Thin-wall high-strength automobile structural part and preparation method thereof

Abstract

The invention relates to a thin-wall high-strength automobile structural part and a preparation method thereof, and belongs to the technical field of automobile structural part preparation, the thin-wall high-strength automobile structural part comprises an integrally-formed main body structure made of high-strength and high-toughness aluminum alloy, the average wall thickness of the main body structure is 1.0-2.5 mm, the tensile strength of the main body structure is larger than or equal to 350 MPa, the yield strength of the main body structure is larger than or equal to 220 MPa, and the elongation of the main body structure is larger than or equal to 8%; the high-strength and high-toughness aluminum alloy is prepared from the following raw materials in percentage by mass: 9.0 to 10.5 percent of Si, 0.3 to 0.5 percent of Mg, 0.2 to 0.4 percent of Mn, 0.09 to 0.12 percent of Fe, 0.01 to 0.03 percent of Cu, 0.02 to 0.05 percent of Zn and the balance of Al and inevitable impurities. According to the thin-wall high-strength automobile structural part and the preparation method thereof, through material-structure-process three-in-one collaborative innovation, the automobile structural part with light weight (thin wall), high strength, high toughness and high rigidity is successfully prepared, and an advanced and reliable solution is provided for automobile light weight.

Description

Technical Field

[0001] This invention relates to the field of automotive structural component manufacturing technology, specifically to a thin-walled high-strength automotive structural component and its manufacturing method. Background Technology

[0002] With the rapid development of the automotive industry towards lightweighting, energy conservation, and safety, increasingly stringent requirements are being placed on the performance of automotive components. Automotive structural parts, such as suspension brackets, longitudinal beams, and battery pack housings, not only need to withstand complex dynamic loads and impacts, but also must be as lightweight as possible to reduce energy consumption. Aluminum alloy die-casting technology, due to its high efficiency and near-net-shape forming capabilities, has become one of the preferred processes for manufacturing such parts.

[0003] However, traditional die-casting aluminum alloys and ordinary die-casting processes face many challenges in manufacturing thin-walled, high-strength structural components: 1. Insufficient material properties: Commonly used die-cast aluminum alloys (such as ADC12) generally have low strength (tensile strength is usually below 250MPa) and poor toughness (elongation is usually below 5%), making it difficult to meet the dual requirements of high strength and high toughness for key automotive structural components.

[0004] 2. Thin-walled filling and density challenges: When the average wall thickness of a part is reduced to 1.0-2.5mm, it is difficult to completely expel the gas and trapped gas in the mold cavity during conventional die casting. This can easily lead to defects such as porosity and shrinkage in the casting, which seriously damages the mechanical properties and vacuum level of the part.

[0005] 3. Risk of deformation and bubbling during heat treatment: Ordinary die castings contain high-pressure air bubbles. When solution treatment or aging heat treatment is performed to improve strength, the air bubbles expand due to heat, which can cause "bubbling" or uncontrollable deformation on the surface of the part. This means that traditional high vacuum die castings can usually only undergo low-temperature heat treatment or no heat treatment at all, which limits the further improvement of their performance.

[0006] 4. The contradiction between structural efficiency and lightweighting: Simply reducing wall thickness will decrease the stiffness and strength of parts. The core issue in achieving effective lightweighting is how to compensate for and improve the overall mechanical properties of parts through optimized structural design while reducing weight.

[0007] While some research has been conducted on the fabrication technology of high-strength aluminum alloys and thin-walled structural components, certain shortcomings remain. For example, the composition design of some high-strength aluminum alloys is not optimal, resulting in an inability to achieve the best balance of overall performance, with shortcomings in strength, toughness, and machinability. Regarding fabrication processes, while some advanced die-casting and heat treatment technologies can improve the performance of structural components, the lack of precise control over process parameters leads to significant fluctuations in product performance, making it difficult to meet the consistency requirements of large-scale industrial production. Therefore, there is an urgent need in this field for a method for manufacturing thin-walled, highly dense, and high-strength automotive structural components that combines excellent mechanical properties and good formability, and can be achieved through a stable and reliable fabrication process. Summary of the Invention

[0008] To address the shortcomings of existing technologies, this invention provides a thin-walled high-strength automotive structural component and its manufacturing method, which possesses advantages such as lightweight, high strength, high toughness, high rigidity, and stability and reliability, thus solving the problems mentioned in the background technology.

