Aluminum-clad steel sheet, thermoformed component and manufacturing methods

Description

1 / 27 Aluminum-clad steel sheet, thermoformed component and manufacturing methods TECHNICAL FIELD

[001] The present invention relates to the field of metal-clad steel sheets, particularly an aluminum-clad steel sheet, a thermoformed component and methods of manufacturing. BACKGROUND

[002] Aluminum-coated steel sheets are widely used in various fields, such as automobiles, household appliances, ovens, and furnaces, due to their good heat resistance and corrosion resistance. An aluminum coating layer can prevent oxidation and decarburization of a steel sheet during heat treatment due to its high-temperature oxidation resistance. Therefore, aluminum films are widely used in the thermoformed steel field (especially hot-stamped steel). The global demand for aluminum-coated hot-stamped steel is approximately 2 million tons. However, thermoforming aluminum-coated steel sheets also faces some challenges, such as the problems of aluminum melt-induced roll sticking and the risk of hydrogen embrittlement during heat treatment.

[003] The problem of melt-induced roll sticking in aluminum reduces production efficiency and the quality of thermoformed components. To improve this problem, researchers generally aim to control the heating rate to avoid aluminum melting caused by rapid heating. For example, patent CN101583486B explicitly proposes that a heating rate of an aluminum-coated steel sheet between 20700°C should not exceed 12°C / s. Patent CN109518114A also discloses a step-down heating method to avoid induced roll sticking. Petition 870230063687, dated 07 / 20 / 2023, p. 56 / 120 2 / 27 by melting the aluminum and reducing the heating rate.

[004] The risk of hydrogen embrittlement will affect properties such as delayed crack resistance of the thermoformed component. To reduce the risk of hydrogen embrittlement of hot-stamped aluminum-silicon steel, patent CN100471595C discloses a hot stamping method in which the risk of hydrogen embrittlement of hot-stamped components is reduced by controlling the atmosphere of a hot pressing process. Patent CN104160050B discloses hot-stamped steel in which the risk of hydrogen embrittlement of a steel sheet is reduced by increasing the concentration of Mn-containing inclusions and Mn oxides in the steel.

[005] The present invention provides an aluminum-coated steel sheet, a thermoformed component and manufacturing methods in response to the shortcomings of existing products and technologies. SUMMARY

[006] One objective of the present invention is to solve the problems of melt-induced roll sticking and hydrogen embrittlement risk that occur during the heat treatment process when manufacturing thermoformed components from aluminum-clad steel sheets. The present invention provides an aluminum-clad steel sheet, a thermoformed component, and manufacturing methods that can alleviate the problems of melt-induced roll sticking and hydrogen embrittlement risk during the thermoforming process of aluminum-clad steel sheets.

[007] The present invention provides an aluminum-coated steel sheet comprising a substrate and a coating layer on the substrate surface, wherein the microstructure of the coating layer includes an Mg2Si phase and an AlMgSiFe phase, and the Mg2Si phase has a diameter of Petition 870230063687, dated 07 / 20 / 2023, page 57 / 120 3 / 27 medium grain size of 0.001-5 μm.

[008] By adopting the above technical solution, the problems of melt-induced roll sticking and the risk of hydrogen embrittlement during the heat treatment of the manufacture of thermoformed components from aluminum-clad steel sheets can be alleviated, and the red rust resistance of thermoformed components manufactured from aluminum-clad steel sheets can be improved.

[009] Preferably, the coating layer includes a surface layer and a barrier layer, wherein the surface layer comprises the Mg2Si phase and the AlMgSiFe phase.

[010] Preferably, the coating layer additionally includes a barrier layer, wherein the barrier layer comprises Fe-Al and Fe-Al-Si alloys, and the barrier layer has a thickness less than or equal to 5 μm.

[011] Preferably, the coating layer of the aluminum-clad steel sheet has a thickness of 5-50 μm.

[012] Preferably, a composition of the aluminum-clad steel sheet substrate comprises, in mass percentage: 0.05-0.5% C, 0.01-2.0% Si, 0.3-3.0% Mn, 0.005-0.3% Al, 0.01% <Ti<0,1%, 0,0005%<B<0,1%, 0,05%<Cr<0,5 %, 0,0005%<Nb<0,1% e Fe.

[013] Preferably, the composition of the aluminum-clad steel sheet substrate comprises, in mass percentage: 0.05-0.5% C, 0.01-2.0% Si, 0.3-3.0% Mn, 0.005-0.3% Al, 0.01% <Ti<0,1%, 0,0005%<B<0,1%, 0,05%<Cr<0,5 %, 0,0005%<Nb<0,1%, com o restante sendo Fe e impurezas inevitáveis.

[014] Preferably, among the unavoidable impurities, in mass percentage, P<0.3%, S<0.1% and V<0.1%.

[015] The present invention also provides a manufacturing method for Petition 870230063687, dated 07 / 20 / 2023, page 58 / 120 4 / 27 the aluminum-clad steel sheet above, including the following steps: melting; rolling; and continuous annealing and hot coating, wherein the annealing temperature is 710-780°C, the temperature of a coating solution is 600-660°C, the temperature of the coating solution minus the temperature of a steel plate entering a coating container is less than or equal to 5°C, the steel plate is cooled after leaving the coating container, an average cooling rate from the temperature of the steel plate leaving the coating container to the solidification temperature of the coating layer is greater than 15°C / s, and an average cooling rate from the temperature of the steel plate leaving the coating container to 200°C is 10-30°C / s.

