Aluminum-silicon coating hot-formed steel plate, aluminum-silicon coating hot-formed steel part with sacrificial anode protection and excellent coating performance and preparation method of aluminum-silicon coating hot-formed steel part

Abstract

The invention relates to the technical field of automobile steel parts, and discloses an aluminum-silicon coating hot-formed steel plate, an aluminum-silicon coating hot-formed steel part with sacrificial anode protection and excellent coating performance and a preparation method of the aluminum-silicon coating hot-formed steel part. The aluminum-silicon coating hot-formed steel plate comprises a steel base plate, at least one surface of the steel base plate is plated with an aluminum alloy coating, and the aluminum alloy coating is arranged on the surface of the steel base plate. The surface of the aluminum alloy plating layer is further coated with a surface treatment layer. The aluminum alloy coating comprises the following chemical elements in percentage by weight: not less than 8% and not more than 12% of Si, not more than 3% of Fe and the balance of aluminum and inevitable impurities; the surface treatment layer contains a copper element; the copper element in the surface treatment layer is selected from one or more than two of copper, copper oxide, copper hydroxide, copper acetate and copper citrate. The aluminum-silicon coating hot-formed steel part has an excellent sacrificial anode protection effect, the painted paint is excellent in adhesive force and good in corrosion resistance, and the problem of paint stripping after painting caused by insufficient alloying is solved.

Description

Technical Field

[0001] This invention relates to the field of automotive steel parts technology, specifically to aluminum-silicon coated hot-formed steel sheets, aluminum-silicon coated hot-formed steel parts with sacrificial anode protection and excellent coating performance, and their preparation methods. Background Technology

[0002] Due to the requirements for lightweighting and corrosion resistance, high-strength coated hot-formed steel is widely used in automotive parts. Among coated hot-formed steels, aluminum-silicon coated hot-formed steel sheets are the most widely used.

[0003] However, it has prominent technical problems: (1) When heated, the aluminum-silicon coating melts and has a mirror-like reflective effect, which reduces the heating efficiency; (2) Since the aluminum-silicon coating cannot undergo pretreatment reaction after hot forming, the blank must be fully heated to allow Fe to diffuse into the aluminum-silicon coating and form a micro-rough aluminum-iron alloy on the surface to ensure the adhesion of subsequent paint; (3) The large amount of Fe diffusion into the coating results in the hot-formed coating having no sacrificial anode protection effect on the substrate, and the large proportion of Fe in the coating also exacerbates the risk of red rust on the cut edges and punched positions of the parts. All of these are unacceptable to some automobile manufacturers.

[0004] The ideal technical solution is to provide sacrificial anode protection for the coating after thermoforming, while also improving the pretreatment properties of the coating and enabling the manufacture of thermoformed parts with high heating efficiency.

[0005] Attempts to improve the sacrificial anode effect or pretreatment effect by adding active metal elements such as zinc into aluminum-silicon coatings have been studied (e.g., 201280073231.4). However, this type of technology has technical problems such as liquid metal intrusion (LME) and the difficulty in industrial application of the drastically changed plating solution composition on existing production lines, and has not yet been commercialized.

[0006] Technical solutions are known to improve the pretreatment performance of aluminum-silicon coatings. For example, patent application 201480068599.0 discloses a steel sheet for press hardening, including an aluminum-based coating and a ZnO coating. Another example is Chinese patent application 201680011130.2, which discloses a steel sheet coated with an aluminum-based coating and also includes a second zinc coating, which improves the surface treatment of phosphate coatings. However, these technologies do not solve the technical problem of the coating lacking sacrificial anode protection after hot forming, nor do they improve heating efficiency.

[0007] There are also known techniques for improving the heating efficiency of hot-formed steel with aluminum-based coatings (201280012158.X, 201580017679.8, 202210869048.0), which improve heating efficiency by applying a substance with higher heat absorption efficiency than aluminum alloy to the surface of the steel plate. However, these methods for improving heating efficiency cannot solve the technical problems of low paint adhesion after hot forming, lack of sacrificial anode protection in the coating, and susceptibility to red rust.

[0008] In summary, there is currently a lack of technical solutions for manufacturing aluminum-silicon coated thermoformed parts with sacrificial anode protection and excellent coating performance using high heating efficiency. Summary of the Invention

[0009] The purpose of this invention is to overcome the current lack of aluminum-silicon coated hot-formed parts with sacrificial anode protection and excellent coating performance that can be manufactured with high heating efficiency. This invention provides aluminum-silicon coated hot-formed steel sheets, aluminum-silicon coated hot-formed steel parts with sacrificial anode protection and excellent coating performance, and their preparation methods. This invention enables the manufacture of hot-formed steel parts with sacrificial anode protection and good adhesion after coating with high heating efficiency, and solves the technical defects of existing aluminum-silicon hot-formed steel parts, such as low heating efficiency, lack of sacrificial anode protection, easy occurrence of red rust, inability to undergo pretreatment reaction, and poor adhesion and corrosion resistance after coating.

[0010] To achieve the above objectives, the present invention provides an aluminum-silicon coated hot-formed steel sheet, the aluminum-silicon coated hot-formed steel sheet comprising a steel substrate, at least one surface of the steel substrate being coated with an aluminum alloy coating, and the surface of the aluminum alloy coating being further coated with a surface treatment layer (i.e., the aluminum alloy coating is located between the steel substrate and the surface treatment layer). The chemical element weight percentage of the aluminum alloy coating includes: 8%≤Si≤12%, Fe≤3%, with the remainder being aluminum and unavoidable impurities; The surface treatment layer contains copper. The copper element in the surface treatment layer comes from one or more of copper, copper oxide, copper hydroxide, copper acetate, and copper citrate.