[0009] To achieve the above objectives, the present invention provides the following technical solution: A thin-walled high-strength automotive structural component includes an integrally formed main structure made of high-strength and tough aluminum alloy, wherein the average wall thickness of the main structure is 1.0-2.5 mm, and its tensile strength is ≥350 MPa, yield strength is ≥220 MPa, and elongation is ≥8%. The high-strength and high-toughness aluminum alloy comprises the following raw materials by weight percentage: Si: 9.0-10.5%, Mg: 0.3-0.5%, Mn: 0.2-0.4%, Fe: 0.09-0.12%, Cu: 0.01-0.03%, Zn: 0.02-0.05%, balance being Al and unavoidable impurities.

[0010] Furthermore, the high-strength and high-toughness aluminum alloy also contains Sr: 0.015-0.03% and Ti: 0.05-0.15%.

[0011] Furthermore, the main structure is provided with a grid-like reinforcing rib designed through topology optimization, and the thickness of the reinforcing rib is 1.3-1.6 times the average wall thickness of the main structure.

[0012] Furthermore, the main structure has a closed multi-chamber structure in the key stress-bearing areas.

[0013] Another technical problem to be solved by the present invention is to provide a method for manufacturing thin-walled high-strength automotive structural components, comprising the following steps: S1. Smelting and refining: Smelting aluminum alloy raw materials and refining them by rotary degassing to make the hydrogen content of the melt ≤0.08ml / 100g Al; S2. Ultra-vacuum die casting: A vacuum of ≤30mbar is established in the die casting cavity, and the molten aluminum obtained in S1 is injected into the mold at an injection speed of 4.5-5.5m / s and a pressurization pressure of 75-85MPa. S3. In-mold quenching: After die casting, the mold is forced to cool with water through a spot cooling pipe during the pressure holding stage, so that the casting is cooled from the solidus temperature to below 200°C within 8 seconds. S4.T5 heat treatment: The casting is aged at 190-210℃ for 2.5-3.5 hours. After the treatment, a high-strength automotive structural component is obtained.

[0014] Furthermore, in S2, the ingate speed of the mold is 45-55 m / s.

[0015] Furthermore, prior to step S2, a water-based nano-ceramic coating is sprayed onto the mold cavity, wherein the coating is applied at a rate of 30-50 ml / m².

[0016] Furthermore, in S3, the temperature of the cooling water for in-mold quenching is 15-25℃, and the water flow rate is 8-12L / min.

[0017] Furthermore, following S4, a post-processing step is included to perform laser cleaning and local shaping on the high-strength automotive structural components.

[0018] Furthermore, the laser cleaning uses a pulsed fiber laser with a wavelength of 1064nm to treat gate, overflow tank residue, and burrs; the local shaping uses a robot to hold a solid-state high-frequency induction heating device for local instantaneous heating. After the material softens, a precise correction force (50-300N) is applied and held for a short time (2-10 seconds).

[0019] Compared with the prior art, the present invention provides a thin-walled high-strength automotive structural component and its manufacturing method, which has the following beneficial effects: 1. This thin-walled high-strength automotive structural component and its preparation method, through optimized aluminum alloy composition (specific content of Si, Mg, Mn, etc.) and combined with a specific T5 heat treatment regime, enables the casting to achieve a high strength and toughness combination with tensile strength ≥350MPa, yield strength ≥220MPa, and elongation ≥8% while maintaining good casting performance, fully meeting the performance requirements of key automotive structural components; by adopting ultra-high vacuum die casting of ≤30mbar and precisely controlling injection parameters (injection speed 4.5-5.5m / s, ingate speed 45-55m / s), the gas in the cavity is greatly reduced, ensuring that the aluminum liquid has excellent fluidity and filling ability when filling a 1.0-2.5mm thin wall, thereby obtaining a high-quality casting with very few internal pores and high density.

[0020] 2. This thin-walled high-strength automotive structural component and its preparation method utilize in-mold quenching to rapidly solidify and initially cool the casting within the mold. This not only refines the grains, preparing the microstructure for subsequent T5 aging treatment, but also fundamentally avoids the "bubbling" risk and severe deformation problems associated with traditional offline solution treatment, making it possible to effectively enhance the strength of die-castings through heat treatment. Furthermore, the topology-optimized mesh-like reinforcing ribs and closed multi-chamber structure reinforce the most critical areas of material distribution, ensuring that "good steel is used where it matters most." The reinforcing rib thickness is 1.3-1.6 times the wall thickness, significantly improving the rigidity and local strength of the part while minimizing weight gain.

