Hot stamping coated steel sheet and aqueous surface treatment liquid therefor

Abstract

The present invention discloses a coated steel sheet for hot stamping and an aqueous surface treatment liquid used therein. The coated steel sheet for hot stamping comprises a coated steel sheet and a composite film layer formed by applying the aqueous surface treatment liquid to the coated steel sheet. The coated steel sheet comprises a substrate and an Al or AlSi coating layer disposed on one or both sides of the substrate. The composite film layer contains an aqueous anionic polymer resin A, a tungsten-containing compound B, a zinc-containing compound C, a boron-containing compound D, a water-soluble thickener E, and an aqueous surface improvement additive F. By designing the composition of the aqueous surface treatment liquid and applying it to the surface of the coated steel sheet, the present invention ensures that the coated steel sheet for hot stamping has good high-temperature lubricity during hot stamping processing, improves the processing performance of the coated steel sheet for hot stamping, reduces wear on the die surface of hot stamping dies, reduces the frequency of die repairs, and improves production efficiency.

Description

Technical Field

[0001] The invention belongs to the field of metal surface treatment, and in particular relates to a coated steel plate for hot stamping and an aqueous surface treatment liquid used therefor. Background Art

[0002] Hot stamping ultra-high-strength steel reduces vehicle weight while improving collision safety, and is an effective way to achieve energy conservation and emission reduction in automobiles. Therefore, hot stamping parts and processes are increasingly used in the automotive industry and are currently widely used in parts such as automobile A-pillars, B-pillars, door rings, center channels and bumpers.

[0003] Among plain carbon steels, only boron alloy steels and other grades can achieve a fully martensitic microstructure transformation during the cooling process after hot stamping. 22MnB5 is the most commonly used hot stamping steel. Before hot forming, this material has a ferrite-pearlite microstructure and a yield strength of approximately 550 MPa. After the fully martensitic transformation, the yield strength can reach approximately 1500 MPa. To achieve a fully martensitic microstructure transformation, the material must be fully austenitized at high temperatures, followed by hot forming and quenching to complete the phase transformation. The austenitization process is performed in a furnace, where the sheet is heated to a temperature above Ac3 (typically 900-950°C) and held for 3-10 minutes, depending on the sheet thickness. After full austenitization, the material is transferred from the furnace to the hot forming press. This process occurs in air, with a cooling rate of >27 K / s before 400°C to achieve a diffusionless martensitic transformation and ultimately achieve the desired mechanical strength.

[0004] However, when hot stamping is applied to boron alloy steel plates, oxidation occurs on the steel plate surface, resulting in decarburization and scale. Decarburization reduces the surface strength of the steel plate, and scale increases friction between the steel plate and the mold, reducing the mold's service life. Descaling adhered to the mold surface also requires removal during production, reducing production efficiency. Hot stamped parts require post-processing with shot blasting, but shot blasting for parts with reduced thickness can easily cause residual stress on the part surface, resulting in deformation. Furthermore, parts requiring corrosion resistance require post-processing cleaning, surface pretreatment, and anti-rust coating, reducing production efficiency.

[0005] To prevent surface oxidation and decarburization of steel sheets and improve the high-temperature and corrosion resistance of hot-stamped steel sheets, high-temperature anti-oxidation technologies suitable for hot-stamped steel sheets have been developed. These include hot-dip aluminum-silicon (Al-10 wt% Si), pure zinc (GI), alloyed zinc-iron (GA), and electroplated zinc-nickel (Zn-11 wt% Ni) coatings, as well as multifunctional protective coatings. However, the heating temperatures (700-1000°C) during hot stamping are higher than the melting and boiling points of zinc metal and its alloys. Liquid-metal-induced embrittlement (LIEM) by the liquid metal (Zn or Zn-Fe) limits the use of GI and GA coatings. While Zn-Ni has some application prospects, it is expensive and has low productivity. Anti-oxidation oils and protective coatings can prevent high-temperature oxidation of the steel substrate to a certain extent, but the coatings suffer from poor surface adhesion and uniformity at high temperatures, prone to powdering and flaking, lack corrosion resistance, and have a small weld window.

[0006] Aluminum silicon (AlSi) coatings have the characteristics of no oxide scale shedding during heating, no need for sandblasting after stamping, high forming precision, no need for nitrogen protection, and a large welding window after heating. They are currently widely used in hot stamping processes. In addition, AlSi coatings also have a certain anti-rust effect, so the corrosion resistance is also improved accordingly. However, during the heating process of the steel plate with AlSi coating on the surface, the Fe element from the steel plate will diffuse into the AlSi coating and then generate a variety of Al-Fe-Si and Al-Fe alloy layers in the bulk and surface of the AlSi coating. Among them, the Al-Fe alloy layer has extremely high hardness. Therefore, during the production process, there are problems such as scratching damage to the processed parts and the mold surface during the contact and friction between the AlSi-coated steel plate and the mold during hot stamping.

[0007] Due to the high surface hardness of the Al-Fe alloy layer, relative sliding is difficult to occur at high temperatures, and the lubricity is poor. It is easy to crack during the hot stamping process. Cracks perpendicular to the interface between the coating and the iron matrix will appear at locations with large deformation, and defects such as surface powdering will occur, resulting in reduced formability. In addition, the peeled Al-Fe metal compound adheres to the mold, further exacerbating the friction between the coated steel plate and the mold, thereby reducing the quality of the finished part and wearing the mold surface. Therefore, it is necessary to increase the frequency of mold repair to remove the Al-Fe metal compound adhering to the mold surface, which reduces the production efficiency of the finished part processing and increases production costs.

[0008] Therefore, in order to prevent processing damage to product parts and mold surfaces during hot stamping of steel plates coated with AlSi coatings, and to reduce the adhesion of Al-Fe metal compounds to the mold surface, publication number CN102066615A provides a ZnO surface film layer having a wurtzite crystal structure on the Al coating, thereby making the Al-coated steel plate lubricated, preventing uneven coating thickness during heating, and improving the formability and productivity of hot stamping. However, in this technology, the ZnO particles need to be attached to the surface of the Al coating by adhesives such as organic resins and / or silane coupling agents. These adhesives will undergo oxidative decomposition under heating temperatures of 700-1000°C, causing a large amount of ZnO to peel off from the surface of the Al coating. This process will cause the ZnO particles that have lost their adhesion to diffuse and contaminate the heating furnace during heating, or adhere to the mold surface during hot stamping, causing mold contamination. In addition, the ZnO particles remaining on the surface of the Al coating also cause deterioration in the weldability of the formed parts.

[0009] Publication No. CN104093880A uses one or more Zn compounds selected from zinc hydroxide, zinc phosphate, and organic zinc acid as the surface film layer on the Al-plated layer. This technology also requires at least one of an organic resin, a silane coupling agent, and a silica sol as a binder. However, zinc hydroxide, zinc phosphate, and organic zinc acid will all oxidize to zinc oxide (ZnO) under heating temperature conditions of 700-1000°C, and the binder used to provide adhesion will also undergo oxidative decomposition. Therefore, similar to the technology of the above-mentioned CN102066615A, this technology cannot solve the problems of poor adhesion of Zn oxide particles to the surface of the Al-plated layer after hot stamping and contamination of the furnace and mold by the peeled Zn oxide particles.

[0010] Publication No. CN104220641A adds one or more transition metal element compounds to the ZnO surface film as an auxiliary agent to improve lubricity. However, like the above two patents, this technology also requires an organic adhesive to assist the film formation and adhesion of ZnO and transition metal compounds. Under heating conditions of 700-1000°C, the organic adhesive decomposes and is also unable to provide continuous adhesion of ZnO and transition metal compounds on the Al coating surface.

[0011] Publication No. CN105121691A improves the hot stamping heating performance of a steel plate by adding 0.02-2 mass % of one or more elements selected from the group consisting of Mg, Ga, Sr, Li, Na, and K to an Al-plated layer, and forming a surface film layer containing ZnO stacked on the Al-plated layer. However, changing the composition of the Al-plated layer does not solve the problem that the ZnO surface film layer containing an organic binder cannot effectively adhere to the surface of the Al-plated layer after heating at 700-1000°C.