[0011] This invention is not limited to the composition of the base steel substrate. As a conventional example, the steel substrate is of type 22MnB5, and its chemical element weight percentages include: 0.20%≤C≤0.25%; 0.15%≤Si≤0.35%; 1.10%≤Mn≤1.40%; 0%≤Cr≤0.30%; 0%≤Mo≤0.35%; 0%≤P≤0.025%; 0%≤S≤0.005%; 0.020%≤Ti≤0.060%; 0.020%≤Al≤0.060%; 0.002%≤B≤0.004%, with the balance being iron and unavoidable impurities from steel manufacturing.

[0012] In the above-mentioned aluminum alloy coating chemical element composition, Si can form an Fe-Al-Si inhibition layer on the steel substrate surface, which can effectively inhibit the formation of the brittle phase Fe2Al5 and improve the coating adhesion. When the Si content is less than 8%, the Fe-Al alloy layer becomes thicker and the coating adhesion decreases. When the Si content is greater than 12.0%, it affects the surface quality of the coating. Based on the above, the Si content in the aluminum alloy coating of the present invention is controlled at 8.0-12.0%.

[0013] In this invention, the steel substrate can be hot-dip coated in either a hot-rolled or annealed state to coat an aluminum alloy coating on at least one surface of the steel substrate. For example, an aluminum alloy coating can be coated on at least one surface of the steel substrate by hot rolling → pickling → hot-dip coating → leveling, or by hot rolling → pickling → cold rolling → cleaning → annealing → hot-dip coating → leveling.

[0014] In a preferred embodiment, after coating an aluminum alloy layer on at least one surface of the steel substrate, the steel substrate coated with the aluminum alloy layer needs to be degreased to remove contaminants from the steel plate surface, and finally a surface treatment layer is formed on the aluminum alloy layer.

[0015] Optionally, a water washing step is performed after the degreasing operation to prevent the degreasing solution used in the degreasing from remaining on the surface.

[0016] Optionally, a drying step is also included after the washing step.

[0017] Furthermore, the surface of the surface treatment layer may optionally be coated with an anti-rust oil layer, that is, at least one surface of the steel substrate of the aluminum-silicon coated hot-formed steel plate is coated with an aluminum alloy coating, and the surface of the aluminum alloy coating is further coated with a surface treatment layer; or, at least one surface of the steel substrate of the aluminum-silicon coated hot-formed steel plate is coated with an aluminum alloy coating, and the surface of the aluminum alloy coating is further coated with a surface treatment layer, and the surface of the surface treatment layer is further coated with an anti-rust oil layer.

[0018] The rust-preventive oil layer is formed by applying rust-preventive oil.

[0019] In this invention, the copper element in the surface treatment layer comes from one or more of copper, copper oxide, copper hydroxide, copper acetate, and copper citrate. This is because the inventors discovered that these elemental copper substances and copper-containing materials can form black copper oxide during thermoforming, thereby significantly improving heating efficiency. The inventors also discovered that copper oxide can re-exist in an ionic state in the zirconization solution and accelerate the zirconization reaction, making it possible for the zirconization film of aluminum-silicon coatings that are originally difficult to zirconize, and can significantly improve the adhesion and corrosion resistance after coating.

[0020] More specifically, the surface treatment layer of the present invention is prepared using one or more materials selected from copper, copper oxide, copper hydroxide, copper acetate, and copper citrate. These copper-containing substances do not release toxic gases during heating and drying, and are non-polluting to the environment and non-corrosive to equipment.

[0021] In a preferred embodiment, the surface treatment layer of the present invention can be obtained by depositing elemental copper metal on the surface of an aluminum alloy coating through physical vapor deposition (PVD); or it can be formed by coating a solution or coating of one or more materials selected from copper, copper oxide, copper hydroxide, copper acetate and copper citrate onto the aluminum alloy coating and then drying it. In this embodiment, the type of material after drying depends on the drying temperature and the drying atmosphere. Generally, it is dried in an air atmosphere at a temperature of 50 to 300°C.

[0022] In a specific embodiment, when the surface treatment layer of the present invention is formed by applying a solution or coating of one or more materials selected from copper, copper oxide, copper hydroxide, copper acetate, and copper citrate onto an aluminum alloy plating layer, and then drying it: When a surface treatment layer is formed using one or more of copper metal powder, copper oxide, and copper hydroxide, since these substances are poorly soluble in water, it is preferable to first disperse these substances with a dispersant to form a dispersion coating before applying the coating. Preferably, the dispersant is one or more of water, ethanol, acetone, butyl ether, and N-methyl-2-pyrrolidone, and a small amount of binder may also be used to enhance the adhesion between the coating and the plating layer. The binder is selected from one or more of polyvinylpyrrolidone, polyacrylic acid resin, polyurethane, silane, and polyvinylidene fluoride.

[0023] When using copper acetate and / or copper citrate to form a surface treatment layer, it is preferable to first prepare these copper salts into appropriate copper salt solutions before coating. These two copper salts do not release toxic gases during drying and react mildly with the aluminum-silicon coating during the drying process after coating, avoiding uneven coloring or black spots caused by severe corrosion of the coating by copper ions (these uneven coloring and severely corroded black spots appear when using copper sulfate, copper nitrate, or copper chloride as copper sources). The substance formed after drying includes not only copper acetate and / or copper citrate, but also elemental copper on the surface due to the partial or complete displacement reaction between aluminum and the copper-containing solution. Some of this elemental copper can be partially oxidized to copper oxide during the drying heating process.

[0024] The aluminum-silicon coated hot-formed steel sheet of the present invention has high heating efficiency in hot forming and excellent sacrificial anode protection performance and good coating performance after hot forming.

