阅读说明：本技术 一种热浸镀锌铝镁合金镀层及其制备方法 (Hot-dip zinc-aluminum-magnesium alloy coating and preparation method thereof ) 是由 江社明 张启富 李远鹏 张�杰 刘昕 于 2020-11-23 设计创作，主要内容包括：本发明涉及一种热浸镀锌铝镁合金镀层及其制备方法,属于金属镀层技术领域,解决了现有溶剂法工艺在钢结构上热浸镀锌铝镁镀层工艺适应性差、镀层质量差的问题。本发明的热浸镀锌铝镁合金镀层按照质量百分比计为：Al：3～13％；Mg：0.8～3％；其余为Zn及不可避免的杂质。制备方法包括,步骤S1：制备热浸镀所需的锌镀液及锌铝镁合金镀液；步骤S2：对钢结构进行除油处理、酸洗处理和熔剂助镀；步骤S3：将熔剂助镀的钢结构置入步骤S1制备的锌镀液中,进行热浸镀锌处理；步骤S4：将热浸镀有锌镀层的钢结构置入步骤S1制备的锌铝镁合金镀液中,进行热浸镀锌铝镁处理。本发明应用于钢结构,且镀层质量好、耐蚀性高。(The invention relates to a hot-dip zinc-aluminum magnesium alloy coating and a preparation method thereof, belongs to the technical field of metal coatings, and solves the problems of poor process adaptability and poor coating quality of the hot-dip zinc-aluminum magnesium alloy coating on a steel structure by the existing solvent method process. The hot-dip galvanized aluminum-magnesium alloy coating comprises the following components in percentage by mass: al: 3-13%; mg: 0.8-3%; the balance of Zn and inevitable impurities. The preparation method comprises the following steps of S1: preparing zinc plating solution and zinc-aluminum-magnesium alloy plating solution required by hot dipping; step S2: carrying out oil removal treatment, acid cleaning treatment and flux plating assistance on the steel structure; step S3: placing the flux-assisted steel structure into the zinc plating solution prepared in the step S1 for hot-dip galvanizing treatment; step S4: and (4) putting the steel structure hot-dipped with the zinc coating into the zinc-aluminum-magnesium alloy plating solution prepared in the step S1, and carrying out hot-dip zinc-aluminum-magnesium plating treatment. The invention is applied to steel structures, and has good plating quality and high corrosion resistance.)

1. A hot-dip zinc-aluminum magnesium alloy coating is characterized by comprising the following chemical components in percentage by mass: al: 3-13%, Mg: 0.8-3%, and the balance of Zn and inevitable impurities.

2. The hot dip zinc aluminum magnesium alloy coating according to claim 1, wherein the coating comprises the following chemical components in percentage by mass: al: 4.5-6%, Mg: 1.5 to 1.8 percent, and the balance of Zn and inevitable impurities.

3. A hot dip galvanized aluminum magnesium alloy coating according to claim 1, wherein the hot dip galvanized aluminum magnesium alloy coating comprises an inner layer and an outer layer, the inner layer is a zinc coating, and the outer layer is a zinc aluminum magnesium alloy coating.

4. The hot dip galvanized aluminum magnesium alloy coating according to claim 1, wherein the hot dip galvanized aluminum magnesium alloy coating is a coating applied to a steel structure.

5. A method for preparing a hot-dip zinc-aluminum-magnesium alloy coating for preparing the zinc-aluminum-magnesium alloy coating of claims 1-4, comprising the steps of:

step S1: preparing zinc plating solution and zinc-aluminum-magnesium alloy plating solution required by hot dipping;

step S2: carrying out oil removal treatment, acid cleaning treatment and flux plating assistance on the steel structure to obtain a flux plating assistance steel structure;

step S3: placing the flux-assisted steel structure into the zinc plating solution prepared in the step S1, and carrying out hot-dip galvanizing treatment to obtain a hot-dip galvanized steel structure;

step S4: and (4) putting the steel structure hot-dipped with the zinc coating into the zinc-aluminum-magnesium alloy plating solution prepared in the step S1, and carrying out hot-dip zinc-aluminum-magnesium plating treatment to obtain the steel structure hot-dipped with the zinc-aluminum-magnesium alloy coating.

