A method for inhibiting the growth of a reaction layer in a zam alloy coating

Abstract

The application discloses a method for inhibiting the growth of a reaction layer in a ZAM alloy coating, which comprises the following steps: firstly, heating the ZAM alloy to 720 DEG C, adding an Al-8B intermediate alloy prepared according to a proportion after the alloy liquid is completely melted, adding Mg blocks and Zn blocks needed to be supplemented after being cooled to 660 DEG C, and finally pouring the alloy after being kept at 460 DEG C for 30 min. Then, the alloy blocks are remelted at 460 DEG C and kept for 10 min; the Q235 steel plate after the previous treatment is immersed in the alloy liquid for 3 min, and then naturally cooled after being taken out. The method can obviously inhibit the growth of the reaction layer in the ZAM alloy coating, and the corrosion resistance of the Zn-6%Al-3%Mg-0.12%B alloy coating obtained by the method is obviously superior to that of the Zn-6%Al-3%Mg alloy.

Description

Technical Field

[0001] This invention belongs to the field of hot-dip galvanized aluminum-magnesium alloys, and specifically relates to a method for inhibiting the growth of a reactive layer in ZAM alloy coatings. Background Technology

[0002] Hot-dip galvanizing is currently the most widely used method for preventing steel corrosion. Statistics show that approximately 20 million tons of steel worldwide are galvanized annually for corrosion prevention. Due to its low cost and excellent performance, hot-dip galvanizing is applied in various fields such as automotive, aerospace, communications, and construction.

[0003] Hot-dip galvanizing involves immersing a steel sheet in molten zinc for a period of time. After removal and natural cooling, a silvery-white protective layer of pure zinc appears on the surface of the steel sheet. The specific advantages of this process are as follows:

[0004] Economically, compared with other surface treatment methods, hot-dip galvanizing is inexpensive, has fewer operating steps, and requires less equipment.

[0005] It has high reliability, strong bonding strength between the coating and the substrate, and good corrosion resistance.

[0006] In terms of appearance, the coating obtained by hot-dip galvanizing has a good surface condition, with a bright and smooth surface, no pores, and the finished product is quite beautiful overall.

[0007] To further improve the corrosion resistance and processing performance of coated steel sheets, alloying methods are often used, adding alloying elements to the zinc bath. Examples include Al, Mg, Si, RE, Sb, and Sn. Adding an appropriate amount of Sn to the zinc bath can improve the brightness of the coating surface after hot-dip galvanizing. However, excessive Sn content can promote the formation of Zn-Sn binary eutectic, causing intergranular corrosion and severely affecting the corrosion resistance of the coating. Adding Sb to the zinc bath can increase the fluidity of the coating, reduce zinc consumption, and lower production costs; however, the addition of Sb can lead to an excessively thick compound layer in the alloy coating, increasing the brittleness and decreasing the plasticity of the sample. Therefore, the Sb content needs to be strictly controlled to obtain a coating with good processing performance.

[0008] In 1990, Nisshin Steel Corporation of Japan developed a high corrosion-resistant alloy coating called ZAM. Its alloy composition is Zn-6%Al-3%Mg (mass fraction), and its corrosion resistance is several times or even tens of times that of traditional hot-dip galvanized pure zinc coatings. At the same time, its mechanical properties are also excellent. However, during the hot-dip galvanizing process, the Al in the ZAM alloy coating reacts violently with the Fe element in the substrate, forming an excessively thick Fe-Al reaction layer. This severely affects the formability of hot-dip galvanized aluminum-magnesium alloy steel sheets and does not meet the market demand for lightweight products. Summary of the Invention

[0009] The purpose of this section is to outline some aspects of embodiments of the present invention and to briefly describe some preferred embodiments. Simplifications or omissions may be made in this section, as well as in the abstract and title of this application, to avoid obscuring the purpose of these documents; however, such simplifications or omissions should not be construed as limiting the scope of the invention.

