Aluminum coating hot forming steel plate with high heating efficiency and hot forming part with excellent phosphating property

Abstract

The invention provides a high-heating-efficiency hot-formed steel plate with an aluminum coating and a hot-formed part with excellent phosphating property, and at least one surface of the hot-formed steel plate with the aluminum coating sequentially comprises a steel substrate, an aluminum alloy coating and a Fe coating from the substrate to the top; the aluminum alloy coating comprises the following components in percentage by mass: 8.0-12.0% of Si, less than or equal to 2.0% of Fe and the balance of aluminum and inevitable impurities; the Fe coating contains 0.1 to 2.0 g / m < 2 > by weight of Fe, preferably 0.1 to 1.0 g / m < 2 > by weight of Fe, in terms of Fe content; the hot-formed steel plate with the aluminum plating layer has high heating efficiency in the hot-pressing forming process and has good phosphating property after hot-pressing forming, the plating layer has a sacrificial anode protection effect on a base body, and the corrosion resistance is good after painting.

Description

Technical Field

[0001] The present invention belongs to the technical field of hot-formed steel, and particularly relates to an aluminum-based coated hot-formed steel plate with high heating efficiency and a hot-formed part with excellent phosphatability. Background Art

[0002] Due to the requirements of lightweight and anti-corrosion performance, high-strength coated hot-formed steel is widely used in automotive parts. Among the coated hot-formed steels, aluminum-based coated hot-formed steel plates are widely used.

[0003] Body parts need to be phosphated to form a phosphate film to ensure the adhesion between the paint and the substrate. However, a dense aluminum-silicon oxide can be formed on the surface of the aluminum-silicon coated hot-formed steel after hot forming, and the presence of these oxides makes it difficult to phosphorate during the painting process.

[0004] For the sake of production efficiency and energy conservation and emission reduction, it is desirable to shorten the heating time in the furnace as much as possible. However, for the sake of painting, a high heating rate will lead to insufficient alloying and thus reduce the adhesion and corrosion resistance after hot forming.

[0005] There are known some technologies for improving the heating efficiency of aluminum-based coated hot-formed steel, such as Chinese Patent CN103492606A, Chinese Patent CN106164184A, and Chinese Patent CN 116219271A, which improve the heating efficiency by applying a substance with a higher heat absorption efficiency than aluminum alloy on the steel plate surface. However, these methods for improving the heating efficiency cannot solve the technical problems of non-phosphatability after hot forming and low corrosion resistance after painting, because these substances will volatilize during the hot forming process and have no contribution to the subsequent phosphating process.

[0006] There are also known technical solutions aimed at improving the phosphating performance of aluminum-silicon coatings. For example, Chinese Patent CN105829578A discloses a steel plate for press hardening including an aluminum-based coating and a ZnO coating. Again, Chinese Patent CN107250414A discloses a steel plate coated with an aluminum-based coating and further including a second zinc coating, which has the effect of improving phosphate surface treatment. However, the ZnO coatings and zinc coatings in these patents do not have the technical effect of improving the heating efficiency.

[0007] In summary, there is currently a lack of a technical solution that can simultaneously improve the phosphatability and heating efficiency of aluminum-silicon coated hot-formed steel. Summary of the Invention

[0008] To solve the above technical problems, the present invention provides an aluminum-based coated hot-formed steel plate and a preparation method thereof. The aluminum-based coated hot-formed steel plate has high heating efficiency during the hot pressing process, good phosphatability after hot pressing, and the coating has a sacrificial anode protection effect on the substrate.

[0009] The present invention also provides a hot - formed component, which is obtained by heating and heat - insulating the aluminum - based coating hot - formed steel sheet of the present invention and then hot - stamping. This hot - formed component has good phosphatability and excellent corrosion resistance after painting.

[0010] The technical solution adopted by the present invention is as follows:

[0011] An aluminum - based coating hot - formed steel sheet, on at least one surface of the aluminum - based coating hot - formed steel sheet, sequentially includes a steel substrate, an aluminum alloy coating, and an Fe coating from the substrate upwards;

[0012] The aluminum alloy coating includes the following components by mass percentage: Si 8.0 - 12.0%, Fe ≤ 2.0%, and the rest is aluminum and inevitable impurities;

[0013] In the Fe coating, in terms of Fe content, it contains 0.1 - 2.0 g / m 2 weight of Fe, preferably contains 0.1 - 1.0 g / m 2 weight of Fe.

[0014] Furthermore, in the Fe coating, except for inevitable impurities, it does not contain any metal other than Fe.