[0025] A second aspect of the present invention provides an aluminum-silicon coated hot-formed steel part with sacrificial anode protection and excellent coating performance, wherein the aluminum-silicon coated hot-formed steel part is obtained by hot-forming the above-mentioned aluminum-silicon coated hot-formed steel sheet. The aluminum-silicon coated hot-formed steel component includes a steel substrate, at least one surface of which is coated with an aluminum alloy metallographic coating, and the surface of the aluminum alloy metallographic coating is further coated with a surface heat treatment layer. The aluminum alloy metallographic coating includes an aluminum-silicon alloy phase located near the surface heat treatment layer, and the area fraction of the aluminum-silicon alloy phase on the surface of the aluminum alloy metallographic coating is ≥20%. The Fe content in the aluminum-silicon alloy phase is less than 5 wt%.

[0026] Among them, the area fraction of aluminum-silicon alloy phase on the surface of aluminum alloy metallographic coating is ≥20%, that is, the coverage area ratio of aluminum-silicon alloy phase on the surface of aluminum alloy metallographic coating is ≥20%, which means that the area fraction of aluminum-silicon alloy phase on the surface of aluminum alloy metallographic coating observed by scanning electron microscope is ≥20%.

[0027] Furthermore, the aluminum alloy metallographic coating of the present invention comprises a mutually diffused layer, a first iron-aluminum-silicon ternary alloy phase, and a surface layer sequentially stacked in a direction away from the steel substrate; the surface layer contains an aluminum-silicon alloy phase.

[0028] Furthermore, the aluminum alloy metallographic coating comprises a cross-diffusion layer, a first iron-aluminum alloy phase, a first iron-aluminum-silicon ternary alloy phase, a second iron-aluminum alloy phase, and a surface layer, which are sequentially stacked along the direction away from the steel substrate; the surface layer contains an aluminum-silicon alloy phase and a second iron-aluminum-silicon ternary alloy phase.

[0029] In preferred embodiments, the Fe content in the interdiffusion layer is greater than 60 wt%; the Fe content in the first iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; the Fe content in the first iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 68 wt%; the Fe content in the second iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; and the Fe content in the second iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 70 wt%.

[0030] In the aluminum-silicon coated hot-formed steel parts, the material of the surface heat treatment layer is copper metal and / or copper oxide, and does not contain zinc oxide. It is formed by the surface treatment layer through a hot forming process.

[0031] The aluminum-silicon coated hot-formed steel parts of this invention exhibit excellent sacrificial anode protection. The outermost layer of the aluminum alloy metallographic coating is an Al-Si alloy phase with an Fe content of less than 5% by weight, giving the hot-formed aluminum alloy metallographic coating a sacrificial anode effect. In particular, it was found that by controlling the area ratio of the surface aluminum-silicon alloy phase to be greater than or equal to 20% through the hot-forming process, the sacrificial anode protection of the aluminum alloy metallographic coating can be guaranteed, and no obvious red rust formation was observed in corrosion tests. This invention solves the problem of paint peeling and large corrosion width after coating caused by insufficient alloying of the aluminum alloy metallographic coating through a surface heat treatment layer. The inventors discovered that copper and / or copper oxides hot-pressed onto the aluminum-silicon surface can re-exist in ionic form in the slightly acidic environment of the zirconium leaching solution, and act as a catalyst to accelerate zirconium oxide deposition, promote the zirconium leaching reaction, and also form a film during the phosphating reaction. Therefore, the paint adhesion after coating is excellent and the corrosion resistance is good.

[0032] A third aspect of the present invention provides a method for preparing the above-mentioned aluminum-silicon coated hot-formed steel parts, comprising: heating and hot stamping the above-mentioned aluminum-silicon coated hot-formed steel sheet to obtain the aluminum-silicon coated hot-formed steel parts.

[0033] Heating and hot stamping constitute the hot forming process. The aforementioned aluminum-silicon coated hot-formed steel sheet can be manufactured into aluminum-silicon coated hot-formed steel parts with high heating efficiency.

[0034] The aluminum-silicon coated hot-formed steel sheet of the present invention can significantly improve heating efficiency. The aluminum-silicon coated hot-formed steel sheet can be cut into blanks of appropriate size before hot forming according to actual needs, or it can be hot-formed directly without cutting.

[0035] Preferably, the heating temperature is 840-1100℃.

[0036] In a preferred embodiment, when the thickness of the aluminum-silicon coated hot-formed steel sheet is >1.4mm, the heating time is 3-5 minutes; when the thickness of the aluminum-silicon coated hot-formed steel sheet is ≤1.4mm, the heating time is 1-3 minutes.

[0037] In this case, the thickness of the aluminum alloy coating and the surface treatment layer of the aluminum-silicon coated hot-formed steel sheet can be ignored. Therefore, the thickness of the steel substrate can be regarded as the thickness of the aluminum-silicon coated hot-formed steel sheet.

[0038] Specifically, the heating atmosphere does not affect the coating performance. For the purpose of coating improvement, heating can be carried out in any atmosphere. Preferably, heating is carried out in an atmosphere containing 15-25% oxygen by volume (air is used for cost reasons). In this preferred embodiment, the highest heating efficiency is achieved. During heating, elemental copper or its compounds are oxidized to copper oxide, and the black surface of copper oxide can be heated at the maximum heating rate. During the subsequent transfer to the hot stamping tool, the surface treatment layer can be partially or completely oxidized to copper oxide, thereby improving the coating performance.

[0039] Furthermore, during the heating process, the surface treatment layer is oxidized by heat to form a black surface, which improves the heat absorption efficiency of the sheet and reduces the time required to heat up to the austenitizing temperature. This heating process shortens the heating time by more than 1 minute compared to conventional thermoforming processes.

[0040] In a preferred embodiment of the present invention, the conditions for hot stamping include: a temperature of 500-700°C and a holding time of 5-40 seconds.

[0041] In a specific implementation, hot stamping is performed using a hot stamping tool. After hot stamping, the obtained part is cooled either within the tool itself or after being transferred to a specific cooling tool to obtain aluminosilicate coated hot-formed steel parts.