[0012] Publication No. CN107636200A provides a surface treatment liquid for hot stamping coated steel plates, which includes a ZnO aqueous dispersion and a water-dispersible organic resin. The water-dispersible organic resin acts as a film-forming adhesive after the surface treatment liquid is applied to the surface of the coated steel plate and dried to form a film. According to the processing procedures of hot stamping steel plates, it can be known that under heating conditions of 700-1000°C, the organic resin decomposes due to high temperature, and the ZnO particles cannot form effective adhesion on the coating surface, just like the aforementioned technology.

[0013] In summary, the technology of applying wurtzite ZnO particles and water-based resin on the surface of Al or AlSi coating to improve thermal lubricity and chemical conversion treatment properties is effective to a certain extent. However, as far as water-based resin is concerned, thermal decomposition will occur under high temperature heat treatment conditions, making it impossible for a large number of ZnO particles to form effective adhesion on the coating surface. Therefore, the coating often requires a higher film weight, for example, more than 3g / m 2 Only wurtzite-type ZnO compounds can exhibit significant thermal lubricity. However, the actual thermal lubricity, chemical conversion treatment advantages after thermoforming, and corresponding coating corrosion resistance improvements are unstable. Furthermore, the use of other adhesives, such as silane coupling agents, cannot address the problem of reduced film adhesion due to adhesive decomposition after high-temperature heat treatment. Thermal decomposition products, such as silicon dioxide, can also be introduced, impairing welding and adhesive properties, as well as chemical conversion treatment during coating, affecting the adhesion and corrosion resistance of the finished paint film. Summary of the Invention

[0014] In response to the above-mentioned defects existing in the prior art, the purpose of the present invention is to provide a coated steel plate for hot stamping and an aqueous surface treatment liquid used therein. By designing the composition of the aqueous surface treatment liquid and applying it to the surface of the coated steel plate, the coated steel plate for hot stamping has good high-temperature lubricity during hot stamping processing, improves the processing performance of the coated steel plate for hot stamping, reduces the wear of the hot stamping die surface, reduces the frequency of die repair, and improves production efficiency. In addition, after hot stamping, the coated steel plate for hot stamping can achieve good weldability and adhesion, good chemical conversion treatment properties, and improved corrosion resistance after coating.

[0015] To achieve the above object, the present invention adopts the following technical solutions:

[0016] A first aspect of the present invention provides a coated steel plate for hot stamping, comprising a coated steel plate and a composite film layer formed by coating the coated steel plate with an aqueous surface treatment liquid;

[0017] The coated steel plate comprises a substrate and an Al or AlSi coating provided on one or both sides of the substrate;

[0018] The composite film layer contains a water-based anionic polymer resin A, a tungsten-containing compound B, a zinc-containing compound C, a boron-containing compound D, a water-soluble thickener E, and a water-based surface improvement additive F.

[0019] Preferably, the dry film weight of the composite film layer is 1 to 5 g / m 2 .

[0020] The second aspect of the present invention provides an aqueous surface treatment liquid for a coated steel sheet for hot stamping as described in the first aspect of the present invention, wherein the aqueous surface treatment liquid is formed by dispersing a solid phase in water;

[0021] The solid phase includes the following components in parts by mass:

[0022] Water-based anionic polymer resin A: 15-65 parts;

[0023] Tungsten-containing compound B: 10 to 40 parts by mass of tungsten element;

[0024] Zinc-containing compound C: 3 to 15 parts, calculated by weight of zinc element;

[0025] Boron-containing compound D: 0.004 to 0.03 parts by mass of boron element;

[0026] Water-soluble thickener E: 0.01-0.5 parts;

[0027] Water-based surface improvement agent F: 0.5 to 2 parts.

[0028] Preferably, the aqueous anionic polymer resin A is selected from one or more of aqueous acrylic resins, aqueous epoxy resins, aqueous polyester resins and aqueous alkyd resins; and / or

[0029] The tungsten-containing compound B is selected from one or more of tungsten oxide, tungstate or tungsten metal salt; and / or

[0030] The zinc-containing compound C is selected from zinc oxide, zinc salt or organic zinc compound; and / or

[0031] The boron-containing compound D is selected from boron oxides, borates or organic boron compounds; and / or

[0032] The water-soluble thickener E is selected from one or more of water-soluble hydroxymethyl cellulose, water-dispersible polyacrylic acid alkali swelling emulsion, and water-dispersible nonionic polyurethane associative thickening resin; and / or

[0033] The aqueous surface improvement agent F is selected from one or two of water-dispersible modified polydimethylsiloxane, water-dispersible polyether-modified silicone and / or

[0034] The mass fraction of the aqueous anionic polymer resin A is 20 to 50 parts; and / or

[0035] The mass fraction of the tungsten-containing compound B is 15 to 35, calculated as the mass fraction of the tungsten element.

[0036] Preferably, the number average molecular weight of the aqueous anionic polymer resin A is greater than 8000, and the mass fraction of harmful substances generated after the aqueous anionic polymer resin A is burned is less than 1wt% of the total solid content of the aqueous anionic polymer resin A; and / or

[0037] When the tungsten-containing compound B is a water-insoluble tungsten compound, the particle size of the tungsten-containing compound B is 5 to 1000 nm; and / or

[0038] When the zinc-containing compound C is a water-insoluble zinc compound, the particle size of the zinc-containing compound C is 5 to 1000 nm; and / or

[0039] The mass ratio of the boron-containing compound D to the zinc-containing compound C is 150 / 1 to 750 / 1; and / or

[0040] The number average molecular weight of the water-soluble thickener E is between 50,000 and 100,000.

[0041] Preferably, the particle size of the tungsten-containing compound B is 20 to 500 nm; and / or

[0042] The particle size of the zinc-containing compound C is 20 to 500 nm.

[0043] The third aspect of the present invention provides a method for preparing a coated steel plate for hot stamping as described in the first aspect of the invention, wherein an aqueous surface treatment liquid is applied to a cleaned Al-plated or AlSi-plated steel plate, and the aqueous surface treatment liquid is solidified at a temperature of 80 to 180°C on the Al-plated or AlSi-plated steel plate to form a composite film layer.

[0044] A fourth aspect of the present invention provides a hot stamping method for a coated steel sheet for hot stamping as described in the first aspect of the invention, wherein the coated steel sheet for hot stamping is punched out, heated, and then stamped.

[0045] Preferably, during the heating process, the hot stamping coated steel sheet after punching is heated from 50° C. to the limit plate temperature and kept warm for 30 to 60 seconds; then the heated hot stamping coated steel sheet is transferred to a mold with a cooling effect for stamping.

[0046] Preferably, during the heating process, the average heating rate is 12 to 200°C / s, and the limit plate temperature of the hot stamping coated steel plate is 850 to 980°C; and / or

[0047] The stamping process is carried out in air, and before the temperature of the hot stamping coated steel sheet drops to 400°C, the cooling rate is ≥27°C.

[0048] The present invention provides a coated steel plate for hot stamping and an aqueous surface treatment liquid therefor, which also has the following beneficial effects:

[0049] 1. The coated steel sheet for hot stamping of the present invention and the aqueous surface treatment liquid used therein, by designing the composition of the aqueous surface treatment liquid and applying it to the surface of the coated steel sheet, enable the coated steel sheet for hot stamping to have good high-temperature lubricity during hot stamping processing, improve the processing performance of the coated steel sheet for hot stamping, reduce the wear of the hot stamping die surface, reduce the frequency of die repair, and improve production efficiency. In addition, after hot stamping, the coated steel sheet for hot stamping can achieve good weldability and adhesion, good chemical conversion treatability, and improved corrosion resistance after coating;

[0050] 2. The present invention can provide Al or AlSi-coated steel plate products for hot forming and a matching aqueous surface treatment solution. The treated products and aqueous surface treatment solution do not contain harmful elements such as chromium, and have little impact on the environment.

[0051] 3. The hot stamping coated steel sheet of the present invention has a composite film containing tungsten (W), zinc (Zn) and an organic resin coated on its surface. This composite film has an anti-corrosion effect, equivalent to that of rust-proof oil, and can withstand long-term transportation or storage without the protection of rust-proof oil. In addition, the hot stamping coated steel sheet has stable thermal lubricity during hot stamping, good chemical conversion treatability after hot stamping, corrosion resistance after coating, and spot welding performance.