[0015] The Fe coating is one or several of Fe, Fe oxides or their hydrates, Fe halogen - group compounds or their hydrates, Fe organic acid salt compounds or their hydrates, Fe carbonate compounds or their hydrates.

[0016] Furthermore, an anti - rust oil layer is also covered on the Fe coating. The purpose of coating the anti - rust oil is for temporary rust prevention and to prevent the coating from being scratched during blanking. Since it decomposes during hot forming, its coating amount does not affect the technical effects of the present invention. The adhesion amount of the anti - rust oil is preferably 0.5 - 2 g / m 2 .

[0017] The Fe - containing coating is formed by electroplating Fe, electroless plating Fe, or vacuum plating Fe on the aluminum alloy coating.

[0018] The Fe - containing coating is formed by attaching an Fe compound layer through contacting a plated aluminum sheet with a solution containing Fe ions.

[0019] The Fe - containing coating is formed by applying a powder or colloidal solution containing Fe oxides, Fe hydroxides, Fe carbonate compounds, or Fe organic acid salt compounds to the aluminum alloy coating. In this embodiment, a binder such as resin can be used to enhance the adhesion between the Fe compound and the aluminum alloy coating, but the selected resin should not contain silicon, phosphorus, and nitrogen elements. Silicon and phosphorus elements are not conducive to the painting quality after hot forming, and nitrogen elements will cause NO x gas emissions.

[0020] The present invention also provides a method for preparing the aluminum-based coated hot forming steel sheet. The preparation method includes the following steps: subjecting a hot-rolled substrate or a cold-rolled substrate to hot dip coating to form an aluminum alloy coating on the surface of the substrate, and then forming an Fe coating on the surface of at least one aluminum alloy coating.

[0021] A hot forming component is obtained by heating and holding the aluminum-based coated hot forming steel sheet of the present invention and then performing hot stamping. On at least one surface thereof, an aluminum alloy coating and iron oxide are successively arranged upward from the steel substrate, wherein the iron oxide is in granular form and is distributed on the surface of the aluminum alloy coating at a ratio of at least 50% by area.

[0022] The heating temperature for the heating and holding is 840°C - 1100°C; for a sheet with a thickness of ≥1.4 mm, the holding time is 2 - 5 min; for a sheet with a thickness of <1.4 mm, the holding time is 1 - 2 min. Due to the presence of the surface treatment layer Fe, the heat absorption efficiency of the sheet is improved, and the time required to rise to the austenitizing temperature is shorter. The heating time of this heating process can be shortened by more than 1 min compared with the conventional hot forming process. The heating furnace can use any atmosphere such as N 2 protective atmosphere, air, etc. For cost considerations, air is preferably used. When using a protective atmosphere, part of the Fe may not be completely oxidized, but then during the process of transferring the blank from the furnace to the mold and hot stamping, the oxide can still be fully formed, thus not affecting the phosphating effect.

[0023] The temperature of the hot stamping is 500 - 700°C.

[0024] The aluminum-based coated hot forming steel sheet provided by the present invention is not restricted by the composition of the steel substrate. As a conventional example, it is 22MnB5, and its chemical composition and weight percentage are: 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%, and the balance is iron and inevitable impurities from steel manufacturing.

[0025] In the aluminum alloy coating composition of the aluminum-based coated hot forming steel sheet provided by the present invention, Si can form an Fe-Al-Si inhibition layer on the surface of the steel sheet, which can effectively hinder the formation of the brittle phase Fe2Al5 and improve the adhesion of the coating. When the Si content is less than 8.0%, the Fe-Al alloy layer becomes thicker and the adhesion of the coating decreases. When the Si content is greater than 12.0%, the surface quality of the coating is affected. According to the above situation, the Si content in the aluminum alloy coating of the present invention is controlled to be 8.0 - 12.0%.

[0026] Based on painstaking research, the inventors have recognized that the amount of Fe attachment needs to be strictly limited to ensure the technical effects of simultaneously improving the heating efficiency and painting performance. When the amount of Fe attachment is greater than 2.0 g / m 2 , although the heating efficiency and phosphating film weight can be improved, the peeling width exceeds the standard in the corrosion test after painting. The reason is that a loose and thick oxide layer is formed on the Fe coating during hot forming, and the phosphating film covers the loose oxide layer during the subsequent painting process, and the coating can be peeled off from between the iron oxide layers. When the amount of Fe attachment is less than 0.1 g / m 2 , the coverage rate of iron oxide formed on the surface during hot forming is insufficient, and the effects of improving the heating efficiency and phosphatability are insufficient. The inventors have also found that when Fe has an attachment amount of 0.1-1.0 g / m 2 , it has the smallest paint peeling width and a high heating rate.

