Hot stamped products with aluminum-silicon coating

Abstract

The present application relates to a hot stamping product with an aluminum-silicon coating, which can extend the service life of an electrode cap. The hot stamping product includes a steel substrate and an aluminum-silicon coating covering the steel substrate, the latter including an interdiffusion layer with a body-centered cubic structure adjacent to the steel substrate and an Fe-Al intermetallic compound layer adjacent to the outer side thereof; the Fe-Al intermetallic compound layer includes an Fe2Al5 region adjacent to the interdiffusion layer and a first Si-rich region with a body-centered cubic structure; the interdiffusion layer includes an α-Fe layer and a second Si-rich region with a BCC structure adjacent to the outer side thereof, the second Si-rich region having the same average composition of Fe, Al, and Si as the first Si-rich region; 0.09≤A H / A T ≤0.52, where A T represents the total area occupied by the second Si-rich region and the Fe-Al intermetallic compound layer; A H Represents the sum of the areas occupied by the first Si-rich region and the second Si-rich region.

Description

Technical Field

[0001] The invention relates to a hot stamping formed product with an aluminum-silicon coating. Background Art

[0002] In the modern automotive industry, hot-stamped aluminum-silicon (Al-Si)-coated products have become a key material for lightweighting and improving vehicle safety due to their excellent formability, oxidation resistance, and ultra-high strength. These hot-stamped products are made by hot-stamping hot-formed steel with an Al-Si pre-coating and are often welded to other components, such as the body-in-white. Therefore, the weldability of these hot-stamped products is a major concern for industrial mass production.

[0003] During resistance spot welding, electrode cap wear directly impacts weld quality and production costs. Under the influence of welding pressure and high temperature, wear of the commonly used Cu-Cr-Zr alloy electrode cap primarily manifests as changes in the morphology of the electrode cap's end face. The mechanisms are generally categorized into the following three types: 1) Mechanical wear: During the repeated application and release of welding pressure, the electrode cap's end face gradually wears due to friction and impact. 2) Thermal softening: The high temperatures generated during welding soften the material near the end face of the electrode cap, reducing its strength and hardness, resulting in a "face enlargement" phenomenon and making it more susceptible to wear. 3) Chemical corrosion: Chemical reactions between the end face of the electrode cap and the workpiece to be welded form a heterogeneous layer on the end face that is unable to withstand the welding pressure and high temperature and is prone to flaking or wear. Regardless of the wear mechanism, the ultimate macroscopic result is an enlarged end face of the electrode cap. This reduces the heat input to the workpiece compared to the original electrode cap at the same welding current and time, resulting in a smaller or even substandard nugget size. Therefore, the electrode cap needs to be ground before its standard service life is reached to ensure welding quality.

[0004] Currently, the service life of electrode caps is generally required to be at least 200 cycles. However, when resistance spot welding hot-stamped products with aluminum-silicon coatings, the service life of electrode caps is typically only 80 to 120 cycles, far below the general requirement. This requires frequent replacement of electrode caps, causing production line pauses and impacting production capacity. Furthermore, after replacing the electrode, pressure and current parameters must be recalibrated. Improper operation can easily lead to batch quality issues, negatively impacting product yield.

[0005] In view of the above, there is at least a need to extend the service life of the electrode cap in the welding process of the hot stamping formed product with aluminum silicon coating. Summary of the Invention

[0006] The present invention is made in view of the above problems existing in the prior art.

[0007] The present invention provides a hot stamping formed product with an aluminum-silicon coating, which can extend the service life of an electrode cap, thereby reducing downtime and calibration frequency, and helping to improve production and yield rate.

[0008] The hot stamping formed product with an aluminum-silicon coating according to the present invention comprises a steel substrate and an aluminum-silicon coating covering the steel substrate.

[0009] The aluminum-silicon coating comprises an interdiffusion layer having a body-centered cubic structure adjacent to the steel substrate and a Fe-Al intermetallic compound layer adjacent to the outer side of the interdiffusion layer;

[0010] The Fe-Al intermetallic compound layer includes a Fe2Al5 region adjacent to the interdiffusion layer and a first Si-rich region having a body-centered cubic structure;

[0011] The interdiffusion layer includes an α-Fe layer adjacent to the steel substrate and a second Si-rich region having a body-centered cubic structure adjacent to the outside of the α-Fe layer, wherein the second Si-rich region has the same average composition of Fe, Al, and Si as the first Si-rich region;

[0012] Among them, 0.09≤A H / A T ≤0.52,

[0013] Among them, A T represents the total area occupied by the second Si-rich region and the Fe-Al intermetallic compound layer; A H Represents the sum of the areas occupied by the first Si-rich region and the second Si-rich region.

[0014] Optionally, the first Si-rich region includes, by mass percentage: Si≥3 wt.%.

[0015] Preferably, A H / A T ≤0.45. Preferably, A H / A T ≤0.34. Preferably, A H / A T ≤0.25. Preferably, A H / A T ≤0.20. Preferably, A H / A T ≤0.16.

[0016] Optionally, 0.10≤A H / A T Optionally, 0.12≤A H / A T .

[0017] Optionally, the average thickness of the aluminum silicon coating is in the range of 6.0 to 21.0 μm, further optionally not less than 10.0 μm, optionally not less than 12.0 μm, optionally not more than 18.0 μm, and optionally not more than 16.0 μm.

[0018] Optionally, the average thickness of the aluminum-silicon coating is within a range of greater than 21.0 μm and less than or equal to 45.0 μm, optionally not less than 22.0 μm, optionally not less than 23.0 μm, optionally not less than 25.0 μm, optionally not less than 30.0 μm, optionally not greater than 42.0 μm, optionally not greater than 40.0 μm, and optionally not greater than 37.0 μm.

[0019] According to the present invention, the above-mentioned aluminum-silicon coating extends the service life of the electrode cap, that is, under the standard test method, the electrode cap is marked on the aluminum-silicon coating more than 200 times, even more than 250 times, and further more than 300 times in a single grinding cycle, showing a good electrode life.

[0020] In order to solve the problem of early failure of the electrode cap during the resistance spot welding process of hot stamping products with aluminum silicon coating, the inventors conducted in-depth research on this resistance spot welding process and found that the failure of the electrode cap is significantly different from the conventional understanding, because the reason for the "end face enlargement" is not only due to high temperature softening.