[0010] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0011] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for suppressing the growth of a reactive layer in a ZAM alloy coating.

[0012] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for suppressing the growth of a reactive layer in a ZAM alloy coating, comprising,

[0013] Weigh the Zn-6%Al-3%Mg alloy, Zn ingot, Mg ingot and Al-8B master alloy by mass percentage, and divide them by mass percentage as follows: 6.0wt.%Al, 3wt.%Mg, 0.03%~0.15wt.%B, with the balance being Zn;

[0014] Place the graphite crucible into the medium-frequency induction furnace, and then add the weighed Zn-6%Al-3%Mg alloy block;

[0015] The furnace is heated and stirred, and then the Al-8B master alloy is pressed to the bottom of the alloy liquid to melt.

[0016] Cool down, then add the necessary Mg and Zn blocks;

[0017] After it has completely melted, stir it, scrape off the slag, and add a coating agent to the surface of the alloy liquid;

[0018] The furnace temperature is lowered and held at that temperature, then poured into a metal mold to obtain an alloy plate;

[0019] The alloy plate is remelted and kept at a certain temperature. The steel plate is then immersed in the alloy liquid for plating, removed, and allowed to cool naturally in the air to obtain the alloy coating.

[0020] In a preferred embodiment of the method described in this invention, the optimal content of element B is 0.06~0.12 wt.%.

[0021] In a preferred embodiment of the method described in this invention, the optimal content of element B is 0.12 wt.%.

[0022] As a preferred embodiment of the method described in this invention, the furnace heating and stirring process involves heating to 720°C.

[0023] In a preferred embodiment of the method described in this invention, the cooling process involves adding Mg and Zn blocks as needed and cooling the temperature to 660°C.

[0024] In a preferred embodiment of the method described in this invention, the furnace temperature is lowered and then held at 460°C for 30 minutes.

[0025] In a preferred embodiment of the method described in this invention, the alloy plate has a size of 20×10×1cm.

[0026] In a preferred embodiment of the method described in this invention, the immersion plating time is 3-5 minutes.

[0027] In a preferred embodiment of the method described in this invention, the covering agent is composed of KCl, NaCl and Na3AlF6 in a mass ratio of KCl:NaCl:Na3AlF6 = 4:5:1.

[0028] In a preferred embodiment of the method described in this invention, the pretreatment process of the pretreated steel plate includes:

[0029] The steel plate was placed in a 15% NaOH aqueous solution and washed at 60°C for 3 minutes. After washing, it was rinsed with water and dried.

[0030] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0031] Finally, immerse it in the flux at 80°C for 10 minutes.

[0032] After removing it, place it in a drying oven for later use;

[0033] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0034] Beneficial effects of this invention:

[0035] The zinc-aluminum-magnesium alloy coating prepared by the method of the present invention has a significantly reduced thickness of the reaction layer, thus solving the problem of poor formability caused by excessive alloy layer thickness; at the same time, the corrosion resistance of the coating is improved. Attached Figure Description

[0036] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort. Wherein:

[0037] Figure 1 These are micrographs of the hot-dip Zn-6%Al-3%Mg alloy coating prepared according to the present invention.

[0038] Figure 2 These are micrographs of the hot-dip Zn-6%Al-3%Mg-0.03%B alloy coating prepared according to the present invention;

[0039] Figure 3 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.06%B alloy coating prepared according to the present invention;

[0040] Figure 4 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.09%B alloy coating prepared according to the present invention;

[0041] Figure 5 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.12%B alloy coating prepared according to the present invention;

[0042] Figure 6 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.15%B alloy coating prepared according to the present invention.

[0043] Figure 7 This is a comparison image showing the salt spray corrosion resistance of the alloy coating obtained by this invention. Detailed Implementation

[0044] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the specific embodiments of the present invention will be described in detail below with reference to the examples in the specification.