[0052] 4. The aqueous surface treatment liquid used for the hot stamping coated steel plate of the present invention has good workability and storage stability;

[0053] 5. The manufacturing method of the coated steel sheet for hot stamping and the hot stamping method of the present invention have few process steps and are easy to implement. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments with reference to the following drawings:

[0055] Figure 1 Schematic diagram of the structure of the coated steel plate for hot stamping of the present invention;

[0056] Figure 2 A schematic diagram of a testing machine for testing the high-temperature friction coefficient of a plate and strip used in an embodiment of the present invention;

[0057] Among them, 10 is a substrate, 11 is an Al or AlSi coating, 12 is a composite film layer; 20 is a sample to be tested, 21 is a motor, 22 is a coupling, 23 is a transmission shaft, 24 is a recorder, 25 is a force sensor, 26 is an upper mold, 27 is a cooling water channel, 28 is a lower mold, and 29 is a heating furnace. DETAILED DESCRIPTION

[0058] In order to better understand the above technical solution of the present invention, the technical solution of the present invention is further described below with reference to embodiments.

[0059] Combine Figure 1 As shown, the present invention provides a coated steel sheet for hot stamping, comprising a coated steel sheet and a composite coating layer 12 formed by applying an aqueous surface treatment liquid onto the coated steel sheet. The coated steel sheet comprises a substrate 10 and an Al or AlSi coating layer 11 disposed on one or both sides of the substrate 10. The composite coating layer 11 contains an aqueous anionic polymer resin A, a tungsten-containing compound B, a zinc-containing compound C, a boron-containing compound D, a water-soluble thickener E, and an aqueous surface-improving agent F.

[0060] The dry film weight of the composite film layer is 1 to 5 g / m 2 , that is, the thickness of the composite film layer on one side is controlled at 1 ~ 5g / m 2 The reason is that when the composite membrane weight is less than 1g / m 2 Due to the small amount of film, the lubrication function of the processing is reduced during the hot forming stamping process. When the film weight of the composite film exceeds 5g / m 2 On the one hand, the surface treatment cost per unit area of ​​the steel plate will increase. On the other hand, an overly thick film may not be able to completely decompose the organic components in the composite film during the heat treatment process. Some inorganic substances in the film cannot form good adhesion with the surface of the Al-plated or AlSi-plated steel plate by sintering, and pollute the furnace and mold in the form of combustion residues.

[0061] The mass fractions of each solid component in the composite film layer are as follows: aqueous anionic polymer resin A: 15 to 65 parts; tungsten-containing compound B: 10 to 40 parts, calculated as the mass fraction of tungsten element; zinc-containing compound C: 3 to 15 parts, calculated as the mass fraction of zinc element; boron-containing compound D: 0.004 to 0.03 parts, calculated as the mass fraction of boron element; water-soluble thickener E: 0.01 to 0.5 parts; aqueous surface improvement additive F: 0.5 to 2 parts.

[0062] The water-based anionic polymer resin A is selected from one or more composite resins selected from water-based acrylic resins, water-based epoxy resins, water-based polyester resins, and water-based alkyd resins. The number average molecular weight of the water-based anionic polymer resin A should be greater than 8000, and the mass fraction of nitrogen, sulfur, and chlorine elements, which may produce harmful substances after combustion of the water-based anionic polymer resin A, should be less than 1wt% of the total solid content of the water-based anionic polymer resin A. The water-based anionic polymer resin A can be dispersed in water in the form of an aqueous solution, a water dispersion, or an emulsion.

[0063] The weight fraction of aqueous anionic polymer resin A in the solid phase is controlled between 15 and 65 parts by weight. This is because, if the weight fraction of aqueous anionic polymer resin A is less than 15 parts by weight, the adhesion of the composite film formed by aqueous anionic polymer resin A to the surface of the Al- or AlSi-coated steel sheet for hot stamping may be reduced. However, if the weight fraction of aqueous anionic polymer resin A exceeds 65 parts by weight, the relative proportion of tungsten-containing compound B, which primarily provides high-temperature lubrication, in the composite film on the Al- or AlSi-coated steel sheet for hot stamping decreases, potentially failing to provide sufficient lubrication during hot stamping. In a further preferred embodiment, the weight fraction of aqueous anionic polymer resin A is between 20 and 50 parts by weight.

[0064] The tungsten-containing compound B, which has a high-temperature lubricating function, is controlled within a range of 10 to 40 parts by weight, calculated as elemental tungsten. This is because when the tungsten-containing compound B, which has a high-temperature lubricating function, has less than 10 parts by weight, calculated as elemental tungsten, it has no additive effect and cannot provide high-temperature lubrication. However, when the tungsten-containing compound B, which has a high-temperature lubricating function, has more than 40 parts by weight, calculated as elemental tungsten, the performance of the composite coating layer deteriorates, potentially affecting adhesion between the coating and the Al- or AlSi-coated steel sheet, water resistance, corrosion resistance, and other properties, and increasing production costs. In a preferred embodiment, the tungsten-containing compound B, which has a high-temperature lubricating function, is controlled within a range of 15 to 35 parts by weight, calculated as elemental tungsten.

[0065] In a preferred embodiment, the tungsten-containing compound B with high-temperature lubrication function is formed during the hot stamping process to form tungsten oxide and tungstate compounds with lubrication function, which act on the interface between the Al or AlSi coated steel plate and the mold to achieve lubrication. The source of the tungsten-containing compound B can be tungsten oxide, such as tungsten trioxide (WO3), tungsten dioxide (WO2) or blue tungsten (WO 2.72 , WO 2.90 、W 20 O 58 and (NH4) хWO3, etc.), or tungstate compounds such as sodium tungstate (Na2WO4), potassium tungstate (K2WO4), lithium tungstate (Li2WO4), magnesium tungstate (MgWO4), calcium tungstate (CaWO4), cobalt tungstate (CoWO4), cadmium tungstate (CdWO4), ferrous tungstate (FeWO4), ammonium tungstate [(NH4)6W7O 24 ] and zinc tungstate (5ZnO·12WO3), etc., or tungsten metal salts such as tungsten chloride [tungsten hexachloride (WCl6), tungsten pentachloride (WCl5), tungsten tetrachloride (WCl4), tungsten dichloride (WCl2)], etc., or other types of tungsten-containing compounds such as nano-tungsten carbide (WC), tungsten disulfide (WS2) and tungsten diselenide (WSe2). The tungsten-containing compound B with high-temperature lubrication function can include one or more tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds, which can be the same tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds, or a mixture of different tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds.

[0066] The tungsten-containing compound B with high-temperature lubrication function will undergo thermal decomposition and thermochemical reaction during the hot stamping heating process (the limit temperature reaches 850℃~980℃). Therefore, from the perspective of environmental protection and protecting the safety of operators and equipment, it is prudent to select tungsten-containing compounds that will decompose and produce harmful substances at high temperatures. In a preferred embodiment, the tungsten-containing compound B can be at least one of tungsten trioxide (WO3), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), magnesium tungstate (MgWO4), ammonium tungstate [(NH4)6W7O24] and nano tungsten carbide (WC).

[0067] The tungsten-containing compound B with high-temperature lubrication can be uniformly dispersed in the surface composite film in the form of a powder or solute. In a preferred embodiment, to improve the dispersibility of the tungsten-containing compound B with high-temperature lubrication, a water-based anionic polymer resin A with good compatibility can be selected. For the powder form, 0.01 to 0.5 parts of a dispersant can be added to improve the dispersion of the tungsten-containing compound B within the water-based anionic polymer resin A matrix. This ensures that the tungsten-containing compound B with high-temperature lubrication maintains substantially stable physical properties below 200°C, preventing agglomeration or segregation in the composite film.

[0068] The tungsten-containing compound B with high-temperature lubrication function, such as tungsten oxide, tungstate, tungsten salt or other tungsten-containing compound insoluble in water, has a particle size in the powder form of 5 to 1000 nm, and a further preferred particle size of 20 to 500 nm.

