Ultra-high corrosion resistant coated steel sheet having good formability and method of manufacturing the same

Abstract

The application discloses a super-high corrosion-resistant coated steel plate with good forming performance and a preparation method thereof. The super-high corrosion-resistant coated steel plate comprises a base body and a coating layer. The coating layer is a double-layer structure. The first layer is an electroplating layer, and the second layer is a hot-dip plating layer. The electroplating layer comprises 0.5-1% of Si and the balance of Al in percentage by weight. The hot-dip plating layer comprises 5-15% of Al, 3-8% of Mg, 0.5-0.9% of Si and the balance of Zn in percentage by weight. The application controls the electroplating process, the heating process and the post-plating cooling process by the base body design, the double-layer coating layer structure design and the coating layer component design, so that a suitable structure and phase structure are obtained. The prepared steel plate has good corrosion resistance and processing performance. The corrosion resistance can be 5-20 times of that of a pure zinc product with the same specification. The crack width is less than or equal to 20 microns after 0T bending processing, so that the balance control of the improvement of the corrosion resistance and the forming performance is realized.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of coated products, and particularly relates to an ultra-high corrosion-resistant coated steel plate with good forming performance and a preparation method thereof. BACKGROUND

[0002] Zinc-aluminum-magnesium products are widely used in the fields of building and photovoltaic due to their excellent corrosion resistance, but when used in C5 and above environments, the existing zinc-aluminum-magnesium products cannot meet the corrosion resistance requirements. In recent years, foreign countries have developed 19Al6Mg and 12Al5Mg ultra-high corrosion-resistant zinc-aluminum-magnesium products. However, with the increase of Mg content, the proportion of MgZn2 phase in the coating structure also increases. Since MgZn2 phase is a brittle phase, the forming performance of the coating deteriorates.

[0003] CN 116426793 A discloses a high corrosion-resistant zinc-aluminum-magnesium coated steel plate and a preparation method thereof. By adding Mg, Al, Si and other elements in the zinc-aluminum-magnesium alloy coating and controlling the mass fraction of Mg element in the coating to be 3-8%, the mass fraction of Al element to be 12-25%, the volume fraction of Mg-Zn compound on the surface of the coating to be not more than 2%, and the ratio of Si element to Al element in the coating to be 0.05-0.15, the zinc-aluminum-magnesium coated steel plate provided by the application has good corrosion resistance and excellent surface quality. However, the proportion of Mg-Zn compound in this technology is relatively low, and the improvement of corrosion resistance is limited.

[0004] CN 114846171 A discloses a hot-dip plated alloy steel material with excellent corrosion resistance and a manufacturing method thereof. The hot-dip plated alloy coating contains Al: more than 8% to 25%, Mg: more than 4% to 12%, the balance of Zn and other unavoidable impurities. The surface X-ray diffraction intensity of the hot-dip plated alloy coating satisfies the following relationship formula 1. [Relationship formula 1] 2000 cps ≤ X-ray diffraction intensity ≤ 20000 cps (wherein, the X-ray diffraction intensity is M-N, the M refers to the highest peak intensity in the interval of 2θ = 20.00° to less than 21°, and the N refers to the peak intensity at 2θ = 20.00°). However, the Al content in this application reaches up to 25%, the Mg content reaches up to 12%, the surface quality control is extremely difficult in production, and the MgZn2 content is high, so the forming performance is difficult to control.

[0005] In view of the prior art, the corrosion resistance of the steel plate is mainly improved in the following ways: 1) increasing the Al and Mg content, but not controlling the proportion of eutectic phase, which has the problem of limited improvement of corrosion resistance; 2) increasing the Al and Mg content while increasing the proportion of eutectic phase, but there is a problem of insufficient forming performance. SUMMARY

[0006] The present application provides an ultra-high corrosion-resistant coated steel plate with good forming performance and a preparation method, so as to realize the balance control of the improvement of corrosion resistance and the forming performance.