6. The hot dip coating method of hot dip coating a zinc aluminum magnesium alloy coating according to claim 5, wherein in step S3, the temperature of the hot dip coating solution is 445 to 465 ℃.

7. The hot dip coating method of hot dip coating a zinc aluminum magnesium alloy coating according to claim 5, wherein in step S3, the hot dip galvanizing time is controlled to be 1-3 min.

8. The hot dip coating method of hot dip galvanizing aluminum magnesium alloy coating according to claim 5, wherein in the step S4, the temperature of the coating solution of hot dip galvanizing aluminum magnesium alloy coating is 420 to 460 ℃.

9. The hot dip coating method of a hot dip zinc aluminum magnesium alloy coating according to claim 5, wherein in step S4, the hot dip coating time of the hot dip zinc aluminum magnesium alloy coating is 1 to 3 min.

10. The hot dip coating method of hot dip galvanized aluminum magnesium alloy coating according to claim 5, wherein in step S4, the hot dip galvanized aluminum magnesium alloy treatment includes hot dip galvanized aluminum magnesium alloy and post-treatment, and the post-treatment is air cooling or water cooling treatment.

Technical Field

The invention relates to the technical field of metal coatings, in particular to a hot-dip zinc-aluminum-magnesium alloy coating and a preparation method thereof.

Background

Galvanizing (galvanizing), also called hot dip galvanizing and hot dip galvanizing, is an effective metal corrosion prevention method, is the most economical and effective surface treatment method for preventing steel from being corroded in the natural environment, and is widely applied to the protection of various structures of steel materials. More than 60 percent of the global consumption of the metal zinc is used for the protective coating of the steel. Under the general atmospheric environment, the corrosion resistance of the existing galvanized layer can meet the use requirement, but under the condition of harsh corrosion environment (such as marine environmental climate and industrial polluted environmental climate), the commonly used galvanized layer protection can not meet the use requirement, so that the corrosion resistance of the plating layer needs to be improved. Meanwhile, the zinc-based alloy coating with better corrosion resistance is developed and adopted, so that the consumption of zinc resources can be reduced, and the development direction of the coating technology is also provided.

At present, the development of the zinc-aluminum-magnesium alloy coating in China mostly focuses on carrying out continuous hot dip coating treatment on a steel strip by adopting a gas reduction process. The batch flux method hot-dip galvanizing of steel structural parts and steel parts basically adopts pure zinc coating, and cannot adapt to zinc-aluminum-magnesium alloy coating, which is mainly caused by two reasons: firstly, when the solvent method is used for hot dip plating, the zinc bath in a plating pot has a safe aluminum content (less than or equal to 0.006-0.007%), if the aluminum and magnesium contents in the plating pot are higher than the safe values, when the solvent method zinc plating process is used for zinc plating, large-area plating leakage of a plating layer is easily caused, and the plating layer with good appearance surface quality cannot be obtained; on the other hand, the chloride in the solvent can react with the aluminum in the zinc pot to generate a large amount of toxic aluminum chloride gas.

Therefore, the development of the high corrosion-resistant zinc-aluminum-magnesium alloy coating for hot dip coating of the steel solvent method process and the preparation method thereof are suitable for the ultrahigh corrosion resistance and corrosion resistance requirements of the coating of steel structural members and steel parts (such as various electric power communication iron towers, various municipal and road and bridge steel structures and the like), and are urgent needs in the technical field of metal coatings.

Disclosure of Invention

In view of the above analysis, the embodiments of the present invention are directed to providing a hot-dip galvanized aluminum magnesium alloy coating and a preparation method thereof, so as to solve the problems of poor process adaptability and poor coating quality of a hot-dip galvanized aluminum magnesium coating on a steel structure by using the existing solvent process.

The invention is realized by the following technical scheme:

a hot-dip zinc-aluminum magnesium alloy coating comprises the following chemical components in percentage by mass: al: 3-13%, Mg: 0.8-3%, and the balance of Zn and inevitable impurities.