[016] Preferably, the chemical composition of the coating solution includes: 5-11% by mass of Si and 0.5-20% by mass of Mg.

[017] Preferably, the coating solution additionally comprises 1-10% Zn by mass.

[018] Preferably, the remainder of the coating solution is Al and unavoidable impurities.

[019] Preferably, the rolling stage includes hot rolling, wherein the hot rolling winding temperature is 630°C or less.

[020] Preferably, the rolling stage includes cold rolling, in which a deformation during cold rolling is 10-70%.

[021] The present invention also provides a thermoformed component manufactured from the aluminum-coated steel sheet described above.

[022] Preferably, the thermoformed component comprises a Petition 870230063687, dated 07 / 20 / 2023, page 59 / 120 5 / 27 surface layer and an inner layer, wherein the ratio of the mass percentage of Mg in the surface layer to the mass percentage of Mg in the inner layer is greater than or equal to 5, and the thermoformed component has a core hardness HV1 of 300 or more.

[023] The present invention further provides a manufacturing method for the thermoformed component above, including the following steps: To process aluminum-coated steel sheet into a billet; Perform heat treatment on the billet, where one form of heat treatment heating is single-stage heating or step-through heating; when the heat treatment heating method is single-stage heating, the heating stop temperature is a certain temperature in 900-1000°C and the total heating time is 10-600 seconds; and when the heat treatment heating method is step-through heating, the heating stop temperature comprises multiple temperatures in 700-1000°C, and the total heating time is 115 minutes, where the highest temperature of the multiple temperatures is a certain temperature in 900-1000°C, and the billet holding time at 900-1000°C is 10-600 seconds; and transfer the billet to a mold for thermoforming, where the billet temperature when transferred to the mold is 650°C or more, and a mold cooling rate is 30°C / s or higher.

[024] Preferably, a thermoforming process is hot stamping or hot rolling.

[025] Preferably, a thickening lamination step is additionally carried out before processing the aluminum-clad steel sheet into a billet. Petition 870230063687, dated 07 / 20 / 2023, pages 60 / 120 6 / 27 BRIEF DESCRIPTION OF THE DRAWINGS

[026] FIG. 1 shows a scanning spectrum of a coating layer of an aluminum-coated steel sheet of Example 2 of the present invention; and FIG. 2 shows the mass percentage of Mg in a coating layer of a thermoformed component of Example 2 of the present invention as a function of the coating layer depth.

[027] Reference numbers: 1. Mg2Si phase; and 2. AlMgSiFe phase. DETAILED DESCRIPTION

[028] The modes of implementation of the present invention are illustrated below by specific embodiments. Those skilled in the art can easily understand other advantages and effects of the present invention based on the content disclosed in the descriptive report. Although the description of the present invention is introduced together with the preferred embodiments, this does not mean that the features of the present invention are limited only to the embodiments. On the contrary, the description of the present invention together with the modes of implementation is intended to cover other alternatives or modifications that may be derived from the claims of the present invention. In order to provide a complete understanding of the present invention, the following description will include many specific details. However, the present invention can also be implemented without the use of these specific details.Additionally, some specific details will be omitted from the description in order to avoid confusion or obscuring the focus of the invention. It should be noted that, unless conflicting, embodiments of the invention and features of embodiments can be combined with each other.

[029] It should be noted that in this description, reference numbers and letters Petition 870230063687, dated 07 / 20 / 2023, p. 61 / 120 7 / 27 similar denote similar items in the following drawings. Therefore, once an item is defined in a drawing, further definitions and explanations are not necessary in subsequent drawings.

[030] In describing the embodiment, it should be noted that the terms in and similar terms indicate an orientation or positional relationship based on the orientation or positional relationship shown in the drawings, or the usual orientation or positional relationship when the invention is used, which is for the convenience of describing the invention and simplifying the description. It does not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation and, therefore, should not be interpreted as a limitation of the present invention.

[031] To make clearer the objective, the technical solutions and the advantages of the present invention, the modes of implementation of the present invention are described in detail together with the accompanying drawings.

[032] The present invention provides an aluminum-coated steel sheet comprising a substrate and a coating layer on the surface of the substrate, wherein the microstructure of the coating layer includes an Mg2Si phase and an AlMgSiFe phase, and the Mg2Si phase has an average grain diameter of 0.001-5 μm.

[033] The formation of the Mg2Si phase and the AlMgSiFe phase in the coating layer can reduce the proportion of the Al phase or the Al-Si phase in a coating layer, which is mainly composed of Al, break the agglomeration of these Al-containing phases on the surface of the coating layer and disperse them as much as possible, thus reducing the melting of aluminum during heat treatment, alleviating the issue of melt-induced roll sticking of aluminum during heat treatment. This allows the aluminum-coated steel sheet to withstand a faster heating rate for Petition 870230063687, dated 07 / 20 / 2023, page 62 / 120 8 / 27 improve production efficiency. In addition, this reduces the likelihood of aluminum reacting with H2O in the atmosphere during heat treatment to generate H2, minimizing the H2 content in the atmosphere during heat treatment, thus mitigating the risk of hydrogen embrittlement.

