A method for preparing highly corrosion-resistant thermal expansion parts

Abstract

This application relates to the field of hot-air expansion part forming and manufacturing technology, and particularly to a method for preparing highly corrosion-resistant hot-air expansion parts. The method includes: hot-air expanding non-zinc-based coated hot-formed steel to obtain a heat-treated substrate; quenching the heat-treated substrate to obtain a quenched hot-air expansion part; hot-dip coating the quenched hot-air expansion part with a zinc-based coating using a zinc-containing plating solution to obtain a hot-air expansion part containing a zinc-based coating; wherein the hot-dip coating temperature is proportional to the thickness of the quenched hot-air expansion part; and heat-treating the hot-air expansion part containing the zinc-based coating to obtain a zinc-based coated hot-air expansion part. This preparation method, through full-process control of "substrate pretreatment → precise hot-dip coating → coating structure optimization," synergistically optimizes the formation quality, structural stability, and bonding performance with the substrate of the zinc-based coating, improving the corrosion resistance of the hot-air expansion part from three dimensions: physical barrier, sacrificial anode protection, and structural reinforcement.

Description

Technical Field

[0001] This application relates to the field of hot gas expansion part forming and manufacturing technology, and in particular to a method for preparing a highly corrosion-resistant hot gas expansion part. Background Technology

[0002] Hot-formed steel tubular parts possess advantages such as good mechanical strength and low weight. Their application in automotive parts manufacturing not only significantly improves the strength of automotive components but also contributes to achieving lightweighting goals. Furthermore, hot-formed steel tubular parts are typically formed through a hot air expansion process. Based on the inherent mechanical strength characteristics of hot-formed steel tubular parts, those treated with this process exhibit exceptional high strength, which can substantially enhance the collision resistance of automobiles. This provides an efficient solution for balancing automotive safety and fuel economy.

[0003] However, at present, the corrosion resistance of non-zinc-based coated hot-dip galvanized parts after hot-dip galvanizing is relatively lower than that of zinc-based coated parts because they do not have a zinc-based coating. In addition, the thickness of non-zinc-based coated hot-dip galvanized parts will have a certain impact on the hot-dip galvanizing effect. However, the parameter relationship between non-zinc-based coated hot-dip galvanized parts and hot-dip galvanizing is not yet clear. Therefore, it is necessary to establish the relationship between part thickness and hot-dip galvanizing parameters. Summary of the Invention

[0004] This application provides a method for preparing a highly corrosion-resistant hot gas expansion part to solve the following technical problem: how to improve the corrosion resistance of non-zinc-based coated hot gas expansion parts. In a first aspect, embodiments of this application provide a method for preparing a highly corrosion-resistant hot-expansion part, the method comprising: Hot-formed steel with non-zinc-based coating is thermally expanded to obtain a heat-treated substrate. The heat-treated substrate is quenched to obtain a quenched hot gas expansion part. The quenched hot-expanded parts are hot-dip coated with a zinc-containing plating solution to obtain hot-expanded parts with a zinc-based coating; wherein the hot-dip coating temperature is proportional to the thickness of the quenched hot-expanded parts. The hot air expansion part containing the zinc-based coating is heat-treated to obtain a zinc-based coated hot air expansion part.

[0005] Optionally, the thickness h of the quenched hot-expanded part and the hot-dip coating temperature T satisfy the following: When h≤1mm, the hot-dip coating temperature T is 420℃ to 476℃; When 1 < h ≤ 2.5 mm, the hot-dip coating temperature T is 440°C to 486°C; When h > 2.5 mm, the hot-dip coating temperature T is 450°C to 500°C.

[0006] Optionally, the hot-dip coating time is from 2 seconds to 150 seconds.

[0007] Optionally, the temperature of the thermal expansion is 880°C to 950°C, and the duration of the thermal expansion is ≤360s.

[0008] Optionally, the thermal expansion includes a first thermal expansion and a second thermal expansion, wherein the pressure of the first thermal expansion is ≤20MPa and the pressure of the second thermal expansion is >20MPa.

[0009] Optionally, the time t1 for the first thermal expansion and the time t2 for the second thermal expansion satisfy: t1:t2=2:1.

[0010] Optionally, the fillet radius of the heat-treated substrate is ≥1mm.