Further, the hot-dip galvanized aluminum magnesium alloy coating comprises the following chemical components in percentage by mass: al: 4.5-6%, Mg: 1.5 to 1.8 percent, and the balance of Zn and inevitable impurities.

Further, the hot-dip galvanized aluminum magnesium alloy coating comprises an inner layer and an outer layer, wherein the inner layer is a zinc coating, and the outer layer is a zinc aluminum magnesium alloy coating.

Further, the hot-dip galvanized aluminum magnesium alloy coating is a coating applied to a steel structure.

A method for preparing a hot-dip galvanized aluminum magnesium alloy coating comprises the following steps:

step S1: preparing zinc plating solution and zinc-aluminum-magnesium alloy plating solution required by hot dipping;

step S2: carrying out oil removal treatment, acid cleaning treatment and flux plating assistance on the steel structure to obtain a flux plating assistance steel structure;

step S3: placing the flux-assisted steel structure into the zinc plating solution prepared in the step S1, and carrying out hot-dip galvanizing treatment to obtain a hot-dip galvanized steel structure;

step S4: and (4) putting the steel structure hot-dipped with the zinc coating into the zinc-aluminum-magnesium alloy plating solution prepared in the step S1, and carrying out hot-dip zinc-aluminum-magnesium plating treatment to obtain the steel structure hot-dipped with the zinc-aluminum-magnesium alloy coating.

Further, in step S3, the temperature of the plating solution for hot-dip galvanizing is 445-465 ℃.

Further, in step S3, the hot-dip galvanizing time is controlled to be 1-3 min.

Further, in step S3, performing hot-dip galvanizing treatment on the flux-assisted steel structure, and if the workpiece thickness is greater than 4.0mm, performing first water cooling treatment, and performing hot-dip galvanizing aluminum magnesium alloy treatment on the water-cooled steel structure; and if the thickness of the workpiece is less than or equal to 4.0mm, directly carrying out hot-dip galvanizing aluminum magnesium alloy treatment.

Further, in step S4, the temperature of the plating solution of the hot-dip galvanized aluminum magnesium alloy plating layer is 420 to 460 ℃.

Further, in step S4, the hot dip coating time of the hot dip zinc-aluminum magnesium alloy coating is 1 to 3 min.

Further, in step S4, the hot dip galvanizing aluminum magnesium treatment includes hot dip galvanizing aluminum magnesium and post treatment, and the post treatment is air cooling or water cooling treatment.

Compared with the prior art, the invention has the following beneficial effects:

1. the invention carries out component research and innovation on the zinc-aluminum-magnesium alloy from the angle of improving the fluidity of the plating solution, improves the fluidity of the plating solution by accurately increasing the content of Al, and improves the quality of the plating layer.

2. From the viewpoint of improving the corrosion resistance of the coating, the invention separates out an aluminum-rich phase and a binary and ternary eutectic phase in the coating by precisely increasing the content of Mg, and an intermetallic compound MgZn formed by magnesium and zinc exists in the eutectic phase₂、Mg₂Zn₁₁，MgZn₂And Mg₂Zn₁₁Has lower anode dissolving current than pure zinc and improves the corrosion resistance of the plating. The results of the neutral salt spray test show that: the rust points of the hot-dip galvanized aluminum magnesium alloy coating still do not appear within 3000 hours, and the rust points of the hot-dip galvanized coating already appear within 500 hours, so that the corrosion resistance of the hot-dip galvanized aluminum magnesium alloy coating is improved by more than 5 times compared with that of the traditional pure zinc coating. The method has great significance for improving the corrosivity of steel structures applied to more severe corrosive environments (such as marine environmental climate and industrial polluted environmental climate).

3. The invention innovatively divides the process of hot dip galvanizing aluminum magnesium alloy into hot dip galvanizing and hot dip galvanizing aluminum magnesium two-step processes from the perspective of improving the adaptability of the steel structure hot dip galvanizing aluminum magnesium coating process, the coating comprises an inner layer and an outer layer, the inner layer is a zinc coating, the outer layer is a zinc aluminum magnesium alloy coating, and the binding force of the coating is obviously improved.