[034] In the embodiment of the present invention, the average grain diameter of the Mg2Si phase in the high-quality coating layer is 0.001-5 μm. The smaller the average grain diameter of the Mg2Si phase, the easier it is to distribute on the surface of the coating layer, which is more conducive to reducing the risk of hydrogen embrittlement.

[035] Preferably, the coating layer includes a surface layer comprising the Mg2Si phase and the AlMgSiFe phase.

[036] The coating layer consists mainly of an Al phase and a Si-rich phase, with the Mg2Si phase and the AlMgSiFe phase uniformly distributed in a clustered or networked manner within the surface layer. Since a Mg-containing phase readily accumulates on the surface of the coating layer, the Mg2Si phase and the AlMgSiFe phase in the coating layer are preferentially distributed on the surface of the coating layer during heat treatment. This effectively blocks the diffusion or penetration of H2 from the external atmosphere into the substrate and additionally reduces the risk of hydrogen embrittlement.

[037] The aforementioned coating layer additionally includes a barrier layer comprising Fe-Al and Fe-Al-Si alloys, and the barrier layer has a thickness less than or equal to 5 pm.

[038] When a substrate composed primarily of Fe is immersed in a coating solution composed primarily of Al and Si, the molten Al and Si will naturally bond with the Fe on the substrate surface, forming a barrier layer composed primarily of Fe-Al and Fe-Al-Si alloys. Petition 870230063687, dated 07 / 20 / 2023, page 63 / 120 9 / 27 The barrier layer is positioned between the steel sheet substrate and the surface layer of the coating. In the actual production process, the thickness of the coating barrier layer can be adjusted by controlling the immersion time of the steel sheet in the coating solution and other conditions. In embodiments of the present invention, the thickness of the barrier layer should be controlled to be within 5 μm. If the thickness of the barrier layer is too great, it may affect changes in the microstructure of the coating layer during cooling, preventing the formation of the Mg2Si and AlMgSiFe phases, causing excessively large grain sizes and potentially leading to delamination of the surface layer during subsequent thermoforming.

[039] Preferably, the coating layer of the aluminum-clad steel sheet has a thickness of 5-50 µm.

[040] During actual production, the coating layer thickness can be controlled by adjusting the immersion time of the substrate in the coating solution, the intensity of the airflow from an air knife, and similar factors. Longer immersion time results in a thicker coating layer, while higher airflow intensity from the air knife leads to a thinner coating layer.

[041] Preferably, a composition of the aluminum-clad steel sheet substrate comprises, in mass percentage: 0.05-0.5% C, 0.01-2.0% Si, 0.3-3.0% Mn, 0.005-0.3% Al, 0.01% <Ti<0,1%, 0,0005%<B<0,1%, 0,05%<Cr<0,5 %, 0,0005%<Nb<0,1% e Fe.

[042] Preferably, the composition of the aluminum-clad steel sheet substrate comprises, in mass percentage: 0.05-0.5% C, 0.01-2.0% Si, 0.3-3.0% Mn, 0.005-0.3% Al, 0.01% <Ti<0,1%, 0,0005%<B<0,1%, 0,05%<Cr<0,5 %, 0,0005%<Nb<0,1%, com o restante sendo Fe Petition 870230063687, dated 07 / 20 / 2023, page 64 / 120 10 / 27 and unavoidable impurities.

[043] In the composition of the substrate, the elements P, S and V are unavoidable impurities; the lower their content in the substrate, the better. Specifically, in the embodiments of the present application, in mass percentage, P<0.3%, S<0.1% and V<0.1%.

[044] The present invention also provides a manufacturing method for the above aluminum-coated steel sheet, including the following steps: foundry; rolling; and continuous annealing and hot coating, wherein the annealing temperature is 710-780°C, the temperature of a coating solution is 600-660°C, the temperature of the coating solution minus the temperature of a steel plate entering a coating container is less than or equal to 5°C, the steel plate is cooled after leaving the coating container, an average cooling rate from the temperature of the steel plate leaving the coating container to the solidification temperature of the coating layer is greater than 15°C / s, and an average cooling rate from the temperature of the steel plate leaving the coating container to 200°C is 10-30°C / s.

[045] If the annealing temperature is below 710°C, this can affect the platability of the steel sheet, causing undercoating or poor adhesion of the coating layer. If the annealing temperature exceeds 780°C, this can lead to wasted energy and further affect the surface condition of the steel sheet, which can affect the surface quality of the coating layer and the grain size of the Mg2Si phase and the formation of the AlMgSiFe phase in the coating layer.

[046] The temperature of the coating solution will affect the reaction of the alloy. Petition 870230063687, dated 07 / 20 / 2023, p. 65 / 120 11 / 27 of molten Al and Fe, thus affecting the composition and thickness of the barrier layer. In the present application, the temperature of the coating solution is controlled within the range of 600-660°C, and the temperature of the steel sheet entering the coating vessel is controlled to be slightly lower than the temperature of the coating solution, in order to obtain a barrier layer with adequate thickness and microstructure, ensuring the formation of the desired AlMgSiFe and Mg2Si phases in the surface layer during subsequent processing and preventing delamination of the surface layer.