[0027] Compared with the prior art, the present invention has the following beneficial effects:

[0028] By applying an Fe-containing coating on the surface of the aluminum coating, the present invention solves the technical defect of poor phosphating performance of traditional aluminum-silicon hot-formed parts, has excellent corrosion resistance after painting, and at the same time improves the heat absorption efficiency of aluminized hot-formed steel during the hot forming process, reduces the hot forming heating time, and this method has the technical advantages of environmental protection and low cost. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 It is a schematic diagram of the evolution of the coating of the aluminum-based coated hot-formed steel plate in the present invention in each process. DETAILED DESCRIPTION OF THE INVENTION

[0030] The present invention will be described in detail below in conjunction with embodiments.

[0031] The chemical composition and weight percentages of the steel plates used for the coated hot-formed steel plates in the following Examples 1-5 and Comparative Examples 1-5 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%, and the balance is iron and unavoidable impurities.

[0032] The steel plates in the above examples and comparative examples are hot-dip galvanized to obtain aluminum alloy coated steel plates in a hot-rolled state or an annealed state. For example, hot-based aluminum alloy coated steel plates are obtained through hot rolling → pickling → hot dip galvanizing → tempering, or aluminum alloy coated steel plates are obtained through hot rolling → pickling → cold rolling → cleaning → annealing → hot dip galvanizing → tempering.

[0033] The aluminum alloy coating contains 8.0 - 12.0% by mass of Si, up to 2% by mass of Fe, and the rest is aluminum and inevitable impurities.

[0034] The following is a detailed description of the methods for obtaining the coatings in each example and comparative example.

[0035] Method for obtaining the aluminum alloy coated sheet in Example 1 and Comparative Example 1: The aluminum alloy coated steel sheet is obtained through hot rolling → pickling → cold rolling → cleaning → annealing → hot dip coating → tempering. After completing the above steps, the aluminum alloy coating contains 8.0% by mass of Si, 2.0% by mass of Fe, and the rest is aluminum and inevitable impurities. The sheet thickness is 1.2 mm, the coating is equally thickly coated on both sides, and the weight of each single-sided coating is 40 g / m 2 。

[0036] Method for obtaining the aluminum alloy coated sheet in Example 2 and Comparative Example 2: The aluminum alloy coated steel sheet is obtained through hot rolling → pickling → hot dip coating → tempering. After completing the above steps, the aluminum alloy coating contains 9.0% by mass of Si, 1.0% by mass of Fe, and the rest is aluminum and inevitable impurities. The sheet thickness is 1.2 mm, the coating is equally thickly coated on both sides, and the weight of each single-sided coating is 60 g / m 2 。

[0037] Method for obtaining the aluminum alloy coated sheet in Example 3 and Comparative Example 3: The aluminum alloy coated steel sheet is obtained through hot rolling → pickling → cold rolling → cleaning → annealing → hot dip coating → tempering. After completing the above steps, the aluminum alloy coating contains 10.0% by mass of Si, 1.5% by mass of Fe, and the rest is aluminum and inevitable impurities. The sheet thickness is 1.4 mm, the coating is equally thickly coated on both sides, and the weight of each single-sided coating is 35 g / m 2 。

[0038] Method for obtaining the aluminum alloy coated sheet in Example 4 and Comparative Example 4: The aluminum alloy coated steel sheet is obtained through hot rolling → pickling → cold rolling → cleaning → annealing → hot dip coating → tempering. After completing the above steps, the aluminum alloy coating contains 12% by mass of Si, 2.0% by mass of Fe, and the rest is aluminum and inevitable impurities. The sheet thickness is 1.6 mm, the coating is equally thickly coated on both sides, and the weight of each single-sided coating is 75 g / m 2 。

[0039] Method for obtaining the aluminum alloy coated sheet in Example 5 and Comparative Example 5: The aluminum alloy coated steel sheet is obtained through hot rolling → pickling → cold rolling → cleaning → annealing → hot dip coating → tempering. After completing the above steps, the aluminum alloy coating contains 10% by mass of Si, 1.5% by mass of Fe, and the rest is aluminum and inevitable impurities. The sheet thickness is 2.0 mm, the coating is equally thickly coated on both sides, and the weight of each single-sided coating is 75 g / m 2。

[0040] Apply an Fe-containing coating on the Al alloy coating by any method such as electroless plating, electroplating, vacuum plating, roll coating, spraying, etc., and control the adhesion amount of the Fe coating to be 0.1 - 2.0 g / m 2 。

[0041] As a specific implementation example, the steps of applying the Fe coating in the following Examples 1 - 3 and Comparative Examples 2 - 3 are as follows:

[0042] (1) Prepare an emulsion with the following components:

[0043] 150 g / L of iron oxide black powder with a particle size of 50 nm;

[0044] 200 g / L of polyacrylate;

[0045] 50 g / L of ethanol;

[0046] 5 g / L of dodecyl glucoside;

[0047] The balance is water.