[0007] To achieve the above object, the present application provides an ultra-high corrosion-resistant coated steel plate with good forming performance, comprising a substrate and a coating layer; wherein the coating layer is a double-layer structure, the first layer (the inner layer directly contacting the substrate) is an electroplating layer, and the second layer (the outer layer) is a hot-dip coating layer; the electroplating layer comprises 0.5-1% of Si and the balance of Al by weight percentage; and the hot-dip coating layer comprises 5-15% of Al, 3-8% of Mg, 0.5-0.9% of Si and the balance of Zn by weight percentage.

[0008] Further, the hot-dip coating layer comprises an Al-rich phase, a MgZn binary alloy phase, a Mg2Si phase and a Zn-Al-MgZn2 ternary eutectic phase.

[0009] Further, in the hot-dip coating layer, the MgZn binary alloy phase accounts for 20-30% by weight percentage, the Al-rich phase accounts for 20-30% by weight percentage, the Mg2Si phase accounts for 0.1-0.2% by weight percentage, and the Zn-Al-MgZn2 ternary eutectic phase accounts for 35-55% by weight percentage.

[0010] Further, the Al-rich phase is divided into two parts A and B, the part A is located at the joint of the electroplating layer and the hot-dip coating layer, and the part B is located in the hot-dip coating layer; the weight ratio of A to B satisfies 2≤B / A≤5.

[0011] Further, the microstructure of the substrate is equiaxed ferrite.

[0012] Further, the present application also provides a preparation method of the ultra-high corrosion-resistant coated steel plate, and the process of the preparation method comprises, in sequence, substrate electrolytic degreasing, pickling activation, electroplating, cleaning, hot air drying, heating, hot-dip plating and cooling; the composition of the electroplating solution in the electroplating process comprises 20-35% of 1-ethyl-3-methylimidazole chloride, 65-75% of chloroaluminate, 1-3% of aluminosilicate, 0.5-1% of benzoic acid and 1-2% of polyethylene glycol by weight percentage; the content of 1-ethyl-3-methylimidazole chloride is defined as a, the content of chloroaluminate is defined as b, and the content of aluminosilicate is defined as c; a, b and c satisfy the relationship 1.68≤(b+c) / a≤3.37.

[0013] Further, the pickling activation solution of the substrate is 10-30% of HCl solution, and the activation temperature is 40-60°C; the current density of the electroplating is 0.5-2 A / dm2, the electroplating temperature is 30-50°C, and the electroplating pH value is 3-5.

[0014] Further, the cleaning is divided into three stages, the first stage is hot water flushing at 60-80 DEG C for 1-2 minutes, the second stage is flowing normal temperature water washing with electric conductivity ≤50 μS / cm, and the third stage is ultrapure water rinsing with resistivity of 5-10 MΩ·cm; and hot air drying is adopted after cleaning.

[0015] Further, the heating temperature is 380-420 DEG C, the heating time is 1-5 min, and 5-10% hydrogen atmosphere is used for protection during the heating process; and the hot-dip plating temperature is 400-490 DEG C.

[0016] Further, the cooling adopts a two-stage cooling process, the first-stage cooling rate is 40-50 DEG C / s, the first-stage cooling end temperature is 335-350 DEG C, the second-stage cooling rate is 1-10 DEG C / s, and the second-stage cooling end temperature is 200-250 DEG C.