[047] High or low coating solution temperature, as well as a significant difference between the temperature of the steel plate entering the coating vessel and the temperature of the coating solution, can affect the surface quality of the coating layer and the grain size of the Mg2Si phase, and the formation of the AlMgSiFe phase in the coating layer. This can result in an average grain diameter of the Mg2Si phase greater than 5 μm and / or the inability to form the AlMgSiFe phase. If the average particle size of the Mg2Si phase in the coating layer is too large, the surface of the coating layer will be visibly rough, affecting the appearance of the steel plate.

[048] The average cooling rate from the temperature of the steel plate exiting the cladding container to the solidification temperature of the cladding layer, as well as the average cooling rate from the temperature of the steel plate exiting the cladding container to 200°C, are both important. If these two cooling rates are too slow, the growth rate of the Al-Si phase will be too rapid, inhibiting the formation of the Mg2Si and AlMgSiFe phases. Consequently, the ability to overcome melt-induced roll sticking problems and the risk of hydrogen embrittlement is compromised. Petition 870230063687, dated 07 / 20 / 2023, p. 66 / 120 The 12 / 27 result found during the thermoforming process of the aluminum-coated steel sheet in the present application cannot be achieved. Furthermore, excessively slow cooling rates can result in the precipitation of the large-grained Mg2Si and AlMgSiFe phases in the coating layer, resulting in a rough coating surface and affecting the product's appearance. Conversely, if these two cooling rates are too fast, it can cause excessive strength in the steel sheet, impairing its elongation or causing other secondary damage such as surface scratches.

[049] The temperature of the steel plate entering the cladding container can be adjusted according to the thickness and width of the steel plate. The temperature of the steel plate entering the cladding container and an appropriate rapid cooling rate after exiting the cladding container (including the average cooling rate from the temperature of the steel plate exiting the cladding container to the solidification temperature of the cladding layer and the average cooling rate from the temperature of the steel plate exiting the cladding container to 200°C) can further improve the uniform distribution and grain refinement of the Mg2Si phase and the AlMgSiFe phase in the surface layer.

[050] During the continuous annealing and hot coating process, control of the cooling rate can be achieved by adjusting the power of a blower.

[051] Preferably, the chemical composition of the coating solution includes, in mass percentage: 5-11% Si and 0.5-20% Mg.

[052] Si in the coating solution is essential, mainly to inhibit the thickness of the barrier layer. If the Si content in the coating solution is too low, the thickness of the barrier layer will be too thick, Petition 870230063687, dated 07 / 20 / 2023, page 67 / 120 13 / 27 resulting in low workability of the steel plate. On the other hand, if the Si content in the coating solution is too high, its inhibiting effect on the barrier layer will be limited, also affecting the fluidity of the coating solution and increasing production difficulties. Therefore, the Si content in the coating solution is 5-11%. The presence of Mg in the coating layer is mainly to improve corrosion resistance and promote the formation of the Mg2Si phase. Mg in the coating layer comes from the coating solution; when the Mg content in the coating solution exceeds a certain value, the Mg2Si phase can be formed during cooling. However, the solubility of Mg in the Al-Si coating solution is limited, and if the Mg content in the coating solution is too high, the Mg is easily oxidized to form slag, causing production difficulties. Thus, the Mg content in the coating solution is 0.5-20%.

[053] Preferably, the coating solution additionally comprises 1-10% by mass of Zn. Zn in the coating layer serves as sacrificial anodes, providing sacrificial protection and increasing the corrosion resistance of the steel.

[054] Preferably, the remainder of the coating solution is Al and unavoidable impurities.

[055] Preferably, the rolling stage includes hot rolling, where the hot rolling coil temperature is 630°C or less. If the coil temperature is too high, it can cause excessive oxide fouling on the surface of the steel sheet, which cannot be completely removed during pickling after rolling, thus affecting the surface quality of the coating layer during subsequent aluminum coating.

[056] Preferably, the lamination stage additionally includes Petition 870230063687, dated 07 / 20 / 2023, page 68 / 120 14 / 27 Cold rolling. If the steel sheet produced from the aforementioned hot rolling step does not meet the requirements for user applications, additional cold rolling may be performed on the hot-rolled steel coil. In the embodiments of this application, deformation during cold rolling is 10-70%.

[057] Aluminum-coated steel sheet can be used for direct cold stamping forming or hot stamping forming.

[058] The present invention further provides a thermoformed component manufactured from the aluminum-coated steel sheet described above.

[059] Preferably, the thermoformed component includes a surface layer and an inner layer, wherein the ratio of the mass percentage of Mg in the surface layer to the mass percentage of Mg in the inner layer is greater than or equal to 5, and the thermoformed component has a core hardness HV1 of 300 or more.

