A method for improving the corrosion resistance of ZAM alloy coatings by refining the eutectic structure of the coating.

Abstract

This invention discloses a method for improving the corrosion resistance of ZAM alloy coatings by refining the eutectic structure. First, the ZAM alloy is heated to 660℃. After the alloy melt is completely melted, a pre-mixed Al-10Ca master alloy, along with additional zinc and magnesium blocks, is added. After holding at this temperature for 30 minutes, the mixture is cast to obtain the master alloy required for hot-dip galvanizing. Then, the alloy blocks are remelted at 460℃ and held for 10 minutes. A pre-treated Q235 steel plate is immersed in the alloy melt for 3 minutes, then removed and air-cooled. This invention can significantly refine the Zn / Al / MgZn2 ternary eutectic structure in the zinc-aluminum-magnesium alloy coating, thereby significantly improving the corrosion resistance of the coating.

Description

Technical Field

[0001] This invention belongs to the field of hot-dip galvanized aluminum-magnesium alloys, and specifically relates to a method for improving the corrosion resistance of coatings based on refining the eutectic structure of ZAM alloy coatings. Background Technology

[0002] Steel, as the most widely used material in modern industry, is highly susceptible to corrosion in many environments (seawater, soil, atmosphere, etc.). Statistics show that approximately one-fifth of the world's annual steel production is scrapped due to corrosion each year. Steel corrosion not only causes serious economic losses but also threatens human lives and causes environmental pollution and damage. Therefore, research on steel corrosion and protection is urgently needed.

[0003] Currently, hot-dip galvanizing is considered one of the most direct and effective methods for protecting steel, and it is widely used in the automotive, aerospace, communications, and construction industries. With economic and social development and increasingly higher requirements for coating quality, traditional pure zinc coatings no longer meet production and usage standards. Therefore, the development of new, high-quality coatings has become a hot research topic.

[0004] To improve the coating thickness, surface quality, mechanical properties, and corrosion resistance of hot-dip galvanized steel sheets, microalloying is often employed, which involves adding specific alloying elements to the zinc bath. The addition of these alloying elements affects the melting point, viscosity, and surface tension of the zinc bath, thereby altering the growth behavior of intermetallic compounds in the coating and ultimately changing its properties. For example, adding Ti to a hot-dip Zn-Al alloy not only improves the surface quality of the coating but also refines its microstructure. The addition of Ti allows for the formation of a dense oxide film on the alloy coating surface, thus enhancing its corrosion resistance. Conversely, adding a small amount of Mg to the zinc bath can improve its fluidity and inhibit excessive coating growth.

[0005] Tong Chen et al., in their study on the effect of Mg content on Zn-6%Al coatings, found that when the Mg content was 3%, the interlamellar spacing of the ternary eutectic structure in the alloy coating decreased, the structure became more uniform and dense, and the coating exhibited the best corrosion resistance. Therefore, further refining the ternary eutectic structure in Zn-6%Al-3%Mg alloy coatings through microalloying to improve the corrosion resistance of the coating has become a current research focus. Summary of the Invention

[0006] 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.

[0007] In view of the problems existing in the above and / or prior art, the present invention is proposed.

[0008] Therefore, the purpose of this invention is to overcome the shortcomings of the prior art and provide a method for improving the corrosion resistance of ZAM alloy coatings based on refining the eutectic structure of the coating.

[0009] To solve the above-mentioned technical problems, the present invention provides the following technical solution: a method for improving the corrosion resistance of ZAM alloy coatings based on refining the eutectic structure of the coating, comprising,

[0010] Weigh the Zn-6%Al-3%Mg alloy, Zn ingot, Mg ingot and Al-10Ca master alloy by mass percentage, wherein the mass percentages are: 6.0wt.%Al, 3wt.%Mg, 0.03%~0.15wt.%Ca, and the balance is Zn;

[0011] Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block.

[0012] As the furnace heats up and is stirred, the Al-10Ca master alloy, Zn block, and Mg block are pressed to the bottom of the alloy liquid to melt.

[0013] After it has completely melted, stir it, scrape off the slag, and add a coating agent to the surface of the alloy liquid;

[0014] The furnace temperature is lowered and kept at a constant temperature, then poured into a metal mold to obtain a master alloy containing calcium.

[0015] After remelting and holding the master alloy at a certain temperature, the pretreated steel plate is immersed in the alloy liquid for plating, and then air-cooled to obtain the alloy coating.

[0016] In a preferred embodiment of the method described in this invention, the optimal content of Ca element is 0.06–0.12 wt.%.

