A laser-welded blank with an aluminum alloy coating, a laser-welded hot formed component and a method for producing the same

Abstract

This application provides a laser-welded plate with an aluminum alloy coating, a laser-welded hot-formed component, and a method for preparing the same. By differentiating the steel plate thickness and coating weight of each sub-blank of the complexly combined aluminum alloy-coated laser-welded plate, and based on the function relationship obtained by curve fitting, the lower limit of the heating time required for austenitization heat treatment of the laser-welded plate under specific welding combination conditions can be accurately calculated, thereby formulating the preparation process of the laser-welded hot-formed component. For laser-welded plates designed according to specific welding combinations, the austenitization heat treatment method of this application can produce laser-welded hot-formed components with fully austenitized steel substrates and excellent spot welding stability. This method ensures that the austenitization heat treatment process has an optimized heating process window, effectively reducing the negative effects of downtime, production speed reduction, and other failures and anomalies on the performance of the hot-formed component.

Description

Technical Field

[0001] This invention relates to the field of steel materials technology, and in particular to a laser-welded plate with an aluminum alloy coating, a laser-welded thermoformed component, and a method for preparing the same. Background Technology

[0002] In the automotive industry, laser-welded hot-formed aluminum alloy coated steel sheets are widely used in the manufacture of critical components. This process first involves laser welding aluminum alloy coated steel sheets to form welded blanks. These blanks are then subjected to heating and heat treatment to achieve complete austenitization of the steel substrate. Finally, they are formed into complete components with specific geometric structures through hot stamping. These components generally possess high mechanical strength, excellent impact resistance, good corrosion resistance, and high dimensional accuracy. Typical applications include vehicle safety structural components such as front longitudinal beams, rear longitudinal beams, roof longitudinal beams, and B-pillars.

[0003] Laser-welded blanks made of aluminum alloy coated steel sheets are welded from multiple sub-blanks, aiming to achieve two goals: first, to obtain blanks with specific contours through the spatial arrangement of sub-blanks, significantly improving material utilization; second, to ensure that the components formed after hot stamping have functional zones with differentiated mechanical properties and mass distribution, achieving lightweight optimization while meeting collision safety requirements. Typical examples include door rings, floor rings, and sunroof rings, which can be customized for different collision conditions in different areas of the vehicle by welding hot-formed materials of different thicknesses and strengths.

[0004] However, during the overall austenitization process of the welded billets, the austenitization process exhibits significant asynchrony due to differences in the coating quality and substrate thickness of each sub-billet. When the thin-walled sub-billets complete the heat absorption process, the alloying elements within their steel matrix have sufficiently diffused and homogenized, achieving full austenitization. In contrast, the thick-walled sub-billets, requiring more heat absorption, have not yet completed the austenitization transformation. Notably, when the thick-walled sub-billets finally achieve full austenitization, the thin-walled sub-billets experience grain coarsening due to continuous heating, leading to a deterioration in material toughness.

[0005] To address this, Chinese patent application CN117305563A discloses a welded steel plate, a hot-formed component of the welded steel plate, a method for preparing the same, and a vehicle. The welded steel plate of this patent application includes steel plates with different thicknesses and coating weights. By adjusting the coating thickness of aluminum alloy coated steel plates (hereinafter referred to as "coated steel plates") with different thicknesses and / or different post-hot stamping strengths, different coated steel plates can achieve full austenitization in a substantially similar amount of time. Thus, while ensuring that different coated steel plates achieve full austenitization, it avoids prolonged overheating of thinner or weaker coated steel plates, fundamentally solving the problem of incomplete austenite transformation or overheating caused by coated steel plates with different thicknesses and / or different post-hot stamping strengths under the same heating time.

[0006] While addressing the issue of incomplete austenite transformation in coated steel sheets is important, resolving the overheating problem is equally crucial. The inventors of this patent application, through practical experience, have discovered that overheating of coated steel sheets not only affects mechanical properties but also has a more significant and severe impact on subsequent spot welding processes. The inventors found that to ensure complete austenitization of thicker coated steel sheet blanks, thinner blanks undergo a holding phase after being heated to the target temperature. During this process, the thicker blank continues to absorb heat and undergo recovery recrystallization, carbide dissolution, and austenite transformation, while the Al in the coating and Fe in the steel matrix of the thinner blank continue to diffuse and alloy, leading to a continuous increase in the Fe content in the coating. Consequently, the type of Al-Fe alloy products and the Al / Fe ratio also change continuously. As the holding time of thinner billets increases, the Al-Fe alloying products in the coating transform from compounds mainly composed of Fe2Al5 and FeAl2 containing 40-65 wt% Al to compounds mainly composed of FeAl and α-Fe containing 1-40 wt% Al and with a higher Si content. Specifically, the compound phases from the steel substrate to the coating surface can be sequentially divided into: interdiffusion layer (hereinafter referred to as IDL layer, including a relatively large α-Fe phase close to the substrate and a relatively small FeAl phase adjacent to it), Fe2Al5 phase layer, FeAl phase layer, and Fe2Al5 phase layer, etc. Therefore, the longer the holding time of thinner billets, the thicker the IDL layer will be. Due to the different elemental ratios of the constituent phases, the IDL layer, Fe2Al5 phase layer, and FeAl phase layer have different physical properties. In the IDL layer, the α-Fe phase has a high Fe content and an Al content below 30 wt%, resulting in a higher proportion of α-Fe phase. This causes the melting point of the IDL layer to be close to that of the steel substrate (approximately 1500℃). In contrast, the melting points of intermetallic compounds such as FeAl and Fe2Al5 are lower than those of the steel substrate, approximately 1310℃ and 1170℃, respectively. Therefore, during subsequent resistance spot welding, the FeAl and Fe2Al5 intermetallic compound phases on the outer side of the IDL layer will melt first under the influence of resistance heat and be extruded simultaneously by electrode pressure. Because their melting points are similar to those of the steel substrate, the IDL layer will form a molten pool while melting. However, the IDL layer has a higher Al and Si content than the steel substrate, making the molten pool extremely unstable during growth, prone to spattering, leading to difficulties in resistance spot welding and a reduced welding process window. Therefore, the thinner the IDL layer, the larger the spot welding process window; the thicker the IDL layer, the smaller the spot welding process window.Thus, the inventors discovered that, on the one hand, in order to ensure the complete austenitization of the thicker sub-blank, it is necessary to determine the lower limit of the heating time of the austenitization heat treatment process to ensure the complete austenitization of the entire weldment blank. On the other hand, in order to prevent the thinner sub-blank from being overheated and causing the IDL layer to be too thick, thus impairing the spot welding performance, it is also necessary to determine a reasonable upper limit of the heating time of the austenitization heat treatment process, that is, to limit the continuous heat input during the holding stage after the thinner sub-blank reaches the target temperature, and the upper limit of the heating time should not be too large in order to control the thickness of the IDL layer.

[0007] However, in the production of coated steel sheets, to cope with furnace shutdowns or production interruptions caused by various unforeseen circumstances, a certain heating process window is usually required for the austenitization process. This requirement is particularly critical for laser-welded slab blanks: not only must each sub-blank be fully austenitized, but a sufficiently wide heating process range must also be provided, i.e., a sufficiently high upper limit for heating time must be set. If the heating process window for laser-welded slab blanks is too narrow, production personnel may not be able to handle shutdown failures in time, resulting in the slab blanks remaining in the furnace deteriorating to the point of being unqualified due to over-austenitization or exceeding the holding time limit, or making subsequent spot welding impossible, ultimately causing significant economic losses.

[0008] In summary, to control the IDL layer thickness and ensure the spot welding performance of hot-formed components, a smaller upper limit for heating time is better. However, to meet the requirements of the heating process range in actual production, a larger upper limit for heating time is also desirable. This seemingly contradictory set of requirements led the inventors to conclude that it is necessary to determine a precise and reasonable upper limit for heating time that satisfies both the requirements of the heating process range and the control of the IDL layer thickness. Chinese patent application CN117305563A did not consider the heating process range issue, nor did it provide precise upper and lower limits for the austenitizing heat treatment process of the weldment blank.

[0009] Furthermore, US patent application US2025 / 0222506A1 discloses a hot-stamped coated steel component and its preparation method. While this patent application provides the correlation factors between the total coating thickness and the interdiffusion layer (IDL layer) thickness, as well as the influence of heating time on the spot weldability of the welded plate, it also fails to provide upper and lower limits for heat treatment heating times that ensure sufficient austenitization of each sub-blank of the laser-welded coated blank within substantially the same time frame and that the IDL layer is beneficial to subsequent spot weld stability.

[0010] With the increasing demand for lightweight design and the ever-improving requirements for collision safety, the sub-bulk combinations of laser-welded billets are becoming increasingly complex, resulting in a significant increase in the number of welds. This makes it significantly more difficult to design the austenitizing heat treatment process window for the welded billets under these complex sub-bulk combination conditions. Therefore, there is an urgent need to develop a laser-welded plate with an aluminum alloy coating, a laser-welded hot-formed component, and its preparation method, which can adapt to more weld combination requirements while ensuring full austenitization of the laser-welded hot-formed component and possessing excellent spot welding stability. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a laser-welded plate with an aluminum alloy coating, a laser-welded hot-formed component, and a method for preparing the same. Using the method of this invention, a fully austenitized aluminum alloy-coated laser-welded hot-formed component with excellent resistance spot welding stability can be produced, ensuring that the laser-welded plate has an optimal heating process window during the austenitization heat treatment process.

[0012] This invention implements differentiated design of the sub-blank thickness and coating layer density (or thickness) for the sub-blanks constituting the laser-welded aluminum alloy coated steel sheet. Through a systematic study of the coupled effects of steel sheet thickness, coating layer density, and austenitic phase transformation on the heating rate of the laser-welded aluminum alloy coated sheet during austenitization heating, lower limit heating process parameters to ensure complete austenitization of the laser-welded sheet were established. Simultaneously, considering the IDL layer thickness distribution characteristics of each sub-component in the hot-formed component and production line process constraints, upper limit heating process parameters that meet the stability requirements of the resistance spot welding process were formulated, thereby obtaining a maximized austenitization heating process window. The aluminum alloy coated laser-welded hot-formed component prepared based on this method possesses a wide resistance spot welding process window.

[0013] In a first aspect, the present invention discloses a laser-welded sheet blank with an aluminum alloy coating. The laser-welded sheet blank is formed by welding sub-blanks together, with at least two welds. The sub-blanks include a steel substrate and an aluminum alloy coating coated on both sides of the steel substrate. The thickness of the thinnest sub-blank is no more than 1.4 mm, and the thickness of the thickest sub-blank is no more than 2.5 mm. The aluminum alloy coating density of the thinnest sub-blank is greater than that of the thickest sub-blank. The thickness ratio of the sub-blanks to the thickest sub-blank is defined as H1, and the thickness ratio of the thickest sub-blank to the thinnest sub-blank is defined as H2. For a sub-blank with H1 ≥ 0.9, if H2 > 1.5, then the sub-blank and the thickest sub-blank have the same aluminum alloy coating density.