[0021] Specifically, for hot stamped products with aluminum silicon coatings, during the resistance spot welding process, the electrode cap and the aluminum silicon coating are in direct contact, and the current applied to the electrode cap passes through the coating, which will inevitably generate a certain amount of resistance heat on the coating. Under the action of resistance heat, Al and Fe in the coating will diffuse to the end face of the electrode cap, thereby forming a harder Fe-Al-Cu intermetallic compound layer on the end face of the electrode cap. The inventors found that, on the one hand, since the resistance of the Fe-Al-Cu intermetallic compound is greater than the original resistance of the electrode cap (Cu material), the Fe-Al-Cu intermetallic compound will generate more heat on the surface of the electrode cap. This further promotes the diffusion of Al and Fe to the surface of the electrode cap and thus the Fe-Al-Cu intermetallic compound becomes thicker. On the other hand, as Figure 1A As shown in Figure 1, the hardness of the Fe-Al-Cu intermetallic compound (between 300 and 550 HV depending on the proportion of each component) is much higher than that of the Cu electrode cap (about 100 HV) and can withstand the high temperature on the surface of the electrode cap, making the new end face formed by the Fe-Al-Cu intermetallic compound layer less likely to undergo "high temperature softening" deformation. Figure 1BAs schematically shown, during the repeated pressurization process of welding, the Fe-Al-Cu intermetallic compound layer (illustrated by the blue line) squeezes the adjacent Cu material, causing internal deformation and extending outward from the periphery of the Fe-Al-Cu intermetallic compound layer covering the electrode cap. This outwardly extended portion also diffuses with Al and Fe, forming an Fe-Al-Cu intermetallic compound layer there, resulting in an enlargement of the end face of the electrode cap. As the Fe-Al-Cu intermetallic compound on the end face thickens, the end face of the electrode cap becomes larger. This indicates that the "end face enlargement" experienced by the electrode cap during the resistance spot welding of hot-stamped products with aluminum-silicon coatings is not simply due to the inevitable "high-temperature softening" as commonly believed, but also due to the hardening effect of the hard Fe-Al-Cu intermetallic compound formed on the end face, which promotes the end face enlargement. These two effects synergistically accelerate the rate of end face enlargement, thereby significantly reducing the service life of the electrode cap during the resistance spot welding process of hot-stamped products with aluminum-silicon coatings. This is a problem that is not recognized by conventional understanding.

[0022] After discovering this phenomenon, the inventors proposed mitigating the "end face enlargement" failure of the electrode cap by inhibiting the formation of Fe-Al-Cu intermetallic compounds on the electrode cap. Based on this, through in-depth research on the resistance spot welding process, the inventors discovered that reducing the resistance heat generated by the aluminum-silicon coating is crucial to alleviating the hardening-induced "end face enlargement" effect. The specific reasons are explained below.

[0023] As we all know, resistance spot welding is a process in which the workpieces to be welded are melted by resistance heat and then rapidly solidified to form a physical connection. The principle of resistance heat generation follows the basic Joule's law, that is, Q = I 2 RT ,in, Q is the resistance heat, I is the welding current, T For time, and R is the resistance of the workpiece to be welded. I and T When fixed, the resistance of the workpiece to be welded R The resistance heat generated will be determined by the heat transfer. Generally, the resistance of the workpiece to be welded consists of the resistance of the substrate itself and the resistance of the surface coating. Generally speaking, the resistance of the steel substrate is related to its composition and is not affected by the hot stamping heating process. However, the hot stamping heating process can affect the structure of the aluminum-silicon coating, thereby affecting the resistance of the workpiece's surface coating.

[0024] During the hot stamping process, the evolution of the aluminum-silicon coating is as follows:

[0025] (1) In the initial state, the Al-Si pre-plating layer consists of a FeSiAl inhibition layer close to the steel substrate and an Al-Si metal alloy;

[0026] (2) During the hot stamping process, the steel sheet with the aluminum-silicon pre-plated layer undergoes a heating process. During the heating process, Fe diffuses from the steel substrate into the pre-plated layer, while Al diffuses from the pre-plated layer into the steel substrate. Depending on the degree of diffusion, aluminum-silicon coatings with different coating structures are formed.

[0027] Generally speaking, for the aluminum silicon coating obtained by hot stamping, e.g. Figure 2 (See Z. Wang, NA Xu, MX Huang, Phase transformation and carbon profile at the interface between Al-Si coating and steel substrate in a press-hardened steel, aterialia, Volume 20, 2021) The coating structure is as follows from the steel substrate (the lowermost part - with a body-centered cubic (BCC) structure) to the outside: (1) an interdiffusion layer with a BCC structure adjacent to the steel substrate and (2) a Fe-Al intermetallic compound layer adjacent to the outside of the interdiffusion layer.

[0028] The Fe-Al intermetallic compound layer may include Fe3Al phase, FeAl phase, FeAl2 phase, Fe2Al5 phase and FeAl3, etc., wherein when the Fe2Al5 phase exists, at least a portion of the Fe2Al5 phase is adjacent to the outside of the interdiffusion layer.

[0029] The interdiffusion layer includes the α-Fe (ferrite) layer and the Fe-Al sublayer adjacent to it, in which the Fe and Al elements are continuously distributed. The closer to the steel matrix, the higher the Fe content and the lower the Al content. The α-Fe layer is mainly composed of α-Fe phase (such as Figure 2 As shown in FIG, the Fe-Al sublayer may contain a small amount of Si and may include an Fe3Al phase. The Fe-Al sublayer may include an Fe3Al phase, an FeAl phase, and the like.

[0030] It should be noted that although Figure 2There is a dotted line between the ferrite and the Fe-Al sublayer (Fe3Al) immediately outside it, but this dotted line is only applicable to this document because in fact there is no clear boundary between the α-Fe phase and the Fe-Al sublayer immediately outside it. The specific reasons are as follows: the α-Fe phase immediately adjacent to the steel matrix is ​​a disordered solid solution with a BCC structure (the solute atoms in the solid solution are disorderedly distributed), which is significantly different from the martensite structure of the steel matrix. Therefore, there is a clear boundary between the two, which can determine the lower edge of the interdiffusion layer. As the distance from the steel matrix increases, the α-Fe phase with this disordered BCC structure gradually transitions to the Fe3Al phase with an ordered BCC structure (i.e., DO3 structure), which further gradually transitions to the FeAl phase with an ordered BCC structure (i.e., B2 structure). Because of the distance from the α-Fe phase to the Fe-Al sublayer outside it (for example, Figure 2 The crystal structures of the Fe3Al phase and FeAl phase shown in FIG5 are both BCC structures, with only the proportions of elements such as Fe, Al, and Si changing. Therefore, in the metallographic image obtained by scanning electron microscopy (SEM), the boundary between the α-Fe layer and the adjacent Fe-Al sublayer in the interdiffusion layer cannot be directly determined. Therefore, in the art, the two are usually collectively referred to as the interdiffusion layer.

[0031] The interdiffusion layer has a different crystal structure from the adjacent Fe-Al intermetallic compound layer, so there is a clear boundary between the two, which can determine the upper edge of the interdiffusion layer. Figure 2 As shown in the figure, based on the relationship between light and dark, combined with compositional analysis (energy dispersive X-ray spectroscopy (EDS) and electron backscatter diffraction (EBSD)), the outermost interdiffusion layer is divided into the FeAl phase, and the phase in the adjacent Fe-Al intermetallic compound layer is the Fe2Al5 phase. Due to the different crystal structures of the two, there is a clear boundary between them on the metallographic diagram. Based on this, the steel substrate and interdiffusion layer can be identified from the inside out of the hot stamped product with aluminum silicon coating, and the portion outside the interdiffusion layer is the Fe-Al intermetallic compound layer.

