Method for eliminating zinc undulation defects of magnesium-based zinc-aluminum-magnesium coating in hot dip

Abstract

The application provides a method for eliminating zinc undulation defects of magnesium system zinc-aluminum-magnesium coating in hot base aluminum-magnesium, and relates to the technical field of preparation of zinc-aluminum-magnesium coating on the surface of rolled steel. The method comprises the following steps: twice pickling of raw material strip steel to obtain pickled strip steel; lowering of the heating temperature of the direct flame section when the pickled strip steel is heated to obtain heated strip steel; control of the power of the cooling fan to improve the surface temperature of the heated strip steel when the heated strip steel enters a zinc pot to obtain temperature-controlled heated strip steel; and hot dip plating of the temperature-controlled heated strip steel in the zinc pot to obtain a magnesium system zinc-aluminum-magnesium coating in the hot base aluminum-magnesium without zinc undulation on the surface. The method can not only overcome the technical difficulty of the zinc undulation on the surface of the coating, but also save energy and reduce consumption, shorten the heating time, reduce the hindering of the core heat of the strip steel on the solidification process of the plating solution, improve the performance of the coating, and the overall process operation is simple, which is beneficial to large-scale industrial production and popularization and use.

Description

Technical Field

[0001] This invention relates to the technical field of zinc-aluminum-magnesium coating preparation on rolled steel surfaces, and particularly to a method for eliminating zinc undulation defects in zinc-aluminum-magnesium coatings based on aluminum and magnesium in hot-dip galvanic bases. Background Technology

[0002] As market demands for corrosion resistance in zinc-based coatings continue to rise, steel companies are intensifying their efforts to develop zinc-aluminum-magnesium coatings with superior corrosion resistance and cut protection. Among these, hot-dip galvanized zinc-aluminum-magnesium coatings not only boast excellent corrosion resistance but also offer advantages such as shorter processing time, lower energy consumption, and lower cost due to the elimination of the cold rolling process. They are currently widely used in photovoltaics, construction, and other fields.

[0003] However, in actual production, zinc undulation defects frequently appear on the surface of hot-dip aluminum-magnesium zinc-aluminum-magnesium coating products. This not only affects the product's aesthetics but also significantly impacts its corrosion resistance, thus severely hindering its application in high-value-added fields.

[0004] Currently, there are relatively few relevant documents and patents on zinc undulation defects on the surface of zinc-aluminum-magnesium coatings, and related research mainly focuses on pure zinc coating products.

[0005] For example, Chinese patent CN116288098A discloses a coating method for hot-dip galvanized steel sheets. This method eliminates zinc undulation defects on the hot-dip galvanized surface by leveling the pickled sheet and controlling the zinc bath temperature and air knife parameters. It can be seen that this patent only focuses on the zinc undulation problem on the surface of pure zinc coatings. However, zinc-aluminum-magnesium coatings differ from pure zinc coatings. The complex composition system of zinc-aluminum-magnesium coatings can cause metal segregation during the immersion and solidification processes, resulting in a completely different outcome from pure zinc coatings.

[0006] Chinese patent CN110273121A discloses a zinc-aluminum-magnesium coated steel strip and its preparation method. The plating solution contains elements such as Si, Cu, Sn, and Re. Although this improves the density, wear resistance, and high-temperature resistance of the coating, the steel strip needs to be rapidly cooled after hot-dip galvanizing. Therefore, the overall process is costly and energy-intensive, and the fluctuation of zinc content is not effectively resolved.

[0007] Chinese patent CN111235509A discloses a method for eliminating zinc dross defects on the surface of zinc-aluminum-magnesium coated products. It requires the use of a small flow rate to control the humidification of nitrogen and hydrogen mixed gas. The injection angle of the humidification gas in the furnace nose is strictly controlled by optimizing the injection point of the humidification nitrogen and hydrogen mixed gas. A single-sided overflow furnace nose is used in conjunction with a zinc ash pump. Although it can remove the zinc dross defects on the surface, the zinc undulation is not effectively solved.