[0069] The tungsten-containing compound B with high-temperature lubrication function is a suitable high-temperature lubricant in the hot stamping process. The reason is that the tungsten-containing compound B, such as tungsten oxide, tungstate, tungsten salt or other tungsten-containing compounds, can be partially or completely decomposed (or converted) into solid lubricant tungsten oxide (WO) with high ionic potential at high temperature. x ), such as tungstate can undergo replacement reaction with Al2O3 on the surface of Al or AlSi coating at high temperature The tungsten oxide formed forms WO3 with high-temperature lubrication function, and the formed tungsten oxide forms good adhesion with the Al or AlSi coating at high temperatures. In addition, zinc tungstate (5ZnO·12WO3), nano-tungsten carbide (WC), tungsten disulfide (WS2) and tungsten diselenide (WSe2) also have good high-temperature oxidation resistance and high-temperature lubrication properties.

[0070] The zinc compound C, calculated as elemental zinc, is controlled to contain 3 to 15 parts by weight because: when the zinc compound C, calculated as elemental zinc, contains less than 3 parts by weight, it has no additive effect and cannot effectively improve the chemical conversion treatment of hot-formed parts and the corrosion resistance after painting. When the zinc compound C, calculated as elemental zinc, contains more than 15 parts by weight, it may lead to poor adhesion between the surface composite coating and the Al- or AlSi-plated steel sheet, and the zinc-containing conversion layer after hot-forming cannot form good adhesion to the surface of the coated steel sheet. When the zinc compound C is selected from a water-insoluble zinc compound, its powder particle size should be controlled between 5 and 1000 nm to ensure uniform dispersion in the surface composite film. In a further preferred embodiment, the particle size of the zinc compound C is controlled between 20 and 500 nm.

[0071] The boron compound D, calculated as elemental boron, is controlled to be between 0.004 and 0.03 parts by mass because: when the boron compound D, calculated as elemental boron, is less than 0.004 parts by mass, it has no additive effect and cannot effectively improve the adhesion of the film layer to the Al or AlSi-coated steel sheet after hot forming. When the boron compound D, calculated as elemental boron, is greater than 0.03 parts by mass, it degrades the reactivity of the composite film layer with chemical treatment agents and coating performance after hot forming. The boron compound D can be derived from a boron oxide, such as boron oxide (B2O3), a borate, such as magnesium borate (MgHBO3), sodium tetraborate (Na2B4O7), sodium borohydride (NaBH4), or an organoboron compound, such as borane, carborane, methyl borate, and an organoborate.

[0072] The mass fraction ratio (W) of the boron compound D and the zinc compound C calculated as elemental zinc (Zn) and boron (B) respectively Zn / W B) is 150 / 1 to 750 / 1. Boron-containing compound D is a suitable adhesion promoter during the hot forming process because boron oxides, borates, or organoboron compounds can decompose into B2O3 under heat treatment, acting as a flux and network former. For example, with zinc-containing compound C, it forms a zinc borate (B2O6Zn3) solid solution, improving the adhesion of the surface composite film layer to the Al- or AlSi-coated steel sheet after hot forming.

[0073] The reason for adding 0.01 to 0.5 parts of water-soluble thickener E is that when its mass fraction is less than 0.01 parts, it has no obvious thickening effect, and when its mass fraction exceeds 0.5 parts, it is very likely to cause the surface composite film on the surface of Al or AlSi coated steel plate to have poor uniformity in film weight.

[0074] The water-soluble thickener E is selected from one or a mixture of two or more of water-soluble hydroxymethyl cellulose, water-dispersible polyacrylic acid alkali-swellable emulsion, and water-dispersible nonionic polyurethane associative thickening resin. The number average molecular weight of the water-soluble thickener E, water-soluble hydroxymethyl cellulose, water-dispersible polyacrylic acid alkali-swellable emulsion, and water-dispersible nonionic polyurethane associative thickening resin is between 50,000 and 100,000.

[0075] The reason why the addition amount of water-based surface improvement agent F is between 0.5 and 2 parts is that when its mass fraction is less than 0.5 parts, the composite film layer cannot form a well-spread and uniform film on the surface of the Al or AlSi-coated steel plate. When the mass fraction exceeds 2 parts, it is very likely to cause shrinkage holes, pinholes and the like in the composite film layer.

[0076] The water-based surface improvement additive F is selected from one of water-dispersible modified polydimethylsiloxane and water-dispersible polyether-modified silicone, or a mixture of the two.

[0077] The aqueous surface treatment liquid used for the hot stamping coated steel plate in the present invention is prepared by dispersing a solid phase in water, wherein the solid phase includes the following components in parts by mass: aqueous anionic polymer resin A: 15 to 65 parts; tungsten-containing compound B: 10 to 40 parts, calculated as the mass of the tungsten element; zinc-containing compound C: 3 to 15 parts, calculated as the mass of the zinc element; boron-containing compound D: 0.004 to 0.03 parts, calculated as the mass of the boron element; water-soluble thickener E: 0.01 to 0.5 parts; and aqueous surface improvement additive F: 0.5 to 2 parts.

[0078] The aqueous anionic polymer resin A is selected from one or more of a water-based acrylic resin, a water-based epoxy resin, a water-based polyester resin, and a water-based alkyd resin. The number average molecular weight of the aqueous anionic polymer resin A should be greater than 8,000, and the mass fraction of nitrogen, sulfur, and chlorine, which may generate harmful substances upon combustion, should be less than 1% of the total solid content of the aqueous anionic polymer resin A. The aqueous anionic polymer resin A can be in the form of an aqueous solution, a water dispersion, or an emulsion. The mass fraction of the aqueous anionic polymer resin A is controlled to be between 15 and 65 parts by mass because, if the mass fraction of the aqueous anionic polymer resin A is less than 15 parts by mass, the adhesion of the aqueous surface treatment agent to the surface of the Al- or AlSi-coated steel sheet for hot stamping may be reduced. If the mass fraction of the aqueous anionic polymer resin A exceeds 65 parts by mass, the relative proportion of the tungsten-containing compound B, which primarily provides high-temperature lubrication, in the surface coating of the Al- or AlSi-coated steel sheet for hot stamping may decrease, potentially failing to provide sufficient lubrication during the hot forming process. In a preferred embodiment, the mass fraction of the aqueous polymer resin A is 20 to 50 parts.

[0079] The tungsten-containing compound B, which has a high-temperature lubricating function, has a weight content of 10 to 40 parts by weight, calculated as elemental tungsten. This is because: if the weight content of the tungsten-containing compound B, calculated as elemental tungsten, is less than 10 parts by weight, it has no additive effect and cannot provide high-temperature lubrication. However, if the weight content of the tungsten-containing compound B, calculated as elemental tungsten, is greater than 40 parts by weight, the performance of the aqueous surface treatment fluid deteriorates, potentially affecting reservoir stability and fluidity during construction, and increasing the production cost of the aqueous surface treatment fluid. In a preferred embodiment, the weight content of the tungsten-containing compound B, calculated as elemental tungsten, is controlled to be between 15 and 35 parts by weight.

[0080] The source of the tungsten-containing compound B can be tungsten oxide, such as tungsten trioxide (WO3), tungsten dioxide (WO2) or blue tungsten (WO 2.72 , WO 2.90 、W 20 O 58 and (NH4) х WO3, etc.), or tungstate compounds such as sodium tungstate (Na2WO4), potassium tungstate (K2WO4), lithium tungstate (Li2WO4), magnesium tungstate (MgWO4), calcium tungstate (CaWO4), cobalt tungstate (CoWO4), cadmium tungstate (CdWO4), ferrous tungstate (FeWO4), ammonium tungstate [(NH4)6W7O 24] and zinc tungstate (5ZnO·12WO3), etc., or tungsten metal salts such as tungsten chlorides [tungsten hexachloride (WCl6), tungsten pentachloride (WCl5), tungsten tetrachloride (WCl4), tungsten dichloride (WCl2)], etc., or other types of tungsten-containing compounds such as nano-tungsten carbide (WC), tungsten disulfide (WS2) and tungsten diselenide (WSe2). The tungsten-containing compound B with high-temperature lubrication function can include one or more tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds, which can be the same tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds, or a mixture of different tungsten oxides, tungstates, tungsten salts or other tungsten-containing compounds. In addition, from the perspective of environmental protection and the protection of operator and equipment safety, it is prudent to select tungsten-containing compounds that will decompose and produce harmful substances at high temperatures (the limit temperature reaches 850℃~980℃). In the preferred embodiment, the tungsten-containing compound B can be tungsten trioxide (WO3), sodium tungstate (Na2WO4), potassium tungstate (K2WO4), magnesium tungstate (MgWO4), ammonium tungstate [(NH4)6W7O 24 ] and at least one of nano tungsten carbide (WC).