[0011] Optionally, the thinning rate of the thermal expansion is ≤15%.

[0012] Optionally, the quenching cooling rate is ≥27℃ / s.

[0013] Optionally, the heat treatment temperature is 300°C to 450°C, and the heat treatment time is 5s to 7200s.

[0014] The technical solutions provided in this application have the following advantages compared with the prior art: This application provides a method for preparing highly corrosion-resistant hot-expanding parts. The method first involves hot-expanding a non-zinc-based coated hot-formed steel to obtain a heat-treated substrate. Furthermore, quenching treatment improves the strength of the heat-treated substrate. Finally, a hot-dip galvanizing process is used, with the galvanizing temperature proportional to the thickness of the quenched steel, ensuring that a continuous, uniform, and strongly bonded zinc-based coating is formed on the surface of quenched steel of varying thicknesses. Subsequently, the substrate containing the zinc-based coating is heat-treated to promote an alloying reaction between the zinc in the coating and the iron in the hot-expanding parts, forming an Fe-Zn alloy phase. This enhances the adhesion between the zinc-based coating and the quenched steel, thereby improving the stability of the zinc-based coating. The zinc in these zinc-based coatings can act as a sacrificial anode, protecting the substrate and improving corrosion resistance. Simultaneously, the zinc-based coating also acts as a physical barrier, effectively preventing corrosive media from directly contacting the hot-expanding parts, significantly improving their corrosion resistance. Attached Figure Description

[0015] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0016] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, for those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0017] Figure 1 This is a schematic flowchart illustrating a method for preparing a highly corrosion-resistant thermally expanded part, as provided in an embodiment of this application. Detailed Implementation

[0018] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application.

[0019] The range descriptions used in this application, such as numerical ranges and proportional ranges, include all possible sub-ranges and single numerical values ​​within that range. For example, the range descriptions of "1 to 6" or "1~6" cover all sub-ranges (such as 1 to 3, 2 to 5, etc.) and single numbers (such as 1, 2, 3, 4, 5, 6) between 1 and 6. Unless otherwise specified, the terms "comprising" and others used herein mean "including but not limited to"; relational terms such as "first" and "second" are used only to distinguish different entities or operations and do not imply an actual order or relationship; "and / or" indicates that multiple situations can exist individually or simultaneously; expressions such as "at least one," "multiple," and "at least one" refer to any combination of the corresponding objects, including combinations of single or multiple objects. The proportional relationships involved in this document, such as mass ratios and molar ratios, should be understood as the correspondence between the first and second terms of a proportional formula, according to the order of description. The raw materials, reagents, instruments, and equipment used herein can all be obtained by purchasing from the market or by existing methods.

[0020] Figure 1 An exemplary schematic diagram of a method for manufacturing a highly corrosion-resistant thermal expansion component according to an embodiment of this application is shown; like Figure 1 As shown in the figure, this application provides a method for preparing a highly corrosion-resistant hot-expansion part, the method comprising: S1. Hot-formed steel with non-zinc-based coating is hot-expanded to obtain a heat-treated substrate; S2. Quench the heat-treated substrate to obtain a quenched hot-expanded part; S3. The quenched hot-expanded part is hot-dip coated with a zinc-containing plating solution to obtain a hot-expanded part with a zinc-based coating; wherein the hot-dip coating temperature is proportional to the thickness of the quenched hot-expanded part; S4. The hot air expansion part containing the zinc-based coating is subjected to heat treatment to obtain the zinc-based coated hot air expansion part.

[0021] It should be noted that the non-zinc-based coating thermal expansion component can be a steel substrate without a coating, or a steel substrate with an aluminum-silicon coating, a nickel-based coating, or other non-zinc-based coating.

[0022] It should be noted that the hot air expansion process mainly involves first heating and protecting the non-zinc-based coated hot air expansion parts, and then transferring them to a hot air expansion mold for venting and expansion. During this process, heating can be performed using methods such as furnace heating, resistance heating, and inductive heating.

[0023] It should be noted that after hot air expansion forming, the non-zinc-based coated hot air expanded parts will form a specific part shape to fit the hot air expansion mold. Cooling water is circulated inside the hot air expansion mold, turning the mold into a cooling device and promoting heat exchange between the mold and the heat-treated substrate. The cooling water removes heat from the heat-treated substrate, achieving quenching and transforming its microstructure into martensite, which is beneficial for subsequent hot-dip plating.