In the invention, the technical schemes can be combined with each other to realize more preferable combination schemes. Additional features and advantages of the invention will be set forth in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The objectives and other advantages of the invention will be realized and attained by the structure particularly pointed out in the written description and drawings.

Drawings

The drawings are only for purposes of illustrating particular embodiments and are not to be construed as limiting the invention, wherein like reference numerals are used to designate like parts throughout.

FIG. 1 is a cross-sectional view of a plating layer of a hot-dip galvanized aluminum-magnesium alloy;

FIG. 2 is a view showing the appearance of the plating layer;

wherein 2(a) is an appearance diagram of a pure zinc plating layer, and 2(b) is an appearance diagram of a zinc-aluminum-magnesium alloy plating layer.

FIG. 3 is a sample diagram of a neutral salt spray test of a pure zinc coating;

wherein, 3(a) is a sample graph after 0h neutral salt spray test, 3(b) is a sample graph after 500h neutral salt spray test, and 3(c) is a sample graph after 1000h neutral salt spray test.

FIG. 4 is a sample diagram of a neutral salt spray test of the zinc-aluminum-magnesium alloy coating of the invention.

Wherein, 4(a) is a sample diagram after 0h neutral salt spray test, 4(b) is a sample diagram after 500h neutral salt spray test, 4(c) is a sample diagram after 1000h neutral salt spray test, 4(d) is a sample diagram after 2000h neutral salt spray test, and 4(e) is a sample diagram after 3000h neutral salt spray test.

Detailed Description

The accompanying drawings, which are incorporated in and constitute a part of this application, illustrate preferred embodiments of the invention and together with the description, serve to explain the principles of the invention and not to limit the scope of the invention.

The invention provides a hot-dip galvanized aluminum magnesium alloy coating, which comprises the following chemical components in percentage by mass: al: 3-13%, Mg: 0.8-3%, and the balance of Zn and inevitable impurities.

Preferably, the hot-dip zinc-aluminum magnesium alloy coating comprises the following chemical components in percentage by mass: al: 4.5-6%, Mg: 1.5 to 1.8 percent, and the balance of Zn and inevitable impurities.

The effects of aluminum and magnesium in the zinc-aluminum-magnesium alloy coating are as follows:

aluminum (Al) can improve the fluidity of the plating melt, improve the quality of the plating, and improve the corrosion resistance of the plating.

The corrosion resistance of the zinc-based alloy coating can be obviously improved by adding magnesium (Mg). On the one hand, magnesium and zinc can form an intermetallic compound MgZn₂、Mg₂Zn₁₁The compounds have equivalent lower anode dissolution current than pure zinc phase, and the formation of the intermetallic compounds ensures that the zinc-magnesium alloy coating has higher corrosion resistance than the pure zinc coating; on the other hand, the addition of magnesium (Mg) can make the corrosion product of the coating more compact, and the main body of the corrosion product of pure zinc is loose ZnO and a small amount of compact Zn₄CO₃(OH)₄·H₂O, and the corrosion product of the Zn-Mg alloy coating is ZnCl₂·4Zn(OH)₄·H2O、Mg(OH)₂、Zn₄CO₃(OH)₄·H₂O, these products are denser and Mg (OH)₂The existence of the Mg can inhibit the oxygen absorption reaction of the cathode, the participation of Mg can also reduce the PH value of the surface of the plating layer, and the Mg is more beneficial to compact and insoluble ZnCl under the condition of low PH value₂·4Zn(OH)₄·H₂O corrosion products, thereby retarding the corrosion process of the zinc coating.