[0032] In aluminum-silicon coatings, the FeAl and Fe2Al5 phases not only have distinct crystal structures but also differ in their Fe, Al, and Si content. These differing atomic ratios of Fe and Al directly lead to differences in their mass fractions. Measurements show that the mass fractions of Fe and Al in these two phases do not fully correspond to the atomic ratios in the molecular formulas. This is primarily due to two factors. Firstly, it relates to the degree of order of each phase. Both the FeAl and Fe2Al5 phases are ordered solid solutions, but their structures differ significantly. The FeAl phase has a B2-ordered structure, resulting in a lower formation energy, more flexible atomic diffusion pathways, and a relatively low degree of order, allowing it to exist stably within a certain composition range. In contrast, the Fe2Al5 crystal structure is complex, with a higher formation energy and a higher degree of order, resulting in a narrower composition window. Second, it relates to the testing method. The elemental fractions in coatings are typically determined using EDS line scanning, which involves scanning a sample along a predetermined path with an electron beam while simultaneously acquiring characteristic X-ray signals to generate elemental line distribution curves. Because the FeAl and Fe2Al5 phases are closely adjacent, the detection signal, depending on the electron beam spot diameter (0.05–2 μm) or detection step size (0.01–10 μm), will be the average of the two-phase mixing region, rather than the true composition of a single phase. This results in the EDS analysis curve at the interface showing a gradual compositional transition and fluctuation, rather than the theoretically observed abrupt change. Therefore, it is generally believed that the Fe2Al5 phase has an orthorhombic structure and contains 35–52 wt.% Fe, 48–65 wt.% Al, and less than 1 wt.% Si by mass. The FeAl phase has a BCC structure and contains 52–80 wt.% Fe, 20–48 wt.% Al, and more than 3 wt.% Si by mass. It is important to note that the Si content in the FeAl phase (above 3 wt.%) is significantly higher than that in the Fe2Al5 phase (less than 1 wt.%) because Si is insoluble in the Fe2Al5 phase and can form a solid solution in the FeAl phase by replacing Al atoms.

[0033] From another perspective, the aluminum-silicon coating of hot stamping products is mainly composed of an α-Fe phase and an Fe-Al phase on its outside. The α-Fe phase is a disordered solid solution, and the Fe-Al phase is an ordered solid solution. The solute atoms of both are Al and Si, and the solvent is Fe. Generally speaking, the resistivity of a solid solution is directly related to the type of solute element and the solubility of the solute: (1) The difference in electronegativity, atomic radius, and number of valence electrons between the solute element and the solvent element will affect the resistivity. The resistivity of pure aluminum (Al) at room temperature is about 2.7 μΩ·cm. On the one hand, aluminum has a high free electron density and less electron scattering. On the other hand, Al has a simple face-centered cubic (FCC) structure, so the resistivity is low. The resistivity of pure silicon (Si) at room temperature is about 640 μΩ·cm. It is a semiconductor with an extremely low free electron density and a resistivity much higher than that of pure Al. (2) As the concentration of the solute element increases, the resistivity of the solid solution usually increases. In particular, the increase in the concentration of the high-resistivity silicon element leads to a significant increase in the resistivity of the solid solution. This is because solute atoms can cause lattice distortion and even changes in the crystal structure, leading to more electron scattering and thus increasing resistivity.

[0034] Without considering Si, the resistivity of phases with higher Al content and more complex crystal structures, such as Fe2Al and Fe2Al5, is theoretically slightly higher (60–70 μΩ·cm) than that of phases with ordered BCC structures, such as Fe3Al and FeAl (55–70 μΩ·cm), and also higher than that of the α-Fe phase (approximately 10 μΩ·cm). However, in Al-Si coatings, the Si content in phases with ordered BCC structures (such as Fe3Al and FeAl) is typically higher (at least 3 wt.%) than in phases with orthorhombic structures (such as Fe2Al and Fe2Al5) (at least less than 1 wt.%). Therefore, the introduction of Si can increase the resistivity of phases with ordered BCC structures by 20–30 μΩ·cm. Although the α-Fe phase also contains some Si, both the Si and Al contents are lower than those of phases with ordered BCC structures, such as Fe3Al and FeAl. Therefore, for each phase of the aluminum-silicon coating, the resistivity follows the following order: Si-rich FeAl phase > Fe2Al5 phase > α-Fe phase.

[0035] It is worth noting that the prior art either believes that the Si-rich layer in the aluminum-silicon coating (which contains 4-8 wt.% Si, 40-70 wt.% Fe, a maximum of 1 wt.% Mn and 20-50 wt.% aluminum in addition to impurities, totaling 100 wt.%) has a positive effect on welding properties, such as CN109207861B, or believes that only the negative impact of the interdiffusion layer in the coating on welding needs to be considered, and the coating structure outside the interdiffusion layer does not need to be considered.

[0036] However, the inventors have discovered that this is not the case, because, as previously described, the Si-rich FeAl phase in the coating exists not only in the interdiffusion layer, denoted as the second Si-rich region, but also in the Fe-Al intermetallic compound layer outside the interdiffusion layer, denoted as the first Si-rich region. Optionally, the first Si-rich region comprises, by mass percentage: 3 wt.% ≤ Si ≤ 13 wt.%, 52 wt.% ≤ Fe ≤ 80 wt.%, 20 wt.% ≤ Al ≤ 48 wt.%; alternatively, 3 wt.% ≤ Si ≤ 13 wt.%, 55 wt.% ≤ Fe ≤ 75 wt.%, 20 wt.% ≤ Al ≤ 40 wt.%; alternatively, 5 wt.% ≤ Si ≤ 10 wt.%, 60 wt.% ≤ Fe ≤ 70 wt.%, 25 wt.% ≤ Al ≤ 35 wt.%. Generally, in the case of a multilayer coating structure, the relative proportion of the Si-rich FeAl phase increases with increasing diffusion. Combined with the resistivity analysis above, the increase in the combined area of ​​the first and second Si-rich regions, both in the interdiffusion layer and in the Fe-Al intermetallic compound layer, indicates an increase in the overall resistance of the Al-Si coating. Consequently, when the welding current flows through the Al-Si coating, more resistive heat is generated, leading to an increase in the coating's temperature. This is particularly true of the first Si-rich region, which is closer to the end face of the electrode cap. The heat generated there directly affects the diffusion between elements, promoting diffusion reactions between the Cu electrode cap and Al and Fe, and forming Fe-Al-Cu intermetallic compounds on the electrode cap surface. This, in turn, contributes to the gradual failure of the electrode cap due to the enlarged end face, as previously described.

[0037] In view of the above, considering the small resistivity of the α-Fe layer, the inventors propose to control the total area A occupied by the first Si-rich region and the second Si-rich region. H The total area A occupied by the coating outside the α-Fe layer T The proportion of A in the aluminum-silicon coating is used to control the resistance heat generated by the aluminum-silicon coating. H Refers to the sum of the areas occupied by the first Si-rich region and the second Si-rich region, A T It refers to the total area occupied by the second Si-rich region immediately outside the α-Fe layer and the Fe-Al intermetallic compound layer outside the interdiffusion layer. In order to slow down the enlargement of the end face of the electrode cap and prolong the service life and ensure the expected performance of the hot stamping formed product, the inventors require 0.09≤A H / A T ≤0.52.0.09≤A H / A T Ensure sufficient heating time so that the steel matrix can be fully austenitized to achieve the expected strength, and A H / A T≤0.52 prevents excessive heat accumulation in the aluminum-silicon coating during welding, thereby delaying the failure of the electrode cap due to "enlargement of the end face", making the service life of the electrode cap not less than 200 times.