[0008] Chinese patent CN113481455A discloses a method for producing high-surface-quality zinc-aluminum-magnesium coated steel strips / sheets using an air knife. This method eliminates defects such as zinc flow marks and horseshoe marks by controlling the composition and temperature of the plating solution during the hot-dip galvanizing process and by reducing the distance between the air knife and the strip, the air knife pressure, and the air knife height. However, in the design of the air knife, various airflow unevenness phenomena are unavoidable. Severe airflow unevenness leads to "zinc undulation" defects on the strip surface. Similarly, Chinese patent CN112575273A discloses a method for producing zinc-aluminum-magnesium coated steel sheets with excellent coating plasticity, which also uses an air knife to control the coating thickness, and similarly suffers from "zinc undulation" defects. Summary of the Invention

[0009] The technical problem this invention aims to solve is that current methods for controlling the coating thickness during hot-dip galvanizing of zinc-aluminum-magnesium coated steel strips involve air knives, which result in uneven airflow and "zinc undulation" defects on the strip surface. Alternatively, methods such as adding plating solution components can lead to complex plating solution composition, increased costs, and reduced coating adhesion. Other methods, such as controlling the flow rate of a humidified nitrogen and hydrogen mixture and controlling the angle of the humidified gas injection at the furnace nose, can improve the surface quality of the coating, but these methods are complex, difficult to operate, and the "zinc undulation" defect still exists on the strip surface.

[0010] To solve the above-mentioned technical problems, the present invention provides the following technical solution:

[0011] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0012] S1. Pickling: The raw strip steel is pickled twice to obtain pickled strip steel;

[0013] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section to obtain heated strip.

[0014] S3. Temperature control: Controlling the power of the cooling fan to increase the surface temperature of the S2 heated strip when it enters the zinc pot, thus obtaining temperature-controlled heated strip.

[0015] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip steel is immersed in a zinc pot for hot-dip galvanizing of zinc, aluminum and magnesium coating to obtain a hot-dip zinc-aluminum-magnesium coating with no zinc undulations on the surface.

[0016] Preferably, the raw material strip steel in S1 is pickled twice, and each pickling process involves six pickling tanks.

[0017] Preferably, in S1, the running speed of the strip is controlled at 80-100 m / min and the temperature of the pickling tank is controlled at 80-85℃ during the first pickling process; and the running speed of the strip is controlled at 100-120 m / min and the temperature of the pickling tank is controlled at 85-90℃ during the second pickling process.

[0018] Preferably, in S2, the temperature of the direct flame section is controlled between 620-650°C, and the temperature of the radiant tube is controlled between 630-660°C.

[0019] Preferably, in step S3, the surface temperature of the temperature-controlled heating strip entering the zinc pot is controlled between 430-460°C.

[0020] Preferably, the cooling fan load adjustment range in S3 is 20-99%.

[0021] Preferably, the composition of the zinc-aluminum-magnesium plating solution in the zinc pot in S4 is: Al 5.7±0.5wt.%, Mg 2.3±0.3wt.%, with the remainder being Zn.

[0022] Preferably, in step S4, the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot is 390-440℃, the hot-dip plating time is 1.5-3s, the coating thickness is 15-50μm, and the mass control of the plating layer on at least one surface of the strip is 40-225g / m. 2 .

[0023] Preferably, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth zinc-free surface in S4 is 6.5-6.7 g / cm³. 3 The hardness is 140-190HV. In the neutral salt spray test, the time for the coated steel strip to show 5% red rust is 3000-4000h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0024] Preferably, the composition of the raw material strip steel in S1, by mass percentage, is: C 0.05-0.2%, Mn 0.28-1.5%, P 0.015-0.02%, S 0.001-0.005%, with the balance being Fe and unavoidable impurities.