[0042] The aluminum-silicon coated hot-formed steel parts of this invention exhibit excellent sacrificial anode protection. Under the high heating rate of this invention, the diffusion time of Fe in the steel substrate within the aluminum alloy coating is short, resulting in insufficient alloying. This leads to a sacrificial anode effect in the hot-formed aluminum alloy metallographic coating. Specifically, by controlling the surface aluminum-silicon alloy phase area ratio to ≥20% through the hot-forming process, the sacrificial anode protection of the coating is guaranteed, and no obvious red rust formation is observed in corrosion tests. Furthermore, the hot-formed parts of this invention possess excellent coating performance because copper or copper oxide can re-exist in ionic form in the slightly acidic environment of the zirconium leaching solution, acting as a catalyst to accelerate zirconium oxide deposition and promote the zirconium leaching reaction. It can also form a film during the phosphating reaction. Therefore, the paint exhibits excellent adhesion and corrosion resistance after painting, solving the problem of paint peeling caused by insufficient alloying.

[0043] This invention enables the manufacture of hot-formed steel parts with sacrificial anode protection and good adhesion after coating with high heating efficiency, and solves the technical defects of existing aluminum-silicon hot-formed steel parts, such as low heating efficiency, lack of sacrificial anode protection, easy occurrence of red rust, inability to undergo pretreatment reaction, and poor adhesion and corrosion resistance after coating. Attached Figure Description

[0044] Figure 1 This is a metallographic structure diagram of the aluminum alloy coating of the aluminum-silicon coated hot-formed steel plate parts in Example 1. Figure 2 This is a metallographic structure diagram of the aluminum alloy coating on the aluminum-silicon coated hot-formed steel plate parts of Example 2. Detailed Implementation

[0045] The specific embodiments of the present invention will be described in detail below with reference to the accompanying drawings. It should be understood that the specific embodiments described herein are for illustration and explanation only and are not intended to limit the present invention.

[0046] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0047] It should be noted that if the present invention involves directional indicators (such as up, down, left, right, front, back, etc.), the directional indicators are only used to explain the relative positional relationship and movement of the components in a specific posture (as shown in the figure). If the specific posture changes, the directional indicators will also change accordingly.

[0048] Furthermore, if the present invention uses terms such as "first" or "second," these descriptions are for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined with "first" or "second" may explicitly or implicitly include at least one of those features. Additionally, the technical solutions of the various embodiments provided by the present invention can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, it should be considered that such a combination of technical solutions does not exist and is not within the scope of protection claimed by the present invention.

[0049] The present invention will be described in detail below through embodiments. Unless otherwise specified, the experimental methods used in the following embodiments are conventional methods in the art. Unless otherwise specified, the experimental materials used in the following embodiments are commercially available.

[0050] The chemical element weight percentages of the steel substrates used in the following examples and comparative examples are as follows: C: 0.2252%, Mn: 1.1735%, P: 0.0126%, S: 0.0009%, Si: 0.2534%, Cr: 0.180%, Al: 0.0371%, Ti: 0.0382%, B: 0.0028%, Mo: 0.0017%, with the balance being iron and unavoidable impurities.

[0051] The rust-preventive oil used in the following examples and comparative examples is Quaker Ferrocoat N 6130 rust-preventive oil, and the application amount is 1.5 g / m². 2 .

[0052] Example 1

[0053] (1) The steel billet is subjected to hot rolling, pickling, cold rolling, cleaning, annealing, hot-dip galvanizing and leveling in sequence to obtain a steel substrate with an aluminum alloy coating on the surface. Then, it is degreased, washed and dried for later use. The chemical element weight percentage of the aluminum alloy coating is as follows: Si: 8.0%, Fe: 2.0%, and the remainder is aluminum and unavoidable impurities. The steel substrate is 1.0 mm thick, and the aluminum alloy coating is coated on both sides with equal thickness. The coating weight on each side is 75 g / m. 2 ; (2) After uniformly mixing copper metal powder, N-methyl-2-pyrrolidone and polyvinylidene fluoride, a dispersion coating is obtained (based on a total weight of 100 parts by weight of copper metal powder, N-methyl-2-pyrrolidone and polyvinylidene fluoride, the amount of copper metal powder is 40 parts by weight, the amount of N-methyl-2-pyrrolidone is 50 parts by weight, and the amount of polyvinylidene fluoride is 10 parts by weight). The dispersion coating is applied to the surface of the aluminum alloy coating of the steel substrate with the aluminum alloy coating obtained in step (1), and then dried in an air atmosphere at a temperature of 200°C to form a surface treatment layer on the surface of the aluminum alloy coating. Then, rust-preventive oil is applied to the surface of the surface treatment layer to form a rust-preventive oil layer, and an aluminum-silicon coated hot-formed steel plate is obtained. The aluminum-silicon coated hot-formed steel plate includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and a rust-preventive oil layer on the surface of the surface treatment layer.

[0054] Example 2

[0055] (1) The steel billet is hot-rolled, pickled, hot-dip galvanized and leveled in sequence to obtain a steel substrate with an aluminum alloy coating on the surface. Then, it is degreased, washed and dried for later use. The weight percentage of the aluminum alloy coating is as follows: Si: 9.0%, Fe: 1.0%, and the remainder is aluminum and unavoidable impurities. The steel substrate is 1.2 mm thick. The aluminum alloy coating is applied on both sides with equal thickness. The weight of the coating on each side is 75 g / m. 2 ; (2) Mix copper acetate with water to prepare a copper acetate solution with a Cu ion content of 0.10 mol / L. Coat the copper acetate solution onto the surface of the aluminum alloy coating of the steel substrate with the aluminum alloy coating obtained in step (1). Then dry it in air at a temperature of 300°C to form a surface treatment layer on the surface of the aluminum alloy coating. Next, coat the surface of the surface treatment layer with anti-rust oil to form an anti-rust oil layer and obtain an aluminum-silicon coated hot-formed steel plate. The aluminum-silicon coated hot-formed steel plate includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and an anti-rust oil layer on the surface of the surface treatment layer.