[0081] The tungsten-containing compound B can be uniformly dispersed or dissolved in the aqueous surface treatment liquid in the form of a powder or solute. In a preferred embodiment, to enhance the dispersion or dissolution of the tungsten-containing compound B with high-temperature lubrication properties, a compatible aqueous anionic polymer resin A can be selected. For the powdered form, 0.01 to 0.5 parts of a water-soluble thickener E can be added to improve the dispersion of the tungsten-containing compound B in the aqueous surface treatment liquid. This ensures that the high-temperature lubrication compound B maintains substantially stable physical properties below 200°C and does not agglomerate or segregate in the surface treatment agent. When the tungsten-containing compound B is a water-insoluble tungsten oxide, tungstate, tungstate salt, or other tungsten-containing compound, the particle size of the powder should be controlled between 5 and 1000 nm, preferably between 20 and 500 nm.

[0082] The source of zinc compound C can be zinc oxide, such as zinc oxide (ZnO), zinc salt, such as zinc nitrate (ZnNO3), zinc chloride (ZnCl2), etc., or organic zinc compound, such as zinc acetate (Zn(Ac)2), zinc stearate (C 36 H 70O4Zn), etc. The weight fraction of the zinc-containing compound C, calculated as elemental zinc, is controlled to be 3 to 15 parts because: when the weight fraction of the zinc-containing compound C, calculated as elemental zinc, is less than 3 parts, the additive has no effect and cannot effectively improve the chemical conversion treatment of the part after hot forming and the corrosion resistance after painting. When the weight fraction of the zinc-containing compound C, calculated as elemental zinc, is greater than 15 parts, the adhesion of the coating to the Al- or AlSi-plated steel sheet may deteriorate, and the conversion layer containing zinc after hot forming may also fail to form good adhesion to the surface of the coated steel sheet. When the zinc-containing compound C is selected to be a zinc-containing compound that is insoluble in water, in order to ensure uniform dispersion in the aqueous surface treatment solution, the particle size of the powder should be controlled to be 5 to 1000 nm, preferably 20 to 500 nm.

[0083] The source of the boron-containing compound D can be boron oxide, such as boron oxide (B2O3), or borate, such as magnesium borate (MgHBO3), sodium tetraborate (Na2B4O7), sodium borohydride (NaBH4), etc., or organic boron compounds, such as borane, carborane, methyl borate and organic borate, etc. The reason why the mass fraction of the boron-containing compound D calculated as elemental boron is controlled to be 0.004 to 0.03 parts is that: when the mass fraction of the boron-containing compound D calculated as elemental boron is less than 0.004, there is no additive effect, and it cannot effectively improve the adhesion of the film layer after hot forming to the surface of the Al or AlSi coated steel plate, and when the mass fraction of the boron-containing compound D calculated as elemental boron is greater than 0.03, the reactivity of the film layer after hot forming with the chemical treatment agent and the coating performance will be deteriorated. The mass fraction ratio (W) of the boron-containing compound D and the above-mentioned zinc-containing compound C calculated as elemental zinc (Zn) and boron (B) is 0.004 to 0.03 parts. Zn / W B ) is: 150 / 1~750 / 1.

[0084] The water-soluble thickener E is selected from one or a mixture of two or more of the following: water-soluble hydroxymethyl cellulose, a water-dispersible polyacrylic acid alkali-swellable emulsion, and a water-dispersible nonionic polyurethane associative thickening resin. The number average molecular weight of the water-soluble thickener E is between 50,000 and 100,000. The reason for adding 0.01 to 0.5 parts by weight of the water-soluble thickener E is that when its weight is less than 0.01 parts by weight, it will not have a significant thickening effect. When its weight exceeds 0.5 parts by weight, it is very likely to cause poor leveling of the aqueous surface treatment liquid after application.

[0085] The water-based leveling agent F is selected from one or a mixture of water-dispersible modified polydimethylsiloxane and water-dispersible polyether-modified silicone. The reason for adding 0.5 to 2 parts by weight of the water-based leveling agent F is that when its weight is less than 0.5 parts by weight, the water-based surface treatment liquid cannot effectively spread and level the surface of the Al- or AlSi-coated steel plate. When its weight exceeds 2 parts by weight, it is very likely to cause shrinkage holes and pinholes in the water-based surface treatment liquid during the drying process after application.

[0086] The aqueous surface treatment liquid is applied to a cleaned Al- or AlSi-plated steel sheet, and the aqueous surface treatment liquid solidifies at a temperature of 80 to 180°C to form a composite film layer on the Al- or AlSi-plated steel sheet, thereby obtaining a coated steel sheet for hot stamping. The Al- or AlSi-plated steel sheet having a composite film layer on its surface obtained by the above method has excellent hot stamping workability, excellent weldability after forming, and good paintability. The aqueous surface treatment liquid can be applied to the Al- or AlSi-plated steel sheet by roller coating, dipping, or spraying. The aqueous surface treatment liquid can be applied to one or both sides of the Al- or AlSi-plated steel sheet.

[0087] The surface treatment liquid is cured at a temperature of 80-200°C because temperatures between 80-180°C can volatilize the solvent water and water-soluble low-boiling-point additives in the aqueous surface treatment liquid, promoting the crosslinking and film formation of the aqueous anionic polymer resin A. When the curing temperature is lower than 80°C, the dry film crosslinking of the composite film formed between the aqueous surface treatment liquid and the Al- or AlSi-plated steel plate is insufficient, potentially resulting in decreased adhesion of the dry film. When the curing temperature is higher than 180°C, the energy cost of the surface treatment of the steel plate is increased, and the properties of some composite film layers are altered, thereby adversely affecting the dry film of the composite film. There are no particularly strict restrictions on the heating and drying method of the aqueous surface treatment liquid applied to the surface of the Al- or AlSi-plated steel plate, and various heating methods such as hot air heating, induction heating, and infrared heating can be used.

[0088] The present invention also provides a hot stamping method for hot stamping coated steel plates, wherein any one of the above-mentioned Al-plated or AlSi-plated steel plates for hot stamping having a composite film layer on the surface is punched out and then heated, and then subjected to stamping. During the heating process, the punched hot stamping coated steel plate is heated from 50°C to the limit plate temperature and kept warm for 30 to 60 seconds; the heated hot stamping coated steel plate is then transferred to a mold with a cooling effect for stamping. During the heating process, the average heating rate is 12 to 200°C / s, and the limit plate temperature of the hot stamping coated steel plate is 850 to 980°C; the stamping process is carried out in air, and before the temperature of the hot stamping coated steel plate drops to 400°C, the cooling rate is ≥27°C.

[0089] The following further describes a hot stamping coated steel plate and its aqueous surface treatment solution with reference to specific examples.

[0090] Examples 1 to 32 and Comparative Examples 1 to 8

[0091] The substrates of Examples 1 to 32 and Comparative Examples 1 to 8 are all hot-dip aluminum silicon (AlSi) alloy coated steel sheets. The surface treatment liquid is applied to the clean surface of the AlSi alloy coated steel sheet and dried at 80 to 200° C. to form a dry film with a film weight of 1 to 5 g / m2 on the surface of the AlSi alloy coated steel sheet. 2 composite film layer.

[0092] The steel plates selected are preferably subjected to a hot stamping process to achieve different strength levels (involving various properties related to mechanical deformation and damage, such as tensile strength, yield strength, elongation after fracture, hardness, cold bending angle, etc.). One embodiment of the present invention is to select steel plates that can achieve a yield strength of ≥950Mpa, a tensile strength of ≥1300Mpa, an elongation after fracture of ≥5% (A 50mm ), steel plates with hardness HV10 ≥ 400 (or HRC ≥ 40) and cold bending angle VDA (1.4mm) ≥ 45°.