[0025] The above technical solution has at least the following advantages compared with the existing technology:

[0026] The above-mentioned solution, proposed by the present invention, is a method for eliminating zinc fluctuation defects in hot-dip aluminum-magnesium zinc-aluminum-magnesium coatings. This method can solve the zinc fluctuation defects in hot-dip aluminum-magnesium zinc-aluminum-magnesium coatings in the prior art, while improving coating performance, reducing energy consumption, and having a short process, high efficiency, and being beneficial to industrial production.

[0027] This invention utilizes a two-stage pickling process to maximize the removal of residual iron oxide scale from the raw material surface, thereby preventing the formation of zinc undulation defects caused by residual iron oxide scale. During the first pickling, reducing the strip running speed allows for sufficient reaction between the acid and the iron oxide scale, effectively removing most of it. During the second pickling, since only a small amount of iron oxide scale remains on the strip surface, increasing the strip running speed increases production efficiency, while lowering the pickling tank temperature helps save energy.

[0028] This invention reduces the core heat inside the strip by lowering the temperature of the direct flame section, thereby reducing the temperature difference between the core and surface of the strip and facilitating the solidification of the plating solution. At the same time, it shortens the heating time and improves production efficiency.

[0029] This invention increases the surface temperature of the strip steel when it enters the zinc bath, resulting in raw strip steel with a smaller internal and external temperature difference. The higher surface temperature facilitates the reaction between the plating solution and the strip steel during the immersion plating process, while the smaller internal and external temperature difference of the raw strip steel reduces the resistance of core heat to the plating solution solidification process, thereby suppressing zinc fluctuation defects caused by plating solution reflow.

[0030] The density of the zinc-aluminum-magnesium zinc-aluminum-magnesium coating with a zinc-free surface, as described in this invention, is 6.5-6.7 g / cm³. 3 The hardness is 140-190HV. In the neutral salt spray test, the time for the coated steel strip to show 5% red rust is 3000-4000h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0031] In summary, compared to other traditional methods, the method of the present invention, through two pickling processes, reducing the temperature of the direct flame section, and increasing the surface temperature of the strip steel when it enters the zinc pot, can not only overcome the surface coating problem... Figure 2 The technical challenge of "zinc fluctuations" shown is thus obtained. Figure 3 The method shown eliminates zinc undulation defects in zinc-aluminum-magnesium coatings based on hot-dip aluminum alloys. It also saves energy, reduces heating time, reduces the obstruction of the core heat of the strip to the solidification process of the plating solution, and improves the performance of the coating. The overall process is simple to operate, has low production cost, and high efficiency, which is conducive to large-scale industrial production and promotion. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying 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.

[0033] Figure 1 This is a schematic diagram illustrating the steps of a method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum according to the present invention.

[0034] Figure 2 Image showing the zinc undulation effect on the surface of a 3mm thick hot-dip aluminum-magnesium zinc-aluminum-magnesium coating product provided for existing technology;

[0035] Figure 3 The image shows the surface zinc undulation effect of a 3mm thick hot-base aluminum-magnesium zinc-aluminum-magnesium coating product prepared according to the method of eliminating zinc undulation defects in hot-base aluminum-magnesium zinc-aluminum-magnesium coatings of the present invention. Detailed Implementation

[0036] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. All other embodiments obtained by those skilled in the art based on the described embodiments of the present invention without creative effort are within the scope of protection of the present invention.

[0037] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates, such as... Figure 1 As shown, the method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum is as follows:

[0038] S1. Pickling: The raw strip steel is pickled twice to obtain pickled strip steel;

[0039] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section to obtain heated strip.

[0040] S3. Temperature control: Controlling the power of the cooling fan to increase the surface temperature of the S2 heated strip when it enters the zinc pot, thus obtaining temperature-controlled heated strip.