[060] During the thermoforming process of aluminum-clad steel sheet, the previously formed surface layer and the barrier layer of the cladding layer are transformed into the surface layer and the inner layer of the thermoformed component. The corresponding microstructure will also change. The surface layer, originally composed of Al-Si alloy, will transform into Fe-Al-Si alloy. The Fe-Al-Si alloy barrier layer will additionally undergo alloy diffusion, with an increased Fe content. The inner layer of the component refers from the substrate of the thermoformed component to the dark Fe-rich layer within the cladding layer, and the surface layer extends from the dark Fe-rich layer within the cladding layer to the surface of the cladding layer.

[061] The Mg2Si phase and the AlMgSiFe phase are distributed in the surface layer of the coating layer and are preferentially Petition 870230063687, dated 07 / 20 / 2023, page 69 / 120 15 / 27 distributed on the surface of the coating layer during heat treatment. After heat treatment, Mg is mainly distributed in the surface layer of the component, and the ratio between the mass percentage of Mg in the surface layer and that in the inner layer of the component is greater than or equal to 5, which is determined by the aggregation characteristics of Mg. Due to the abundant presence of Mg on the surface of the thermoformed component, the resistance to red rust of the thermoformed component during transport and storage can be improved.

[062] The aluminum-clad steel sheet substrate will become the core of the thermoformed component after thermoforming. The microstructure of the thermoformed component core comprises one or more of martensite, bainite, and ferrite. The specific composition and content depend on the substrate composition and the cooling rate of a mold during thermoforming. The final microstructure of the core will affect the hardness of the thermoformed component core.

[063] The present invention also provides a manufacturing method for the thermoformed component above, including the following steps: To process aluminum-coated steel sheet into a billet; Perform heat treatment on billets, where one form of heat treatment is single-stage heating or step-by-step heating; when the heat treatment method is single-stage heating, the stopping temperature is a certain temperature between 900-1000°C and the total heating time is 10-600 seconds; and when the heat treatment method is step-by-step heating, the stopping temperature includes multiple temperatures between 700-1000°C, and the total heating time is 1-15 minutes, where the highest temperature of the multiple temperatures Petition 870230063687, dated 07 / 20 / 2023, pages 70 / 120 16 / 27 is a certain temperature of 900-1000°C, and the retention time of the billet at 900-1000°C is 10-600 seconds; and transferring the billet to the mold for thermoforming, where the temperature of the billet when transferred to the mold is 650°C or more, and a cooling rate of the mold is 30°C / s or more. In the embodiments of the present application, water cooling is applied to the thermoforming mold and the cooling rate of the mold is controlled by adjusting conditions such as flow, flow rate, and pressure of the cooling water.

[064] When the heating method of the heat treatment is single-stage heating, the stopping temperature of the heating is a certain temperature between 900-1000°C and the total heating time is the time from the start of billet heating to the end. When the heating method of the heat treatment is step heating, the stopping temperature includes multiple temperatures within the range of 700-1000°C, and the total heating time is the time from the start of billet heating to the end. The final stopping temperature of the heating should be 900°C or higher, whether single-stage heating or step heating, to ensure complete austenitization of the steel and prepare for the formation of the desired structure during cooling. An upper limit of the stopping temperature of the heating is set at 1000°C for energy saving.

[065] Preferably, a thermoforming process is hot stamping or hot rolling.

[066] Preferably, a thickening lamination step is additionally carried out before processing the aluminum-clad steel sheet into a billet. Examples 1-6 and Comparative Examples 1-2

[067] Aluminum-coated steel sheets and components Petition 870230063687, dated 07 / 20 / 2023, page 71 / 120 17 / 27 thermoformed specimens of Examples 1-6 and Comparative Examples 1-2 were manufactured using the following manufacturing method.

[068] Step 1: Casting to obtain a substrate with a composition as shown in Table 1.

[069] Step 2: Rolling to obtain a rolled steel sheet. After rolling, pickling was carried out to remove an oxide layer on the surface of the steel sheet.

[070] Step 3: Continuous annealing and hot coating, in which the rolled steel sheet was subjected to continuous annealing and then placed in a coating container (immersed in a coating solution). The steel sheet was cooled after immersion to obtain the aluminum-coated steel sheet.

[071] The specific process parameters for continuous rolling and annealing and hot coating are shown in Table 2.

[072] Step 4: Processing the aluminum-clad steel sheet into a billet.

[073] Step 5: Heat treatment of the billet.

[074] Step 6: Transfer the heat-treated billet to a thermoforming mold to obtain the thermoformed component.

[075] The specific process parameters for heat treatment and thermoforming are shown in Table 3.