[0024] It should be noted that the zinc plating solution can be a high-purity zinc melt, a zinc-aluminum-magnesium melt, or a zinc-aluminum melt.

[0025] It should be noted that the obtained zinc-based coated hot-expansion parts need to be tested for shape accuracy and microstructure. Only if the test results are satisfactory can the zinc-based coated hot-expansion parts be mass-produced and applied. However, if the test results are unsatisfactory, the process parameters need to be readjusted and optimized, and then production and trial production must continue until they are satisfactory.

[0026] It should be noted that this application provides a method for preparing highly corrosion-resistant hot-expansion parts. This method improves the corrosion resistance of non-zinc-based coating hot-expansion parts from three dimensions: physical barrier, sacrificial anode protection, and structural reinforcement, by synergistically optimizing the formation quality, structural stability, and bonding performance of the zinc-based coating with the substrate through multiple steps. The specific mechanism is as follows: I. Substrate Pretreatment: Optimize the substrate for coating adhesion and reduce corrosion risks: Non-zinc-based coated hot-expansion parts first undergo hot-expansion and quenching treatment, a step that plays a fundamental role in improving subsequent corrosion resistance: (1) Hot gas expansion is essentially a high-temperature heat treatment process that can remove the original oxide scale, oil stains or impurities on the surface of the substrate, while refining the internal grains of the substrate and adjusting the structure (for example, reducing the loose structure or the generation of microcracks), making the surface of non-zinc-based coated hot gas expansion parts cleaner and smoother, providing a "defect-free substrate" for subsequent hot-dip plating. If there are impurities or defects on the surface of the substrate of non-zinc-based coated hot gas expansion parts, the zinc layer is prone to incomplete plating or poor bonding during hot-dip plating, causing corrosive media to penetrate from the defects. Hot gas expansion pretreatment can significantly reduce such problems.

[0027] (2) Quenching can enable the substrate to form a strong and tough martensitic structure, improve the mechanical properties of the substrate itself, and reduce the internal stress concentration of the substrate. If the stress of the substrate is low, it is not easy to generate microcracks in subsequent processing or service, thus avoiding the extension of cracks to the coating and causing the penetration of corrosive media.

[0028] II. Hot-dip plating process: Precisely controlling the formation of the coating to strengthen the physical barrier and adhesion. Hot-dip galvanizing is the core step in introducing a zinc-based coating. The key to improving corrosion resistance lies in the design where the hot-dip galvanizing temperature is directly proportional to the thickness of the quenched part due to thermal expansion. (1) The core protective function of zinc-based coatings: The electrode potential of zinc is lower than that of iron (standard electrode potential: Zn 2+ / Zn is -0.76V, Fe 2+ (Fe = -0.44V) In a corrosive environment, zinc will preferentially oxidize (sacrificial anode protection). At the same time, the zinc coating itself can act as a physical barrier to prevent corrosive media such as water, oxygen, and chloride ions from directly contacting the quenched hot gas-expanded parts.

[0029] (2) Necessity of temperature and thickness matching: During hot-dip galvanizing, the zinc liquid needs to undergo a diffusion reaction with the surface of the quenched hot-expanded parts to form an Fe-Zn alloy layer (e.g., ζ phase, δ phase). This alloy layer is the bridge between the coating and the quenched hot-expanded parts. The continuity and thickness of this alloy layer will directly affect the bonding force between the coating and the quenched hot-expanded parts.

[0030] 1) For thick steel: Thick steel has a large heat capacity and slow heat transfer. If the heating temperature of hot-dip galvanizing is insufficient, the zinc-containing plating solution will not react sufficiently with the surface of the substrate, resulting in a thin alloy layer and a discontinuous coating, which makes the coating easy to peel off from the surface of the substrate. 2) For thin steel: Thin steel has a small heat capacity. If the heating temperature of hot-dip galvanizing is too high, the quenched hot gas expansion parts will be overheated and softened, or the alloy layer will be too thick and brittle (for example, too much ζ phase will easily crack).

[0031] Therefore, the control of hot-dip galvanizing temperature in proportion to the thickness of quenched steel can ensure that quenched hot-expanded parts of different thicknesses form a continuous, uniform, and strongly bonded zinc-based coating (containing an Fe-Zn alloy layer), avoiding the formation of pores, peeling, or embrittlement of the coating, and maximizing the physical barrier effect of the coating.