[0017] In a preferred embodiment of the method described in this invention, the optimal content of Ca element is 0.09 wt.%.

[0018] In a preferred embodiment of the method described in this invention, the furnace is heated and stirred to press the Al-10Ca master alloy, Zn block, and Mg block to the bottom of the alloy liquid for melting, wherein the temperature is raised to 660°C.

[0019] In a preferred embodiment of the method described in this invention, the furnace temperature is reduced to 440-460°C and the holding time is 30-45 minutes.

[0020] In a preferred embodiment of the method described in this invention, the furnace temperature is lowered to 460°C and the holding time is 30 minutes.

[0021] In a preferred embodiment of the method described in this invention, the remelting and holding of the master alloy is carried out at a remelting temperature of 440–460°C and a holding time of 10–20 min.

[0022] In a preferred embodiment of the method described in this invention, the remelting temperature is 460°C and the holding time is 10 min.

[0023] In a preferred embodiment of the method described in this invention, the immersion time is 3 to 6 minutes.

[0024] In a preferred embodiment of the method described in this invention, the immersion time is 3 minutes.

[0025] Beneficial effects of this invention:

[0026] This invention provides a method for improving the corrosion resistance of ZAM alloy coatings by refining the eutectic structure. The prepared zinc-aluminum-magnesium alloy coating has a significantly refined eutectic structure, and its corrosion resistance is improved. Attached Figure Description

[0027] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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:

[0028] Figure 1 These are micrographs of the hot-dip Zn-6%Al-3%Mg alloy coating prepared according to the present invention.

[0029] Figure 2 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.03%Ca alloy coating prepared according to the present invention;

[0030] Figure 3 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.06%Ca alloy coating prepared according to the present invention;

[0031] Figure 4 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.09%Ca alloy coating prepared according to the present invention;

[0032] Figure 5This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.12%Ca alloy coating prepared according to the present invention;

[0033] Figure 6 This is a micrograph of the hot-dip Zn-6%Al-3%Mg-0.15%Ca alloy coating prepared according to the present invention.

[0034] Figure 7 This is a comparison chart of the corrosion resistance performance of the alloy coatings prepared in this invention, as evaluated by the salt spray test method. Detailed Implementation

[0035] 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.

[0036] 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.

[0037] 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.

[0038] Example 1

[0039] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-10Ca alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, Ca 0.03%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.03%Ca.

[0040] (2) Place the graphite crucible into the medium frequency induction furnace and put in the weighed Zn-6%Al-3%Mg alloy block.

[0041] (3) Heat the furnace to 660°C, stir, and press the Al-10Ca intermediate alloy, the Zn block and Mg block that need to be added to the bottom of the alloy liquid to melt.

[0042] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (a mixture of KCl, NaCl and Na3AlF6 in a mass ratio of 4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and hold for 30 minutes, and pour it into a metal mold to obtain a master alloy containing calcium.

[0043] (5) Remelt the master alloy at 460℃, hold for 10 minutes, then immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, remove and air cool. The pretreatment process for the Q235 steel plate is as follows:

[0044] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0045] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.03%Ca alloy coating obtained through the above steps are shown below. Figure 2 As shown, it can be seen that the eutectic structure of the coating is refined, and the thickness of the alloy layer is also slightly reduced.

[0046] Example 2

[0047] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-10Ca alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, Ca 0.06%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.06%Ca.

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

[0049] (3) Heat the furnace to 660°C, stir, and press the Al-10Ca intermediate alloy, the Zn block and Mg block that need to be added to the bottom of the alloy liquid to melt.

[0050] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (a mixture of KCl, NaCl and Na3AlF6 in a mass ratio of 4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and hold for 30 minutes, and pour it into a metal mold to obtain a master alloy containing calcium.

[0051] (5) Remelt the master alloy at 460℃, hold for 10 minutes, then immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, remove and air cool. The pretreatment process for the Q235 steel plate is as follows:

[0052] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0053] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.06%Ca alloy coating obtained through the above steps are shown below. Figure 3 As shown, it can be seen that the thickness of the alloy layer continues to decrease, while the eutectic structure in the coating is completely refined, and the coating structure becomes more compact.

[0054] Example 3

[0055] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-10Ca alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, Ca 0.09%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.09%Ca.

[0056] (2) Place the graphite crucible into the medium frequency induction furnace and put in the weighed Zn-6%Al-3%Mg alloy block.