[0041] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip steel is immersed in a zinc pot for hot-dip galvanizing of zinc, aluminum and magnesium coating to obtain a hot-dip zinc-aluminum-magnesium coating with no zinc undulations on the surface.

[0042] Specifically, the raw material strip steel in S1 is pickled twice, with each pickling process involving six pickling tanks.

[0043] Specifically, in S1, the running speed of the strip is controlled at 80-100 m / min and the temperature of the pickling tank is controlled at 80-85℃ during the first pickling process; and the running speed of the strip is controlled at 100-120 m / min and the temperature of the pickling tank is controlled at 85-90℃ during the second pickling process.

[0044] Specifically, in S2, the temperature of the direct flame section is controlled between 620-650℃, and the temperature of the radiant tube is controlled between 630-660℃.

[0045] Specifically, in S3, the surface temperature of the heated strip steel entering the zinc pot is controlled between 430-460℃.

[0046] Specifically, the cooling fan load adjustment range in S3 is 20-99%.

[0047] Specifically, the composition of the zinc-aluminum-magnesium plating solution in the zinc pot of S4 is: Al 5.7±0.5wt.%, Mg 2.3±0.3wt.%, with the remainder being Zn.

[0048] Specifically, in S4, the temperature of the zinc-aluminum-magnesium plating bath in the zinc pot is 390-440℃, the hot-dip plating time is 1.5-3s, the coating thickness is 15-50μm, and the quality control of the plating layer on at least one surface of the strip is 40-225g / m. 2 .

[0049] Specifically, the density of the S4 hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface and no zinc undulations is 6.5-6.7 g / cm³. 3 The hardness is 140-190HV. In the neutral salt spray test, the time for the coated steel strip to show 5% red rust is 3000-4000h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0050] Specifically, the composition of the raw material strip steel in S1, by mass percentage, is: C 0.05-0.2%, Mn 0.28-1.5%, P 0.015-0.02%, S 0.001-0.005%, with the balance being Fe and unavoidable impurities.

[0051] Example 1

[0052] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0053] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 80 m / min, and the pickling tank temperature is controlled at 82℃. During the second pickling, the strip's running speed is controlled at 105 m / min, and the pickling tank temperature is controlled at 86℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.12%, Mn 1.3%, P 0.016%, S 0.001%. The strip's width is 1000 mm, and its thickness is 2.5 mm.

[0054] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 630℃, and control the temperature of the radiation tube at 640℃ to obtain the heated strip.

[0055] S3. Temperature control: Control the power of the cooling fan to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 430℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 60%;

[0056] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 6.0 wt.%, Mg 2.6 wt.%, with the remainder being Zn. The temperature of the plating solution is 410℃, the hot-dip galvanizing time is 2.5 s, the coating thickness is 30 μm, and the quality control of the plating layer on at least one surface of the strip is 80 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0057] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface and no zinc undulations is 6.5 g / cm³. 3 The hardness is 148HV. The time for 5% red rust to appear on the coated strip in the neutral salt spray test is 3188h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0058] Example 2

[0059] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0060] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 95 m / min, and the pickling tank temperature is controlled at 80℃. During the second pickling, the strip's running speed is controlled at 110 m / min, and the pickling tank temperature is controlled at 90℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.08%, Mn 0.45%, P 0.015%, S 0.003%; the strip width is 1200 mm, and the thickness is 3.5 mm.

[0061] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 640℃, and control the temperature of the radiation tube at 650℃ to obtain the heated strip.

[0062] S3. Temperature control: Control the power of the cooling fan to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 460℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 80%;

[0063] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 5.7 wt.%, Mg 2.0 wt.%, with the remainder being Zn. The temperature of the plating solution is 440℃, the hot-dip galvanizing time is 3.0 s, the coating thickness is 40 μm, and the mass control of the plating layer on at least one surface of the strip is 180 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0064] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth zinc surface is 6.6 g / cm³. 3 The hardness is 170HV. The time for 5% red rust to appear on the coated strip in the neutral salt spray test is 3215h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0065] The hot-based aluminum-magnesium zinc-aluminum-magnesium coating products prepared in Example 1 and Example 2 were compared with hot-based aluminum-magnesium zinc-aluminum-magnesium coating products prepared by other identical preparation processes in the prior art. The specific process conditions and performance parameters are shown in Table 1.