[0017] (1) The present application forms a multi-layer structure protection through the design of the coating layer, realizes super high corrosion resistance, and when the steel plate contacts corrosion factors (O2, Cl - ), firstly, the outermost hot-dip plating layer forms the first guarantee, on the one hand, the Al content and Mg content of the plating layer are controlled to improve the corrosion resistance, when the Al content is too small, the corrosion resistance improvement effect is not ideal, when the Al content is too high, a coarse Al-rich phase is formed, and the corrosion resistance is deteriorated, therefore, the Al content is controlled to be 5-15% in the present application, when the Mg content is too low, the corrosion resistance improvement is limited, when the Mg content is too high, too much MgZn phase will destroy the phase balance, therefore, the Mg content in the plating layer is controlled to be 3-8% in the present application, on the other hand, the microstructure of the hot-dip plating layer is controlled to further improve the corrosion resistance, firstly, the proportion of the MgZn phase is controlled to be more than 20%, which can improve the cathode protection effect of the plating layer, further, the proportion of the ternary eutectic phase is controlled to be more than 35%, which promotes the formation of a dense basic zinc carbonate film, realizes self-repairing and blocks the corrosion diffusion, further, a trace amount of Mg2Si generated in the plating layer can inhibit the coarsening of the MgZn phase and improve the corrosion resistance, but excessive Mg2Si hinders the generation of dense corrosion products such as Mg(OH)2, and affects the corrosion resistance, therefore, the proportion of the Mg2Si phase is controlled to be 0.1-0.2% in the present application, secondly, the second layer of the electroplated Al layer forms the second guarantee, when the hot-dip plating layer is damaged, the Al plating layer is oxidized to generate a new Al2O3 film, automatically seals the damaged area and prevents the corrosion from further spreading.

[0018] The trace amount of Mg2Si is preferentially dispersed and precipitated at the grain boundary or eutectic zone in the solidification process, can be used as a heterogeneous nucleation point to refine the eutectic structure, and thereby inhibits the MgZn2 phase from growing into a coarse skeleton in the continuous eutectic liquid film.

[0019] 2-3 mg / L of Mg needs to be dissolved within 0-2 h at the beginning of corrosion -1 ​2+ to Al 3+ , Zn 2+ co-precipitate into Zn6Al2(OH) 16 CO3·4H2O (LDH) film; when Mg2Si < 0.1%, the active Mg surface area provided < 0.3 cm 2 cm -2 , the peak concentration of Mg 2+ in solution only 0.8 mg / L -1 , not enough to form a complete LDH layer, instead generating a loose ZnO / Zn5(CO3)2(OH)6 film, with a drop in film resistance by an order of magnitude (R_f from 8 kΩ cm 2 to 1 kΩ cm 2 below), which cannot self-repair later, with a 40% increase in weight loss in 96 h salt spray.

[0020] Mg2Si 0.1-0.2% can be slightly dissolved by weak acid-neutral electrolyte at the initial stage of corrosion, continuously providing Mg 2+ , which co-precipitates with Zn 2+ , Al 3+ to form a layered double hydroxide (LDH) and basic zinc chloride / zinc carbonate aluminum colloidal film; these products are dense and have high resistance, which can block electron transmission and self-repair cracks. LDH is a two-dimensional layered inorganic film formed by the alternating stacking of positively charged host lamella and negatively charged interlayer anions.

[0021] When Mg2Si > 0.2%, the particles are dense and the potential is negatively biased, easily forming a large cathode-small anode galvanic couple, which rapidly increases the local pH, prompting Mg 2+ to directly precipitate as a thick and loose Mg(OH)2 outer layer, hindering the filling of Zn-Al corrosion products inward; at the same time, excess Si is adsorbed on the surface of Mg(OH)2, reducing its subsequent carbonation-densification ability. When controlled at 0.1-0.2%, Mg(OH)2 only inserts into the LDH film in the form of a nanometer interlayer, which buffers the pH and does not destroy the overall denseness of the film, achieving the dual effects of "fine grain inhibition of coarsening + appropriate Mg supply to promote the film", thus balancing the forming and long-life corrosion resistance.