It should be noted that the hot-dip galvanized aluminum magnesium alloy coating in the present invention includes an inner layer and an outer layer, as shown in fig. 1, the inner layer is a zinc coating, the outer layer is a zinc aluminum magnesium alloy coating, and the coating has a strong bonding force. The hot dip galvanized aluminum-magnesium alloy coating comprises an aluminum-rich phase and a binary and ternary eutectic phase, and an intermetallic compound MgZn formed by magnesium and zinc exists in the eutectic phase₂、Mg₂Zn₁₁，MgZn₂And Mg₂Zn₁₁Has the same quality as pure zincLow anode dissolving current and improved corrosion resistance of the plating. The surface of the plating layer is white, and the surface is bright without plating leakage. As shown in fig. 2, 2(a) is an appearance of a conventional pure zinc plating layer, and 2(b) is an appearance of a hot-dip zinc-aluminum magnesium alloy plating layer. Compared with the appearance of the traditional pure zinc coating, the surface of the hot-dip zinc-aluminum magnesium alloy coating is whiter and brighter.

The invention provides a preparation method of a zinc-aluminum-magnesium alloy coating, which comprises the following steps:

step S1: preparing zinc plating solution and zinc-aluminum-magnesium alloy plating solution required by hot dipping;

taking zinc and aluminum magnesium according to the proportion, heating the zinc to 500-540 ℃ for complete melting, wrapping and pressing the magnesium with an aluminum sheet into blocks, pressing the blocks into zinc liquid, keeping the blocks at 500-540 ℃ for 1-2 hours, and stirring the blocks with a quartz rod every 10-20 min in the process until the blocks are fully melted to obtain the zinc-aluminum-magnesium alloy plating solution.

And heating the zinc to 500-540 ℃ for complete melting, and stirring the zinc with a quartz rod every 10-20 min in the process until the zinc is fully melted to obtain the zinc plating solution.

Step S2: carrying out oil removal treatment, acid cleaning treatment and flux plating assistance on the steel structure to obtain a flux plating assistance steel structure;

specifically, the steel structure is kept in NaOH alkaline liquor with the concentration of 10-15 wt% for 3-5 min for alkali washing and oil removal; then taking out and washing with clear water; then, pickling with 14-20 wt% hydrochloric acid solution for 8-20 min to remove rust; then cleaning with clear water; putting the steel structure in ZnCl with the concentration of 200-250 g/L₂NH with a concentration of 160-200 g/L₄Carrying out solvent plating assisting treatment in a Cl aqueous solution plating assisting agent, wherein the plating assisting temperature is 65-85 ℃, and the plating assisting time is 1-2 min; and then drying the steel structure at 110-140 ℃ for 5-10 min at 110-140 ℃.

Step S3: placing the flux-assisted steel structure into the plating solution prepared in the step S1, and carrying out hot-dip galvanizing treatment to obtain a hot-dip galvanized steel structure;

and (4) placing the steel structure pretreated in the step S2 into the galvanizing liquid prepared in the step S1, wherein the hot dipping temperature is 445-465 ℃, and the hot dipping time is 1-3 min.

The hot-dip galvanizing treatment is carried out on the flux-assisted steel structure, the judgment is made according to the thickness of the workpiece after the hot-dip galvanizing, if the thickness of the workpiece is more than 4.0mm, the first water cooling treatment is needed, and the hot-dip galvanizing aluminum magnesium alloy treatment is carried out on the steel structure after the water cooling. The water cooling treatment is mainly used for avoiding the influence on the overall coating adhesion of the hot-dip zinc-aluminum-magnesium alloy due to the fact that the zinc-iron alloy layer in the coating is too thick. And if the thickness is less than or equal to 4.0mm, directly carrying out hot dip galvanizing aluminum magnesium alloy treatment.

Step S4: and (4) putting the steel structure hot-dipped with the zinc coating into the zinc-aluminum-magnesium alloy plating solution prepared in the step S1, and carrying out hot-dip zinc-aluminum-magnesium plating treatment to obtain the steel structure hot-dipped with the zinc-aluminum-magnesium alloy coating.

And (3) placing the steel structure subjected to hot dip galvanizing in the step (S3) into the zinc-aluminum-magnesium alloy plating solution prepared in the step (S1), wherein the hot dip galvanizing temperature is 420-460 ℃, the hot dip galvanizing time is 1-3 min, so that the steel structure plated with the zinc-aluminum-magnesium alloy coating is obtained, and air cooling or water cooling is performed on the steel structure plated with the zinc-aluminum-magnesium alloy coating.