[0032] III. Subsequent heat treatment: Optimize the coating structure to enhance stability and protection. For hot-expanding parts with zinc-based coatings, subsequent heat treatment promotes alloying of the zinc-based coating, further enhancing corrosion resistance. (1) Eliminate internal stress in the coating: During the hot-dip coating process, rapid cooling of the coating can easily generate internal stress, which may lead to microcracks; heat treatment can release stress, reduce the risk of cracks, and ensure the integrity of the coating.

[0033] (2) Optimize the phase structure of the coating: Heat treatment can promote the uniform diffusion of Fe-Zn alloy phase in the coating (e.g., the δ phase is more stable), reduce the segregation of brittle phase (e.g., the ζ phase), and improve the toughness and anti-peeling ability of the coating.

[0034] (3) Formation of dense oxide film: Heat treatment can promote the formation of a more stable ZnO or zinc hydroxyl oxide Zn(OH)2 oxide film on the surface of zinc coating. This oxide film has high chemical stability and can further block the intrusion of corrosive media and enhance the barrier protection effect.

[0035] In summary, the present application provides a method for preparing a highly corrosion-resistant hot-dip expansion part. This method, through full-process control of "substrate pretreatment → precise hot-dip plating → coating structure optimization", ultimately forms a continuous, defect-free, strongly bonded, and structurally stable zinc-based coating on the surface of the non-zinc-based coated hot-dip expansion part. This method actively protects the substrate through the sacrificial anode effect of zinc in the zinc-based coating, and forms a physical barrier through the complete coating and dense oxide film. At the same time, it avoids accelerated corrosion caused by defects in the hot-dip expansion part or the coating, thereby significantly improving the corrosion resistance of the non-zinc-based coated hot-dip expansion part.

[0036] In some optional embodiments, the thickness h of the quenched hot-expanded part and the hot-dip coating temperature T satisfy: When h≤1mm, the hot-dip coating temperature T is 420℃ to 476℃; When 1 < h ≤ 2.5 mm, the hot-dip coating temperature T is 440°C to 486°C; When h > 2.5 mm, the hot-dip coating temperature T is 450°C to 500°C.

[0037] In these embodiments, the specific range of the hot-dip galvanizing temperature T is determined according to the thickness h of the quenched hot-expanded parts. For example, when h ≤ 1 mm, hot-dip galvanizing at a temperature of 420°C to 476°C allows the zinc-containing plating solution to form a uniform zinc-based coating on the surface of thinner quenched hot-expanded parts. When 1 < h ≤ 2.5 mm, hot-dip galvanizing at a temperature of 440°C to 486°C allows the zinc-containing plating solution to form a uniform zinc-based coating on the surface of quenched hot-expanded parts of general thickness. When h > 2.5 mm, hot-dip galvanizing at a temperature of 450°C to 500°C allows the zinc-containing plating solution to form a uniform zinc-based coating on the surface of thicker quenched hot-expanded parts. The zinc-based coatings formed under these different thickness conditions are beneficial to improving the corrosion resistance of non-zinc-based coated hot-expanded parts.

[0038] When h≤1mm, the hot-dip galvanizing temperature T can be 420℃, 424℃, 428℃, 432℃, 436℃, 440℃, 444℃, 448℃, 452℃ or 456℃.

[0039] When 1 < h ≤ 2.5 mm, the hot-dip galvanizing temperature T can be 440℃, 444℃, 448℃, 452℃, 456℃, 460℃, 464℃, 468℃, 472℃, 476℃, 480℃, 484℃ or 486℃.

[0040] When h > 2.5 mm, the hot-dip galvanizing temperature T can be 450℃, 460℃, 470℃, 480℃, 490℃ or 500℃.

[0041] It should be noted that, in special cases involving quenched hot-expanded parts, the hot-dip galvanizing temperature can be adjusted to above 500℃.

[0042] In some alternative embodiments, the hot-dip coating time is from 2 seconds to 150 seconds.

[0043] In these embodiments, hot-dip galvanizing for a time of 2s to 150s allows the zinc-containing plating solution to effectively adhere to the surface of the quenched hot-expanded parts, forming a continuous, uniform, and strongly bonded zinc-based coating.