[0014] Furthermore, the thinnest sub-blank has the highest aluminum alloy coating density, while the thickest sub-blank has the lowest aluminum alloy coating density.

[0015] Furthermore, the aluminum alloy coating of the sub-bill is selected from AS50, AS80, and AS150; the AS50 is a double-sided coating on a steel substrate, with an average areal density of 15~35 g / m² on one side. 2 (excluding 35g / m 2 The AS150 is a double-sided coated steel substrate with an average areal density of 65~100 g / m² on one side. 2 The AS80 is a double-sided coated steel substrate with an average areal density of 35~65 g / m² on one side. 2 (excluding 65g / m 2 ).

[0016] Furthermore, the average areal density of the single-sided coating of the AS50 is 15~30 g / m². 2 Alternatively, the average thickness of the coating on one side is 7~13μm; the average areal density of the coating on one side of the AS80 is 35~60g / m³. 2 Alternatively, the average thickness of the coating on one side is 14~21μm; the average areal density of the coating on one side of the AS150 is 65~95g / m². 2 Alternatively, the average thickness of the coating on one side is 22~30μm.

[0017] Furthermore, the steel substrate of the sub-bulk contains, by mass percentage: C: 0.05%~0.45%, Mn: 0.60%~2.0%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.01%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.20%, P: 0.001%~0.100%, S: 0.0001%~0.100%, with the balance being Fe and other unavoidable impurity elements.

[0018] Furthermore, the aluminum alloy coating of the sub-blank is obtained by hot-dip immersing the steel substrate of the sub-blank into an aluminum alloy plating solution. The chemical composition of the aluminum alloy plating solution, by mass percentage, includes Si: 8~14%, Fe: 0~3%, with the balance being Al and other unavoidable impurity elements.

[0019] Secondly, this invention discloses a laser-welded thermoformed component with an aluminum alloy coating. The laser-welded thermoformed component is composed of multiple sub-components, and the number of welds in the laser-welded thermoformed component is not less than two. Each sub-component includes a steel substrate and an aluminum alloy coating coated on both sides of the steel substrate. The aluminum alloy coating of each sub-component contains an interdiffusion layer (IDL layer) near the steel substrate, and the average thickness of the IDL layer is 3.0~15.0 μm. The thickness of the thinnest sub-component does not exceed 1.4 mm, and the thickness of the thickest sub-component does not exceed 2.5 mm. The surface density of the aluminum alloy coating of the thinnest sub-component is greater than that of the thickest sub-component. The ratio of the thickness of the sub-component to the thickest sub-component is defined as HD1, and the ratio of the thickness of the thickest sub-component to the thinnest sub-component is defined as HD2. For a sub-component with HD1 ≥ 0.9, if HD2 > 1.5, then the sub-component and the thickest sub-component have the same surface density of the aluminum alloy coating.

[0020] Furthermore, the thinnest sub-component has the thickest aluminum alloy coating, and the thickest sub-component has the thinnest aluminum alloy coating.

[0021] Furthermore, the aluminum alloy coating of the sub-component is selected from AS50, AS80 and AS150; AS150 is a double-sided coating on a steel substrate with an average coating thickness of 30~40μm on one side; AS80 is a double-sided coating on a steel substrate with an average coating thickness of 20~30μm (excluding 30μm) on one side; AS50 is a double-sided coating on a steel substrate with an average coating thickness of 10~20μm (excluding 20μm) on one side.

[0022] Furthermore, the steel substrate of the sub-component contains, by mass percentage: C: 0.05%~0.45%, Mn: 0.60%~2.0%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.01%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.20%, P: 0.001%~0.100%, S: 0.0001%~0.100%, with the balance being Fe and other unavoidable impurity elements.

[0023] Furthermore, the tensile strength of the sub-component is 1000~2200MPa.

[0024] Furthermore, the microstructure of the steel substrate of the thickest sub-component is mainly martensite, with a volume fraction of martensite ≥97%.

[0025] Furthermore, the maximum thickness difference of the IDL layer of each sub-component does not exceed 4.0 μm.

[0026] Furthermore, the average thickness of the sub-component IDL layer is 3.0~10.8μm.

[0027] Furthermore, the average thickness of the sub-component IDL layer is 3.0~9.5μm.

[0028] Furthermore, the average thickness of the sub-component IDL layer is 3.0~7.5μm.

[0029] Thirdly, the present invention also discloses an austenitizing heat treatment method for laser-welded aluminum alloy coated blanks, comprising: heating the laser-welded blanks of the first aspect of the present invention to a target temperature of 850~950℃ and fully austenitizing them;

[0030] The lower limit heating time t of the austenitizing heat treatment of the laser-welded slab blank 下限 Determine it using the following method:

[0031] The heating time t for each sub-bulb to reach the target temperature is calculated using formula (1). 子坯料 The longest heating time is selected as the lower limit heating time t for the austenitizing heat treatment of the laser-welded slab blank. 下限 ;

[0032] t 子坯料 =t1+t2+t3 (1)

[0033] (2),

[0034] (3),

[0035] (4),

[0036] in,

[0037] B=12.52336-0.15311×(As×L)+6.72866×10 -4 ×(As×L) 2 -5.52606×10 -7 ×(As×L) 3 -1.34674×10 -9 ×(As×L) 4 ;

[0038] C = -0.08502 + 8.96693 × 10 -4 ×(As×L)-2.92784×10 -7 ×(As×L) 2 -1.90065×10 -8 ×(As×L) 3 +4.36768×10 -11 ×(As×L)4 ;

[0039] D=18.83518-0.31028×(As×L)+0.00187×(As×L) 2 -3.35082×10 -6 ×(As×L) 3 ;

[0040] E=-0.11615+0.00232×(As×L)-1.51656×10 -5 ×(As×L) 2 +2.84581×10 -8 ×(As×L) 3 ;

[0041] t1 is the heating time of the sub-bulk to 600℃, in seconds;

[0042] t2 is the heating time (in seconds) for the sub-bulk to be heated from 600℃ to the target temperature.

[0043] t3 is the hysteresis time caused by heat transfer after liquefaction and alloying of the aluminum alloy coating on the sub-bulk, in seconds;

[0044] L represents the thickness of the sub-blank steel plate, in mm;

[0045] T 目标 The target temperature for austenitizing heating, in °C;

[0046] As is the areal density of the coating on both sides of the billet steel sheet, in g / m³. 2 .

[0047] Furthermore, the heating time t=t for the austenitizing heat treatment of the laser-welded slab blank. 下限 +t 保温 During the heat preservation time t 保温 Inside, the heat input from the continuous heating of each sub-bulb is H 子坯料 Calculated by formula (5),

[0048] H 子坯料 =T 目标 ×(t 下限 -t 子坯料 +t 保温 ) / As (5),

[0049] To ensure spot welding stability, the H of each sub-blank blank... 子坯料 The standard deviation is no greater than 300.

[0050] Furthermore, after the laser-welded blank undergoes austenitizing heat treatment, it is transferred to a forming mold for stamping. The temperature of the laser-welded blank placed on the mold is ≥750℃. After stamping, it is held under pressure and quenched to below 200℃ before being demolded to obtain an aluminum alloy coated laser-welded thermoformed component.

[0051] Compared with the prior art, this application has at least the following beneficial effects:

[0052] (1) This invention designs the steel plate thickness and coating weight of each sub-blank of the complex combination of aluminum alloy coated laser welded blanks. Combining the influence of steel plate thickness, coating weight and austenite transformation on the heating rate of aluminum alloy coated laser welded blanks during the austenitization heating process, a lower limit heating process that can ensure the complete austenitization of the laser welded blanks of the above combination is formulated. Considering the IDL layer thickness of each sub-component in the welded hot forming component and the actual production situation, an upper limit heating process that meets the spot welding performance requirements is formulated, thereby obtaining the largest austenitization heating process window.

[0053] (2) This invention creatively divides the austenitizing heat treatment heating process of aluminum alloy coated laser welded sheet blank into three functionally characterizable heating stages. By fitting the actual heating curves of the three heating stages in the austenitizing heat treatment process, three heating functions of the laser welded sheet blank in the low temperature stage, high temperature stage, and aluminum alloy coating liquefaction and FeAl alloying heat transfer stage are obtained. The heating time required for each sub-blank of the laser welded sheet blank to reach the austenitizing target temperature can be accurately calculated. The longest heating time is selected as the lower limit of the heating time for the laser welded sheet blank to reach the target temperature, and this is used as the lower limit of the heating time for the austenitizing heat treatment process. This ensures that the IDL layer thickness of the laser welded sheet blank is minimized when it is fully austenitized, so as to ensure that the austenitized laser welded sheet blank has the best spot welding stability.

[0054] (3) Through extensive research and summarization, this invention has found that the differences in steel plate thickness and coating weight among the various sub-bills in the laser-welded slab blank lead to differences in the IDL layer thickness after complete austenitization, which in turn results in differences in the spot welding performance of different sub-components on the laser-welded hot-formed component. To reduce the differences in spot welding performance, the holding time t of each sub-bill is controlled. 保温 Heat absorption H inside 子坯料 The standard deviation can regulate the continuous heat input of each sub-blank after reaching the target heating temperature, thereby optimizing the austenitizing heat treatment process of the laser-welded blank, reducing the IDL layer thickness difference of each sub-component in the laser-welded hot-formed component, and enabling the laser-welded hot-formed component to have the best spot welding performance. Attached Figure Description

[0055] To more clearly illustrate the technical solutions of the embodiments of this invention, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments recorded in this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0056] Figure 1 Temperature rise curves of various sheet thicknesses of sub-blanks with AS50 aluminum alloy coating in the low-temperature heating section.

[0057] Figure 2 The temperature rise curves of various sheet thicknesses of sub-blanks with AS150 aluminum alloy coating in the low-temperature heating section.

[0058] Figure 3 The temperature rise curves of various sheet thicknesses of blanks with AS50 aluminum alloy coating in the high-temperature heating section.

[0059] Figure 4 The temperature rise curves of various sheet thicknesses of sub-blanks with AS150 aluminum alloy coating in the high-temperature heating section.

[0060] Figure 5 The temperature rise curves of the heat transfer section after coating liquefaction and alloying are shown for various plate thicknesses of sub-blanks with AS50 aluminum alloy coating.

