cooling treatment to obtain a zinc - aluminum - magnesium alloy coating.

[0089] Observe the appearance of the substrate surface after fluxing and the surface quality of the coating obtained after hot - dipping in Examples 1 - 7 and Comparative Examples 1 - 4 respectively, and summarize them to obtain Table 1

[0090] Table 1 Summary table of the fluxing and dipping effects of the flux for batch hot - dip galvanizing

[0091] Test item Quality of the assisting coating surface Quality condition of the coating surface Example 1 Colorless, relatively thin thickness Surfaces of both coatings are complete, and there is no missing plating phenomenon Example 2 Colorless, relatively thin thickness Surfaces of both coatings are complete, and there is no missing plating phenomenon Example 3 Colorless, relatively thin thickness Surfaces of both coatings are complete, and there is no missing plating phenomenon Example 4 Colorless, relatively thin thickness Surfaces of both coatings are complete, and there is no missing plating phenomenon Example 5 Colorless, relatively thin thickness Surfaces of both coatings are complete, and there is no missing plating phenomenon Example 6 Colorless, relatively thin thickness Coating on the structural part is complete, and there is no obvious missing plating phenomenon Example 7 Colorless, relatively thin thickness Coating on the structural part is complete, and there is no obvious missing plating phenomenon Comparative example 1 White, relatively thick thickness There is no missing plating in the zinc-aluminum coating, and defects appear in the zinc-aluminum-magnesium coating Comparative example 2 Colorless, relatively thin thickness There is no missing plating in both coatings, but wrinkles are formed on the surfaces Comparative example 3 Colorless, relatively thin thickness Missing plating phenomenon appears on the surface of the coating on the structural part Comparative example 4 Colorless, relatively thin thickness The thickness of the coating on the structural part is uneven, and the concave holes are covered by the coating

[0092] It can be analyzed from Table 1 that the fluxes and galvanizing processes in Examples 1 - 7 have a certain universality, can meet the preparation requirements of batch hot - dip galvanized zinc - aluminum coatings and zinc - aluminum - magnesium coatings, and can also meet the preparation requirements of batch hot - dip galvanized zinc - aluminum - magnesium coatings for steel plates or standard structural parts. The surface quality of the obtained coatings is good, and the application of batch hot - dip galvanizing in industrial production can be further promoted.

Claims

1. A batch hot-dip galvanized zinc-aluminum-magnesium flux, characterized in that The following concentrations Composition: 100 - 400 g / L ZnCl2, 5 - 30 g / L SnCl2, 5 - 20 g / L CeCl3, 20 - 40 g / L K2ZrF6, 5 - 20 g / L Bi2O3, and the balance is water.

2. The batch hot-dip galvanizing process is characterized by the following steps: (1) Material pretreatment: Use #280 sandpaper to polish the surface of the substrate until it is bright, flat, without obvious rust, other oxide films or impurities. (2) Alkali washing and acid washing: Alkali wash with 10 wt.% NaOH solution for 5 - 10 min, wash with water for 1 min; Acid wash with 10 wt.% HCl solution for 2 - 4 min, wash with water for 1 min. (3) Fluxing: Immerse the substrate treated in step (2) into the fluxing agent for fluxing. (4) Drying: Dry the fluxed substrate. (5) Hot dip galvanizing: Put the dried substrate into the alloy liquid for hot dip galvanizing, and cool it naturally in the air after hot dipping.

3. According to step (2) in claim 2, characterized in that Ultrasound is used for alkali washing and acid washing, and the temperature is 40°C - 60°C.

4. According to step (3) in claim 2, characterized in that It is necessary to adjust the pH to 2 - 4 with 95 - 97% HCl solution before fluxing.

5. According to step (4) in claim 2, it is characterized in that The drying temperature is 100°C - 150°C, and the drying time is 1 - 3 min.

6. According to step (5) in claim 2, characterized in that The hot dip galvanizing temperature is 470°C - 500°C, the hot dip galvanizing time is about 30 - 120 s, and air cooling is carried out at 15°C - 30°C.

7. According to step (5) in claim 2, it is characterized in that After the structural part is hot dip galvanized, it needs to be taken out of the alloy bath and immediately shaken slightly for 5 - 10 s.

8. The galvanizing method according to claim 2, characterized in that The mass fraction of the zinc-aluminum-magnesium alloy liquid is: Zn 98.5 - 99.7%, Al 0.2 - 1.0%, Mg 0.1 - 0.5%.

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