[0038] Furthermore, the coefficient A of the aluminum-silicon coating of the hot stamping product H / A T The smaller the value, the lower the resistance of the aluminum-silicon coating, which can reduce the surface temperature of the coating and the surface temperature of the electrode cap during resistance spot welding, thereby reducing the tendency of Fe and Al to diffuse into the electrode cap to form Fe-Al-Cu intermetallic compounds, and slowing down the failure of the electrode cap due to "enlarged end face". Therefore, preferably, 0.09≤A H / A T ≤0.45, preferably, 0.09≤A H / A T ≤0.34, more preferably 0.09≤A H / A T ≤0.20, so that when the proportion of the "first Si-rich region + the second Si-rich region" in the coating decreases, the service life of the electrode cap can be no less than 220 times, no less than 250 times, and no less than 300 times. The extended service life of the electrode cap effectively reduces downtime and calibration frequency, which is conducive to improving production and yield rate.

[0039] Those skilled in the art will understand that any range or any value within the above intervals is applicable to the present invention. H / A T It can be any range or any specific value within the range of 0.09~0.52, for example, any range of 0.10~0.50, 0.10~0.45, 0.10~0.40, 0.10~0.34, 0.10~0.30, 0.10~0.20, etc., or any value such as 0.15, 0.18, 0.20, 0.22, 0.24, 0.28, 0.32, 0.36, 0.40, 0.42, 0.43, 0.45, 0.48, etc. BRIEF DESCRIPTION OF THE DRAWINGS

[0040] The embodiments, features and advantages of the present invention will become clear from the detailed description taken in conjunction with the accompanying drawings. It should be understood that the drawings only illustrate some embodiments, are not necessarily drawn to scale, and are exaggerated in some areas for clarity of illustration, and therefore should not be considered limiting. In the drawings:

[0041] Figure 1A Schematically shows the hardness distribution of the end portion of the electrode cap;

[0042] Figure 1B The process of gradually enlarging the end of the electrode cap is schematically shown;

[0043] Figure 2 The aluminum-silicon coating obtained by hot stamping a hot stamped steel plate with an aluminum-silicon pre-coating layer in the prior art is schematically shown;

[0044] Figure 3A-3C Schematically illustrates the detection process of Si-rich areas in the aluminum-silicon coating according to the present invention;

[0045] Figure 4 Schematically illustrating the stretching and breaking of two welded hot stamping product samples according to the present invention;

[0046] Figure 5 and Figure 6 Schematically illustrates a process of determining the service life of an electrode cap according to embodiment SH2 of the present invention;

[0047] Figure 7 The identified plating structure of the hot stamped formed product SH3 according to the embodiment of the present invention is schematically shown. DETAILED DESCRIPTION

[0048] In order to more clearly illustrate the technical solution of the present application, the present invention is described below by means of exemplary embodiments with reference to the accompanying drawings. The following examples or experimental data are intended to illustrate the present invention by way of example. It should be clear to those skilled in the art that the present invention is not limited to these examples or experimental data. The descriptions of the chemical element contents (wt.%) herein all refer to mass percentages. Unless otherwise specified, the preferred embodiments can be freely combined as needed. Unless explicitly stated, all ranges include end values. Those skilled in the art will understand that the data and various parameters described in the examples are merely exemplary and do not constitute a limitation of the present invention.

[0049] The present invention provides a hot stamped product with an aluminum-silicon coating, which is obtained by a hot stamping process from a hot stamped steel plate with an aluminum-silicon pre-coating. It will be understood that the present invention focuses on the control of the coating structure to solve the problems existing in the electrode cap. The specific composition of the steel matrix of the hot stamped product does not affect the realization of the technical effect of the coating structure required to be protected. On the one hand, the steel matrix will not be in direct contact with the electrode cap, and changes in the matrix composition will not affect the interaction between the coating and the electrode cap. On the other hand, changes in the composition of the steel matrix will not change the structural characteristics of the coating. Therefore, there is no need to limit the composition of the steel matrix of the hot stamped product. Based on this, the following only takes the three components of the steel matrix of the hot stamped steel plate listed in Table 1 (which remain unchanged after the hot stamping process) as examples to demonstrate the technical effects that can be achieved by controlling the coating structure. Optionally, the steel matrix may contain the following components in weight percentage: 0.05-0.50 wt.% C, 0.2-5 wt.% Mn, 0-0.004 wt.% B, 0-0.4 wt.% Nb+Ti+V, 0.05-1 wt.% Si, 0.01-1 wt.% Al, Cr, Mo, Ni, and Cu with a total content of less than 5 wt.%; the balance is Fe and impurities.

[0050] As an example, a hot stamped steel sheet having the composition shown in Table 1 is prepared, and the corresponding manufacturing process is as follows:

[0051] a) Steelmaking: Steel is smelted in a vacuum induction furnace, electric furnace or converter according to the composition in Table 1, and cast ingots are produced by continuous casting technology, or directly by thin slab continuous casting and rolling process;

[0052] b) Hot rolling: The steel slab is heated to 1120-1280℃ for hot rolling, with a total hot rolling reduction of more than 50% and a final rolling temperature of more than 800℃ to obtain hot-rolled steel sheets, which are then coiled at a temperature below 700℃ to form hot-rolled coils, which are then pickled to remove the oxide scale produced during the hot rolling process; and

[0053] c) Cold Rolling: The pickled hot-rolled coil is cold rolled at a reduction of 30-70% to obtain a cold-rolled coil with a thickness of approximately 1.4 mm. It will be understood that the thickness of the steel plate is not limited to this and can be rolled to a different thickness as required, for example, within the range of 0.5-3.0 mm, such as for vehicle body applications, but not limited thereto;

[0054] d) Hot-dip coating: The cold-rolled steel coils were subjected to continuous annealing and then pre-coated on both sides. The coating solution consisted of 9 wt.% Si, 3 wt.% Fe, with the remainder being Al and impurities. The bath temperature was 680°C, the pre-set temperature of the steel sheet entering the bath (i.e., the temperature at which the steel sheet enters the bath) was 640°C, and the hot-dip coating time was 2-7 seconds. Excess coating solution was then removed by air knife blowing to control the coating weight on both surfaces, achieving 20 g / m².2 , 40 g / m 2 , 75 g / m 2 Three aluminum-silicon pre-coatings with different single-side coating weights. The average aluminum content in the aluminum-silicon pre-coating is greater than or equal to 60 wt.%.

[0055] It will be understood that the hot dip coating process is not limited to the above but can be selected from the following: for example, the plating solution contains, by mass, 7-12 wt.% Si, less than 4 wt.% Fe, and the balance Al and impurities; the plating solution temperature can be 650°C-700°C; and the steel plate entering the pot temperature can be 600°C-650°C. For another example, the weight of the single-sided Al-Si pre-coating can be controlled by air knife blowing according to different requirements, for example, selected from 10-80 g / m 2 The weight between.