[0061] Figure 6 The temperature rise curves of the heat transfer section after coating liquefaction and alloying are shown for various plate thicknesses of sub-blanks with AS150 aluminum alloy coating.

[0062] Figure 7 The image shows a metallographic photograph of the coating of sub-component 1 of the laser-welded thermoformed component in Example 1 under the lower limit heating process.

[0063] Figure 8 The image shows a metallographic photograph of the coating of sub-component 2 of the laser-welded thermoformed component in Example 1 under the lower limit heating process.

[0064] Figure 9 The image shows a metallographic photograph of the coating of sub-component 1 of the laser-welded thermoformed component in Example 2 under the upper limit heating process.

[0065] Figure 10 The image shows a metallographic photograph of the coating of sub-component 2 of the laser-welded thermoformed component in Example 2 under the upper limit heating process.

[0066] Figure 11 The graphs showing the relationship between IDL layer thickness and solderable current range for the upper / lower limit heating processes in all embodiments and comparative examples.

[0067] Figure 12 This is a schematic diagram of the combined structure of the various sub-blanks of the laser-welded blank for the door ring. Detailed Implementation

[0068] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. It should be noted that the described embodiments are only some embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0069] Unless otherwise stated, all temperatures mentioned herein are in degrees Celsius (°C), all component contents are expressed as weight percentages (wt%), and all steel plate microstructure contents are expressed as volume percentages (vol%). When numerical ranges are mentioned in the specification and claims, the upper and lower limits of the range are included by default. Preferred technical solutions can be freely combined as needed, unless specifically specified. Those skilled in the art should understand that the specific data and parameters described in the embodiments are illustrative and do not constitute a limitation of the invention. In the following embodiments and comparative examples, all components used are monomers or compounds known in the art, and all equipment involved is standardized equipment known in the art, which can be obtained commercially or prepared using conventional techniques.

[0070] In a first aspect, the present invention provides a laser-welded aluminum alloy plate blank, wherein the laser-welded plate blank is formed by welding sub-blanks together, with at least two welds. The sub-blanks include a steel substrate and an aluminum alloy coating coated on both sides of the steel substrate. The thinnest sub-blank has a thickness not exceeding 1.4 mm, and the thickest sub-blank has a thickness not exceeding 2.5 mm. The aluminum alloy coating density of the thinnest sub-blank is greater than that of the thickest sub-blank. The thickness ratio of the sub-blanks to the thickest sub-blank is defined as H1, and the thickness ratio of the thickest sub-blank to the thinnest sub-blank is defined as H2. For sub-blanks with H1 ≥ 0.9, if H2 > 1.5, then the sub-blank and the thickest sub-blank have the same aluminum alloy coating density. Preferably, the thinnest sub-blank has the largest aluminum alloy coating density, and the thickest sub-blank has the smallest aluminum alloy coating density. In this invention, the description of the thickness and thinness of the sub-blank refers to the overall thickness and thinness of the sub-blank, including the steel substrate and the aluminum alloy coating on both sides of the steel substrate.

[0071] Depending on the number of welds in the laser-welded slab blank, the thickness combination and coating density (or thickness) selection of each sub-blank in the laser-welded slab will vary. Thinner sub-blanks are easier to heat to the target temperature, while the formation of more intermetallic compounds during heating with a thick aluminum alloy coating will reduce heat transfer efficiency and delay the heating of the steel substrate. Therefore, choosing a thick aluminum alloy coating for thin sub-blanks will help delay their heating process. Similarly, choosing a thin aluminum alloy coating for thick sub-blanks will promote their heating process. Based on the above considerations, when the number of welds in the laser-welded slab blank is not less than two, the aluminum alloy coating density (or thickness) of the thin and thick sub-blanks can be reasonably selected to ensure that the laser-welded slab blank completes full austenitization with minimal heat absorption, minimizes the IDL layer thickness and thickness standard deviation of each sub-blank to obtain optimal spot welding performance, and minimizes the impact of overheating of the laser-welded slab blank. Therefore, the core inventive concept of this invention is first reflected in the fact that, when the thickness of the thinnest sub-blank does not exceed 1.4 mm and the thickness of the thickest sub-blank does not exceed 2.5 mm, the surface density (or thickness) of the aluminum alloy coating on the thinnest sub-blank is greater than that on the thickest sub-blank. In particular, this invention defines the thickness ratio of any sub-blank to the thickest sub-blank as H1, and the thickness ratio of the thickest sub-blank to the thinnest sub-blank as H2. For sub-blanks with H1 ≥ 0.9, if H2 > 1.5, it indicates that the thickness difference of each sub-blank in the laser-welded slab has a significant impact on the austenitization process, and the thickness of this sub-blank is close to that of the thickest sub-blank. Therefore, in order to balance austenitization and spot welding performance, the aluminum alloy coating of this sub-blank should have the same surface density as that of the thickest sub-blank.

[0072] Preferably, the thinnest sub-blank has the highest aluminum alloy coating density (or thickness), and the thickest sub-blank has the lowest aluminum alloy coating density (or thickness).

[0073] Preferably, the aluminum alloy coating of the sub-brush is selected from AS50, AS80, and AS150; the AS50 is a double-sided coating on a steel substrate, with an average areal density of 15~35 g / m² on one side. 2 (excluding 35g / m 2 The AS150 is a double-sided coated steel substrate with an average areal density of 65~100 g / m² on one side. 2 The AS80 is a double-sided coated steel substrate with an average areal density of 35~65 g / m² on one side. 2 (excluding 65g / m 2 More preferably, to ensure the stability of the coating, the present invention requires the coating weight or thickness to have a more stringent fluctuation range, and the average areal density of the single-sided coating of the AS50 is 15~30 g / m². 2Alternatively, the average thickness of the coating on one side is 7~13μm; the average areal density of the coating on one side of the AS80 is 35~60g / m³. 2 Alternatively, the average thickness of the coating on one side is 14~21μm; the average areal density of the coating on one side of the AS150 is 65~95g / m². 2 Alternatively, the average thickness of the coating on one side can be 22~30μm. The above average coating density and average coating thickness are the average values ​​of three-point tests. The coating density test method refers to the chemical weighing method in Appendix B of GB / T 3639 or the X-ray fluorescence method in Appendix E.

[0074] Preferably, the steel substrate of the sub-billet comprises, by weight percentage: C: 0.05%~0.45%, Mn: 0.60%~2.0%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.01%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.20%, P: 0.001%~0.100%, S: 0.0001%~0.100%, with the balance being Fe and other unavoidable impurity elements. Specifically,

[0075] C: 0.05%~0.45%

[0076] Carbon (C) is an important interstitial solid solution strengthening element in steel, enabling materials to achieve extremely high strength and hardness. Therefore, this invention adds more than 0.05% C to ensure that the material achieves a tensile strength of 1000~2200 MPa after hot stamping. However, excessive addition of C will promote the formation of brittle twinned martensite, severely deteriorating toughness. Therefore, the carbon content in this invention is controlled at 0.05%~0.45%.

[0077] Mn: 0.60%~2.0%

[0078] Manganese (Mn) is an economical and effective element for improving the hardenability of steel. Furthermore, the addition of Mn significantly expands the austenite phase region, thus affecting the martensitic transformation process. Therefore, an appropriate amount of Mn is commonly added to hot-stamped steel. However, adding too much Mn leads to increased hydrogen embrittlement sensitivity, which is detrimental to processing methods such as laser cutting. In addition, a high Mn content causes the martensitic transformation to occur at lower temperatures, resulting in the formation of a large amount of hard and brittle twinned martensite, reducing the material's toughness. Simultaneously, the internal phase transformation stress increases, and severe banded segregation is easily generated, further deteriorating the steel's properties. Therefore, this invention sets the Mn content to 0.60%~2.0%, which balances the material's hardenability and martensitic transformation temperature.

[0079] Si: 0.10%~0.50%

[0080] Si has the effect of solid solution strengthening of the matrix, and the addition of an appropriate amount can significantly improve the strength of the martensitic matrix. However, the addition of excessive Si will lead to the formation of oxides on the surface of the steel during the production process that are difficult to eliminate, affecting the surface quality of the final product. Therefore, the Si content in this invention is set to 0.10~0.50%.

[0081] Cr: 0.01%~0.60%

[0082] Cr (Cr) significantly delays the pearlite transformation by hindering cementite nucleation and growth, shifting the isothermal transformation C-curve of steel to the right. Furthermore, Cr reduces the austenite decomposition rate, lowering the critical cooling rate of the steel and promoting martensite formation. The effect of Cr on lowering the martensite transformation temperature is significantly less than that of Mn (Mn), thus Cr is more conducive to promoting the formation of dislocation-type martensite with good toughness. However, excessive Cr addition increases alloy costs and makes it difficult to completely remove the oxide scale formed on the surface of hot-rolled coils through pickling, affecting the surface quality of the final product. Therefore, the Cr content in this invention is controlled between 0.01% and 0.60%.

[0083] Al: 0.01%~0.40%

[0084] The addition of Al can combine with Nitrogen (N) to form AlN, effectively consolidating Nitrogen and preventing the combination of Nitrogen and nitrogen (B), thus ensuring the added B improves hardenability. Furthermore, Al can increase the martensitic transformation temperature, helping to reduce the formation of brittle twinned martensite. However, excessive Al addition can cause excessive resistance at the crystallizer inlet during continuous casting, affecting billet production and increasing the difficulty of controlling alumina inclusions in the steel. Therefore, the Al content in this invention is controlled between 0.01% and 0.40%.

[0085] B: 0.001%~0.01%

[0086] Boron readily segregates at austenite grain boundaries, which can suppress the phase transformation from austenite to ferrite. A low amount of boron can significantly improve the hardenability of steel. However, a high amount of boron can lead to boron embrittlement, which is detrimental to performance. Therefore, the boron content in this invention is set to 0.001~0.010%.

[0087] P: 0.001%~0.100%

[0088] Phosphorus (P) is an unavoidable impurity element in steel. On the one hand, P, as a solid solution strengthening element, can relatively inexpensively improve the strength of steel plates. On the other hand, when the P content exceeds 0.100%, P will segregate at grain boundaries, significantly leading to adverse effects such as decreased toughness. Therefore, the upper limit of P content is no greater than 0.100%. Optionally, considering that reducing the P content to less than 0.001% would increase smelting costs, the lower limit of P content can be no less than 0.001%.

[0089] S: 0.0001%~0.100%

[0090] Similar to phosphorus (P), sulfur (S) is an unavoidable impurity element in steel. It reacts with manganese (Mn) in the steel to form MnS, becoming inclusions. When the S content exceeds 0.100%, the large amount of MnS will significantly impair the ductility and toughness of the steel, leading to deterioration in workability. Therefore, the upper limit of S content is no greater than 0.100%. Alternatively, considering that keeping the S content below 0.0001% would increase smelting costs, the lower limit of S content can be no less than 0.0001%.