[0093] The chemical composition of the steel plate is calculated by mass wt% as follows: 0.20-0.25wt% carbon (C), 0.01-0.4wt% silicon (Si), 1.0-1.4wt% manganese (Mn), 0.02-0.05wt% titanium (Ti), 0.001-0.005wt% boron (B), and the balance is iron (Fe) and other inevitable impurities.

[0094] The addition of C ensures the mechanical strength of the steel sheet. When the C content is less than 0.2wt%, the yield strength and tensile strength described cannot be obtained. On the other hand, when the C content exceeds 0.25wt%, although the steel sheet can be further hardened, melt cracks are easily generated during hot stamping, resulting in a decrease in elongation at break and cold bending angle performance. Therefore, the C content is preferably 0.20-0.25wt%.

[0095] Si, like C, is an element that ensures the mechanical strength of steel sheets. If the Si content is less than 0.01 wt%, the mechanical strength enhancement effect is not achieved, and the yield strength and tensile strength described above cannot be achieved. On the other hand, Si is an easily oxidized element. If the Si content exceeds 0.4 wt%, it reduces the surface energy of the steel sheet, affecting wettability during hot-dip plating, resulting in plating skipping or non-plating. Therefore, the Si content is preferably between 0.01 and 0.4 wt%.

[0096] Mn is an element that improves the hardenability of steel sheets after hot stamping and increases the strength of the steel sheets. In addition, Mn reacts with the impurity element sulfur (S) to form manganese sulfide (MnS), thereby preventing the steel sheets from becoming hot brittle due to S. When the Mn content is less than 1.0wt%, the yield strength and tensile strength described cannot be obtained. On the other hand, when the Mn content exceeds 1.4wt%, the residual γ phase after hot stamping is too much, which may lead to a decrease in the yield strength and tensile strength described. Therefore, the Mn content is preferably 1.0 to 1.4wt%.

[0097] The addition of Ti improves the strength of the steel sheet and the heat resistance of the Al-based coating. However, if the Ti content is less than 0.02 wt%, the mechanical strength and oxidation resistance effects are not achieved. On the other hand, if the Ti content exceeds 0.05 wt%, the excessive Ti reacts with elements such as C and N to form carbides and nitrides that soften the steel, potentially failing to achieve the desired yield and tensile strengths. Therefore, the Ti content is preferably between 0.02 and 0.05 wt%.

[0098] B is an element that improves the mechanical strength of steel sheets during quenching. If the B content is less than 0.001 wt%, the post-quenching strength improvement effect is lost, and the yield and tensile strengths described cannot be achieved. On the other hand, if the B content exceeds 0.005 wt%, the rolling load during hot rolling increases significantly, and inclusions are more likely to form in the steel sheet, causing embrittlement and potentially reducing the fatigue strength of the steel sheet. Therefore, the B content is preferably between 0.001 and 0.005 wt%.

[0099] The composition of the steel sheet before plating described above is merely an example; other compositions are possible. For example, as deoxidizing elements, 0.01-0.06 wt% aluminum (Al) and 0.01-0.35 wt% chromium (Cr) may also be included, similar to Mn in improving hardenability. Furthermore, steel sheets also contain impurities that inevitably enter during the manufacturing process.

[0100] The Al or AlSi coating is formed on one or both sides of the pre-plated steel sheet. In this embodiment, hot-dip coating is used, but this method is not limited to this. The Al or AlSi coating prevents the formation of oxide scale (primarily Fe oxide) on the steel sheet surface during the heating process during hot stamping. Therefore, it is preferably applied to both sides of the steel sheet. The Al coating composition only requires an Al component content of 70 wt% or greater, and elements other than Al are not particularly limited.

[0101] The AlSi coating used in this embodiment contains, in addition to the Al component, silicon (Si). Si participates in the formation of tough phases such as Fe2SiAl7, Fe2SiAl2, and Fe(Al,Si) at the interface between the steel strip and the coating during hot-dip plating, inhibiting the formation of Fe-Al brittle phases at the interface. When the Si addition in the coating is less than 5wt%, the Fe-Al brittle phase accounts for a high proportion at the interface between the coating and the substrate during hot-dip plating, and cracks that penetrate the coating are easily formed during processing, thereby impairing the corrosion resistance of the processed parts. In addition, when the Si addition is greater than 11wt%, the corrosion resistance and weldability of the coating are reduced. Therefore, the Si addition in the AlSi coating is preferably 5-11wt%.

[0102] In addition to Si, the AlSi coating also contains 2 to 4 wt% of Fe dissolved from the equipment, steel strip or plate during the coating process. It may also contain elements such as Zn, Mg, Ca, and Mn, and the rest is Al.

[0103] The AlSi coating is alloyed with Fe in the steel sheet to varying degrees during the hot-dip and hot stamping heating processes. Therefore, the coating does not necessarily consist of a single layer with uniform composition, but may include a structure of phase separation layers (alloy layers) with varying degrees of alloying. AlSi-coated steel sheets are obtained by immersing pretreated steel strips in a molten solution consisting of Al and 5-11% by weight (wt) of Si on a continuous hot-dip AlSi production line. The coating amount of the AlSi coating is preferably 25-90 g / m² per side. 2 . Plating amount is less than 25g / m 2 In the case of the above-mentioned Al or AlSi coating, the effect of anti-oxidation of the steel substrate cannot be fully obtained. In addition, the coating amount is greater than 90g / m 2 In the case of hot stamping, the surface roughness increases, and the high hardness Al-Fe alloy layer is formed during the hot stamping heating process, and the surface roughness further increases, resulting in an increase in the friction coefficient during the hot stamping process. Therefore, the coating amount of the AlSi coating is preferably 25 to 90 g / m2 per side. 2 .

[0104] Table 1 lists the mass fractions of each solid component in the composite film on the surface of the AlSi-coated steel plate and the aqueous surface treatment liquid in Examples 1 to 30 and Comparative Examples 1 to 8.

[0105] Table 1 Mass fractions of each solid component in the composite film on the surface of AlSi-coated steel plate and the aqueous surface treatment solution

[0106]

[0107]

[0108] *Note: A1 is water-based acrylic resin, A2 is water-based epoxy resin, A3 is water-based alkyd resin; B1-1 is nano-tungsten trioxide (~20nm), B1-2 is nano-tungsten trioxide (~200nm), B1-3 is nano-tungsten trioxide (~500nm), B2 is sodium tungstate, B3 is potassium tungstate, B4 is magnesium tungstate, B5 is ammonium tungstate; B6 is tungsten carbide; C1-1 is nano-zinc oxide (~20nm), C 1-2 is nano zinc oxide (~200nm), C1-3 is nano zinc oxide (~500nm), C2 is zinc nitrate, and C3 is zinc stearate; D1 is boron oxide, and D2 is sodium tetraborate; E1 is water-soluble hydroxymethyl cellulose, E2 is a water-dispersible polyacrylic acid alkali swelling emulsion, and E3 is a water-dispersible nonionic polyurethane associative thickening resin; F1 is a water-dispersible modified polydimethylsiloxane, and F2 is a water-dispersible polyether modified silicone.

[0109] Table 2 lists the specifications of the AlSi coated steel sheets in Examples 1 to 32 and Comparative Examples 1 to 8 and the specific parameters when curing the dry film of the organic composite coating.

[0110] Table 2 Specifications of AlSi coated steel plates and specific parameters when curing the dry film of organic composite coatings

[0111]

[0112] The AlSi-plated steel sheets in Examples 1 to 32 and Comparative Examples 1 to 8 were sampled and tested according to the following test methods, and the test data obtained for evaluating various properties are listed in Table 3. The tests for evaluating various performance parameters are as follows:

[0113] 1) Adhesion of surface film

[0114] Apply 3M 610 tape to the surface of an AlSi-coated steel plate, ensuring full contact between the tape and the steel surface. Then, quickly remove the tape at a 60° angle to the specimen surface. XRF was used to determine the residual W or Zn (for comparative examples) content before and after the specimen was tested.