[0022] (2) The present application realizes the balance of super high corrosion resistance and forming performance through the control of the matrix and the coating layer structure and proportion. First, the Si content in the coating layer is controlled: a small amount of Si can inhibit the growth of Fe-Al compound and prevent the poor adhesion of the alloy layer caused by the excessive thickness of the alloy layer, and on the other hand, it can improve the uniformity of the eutectic phase; but when the content is too high, on the one hand, the brittleness of the electroplated layer is increased, and on the other hand, the Mg2Si phase of the hot-dip coating layer organization is increased, the brittleness of the coating layer is increased, and the forming performance is affected, therefore, the present application controls the Si content in the electroplated layer to be 0.5-1%, and the Si content in the hot-dip coating layer is 0.5-0.9%. Secondly, the Al-rich phase of B part can be used as an inhibitor of brittle intermetallic compounds such as Mg2Zn 11 When too little, the effect is not obvious, and when too much, the difference between the tensile coefficient of the Al-rich phase and the eutectic zone is enlarged, and local internal stress is generated in the forming process, and cracking occurs in the bending test, therefore, the Al-rich phase (A part+B part) of the present application accounts for 20-30%. Further, the insufficient content of MgZn phase leads to the reduction of the cathodic protection efficiency of the coating layer and the increase of the risk of local perforation corrosion; when the content is too high, the brittleness is significantly increased, which affects the stamping performance; therefore, the present application controls the proportion of MgZn phase to be 20-30%. Further control the proportion of ternary eutectic phase, ternary eutectic phase can promote the formation of dense basic zinc carbonate film, realize self-repair, block corrosion diffusion, too little, the effect is not obvious, the corrosion resistance is reduced, too much, the excess ternary eutectic phase forms a continuous network structure, local stress concentration, affects the forming performance; therefore, the present application controls the proportion of ternary eutectic phase to be 35-55%. Further, the electroplated aluminum layer diffuses at the hot-dip plating temperature, when B / A>5, the content of Al-rich phase A is too small, the buffering effect of bending deformation is weak; when B / A<2, the Al-rich phase B is too small, which leads to the increase of Mg2Zn 11The formation of the eutectic phase increases the brittleness of the plating layer and reduces the forming performance; therefore, the present application controls the relationship between the aluminum-rich phase A at the joint of the electroplated aluminum layer and the hot-dip plating layer and the aluminum-rich phase B in the hot-dip plating layer to satisfy 2≤B / A≤5, which can reduce the plating layer crack tendency during the bending deformation and improve the forming performance. Further controlling the plating layer cooling process, at 335-350℃, the cooling rate v is controlled to be 40-50℃ / s, which not only can promote the formation of the eutectic phase, but also can inhibit the eutectic phase segregation, so as to reduce the eutectic size, which can improve the corrosion resistance and ductility; at the same time, at 200-250℃, the cooling rate v is controlled to be 1-10℃ / s to promote the growth of the eutectic phase. Further, the substrate structure is controlled to be equiaxed ferrite, at a lower heating temperature, the grains will not occur re-crystallization, and the equiaxed ferrite structure is more conducive to the forming. Further, the heating temperature is controlled to be 380-420℃, when the heating temperature is too low, it is not conducive to the hot-dip plating, and when the heating temperature is too high, the electroplated aluminum layer is locally melted to form liquid aluminum drops, the molten aluminum is gathered into spherical particles on the surface of the steel substrate, which leads to the loss of the continuity of the plating layer; at the same time, the electroplated aluminum layer occurs re-crystallization at 380-420℃, the original fine grains are coarsened, which is conducive to the improvement of the ductility of the plating layer, so as to improve the forming performance.