[0091] N: ≤0.006%

[0092] Nitrogen (N) is an unavoidable impurity element in steel, especially for steel containing boron (B). Nitrogen combines with B to significantly reduce the effect of B in improving hardenability. Therefore, it is necessary to minimize the content of Ni. Thus, the Ni content in this invention is controlled to be ≤0.006%.

[0093] Nb+Ti+V: 0.001%~0.20%

[0094] The addition of Nb, Ti, and V elements can form carbides, nitrides, or carbonitrides with carbon and nitrogen. The uniform and fine precipitates pin the austenite grain boundaries, refining the grain size and improving the strength and toughness of the steel. Simultaneously, the precipitates are dispersed throughout the steel matrix, providing precipitation strengthening and acting as hydrogen traps to inhibit diffusible hydrogen in the steel matrix, reducing its segregation in stress concentration areas at the edges of hot-stamped components and lowering the hydrogen embrittlement sensitivity of the final hot-stamped component. Therefore, appropriate amounts of these elements can be added to the steel substrate of this invention. Furthermore, V elements can precipitate in large quantities during the heating process of hot stamping, further consuming C elements in the matrix and promoting the formation of dislocation-type martensite. In addition, Ti has a strong binding force with N. Adding a certain amount of Ti to hot-stamped steel can form TiN with the N in solid solution in the steel, preventing the combination of N and B elements, thus consolidating N and protecting B, ensuring hardenability. However, excessive addition of the above three microalloying elements will lead to a significant increase in cost. Therefore, in this invention, the total amount of Nb, Ti and V added is controlled within the range of 0.001% to 0.20%.

[0095] Preferably, the aluminum alloy coating of the sub-blank is obtained by hot-dip immersing the steel substrate of the sub-blank into an aluminum alloy plating solution. The chemical composition of the aluminum alloy plating solution, by mass percentage, includes Si: 8-14%, Fe: 0-3%, with the balance being Al and other unavoidable impurity elements.

[0096] Secondly, the present invention also provides a laser-welded thermoformed component with an aluminum alloy coating. The laser-welded thermoformed component comprises multiple sub-components, and has at least two weld seams. Each sub-component includes a steel substrate and an aluminum alloy coating coated on both sides of the steel substrate. The aluminum alloy coating of each sub-component contains an IDL layer near the steel substrate, and the average thickness of the IDL layer at three points is 3.0~15.0 μm. The thickness of the thinnest sub-component does not exceed 1.4 mm, and the thickness of the thickest sub-component does not exceed 2.5 mm. The thickness of the aluminum alloy coating of the thinnest sub-component is greater than that of the thickest sub-component. Preferably, the thickness ratio of the sub-component to the thickest sub-component is defined as HD1, and the thickness ratio of the thickest sub-component to the thinnest sub-component is defined as HD2. For a sub-component with HD1 ≥ 0.9, if HD2 > 1.5, then the sub-component has the same aluminum alloy coating surface density as the thickest sub-component. Preferably, the thinnest sub-component has the thickest aluminum alloy coating, and the thickest sub-component has the thinnest aluminum alloy coating. In this invention, the descriptions of the plate thickness and thickness of sub-components refer to the overall plate thickness and thickness of the sub-component, including the steel substrate and the aluminum alloy coatings coated on both sides of the steel substrate.

[0097] Preferably, the aluminum alloy coating of the sub-component is selected from AS50, AS80 and AS150; AS150 is a double-sided coating on a steel substrate with an average coating thickness of 30~40μm on one side; AS80 is a double-sided coating on a steel substrate with an average coating thickness of 20~30μm (excluding 30μm) on one side; AS50 is a double-sided coating on a steel substrate with an average coating thickness of 10~20μm (excluding 20μm) on one side, and the coating thickness is the average of three points.

[0098] Preferably, the steel substrate of the sub-component contains, by mass percentage: C: 0.05%~0.45%, Mn: 0.60%~2.0%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.01%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.20%, P: 0.001%~0.100%, S: 0.0001%~0.100%, with the balance being Fe and other unavoidable impurity elements.

[0099] Preferably, the tensile strength of the sub-component is 1000~2200MPa.

[0100] Preferably, the microstructure of the steel substrate of the thickest sub-component is mainly martensite, with a volume fraction of martensite ≥97%, to ensure that all sub-components reach the target strength.

[0101] Preferably, the maximum thickness difference of the IDL layer of each sub-component does not exceed 4.0 μm.

[0102] Preferably, the average thickness of the sub-component IDL layer at three points is 3.0~10.8μm; more preferably, the average thickness of the sub-component IDL layer at three points is 3.0~9.5μm; even more preferably, the average thickness of the sub-component IDL layer at three points is 3.0~7.5μm.

[0103] After hot stamping, an IDL (Independent Layer) layer exists in the aluminum alloy coating of each sub-component near the steel substrate. To ensure the resistance spot welding performance of each sub-component, the IDL layer thickness of sub-components with different coating thicknesses (or areal densities) needs to be set with corresponding upper limits. Based on this, the inventors discovered that to ensure a weldable current range of not less than 0.7kA, the IDL layer thickness of each sub-component is 3.0~15.0μm, thereby ensuring stable spot welding performance and a large spot welding process window. Preferably, to ensure a weldable current range of not less than 0.9kA, the IDL layer thickness of each sub-component does not exceed 10.8μm. More preferably, to ensure a weldable current range of not less than 1.0kA, the IDL layer thickness of each sub-component does not exceed 9.5μm. Even more preferably, to ensure a weldable current range of not less than 1.2kA, the IDL layer thickness of each sub-component does not exceed 7.5μm.

[0104] Thirdly, the present invention also provides an austenitizing heat treatment method for laser-welded sheet blanks, comprising: heating the laser-welded sheet blank of the present invention to a target temperature of 850~950℃ and fully austenitizing it. Preferably, the laser-welded sheet blank is heated to a target temperature of 880~950℃.

[0105] Generally, based on the different coating density (or thickness), the coating of aluminum alloy coated laser-welded plates can be divided into AS50, AS80 and AS150. The heating time required for sub-bills with different coating density (or thickness) and thickness to reach the same target temperature varies. The heating process of the sub-bills includes: liquefaction and FeAl alloying of the aluminum alloy coating at around 600℃, austenitization phase transformation of the steel plate at above 700℃, and heat absorption during the heating of the coating and the steel plate itself.

[0106] Through long-term research and summarization, the inventors discovered that aluminum alloy coated steel sheets with different coating layer densities (or thicknesses) have differences in thermal conduction after alloy coating liquefaction and FeAl alloying, which leads to different heating processes. By utilizing these differences in heating processes and optimizing the combination of coating layer densities (or thicknesses) of each sub-blank in the laser-welded plate, it is expected to obtain the largest austenitizing heat treatment heating process window. Based on the above analysis, the inventors accurately tested the heating curves of aluminum alloy coated steel sheets with different steel sheet thicknesses and coating layer densities. Through curve fitting, key factors affecting the heating process of the steel sheet, such as coating layer density, steel sheet thickness, and heating time, were coupled into the heating function of the aluminum alloy coated steel sheet. This allows for accurate prediction of the heating time required for aluminum alloy coated steel sheets with different coating layer densities and steel sheet thicknesses to reach the target temperature. When there are multiple aluminum alloy coated steel sheets, such as multiple blanks in a laser-welded plate, the longest heating time is selected as the lower limit of the heating time required to heat all aluminum alloy coated steel sheets with different coating layer densities and steel sheet thicknesses to the same target temperature for complete austenitization.

[0107] Based on this, the heating time for each sub-bulk in the laser-welded slab blank to reach the target temperature during the austenitizing heat treatment process is calculated. Selecting the longest heating time allows for the precise determination of the lower limit heating time for the laser-welded slab blank to reach the target temperature. This lower limit heating time can also be defined as the lower limit heating time for the austenitizing heat treatment process of the laser-welded slab blank. Due to various reasons, the austenitizing heat treatment process of the laser-welded slab blank not only includes heating the blank to the target temperature but may also involve a holding period after reaching the target temperature. Therefore, the upper limit heating time for the austenitizing heat treatment process of the laser-welded slab blank is the sum of the lower limit heating time and the holding time.

[0108] In order to accurately describe the heating curve of the aluminum alloy coated steel plate, the inventors creatively divided the heating function into three stages.

[0109] (1) Low-temperature heating section (≤600℃): The aluminum alloy coating and steel substrate absorb heat during the heating process.

[0110] At this stage, the Al in the aluminum alloy coating does not liquefy and the steel plate does not undergo austenitization; the material temperature rise is only affected by the plate thickness. By testing the low-temperature heating and temperature rise curves of aluminum alloy coated steel plates with different steel plate thicknesses and aluminum alloy coating surface densities below 600℃, the corresponding low-temperature heating and heat absorption formula for the aluminum alloy coated steel plate (i.e., the blank in the laser-welded plate) can be fitted:

[0111] T 低温 =20+(T 目标 -20)×(1-exp((-0.02 / L)×t1)), T低温 ≤600℃,

[0112] Where t1 is the heating time of the sub-billet during the low-temperature heating stage, also known as the heating time of the sub-billet to 600℃, in seconds; L is the thickness of the sub-billet steel plate, in mm; T 目标 The final target temperature is measured in °C (°C); T 低温 The temperature of the billet during the low-temperature heating stage is expressed in °C.

[0113] When the final blank is heated to T 目标 When the temperature is >600℃, then T 低温 =600℃, at which point the relationship between heating time t1 and steel plate thickness can be simplified as follows:

[0114] ,

[0115] (2) High-temperature heating section (above 600℃): phase change heat absorption of steel substrate

[0116] When the coated steel sheet is heated to above 600℃, in addition to continued heating, the steel substrate will undergo an austenitic transformation when it reaches 700~850℃. This transformation results in heat absorption due to the latent heat of phase transformation, thus lowering the heating temperature. The formula for the heat absorption during this process can be obtained by testing the temperature change over time of aluminum alloy coated steel sheets of the same composition with different steel sheet thicknesses and using curve fitting. The corresponding formula is as follows:

[0117] T 目标 =730+B×t2+C×t2 2 ,

[0118] B=12.52336-0.15311×(As×L)+6.72866×10 -4 ×(As×L) 2 -5.52606×10 -7 ×(As×L) 3 -1.34674×10 -9 ×(As×L) 4

[0119] C = -0.08502 + 8.96693 × 10 -4 ×(As×L)-2.92784×10 -7 ×(As×L) 2 -1.90065×10 -8 ×(As×L) 3 +4.36768×10 -11 ×(As×L) 4

[0120] Where t2 is the heating time for the sub-billet to reach the target temperature during the high-temperature heating stage, also known as the heating time for the sub-billet to rise from 600℃ to the target temperature, in seconds; L is the thickness of the sub-billet steel plate, in mm; As is the density of the double-sided coating on the sub-billet steel plate, in g / m³. 2 ;T 目标 The final target temperature is measured in °C.