[0115] ◎(Excellent): Residue 95-100%

[0116] ○ (good): Residue 80-94%

[0117] △(Medium): Residue 50-79%

[0118] ×(bad): Residue <49%

[0119] 2)Solvent resistance:

[0120] The surface of the AlSi-plated steel plate was wiped back and forth 30 times with a fine gauze dipped in 80% ethanol, and the residual amount of W element or Zn element (comparative example) before and after the sample was determined by XRF.

[0121] ◎(Excellent): Residue 95-100%

[0122] ○ (good): Residue 80-94%

[0123] △(Medium): Residue 50-79%

[0124] ×(bad): Residue <49%

[0125] 3) Resistance to moisture and heat:

[0126] The AlSi plated steel plate was placed in a constant temperature and humidity chamber at 49°C and 98% humidity for 120 hours. Evaluation criteria:

[0127] ◎(Excellent): Surface rust area ≤5%

[0128] ○(Good): Surface rust area 5% to 10%

[0129] △(middle): surface rust area 11% to 50%

[0130] ×(poor): surface rust area>51%

[0131] 4) Thermal lubricity:

[0132] Used Figure 2 The plate and strip high temperature friction coefficient tester shown in the figure is to weld a thermocouple to a 500×100mm test sample 20, insert it into a 930°C heating furnace 29 and keep it for 4 minutes. The stepper motor 21 is operated to drive the coupling 22 to pull out the test material. When the surface temperature of the test sample 20 drops to 700°C, a pressure of 3MPpa is applied to the surface of the test sample through the mold (mold area (10×10mm). The mold surface is cooled by a water cooling channel inside the mold. The test sample 21 is dragged at a speed of 20mm / s by the stepper motor 21 to drive the coupling 22, and the pulling load is recorded by the force sensor 25. The value obtained by pulling load / (2×loaded pressure×mold area) is used as the thermal friction coefficient. The evaluation criteria are as follows:

[0133] ◎(Excellent): Thermal friction coefficient ≤0.35

[0134] ○(Good): Thermal friction coefficient 0.35~0.4

[0135] △(Medium): Thermal friction coefficient 0.4~0.5

[0136] ×(bad): thermal friction coefficient>0.5

[0137] 5) Spot weldability:

[0138] Place the sample to be tested in a heating furnace at 930℃ for 4 minutes, then take it out and immediately place it in a stainless steel flat mold with water cooling function for rapid cooling. The cooling rate is 100℃ / second. Then cut the sample to be tested into 30×80mm and measure the available current range of spot welding (the difference between the upper limit current and the lower limit current). The measurement conditions are as follows: the lower limit current is when the fusion diameter reaches 4.25d 1 / 2 (d: plate thickness) When the current is taken, taking the plate thickness of 1.4mm as an example, the lower limit current is 5.0kA, and the upper limit current is the current when the welding spatter phenomenon just occurs.

[0139] Electrode: Chrome copper, DR type (top diameter 6mm, 40R radius)

[0140] Pressurization: 4300N

[0141] Power-on time: 20 cycles (50Hz)

[0142] The evaluation criteria are as follows:

[0143] ○(Good): Available current range ≥1.5kA

[0144] ×(difference): Available current range <1.5kA

[0145] 5) Adhesion:

[0146] Place the test sample into a 930°C heating furnace and keep it for 4 minutes. After taking it out, immediately place it in a stainless steel flat mold with water cooling function for rapid cooling. The cooling rate is 100°C / second. Then cut the test sample into 25×100mm. After wiping the surface of the sample with acetone to remove surface dirt, immerse the sample in anti-rust oil for 3-5 seconds, take it out and keep it at a vertical angle for 24 hours, apply 13mm long and 0.1mm thick (glass beads are used to set the thickness, and the amount of glass beads added is within 10) structural glue on the short side of an oiled sample, align the end of the other oiled sample in the opposite direction and cover it with glue, then fix the two samples with clamps, heat them in a 170°C oven for 20 minutes, and test them after placing them under standard conditions for 24 hours. The long axis of the adhesive-coated specimen is used as the centerline of the specimen. The tensile fixture clamps the gasket and the ends of the specimen at both ends, passing the tensile load through the centerline at a tensile speed of 50 mm / min. The failure morphology of the specimen is recorded (CF: failure of the structural adhesive itself; AF: failure due to separation of the structural adhesive from the substrate surface; PF: failure within the substrate or AlSi coating). The evaluation criteria are as follows:

[0147] ○ (good): The failure mode of the structural adhesive and the bonding substrate is CF.

[0148] × (poor): The failure mode of the structural adhesive being separated from the bonding substrate is AF or PF

[0149] Chemical conversion treatment after hot pressing:

[0150] The test sample was placed in a 930°C heating furnace for 4 minutes. After removal, it was immediately placed in a water-cooled stainless steel flat mold for rapid cooling. The cooling rate was 100°C / second. The test material was degreased with Parkase FC-E2032 alkaline degreaser to remove surface dirt. After rinsing with pure water, the test sample was immersed in Parkase PL-Z surface conditioner for 30 seconds. The test sample was then transferred to Parkase PB-L3020 phosphating solution at 35°C for 2 minutes. The evaluation criteria are as follows:

[0151] ○ (good): Zinc phosphate crystal film is precipitated

[0152] × (poor): No zinc phosphate crystal film was precipitated

[0153] Corrosion resistance after painting:

[0154] After the chemical conversion treatment, a 20μm thick layer of Kansai HG-350 electrophoretic paint was applied and cured in a 170°C oven for 20 minutes. The coated panels were tested using the method specified in the Japanese JASO M610 standard. The coating was previously scribed with a tool and tested for 180 cycles (60 days). The maximum drum width on one side was measured from the scribe line. The evaluation criteria are as follows:

[0155] ◎(Excellent): Blister width ≤ 3mm

[0156] ○ (good): bubble width 3 to 6 mm

[0157] ×(poor): bubble width>6mm

[0158] Table 3 lists various performance parameters of the AlSi plated samples in Examples 1 to 32 and Comparative Examples 1 to 8 after testing.

[0159] Table 3 Performance parameters of AlSi plated samples after testing

[0160]

[0161]

[0162] As can be seen from Table 3, after the AlSi-plated steel plates in Examples 1 to 32 were subjected to the above tests, their evaluation results were all "◎" and "○", indicating that the AlSi-plated steel plates coated with the water-based surface treatment agent have excellent or good comprehensive properties such as solvent resistance, corrosion resistance, high-temperature thermal lubricity, weldability, adhesiveness and paintability.

[0163] Combining Table 1 and Table 3, it can be seen that compared with Examples 1 to 32, since the content of aqueous anionic polymer resin A in the surface treatment agent of Comparative Examples 1-3 and 8 is too low, the film-forming property of the applied aqueous surface treatment liquid after drying is poor, and the adhesion, solvent resistance and corrosion resistance of the composite film layer are poor. In addition, since there is no tungsten-containing compound B in Comparative Examples 4 and 7, there is no tungsten oxide with high-temperature lubrication function in the hot stamping process, and the high-temperature thermal lubricity is poor. The amount of boron-containing compound D added in Comparative Example 5 is low, and the mass fraction ratio (W) calculated by elemental zinc (Zn) and boron (B) is 0. Zn / W B ) reaches 10000, the zinc-containing compound C cannot form a good bond with the AlSi-plated steel sheet during the heating stage of hot stamping, and forms a loose zinc oxide layer on the AlSi-plated steel sheet, resulting in poor weldability and adhesiveness. In Comparative Example 6, the amount of boron-containing compound D added is too much, and the mass fraction ratio (W Zn / W B ) is 50, the boron-containing compound D affects the formation of zinc phosphate crystal film during the chemical conversion treatment after hot pressing, and the corrosion resistance after coating is poor.