[0048] (2) Coat the emulsion on the above aluminum alloy coated plate.

[0049] (3) Heat to 200 °C and dry for 30 s, then cool to room temperature.

[0050] As a specific implementation example, the steps of applying the Fe coating in the following Examples 4, 5 and Comparative Examples 4, 5 are as follows:

[0051] (1) Alkaline wash the surface of the aluminized silicon steel plate to remove oil stains, and rinse with deionized water;

[0052] (2) Prepare a solution with the following components:

[0053] 80 g / L of ferrous chloride;

[0054] 14 g / L of hydrofluoric acid;

[0055] 5 g / L of sulfamic acid;

[0056] 1 g / L of dodecyl glucoside;

[0057] The balance is water.

[0058] (3) At room temperature, immerse the aluminized silicon steel plate in the above solution for 2 - 3 min.

[0059] (4) Rinse the surface of the steel plate with deionized water to remove the residual acid, and then blow dry.

[0060] Select to use an anti-rust oil to coat on the aluminum alloy coating or Fe coating. The purpose of coating the anti-rust oil is for temporary anti-rust and to prevent scratching of the coating during blanking. Since it decomposes during hot forming, its coating amount does not affect the effect of the present invention. The following examples and comparative examples are all coated with 1.5 g / m of Quaker Ferrocoat N 6130 anti-rust oil 2 An anti-rust oil is coated on each of the examples and comparative examples.

[0061] The steel plates coated as above are evaluated for performance according to the following method.

[0062] Measurement of the time required from 20 °C to 900 °C / s and the heating rate: Place the cut sheet in a 900 °C box furnace, use a thermocouple to measure the time required to heat to 900 °C, and calculate the heating rate.

[0063] Total heating time: Place the cut sheet in a 900 °C box furnace, starting from 1 min, extend it by 30 s in sequence, then cool it in a flat die. Samples of 10 mm × 10 mm × sheet thickness cut from the experimental steel after the die is quenched are ground, mechanically polished, and etched with picric acid. Observe and measure the original austenite grain size under an optical microscope to observe the martensite structure. The heating time when martensite is completely formed is the total heating time.

[0064] Performance evaluation of pre-treatment before painting:

[0065] Phosphating performance evaluation: Use the two-component automotive degreaser FC-L5000A (40 g / L) / FC-E2021SB (16 g / L) of Shanghai Pakara Kogyo Co., Ltd. The temperature of the degreasing solution is 50 °C. Immerse the steel plate after hot forming in the degreasing solution for 2 minutes, then take it out and rinse it with deionized water. After degreasing, perform phosphating treatment. Use a PL-X surface conditioner (Shanghai Pakara Kogyo Co., Ltd.) to condition for 30 s (immersion), and then use Pakara PB-3035SB ternary phosphating treatment. The parameters of the phosphating solution are: total acidity 22.0 pt, free acidity 1.0 pt, accelerator concentration 2.0 pt, temperature 35 °C, time 2 min. After the pre-treatment, wash it with water and blow it dry, and then perform a phosphating film weight test according to the GB / T 9792-2003 standard.

[0066] Method for evaluating corrosion resistance after painting: After pretreatment, electrophoresis is carried out, and an optimized process is used to make the dry film thickness of electrophoresis reach 20±2μm. The model of the electrophoretic paint is HT8000C of Hunan Xiangjiang Kansai Paint Co., Ltd. After electrophoresis, a scratch corrosion test is carried out. A scratch knife is used to scratch the paint, and then it is placed in a corrosion environment for 26 days and then taken out. The floating rust is removed, and the tape is used to peel the scratched area. The width of the paint peeling in the scratched area is used as the evaluation index. The cyclic corrosion environment test method includes 8h at normal temperature (25±3℃, during which the salt solution is sprayed 4 times for 3min each, and the composition of the salt solution is: 0.9wt% NaCl, 0.1wt% CaCl 2 , 0.0750.9wt% NaHCO 3 ), 8h of damp heat (49±2℃, 100% RH), 8h of drying (60±2℃, <30% RH), a total of 26 cycles.