[0121] Therefore, when T 目标 When determined, the relationship between heating time and steel plate thickness and coating weight can be transformed into:

[0122] ,

[0123] (3) Heat transfer stages of Al liquefaction and FeAl alloying in aluminum alloy coating

[0124] When aluminum alloy coated steel sheets are heated to above 600℃, the Al in the coating on the steel sheet surface liquefies and Fe and Al alloy. After alloying, the coating contains a large number of intermetallic compounds with low thermal conductivity, less than half that of the steel substrate, resulting in reduced heat transfer efficiency. Therefore, the presence of intermetallic compounds in the coating hinders the heating of the steel sheet during subsequent heating. During this stage, the coating thickness significantly affects the proportion of intermetallic compounds in the coating, thus affecting heat transfer efficiency and causing the heating efficiency of the aluminum alloy coating to decrease with coating thickness at high temperatures. Compared to uncoated steel sheets of the same composition, aluminum alloy coated steel sheets require more heat to heat above 600℃, meaning they heat up more slowly and for a longer time. The effect of heating time on this process can be determined by testing the temperature-time curves of aluminum alloy coated steel sheets with different coating densities and thicknesses, and comparing them with the temperature rise curves of uncoated steel sheets of the same thickness and composition. The effect of coating density on the heat absorption during coating liquefaction and the heat transfer after alloying can be fitted from the temperature rise difference between the two curves. The corresponding formula is as follows:

[0125] T 液化 =597+D×t3+E×t3 2 600℃≤T 液化 ≤700℃,

[0126] D=18.83518-0.31028×(As×L)+0.00187×(As×L) 2 -3.35082×10 -6 ×(As×L) 3 ;

[0127] E=-0.11615+0.00232×(As×L)-1.51656×10 -5 ×(As×L) 2+2.84581×10 -8 ×(As×L) 3 ;

[0128] Where t3 is the hysteresis time caused by heat transfer after liquefaction and alloying of the aluminum alloy coating on the sub-billet, in seconds; L is the thickness of the steel plate on the sub-billet, in mm; T 液化 The melting temperature of the aluminum alloy coating on the sub-billet is ℃; As is the density of the coating on both sides of the sub-billet steel plate, in g / m³. 2 .

[0129] Therefore, the relationship between the additional heating time t3 caused by the decrease in heat transfer efficiency after liquefaction and alloying of the aluminum alloy coating and the coating surface density As can be transformed into:

[0130] 600℃≤T 液化 ≤700℃,

[0131] To ensure complete austenitization of the steel substrate, the target heating temperature T is... 目标 The temperature is 850~1000℃, preferably 880~950℃. At this temperature, the aluminum alloy coating has undergone a complete liquefaction and alloying process, meaning the above formula is updated to:

[0132] ,

[0133] In summary, the heating time t for aluminum alloy coated steel sheets (i.e., the various sub-bills of laser-welded steel blanks) with different steel sheet thicknesses and coating surface densities to reach the target temperature. 子坯料 This can be expressed as the following formula:

[0134] t 子坯料 =t1+t2+t3,

[0135] Since the thickness of aluminum alloy coated steel sheet is almost the same as that of steel sheet, the thickness of the billet steel sheet in the above formula can also be the sheet thickness in actual calculation.

[0136] The heating time t for heating each sub-piece of the laser-welded slab to the target temperature is calculated using the above formulas. 子坯料 The longest heating time t 子坯料 This refers to the lower limit heating time t required to heat the laser-welded sheet blank to the target temperature for complete austenitic transformation. 下限 This is used as the lower limit heating time for the austenitizing heat treatment process of laser-welded plate blanks.

[0137] Considering potential downtime or production slowdowns during actual production, troubleshooting and equipment restarting typically require time. Therefore, the heating time for the austenitizing heat treatment of laser-welded plates may exceed the lower limit of the required austenitizing heating time. 下限 That is, at the lower limit of heating time t 下限 Even after the austenitic transformation is complete, there may still be a certain holding time. Therefore, the upper limit t of the heating time for the austenitizing heat treatment process of laser-welded panels is defined. 上限 , t 上限 =t 下限 +t 保温 This also determined the upper and lower limits of the heating process for the austenitizing heat treatment of laser-welded plates.

[0138] However, due to differences in the steel plate thickness and coating density (or thickness) among the sub-blanks in the laser-welded slab blank, the holding period after each sub-blank reaches the target temperature also varies during heating. This means the continuous heat input to each sub-blank differs, leading to variations in the IDL layer thickness. Excessive IDL layer thickness variation results in differences in spot welding performance, hindering subsequent welding process debugging and stable production in the hot-stamped assembly. Therefore, it is desirable to control the heat input during the holding period, ensuring that the IDL layer thickness does not exceed a certain limit while also controlling the variation in IDL layer thickness among the sub-blanks. This guarantees both the weldable current range and the spot welding stability of each sub-component in the hot-formed assembly.

[0139] When the target temperature T 目标 Once the combination of coating density and steel plate thickness of each sub-billet in the welded slab is determined, the austenitizing heating time t for each sub-billet is then determined. 子坯料 The lower limit heating time t of laser-welded plate blanks 下限 All can be confirmed. Because the welded plate blank may need to be held at the target temperature for a period of time after heating. 保温 Therefore, each sub-bulb reaches the target temperature T. 目标 It also needs to undergo an additional insulation time afterwards. 保温 During the heat preservation time t 保温 Inside, the continuous heat input H per unit coating weight of each sub-blank blank 子坯料 It can be represented as:

[0140] H 子坯料 =T 目标 ×(t 下限 -t 子坯料 +t 保温 ) / As.

[0141] For different sub-bills, although their coating layer density varies, it is desirable for the coating layer of each sub-bills to have uniform heat absorption, thereby promoting the uniform growth of the IDL layer thickness of each sub-bills, i.e., H. 子坯料 The standard deviation needs to be as small as possible to ensure stable spot welding performance of each sub-component during assembly welding. Through extensive research and calculations, the inventors discovered that controlling the H of each sub-brush blank... 子坯料 When the standard deviation is ≤300, the spot welding stability of each sub-component of the laser-welded thermoformed component can be ensured.

[0142] After austenitizing heat treatment, the laser-welded sheet blank will undergo stamping and cooling processes as required by the process. The laser-welded sheet blank is transferred to a forming mold for stamping. The temperature of the laser-welded sheet blank placed on the mold should be maintained at ≥750℃. After stamping, it is held under pressure and quenched to below 200℃ before being demolded to obtain a laser-welded thermoformed component with an aluminum alloy coating.

[0143] The present invention will now be described in more detail with reference to exemplary embodiments. The following embodiments or experimental data are intended to illustrate the present invention by way of example, and those skilled in the art should understand that the present invention is not limited to these embodiments or experimental data.

[0144] Fitting the heating curve and calculating the lower limit of heating time.

[0145] Commercially available PHS1500 stamping steel was selected as the steel substrate (alloy composition shown in Table 1). The steel plate thickness was 1.4~2.2mm, and the aluminum alloy coatings were AS50 and AS150. The aluminum alloy coating was obtained by hot-dip immersion of the steel plate in an aluminum plating bath. The chemical composition of the aluminum plating bath was 9.5% Si, 1.8% Fe, with the balance being Al and impurity elements, the proportion of which did not exceed 2%. Samples of aluminum alloy coated steel plate blanks with different steel plate thicknesses and different coating layer densities (see Table 2) were heated in a box furnace at a target temperature of 900℃. The tensile strength of the hot-stamped components made from aluminum alloy coated steel plates using PHS1000, PHS1500, and PHS2000 materials as the substrate was not less than 1000MPa, 1400MPa, and 1700MPa, respectively.

[0146] Table 1 Alloy composition (wt%) of steel substrates with different tensile strengths

[0147]

[0148] Thermocouples were used to record the temperature rise curves of each sample throughout the heating process, and the temperature rise curves were analyzed according to t 子坯料 Piecewise fitting was performed on t1+t2+t3, and the fitting results are as follows:

[0149] (1) Heat absorption during heating in the low-temperature heating section (≤600℃):

[0150] During this stage, the Al in the aluminum alloy coating is not liquefied and the steel substrate has not undergone austenitization. The temperature rise of the steel plate is only dominated by the plate thickness. Actual temperature rise curves of aluminum alloy coated steel plate blanks with different steel plate thicknesses and coating layer densities are shown in the attached figure. Figure 1 and 2 The heating time t1 can be obtained by the following formula:

[0151] ,

[0152] Where t1 is the heating time of the sub-billet during the low-temperature heating stage, in seconds; L is the thickness of the sub-billet steel plate, in mm; T 目标 The final target temperature is measured in °C (°C); T 低温 The temperature of the billet during the low-temperature heating stage is expressed in °C.

[0153] Figure 1 The figure shows the temperature rise curves of four aluminum alloy blanks with an AS50 coating density and thicknesses of 1.4 mm, 1.8 mm, 2.0 mm, and 2.2 mm in the low-temperature heating section. Figure 1 The solid line represents the measured temperature rise curve, and the dashed line represents the actual temperature rise curve. Figures 1-2 The heating curve obtained by fitting the nine measured heating curves satisfies the formula for calculating the heating time t1 mentioned above. Figure 1 In the legend, AS50 represents the surface density of the aluminum alloy coating on the sub-billet, and t1.4, t1.8, t2.0, and t2.2 represent the steel plate thicknesses of the sub-billets, which are 1.4mm, 1.8mm, 2.0mm, and 2.2mm, respectively. For example, the solid black line in the AS50-t1.4 figure represents the measured temperature rise curve of a sub-billet with an surface density of AS50 and a plate thickness of 1.4mm. The dashed black line in the AS50-t1.4 figure represents the temperature rise curve based on... Figures 1-2 The heating curves of a sub-bulk with an areal density of AS50 and a plate thickness of 1.4 mm were obtained by fitting nine measured heating curves.