[0066] Table 1 Comparison of Performance Parameters

[0067]

[0068] As can be seen from Table 1, the production method of the hot-base aluminum-magnesium zinc-aluminum-magnesium coated steel sheet of the present invention can effectively eliminate zinc undulation defects on the surface of the hot-base aluminum-magnesium zinc-aluminum-magnesium coated steel sheet.

[0069] First, iron oxide scale can be effectively removed by two pickling processes and by optimizing the pickling process parameters, thus preventing the formation of zinc fluctuation defects caused by residual iron oxide scale.

[0070] Secondly, the core heat inside the strip can be effectively reduced by lowering the temperature of the direct flame section, thereby reducing the temperature difference between the core and surface of the strip, which is beneficial for the subsequent solidification of the plating solution.

[0071] Finally, the reaction between the plating solution and the strip during the immersion plating process can be promoted by increasing the surface temperature of the strip when it enters the zinc pot.

[0072] Through the above measures, the present invention effectively avoids the occurrence of zinc undulation defects on the surface of hot-base aluminum-magnesium zinc-aluminum-magnesium coated steel plates, which is conducive to large-scale industrial production and promotion.

[0073] Example 3

[0074] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0075] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 88 m / min, and the pickling tank temperature is controlled at 85℃. During the second pickling, the strip's running speed is controlled at 100 m / min, and the pickling tank temperature is controlled at 88℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.16%, Mn 1.5%, P 0.018%, S 0.002%; the strip width is 1500 mm, and the thickness is 3.0 mm.

[0076] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 620℃, and control the temperature of the radiation tube at 630℃ to obtain the heated strip.

[0077] S3. Temperature control: Control the cooling fan load to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 440℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 30%;

[0078] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 6.2 wt.%, Mg 2.3 wt.%, with the remainder being Zn. The temperature of the plating solution is 430℃, the hot-dip galvanizing time is 1.5 s, the coating thickness is 50 μm, and the mass control of the plating layer on at least one surface of the strip is 225 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0079] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface and no zinc undulations is 6.5 g / cm³. 3 The hardness is 190HV. The time for 5% red rust to appear on the coated strip in the neutral salt spray test is 3899 hours. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0080] Example 4

[0081] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0082] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 100 m / min, and the pickling tank temperature is controlled at 81℃. During the second pickling, the strip's running speed is controlled at 120 m / min, and the pickling tank temperature is controlled at 90℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.2%, Mn 1.4%, P 0.015%, S 0.005%; the strip width is 1100 mm, and the thickness is 4.0 mm.

[0083] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 650℃, and control the temperature of the radiation tube at 660℃ to obtain the heated strip.

[0084] S3. Temperature control: Control the cooling fan load to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 430℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 90%;

[0085] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 5.2 wt.%, Mg 2.2 wt.%, with the remainder being Zn. The temperature of the plating solution is 390℃, the hot-dip galvanizing time is 2.0 s, the coating thickness is 15 μm, and the mass control of the plating layer on at least one surface of the strip is 40 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0086] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface and no zinc undulations is 6.7 g / cm³. 3 The hardness is 160HV. The time for 5% red rust to appear on the coated strip in the neutral salt spray test is 3539h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0087] Example 5

[0088] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0089] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 90 m / min, and the pickling tank temperature is controlled at 82℃. During the second pickling, the strip's running speed is controlled at 120 m / min, and the pickling tank temperature is controlled at 85℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.05%, Mn 0.28%, P 0.02%, S 0.003%; the strip width is 1200 mm, and the thickness is 3.5 mm.