[076] The aluminum-clad steel sheets and thermoformed components of Examples 1-6 and Comparative Examples 1-2 were tested according to the following test methods and the test results are shown in Tables 2 and 3. 1) Average grain diameter of the Mg2Si phase (μm)

[077] A grain size was calculated using a method of Petition 870230063687, dated 07 / 20 / 2023, page 72 / 120 18 / 27 interception. The average grain diameter = the length / number of grains in an intercepted section. 2) Presence of the AlMgSiFe phase

[078] Observed using a Zeiss EVO10 scanning electron microscope, combined with energy dispersive X-ray spectrometer (EDS) analysis, with V indicating presence and / indicating absence. 3) Roller sticking phenomenon

[079] Judged by visual inspection. x indicates no occurrence of gripping and V indicates occurrence of gripping. 4) Resistance to hydrogen embrittlement

[080] The hydrogen content of the thermoformed component was evaluated using a G4-PHONEX micro hydrogen concentration analyzer. The maximum heating temperature did not exceed 400°C. The amount of hydrogen released was recorded, and the greater the amount released, the lower the resistance to hydrogen embrittlement. The rating scale ranges from 1 (worst) to 5 (best). 5) Mass percentage of Mg in a surface layer of the component / mass percentage of Mg in an interior layer of the component

[081] Tested using a GDS850A glow discharge spectrometer. The inner layer of the component is related to the thermoformed component substrate to a dark Fe-rich layer in the coating layer, and the surface layer of the component is related to the dark Fe-rich layer in the coating layer to the surface of the coating layer. 6) Resistance to red rust

[082] Evaluated using a neutral salt spray test. The thermoformed component to be evaluated did not have an electrophoretic film. After 24 hours, the Petition 870230063687, dated 07 / 20 / 2023, page 73 / 120 The 19 / 27 degree of red rust coverage is checked, with less than 5% coverage indicating the best performance. In this experiment, a rating scale of 1 (worst) to 5 (best) is used. 7) Core hardness HV1

[083] Determined in accordance with GB / T 4340.1-2009 standard for Vickers hardness of the thermoformed component.

[084] FIG. 1 is obtained by scanning a coating layer of an aluminum-coated steel sheet obtained in Example 2 of the present invention using a Zeiss field emission electron microscope.

[085] A thermoformed component obtained in Example 2 of the present invention was tested using a GDS850A glow discharge spectrometer to obtain FIG. 2 which shows the variation of the mass percentage of Mg as a function of the coating layer depth.

[086] Table 1 shows the chemical element composition of the substrates in Examples 1-6 and Comparative Examples 1-2. Petition 870230063687, dated 07 / 20 / 2023, page 74 / 120 Table 1 (%, the remainder being Fe and other unavoidable impurities besides P, S and V) N2. C Si Mn PS Al Ti B Cr Nb V Example 1 0.05 0.05 1.90 0.059 0.038 0.006 0.090 0.0005 0.05 0.0031 0.0051 Example 2 0.23 0.23 1.19 0.015 0.001 0.04 0.010 0.0040 0.23 0.0010 0.0010 Example 3 0.29 0.50 2.51 0.024 0.04 0.08 0.027 0.0052 0.21 0.0005 0.0022 Example 4 0.36 0.36 1.50 0.044 0.03 Example 5: 0.50 0.48 0.40 0.081 0.02 0.05 0.090 0.0071 0.20 0.071 0.0021 Example 6: 0.15 1.80 2.90 0.039 0.038 0.29 0.090 0.0031 0.15 0.0031 0.0031 Comparative Example 1: 0.23 0.23 1.19 0.015 0.001 0.04 0.030 0.0040 0.23 0.0010 0.0010 Comparative Example 2 0.20 0.20 1.31 0.024 0.004 0.08 0.027 0.0052 0.21 0.0005 0.0022 Petition 870230063687, dated 07 / 20 / 2023, page 75 / 120 21 / 27

[087] Table 2 shows the process parameters for continuous rolling and annealing and hot coating, the composition of a coating solution and the microstructure and thickness of a coating layer of the steel sheets of Examples 1-6 and Comparative Examples 12. Petition 870230063687, dated 07 / 20 / 2023, page 76 / 120 Table 2 NS. Rolling Continuous annealing and hot coating Coating layer Hot coiling temperature / °C Cold rolling deformation / % Annealing temperature / °C Coating solution temperature / °C Temperature of a steel plate entering a container / °C Coating solution temperature - temperature of the steel plate entering the coating container / °C Average cooling rate of the steel plate leaving the coating container to the coating layer solidification temperature / °C / s Average cooling rate of the steel plate leaving the coating container to 200°C / °C / s Chemical composition of the coating solution Average grain diameter of a Mg2Si phase / μm Phase AlMgSiFe Thickness / μm Si / % Mg / % Zn / % Example 1 600 60 710 600 605 5 16 10 5 0,Example 2: 630 50 730 620 620 0 18 15 9 1 / 4 V 20 Example 3: 610 45 750 630 633 3 20 18 7 5 5 3 V 17 Example 4: 550 40 760 650 645 5 25 20 8 10 10 2 V 28 Example 5: 500 10 780 650 650 0 30 25 9 15 1 2 V 30 Example 6: 600 70 770 660 660 0 35 30 11 20 5 1 V 50 Comparative Example 1: 600 50 730 620 620 0 10 10 9 / / / / 20 Comparative Example 2 630 60 750 650 670 20 5 8 8 0.3 7 / / 23, 22 / 27 Petition 870230063687, dated 07 / 20 / 2023, page 77 / 120 23 / 27