[0154] Figure 2 The figure shows the temperature rise curves of five different aluminum alloy blanks with a coating density of AS150 and thicknesses of 1.4mm, 1.8mm, 2.0mm, 2.2mm, and 2.5mm in the low-temperature heating section. Figure 2 The solid line represents the measured temperature rise curve, and the dashed line represents the actual temperature rise curve. Figures 1-2 The heating curve obtained by fitting the nine measured heating curves satisfies the formula for calculating the heating time t1 mentioned above. Figure 2In the legend, AS150 represents the aluminum alloy coating density of the sub-billet as AS150, and t1.4, t1.8, t2.0, t2.2, and t2.5 represent the steel plate thicknesses of the sub-billets as 1.4mm, 1.8mm, 2.0mm, 2.2mm, and 2.5mm, respectively. For example, the solid black line in the AS150-t1.4 figure represents the measured temperature rise curve of a sub-billet with a coating density of AS150 and a plate thickness of 1.4mm. The dashed black line in the AS150-t1.4 figure represents the temperature rise curve based on... Figures 1-2 The heating curves of a sub-blank with a coating density of AS150 and a plate thickness of 1.4 mm were obtained by fitting nine measured heating curves.

[0155] Figures 3-4 , Figures 5-6 and Figures 1-2 The principles are similar, and the illustrations are exactly the same. Figures 3-4 The measured temperature rise curves of the high-temperature heating section and their corresponding fitted temperature rise curves are shown. Figures 5-6 The measured temperature rise curves and their corresponding fitted temperature rise curves for the heat transfer sections after Al liquefaction and FeAl alloying in the aluminum alloy coating are shown below. They will not be repeated hereafter.

[0156] (2) High-temperature heating section (above 600℃) heat rise and heat absorption:

[0157] In this temperature range, the steel substrate absorbs heat due to the latent heat of phase transformation. Curve fitting was performed based on the measured changes in austenitizing temperature versus time for aluminum alloy coated steel sheet billets with different steel sheet thicknesses and coating layer densities (see attached). Figure 3 and 4 The heating time t2 obtained satisfies the following formula:

[0158] ,

[0159] in,

[0160] B=12.52336-0.15311×(As×L)+6.72866×10 -4 ×(As×L) 2 -5.52606×10 -7 ×(As×L) 3 -1.34674×10 -9 ×(As×L) 4 ;

[0161] C = -0.08502 + 8.96693 × 10 -4 ×(As×L)-2.92784×10 -7 ×(As×L) 2 -1.90065×10 -8 ×(As×L)3 +4.36768×10 -11 ×(As×L) 4 ;

[0162] t2 is the heating time (in seconds) for the sub-billet to reach the target temperature during the high-temperature heating stage; L is the thickness of the sub-billet steel plate (in mm); As is the density of the double-sided coating on the sub-billet steel plate (in g / m³). 2 ;T 目标 The final target temperature is measured in °C.

[0163] (3) Heat transfer sections after Al liquefaction and FeAl alloying in aluminum alloy coatings:

[0164] When the billet temperature rises above 600℃, the Al in the coating on the billet surface liquefies and Fe and Al alloy. After alloying, the coating contains a large number of intermetallic compounds with low thermal conductivity, less than half that of the steel substrate, resulting in reduced heat transfer efficiency. Therefore, the presence of intermetallic compounds in the coating hinders the heating of the steel sheet during subsequent heating. During this stage, the coating thickness significantly affects the proportion of intermetallic compounds in the coating, thus impacting heat transfer efficiency and causing the heating efficiency of the aluminum alloy coating to decrease after the coating thickness reaches high temperatures. Compared to uncoated steel sheets of the same composition, aluminum alloy coated steel sheets require more heat to heat above 600℃, meaning they heat more slowly and for a longer time. The effect of heating time on this process can be determined by testing the temperature change curves of aluminum alloy coated steel sheet billets with different coating layer densities and steel sheet thicknesses over time, and comparing them with the temperature rise curves of uncoated steel sheets of the same thickness and composition. The difference in temperature rise between the two curves can be used to fit the effect of coating layer density on heat transfer after coating liquefaction and alloying (see appendix). Figure 5 and 6 The corresponding formula is as follows:

[0165] ,

[0166] in,

[0167] D=18.83518-0.31028×(As×L)+0.00187×(As×L) 2 -3.35082×10 -6 ×(As×L) 3 ;

[0168] E=-0.11615+0.00232×(As×L)-1.51656×10 -5 ×(As×L) 2 +2.84581×10 -8 ×(As×L) 3 ;

[0169] t3 is the hysteresis time caused by heat transfer after liquefaction and alloying of the aluminum alloy coating on the sub-billet, in seconds; L is the thickness of the steel plate on the sub-billet, in mm; T 液化 The melting temperature of the aluminum alloy coating on the sub-billet is ℃; As is the density of the coating on both sides of the sub-billet steel plate, in g / m³. 2 .

[0170] In summary, the heating time t for aluminum alloy coated steel sheet blanks with different steel sheet thicknesses and coating surface densities to reach the target temperature is... 子坯料 This can be expressed as the following formula:

[0171] t 子坯料 =t1+t2+t3.

[0172] Since the thickness of aluminum alloy coated steel sheet is almost the same as that of steel sheet, the thickness of the billet steel sheet in the above formula can also be the sheet thickness in actual calculation.

[0173] The heating time for aluminum alloy coated steel sheet sub-bills with different steel plate thicknesses and coating layer densities to reach the target temperature was calculated using the above formula. Measured times are listed for comparison in Table 2. Table 2 shows that the calculated heating time for the sub-bills to reach the target temperature deviates from the measured heating time by less than 7%. It should be noted that the measured heating curves were obtained by embedding thermocouples in the sub-bills and heating them together with the sub-bills.

[0174] Table 2 Heating processes for sub-bills with different plate thicknesses and coating layer densities

[0175]

[0176] Note: Deviation between calculated and measured values ​​= (Calculated heating time - Measured heating time) / Measured heating time × 100%.

[0177] Example 1

[0178] A laser-welded thermoformed component with an aluminum alloy coating is prepared from a laser-welded blank through austenitizing heat treatment, stamping, and cooling. In this embodiment, the laser-welded blank has two weld seams and is formed by welding three sub-blanks. The sub-blanks are aluminum alloy coated steel plates, and the steel substrate is selected from commercially available PHS1500 material (alloy composition is shown in Table 1). The aluminum alloy coating of each sub-blank is obtained by hot-dip immersion of the steel plate in an aluminum plating solution. The chemical composition of the aluminum plating solution is 9.5% Si, 1.8% Fe, and the balance is Al and impurity elements, with the proportion of impurity elements not exceeding 2%. The thicknesses of sub-blanks 1 to 3 are 1.4 mm, 1.8 mm, and 1.4 mm, respectively. Among them, sub-blanks 1 and 3 are the thinnest, and sub-blank 2 is the thickest. The thickness ratio of the thickest and thinnest sub-blanks is 1.29, and the thickness ratio of sub-blank 3 to sub-blank 2 is 0.77. The surface density of the aluminum alloy coating on blanks 1-3 is 150 g / m². 2 50g / m 2 and 150g / m 2 .

[0179] The laser-welded sheet blank of this embodiment is placed in a box furnace and heated to the target temperature of 900℃. As shown in Table 2, the longest heating time corresponding to the three sub-blanks of the laser-welded sheet blank in this embodiment is 191s, which is taken as the lower limit heating time of the laser-welded sheet blank. The lower limit heating time of the laser-welded sheet blank in each embodiment and comparative example of this invention is shown in Table 3. After completing the heat treatment process according to this lower limit heating time, a blank to be stamped is obtained. Subsequently, the blank to be stamped is quickly transferred to a forming mold for stamping, with a transfer time of 10s and a temperature of 800℃ on the mold. After stamping, it is subjected to pressure holding and quenching to 190℃ before demolding.

[0180] Comparative Example 1

[0181] In this comparative example, the preparation process of the laser-welded thermoformed aluminum alloy coated components is exactly the same as that in Example 1, the only difference being the density of the aluminum alloy coating on the sub-blanks. In this comparative example, the density of the aluminum alloy coating on sub-blanks 1-3 is 50 g / m³. 2 .

[0182] As shown in Table 2, the longest heating time for the three sub-blanks of the laser-welded plate blank in this comparative example is 191s. This is taken as the lower limit heating time for the laser-welded plate blank, and the heat treatment process is completed according to this lower limit heating time.

[0183] Example 2

[0184] A laser-welded thermoformed component with an aluminum alloy coating is prepared from a laser-welded slab blank through austenitizing heat treatment, stamping, and cooling. The number of welds, the blank material, and the material of the aluminum alloy coated steel sheet are consistent with those in Example 1. The thicknesses of sub-blanks 1-3 are 1.4 mm, 2.0 mm, and 1.8 mm, respectively, with sub-blank 1 being the thinnest and sub-blank 2 being the thickest. The thickness ratio of the thickest to the thinnest sub-blank is 1.43, and the thickness ratio of sub-blank 3 to sub-blank 2 is 0.90. The surface density of the aluminum alloy coating on sub-blanks 1-3 is 150 g / m³. 2 50g / m 2 and 50g / m 2 .

[0185] The laser-welded sheet blank of this embodiment is placed in a box furnace and heated to the target temperature of 900℃. As shown in Table 2, the longest heating time corresponding to the three sub-blanks of the laser-welded sheet blank in this embodiment is 230s, which is taken as the lower limit heating time for the laser-welded sheet blank. After completing the heat treatment process according to this lower limit heating time, the blank to be stamped is obtained. Subsequently, the blank to be stamped is quickly transferred to a forming mold for stamping, with a transfer time of 10s and a temperature of 800℃ on the mold. After stamping, it is subjected to pressure holding and quenching to 190℃ before demolding.

[0186] Example 3

[0187] In this embodiment, the preparation process of the aluminum alloy coated laser-welded thermoformed component is exactly the same as in Example 2, the only difference being the density of the aluminum alloy coating on the sub-blanks. In this embodiment, the density of the aluminum alloy coating on sub-blanks 1-3 is 150 g / m³, respectively. 2 50g / m 2 and 150g / m 2 .

[0188] As shown in Table 2, the longest heating time corresponding to the three sub-blanks of the laser-welded plate blank in this embodiment is 237s. This is taken as the lower limit heating time of the laser-welded plate blank, and the heat treatment process is completed according to this lower limit heating time.

[0189] Comparative Example 2

[0190] In this comparative example, the preparation process of the laser-welded thermoformed aluminum alloy coated component is exactly the same as that in Example 2, the only difference being the density of the aluminum alloy coating on the sub-blanks. In this comparative example, the density of the aluminum alloy coating on sub-blanks 1-3 is 150 g / m³. 2 .

[0191] As shown in Table 2, the longest heating time for the three sub-blanks of the laser-welded plate blank in this comparative example is 295s. This is taken as the lower limit heating time for the laser-welded plate blank, and the heat treatment process is completed according to this lower limit heating time.