[0021] 3. The thin-walled high-strength automotive structural component and its preparation method form a complete, tightly integrated, and precisely controlled process flow, from melting and refining (hydrogen content control), mold nano-ceramic coating spraying (improving filling and demolding), to ultra-vacuum die casting, in-mold quenching, and T5 heat treatment. This process has high stability and good repeatability, making it suitable for large-scale industrial production. Subsequent laser cleaning and robot local high-frequency induction correction achieve non-contact, high-precision post-processing, effectively solving the problems of easy deformation of thin-walled parts and easy damage to parts by traditional cleaning methods, ensuring the dimensional accuracy and appearance quality of the final product. Detailed Implementation

[0022] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0023] Example 1 (Preparation of a car shock absorber tower): This embodiment presents a thin-walled, high-strength automotive shock absorber tower.

[0024] Structure: The shock absorber tower is integrally die-cast, with an average wall thickness of 2.0 mm for its main structure. Through computer-aided topology optimization analysis, grid-like reinforcing ribs were designed at the installation points and along the stress paths, with each rib being 3.0 mm thick (1.5 times the main wall thickness). Simultaneously, a closed multi-chamber structure was formed within the main structure to further enhance bending stiffness and torsional resistance.

[0025] Material: The high-strength and high-toughness aluminum alloy of this invention has the following specific chemical composition by mass percentage: Si: 9.8%, Mg: 0.4%, Mn: 0.3%, Fe: 0.10%, Cu: 0.02%, Zn: 0.03%, Sr: 0.02%, Ti: 0.10%, balance Al and unavoidable impurities.

[0026] The method for preparing a thin-walled, high-strength automotive shock absorber tower in this embodiment includes the following steps: S1. Smelting and Refining: Weigh the raw materials according to the above proportions and smelt them in a smelting furnace at 720℃.

[0027] After the alloy has completely melted and been stirred evenly, it is transferred to a holding furnace for rotary degassing and refining. High-purity argon is used as the refining gas, the rotor speed is adjusted to 450 rpm, and the refining time is 15 minutes. After refining, a vacuum hydrogen analyzer is used to ensure that the hydrogen content of the melt is ≤0.08 ml / 100g Al.

[0028] S2. Ultra-vacuum die casting: First, water-based nano-ceramic coating is uniformly sprayed onto the surface of the mold cavity, with the spraying amount strictly controlled at 40ml / m² to ensure demolding effect and mold insulation.

[0029] After the mold is closed, the vacuum system is activated to establish and maintain a vacuum of ≤20mbar in the die-casting cavity.

[0030] The molten aluminum obtained from S1 was injected into the pressure chamber at 650°C.

[0031] Injection is performed: a slow injection speed of 0.3 m / s is used to smoothly push the molten aluminum to the ingate; a fast injection speed of 5.0 m / s is used, at which point the ingate speed reaches 50 m / s. Near the end of the filling process, a booster pressure of 80 MPa is applied and maintained.

[0032] S3. In-mold hardening: After die casting, the forced water cooling system inside the mold is immediately activated during the pressure holding stage.

[0033] The cooling water temperature is controlled at 20℃, and the water flow rate is controlled at 10L / min.

[0034] Monitoring with a mold temperature sensor, the casting cools from the solidus temperature (approximately 550°C) to below 180°C within 6 seconds, and then the mold is opened and the casting is removed.

[0035] S4.T5 heat treatment: The removed castings are placed in an aging heat treatment furnace and held at 200℃ for 3 hours.

[0036] After the heat preservation is complete, remove it and air-cool it to room temperature.

[0037] S5. Post-processing: Laser cleaning: Using a pulsed fiber laser with a wavelength of 1064nm, and setting appropriate power and frequency, the sprue, overflow groove residue, and flash burrs on the parting line of the casting are scanned and cleaned. The process is non-contact, stress-free, and results in a clean surface.

[0038] Localized Correction: Inspection revealed a slight deformation of approximately 0.5mm on a certain mounting surface of the casting. A robot was used to clamp a solid-state high-frequency induction heating device to momentarily heat the area to 250℃ (approximately 3 seconds). After the material softened, a precise correction force of 150N was immediately applied and held for 5 seconds before being released. After cooling, the flatness of the mounting surface met the drawing requirements.

[0039] Performance testing in this embodiment: The mechanical properties of the vibration damping tower prepared according to the above process were sampled and tested. Tensile strength: 365 MPa; Yield strength: 235 MPa; Elongation: 9.5%.

[0040] The test structure fully meets the design requirements.

[0041] Example 2 (Lower housing of electric vehicle battery pack): This embodiment presents a thin-walled, high-strength electric vehicle battery pack lower housing.

[0042] Structure: The lower casing of this battery pack is relatively large (approximately 2000mm × 1500mm) with an average wall thickness of 1.8mm. To protect the battery cells and withstand bottom impacts, the bottom is designed with dense mesh-like reinforcing ribs, each rib with a thickness of 2.5mm (approximately 1.39 times the wall thickness), forming multiple continuous closed multi-chamber anti-collision structures.