[0067] The adhesion amount and evaluation results of the Fe coating in the aluminum-based plated hot-formed steel plates in each example and comparative example are listed in Table 1.

[0068] Evaluation results:

[0069] Compared with Comparative Example 1, Example 1 significantly shortens the heating time from 20 to 900℃, and the total heating time is shortened by 1min. And compared with Comparative Example 1, the pretreatment performance of Example 1 is significantly improved, with a higher pretreatment film weight, and excellent corrosion resistance after electrophoretic coating.

[0070] The Fe adhesion amount of Comparative Example 2 is 0.05g / m 2 , and compared with Example 2, the improvement in heating efficiency, phosphating film weight and paint peeling width is insufficient.

[0071] Compared with Comparative Examples 3 and 4, Examples 3 and 4 have relatively close heating rates. In terms of phosphating film weight, Comparative Examples 3 / 4 increase slightly, while the paint peeling width after corrosion test for Comparative Examples 3 / 4 becomes worse. This is because more Fe oxides fail to react with the phosphating solution to form a film completely.

[0072] Compared with Comparative Example 5, Example 5 has similar heating rate and phosphating film weight, but the paint peeling width of Comparative Example 5 increases significantly. This is because more Fe oxides fail to react with the phosphating solution to form a film completely.

[0073] Table 1 Surface treatment methods and evaluation results of each example and comparative example

[0074]

[0075]

[0076] The above detailed description of an aluminum-based plated hot stamping steel sheet with high heating efficiency and a hot stamping component with excellent phosphating property with reference to the embodiments is illustrative rather than restrictive. Several embodiments can be enumerated within the defined scope. Therefore, changes and modifications without departing from the general concept of the present invention shall fall within the protection scope of the present invention.

Claims

1. An aluminum-coated hot-formed steel plate, characterized in that: At least one side of the aluminum-coated hot-formed steel plate includes, from the substrate upward, a steel substrate, an aluminum alloy coating and an Fe coating; The aluminum alloy coating comprises the following components in mass percentage: Si 8.0-12.0%, Fe≤2.0%, and the rest is aluminum and unavoidable impurities; The Fe coating contains 0.1 to 2.0 g / m 2 Weight of Fe.

2. The aluminum-coated hot-formed steel sheet according to claim 1, characterized in that: The Fe coating is one or more of Fe, Fe oxide or its hydrate, Fe halogen compound or its hydrate, Fe organic acid salt compound or its hydrate, Fe carbonate compound or its hydrate.

3. The aluminum-coated hot-formed steel sheet according to claim 1, characterized in that: The Fe coating is also covered with an anti-rust oil layer.

4. The aluminum-coated hot-formed steel sheet according to any one of claims 1 to 3, characterized in that: The Fe-containing coating is formed by plating Fe on the aluminum alloy coating by chemical plating, electroplating or vacuum plating.

5. The aluminum-coated hot-formed steel sheet according to any one of claims 1 to 3, characterized in that: The Fe-containing coating is an Fe compound layer formed by contacting the aluminum plate with a solution containing Fe ions.

6. The aluminum-coated hot-formed steel sheet according to any one of claims 1 to 3, characterized in that: The Fe-containing coating layer is formed by applying a powder or a colloidal solution containing Fe oxide, Fe hydroxide, Fe carbonate compound or Fe organic acid salt compound onto the aluminum alloy plating layer.

7. The method for preparing an aluminum-coated hot-formed steel sheet according to any one of claims 1 to 6, characterized in that: The preparation method comprises the following steps: hot-dip plating a hot-rolled substrate or a cold-rolled substrate to form an aluminum alloy coating on the surface of the substrate, and then forming an Fe coating on the surface of at least one aluminum alloy coating.

8. A thermoformed component, characterized in that: The hot-formed component is made by heating and heat-insulating the aluminum-coated hot-formed steel plate according to any one of claims 1 to 6, and then hot stamping.

9. The hot formed component according to claim 8, characterized in that The heating temperature of the heating and heat preservation is 840°C-1100°C; for the plate material with a thickness of ≥1.4mm, the heat preservation time is 2-5min; for the plate material with a thickness of <1.4mm, the heat preservation time is 1-2min.

10. The hot formed component according to claim 8, characterized in that The temperature of the hot stamping is 500-700°C.

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