[0044] The hot-dip coating time can be 2s, 4s, 6s, 8s, 10s, 20s, 30s, 40s, 50s, 100s or 150s.

[0045] In some alternative implementations, the temperature of the thermal expansion is 880°C to 950°C, and the duration of the thermal expansion is ≤360s.

[0046] In these embodiments, hot gas expansion at a temperature of 880°C to 950°C and a time of ≤360s can transform the material microstructure into austenite; it also facilitates subsequent quenching, enabling the microstructure of non-zinc-based coated hot-formed steel to undergo phase transformation and form a large amount of martensite.

[0047] The temperature for this thermal expansion can be 880℃, 890℃, 900℃, 910℃, 920℃, 930℃, 940℃, or 950℃.

[0048] The time for the thermal expansion can be 100s, 150s, 200s, 250s, 300s, or 360s.

[0049] In some alternative implementations, the thermal expansion includes a first thermal expansion and a second thermal expansion, wherein the pressure of the first thermal expansion is ≤20MPa and the pressure of the second thermal expansion is >20MPa.

[0050] In these embodiments, the first hot air expansion with a pressure ≤20MPa allows the non-zinc-based coated hot-formed steel to slowly expand and deform, while initially releasing the internal stress inside the hot-expanded part and refining the grains, which is beneficial for the subsequent second hot air expansion. Furthermore, the second hot air expansion with a pressure >20MPa can further improve the formability of the heat-treated substrate through high pressure, while refining the grains to form a finer, denser, and more uniform grain structure, thus improving the density of the heat-treated substrate. In addition, the high-pressure second hot air expansion can also improve the adhesion between the heat-treated substrate and the surface of the hot air expansion mold, ensuring the formability of the heat-treated substrate. High pressure and good adhesion also improve the surface quality of the heat-treated substrate. A heat-treated substrate with high surface quality can improve the subsequent hot-dip coating effect, thereby improving the corrosion resistance of the non-zinc-based coated hot-expanded parts.

[0051] In some alternative implementations, the time t1 for the first thermal expansion and the time t2 for the second thermal expansion satisfy: t1:t2=2:1.

[0052] In these embodiments, the first and second hot air expansions with a time ratio of 2:1 can control the effect of hot air expansion stages of non-zinc-based coated hot air expansion parts at different pressures, improving the formability of the heat-treated substrate and the adhesion between the heat-treated substrate and the surface of the hot air expansion mold. High pressure and good adhesion improve the surface quality of the heat-treated substrate, and a high-quality heat-treated substrate can improve the subsequent hot-dip coating effect, thereby improving the corrosion resistance of non-zinc-based coated hot air expansion parts.

[0053] In some alternative embodiments, the fillet radius of the heat-treated substrate is ≥1mm.

[0054] In these embodiments, a heat-treated substrate with a fillet radius ≥1mm indicates that thermal expansion is sufficient, which is beneficial for subsequent hot-dip plating.

[0055] In some alternative implementations, the thinning rate of the thermal expansion is ≤15%.

[0056] In these embodiments, hot air expansion with a thinning rate of ≤15% indicates that the hot air expansion of non-zinc-based coated hot air expansion parts is sufficient to expand and form, which is beneficial to the subsequent hot-dip plating.

[0057] The thinning rate of this thermal expansion can be 5%, 10%, or 15%.

[0058] In some alternative implementations, the quenching cooling rate is ≥27°C / s.

[0059] In these embodiments, quenching with a cooling rate ≥27℃ / s can ensure uniform cooling of the heat-treated substrate, and can make the cooling rate of the heat-treated substrate higher than the critical rate of phase transformation of the substrate, which is beneficial to the transformation of the metallographic structure in the heat-treated substrate into the martensitic structure.

[0060] In some alternative embodiments, the heat treatment temperature is 300°C to 450°C, and the heat treatment time is 5s to 7200s.

[0061] In these embodiments, heat treatment at a temperature of 300°C to 450°C and a time of 5s to 7200s can alloy the hot-expansion parts containing zinc-based coatings, improve the bonding strength between the zinc-based coating and the hot-expansion parts, and eliminate the internal stress of the zinc-based coating, which is beneficial to obtaining hot-expansion parts with zinc-based coatings that have high corrosion resistance.