[088] Table 3 shows the process parameters for heat treatment, whether the roll sticking phenomenon occurred, and the process parameters for thermoforming aluminum-clad steel sheets and the properties of the thermoformed components in Examples 1-6 and Comparative Examples 1-2. Petition 870230063687, dated 07 / 20 / 2023, page 78 / 120 Table 3 N2. Heat Treatment Thermoforming Thermoformed Component Heating Method Heating Stop Temperature / °C Total Heating Time / min Maximum Heating Temperature / °C Time at a Defined Temperature of 900-1000°C / s Roll Stick Phenomenon Temperature of a Billet When Transferred to a Mold / °C Mold Cooling Rate °C / s Hydrogen Embrittlement Resistance Mg Mass Percentage in a Surface Layer / Inner Layer Red Rust Resistance Core Hardness HV1 Example 1 Single Stage 900 1 900 60 X 650 30 4 5 4 305 Example 2 In Stages 720-930 6 930 300 X 680 38 5 6 4 400 Example 3 In Stages 750-945 5 945 240 X 700 37 4 7 5 450 Example 4 In Steps 760-950 5 950 180 X 780 50 5 8 5 470 Example 5 In steps 750-910 15 910 600 X 750 60 5 9 5 480 Example 6 In steps 700-1000 2,5 1000 10 X 700 70 5 10 5 350 Comparative Example 1 In steps 720-930 6 930 300 V 600 25 2 / 2 250 Comparative Example 2 In steps 720-930 6 930 250 V 600 25 2 3 3 250, Lz / ντ Petition 870230063687, dated 07 / 20 / 2023, page 79 / 120 25 / 27

[089] From Tables 1-3, it can be seen that for aluminum-clad steel sheets obtained in Examples 1-6, a coating layer microstructure is exhibiting comprising a Mg2Si phase and an AlMgSiFe phase. The average grain diameter of the Mg2Si phase is 1-5 μm. During heat treatment, no melt-induced roll-stick phenomenon occurs. The thermoformed components obtained in Examples 1-6 are excellent in hydrogen embrittlement resistance, with a mass percentage ratio of Mg in a surface layer to that of Mg in an inner layer being greater than or equal to 5. Furthermore, the thermoformed components exhibit excellent red rust resistance and have a core hardness HV1 of 300 or more.

[090] FIG. 1 is a scanning spectrum of a coating layer of an aluminum-coated steel sheet of Example 2 of the present invention, and it can be seen that a microstructure of the coating layer comprises a Mg2Si phase and an AlMgSiFe phase. FIG. 2 shows the variation of the mass percentage of Mg in a thermoformed component of Example 2 of the present invention as a function of the depth of the coating layer, and it can be observed that the closer the measurement is to the surface of the coating layer, the higher the mass percentage of Mg.

[091] In contrast, for Comparative Example 1, the average cooling rate of the steel plate exiting the coating container to the solidification temperature of the coating layer is very slow, at only 10°C / s. The chemical composition of the coating solution does not contain Mg, and the coating layer of the aluminum-coated steel sheet does not contain the Mg2Si phase and the AlMgSiFe phase. The melt-induced roll stick phenomenon occurs during heat treatment; the billet temperature when transferred to the mold is very low, at only Petition 870230063687, dated 07 / 20 / 2023, pp. 80 / 120 26 / 27 600°C, and the mold cooling rate is very low, at only 25°C / s. Consequently, the hydrogen embrittlement resistance and red rust resistance of the thermoformed component are low, and the HV1 core hardness is only 250.

[092] For Comparative Example 2, there is a significant difference between the temperature of the coating solution and the temperature of the steel plate entering the coating vessel, within 20°C. The average cooling rate from the temperature of the steel plate exiting the coating vessel to the solidification temperature of the coating layer is very slow, at only 5°C / s, and the average cooling rate from the temperature of the steel plate exiting the coating vessel to 200°C is very slow, at only 8°C / s. The Mg content in the coating solution is only 0.3%, and there is no Mg2Si phase or AlMgSiFe phase. The melt-induced roll stick phenomenon occurs during heat treatment. The billet temperature when transferred to the mold is very low, at only 600°C, and the mold cooling rate is also low, at only 25°C / s.As a result, the hydrogen embrittlement resistance of the thermoformed component is low, and the ratio between the mass percentage of Mg in the surface layer and that of the inner layer of the component is only 3. Furthermore, the red rust resistance is low, and the HV1 core hardness is only 250.

[093] Since the processing parameters of the steel sheets of Comparative Examples 1 and 2 are not adequately controlled during continuous annealing and hot coating and thermoforming, the resulting thermoformed components do not possess the desired properties of the present application.

[094] In summary, the present invention provides an aluminum-coated steel sheet, a thermoformed component and methods of manufacture, which Petition 870230063687, dated 07 / 20 / 2023, page 81 / 120 27 / 27 can alleviate the problem of melt-induced roll sticking and reduce the risk of hydrogen embrittlement during the heat treatment of aluminum-clad steel sheet, while improving the red rust resistance of the thermoformed component.