[0045] Many specific details are set forth in the following description in order to provide a full understanding of the invention. However, the invention may also be practiced in other ways different from those described herein, and those skilled in the art can make similar extensions without departing from the spirit of the invention. Therefore, the invention is not limited to the specific embodiments disclosed below.

[0046] Secondly, the term "one embodiment" or "embodiment" as used herein refers to a specific feature, structure, or characteristic that may be included in at least one implementation of the present invention. The phrase "in one embodiment" appearing in different places in this specification does not necessarily refer to the same embodiment, nor is it a single or selective embodiment that is mutually exclusive with other embodiments. Example 1

[0047] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-8B alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, B 0.03%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.03%B.

[0048] (2) Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block;

[0049] (3) Heat the furnace to 720℃, stir, and then press the Al-8B master alloy to the bottom of the molten alloy to melt. Cool down to 660℃ and add the required Mg and Zn blocks;

[0050] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and keep it for 30 minutes, then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0051] (5) Remelt the alloy plate at 460℃, hold for 10 minutes, then immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating, remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process of the pretreated steel plate includes...

[0052] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0053] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0054] Finally, immerse it in the flux at 80°C for 10 minutes.

[0055] After removing it, place it in a drying oven for later use;

[0056] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0057] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.03%B alloy coating obtained through the above steps are shown below. Figure 2 As shown, the thickness of the Fe-Al reaction layer is slightly smaller, but overall the thickness is still relatively large. Example 2

[0058] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-8B alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, B 0.06%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.06%B.

[0059] (2) Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block;

[0060] (3) Heat the furnace to 720℃, stir, and then press the Al-8B master alloy to the bottom of the molten alloy to melt. Cool down to 660℃ and add the required Mg and Zn blocks;

[0061] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and keep it for 30 minutes, then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0062] (5) Remelt the alloy plate at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating. Remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process for the pretreated steel plate includes...

[0063] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0064] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0065] Finally, immerse it in the flux at 80°C for 10 minutes;

[0066] After removing it, place it in a drying oven for later use;

[0067] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0068] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.06%B alloy coating obtained through the above steps are shown below. Figure 3 As shown, the thickness of the Fe-Al reaction layer is significantly reduced. Example 3

[0069] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-8B alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, B 0.09%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.09%B.

[0070] (2) Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block;

[0071] (3) Heat the furnace to 720℃, stir, and then press the Al-8B master alloy to the bottom of the molten alloy to melt. Cool down to 660℃ and add the necessary Mg and Zn blocks;

[0072] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and keep it for 30 minutes, then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0073] (5) Remelt the alloy plate at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating. Remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process for the pretreated steel plate includes...

[0074] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0075] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0076] Finally, immerse it in the flux at 80°C for 10 minutes.

[0077] After removing it, place it in a drying oven for later use;

[0078] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0079] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.06%B alloy coating obtained through the above steps are shown below. Figure 4 As shown, the thickness of the Fe-Al reaction layer continues to decrease. Example 4

[0080] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-8B alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, B 0.12%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.12%B.

[0081] (2) Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block;

[0082] (3) Heat the furnace to 720℃, stir, and then press the Al-8B master alloy to the bottom of the molten alloy to melt. Cool down to 660℃ and add the necessary Mg and Zn blocks;

[0083] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and keep it for 30 minutes, then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0084] (5) Remelt the alloy plate at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating. Remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process for the pretreated steel plate includes...

[0085] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0086] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0087] Finally, immerse it in the flux at 80°C for 10 minutes.

[0088] After removing it, place it in a drying oven for later use;

[0089] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0090] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.06%B alloy coating obtained through the above steps are shown below. Figure 5 As shown, it can be seen that the thickness of the Fe-Al reaction layer is reduced to the minimum. Example 5

[0091] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-8B alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, B 0.15%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.15%B.