[0056] Example 3

[0057] (1) The steel billet is subjected to hot rolling, pickling, cold rolling, cleaning, annealing, hot-dip galvanizing and leveling in sequence to obtain a steel substrate with an aluminum alloy coating on the surface. Then, it is degreased, washed and dried for later use. The chemical element weight percentage of the aluminum alloy coating is as follows: Si: 10.0%, Fe: 1.5%, and the remainder is aluminum and unavoidable impurities. The steel substrate is 1.4 mm thick, and the aluminum alloy coating is applied on both sides with equal thickness. The coating weight on each side is 75 g / m. 2 ; (2) Mix copper acetate with water to prepare a copper acetate solution with a Cu ion content of 0.10 mol / L. Coat the copper acetate solution onto the surface of the aluminum alloy coating of the steel substrate with the aluminum alloy coating obtained in step (1). Then dry it in air at a temperature of 100°C to form a surface treatment layer on the surface of the aluminum alloy coating. Next, coat the surface of the surface treatment layer with anti-rust oil to form an anti-rust oil layer and obtain an aluminum-silicon coated hot-formed steel plate. The aluminum-silicon coated hot-formed steel plate includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and an anti-rust oil layer on the surface of the surface treatment layer.

[0058] Example 4

[0059] (1) The steel billet is subjected to hot rolling, pickling, cold rolling, cleaning, annealing, hot-dip galvanizing and leveling in sequence to obtain a steel substrate with an aluminum alloy coating on the surface. Then, it is degreased, washed and dried for later use. The chemical element weight percentage of the aluminum alloy coating is as follows: Si: 12%, Fe: 2.0%, and the remainder is aluminum and unavoidable impurities. The steel substrate is 1.6 mm thick, and the coating is applied to both sides with equal thickness. The coating weight on each side is 75 g / m. 2 ; (2) Mix copper citrate with water to prepare a copper citrate solution with a Cu ion content of 0.10 mol / L. Coat the copper citrate solution onto the surface of the aluminum alloy coating of the steel substrate with the aluminum alloy coating obtained in step (1). Then dry it in air at a temperature of 50°C to form a surface treatment layer on the surface of the aluminum alloy coating. Next, coat the surface of the surface treatment layer with anti-rust oil to form an anti-rust oil layer and obtain an aluminum-silicon coated hot-formed steel plate. The aluminum-silicon coated hot-formed steel plate includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and an anti-rust oil layer on the surface of the surface treatment layer.

[0060] Example 5

[0061] (1) The steel billet is subjected to hot rolling, pickling, cold rolling, cleaning, annealing, hot-dip galvanizing and leveling in sequence to obtain a steel substrate with an aluminum alloy coating on the surface. Then, it is degreased, washed and dried for later use. The chemical element weight percentage of the aluminum alloy coating is as follows: Si: 10%, Fe: 3.0%, and the remainder is aluminum and unavoidable impurities. The steel substrate is 2.0 mm thick, and the coating is applied to both sides with equal thickness. The weight of the coating on each side is 75 g / m. 2 ; (2) Mix copper acetate with water to prepare a copper acetate solution with a Cu ion content of 0.10 mol / L. Coat the copper acetate solution onto the surface of the aluminum alloy coating of the steel substrate with the aluminum alloy coating obtained in step (1). Then dry it in air at a temperature of 180°C to form a surface treatment layer on the surface of the aluminum alloy coating. Next, coat the surface of the surface treatment layer with anti-rust oil to form an anti-rust oil layer and obtain an aluminum-silicon coated hot-formed steel plate. The aluminum-silicon coated hot-formed steel plate includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and an anti-rust oil layer on the surface of the surface treatment layer.

[0062] Comparative Example 1 The method of Example 1 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, thereby obtaining a coated steel plate. The coated steel plate includes a steel substrate, on the surface of which an aluminum alloy coating is plated, and the surface of the aluminum alloy coating is also covered with a rust-preventive oil layer.

[0063] Comparative Example 2 The method of Example 2 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, resulting in a coated steel plate. The coated steel plate includes a steel substrate, on the surface of which an aluminum alloy coating is plated, and the surface of the aluminum alloy coating is also covered with a rust-preventive oil layer.

[0064] Comparative Example 3 The method of Example 3 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, resulting in a coated steel plate. The coated steel plate includes a steel substrate, on the surface of which an aluminum alloy coating is plated, and the surface of the aluminum alloy coating is also covered with a rust-preventive oil layer.

[0065] Comparative Example 4 The method of Example 4 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, resulting in a coated steel plate. The coated steel plate includes a steel substrate, on which an aluminum alloy coating is plated, and on which a rust-preventive oil layer is also applied.

[0066] Comparative Example 5 The method of Example 5 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, resulting in a coated steel plate. The coated steel plate includes a steel substrate, on the surface of which an aluminum alloy coating is plated, and the surface of the aluminum alloy coating is also covered with a rust-preventive oil layer.

[0067] Comparative Example 6 The method of Example 5 is implemented, except that no surface treatment layer is formed. Instead, rust-preventive oil is directly applied to the surface of the aluminum alloy coating to form a rust-preventive oil layer, resulting in a coated steel plate. The coated steel plate includes a steel substrate, on which an aluminum alloy coating is plated, and on which a rust-preventive oil layer is applied.

[0068] Comparative Example 7 The method of Example 5 is implemented, except that copper sulfate is used instead of copper acetate; an aluminum-silicon coated hot-formed steel sheet is obtained, the aluminum-silicon coated hot-formed steel sheet includes a steel substrate, an aluminum alloy coating is coated on the surface of the steel substrate, a surface treatment layer is also coated on the surface of the aluminum alloy coating, and an anti-rust oil layer is also coated on the surface of the surface treatment layer.