[0062] The heat treatment temperature can be 300℃, 310℃, 320℃, 330℃, 340℃, 350℃, 400℃ or 450℃.

[0063] The heat treatment time can be 5s, 10s, 15s, 20s, 25s, 30s, 50s, 100s, 200s, 300s, 400s, 500s, 1000s, 2000s, 3000s, 4000s, 5000s, 6000s, 7000s, or 7200s.

[0064] The present application is further illustrated below with reference to specific embodiments. Experimental methods in the following embodiments that do not specify specific conditions are generally determined according to national / industry standards; if there is no corresponding national / industry standard, they are performed according to general international standards, conventional conditions, or conditions recommended by the manufacturer.

[0065] Example 1 like Figure 1 As shown, a method for manufacturing a highly corrosion-resistant hot-expansion part includes: S1. Hot-formed bare steel sheets are subjected to hot air expansion to obtain heat-treated base materials; S2. Quench the heat-treated substrate to obtain quenched hot gas expansion parts; S3. The quenched hot gas expansion parts are hot-dip coated with a zinc-containing plating solution to obtain hot gas expansion parts with a zinc-based coating; wherein the hot-dip coating temperature is proportional to the thickness of the quenched hot gas expansion parts. S4. Heat-treat the hot air expansion parts containing zinc-based coating to obtain zinc-based coated hot air expansion parts.

[0066] The thickness h of the quenched hot-dip expansion part is 0.8 mm. The thickness h and the hot-dip coating temperature T of the quenched hot-dip expansion part satisfy the following: When h≤1mm, the hot-dip galvanizing temperature T is 456℃; The hot-dip plating time is 10 seconds.

[0067] The temperature of the thermal expansion was 920℃, and the expansion time was 10 seconds.

[0068] Thermal expansion includes first thermal expansion and second thermal expansion. The pressure of the first thermal expansion is ≤20MPa, and the pressure of the second thermal expansion is >20MPa.

[0069] The time t1 for the first thermal expansion and the time t2 for the second thermal expansion satisfy the following: t1:t2=2:1.

[0070] The fillet radius of the heat-treated substrate is ≥1mm.

[0071] The thinning rate due to thermal expansion is ≤15%.

[0072] The quenching cooling rate is ≥27℃ / s.

[0073] The heat treatment temperature is 300°C to 450°C, and the heat treatment time is 5s to 7200s.

[0074] Example 2 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The thickness h of the quenched hot-dip expansion part is 2.0 mm. The thickness h and the hot-dip coating temperature T of the quenched hot-dip expansion part satisfy the following: When 1 < h ≤ 2.5 mm, the hot-dip galvanizing temperature T is 470℃; The hot-dip plating time is 10 seconds.

[0075] The temperature of the thermal expansion was 910℃, and the expansion time was 12 seconds.

[0076] Example 3 Compared to Example 1, the differences in this example are as follows, while the rest are the same: The thickness h of the quenched hot-expanded part is 3.0 mm. The thickness h and the hot-dip galvanizing temperature T of the quenched hot-expanded part satisfy the following: When h > 2.5 mm, the hot-dip galvanizing temperature T is 456℃.

[0077] The hot-dip plating time is 10 seconds.

[0078] The temperature of the thermal expansion was 930℃, and the expansion time was 10 seconds.

[0079] Comparative Example 1 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The thickness h of the quenched hot-expanded parts is 2mm, and no hot-dip galvanizing treatment is performed after hot-expanding.

[0080] The temperature of the thermal expansion was 910℃, and the expansion time was 10 seconds.

[0081] Comparative Example 2 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: A heat-treated substrate is obtained by hot-expanding aluminum-silicon coated hot-formed steel.

[0082] The thickness h of the quenched hot-expanded parts is 2mm, and no hot-dip galvanizing treatment is performed after hot-expanding.

[0083] The temperature of the thermal expansion was 910℃, and the expansion time was 10 seconds.

[0084] Comparative Example 3 Compared to Example 1, the differences in this comparative example are as follows, while the rest are the same: The thickness h of the quenched hot-expanded parts is 3.0 mm, and the hot-dip galvanizing temperature T is 440℃.