[0090] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 620℃, and control the temperature of the radiation tube at 630℃ to obtain the heated strip.

[0091] S3. Temperature control: Control the cooling fan load to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 440℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 20%;

[0092] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 6.0 wt.%, Mg 2.1 wt.%, with the remainder being Zn. The temperature of the plating solution is 420℃, the hot-dip galvanizing time is 3.0 s, the coating thickness is 20 μm, and the mass control of the plating layer on at least one surface of the strip is 50 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0093] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface and no zinc undulations is 6.5 g / cm³. 3 The hardness is 155HV. The time for 5% red rust to appear on the coated steel strip in the neutral salt spray test is 3326 hours. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0094] Example 6

[0095] A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings on hot-dip galvanized aluminum substrates is described below:

[0096] S1. Pickling: The raw steel strip is pickled twice, each time passing through six pickling tanks. During the first pickling, the strip's running speed is controlled at 90 m / min, and the pickling tank temperature is controlled at 85℃. During the second pickling, the strip's running speed is controlled at 100 m / min, and the pickling tank temperature is controlled at 86℃. The resulting pickled steel strip has the following composition by mass percentage: C 0.1%, Mn 0.5%, P 0.017%, S 0.002%; the strip width is 1200 mm, and the thickness is 3.5 mm.

[0097] S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section at 630℃, and control the temperature of the radiation tube at 650℃ to obtain the heated strip.

[0098] S3. Temperature control: Control the cooling fan load to increase the surface temperature of the S2 heated strip when it enters the zinc pot, and control the surface temperature of the temperature-controlled heated strip into the zinc pot at 450℃ to obtain the temperature-controlled heated strip; wherein, the cooling fan load is 99%;

[0099] S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The composition of the zinc-aluminum-magnesium plating solution in the zinc bath is: Al 6.0 wt.%, Mg 2.5 wt.%, with the remainder being Zn. The temperature of the plating solution is 430℃, the hot-dip galvanizing time is 2.5 s, the coating thickness is 25 μm, and the mass control of the plating layer on at least one surface of the strip is 60 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

[0100] In this embodiment, the density of the hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth zinc surface is 6.6 g / cm³. 3 The hardness is 141HV. The time for 5% red rust to appear on the coated strip in the neutral salt spray test is 3024 hours. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0101] The above-mentioned solution, proposed by the present invention, is a method for eliminating zinc fluctuation defects in hot-dip aluminum-magnesium zinc-aluminum-magnesium coatings. This method can solve the zinc fluctuation defects in hot-dip aluminum-magnesium zinc-aluminum-magnesium coatings in the prior art, while improving coating performance, reducing energy consumption, and having a short process, high efficiency, and being beneficial to industrial production.

[0102] This invention utilizes a two-stage pickling process to maximize the removal of residual iron oxide scale from the raw material surface, thereby preventing the formation of zinc undulation defects caused by residual iron oxide scale. During the first pickling, reducing the strip running speed allows for sufficient reaction between the acid and the iron oxide scale, effectively removing most of it. During the second pickling, since only a small amount of iron oxide scale remains on the strip surface, increasing the strip running speed increases production efficiency, while lowering the pickling tank temperature helps save energy.

[0103] This invention reduces the core heat inside the strip by lowering the temperature of the direct flame section, thereby reducing the temperature difference between the core and surface of the strip and facilitating the solidification of the plating solution. At the same time, it shortens the heating time and improves production efficiency.

[0104] This invention increases the surface temperature of the strip steel when it enters the zinc bath, resulting in raw strip steel with a smaller internal and external temperature difference. The higher surface temperature facilitates the reaction between the plating solution and the strip steel during the immersion plating process, while the smaller internal and external temperature difference of the raw strip steel reduces the resistance of core heat to the plating solution solidification process, thereby suppressing zinc fluctuation defects caused by plating solution reflow.