[0069] Comparative Example 8 The method of Example 5 is implemented, except that copper nitrate is used instead of copper acetate; an aluminum-silicon coated hot-formed steel sheet is obtained, which includes a steel substrate, an aluminum alloy coating on the surface of the steel substrate, a surface treatment layer on the surface of the aluminum alloy coating, and an anti-rust oil layer on the surface of the surface treatment layer.

[0070] Comparative Example 9 The method of Example 5 is implemented, except that copper chloride is used instead of copper acetate; an aluminum-silicon coated hot-formed steel sheet is obtained, the aluminum-silicon coated hot-formed steel sheet includes a steel substrate, an aluminum alloy coating is coated on the surface of the steel substrate, a surface treatment layer is also coated on the surface of the aluminum alloy coating, and an anti-rust oil layer is also coated on the surface of the surface treatment layer.

[0071] Test Example 1 The performance of the aluminum-silicon coated hot-formed steel sheets obtained in Examples 1-5 and the coated steel sheets obtained in Comparative Examples 1-6 were evaluated according to the following methods: Total time for complete austenitization: Each steel plate was cut and placed in a box furnace at 930℃. Starting from 1 minute, the temperature was increased by 30 seconds each time. The plates were then cooled in a flat mold. Samples of 10 mm × 10 mm × plate thickness were cut from the quenched experimental steel and ground, mechanically polished, and etched with picric acid. The original austenite grain size was observed and the martensite structure was observed under an optical microscope. The heating time for complete martensite formation was taken as the total time for complete austenitization. The total time for complete austenitization of each steel plate is shown in Table 1.

[0072] The aluminum-silicon coated hot-formed steel sheets obtained in Examples 1-5 and the coated steel sheets obtained in Comparative Examples 1-6 were heated in air at 930°C for the time shown in Table 1 (the heating times for Comparative Examples 5 and 6 were different). Then, they were hot-stamped in a hot stamping tool at 650°C for 30 seconds. After that, they were removed and cooled to room temperature in air to obtain aluminum-silicon coated hot-formed steel sheet parts. (The aluminum-silicon coated hot-formed steel parts obtained in Examples 1-5 include a steel substrate with an aluminum alloy metallographic coating on its surface, and the surface of the aluminum alloy metallographic coating is also covered with a surface heat treatment layer; the aluminum-silicon coated hot-formed steel parts obtained in Comparative Examples 1-6 include a steel substrate with an aluminum alloy metallographic coating on its surface.)

[0073] Coating structure: A 10mm×10mm×plate thickness sample cut from the hot-formed steel plate parts with aluminum-silicon coating obtained by the above mold quenching was ground and mechanically polished. The structure of the coating was observed in a scanning electron microscope, and the area ratio of the aluminum-silicon alloy phase on the surface of the aluminum-silicon coating was recorded. The aluminum alloy metallographic coating structures of the aluminum-silicon coated hot-formed steel plate parts in Examples 1 and 2 are respectively as follows: Figure 1 and Figure 2 As shown, the Fe content in each metallographic structure was further detected using the EDS measurement method; Figure 1 The aluminum alloy metallographic coating comprises, sequentially stacked along the direction away from the steel substrate, an interdiffusion layer (α-Fe containing Al and Si elements), a first iron-aluminum-silicon ternary alloy phase, and a surface layer; the surface layer is an aluminum-silicon alloy phase, wherein the Fe content in the aluminum-silicon alloy phase is 1.2 wt%, the Fe content in the interdiffusion layer is 70 wt%, and the Fe content in the first iron-aluminum-silicon ternary alloy phase is 34 wt%. Figure 2 The aluminum alloy metallographic coating comprises, sequentially stacked along the direction away from the steel substrate, an interdiffusion layer, a first iron-aluminum alloy phase, a first iron-aluminum-silicon ternary alloy phase, a second iron-aluminum alloy phase, and a surface layer; the surface layer is an aluminum-silicon alloy phase and a second iron-aluminum-silicon ternary alloy phase, wherein the aluminum-silicon alloy phase contains 2.0 wt% Fe, the interdiffusion layer contains 75 wt% Fe, the first iron-aluminum alloy phase contains 44.8 wt% Fe, the first iron-aluminum-silicon ternary alloy phase contains 49.5 wt% Fe, the second iron-aluminum alloy phase contains 45 wt% Fe, and the second iron-aluminum-silicon ternary alloy phase contains 28.9 wt% Fe. The aluminum alloy metallographic coatings of the hot-formed steel sheet parts with aluminum-silicon coatings obtained in Examples 3-5 all include, sequentially stacked along the direction away from the steel substrate, an interdiffusion layer, a first iron-aluminum alloy phase, a first iron-aluminum-silicon ternary alloy phase, a second iron-aluminum alloy phase, and a surface layer; the surface layer is an aluminum-silicon alloy phase and a second iron-aluminum-silicon ternary alloy phase; the Fe content in the interdiffusion layer is greater than 60 wt%; the Fe content in the first iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; the Fe content in the first iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 68 wt%; the Fe content in the second iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; the Fe content in the second iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 70 wt%; and the Fe content in the aluminum-silicon alloy phase is less than 5 wt%. The aluminum alloy metallographic coatings of the aluminum-silicon coated hot-formed steel plate parts obtained in Comparative Examples 1-5 all include interdiffusion layers, an iron-aluminum layer, an iron-aluminum-silicon ternary alloy phase, and an iron-aluminum layer stacked sequentially in the direction away from the steel substrate, without an aluminum-silicon alloy phase; the aluminum alloy metallographic coating of the aluminum-silicon coated hot-formed steel plate parts obtained in Comparative Example 6 includes interdiffusion layers, a first iron-aluminum alloy phase, a first iron-aluminum-silicon ternary alloy phase, a second iron-aluminum alloy phase, and a surface layer stacked sequentially in the direction away from the steel substrate; the surface layer is an aluminum-silicon alloy phase and a second iron-aluminum-silicon ternary alloy phase; the Fe content in the interdiffusion layer is greater than 60 wt%; the Fe content in the first iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; the Fe content in the first iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 68 wt%; the Fe content in the second iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%; the Fe content in the second iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 70 wt%; the Fe content in the aluminum-silicon alloy phase is less than 5 wt%.