[0192] Example 4

[0193] A laser-welded thermoformed component with an aluminum alloy coating is prepared from a laser-welded slab blank through austenitizing heat treatment, stamping, and cooling. The number of welds, the blank material, and the material of the aluminum alloy coated steel plate are consistent with those in Example 1. The thicknesses of sub-blanks 1-3 are 1.4 mm, 2.2 mm, and 2.0 mm, respectively. Among them, the thinnest and thickest sub-blanks are 1 and 2, respectively, the thickness ratio of the thickest to the thinnest sub-blank is 1.57, and the thickness ratio of sub-blank 3 to sub-blank 2 is 0.91. The aluminum alloy coating weight of sub-blanks 1-3 is 150 g / m³. 2 50g / m 2 and 50g / m 2 .

[0194] The laser-welded sheet blank of this embodiment is heated to a target temperature of 900℃ in a box furnace. As shown in Table 2, the longest heating time for the three sub-blanks of the laser-welded sheet blank in this embodiment is 255s, which is taken as the lower limit heating time for the laser-welded sheet blank. After completing the heat treatment process according to this lower limit heating time, a blank to be stamped is obtained. Subsequently, the blank to be stamped is quickly transferred to a forming mold for stamping, with a transfer time of 9s and a temperature of 820℃ on the mold. After stamping, it is subjected to pressure quenching to 195℃ before demolding.

[0195] Comparative Example 3

[0196] In this comparative example, the preparation process of the laser-welded thermoformed aluminum alloy coated component is exactly the same as that in Example 4, the only difference being the density of the aluminum alloy coating on the sub-blanks. In this comparative example, the density of the aluminum alloy coating on sub-blanks 1-3 is 50 g / m³. 2 .

[0197] As shown in Table 2, the longest heating time for the three sub-blanks of the laser-welded plate blank in this comparative example is 255s. This is taken as the lower limit heating time for the laser-welded plate blank, and the heat treatment process is completed according to this lower limit heating time.

[0198] Comparative Example 4

[0199] In this comparative example, the preparation process of the laser-welded thermoformed aluminum alloy coated component is exactly the same as that in Example 4, the only difference being the surface density of the aluminum alloy coating on the sub-blanks. In this comparative example, the surface density of the aluminum alloy coating on sub-blanks 1-3 is 150 g / m³, respectively. 2 50g / m 2 and 150g / m 2 .

[0200] As shown in Table 2, the longest heating time for the three sub-blanks of the laser-welded plate blank in this comparative example is 295s. This is taken as the lower limit heating time for the laser-welded plate blank, and the heat treatment process is completed according to this lower limit heating time.

[0201] Table 3. Lower limit heating process for different welding combinations

[0202]

[0203] The coating structure and microstructure of each sub-component of the thermoformed components in Examples 1-4 and Comparative Examples 1-4 were observed by metallographic method, and the coating thickness and microstructure characteristics were recorded. The results are shown in Table 4. The coating thickness and IDL layer thickness are both three-point average thicknesses. Under the lower limit heating process, the coating structure of sub-components 1 and 2 of the welded thermoformed component in Example 1 is as follows: Figure 7 and 8 As shown.

[0204] Table 4. Coating structure and microstructure of different welding combinations under the lower limit heating process.

[0205]

[0206] Furthermore, to investigate the influence of different steel plate thicknesses and coating densities on the upper limit of heating time for the austenitizing heat treatment process of laser-welded sheet blanks, the laser-welded sheet blanks from the above embodiments and comparative examples were heated to 900°C according to the corresponding lower limit heating time for each embodiment and comparative example, and then subjected to heat treatment for different times to form blanks to be stamped. Subsequently, the blanks to be stamped were further stamped and cooled according to the stamping and cooling process parameters corresponding to each embodiment and comparative example to obtain welded hot-formed components. Using a metallographic microscope to examine the IDL layer thickness of each sub-component, the inventors, through extensive experiments, discovered that when the IDL layer thickness of the aluminum alloy coated hot-formed component exceeds 15μm, the coating resistance increases significantly, welding spatter and electrode adhesion problems become significant, spot welding becomes difficult to perform stably, and the weld nugget diameter and performance are difficult to guarantee, resulting in a significant reduction in the weldable current range. Therefore, the time when the IDL layer thickness of any sub-component in the welded hot-formed component first approaches 15μm is taken as the upper limit heating time of the austenitizing heat treatment process of the laser-welded slab blank in each embodiment or comparative example. The time difference between the upper and lower limit heating times of each welded combination is calculated, which is the longest holding time of the laser-welded slab blank. The results are shown in Table 5.

[0207] Table 5. Upper and lower limits of heating process and maximum holding time for different welding combinations

[0208]

[0209] Table 6 shows the IDL layer thickness and martensite ratio of each sub-component in each embodiment and comparative example under the upper limit heating time. Under the upper limit heating process, the plating structure of sub-component 1 and sub-component 2 of the welded thermoformed component in Example 2 is as follows. Figure 9 and 10 As shown.

[0210] Table 6. Coating structure and microstructure of different welding combinations under the upper limit heating process.

[0211]

[0212] As shown in Table 6, for the welded assemblies of Examples 1-4 and Comparative Examples 1-4, the IDL layer thickness of each sub-component in the thermoformed components is 3.0-15.0 μm, and the martensite content in the microstructure is not less than 97%. As shown in Tables 3 and 5, due to the reasonable selection of the coating weight, the t in Examples 1-4... 保温 All achieved a process window of over 300 seconds, offering a larger process window compared to the comparative examples, especially when using thin steel sheet blanks with thick coatings. The process window is significantly larger compared to Comparative Examples 1 and 4. Specific comparisons are as follows:

[0213] (1) Comparing Example 1 and Comparative Example 2 with Example 3, under the scheme of selecting a thin coating on a thick steel plate blank and selecting a thick coating on a thin steel plate blank, for the same combination of steel plate thicknesses, the aluminum alloy coating weight of the thin steel plate is higher than that of the thick steel plate. The t of Examples 1 and 3 保温 The heating process windows of 369s and 343s respectively are significantly better than those of Comparative Example 1, where all steel plate blanks are coated with thin coatings or Comparative Example 2, where all steel plate blanks are coated with thick coatings. In other words, Examples 1 and 3 are more conducive to production organization.

[0214] (2) Comparing Examples 2 and 3 with Comparative Example 2, the thickness ratio of the thickest and thinnest steel plate sub-bills is 1.43, and the thickness ratio of sub-bills 3 to the thickest steel plate sub-bills is not less than 0.9. Regardless of whether a thin or thick coating is selected, the heating process window of sub-bills 3 is relatively large. However, for Examples 4 and Comparative Example 3, the thickness ratio of the thickest and thinnest steel plates is 1.57, and the thickness difference between the thickest and thinnest steel plates is further increased. When the thickness ratio of sub-bills 3 to the thickest steel plate sub-bills is also not less than 0.9, if sub-bills 3 selects the same coating weight as the thickest steel plate, i.e., a thin coating, its process window is larger and more conducive to production organization.

[0215] Meanwhile, in the embodiments of the present invention, the thickness difference of the IDL layer between each sub-component is generally small. Under the upper and lower limit processes, the maximum thickness difference does not exceed 4.0 μm. However, in the comparative examples, the maximum thickness difference of the IDL layer corresponding to each sub-component generally reaches more than 5.0 μm. In particular, in comparative example 4, the maximum thickness difference of the IDL layer reaches 6.3 μm and 5.2 μm respectively under the upper and lower limit processes.

[0216] In addition, samples of each sub-component of the laser-welded thermoformed component obtained through the austenitization upper and lower limit heating process were evaluated by spot welding of the same material. The welding evaluation method was as follows: electrode cap pressure was selected as 4.0 kN, electrode cap end face diameter was selected as 6 mm, welding time was 380 ms, and cooling water flow rate was 6 L / min. The process window for weldable current is the range between the minimum current and the spatter current, with the minimum current being a weld nugget diameter of not less than 4 × t. 1 / 2 (t is the thickness of the product to be welded, and the weld nugget diameter is measured using metallographic methods.) The minimum current required is defined as the spatter current, which is the current that generates spatter during spot welding. The weldable current ranges for each sub-component in the laser-welded thermoformed component after the lower and upper limit heating processes are recorded, and the results are shown in Table 7. The correspondence between all IDL layer thicknesses and weldable current ranges is plotted as curves, and the IDL layer thicknesses corresponding to weldable current ranges of 0.7kA, 0.9kA, and 1.0kA are obtained through polynomial fitting, as shown in Table 7. Figure 11 As shown.

[0217] Table 7. Weldable current range for spot welding of each sub-component under upper and lower limit heating processes.

[0218]

[0219] Depend on Figure 11 It can be seen that as the IDL layer thickness increases, the weldable current range decreases. To ensure that the spot welding current range is not less than 0.7 kA, the IDL layer thickness of the welded sub-component should be 3.0~15.0 μm; to ensure that it is not less than 0.9 kA, the IDL layer thickness of the welded sub-component should be 3.0~10.8 μm; to ensure that it is not less than 1.0 kA, the IDL layer thickness of the welded sub-component needs to be strictly controlled within 3.0~9.5 μm; to ensure that it is not less than 1.2 kA, the IDL layer thickness of the welded sub-component needs to be strictly controlled within 3.0~7.5 μm.

[0220] In summary, through experimental verification, the function obtained by fitting the heating curve of this invention can accurately calculate the lower limit heating time for austenitization heat treatment of laser-welded slab blanks with specific welding combinations. This allows for the development of a reasonable austenitization heat treatment method. Using the laser-welded slab blanks with specially designed welding combinations and their austenitization heat treatment method, laser-welded hot-formed aluminum alloy coated components with fully austenitized steel substrates and excellent spot welding stability can be produced. Furthermore, using the laser-welded slab blanks with specially designed welding combinations ensures that the austenitization heat treatment method achieves the optimal heating process window, greatly facilitating the development of austenitization heat treatment processes and significantly reducing the impact of shutdowns or decelerations on the microstructure and mechanical properties of the final components.

[0221] Examples 5-9

[0222] Taking a laser-welded thermoformed door ring component with an aluminum-silicon coating as an example, the door ring has four weld seams. The material combination includes three types: PHS1000, PHS1500, and PHS2000, with thicknesses of 1.4mm, 2.0mm, and 2.2mm. The coating preparation process is the same as in Example 1. The specific laser-welded blank drawing is as follows: Figure 12 As shown. Following the strategy of selecting sub-blanks with H1≥0.9 and H2>1.5 that have the same coating density as the thickest sub-blank, the inventors designed a reasonable aluminum alloy coating density for the plate thickness combination of this door ring component. Specifically: Plate A and Plate B have a coating density of 1.4 mm & AS150 (150g / cm²). 2 C-plate is 2.0 mm thick and AS50 (50 g / cm²). 2 D-plate is 2.2 mm & AS50 (50 g / cm). 2 Subsequently, following the aforementioned method, the lower limit heating time for austenitization of the door ring welded blank was determined to be 255 s. Simultaneously, the austenitization heating time of the door ring welded blank was extended to 295 s, 335 s, 395 s, and 580 s (upper limit heating time), respectively. The welded blanks subjected to these different austenitization heating times were then hot-stamped to obtain five hot-formed door ring components. Except for the heating time, the hot-stamping process was identical to that in Example 1. The H of each sub-blank in the five door ring welded blanks under the above austenitization heating process was calculated. 子坯料 The IDL layer thickness of each sub-component of the final thermoformed door ring was measured, and the results are shown in Tables 8 and 9.