[0023] (3) The present application forms a uniform electroplated aluminum layer with good bonding force with hot-dip plated layer and substrate through suitable electroplating solution composition and process design. Firstly, when the pickling concentration is too low, the activation effect is not ideal; when the pickling concentration is too high, the reaction with the base material occurs; therefore, the present application controls the pickling activation concentration to be 10-30%. Further, when the pickling temperature is too low, the oxide layer is not completely removed; when the pickling temperature is too high, the adhesion of the electroplated layer is reduced; therefore, the present application controls the pickling temperature to be 40-60℃. Further, the electroplating solution composition is controlled to be 20-35% 1-ethyl-3-methyl imidazole chloride to provide a stable solution environment, 65-75% chloroaluminate, 1-3% aluminosilicate to form a suitable electroplated layer composition, and 0.5-1% benzoic acid is added to inhibit the corrosion of the steel substrate, and 1-2% polyethylene glycol is added to improve the uniformity of the plated layer. Further, the content of 1-ethyl-3-methyl imidazole chloride is defined as a, the content of chloroaluminate is defined as b, and the content of aluminosilicate is defined as c; when (b+c) / a<1.68, the adhesion of the plated layer to the substrate is reduced and easy to peel off; when (b+c) / a>3.37, the deposition of Al ions is hindered, and the corrosion resistance is reduced; therefore, the present application controls a and b, c to satisfy the relationship: 1.68≤(b+c) / a≤3.37. Further, when the electroplating temperature is too high, the difference in thermal expansion between the substrate and the electroplated layer causes internal stress, the bonding strength is reduced, and the electroplated layer is easy to peel off; when the electroplating temperature is too low, the ion migration rate is reduced, the cathode current efficiency is reduced, and the deposition time is prolonged; therefore, the present application controls the electroplating temperature to be 30-50℃. Further, when the electroplating current density is too low, the reduction rate of aluminum ions is slow, and the plated layer is loose and porous; when the electroplating current density is too high, the hardness of the plated layer is too high; therefore, the present application controls the electroplating current density to be 0.5-2 A / dm 2 . Further, when the electroplating pH value is too low, the internal stress increases, leading to easy peeling of the electroplated layer; when the electroplating pH value is too high, the stability of the plating solution is reduced, hydrogen gas is retained in the cathode area, and the pinhole rate is significantly increased; therefore, the present application controls the electroplating pH value to be 3-5. Further, the first stage cleaning is used to dissolve organic matter and ion liquid residue, the second stage cleaning is used to remove soluble salts, and the third stage cleaning is used to completely remove ion residue, so as to improve the cleanliness of the electroplated layer and increase the bonding force between the electroplated layer and the hot-dip plated layer.

[0024] Compared with the prior art, the present application has the following beneficial effects: through the substrate design, double-layer plated layer structure design, plated layer composition design, and the control of electroplating process, heating process and post-plating cooling process, a suitable organization and phase structure are obtained, the prepared steel plate has good corrosion resistance and processing performance, the corrosion resistance can reach 5-20 times of the same specification pure zinc product, and the crack width after 0T bending processing is ≤20μm, so as to realize the balance control of the improvement of corrosion resistance and the forming performance. DETAILED DESCRIPTION

[0025] The application will be further described in connection with specific examples.

[0026] The process control of the super high corrosion resistant coated steel plate with good forming performance of the application is shown in Table 1-Table 3. The composition of the base material is 0.001≤C≤0.25, 0.02≤Mn≤1.5, Si≤0.1, P≤0.02, S≤0.02, Ti≤0.2, Nb≤0.2, V≤0.2, Cr≤0.2, Mo≤0.2, Cu≤0.2, and the balance of Fe. The coating thickness is 60-600g / m 2 / both sides, wherein the electroplating layer is 10-40g / m 2 / both sides, and the others are hot-dip coating layers.

[0027] Table 1 Coating composition and structure control

[0028]

[0029] Table 2 Electroplating composition and process control

[0030]

[0031] Table 3 Heating and galvanizing process control

[0032]

[0033] Table 4 Electroplating layer cleaning process control

[0034]

[0035] The implementation effect of the super high corrosion resistant coated steel plate with good forming performance of the application is shown in Table 5.

[0036] The corrosion resistance is compared with the pure zinc product with the same coating, and is measured according to GB / T 10125. 1-3 times is rated as 1 level, 3-5 times is rated as 2 level, 5-10 times is rated as 3 level, 10-15 times is rated as 4 level, and 15-20 times is rated as 5 level. The forming performance is compared by the crack width after 0T bending.