[0074] Sacrificial anode protection test: Each aluminum-silicon coated hot-formed steel plate component was cut into 20mm × 20mm × plate thickness samples. The material polarization curves were analyzed using a CHI 660D electrochemical workstation and its accompanying software. A three-electrode system was used: a saturated calomel electrode (SCE) as the reference electrode, a Pt electrode as the auxiliary electrode, and the steel plate as the working electrode. The electrolyte was a 5% (w / w) NaCl solution, and the test temperature was room temperature. If the coating potential was below -0.74V (the self-corrosion potential of the 22MnB5 steel substrate was -0.591V), the aluminum alloy metallographic coating was deemed to provide sacrificial anode protection to the steel substrate; otherwise, no protection was provided.

[0075] Zirconization pretreatment performance evaluation: Using a two-component automotive degreaser (FC-L5000A (40g / L) / FC-E2021SB (16g / L) from Shanghai Pakasek Co., Ltd.) at 50℃, each aluminum-silicon coated hot-formed steel sheet component was immersed in the degreaser for 2 minutes, then rinsed with deionized water. After degreasing, zirconia treatment was performed using Pakasek CT8000 zirconium-based phosphorus-free pretreatment agent (Shanghai Pakasek Co., Ltd.). The temperature was 35℃, pH 3.8, and the treatment time was 2 minutes. After pretreatment, the components were rinsed with water and dried. The film weight was measured using XRF fluorescence spectroscopy, with Zr as the characteristic element.

[0076] Evaluation of Phosphating Pretreatment Performance: Using a two-component automotive degreasing agent (FC-L5000A (40g / L) / FC-E2021SB (16g / L) from Shanghai Pakasek Co., Ltd.) at a degreasing solution temperature of 50℃, each aluminum-silicon coated hot-formed steel sheet component was immersed in the degreasing solution for 2 minutes, then rinsed with deionized water. After degreasing, phosphating was performed. The components were immersed in 2g / L PL-X surface conditioner for 30 seconds, then placed in PB-L3035SM phosphating agent (Shanghai Pakasek Co., Ltd.) for phosphating at a temperature of 35℃, with a free acidity (FA) of 0.9 pt, a total acidity (TA) of 20.0 pt, an accelerator concentration (AC) of 3.0 pt, and a treatment time of 2 minutes. After pretreatment, the components were rinsed with water and dried. The coverage of the phosphating film was observed using a scanning electron microscope.

[0077] Evaluation method for corrosion resistance after coating: Samples after zirconium pretreatment were subjected to electrophoresis. An optimized process was used to achieve a dry film thickness of 20±2μm. The electrophoretic paint model was Hunan Xiangjiang Kansai Coatings HT8000C. After electrophoresis, a scratch corrosion test was performed. The paint was scratched with a scratching knife, and then placed in a corrosive environment for 26 days. The samples were then removed, and the presence of red rust in the scratched areas was observed. Surface rust was removed, and the scratched areas were peeled off with tape. The width of the peeled paint in the scratched areas was used as the evaluation index. The cyclic corrosion environment test method included 8 hours of ambient temperature maintenance (25±3℃, with four 3-minute sprays of salt solution during this period; the salt solution composition was: 0.9wt% NaCl, 0.1wt% CaCl2, 0.075-0.9wt% NaHCO3), 8 hours of humid heat (49±2℃, 100%RH), and 8 hours of drying (60±2℃, <30%RH), for a total of 26 cycles.

[0078] The evaluation results are listed in Table 1.

[0079] Table 1 serial number Source of copper in the surface treatment layer of aluminum-silicon coated hot-formed steel sheet Total time required for complete austenitization / min Heating time / min Area fraction of aluminum-silicon alloy phase on the surface of aluminum alloy metallographic coating / % Is there sacrificial anode protection? <![CDATA[Zr conversion coating adhesion amount (mg / m 2 )]]> Paint peel width (mm) Are there any red rusts in the scratched areas? Phosphating film coverage % Example 1 Copper metal 1.5 1.5 100 have 20 2.5 none 100 Example 2 Copper acetate 2.0 2.0 80 have 30 2.5 none 100 Example 3 Copper acetate 2.5 2.5 60 have 18 2.0 none 100 Example 4 Copper citrate 3.0 3.0 40 have 35 2.5 none 100 Example 5 Copper acetate 5.0 5.0 20 have 19 2.5 none 95 Comparative Example 1 / 2.5 2.5 0 none 5 3.5 have 0 Comparative Example 2 / 3.5 3.5 0 none 2 4.5 have 0 Comparative Example 3 / 4.5 4.5 0 none 5 4.5 have 1 Comparative Example 4 / 5.0 5.0 0 none 3 4.0 have 0 Comparative Example 5 / 8.0 8.0 0 none 1 5.0 have 0 Comparative Example 6 / 8.0 6.0 10 none 4 9.0 have 5 As can be seen from the results in Table 1, for the same steel substrate thickness, the total heating time required for complete austenitization in the examples is significantly shorter than that in the comparative examples, by 1-3 minutes. Furthermore, compared to the comparative examples, the pretreatment performance of the examples is significantly improved, resulting in a higher pretreatment film weight and excellent corrosion resistance after electrophoretic coating.