[0056] Table 1 Chemical composition of the steel matrix of an exemplary hot stamping steel sheet (wt.%), the balance being Fe and impurities

[0057] Element C Si Mn B Al Cr Ti V Matrix 1 0.22 0.20 1.2 0.003 / 0.12 0.03 / Base 2 0.06 0.21 1.0 0.003 / 0.10 0.04 / Base 3 0.34 0.30 1.0 0.003 0.30 0.26 / 0.15

[0058] After the above process, hot stamped steel sheets with aluminum-silicon pre-plating layers of different pre-plating thicknesses were obtained. Samples with a size of 300*200 mm were prepared from the pre-plated steel sheets, and then each sample was subjected to flat-plate hot stamping simulation. The hot stamping process was as follows:

[0059] 1) Heating process: The hot stamped steel sheet with aluminum-silicon pre-plating layer is placed in a roller hearth furnace in zones 1 to 10 for the same time according to the heating conditions in Table 2. The total residence time is shown in Table 3 for the heating time, and then cooled to above 700°C.

[0060] 2) Hot stamping process: The heated hot stamping steel plate is then transferred to a flat plate special mold within 5-10 seconds and maintained at a pressure of 600 tons for 8 seconds for hot stamping. It is then taken out after cooling to below 100°C in the mold to obtain a hot stamped product with an aluminum silicon coating. The weight of the single-sided aluminum silicon pre-coating is 10-80g / m 2 The average thickness of the obtained aluminum-silicon coating can be 6.0~45.0 μm.

[0061] As mentioned above, changes in heating time mean changes in the degree of diffusion, that is, the proportion of the Si-rich FeAl phase in the coating structure will also change continuously. Therefore, through comparative analysis, the effects of different proportions of Si-rich FeAl phases on resistance spot welding can be understood. It will be understood that the method for manufacturing the hot stamping formed product according to the present invention is not limited to the above. Knowing the expected coating structure, those skilled in the art can select an appropriate product production method from conventional methods as needed. For example, the heating process can be divided into 8 zones.

[0062] Table 2 Heating process of exemplary hot stamping process

[0063]

[0064] The samples that underwent the aforementioned hot stamping process are listed in Table 3, with SH1-SH20 representing examples of the present invention and DB1-DB4 representing comparative examples. Using the following methods for measuring average coating thickness, detecting Si-rich regions in the aluminum-silicon coating, and measuring the service life of the electrode cap, the average thickness of the pre-coating layer and the average thickness of the aluminum-silicon coating obtained after hot stamping were measured for SH1-SH20 and DB1-DB4, respectively. The proportion of Si-rich regions in the aluminum-silicon coating was calibrated, and the service life of the electrode cap was measured on the corresponding samples. The specific results are listed in Table 3.

[0065] Method for detecting the average thickness of the coating

[0066] According to standard GB / T13298-2015, metallographic specimens are prepared in the thickness direction for hot-stamped steel sheets / hot-stamped products with aluminum-silicon pre-coating on both sides. Within a field of view of at least 500x (e.g., 1000x, with a field of view of 110 μm × 150 μm), a clear boundary between the (pre-)coating and the steel substrate, as well as a clear boundary between the (pre-)coating and the mounting material, must be observed on either side of the steel substrate. The two boundaries of the (pre-)coating can be determined for that side, and the thickness of the (pre-)coating is the distance between them. For each specimen, thickness measurements are taken at least three points on either side and in the center of the field of view, perpendicular to the (pre-)coating thickness. The average thickness is then calculated. The specimens are marked so that the pre-coating and coating thicknesses are measured on the same side.

[0067] Detection method of Si-rich area in aluminum-silicon coating

[0068] A metallographic sample was prepared by taking a cross-section through the thickness of a hot-stamped product with an aluminum-silicon coating. After grinding and physical polishing, the sample was then electrolytically polished, ion-polished, or vibratory-polished. The sample was then examined under a field electron emission microscope (e.g., GEMINI 300) using EBSD at appropriate magnification (e.g., 1000x, field of view: 110 μm × 150 μm) to identify Si-rich regions, while still allowing for visibility of the complete coating structure and a portion of the steel substrate. The detailed process is as follows.

[0069] Figure 3AThe diagram schematically shows a portion of the metallographic image obtained by the EBSD function (for illustration, only a portion of the metallographic image is shown. The actual field of view of the metallographic image is approximately 32 μm × 18 μm, and specific measurements are performed based on the detection and calculation of each area within the actual field of view). The steel matrix is ​​at the bottom, and although the steel matrix and its adjacent α-Fe phase are both BCC structures, the microstructure of the steel matrix is ​​obviously different from that of the α-Fe phase, resulting in a clear interface between the steel matrix and the coating, namely the lower edge of the interdiffusion layer. Figure 3A By comparing the Fe2Al5 and BCC crystal structures in the standard database of known crystal structures, the EBSD function automatically calculates the crystal plane spacing and crystal orientation based on the position and spacing of the diffraction spots, thereby determining the Fe2Al5 area and BCC structure area in the coating and marking them with different colors to distinguish them. Figure 3B , which shows the Fe2Al5 region (region 1) and two separated BCC structure regions: one is close to the steel substrate, which is the interdiffusion layer (region 2); the other is closer to the coating surface, which is the first Si-rich region (region 3). In this case, region 2 and region 3 are shown in the same color. It is worth noting that the boundaries between region 1 and regions 2 and 3 are Figure 3A The Fe2Al5 region, as indicated by contrast, coincides with the boundary between the interdiffusion layer and the FeAl region, consistent with the previous discussion. Therefore, in SEM micrographs, the boundary between the interdiffusion layer and the adjacent Fe2Al5 region, as well as the boundary between the Si-rich FeAl region and other regions (such as the illustrated Fe2Al5 region) in the Fe-Al intermetallic compound layer, can be identified by contrast differences. Furthermore, it is noted that the entire interdiffusion layer is identified as a BCC structure, making it difficult to identify the boundary between the α-Fe layer and the second Si-rich region. Therefore, the present inventors determined the second Si-rich region in the interdiffusion layer using the following method.

[0070] Specifically, Figure 3B For further processing, a rectangular "reference area" with a length of 0.5~2.0 μm and a width of 0.5~1.0 μm is selected at the center position in the thickness direction of the identified first Si-rich area (area 3), and EDS element analysis is performed on the area to obtain the average composition of Fe, Al and Si contained therein. It should be noted that the selection of the "reference area" should be located in the middle of the first Si-rich area as much as possible, that is, avoiding the boundary of the first Si-rich area, so as to avoid the composition of other phases affecting the average composition measurement of the "reference area". Then, using the TURPHASE function module, based on this average composition, Figure 3BThe portion with the same average composition in region 2 (i.e., the interdiffusion layer) is identified as the second Si-rich region, which is marked as region 4 and shown in the same color as the first Si-rich region (e.g., blue), and the result is Figure 3C .