[0223] Table 8. Heat input of each sub-blank of the welded door ring after different austenitizing heating processes

[0224]

[0225] Table 9. IDL layer thickness of each sub-component of the welded door ring after undergoing different austenitizing heating processes.

[0226]

[0227] The spot welding stability of each sub-component of the thermoformed door ring in the above embodiments was evaluated. The welding evaluation method was as follows: the electrode cap pressure was selected as 4.0 kN, the diameter of the electrode cap end face was selected as 6 mm, the welding time was 380 ms, the cooling water flow rate was 6 L / min, and the A plate spatter current under different heating processes was selected as -0.2kA as the welding current. 100 consecutive spot welds of the same material were performed on each sub-component in the order of A / B / C / D. After the welding of each sub-component was completed, the electrode was re-grinded. After the welding of all four types of sub-components was completed, a total of 400 weld points were obtained. The weld nugget diameter was tested and the total number of unqualified weld points was recorded. The weld nugget diameter was required to be no less than 3×t. 1 / 2 Or 4×t 1 / 2 (t represents the thickness of the product to be welded, and the weld nugget diameter was measured using metallographic methods). The test results are shown in Table 10. It can be seen that H... 子坯料 When the standard deviation is ≤300, all sub-components of the welded door ring thermoformed component exhibit excellent spot welding stability. During the spot welding stability evaluation process, the diameter without a weld nugget does not meet the requirement of 3×t. 1 / 2 The weld nugget diameter does not meet the requirement of 4×t. 1 / 2 The number of weld points did not exceed 10. However, when a heating time of 395s or longer was selected, the welding stability showed a significant deterioration trend; among 400 weld points, the weld nugget diameter did not meet the requirement of 3×t. 1 / 2 The number of solder joints reaches 10-34, and the diameter of the weld nugget does not meet 4×t. 1 / 2 The number of solder joints reaches 37 to 62.

[0228] Table 10 Spot weld stability of various sub-components of the welded door ring after undergoing different austenitizing heating processes

[0229]

[0230] All materials involved in this invention are commercially available materials that can be obtained through open market channels.

[0231] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, and process improvements that fall within the spirit and principles of the present invention are included within the scope of protection of the claims of the present invention.

Claims

1. A laser-welded sheet blank with an aluminum alloy coating, characterized in that, The laser-welded slab blank is formed by welding sub-blanks together, with no fewer than two welds. The sub-blanks include a steel substrate and an aluminum alloy coating plated on both sides of the steel substrate. The thickness of the thinnest sub-blank does not exceed 1.4 mm, and the thickness of the thickest sub-blank does not exceed 2.5 mm. The aluminum alloy coating density of the thinnest sub-blank is greater than that of the thickest sub-blank. The thickness ratio of the sub-blanks to the thickest sub-blank is defined as H1, and the thickness ratio of the thickest sub-blank to the thinnest sub-blank is defined as H2. For a sub-blank with H1 ≥ 0.9, if H2 > 1.5, then the sub-blank and the thickest sub-blank have the same aluminum alloy coating density. The thinnest blank has the highest aluminum alloy coating density, while the thickest blank has the lowest aluminum alloy coating density.

2. The laser-welded plate blank according to claim 1, characterized in that, The aluminum alloy coating of the sub-brush is selected from AS50, AS80 and AS150; the AS50 is a double-sided coating on a steel substrate, and the average areal density of the coating on one side is 15~35 g / m². 2 The AS150 is a double-sided coated steel substrate with an average areal density of 65~100 g / m² on one side. 2 The AS80 is a double-sided coated steel substrate with an average areal density of 35~65 g / m² on one side. 2 .

3. The laser-welded plate blank according to claim 2, characterized in that, The average areal density of the single-sided coating of the AS50 is 15~30 g / m². 2 Alternatively, the average thickness of the coating on one side is 7~13μm; the average areal density of the coating on one side of the AS80 is 35~60g / m³. 2 Alternatively, the average thickness of the coating on one side is 14~21μm; the average areal density of the coating on one side of the AS150 is 65~95g / m². 2 Alternatively, the average thickness of the coating on one side is 22~30μm.

4. The laser-welded plate blank according to claim 1, characterized in that, The steel substrate of the sub-bulk contains, by mass percentage, the following: C: 0.05%~0.45%, Mn: 0.60%~2.00%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.010%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.200%, P: 0.001%~0.100%, S: 0.0001%~0.1000%, with the balance being Fe and other unavoidable impurity elements.

5. The laser-welded plate blank according to claim 1, characterized in that, The aluminum alloy coating of the sub-blank is obtained by hot-dip immersing the steel substrate of the sub-blank into an aluminum alloy plating solution. The chemical composition of the aluminum alloy plating solution, by mass percentage, includes Si: 8~14%, Fe: 0~3%, with the balance being Al and other unavoidable impurity elements.

6. A laser-welded thermoformed component with an aluminum alloy coating, characterized in that, The laser-welded hot-formed component is composed of multiple sub-components. The laser-welded hot-formed component has at least two welds. Each sub-component includes a steel substrate and an aluminum alloy coating coated on both sides of the steel substrate. The aluminum alloy coating of each sub-component contains an interdiffusion layer near the steel substrate, with an average thickness of 3.0~15.0 μm. The thinnest sub-component has a plate thickness not exceeding 1.4 mm, and the thickest sub-component has a plate thickness not exceeding 2.5 mm. The aluminum alloy coating density of the thinnest sub-component is greater than that of the thickest sub-component. The plate thickness ratio between the sub-component and the thickest sub-component is defined as HD1, and the plate thickness ratio between the thickest and thinnest sub-component is defined as HD2. For a sub-component with HD1 ≥ 0.9, if HD2 > 1.5, then the sub-component and the thickest sub-component have the same aluminum alloy coating density. The thinnest sub-component has the thickest aluminum alloy coating, and the thickest sub-component has the thinnest aluminum alloy coating.

7. The thermoformed component according to claim 6, characterized in that, The aluminum alloy coating of the sub-component is selected from AS50, AS80 and AS150; AS150 is a double-sided coating on a steel substrate with an average coating thickness of 30~40μm on one side; AS80 is a double-sided coating on a steel substrate with an average coating thickness of 20~30μm on one side; AS50 is a double-sided coating on a steel substrate with an average coating thickness of 10~20μm on one side.

8. The thermoformed component according to claim 6, characterized in that, The steel substrate of the sub-component contains, by mass percentage: C: 0.05%~0.45%, Mn: 0.60%~2.00%, Si: 0.10%~0.50%, Cr: 0.01%~0.60%, B: 0.001%~0.010%, Al: 0.01%~0.40%, N: ≤0.006%, Nb+Ti+V: 0.001%~0.200%, P: 0.001%~0.100%, S: 0.0001%~0.1000%, with the balance being Fe and other unavoidable impurity elements.

9. The thermoformed component according to claim 6, characterized in that, The tensile strength of the sub-component is 1000~2200MPa.

10. The thermoformed component according to claim 6, characterized in that, The microstructure of the steel substrate of the thickest sub-component is mainly martensite, with a volume fraction of martensite ≥97%.

11. The thermoformed component according to claim 6, characterized in that, The maximum thickness difference of the interdiffusion layers of each sub-component does not exceed 4.0 μm.

12. The thermoformed component according to claim 6, characterized in that, The average thickness of the interdiffusion layer of the sub-component is 3.0~10.8μm.

13. The thermoformed component according to claim 12, characterized in that, The average thickness of the interdiffusion layer of the sub-component is 3.0~9.5μm.

14. The thermoformed component according to claim 13, characterized in that, The average thickness of the interdiffusion layer of the sub-component is 3.0~7.5μm.

15. A method for austenitizing heat treatment of laser-welded aluminum alloy coated blanks, characterized in that, The laser-welded plate blank as described in any one of claims 1-5 is heated to a target temperature of 850~950℃ and fully austenitized; The lower limit heating time t of the austenitizing heat treatment of the laser-welded slab blank 下限 Determine it using the following method: The heating time t for each sub-bulb to reach the target temperature is calculated using formula (1). 子坯料 The longest heating time is selected as the lower limit heating time t for the austenitizing heat treatment of the laser-welded slab blank. 下限 ; t 子坯料 =t1+t2+t3(1) （2）， （3）， （4）， in, B=12.52336-0.15311×(As×L)+6.72866×10 -4 ×(As×L) 2 -5.52606×10 -7 ×(As×L) 3 -1.34674×10 -9 ×(As×L) 4 ; C=-0.08502+8.96693×10 -4 ×(As×L)-2.92784×10 -7 ×(As×L) 2 -1.90065×10 -8 ×(As×L) 3 +4.36768×10 -11 ×(As×L) 4 ; D=18.83518-0.31028×(As×L)+0.00187×(As×L) 2 -3.35082×10 -6 ×(As×L) 3 ; E=-0.11615+0.00232×(As×L)-1.51656×10 -5 ×(As×L) 2 +2.84581×10 -8 ×(As×L) 3 ; t1 is the heating time of the sub-bulk to 600℃, in seconds; t2 is the heating time (in seconds) for the sub-bulk to be heated from 600℃ to the target temperature. t3 is the hysteresis time caused by heat transfer after liquefaction and alloying of the aluminum alloy coating on the sub-bulk, in seconds; L represents the thickness of the sub-blank steel plate, in mm; T 目标 The target temperature for austenitizing heating, in °C; As is the areal density of the coating on both sides of the billet steel sheet, in g / m³. 2 .

16. The austenitizing heat treatment method according to claim 15, characterized in that, The heating time t=t for the austenitizing heat treatment of the laser-welded slab blank. 下限 +t 保温 During the heat preservation time t 保温 Inside, the heat input from the continuous heating of each sub-bulb is H 子坯料 Calculated by formula (5), H 子坯料 =T 目标 ×(t 下限 -t 子坯料 +t 保温 / As (5), To ensure spot welding stability, the H of each sub-blank blank... 子坯料 The standard deviation is no greater than 300.

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