[0057] (3) Heat the furnace to 660°C, stir, and press the Al-10Ca intermediate alloy, the Zn block and Mg block that need to be added to the bottom of the alloy liquid to melt.

[0058] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (a mixture of KCl, NaCl and Na3AlF6 in a mass ratio of 4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and hold for 30 minutes, and pour it into a metal mold to obtain a master alloy containing calcium.

[0059] (5) Remelt the master alloy at 460℃, hold for 10 minutes, then immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, remove and air cool. The pretreatment process for the Q235 steel plate is as follows:

[0060] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0061] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.09%Ca alloy coating obtained through the above steps are shown below. Figure 4 As shown, the thickness of the Fe-Al alloy layer is reduced to the minimum, the degree of refinement of the eutectic structure of the coating is similar to that of Example 3, and the coating structure is uniform and dense.

[0062] Example 4

[0063] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-10Ca alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, Ca 0.12%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.12%Ca.

[0064] (2) Place the graphite crucible into the medium frequency induction furnace and put in the weighed Zn-6%Al-3%Mg alloy block.

[0065] (3) Heat the furnace to 660°C, stir, and press the Al-10Ca intermediate alloy, the Zn block and Mg block that need to be added to the bottom of the alloy liquid to melt.

[0066] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (a mixture of KCl, NaCl and Na3AlF6 in a mass ratio of 4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and hold for 30 minutes, and pour it into a metal mold to obtain a master alloy containing calcium.

[0067] (5) Remelt the master alloy at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, then remove and air cool. The pretreatment process for the Q235 steel plate is as follows:

[0068] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0069] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.12%Ca 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 alloy layer has increased slightly, and the size of the eutectic structure in the coating structure has also gradually increased.

[0070] Example 5

[0071] (1) Weigh out the Zn-6Al-3Mg alloy block, Zn block, Mg block and Al-10Ca alloy block according to the ratio. The composition of the alloy by mass percentage is: Al 6.0%, Mg 3%, Ca 0.15%, balance Zn. The corresponding alloy is Zn-6%Al-3%Mg-0.15%Ca.

[0072] (2) Place the graphite crucible into the medium frequency induction furnace and put in the weighed Zn-6%Al-3%Mg alloy block;

[0073] (3) Heat the furnace to 660°C, stir, and press the Al-10Ca intermediate alloy, the Zn block and Mg block that need to be added to the bottom of the alloy liquid to melt.

[0074] (4) After it is completely melted, stir, scrape off the slag, add a layer of covering agent (a mixture of KCl, NaCl and Na3AlF6 in a mass ratio of 4:5:1) to the surface of the alloy liquid, lower the furnace temperature to 460℃ and hold for 30 minutes, and pour it into a metal mold to obtain a master alloy containing calcium.

[0075] (5) Remelt the master alloy at 460℃. After holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, then remove and air cool. The pretreatment process for the Q235 steel plate is as follows:

[0076] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0077] Scanning electron microscope (SEM) images of the hot-dip Zn-6%Al-3%Mg-0.15%Ca 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 alloy layer stops changing, and the thickness dimension is similar to that of Example 4.

[0078] The size of the eutectic structure in the coating is increased compared to Example 4.

[0079] Comparative Example 1

[0080] (1) Weigh the Zn-6%Al-3%Mg alloy by mass percentage.

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

[0082] (3) The furnace is heated to 460°C, stirred, and slag is scraped off. A layer of covering agent (a mixture of KCl, NaCl, and Na3AlF6 in a mass ratio of 4:5:1) is added to the surface of the alloy liquid. After holding the temperature for 30 minutes, it is poured into a metal mold to obtain the ZAM master alloy.

[0083] (4) Remelt the master alloy at 460℃; after holding at this temperature for 10 minutes, immerse the pretreated Q235 steel plate in the alloy liquid for 3 minutes, remove it, and air cool it. The pretreatment process for the Q235 steel plate is as follows:

[0084] The Q235 steel plate was immersed in a 15% NaOH aqueous solution and alkaline washed at 60℃ for 5 minutes. After removal, it was rinsed with water and dried. Then, it was immersed in a 10% hydrochloric acid solution and acid-washed at room temperature for 5 minutes. After removal, it was rinsed with water and dried. Finally, it was immersed in a flux (a mixed aqueous solution of NH4Cl + ZnCl2 + SnCl2 + KCl with concentrations of 170 g / L, 230 g / L, 50 g / L, and 100 g / L, respectively) at 80℃ for 10 minutes. After removal, it was placed in a drying oven for later use.