Example 1

The hot-dip galvanized aluminum-magnesium alloy coating comprises the following chemical components in percentage by mass: al: 4.5%, Mg: 1.5 percent, and the balance of Zn and inevitable impurities.

The preparation method of the hot dip galvanized aluminum magnesium alloy coating, wherein the thickness of the steel structural member is 1.5mm, comprises the following steps:

step 1: preparing zinc plating solution and zinc-aluminum-magnesium alloy plating solution required by hot dipping;

taking zinc and aluminum magnesium according to the proportion, heating the zinc to 530 ℃ to be completely melted, wrapping magnesium with an aluminum sheet, pressing the wrapped magnesium into blocks, pressing the blocks into zinc liquid, keeping the blocks at 530 ℃ for 2 hours, and stirring the blocks with a quartz rod every 15min in the process until the blocks are fully melted to obtain the zinc-aluminum-magnesium plating solution.

And heating the zinc to 530 ℃ for complete melting, and stirring the zinc by using a quartz rod every 10min in the process until the zinc is fully melted to obtain the zinc plating solution.

Step 2: carrying out oil removal treatment, acid cleaning treatment and flux plating assistance on the steel structure to obtain a flux plating assistance steel structure;

keeping the steel structure in NaOH alkali liquor with the concentration of 15 wt% for 5min for alkali washing and oil removal; then taking out and washing with clear water; then, using 20 wt% hydrochloric acid solution to perform acid pickling for 20min to remove rust; then cleaning with clear water; the steel structure is treated with ZnCl with the concentration of 250g/L₂NH concentration of 200g/L₄Carrying out solvent plating assisting treatment in a Cl aqueous solution plating assisting agent, wherein the plating assisting temperature is 85 ℃, and the plating assisting time is 2 min; the steel structure was then oven dried at 140 ℃ for 5 min.

And step 3: placing the steel structure dried in the step 2 into the zinc plating solution prepared in the step 1, wherein the hot dipping temperature is 455 ℃, and the soaking time is 1.5 minutes, so as to obtain a steel structure hot-dipped with a zinc coating;

and 4, step 4: and (3) placing the steel structure subjected to hot dip galvanizing in the step (3) into the zinc-aluminum-magnesium alloy plating solution prepared in the step (1), wherein the hot dip galvanizing temperature is 420 ℃, the soaking time is 2 minutes, so that the steel structure subjected to hot dip galvanizing with a zinc-aluminum-magnesium alloy coating is obtained, and the steel structure subjected to hot dip galvanizing with the zinc-aluminum-magnesium alloy coating is subjected to air cooling treatment for 5 minutes.

Example 2

The hot-dip galvanized aluminum-magnesium alloy coating comprises the following chemical components in percentage by mass: al: 4.5%, Mg: 1.5 percent, and the balance of Zn and inevitable impurities.

The preparation method of the hot dip galvanized aluminum magnesium alloy coating, wherein the thickness of the steel structural member is 4mm, comprises the following steps:

step 1 and step 2 in embodiment 2 are the same as those provided in embodiment 1, and are not described herein again.

Wherein the differences are:

and step 3: and (3) placing the steel structure dried in the step (2) into the galvanizing solution prepared in the step (1), wherein the hot dipping temperature is 465 ℃, and the soaking time is 2 minutes. Carrying out water cooling treatment on the galvanized steel structural member for 30s to obtain a hot-dip galvanized steel structure;

and 4, step 4: and (3) placing the steel structure subjected to water cooling treatment in the step (3) into the zinc-aluminum-magnesium alloy plating solution prepared in the step (1), carrying out hot dipping at the temperature of 430 ℃ for 2 minutes to obtain a steel structure hot-dipped with a zinc-aluminum-magnesium alloy coating, and carrying out air cooling treatment on the steel structure hot-dipped with the zinc-aluminum-magnesium alloy coating for 20 minutes.

Example 3

The hot-dip galvanized aluminum-magnesium alloy coating comprises the following chemical components in percentage by mass: al: 8%, Mg: 2.5 percent, and the balance of Zn and inevitable impurities.