[0164] In summary, through the present invention, the surface treatment liquid is applied to the surface of the AlSi steel plate to achieve good high-temperature thermal lubricity during hot stamping processing, thereby improving the processability of the AlSi-plated steel plate. Therefore, compared with untreated materials, complex deformation forming processing can be achieved, and the wear of the hot stamping die surface can be reduced, the frequency of die repair can be reduced, and production efficiency can be improved. For the parts products after hot stamping processing, good weldability and adhesiveness can be achieved, chemical conversion treatment is good, and corrosion resistance after coating is also improved. Utilizing the present invention, the application scope of hot stamping processing of AlSi-plated steel plates or Al-plated steel plates is expanded, and the applicability of related parts in the automotive and mechanical processing industries is also improved.

[0165] Those skilled in the art should recognize that the above embodiments are merely intended to illustrate the present invention and are not intended to limit the present invention. As long as they are within the spirit of the present invention, any changes or modifications to the above embodiments will fall within the scope of the claims of the present invention.

Claims

1. A coated steel sheet for hot stamping, characterized in that: It comprises a coated steel plate and a composite film layer formed by coating an aqueous surface treatment liquid on the coated steel plate; The coated steel plate comprises a substrate and an Al or AlSi coating provided on one or both sides of the substrate; The composite film layer contains water-based anionic polymer resin A, tungsten-containing compound B, zinc-containing compound C, boron-containing compound D, water-soluble thickener E and water-based surface improvement additive F. An aqueous surface treatment solution is formed by dispersing a solid phase in water; The solid phase consists of the following components in parts by mass: Water-based anionic polymer resin A: 15-65 parts; Tungsten-containing compound B: 15-40 parts by mass of tungsten element; Zinc-containing compound C: 3 to 15 parts, calculated by weight of zinc element; Boron-containing compound D: 0.004 to 0.03 parts by mass of boron element; Water-soluble thickener E: 0.01-0.5 parts; Water-based surface improvement agent F: 0.5-2 parts, The water-based anionic polymer resin A is selected from one or more of water-based acrylic resin, water-based epoxy resin, water-based polyester resin and water-based alkyd resin; The tungsten-containing compound B is selected from one or more of tungsten oxide, tungstate or tungsten metal salt; The zinc-containing compound C is selected from zinc oxide, zinc salt or organic zinc compound; The boron-containing compound D is selected from boron oxides, borates or organic boron compounds; The water-soluble thickener E is selected from one or more of water-soluble hydroxymethyl cellulose, water-dispersible polyacrylic acid alkali swelling emulsion, and water-dispersible nonionic polyurethane associative thickening resin; The water-based surface improvement agent F is selected from one or both of water-dispersible modified polydimethylsiloxane and water-dispersible polyether-modified silicone; The mass ratio of the boron-containing compound D to the zinc-containing compound C, calculated as elemental zinc (Zn) and boron (B), is 150 / 1 to 750 / 1; The hot stamping coated steel plate has a yield strength of ≥950 MPa, a tensile strength of ≥1300 MPa, and an elongation after fracture of A 50mm ≥5%, hardness HV10 ≥ 400 or HRC ≥ 40, cold bending angle VDA ≥ 45°.

2. The hot stamping coated steel sheet according to claim 1, wherein: The dry film weight of the composite film layer is 1 to 5 g / m 2 .

3. An aqueous surface treatment liquid for a hot stamping coated steel sheet according to claim 1 or 2, characterized in that: An aqueous surface treatment solution is formed by dispersing a solid phase in water; The solid phase consists of the following components in parts by mass: Water-based anionic polymer resin A: 15-65 parts; Tungsten-containing compound B: 15-40 parts by mass of tungsten element; Zinc-containing compound C: 3 to 15 parts, calculated by weight of zinc element; Boron-containing compound D: 0.004 to 0.03 parts by mass of boron element; Water-soluble thickener E: 0.01-0.5 parts; Water-based surface improvement agent F: 0.5-2 parts, The water-based anionic polymer resin A is selected from one or more of water-based acrylic resin, water-based epoxy resin, water-based polyester resin and water-based alkyd resin; The tungsten-containing compound B is selected from one or more of tungsten oxide, tungstate or tungsten metal salt; The zinc-containing compound C is selected from zinc oxide, zinc salt or organic zinc compound; The boron-containing compound D is selected from boron oxides, borates or organic boron compounds; The water-soluble thickener E is selected from one or more of water-soluble hydroxymethyl cellulose, water-dispersible polyacrylic acid alkali swelling emulsion, and water-dispersible nonionic polyurethane associative thickening resin; The water-based surface improvement agent F is selected from one or both of water-dispersible modified polydimethylsiloxane and water-dispersible polyether-modified silicone; the mass ratio of the boron-containing compound D to the zinc-containing compound C, calculated as elemental zinc (Zn) and boron (B), is 150 / 1 to 750 / 1, respectively; The aqueous surface treatment liquid is applied on a cleaned Al-plated or AlSi-plated steel plate, and the aqueous surface treatment liquid is solidified at a temperature of 80 to 180° C. on the Al-plated or AlSi-plated steel plate to form a composite film layer, thereby producing a coated steel plate for hot stamping. The yield strength of the hot stamping coated steel plate is ≥950 MPa, the tensile strength is ≥1300 MPa, and the elongation after fracture is A 50mm ≥5%, hardness HV10 ≥ 400 or HRC ≥ 40, cold bending angle VDA ≥ 45°.

4. The aqueous surface treatment liquid for hot stamping coated steel sheet according to claim 3, characterized in that: The mass fraction of the aqueous anionic polymer resin A is 20 to 50 parts; and / or The mass fraction of the tungsten-containing compound B is 15 to 35, calculated as the mass fraction of the tungsten element.

5. The aqueous surface treatment liquid for hot stamping coated steel sheet according to claim 4, characterized in that: The number average molecular weight of the aqueous anionic polymer resin A is greater than 8000, and the mass fraction of harmful substances generated after the aqueous anionic polymer resin A is burned is less than 1wt% of the total solid content of the aqueous anionic polymer resin A; and / or When the tungsten-containing compound B is a water-insoluble tungsten compound, the particle size of the tungsten-containing compound B is 5 to 1000 nm; and / or When the zinc-containing compound C is a water-insoluble zinc compound, the particle size of the zinc-containing compound C is 5 to 1000 nm; and / or The number average molecular weight of the water-soluble thickener E is between 50,000 and 100,000.

6. The aqueous surface treatment liquid for hot stamping coated steel sheet according to claim 5, characterized in that: The particle size of the tungsten-containing compound B is 20 to 500 nm; and / or The particle size of the zinc-containing compound C is 20 to 500 nm.

7. A method for preparing a coated steel sheet for hot stamping according to claim 1 or 2, characterized in that: The aqueous surface treatment liquid is applied to the cleaned Al-plated or AlSi-plated steel sheet, and the aqueous surface treatment liquid is solidified at a temperature of 80 to 180° C. on the Al-plated or AlSi-plated steel sheet to form a composite film layer, thereby producing a coated steel sheet for hot stamping. The yield strength of the hot stamping coated steel plate is ≥950 MPa, the tensile strength is ≥1300 MPa, and the elongation after fracture is A 50mm ≥5%, hardness HV10 ≥ 400 or HRC ≥ 40, cold bending angle VDA ≥ 45°.

8. A hot stamping method for a coated steel sheet for hot stamping according to claim 1 or 2, characterized in that: Hot stamping is done by punching out the coated steel sheet and then heating it for stamping. The yield strength of the coated steel plate after hot stamping is ≥950 MPa, the tensile strength is ≥1300 MPa, and the elongation after fracture is A 50mm ≥5%, hardness HV10 ≥ 400 or HRC ≥ 40, cold bending angle VDA ≥ 45°.

9. The hot stamping method of the coated steel sheet for hot stamping according to claim 8, wherein: During the heating process, the hot stamping coated steel plate after punching is heated from 50° C. to the limit plate temperature and kept warm for 30 to 60 seconds; then the heated hot stamping coated steel plate is transferred to a mold with a cooling effect for stamping.

10. The hot stamping method of the coated steel sheet for hot stamping according to claim 9, wherein: During the heating process, the average heating rate is 12 to 200° C. / s, and the limit plate temperature of the hot stamping coated steel plate is 850 to 980° C.; and / or The stamping process is carried out in air, and before the temperature of the hot stamping coated steel sheet drops to 400° C., the cooling rate is ≥27° C.

Images