[0092] (2) Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block;

[0093] (3) Heat the furnace to 720℃, stir, and then press the Al-8B master alloy to the bottom of the molten alloy to melt. Cool down to 660℃ and add the necessary Mg and Zn blocks;

[0094] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and keep it for 30 minutes, then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0095] (5) Remelt the alloy plate at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating. Remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process for the pretreated steel plate includes...

[0096] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0097] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0098] Finally, immerse it in the flux at 80°C for 10 minutes.

[0099] After removing it, place it in a drying oven for later use;

[0100] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0101] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.06%B alloy coating obtained through the above steps are shown below. Figure 6 As shown, it can be seen that the thickness of the Fe-Al reaction layer has stopped decreasing, and the thickness dimension is similar to that of Example 4. Comparative Example 1

[0102] (1) Weigh the Zn-6%Al-3%Mg alloy by mass percentage;

[0103] (2) Place the graphite crucible into the medium frequency induction furnace and put in the Zn-6%Al-3%Mg alloy block;

[0104] (3) Heat the furnace to 460°C, stir, scrape off the slag, add a layer of covering agent (composed of KCl, NaCl and Na3AlF6 in mass ratio of KCl:NaCl:Na3AlF6=4:5:1) on the surface of the alloy liquid, keep it at the temperature for 30 minutes, and then cast it into a metal mold to obtain an alloy plate of 20×10×1cm.

[0105] (4) Remelt the alloy plate at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for immersion plating. Remove it after 3 minutes and allow it to cool naturally in air. The pretreatment process for the pretreated steel plate includes...

[0106] The Q235 steel plate was placed in a 15% NaOH aqueous solution and washed at 60℃ for 3 minutes. After that, it was rinsed with water and dried.

[0107] Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry.

[0108] Finally, immerse it in the flux at 80°C for 10 minutes.

[0109] After removing it, place it in a drying oven for later use;

[0110] The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

[0111] The scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg alloy coating obtained through the above steps are shown below. Figure 1As shown, it can be seen that the thickness of the Fe-Al reaction layer in the tissue is too large.

[0112] The hot-dip galvanized steel sheet was wiped with anhydrous ethanol and then quickly dried with a hair dryer. Next, the dimensions of the steel sheet were measured with vernier calipers, and its surface area S was calculated. The samples were then placed in a salt spray test chamber with a 2cm interval between samples, the angle between the test surface and the vertical direction being 20°, the temperature at 35±2℃, and the pH value at 6.5~7.2, with continuous spraying. The spray solution was a 5% NaCl aqueous solution. The salt spray corrosion time was 30 days, and samples were taken out and weighed every 6 days.

[0113] During weighing, deionized water was used to remove residual NaCl salt from the surface, and the surface was dried with a hair dryer before weighing. The resulting change curve is shown below. Figure 7 .

[0114] This invention uses the weight gain method to measure the corrosion rate of the sample, thereby evaluating the effect of element B on the corrosion resistance of the coating. The calculation formula is as follows:

[0115] V = (W2 - W1)·S -1 ·T -1

[0116] In the formula, V represents the corrosion rate of the galvanized sheet, expressed in g·m³. -2 ·h -1 ;

[0117] W1: Weight of the sample before corrosion, in g;

[0118] W2: Weight of the sample after corrosion, in g;

[0119] S: Exposed area of ​​the sample, m 2 ;

[0120] T: Corrosion cycle, h.

[0121] The mass of the coating before and after corrosion was measured and then substituted into the calculation formula to obtain the corrosion rate of coatings with different B contents, as shown in Table 1 below.

[0122] Table 1

[0123] Coating composition <![CDATA[Corrosion rate (g·m -2 ·h -1 )]]> Zn-6Al-3Mg 0.9306 Zn-6Al-3Mg-0.03B 0.8333 Zn-6Al-3Mg-0.06B 0.7611 Zn-6Al-3Mg-0.09B 0.6111 Zn-6Al-3Mg-0.12B 0.5694 Zn-6Al-3Mg-0.15B 0.5972

[0124] The results showed that the corrosion rate of the Zn-6%Al-3%Mg alloy coating decreased continuously with the addition of boron (B); the corrosion rate was lowest at a B content of 0.12%, reaching 0.5694 g·m⁻¹. -2 ·h -1 Therefore, the Zn-6%Al-3%Mg alloy coating containing 0.12%B exhibits the best corrosion resistance.