[0037] Table 5 Steel plate corrosion resistance and forming performance

[0038]

[0039] From the above, it can be seen that the super-high corrosion-resistant coated steel plate with good forming performance in the embodiment according to the technical solution of the present application has the following properties: the MgZn binary alloy phase accounts for 20-30%, the Al-rich phase accounts for 20-30% (the Al-rich phase is divided into two parts A and B, part A is located at the joint of the electroplated layer and the hot-dip plated layer, part B is located in the hot-dip plated layer, and the weight ratio of A to B satisfies: 2≤B / A≤5), the Mg2Si phase accounts for 0.1-0.2%, and the Zn-Al-MgZn2 ternary eutectic phase accounts for 35-55%. The corrosion resistance can reach 5-20 times that of the same specification pure zinc product, and the crack width after 0T bending processing is ≤20 μm. In the comparative example 1, the Al and Mg contents are lower, the corrosion resistance is 5-10 times that of the same plated pure zinc product, and with the increase of the Al and Mg contents, the corrosion resistance of the embodiment 5 is 15-20 times that of the same plated pure zinc product. In the comparative example 1, there is no electroplated aluminum layer. First, the buffering effect of bending deformation is weak, the forming performance is poor, and the 0T bending crack width is 55 μm. Second, when the outermost hot-dip plated layer is damaged, it cannot provide a second guarantee, and the corrosion resistance is only 3-5 times that of the same plated pure zinc product. In the comparative example 2, there is no Si element in the electroplated layer. The alloy layer at the joint of the plated layer and the substrate is too thick without Si element, the bending performance is poor, and the 0T bending crack width is 50 μm. In the comparative example 3, the Mg content in the hot-dip plated layer is low, and the insufficient MgZn phase content leads to the decrease of the cathode protection efficiency of the plated layer and the decrease of the corrosion resistance, the corrosion resistance is only 3-5 times that of the same plated pure zinc product. Moreover, the first cooling rate after plating is high, the ternary eutectic phase ratio is higher than 55%, the excess ternary eutectic phase forms a continuous network structure, the local stress is concentrated, the forming performance is affected, and the 0T bending crack width is 39 μm. In the comparative example 4, the Al-rich phase B is less and the Al-rich phase B / A ratio is <2, which leads to the decrease of the Mg2Zn 11The phase formation, the plating layer brittleness increases, the forming performance reduces, the 0T bending crack width is 35 μm, simultaneously, the chloroaluminate content is high, the ratio of (chloroaluminate content b+aluminosilicate content c) / 1-ethyl-3-methyl imidazole chlorate content a>3.37, hinders the Al ion deposition, reduces the corrosion resistance, the corrosion resistance is only 3-5 times of the same plating layer pure zinc product. The Al-rich phase A in the comparative example 5 is less and the ratio of Al-rich phase B / A>5, the bending deformation buffer effect is weak, simultaneously, the chloroaluminate content is low, the ratio of (chloroaluminate content b+aluminosilicate content c) / 1-ethyl-3-methyl imidazole chlorate content a<1.68, the adhesion of the electroplating layer and the substrate reduces, the forming performance reduces, the 0T bending crack width is 32 μm. The heating temperature in the comparative example 6 is too high, the electroplating aluminum layer is locally melted, forms the liquid aluminum drop, the molten aluminum is gathered into spherical particles on the steel substrate surface, causes the electroplating aluminum layer continuity loss, influences the corrosion resistance and the deformation buffer effect, compared with the example 3, the corrosion resistance and the forming performance reduce, is 5-10 times of the same plating layer pure zinc product, the 0T bending crack width is 36 μm. The first stage cooling rate in the comparative example 7 after plating is low, the ternary eutectic phase content reduces, compared with the example 5, the corrosion resistance reduces, is 10-15 times of the same plating layer pure zinc product, simultaneously, the MgZn phase content has a certain increase, the plating layer brittleness rises, influences the forming performance, the 0T bending crack width is 25 μm.