[0085] The zinc-based coated hot-expansion parts of each embodiment and comparative example were collected, and the maximum single-sided etch width at the electrophoretic cross-section was detected under cyclic salt spray conditions. The results are shown in Table 1.

[0086] Table 1 Corrosion Resistance Evaluation

[0087] As shown in Table 1, the method for preparing a high corrosion-resistant hot-dip expansion part provided in this application involves full-process control of "substrate pretreatment → precise hot-dip plating → coating structure optimization". Ultimately, a continuous, defect-free, strongly bonded, and structurally stable zinc-based coating is formed on the surface of non-zinc-based coated hot-formed steel. As a result, the corrosion resistance of the zinc-based coated hot-dip expansion part obtained by this method is relatively good.

[0088] Compared to Example 1, neither Comparative Example 1 nor Comparative Example 2 underwent hot-dip galvanizing, which resulted in the absence of a zinc-based coating on the surface of their quenched hot-expanded parts, leading to poor corrosion resistance.

[0089] Compared to Example 1, Comparative Example 3 did not adjust the hot-dip galvanizing temperature according to the thickness of the quenched hot-dip galvanized parts, which resulted in the hot-dip galvanizing temperature being too low, affecting the corrosion resistance of the final zinc-based coating on the hot-dip galvanized parts.

[0090] In summary, the present application provides a method for preparing a high corrosion-resistant hot-dip expansion part. This method controls the entire process of "substrate pretreatment → precise hot-dip plating → coating structure optimization" to synergistically optimize the formation quality, structural stability, and bonding performance of the zinc-based coating with the substrate. This improves the corrosion resistance of non-zinc-based coated hot-formed steel from three dimensions: physical barrier, sacrificial anode protection, and structural reinforcement.

[0091] In addition, the embodiments of this application provide a method for preparing a high corrosion-resistant hot-expansion part. The non-zinc-based coated hot-formed steel obtained by this method can be applied on a large scale, which is beneficial to the preparation of highly corrosion-resistant parts.

[0092] The above description is merely a specific embodiment of this application, enabling those skilled in the art to understand or implement this application. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this application. Therefore, this application is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features claimed in this application.

Claims

1. A method for preparing a highly corrosion-resistant thermal expansion part, the method comprising: Hot-formed steel with non-zinc-based coating is thermally expanded to obtain a heat-treated substrate. The heat-treated substrate is quenched to obtain a quenched hot gas expansion part. The quenched hot-expanded parts are hot-dip coated with a zinc-containing plating solution to obtain hot-expanded parts with a zinc-based coating; wherein the hot-dip coating temperature is proportional to the thickness of the quenched hot-expanded parts. The hot air expansion part containing the zinc-based coating is heat-treated to obtain a zinc-based coated hot air expansion part.

2. The preparation method according to claim 1, characterized in that, The thickness h of the quenched hot-expanded part and the hot-dip coating temperature T satisfy the following: When h≤1mm, the hot-dip coating temperature T is 420℃ to 476℃; When 1 < h ≤ 2.5 mm, the hot-dip coating temperature T is 440°C to 486°C; When h > 2.5 mm, the hot-dip coating temperature T is 450°C to 500°C.

3. The preparation method according to claim 1, characterized in that, The hot-dip coating time is from 2 seconds to 150 seconds.

4. The preparation method according to claim 1, characterized in that, The temperature of the thermal expansion is between 880°C and 950°C, and the duration of the thermal expansion is ≤360s.

5. The preparation method according to claim 1 or 4, characterized in that, The thermal expansion includes a first thermal expansion and a second thermal expansion, wherein the pressure of the first thermal expansion is ≤15MPa and the pressure of the second thermal expansion is >20MPa.

6. The preparation method according to claim 5, characterized in that, The time t1 for the first thermal expansion and the time t2 for the second thermal expansion satisfy: t1:t2=2:

1.

7. The preparation method according to claim 1, characterized in that, The fillet radius of the heat-treated substrate is ≥1mm.

8. The preparation method according to claim 1, characterized in that, The thinning rate of the thermal expansion is ≤15%.

9. The preparation method according to claim 1, characterized in that, The quenching cooling rate is ≥27℃ / s.

10. The preparation method according to claim 1, characterized in that, The heat treatment temperature is from 300°C to 550°C, and the heat treatment time is from 5 seconds to 7200 seconds.

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