[0125] This invention provides a method for inhibiting the growth of a reactive layer in ZAM alloy coatings by adding trace amounts of boron. First, the ZAM alloy is heated to 720°C. After the alloy melt is completely melted, a pre-mixed Al-8B master alloy is added. The temperature is then lowered to 660°C, and Mg and Zn blocks are added as needed. Finally, the mixture is held at 460°C for 30 minutes before casting. The alloy blocks are then remelted at 460°C and held for 10 minutes. A pre-treated Q235 steel plate is immersed in the alloy melt for 3 minutes, then removed and allowed to cool naturally. This invention significantly inhibits the growth of the reactive layer in ZAM alloy coatings. The corrosion resistance of the Zn-6%Al-3%Mg-0.12%B alloy coating obtained using this invention is significantly better than that of Zn-6%Al-3%Mg.

[0126] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention and are not intended to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the present invention.

Claims

1. A method for suppressing the growth of a reactive layer in a ZAM alloy coating, characterized in that: include, Weigh the Zn-6%Al-3%Mg alloy, Zn ingot, Mg ingot, and Al-8B master alloy by mass percentage, wherein the mass percentages are: 6.0 wt.%Al, 3 wt.%Mg, 0.09~0.15 wt.%B, and the balance is Zn; Place the graphite crucible into the medium-frequency induction furnace, and then add the weighed Zn-6%Al-3%Mg alloy block; The furnace is heated and stirred, and then the Al-8B master alloy is pressed to the bottom of the alloy liquid to melt. Cool down, then add the necessary Mg and Zn ingots; After it has completely melted, stir, scrape off the slag, and add a layer of covering agent to the surface of the alloy liquid. The covering agent is composed of KCl, NaCl and Na3AlF6 in a mass ratio of KCl:NaCl:Na3AlF6=4:5:

1. The furnace temperature is lowered and held at that temperature, then poured into a metal mold to obtain an alloy plate; The alloy plate is remelted and kept at a certain temperature. The pretreated steel plate is then immersed in the alloy liquid for plating. After being removed, it is allowed to cool naturally in the air to obtain the alloy coating.

2. The method as described in claim 1, characterized in that: The mass percentage of B is 0.12 wt.%.

3. The method as described in claim 1, characterized in that: The process involves heating and stirring the furnace, with the temperature reaching 720°C.

4. The method as described in claim 3, characterized in that: The cooling process involves adding the necessary Mg and Zn ingots and cooling the temperature to 660°C.

5. The method as described in claim 4, characterized in that: The process involves lowering and maintaining the furnace temperature, wherein the furnace temperature is lowered to 460°C and the holding time is 30 minutes.

6. The method as described in claim 5, characterized in that: The alloy plate has dimensions of 20×10×1cm.

7. The method as described in claim 6, characterized in that: The immersion plating process involves a plating time of 3 to 5 minutes.

8. The method as described in claim 1, characterized in that: The pretreated steel plate has a pretreatment process including, The steel plate was placed in a 15% NaOH aqueous solution and washed at 60°C for 3 minutes. After washing, it was rinsed with water and dried. Then place it in a 10% hydrochloric acid solution and acid wash for 2 minutes at room temperature. After removing it, rinse it with water and blow it dry. Finally, immerse it in the flux at 80°C for 10 minutes. After removing it, place it in a drying oven for later use; The flux is a mixed solution of NH4Cl, ZnCl2, SnCl2, KCl, K2ZrF6 and water, with concentrations of 170 g / L, 230 g / L, 50 g / L, 100 g / L and 20 g / L, respectively.

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