The preparation method of the hot dip galvanized aluminum magnesium alloy coating, wherein the thickness of the steel structural member is 1.5mm, comprises the following steps:

step 1 and step 2 in embodiment 3 are the same as those provided in embodiment 1, and are not described herein again.

Wherein the differences are:

and step 3: placing the steel structure dried in the step 2 into the zinc plating solution prepared in the step 1, wherein the hot dipping temperature is 455 ℃, and the soaking time is 1.5 minutes, so as to obtain a steel structure hot-dipped with a zinc coating;

and 4, step 4: and (3) placing the steel structure subjected to hot dip galvanizing in the step (3) into the zinc-aluminum-magnesium alloy plating solution prepared in the step (1), wherein the hot dip galvanizing temperature is 430 ℃, the soaking time is 2 minutes, so that the steel structure subjected to hot dip galvanizing with a zinc-aluminum-magnesium alloy coating is obtained, and the steel structure subjected to hot dip galvanizing with the zinc-aluminum-magnesium alloy coating is subjected to air cooling treatment for 5 minutes.

Example 4

The zinc-aluminum-magnesium alloy coating comprises the following chemical components in percentage by mass: al: 13%, Mg: 3 percent, and the balance of Zn and inevitable impurities.

The preparation method of the zinc-aluminum-magnesium alloy coating, wherein the thickness of the steel structural member is 1.5mm, comprises the following steps:

step 1 and step 2 in embodiment 4 are the same as those provided in embodiment 1, and are not described herein again.

Wherein the differences are:

and step 3: step 2, drying the pretreated steel structure, and putting the steel structure into the galvanizing solution prepared in the step 1, wherein the hot dipping temperature is 455 ℃, and the dipping time is 1.5 minutes, so as to obtain a hot-dipped galvanized steel structure;

and 4, step 4: and (3) placing the steel structure subjected to hot dip galvanizing in the step (3) into the zinc-aluminum-magnesium alloy plating solution prepared in the step (1), wherein the hot dip galvanizing temperature is 440 ℃, the soaking time is 2 minutes, so that the steel structure subjected to hot dip galvanizing with a zinc-aluminum-magnesium alloy coating is obtained, and the steel structure subjected to hot dip galvanizing with the zinc-aluminum-magnesium alloy coating is subjected to air cooling treatment for 5 minutes.

And (3) performance testing:

the hot dip galvanized aluminum magnesium alloy coating prepared in the embodiment of the invention is subjected to a neutral salt spray test according to the national standard (GB/T10125-1997). FIG. 3 shows a diagram of a neutral salt spray test sample of a conventional pure zinc plating layer. Wherein, 3(a) is a sample graph after 0h neutral salt spray test, and 3(b) is a sample graph after 500h neutral salt spray test, and the sample has rusty spot in 500 h. And 3(c) is a sample graph after a 1000-hour neutral salt spray test, wherein the sample is over-corroded within 1000 hours. FIG. 4 shows a neutral salt spray test sample of the hot dip galvanized aluminum magnesium alloy coating according to the present invention. Wherein, 4(a) is a sample diagram after 0h neutral salt spray test, 4(b) is a sample diagram after 500h neutral salt spray test, 4(c) is a sample diagram after 1000h neutral salt spray test, 4(d) is a sample diagram after 2000h neutral salt spray test, and 4(e) is a sample diagram after 3000h neutral salt spray test. The sample still showed no rust spots at 3000 h.

The results show that: the rust points of the neutral salt spray test sample of the hot-dip galvanized aluminum magnesium alloy coating still do not appear within 3000 hours, while the rust points of the traditional pure zinc coating already appear within 500 hours, so that the corrosion resistance of the hot-dip galvanized aluminum magnesium alloy coating is improved by more than 5 times compared with that of the traditional pure zinc coating.

The above description is only for the preferred embodiment of the present invention, but the scope of the present invention is not limited thereto, and any changes or substitutions that can be easily conceived by those skilled in the art within the technical scope of the present invention are included in the scope of the present invention.