[0040] The above description only specifically exemplarily describes the present application, it should be noted that the specific implementation of the present application is not limited by the above mode, as long as various non-essential improvements are made by using the technical concept and technical scheme of the present application, or the technical concept and technical scheme of the present application are directly applied to other occasions without improvement, all are within the protection scope of the present application.

Claims

1. A supercorrosion resistant coated steel sheet having excellent formability, characterized in that: The coating layer is a double-layer structure, the first layer is an electroplating layer, and the second layer is a hot-dip coating layer, the electroplating layer comprises 0.5-1% of Si and the balance of Al in terms of percentage by weight, and the hot-dip coating layer comprises 5-15% of Al, 3-8% of Mg, 0.5-0.9% of Si and the balance of Zn in terms of percentage by weight; the electroplating layer is directly in contact with the substrate, and the hot-dip coating layer is an outer layer. The hot-dip coating layer comprises an Al-rich phase, an MgZn binary alloy phase, an Mg2Si phase and a Zn-Al-MgZn2 ternary eutectic phase; the MgZn binary alloy phase accounts for 20-30%, the Al-rich phase accounts for 20-30%, the Mg2Si phase accounts for 0.1-0.2% and the Zn-Al-MgZn2 ternary eutectic phase accounts for 35-55% in terms of percentage by weight; the Al-rich phase is divided into two parts A and B, the part A is located at the joint of the electroplating layer and the hot-dip coating layer, and the part B is located in the hot-dip coating layer, and the weight ratio of A to B satisfies 2≤B / A≤5.

2. The supercorrosion resistant coated steel sheet having excellent formability according to claim 1, characterized in that: The microstructure of the substrate is equiaxed ferrite.

3. A method of producing the ultra-high corrosion resistant coated steel sheet according to claim 1, wherein the production method comprises the steps of, in this order: The substrate is subjected to electrolytic degreasing, pickling activation, electroplating, cleaning, hot air drying, heating, hot-dip plating and cooling; characterized by that the composition of the electroplating solution in the electroplating process comprises 20-35% of 1-ethyl-3-methylimidazole chloride, 65-75% of chloroaluminate, 1-3% of aluminosilicate, 0.5-1% of benzoic acid and 1-2% of polyethylene glycol in terms of percentage by weight; the content of 1-ethyl-3-methylimidazole chloride is defined as a, the content of chloroaluminate is defined as b, and the content of aluminosilicate is defined as c, and a, b and c satisfy the relationship 1.68≤(b+c) / a≤3.

37. ​ 4. The method of claim 3, wherein: The pickling activation solution for the substrate is an HCl solution with a concentration of 10-30%, and the activation temperature is 40-60℃; the current density for electroplating is 0.5-2 A / dm2, the electroplating temperature is 30-50℃, and the electroplating pH value is 3-5.

5. The method of claim 3, wherein: The cleaning is divided into three stages, the first stage is hot water flushing at 60-80℃ for 1-2 minutes, the second stage is flowing normal-temperature water washing with an electric conductivity of ≤50 μS / cm, and the third stage is ultrapure water rinsing with a resistivity of 5-10 MΩ·cm, and hot air drying is adopted after cleaning.

6. The method of claim 3, wherein: The heating temperature is 380-420℃, the heating time is 1-5 min, and a hydrogen atmosphere with a concentration of 5-10% is used for protection during the heating process; the hot-dip plating temperature is 400-490℃.

7. The method of claim 3, wherein: The cooling adopts a two-stage cooling process, the first-stage cooling rate is 40-50℃ / s, and the first-stage cooling end temperature is 335-350℃; the second-stage cooling rate is 1-10℃ / s, and the second-stage cooling end temperature is 200-250℃.

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