[0085] 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 eutectic structure of the coating is relatively coarse, and the alloy layer is relatively thick.

[0086] The present invention uses a neutral salt spray test to evaluate the corrosion resistance of the coating.

[0087] First, prepare a 5 wt.% NaCl solution and add it to the salt spray chamber;

[0088] Wash the surface of the sample with anhydrous ethanol and dry it with a hair dryer.

[0089] The surface area S is obtained by measuring the dimensions of the sample with vernier calipers.

[0090] Next, the weight of the sample was measured using an electronic balance;

[0091] After all measurements are completed, place the sample into the salt spray chamber. The temperature of the salt spray chamber should be controlled at 35±2℃ and the pH should be 6.5~7.2.

[0092] The sample was placed at an angle of 65±5° to the horizontal direction, and the corrosion time was 30 days.

[0093] Every 6 days, the samples were removed, rinsed with water for 3 minutes, and dried in a 100℃ drying oven for 30 minutes before being weighed. The resulting change curve is shown in the figure. Figure 7 As shown.

[0094] This study uses the weight gain method to measure the corrosion rate of the samples, thereby evaluating the effect of Ca on the corrosion resistance of the coating. The calculation formula is as follows:

[0095] V = (W2 - W1)·S -1 ·T -1

[0096] In the formula, V represents the corrosion rate of the galvanized sheet, expressed in g·m³. -2 ·h -1 ;

[0097] W1: Weight of the sample before corrosion, in g;

[0098] W2: Weight of the sample after corrosion, in g;

[0099] S: Exposed area of ​​the sample, m2;

[0100] T: Corrosion cycle, h.

[0101] The mass of the coating before and after corrosion was measured and substituted into the calculation formula to obtain the corrosion rate of coatings with different Ca contents, as shown in Table 1 below.

[0102] Table 1

[0103]

[0104]

[0105] The results show that with the addition of Ca, the corrosion rate of the Zn-6%Al-3%Mg alloy coating continuously decreases; and the lower the corrosion rate of the coating, the higher its corrosion resistance.

[0106] The corrosion rate was minimized to 0.4444 g·m when the Ca content was 0.09%. -2 ·h -1 Therefore, the alloy coating with Zn-6%Al-3%Mg-0.09%Ca exhibits the best corrosion resistance.

[0107] In summary, this invention provides a method for refining the eutectic structure of ZAM alloy coatings and improving their corrosion resistance by adding trace amounts of calcium. First, the ZAM alloy is heated to 660°C. After the alloy melt is completely melted, a pre-mixed Al-10Ca master alloy, along with additional zinc and magnesium blocks, is added. After holding at this temperature for 30 minutes, the mixture is cast to obtain the master alloy required for hot-dip galvanizing. Then, the alloy blocks are 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 air-cooled. This invention can significantly refine the Zn / Al / MgZn2 ternary eutectic structure in the zinc-aluminum-magnesium alloy coating, thereby significantly improving its corrosion resistance.

[0108] 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 improving the corrosion resistance of ZAM alloy coatings by refining the eutectic structure, characterized in that: include, Weigh the Zn-6%Al-3%Mg alloy, Zn ingot, Mg ingot and Al-10Ca master alloy by mass percentage, wherein the mass percentages are: 6.0%Al, 3%Mg, 0.09%Ca, and the balance is Zn; Place the graphite crucible into the medium-frequency induction furnace and add the weighed Zn-6%Al-3%Mg alloy block. As the furnace heats up, the mixture is stirred and pressed to the bottom of the molten alloy to melt the Al-10Ca master alloy, Zn block, and Mg block, while the temperature is raised to 660℃. After it has completely melted, stir it, scrape off the slag, and add a coating agent to the surface of the alloy liquid; The furnace temperature is lowered and held at that temperature before being poured into a metal mold to obtain a calcium-containing master alloy. The furnace temperature is lowered to 440-460℃ and held for 30-45 minutes. After remelting and holding the master alloy at a certain temperature, the pretreated steel plate is immersed in the alloy liquid for plating, and then air-cooled to obtain an alloy coating. The remelting temperature is 440~460℃, the holding time is 10~20min, and the plating time is 3~6min.

2. The method as described in claim 1, characterized in that: The furnace temperature is lowered to 460℃ and held for 30 minutes.

3. The method as described in claim 1, characterized in that: The remelting temperature is 460℃ and the holding time is 10 minutes.

4. The method as described in claim 1, characterized in that: The immersion time is 3 minutes.

Images