[0071] Afterwards, Image J software was used to identify the corresponding color blocks in the coating and to count the area they occupied. Figure 3C For example, A T A represents the total area occupied by the second Si-rich region and the Fe-Al intermetallic compound layer outside the interdiffusion layer, that is, the sum of the areas of the blue part (the first Si-rich region + the second Si-rich region, i.e., regions 3 and 4) + the green part (Fe2Al5 region, i.e., region 1) in the picture; H Represents the sum of the areas occupied by the first Si-rich region and the second Si-rich region (i.e., the blue portion in the image). To ensure data accuracy, the resolution must be above 80% during EBSD testing. It should be noted that when using Image J software to identify color blocks, the statistical result is the number of pixels, and the area occupied by each pixel is a fixed value. In theory, the area occupied by the color block should be the number of pixels × the area per pixel. Therefore, in order to simplify the calculation, A H / A T The value can be directly calculated using the number of pixels. It will be understood that other image processing software with the above functions can be used to perform the above process.

[0072] For each metallographic sample, take at least three fields of view (at the same magnification) in the direction perpendicular to the coating thickness to carry out the above process, and then H / A T Take the average value as the final A of the metallographic sample H / A T .

[0073] Electrode cap service life detection method

[0074] The service life of electrode caps was tested on hot stamping products with different aluminum silicon coatings.

[0075] The electrode cap pressure was set to 4.0 kN, the electrode cap end diameter was set to 6 mm, the welding time was 380 ms, and the cooling water flow rate was 6 L / min. The welding current was increased from 5 kA by 100 A until spattering occurred. The current that produced spatter was recorded as I max . Select welding current as I max-200 A, use a new electrode cap to weld two overlapping hot stamping product specimens (for example, SH1-SH1, welding current is 8.0 kA) with a size of 30*100 mm, so as to form a nugget at the overlapping part of the two hot stamping product specimens to weld the two specimens. Each group (two pieces) of specimens completes one weld point, and every 50 points constitutes a cycle. Figure 4 As shown in Figure 2, at the 50th point in each cycle, the two welded hot stamping product specimens were tensile broken. Figure 5 As shown, the diameter of the weld core is measured in two directions perpendicular to each other to obtain a first value of the weld core diameter. D 1 and the first value D 2. Then the diameter of the weld nugget D Denoted as ( D 1+ D 2) / 2.

[0076] When the nugget size measured at the 50th point in the cycle is found D Less than 4× t 1 / 2 (in, t is the thickness of the hot stamping product sample, which is 1.4 mm in the current embodiment, so 4× t 1 / 2 When the diameter of the nugget is about 4.73 mm, the marking is stopped and the nugget diameter is measured by breaking the weld points in sequence within the cycle. t 1 / 2 The number of points is recorded as the electrode cap life. Figure 5 As shown, at the 50th point in the 5th cycle (i.e. the 250th point in total), it is found that D <4× t 1 / 2 , then stop the dotting test. Then, in the 5th cycle, break and measure the corresponding points at 49, 48, 47, 46, ... n (n ≥ 1) in turn. D ,until D ≥4× t 1 / 2 (4.73 mm). For example, Figure 6 As shown, it is found that the 46th point measurement D It is about 4.55mm, which is smaller than 4× t 1 / 2 , but the 45th point is measured D is 4.82 mm, larger than 4× t 1 / 2 , then the service life of the electrode cap is 50×4+45=245 times. Generally, the industry requires the service life of the electrode cap to be no less than 200 times.

[0077] Table 3 Coating structures and corresponding welding results according to the embodiments and comparative examples of the present invention

[0078] serial number substrate Average thickness of pre-plating layer (μm) Heating time (s) Average thickness of coating (μm) <![CDATA[A H / A T ]]> Test current / kA Service life of electrode cap DB1* Matrix 1 10.5 180 11.3 <![CDATA[ 0.08 ]]> / / SH1 Matrix 1 11.3 200 12.2 0.15 8.0 336 SH2 Matrix 1 10.5 230 13.8 0.22 7.8 282 SH3 Matrix 1 11.4 260 15.4 0.33 7.6 268 SH4 Matrix 1 11.3 290 16.0 0.37 7.6 245 SH5 Matrix 1 11.6 330 16.3 0.49 7.5 210 DB2 Matrix 1 12.0 350 16.6 <![CDATA[ 0.54 ]]> 7.4 <![CDATA[ 196 ]]> SH6 Matrix 1 18.5 220 20.4 0.16 7.8 326 SH7 Matrix 1 19.4 250 22.0 0.25 7.6 276 SH8 Matrix 1 17.8 280 23.4 0.34 7.4 255 SH9 Matrix 1 19.4 310 24.9 0.45 7.4 228 SH10 Matrix 1 18.7 340 25.4 0.52 7.3 204 DB3 Matrix 1 17.9 380 26.8 <![CDATA[ 0.69 ]]> 7.2 <![CDATA[ 135 ]]> SH11 Matrix 1 26.4 250 30.6 0.09 7.6 345 SH12 Matrix 1 27.8 300 32.9 0.20 7.4 302 SH13 Matrix 1 26.6 350 36.5 0.39 7.2 230 SH14 Matrix 1 28.9 400 39.2 0.47 7.0 224 DB4 Matrix 1 28.4 450 41.2 <![CDATA[ 0.56 ]]> 7.0 <![CDATA[ 162 ]]> SH15 Base 2 16.2 240 20.3 0.16 7.4 317 SH16 Base 2 17.1 300 22.8 0.32 7.1 260 SH17 Base 2 17.4 360 24.2 0.51 6.9 212 SH18 Base 3 27.4 260 31.8 0.18 7.5 303 SH19 Base 3 26.4 320 34.7 0.30 7.3 264 SH20 Base 3 28.0 380 37.5 0.45 7.0 223

[0079] *: DB1 failed the test due to insufficient heating, so the steel matrix of the hot stamped product was not completely austenitized. Therefore, the expected tensile strength of 1350 MPa or more was not achieved.

[0080] As shown in Table 3, when resistance spot welding was performed on the hot stamped products SH1 to SH20 according to the embodiments of the present invention, the service life of the electrode caps exceeded 200 times, and even reached over 300 times. In contrast, when resistance spot welding was performed on the hot stamped products DB1 to DB4 according to the comparative examples, the service life of the electrode caps did not reach 200 times. This indicates that the hot stamped products according to the present invention can extend the service life of the electrode caps to over 200 times, achieving the expected technical effect. The specific reasons are analyzed as follows.