[095] Although the present invention has been illustrated and described with reference to some preferred embodiments of the present invention, it should be understood by a person skilled in the art that the above content is a further detailed description of the present invention in conjunction with specific embodiments, and the specific implementations of the present invention cannot be considered limited to the foregoing description. Persons skilled in the art may make various alterations in form and detail, including making certain deductions or substitutions, without departing from the essence and scope of the present invention. Petition 870230063687, dated 07 / 20 / 2023, page 82 / 120

Claims

1 / 4 CLAIMS 1. Aluminum-clad steel sheet, characterized in that it comprises a substrate and a coating layer on the surface of the substrate, wherein the coating layer is formed by hot coating in a coating solution containing, by mass: 5-11% Si, 0.520% Mg, and optionally, 1-10% Zn, with the remainder being Al and unavoidable impurities, the coating layer includes a barrier layer formed on the surface of the substrate and a surface layer formed on the barrier layer, wherein the barrier layer is mainly composed of Fe-Al and Fe-Al-Si alloys, and a microstructure of the surface layer comprises an Mg2Si phase and an AlMgSiFe phase, and the Mg2Si phase has an average grain diameter of 0.001-5 µm.

2. Aluminum-clad steel sheet, according to claim 1, characterized in that the barrier layer has a thickness of less than or equal to 5 µm.

3. Aluminum-clad steel sheet, according to claim 1, characterized in that the coating layer has a thickness of 5-50 µm.

4. Aluminum-clad steel sheet according to claim 1, characterized in that the composition of the substrate of the aluminum-clad steel sheet comprises, in mass percentage: 0.05-0.5% C, 0.01-2.0% Si, 0.3-3.0% Mn, 0.005-0.3% Al, 0.01% <Ti<0,1%, 0,0005%<B<0,1%, 0,05%<Cr<0,5%, 0,0005%<Nb<0,1%, com o restante sendo Fe e impurezas inevitáveis; em que entre as impurezas inevitáveis, em porcentagem em massa, P<0,3%, S<0,1% e V<0,1%. Petição 870250084265, de 18 / 09 / 2025, pág. 14 / 17 2 / 4 5. A manufacturing method for aluminum-clad steel sheet, defined in any one of claims 1 to 4, characterized in that it comprises the following steps: casting; rolling; and continuous annealing and hot coating, wherein the annealing temperature is 710-780°C, the temperature of a coating solution is 600-660°C, the temperature of the coating solution less the temperature of a steel plate entering a coating container is less than or equal to 5°C, the steel plate is cooled after exiting the coating container, an average cooling rate from the temperature of the steel plate exiting the coating container to the coating layer solidification temperature is greater than 15°C / s, and an average cooling rate from the temperature of the steel plate exiting the coating container to 200°C is 10-30°C / s;wherein the chemical composition of the coating solution comprises, by mass percentage: 5-11% Si and 0.5-20% Mg and, optionally, 1-10% by mass of Zn, wherein the remainder of the coating solution is Al and unavoidable impurities.

6. A manufacturing method for aluminum-clad steel sheet according to claim 5, characterized in that the rolling step comprises hot rolling, wherein the coiling temperature of the hot rolling is 630°C or less.

7. Manufacturing method for aluminum-clad steel sheet according to claim 6, characterized in that the rolling step comprises cold rolling, wherein the deformation during cold rolling is 10-70%. Petition 870250084265, dated 09 / 18 / 2025, page 15 / 17 3 / 4 8. Thermoformed component, characterized in that it is manufactured using aluminum-coated steel sheet, as defined in any one of claims 1 to 4.

9. Thermoformed component, according to claim 8, characterized in that the thermoformed component comprises a surface layer and an inner layer, wherein the ratio of the mass percentage of Mg of the surface layer to that of the inner layer is greater than or equal to 5, and the thermoformed component has a core hardness HV1 of 300 or more; wherein the thermoformed component is obtainable by thermoforming aluminum-clad steel sheet at a thermoforming temperature of 650°C or more and a cooling rate of 30°C / s or more, and wherein during the thermoforming of the aluminum-clad steel sheet, the surface layer of the coating layer forms the surface layer of the thermoformed component, while the barrier layer forms the inner layer.

10. Manufacturing method for the thermoformed component, defined in claim 8 or 9, characterized in that it comprises the following steps: processing the aluminum-coated steel sheet into a blank; performing heat treatment on the blank, wherein one form of heat treatment is single-stage heating or staged heating; when the form of heat treatment is single-stage heating, the heating stop temperature is a certain temperature in 900-1000°C, and the total heating time is 10-600 seconds; and when the form of heat treatment is staged heating, the stopping temperature is a certain temperature in 900-1000°C.16 / 17 4 / 4 heating comprises multiple temperatures in the 700-1000°C range, and the total heating time is 1-15 minutes, wherein the highest temperature of the multiple temperatures is a certain temperature in the 900-1000°C range, and the blank holding time at 900-1000°C is 10-600 s; and transferring the blank to a mold for thermoforming, wherein the temperature of the blank when transferred to the mold is 650°C or more, and a mold cooling rate is 30°C / s or higher.

11. Manufacturing method for the thermoformed component, according to claim 10, characterized in that one thermoforming process is hot stamping or hot rolling.

12. Manufacturing method for the thermoformed component, according to claim 10 or 11, characterized in that a thickening lamination step is additionally performed before processing the aluminum-clad steel sheet into a blank. Petition 870250084265, dated 09 / 18 / 2025, p. 17 / 17

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