[0105] The density of the zinc-aluminum-magnesium zinc-aluminum-magnesium coating on the hot-dip galvanized substrate of this invention, which has no zinc undulations on its surface, is 6.5-6.7 g / cm³. 3 The hardness is 140-190HV. In the neutral salt spray test, the time for the coated steel strip to show 5% red rust is 3000-4000h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

[0106] In summary, compared to other traditional methods, the method of the present invention, through two pickling processes, reducing the temperature of the direct flame section, and increasing the surface temperature of the strip steel when it enters the zinc pot, can not only overcome the surface coating problem... Figure 2 The technical challenge of "zinc fluctuations" shown is thus obtained. Figure 3 The method shown eliminates zinc undulation defects in zinc-aluminum-magnesium coatings based on hot-dip aluminum alloys. It also saves energy, reduces heating time, reduces the obstruction of the core heat of the strip to the solidification process of the plating solution, and improves the performance of the coating. The overall process is simple to operate, has low production cost, and high efficiency, which is conducive to large-scale industrial production and promotion.

[0107] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications should also be considered within the scope of protection of the present invention.

Claims

1. A method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates, characterized in that, The method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in thermal bases is as follows: S1. Pickling: The raw strip steel is pickled twice to obtain pickled strip steel. During the first pickling process, the running speed of the strip steel is controlled at 80-100m / min and the temperature of the pickling tank is controlled at 80-85℃. During the second pickling process, the running speed of the strip steel is controlled at 100-120m / min and the temperature of the pickling tank is controlled at 85-90℃. S2. Heating: When heating the S1 pickled strip, reduce the heating temperature of the direct flame section and control the temperature of the direct flame section between 620-650℃, and control the temperature of the radiation tube between 630-660℃ to obtain the heated strip. S3. Temperature control: Control the power of the cooling fan to increase the surface temperature of the S2 heated strip steel when it enters the zinc pot. Control the surface temperature of the temperature-controlled heated strip steel when it enters the zinc pot between 430-460℃. The load adjustment range of the cooling fan is 20-99%, thus obtaining the temperature-controlled heated strip steel. S4. Hot-dip galvanizing: The S3 temperature-controlled heated strip is immersed in a zinc bath for hot-dip galvanizing with a zinc-aluminum-magnesium coating. The temperature of the zinc-aluminum-magnesium plating solution in the zinc bath is 390-440 ℃, the hot-dip galvanizing time is 1.5-3 s, the coating thickness is 15-50 μm, and the mass control of the plating layer on at least one surface of the strip is 40-225 g / m. 2 A hot-base aluminum-magnesium zinc-aluminum-magnesium coating with a smooth surface free of zinc undulations was obtained.

2. The method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates according to claim 1, characterized in that, In S1, the raw material strip steel is pickled twice, and each pickling process involves six pickling tanks.

3. The method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates according to claim 1, characterized in that, The composition of the zinc-aluminum-magnesium plating solution in the zinc pot of S4 is: Al 5.7±0.5 wt.%, Mg 2.3±0.3 wt.%, with the remainder being Zn.

4. The method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates according to claim 1, characterized in that, The density of the S4 hot-dip aluminum-magnesium zinc-aluminum-magnesium coating with a smooth, zinc-free surface is 6.5-6.7 g / cm³. 3 The hardness is 140-190 HV. In the neutral salt spray test, the time for the coated steel strip to show 5% red rust is 3000-4000h. The results of the 0T bending test or the 10% deformation tensile test show no cracking or peeling.

5. The method for eliminating zinc undulation defects in magnesium-based zinc-aluminum-magnesium coatings in hot-dip galvanized aluminum substrates according to claim 1, characterized in that, The composition of the raw material strip in S1, by mass percentage, is: C 0.05-0.2%, Mn 0.28-1.5%, P 0.015-0.02%, S 0.001-0.005%, with the balance being Fe and unavoidable impurities.

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