[0081] The hot stamped products SH1, SH2, SH3, SH4, SH5 (abbreviated as SH1-5) of the substrate 1 according to the embodiment of the present invention and the comparative example DB2 all start with the same pre-plating layer single-side weight, i.e., 20 g / m 2 The average thicknesses of the Al-Si pre-coatings were measured to be 11.3 μm, 10.5 μm, 11.4 μm, 11.3 μm, 11.6 μm, and 12.0 μm, respectively. SH1-5 and DB2 were then subjected to a hot stamping process with heating times of 200 s, 230 s, 260 s, 290 s, 330 s, and 350 s, respectively. Following this, the hot stamping process yielded Al-Si coatings with average thicknesses of 12.2 μm, 13.8 μm, 15.4 μm, 16.0 μm, 16.3 μm, and 16.6 μm, respectively. Each Al-Si coating consisted of a body-centered cubic interdiffusion layer adjacent to the steel substrate and an Fe-Al intermetallic compound layer adjacent to the interdiffusion layer. The Al-Si coatings of SH1-5 and DB2 were then analyzed using the aforementioned method for detecting Si-rich regions in Al-Si coatings. Taking a field of view of the hot stamping formed product SH3 according to an embodiment of the present invention as an example, the aluminum silicon coating is marked by the above-mentioned Si-rich area detection method. Figure 7As shown, the α-Fe layer with BCC structure is marked in red, the Si-rich region with BCC structure is marked in blue, and the Fe2Al5 region with orthorhombic structure is marked in green. That is to say, the aluminum-silicon coating of SH3 includes an interdiffusion layer with a BCC structure adjacent to the steel substrate and an Fe-Al intermetallic compound layer adjacent to the outside of the interdiffusion layer. The Fe-Al intermetallic compound layer includes the Fe2Al5 region adjacent to the interdiffusion layer and the Fe2Al5 region on the coating surface (totaling region 1-green) and a first Si-rich region with a BCC structure (region 3-blue); and the interdiffusion layer includes an α-Fe layer (red) adjacent to the steel substrate and a second Si-rich region (region 4-blue) with a BCC structure adjacent to the outside of the α-Fe layer. The second Si-rich region is identified by the average composition of the "reference region" in the first Si-rich region, where the "reference region" is a rectangle with a length of 1 μm and a width of 0.5 μm. The identified average composition is: 7.6 wt.% Si, 29.7 wt.% Al, 62.6 wt.% Fe. Using Image J software, A H and A T The pixels occupied by SH3 are 147936 and 451149 respectively. H / A T The value is 0.3279, which is 0.33 after the decimal point. Similarly, two different fields of view are taken on the sample to calculate A. H / A T , which are approximately 0.31 and 0.34 respectively. The average of the three values ​​is 0.33 with two decimal places. H / A T The service life of the electrode caps on SH1-5 and DB2 are 336, 282, 268, 245, 210 and 196 times respectively, showing a gradually decreasing trend.

[0082] In the case of thicker pre-plating, for example, 17.8~19.4 μm thick pre-plating for SH6-10 and DB3, 26.4~28.9 μm thick pre-plating for SH11-14 and DB4, the A of Al-Si coating H / A T The service life of the electrode cap shows the same rule as above. That is, by prolonging the heating process, the A in the aluminum silicon coating H / A T The service life of the electrode cap decreases accordingly.

[0083] The above phenomenon occurs because extending the heating time during hot stamping will promote the formation of Si-rich regions, thereby obtaining higher A H / A T As discussed above, at the same thickness, the total area A occupied by the Si-rich region is H The total area A occupied by the coating outside the α-Fe layer T The higher the proportion of A, the higher the resistance heat brought by the Si-rich area during the resistance spot welding process, which will be detrimental to the service life of the electrode cap. Therefore, based on the above-mentioned findings, the inventors propose to reduce A H / A T To extend the service life of the electrode cap.

[0084] In addition, when the specific composition of the steel substrate of the hot stamping steel plate changes, it does not affect the technical effect of improving the use of the electrode cap through the coating structure according to the present invention. For example, the SH15-17 according to the present invention adopts the composition of substrate 2, and the SH18-20 adopts the composition of substrate 3. According to the results in Table 3, it can be confirmed that the technical effect achieved by substrate 1 is consistent with that achieved by substrate 1. The A of the aluminum-silicon coating of substrate 2 (SH15-17) and substrate 3 (SH18-20) is H / A T The service life of the electrode cap shows the same rule as above and is H / A T When ≤0.52, the substrate 2 and the substrate 3 also achieve the technical effect of extending the service life of the electrode cap. Therefore, it can be seen that the change in the composition of the steel substrate will not affect the technical effect of the coating structure according to the present invention of extending the service life of the electrode cap.

[0085] Combined with the results in Table 3, the present invention requires A H / A T ≤0.52, so as to ensure that when the hot stamping formed product with such a coating structure is subjected to resistance spot welding, the electrode cap can be continuously spot welded more than 200 times in a single electrode cap grinding cycle. H / A T ≤0.45, so that the electrode cap can be continuously tapped more than 220 times in a single electrode cap grinding cycle; optional A H / A T ≤0.34, so that the electrode cap can be continuously tapped more than 250 times in a single electrode cap grinding cycle; optional A H / A T ≤0.25, so that the electrode cap can be continuously tapped more than 270 times in a single electrode cap grinding cycle; optional A H / A T≤0.20, so that the electrode cap can be continuously tapped more than 300 times in a single electrode cap grinding cycle; optional A H / A T ≤0.16, so that the electrode cap can be continuously tapped more than 315 times in a single electrode cap grinding cycle.

[0086] On the other hand, it is worth noting that A H / A T It cannot be infinitely small, because reducing A H / A T This means reducing the heating process of the hot stamping process. According to Table 3, if the heating process is too short, such as DB1 is only heated for 180 s, although its A H / A T The tensile strength of the hot stamped product is only 0.08, but the steel matrix cannot be fully austenitized, so that the strength of the hot stamped product obtained after hot stamping cooling is only 1250 MPa, which cannot meet the requirement of tensile strength of the hot stamped product being not less than 1350 MPa, and becomes a defective product. In contrast, according to the SH11 of the present invention, a hot stamped product that meets the strength requirements is obtained under extended heating time, and its A H / A T The service life of the electrode cap is extended to 345 times. Therefore, in order to ensure that the steel matrix is ​​fully austenitized during the heating process to ensure the strength of the product, the present invention requires 0.09≤A H / A T Optionally, to further ensure strength, 0.10≤A H / A T ; Optionally 0.12≤A H / A T It will be understood that the above tensile strength is an expected performance related to the composition of the steel matrix and is not necessarily not less than 1350 MPa. It may also be less than 1350 MPa. For example, the expected tensile strength of the matrix 2 is above 1000 MPa.

[0087] In view of the above two reasons, the present invention requires 0.09≤A H / A T ≤0.52. Within this range, any combination of the above required ranges can be used to further narrow the range. For example, optionally, 0.09≤A H / A T ≤0.45, optionally 0.09≤A H / A T ≤0.34, optionally 0.09≤A H / A T ≤0.25, optionally 0.09≤A H / AT ≤0.16, optionally, 0.10≤A H / A T ≤0.52, optionally 0.10≤A H / A T ≤0.45, optionally 0.10≤A H / A T ≤0.34, optionally 0.10≤A H / A T ≤0.25, optionally 0.10≤A H / A T ≤0.16, optionally 0.12≤A H / A T ≤0.52, optionally 0.12≤A H / A T ≤0.45, optionally 0.12≤A H / A T ≤0.34, optionally 0.12≤A H / A T ≤0.25, optionally 0.12≤A H / A T ≤0.16.