[0080] Coating structure and sacrificial anode protection: Since the area ratio of aluminum-silicon alloy phase on the surface of the aluminum alloy metallographic coating in the examples is greater than 20%, the examples all have sacrificial anode protection. However, the aluminum alloy metallographic coating surface in the comparative examples is Fe2Al5 (Comparative Examples 1-5) or a small amount of AlSi alloy phase (Comparative Example 6), and there is no sacrificial anode protection.

[0081] Coating performance: Compared with Comparative Examples 1-6, the examples significantly improved the zirconium film weight and the paint peel width, and no red rust was generated at the scratched areas. Comparative Example 6, due to the short heating time, did not reach the total time required for complete austenitization, and therefore the substrate was not fully austenitized. The resulting aluminum-silicon coated hot-formed steel sheet parts retained 10% of the aluminum-silicon alloy phase on the surface, but the paint corrosion resistance decreased significantly after coating, and red rust was generated in the scratched areas.

[0082] Test Example 2 Comparative Examples 7-9 were heated and hot-stamped according to the method of Test Example 1 to obtain aluminum-silicon coated hot-formed steel sheet parts. The appearance quality of the aluminum-silicon coated hot-formed steel sheet parts of Examples 1, 2 and 4 and Comparative Examples 7-9 is shown in Table 2.

[0083] Table 2 serial number Source of copper in the surface heat treatment layer Appearance quality of the parts after processing Example 1 Copper metal Uniform appearance, yellow-red Example 2 Copper acetate Uniform appearance, dark green Example 4 Copper citrate Uniform appearance, dark green Comparative Example 7 Copper sulfate Uneven distribution, large areas of black spots Comparative Example 8 Copper nitrate Uneven distribution, large areas of black spots Comparative Example 9 Copper chloride Uneven distribution, large areas of black spots As shown in Table 2, the aluminum-silicon coated hot-formed steel plate parts obtained by the present invention have better surface appearance quality. However, the comparative example uses copper sulfate, copper nitrate, and copper chloride, which will cause severe corrosion to the coating on the steel plate surface, resulting in poor surface quality and a large number of unevenly distributed black spots.

[0084] It should be understood that any parts not described in detail in this specification belong to the prior art.

[0085] The preferred embodiments of the present invention have been described in detail above; however, the present invention is not limited thereto. Within the scope of the inventive concept, various simple modifications can be made to the technical solutions of the present invention, including combinations of various technical features in any other suitable manner. These simple modifications and combinations should also be considered as the content disclosed in the present invention and are all within the protection scope of the present invention.

Claims

1. A hot-formed steel sheet with an aluminum-silicon coating, characterized in that, The aluminum-silicon coated hot-formed steel sheet includes a steel substrate, at least one surface of the steel substrate is coated with an aluminum alloy coating, and the surface of the aluminum alloy coating is further coated with a surface treatment layer. The chemical element weight percentage of the aluminum alloy coating includes: 8%≤Si≤12%, Fe≤3%, with the remainder being aluminum and unavoidable impurities; The surface treatment layer contains copper. The copper element in the surface treatment layer comes from one or more of copper, copper oxide, copper hydroxide, copper acetate, and copper citrate.

2. A hot-formed steel part with an aluminum-silicon coated layer, characterized in that, The aluminum-silicon coated hot-formed steel parts are obtained by hot-forming the aluminum-silicon coated hot-formed steel sheet as described in claim 1. The aluminum-silicon coated hot-formed steel component includes a steel substrate, at least one surface of which is coated with an aluminum alloy metallographic coating, and the surface of the aluminum alloy metallographic coating is further coated with a surface heat treatment layer. The aluminum alloy metallographic coating includes an aluminum-silicon alloy phase located near the surface heat treatment layer, and the area fraction of the aluminum-silicon alloy phase on the surface of the aluminum alloy metallographic coating is ≥20%. The Fe content in the aluminum-silicon alloy phase is less than 5 wt%.

3. The aluminum-silicon coated hot-formed steel parts according to claim 2, characterized in that, The aluminum alloy metallographic coating comprises a mutually diffused layer, a first iron-aluminum-silicon ternary alloy phase, and a surface layer, which are sequentially stacked in a direction away from the steel substrate; the surface layer contains an aluminum-silicon alloy phase.

4. The aluminum-silicon coated hot-formed steel sheet component according to claim 2, characterized in that, The aluminum alloy metallographic coating comprises a mutually diffused layer, a first iron-aluminum alloy phase, a first iron-aluminum-silicon ternary alloy phase, a second iron-aluminum alloy phase, and a surface layer, which are sequentially stacked in a direction away from the steel substrate; the surface layer contains an aluminum-silicon alloy phase and a second iron-aluminum-silicon ternary alloy phase.

5. The aluminum-silicon coated hot-formed steel sheet component according to claim 4, characterized in that, The Fe content in the interdiffusion layer is greater than 60 wt%; The Fe content in the first iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%. The Fe content in the first iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 68 wt%.

6. The aluminum-silicon coated hot-formed steel sheet component according to claim 5, characterized in that, The Fe content in the second iron-aluminum alloy phase is greater than 40 wt% and less than 75 wt%. The Fe content in the second iron-aluminum-silicon ternary alloy phase is greater than 25 wt% and less than 70 wt%.

7. The method for preparing aluminum-silicon coated hot-formed steel parts according to any one of claims 2-6, characterized in that, include: The aluminum-silicon coated hot-formed steel sheet of claim 1 is heated and hot-stamped to obtain aluminum-silicon coated hot-formed steel parts.

8. The preparation method according to claim 7, characterized in that, The heating temperature is 840-1100℃.

9. The preparation method according to claim 7 or 8, characterized in that, When the thickness of the aluminum-silicon coated hot-formed steel sheet is >1.4mm, the heating time is 3-5min; When the thickness of the aluminum-silicon coated hot-formed steel sheet is ≤1.4mm, the heating time is 1-3min.

10. The preparation method according to claim 7, characterized in that, The conditions for hot stamping include: a temperature of 500-700℃ and a holding time of 5-40s.

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