[0088] It is worth pointing out that the results of thick Al-Si coatings are not comparable to those of thin Al-Si coatings. For example, SH5 and SH14 have coating thicknesses of 16.3 µm and 39.2 µm, respectively. H / A T The values ​​are close, 0.49 and 0.47 respectively. If we only look at these two parameters, under similar proportions, the resistance of the aluminum silicon coating of SH14 is greater, which will generate more resistance heat, thus resulting in a shorter electrode cap life than SH5. However, as listed in Table 3, the service life of the electrode caps for SH5 and SH14 are 210 and 224 respectively, and the service life of the latter electrode cap is even longer. This is because, according to the test method, the test current must be determined before the electrode cap life test is carried out. The test current is I max -200 A, of which I max The current that produces spatter. The generation of spatter current is related to the welding heat input, that is, spatter is likely to occur when the heat input is greater than the critical value. The heat input conforms to Joule's law. Q = I 2 RT , Ris the resistance of the welding material. SH5 and SH14 have the same base resistance (same steel base composition), but different coating resistance (different coating thickness). Overall SH14 has a higher resistance, so its corresponding I max The current is lower, corresponding to the test current of SH14 is 7.0 kA. In contrast, the test current of SH5 is 7.5 kA. Therefore, it has a larger A H The SH14, at a lower test current and with a smaller A H The SH5 finally achieved similar electrode life at a larger test current.

[0089] Optionally, the average thickness of the aluminum-silicon coating is in the range of 6.0-21.0 μm, further optionally not less than 10.0 μm, optionally not less than 12.0 μm; further, the average thickness of the aluminum-silicon coating is optionally not greater than 18.0 μm, optionally not greater than 16.0 μm. It will be understood that these ranges can be combined in any manner, for example, the average thickness of the aluminum-silicon coating is in the range of 10.0-21.0 μm, optionally 12.0-21.0 μm, optionally 6.0-18.0 μm, optionally 10.0-18.0 μm, optionally 12.0-18.0 μm, optionally 6.0-16.0 μm, optionally 10.0-16.0 μm, optionally 12.0-16.0 μm.

[0090] Optionally, the average thickness of the aluminum-silicon coating is within a range greater than 21.0 µm and less than or equal to 45.0 µm, optionally not less than 22.0 µm, optionally not less than 23.0 µm, optionally not less than 25.0 µm, optionally not less than 30.0 µm; further, the average thickness of the aluminum-silicon coating is optionally not greater than 42.0 µm, optionally not greater than 40.0 µm, optionally not greater than 37.0 µm. It will be understood that these ranges can be combined in any way, for example, the average thickness of the aluminum silicon coating is in the range greater than 21.0 μm and less than or equal to 42.0 μm, optionally 22.0~42.0 μm, optionally 23.0~42.0 μm, optionally 25.0~42.0 μm, optionally 30.0~42.0 μm, optionally 22.0~40.0 μm, optionally 23.0~40.0 μm, optionally 25.0~40.0 μm, optionally 30.0~40.0 μm, optionally 22.0~37.0 μm, optionally 23.0~37.0 μm, optionally 25.0~37.0 μm, optionally 30.0~37.0 μm.

[0091] In summary, by controlling the structure of the aluminum-silicon coating of the hot stamping product, namely A H / AT The ratio of 1 / 4 to 1 / 8 can not only ensure the strength of the hot stamping product, but also ensure that the service life of the electrode cap is not less than 200 times during the resistance spot welding process. This helps to reduce the consumption of the electrode cap and save production costs.

[0092] The detailed description and accompanying drawings support and describe the present invention, but the scope of the present invention is limited only by the claims. Although some modes or embodiments for carrying out the present invention have been described in detail, various alternative designs and embodiments exist for practicing the present invention as defined in the appended claims. It should be clear to those skilled in the art that the present invention is not limited to these embodiments and that various modifications may be made without departing from the scope of protection of the present invention.

Claims

1. A hot stamping formed product with an aluminum-silicon coating, comprising a steel substrate and an aluminum-silicon coating covering the steel substrate. in, The aluminum-silicon coating includes an interdiffusion layer having a body-centered cubic structure adjacent to the steel substrate and a Fe-Al intermetallic compound layer adjacent to the outer side of the interdiffusion layer; The Fe-Al intermetallic compound layer includes a Fe2Al5 region adjacent to the interdiffusion layer and a first Si-rich region having a body-centered cubic structure; The interdiffusion layer includes an α-Fe layer adjacent to the steel substrate and a second Si-rich region having a body-centered cubic structure adjacent to the outside of the α-Fe layer, wherein the second Si-rich region has the same average composition of Fe, Al, and Si as the first Si-rich region; Among them, 0.09≤A H / A T ≤0.52, Wherein, on the cross section in the thickness direction of the hot stamping formed product with aluminum silicon coating, A T represents the total area occupied by the second Si-rich region and the Fe-Al intermetallic compound layer; A H Represents the sum of the areas occupied by the first Si-rich region and the second Si-rich region.

2. The hot stamped product according to claim 1, wherein A H / A T ≤0.45。 3. The hot stamped product according to claim 1, wherein A H / A T ≤0.34。 4. The hot stamped product according to claim 1, wherein A H / A T ≤0.25。 5. The hot stamped product according to claim 1, wherein A H / A T ≤0.20。 6. The hot stamped product according to claim 1, wherein A H / A T ≤0.16。 7. The hot stamped product according to any one of claims 1 to 6, wherein 0.10≤A H / A T 。 8. The hot stamped product according to any one of claims 1 to 6, wherein 0.12≤A H / A T 。 9. The hot stamped product according to any one of claims 1 to 6, wherein The first Si-rich region comprises Si≥3 wt.% by mass.

10. The hot stamped product according to claim 1, wherein The average thickness of the aluminum-silicon coating is in the range of 6.0 to 21.0 μm.

11. The hot stamped product according to claim 10, wherein The average thickness of the aluminum-silicon coating is not less than 10.0 μm.

12. The hot stamped product according to claim 10, wherein The average thickness of the aluminum-silicon coating is not less than 12.0 μm.

13. The hot stamped product according to any one of claims 10 to 12, wherein The average thickness of the aluminum-silicon coating is no more than 18.0 μm.

14. The hot stamped product according to any one of claims 10 to 12, wherein The average thickness of the aluminum-silicon coating is no more than 16.0 μm.

15. The hot stamped product according to claim 1, wherein The average thickness of the aluminum-silicon coating is in a range of greater than 21.0 μm and less than or equal to 45.0 μm.

16. The hot stamped product according to claim 15, wherein The average thickness of the aluminum-silicon coating is not less than 22.0 μm.

17. The hot stamped product according to claim 15, wherein The average thickness of the aluminum-silicon coating is not less than 25.0 μm.

18. The hot stamped product according to claim 15, wherein The average thickness of the aluminum-silicon coating is not less than 30.0 μm.

19. The hot stamped product according to any one of claims 15 to 18, wherein The average thickness of the aluminum-silicon coating is no more than 37.0 μm.

20. The hot stamped product according to claim 9, wherein The first Si-rich region comprises, by mass percentage, 3 wt.%≤Si≤13 wt.%, 52 wt.%≤Fe≤80 wt.%, and 20 wt.%≤Al≤48 wt.%.

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