[0043] Material: The high-strength and high-toughness aluminum alloy of this invention has the following specific chemical composition by mass percentage: Si: 10.2%, Mg: 0.35%, Mn: 0.25%, Fe: 0.11%, Cu: 0.025%, Zn: 0.04% (Sr and Ti were not added in this example), with the balance being Al and unavoidable impurities. This embodiment describes a method for preparing a thin-walled, high-strength electric vehicle battery pack lower casing, comprising the following steps: (focusing on the differences from Embodiment 1) S1. Smelting and Refining: The process is the same as in Example 1, ensuring that the hydrogen content meets the standard.

[0044] S2. Ultra-vacuum die casting: To better fill large, thin-walled parts, the fast injection speed was adjusted to 5.5 m / s, and the ingate speed was increased to 55 m / s to ensure the integrity of the flow front. The vacuum level was maintained at ≤30 mbar.

[0045] S3. In-mold hardening: Due to the large projected area of ​​the part, in order to ensure uniform cooling, the cooling water flow rate was increased to 12L / min, and the casting was cooled to 190℃ within 7 seconds.

[0046] S4.T5 heat treatment: Keep warm at 195℃ for 3.5 hours.

[0047] S5. Post-processing: The laser cleaning process is the same as in Example 1. During localized correction, for a deformed long side, a correction force of 280N is applied after high-frequency induction heating and held for 8 seconds.

[0048] Performance testing in this embodiment: The mechanical properties of the shell body prepared according to the above process were sampled and tested. Tensile strength: 355 MPa; Yield strength: 225 MPa; Elongation: 8.2%.

[0049] Meanwhile, the entire housing passed the required sealing and bottom impact tests.

[0050] Comparative example: Vibration damping towers with the same structure were prepared using conventional die-cast aluminum alloy ADC12 (composition approximately: Si, 10.5%, Cu, 2.0%, Mg, 0.3%, Fe, 0.8%), employing ordinary vacuum die casting (vacuum degree approximately 80 mbar), without in-mold quenching or T5 heat treatment.

[0051] Test results: Tensile strength: 240 MPa; Yield strength: 150 MPa; Elongation: 3%.

[0052] Internal X-ray inspection revealed multiple pores and shrinkage defects.

[0053] Conclusion: Through the comparison of the examples and comparative examples, it can be clearly seen that the present invention, through a unique alloy composition design and combined with a complete set of synergistic processes of ultra-vacuum die casting, in-mold quenching and T5 heat treatment, has successfully achieved comprehensive mechanical properties and internal quality far superior to traditional processes while significantly reducing the wall thickness, perfectly realizing the goal of "thin wall, high strength and high toughness" for automotive structural parts.

[0054] It should be noted that the specific values ​​(such as temperature, pressure, time, etc.) in the above embodiments are all within the parameter range of the claims of this invention, and are further illustrative examples of the scope of protection of the claims, and should not be construed as limiting the scope of protection of this invention. Those skilled in the art can make appropriate adjustments to the above parameters within the scope defined by the claims. It should be noted that, in this document, the terms "comprising," "including," or any other variations thereof are intended to cover non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements includes not only those elements but also other elements not expressly listed, or elements inherent to such a process, method, article, or apparatus. Unless otherwise specified, an element defined by the phrase "comprising one..." does not exclude the presence of other identical elements in the process, method, article, or apparatus that includes said element.

[0055] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A thin-walled high-strength automotive structural member characterized by: The application relates to a high-strength and high-toughness aluminum alloy automobile structure, which comprises an integrally-formed main body structure made of a high-strength and high-toughness aluminum alloy, wherein the average wall thickness of the main body structure is 1.0-2.5 mm, the tensile strength of the main body structure is greater than or equal to 350 MPa, the yield strength of the main body structure is greater than or equal to 220 MPa, and the elongation of the main body structure is greater than or equal to 8%. The high-strength and high-toughness aluminum alloy comprises the following raw materials in percentage by mass: Si: 9.0-10.5%, Mg: 0.3-0.5%, Mn: 0.2-0.4%, Fe: 0.09-0.12%, Cu: 0.01-0.03%, Zn: 0.02-0.05%, and the balance of Al and inevitable impurities. The high-strength and high-toughness aluminum alloy further comprises Sr: 0.015-0.03% and Ti: 0.05-0.15%.

2. The thin-walled high-strength automotive structural member according to claim 1, characterized by: The main body structure is provided with a grid-shaped reinforcing rib designed by topology optimization, and the thickness of the reinforcing rib is 1.3-1.6 times the average wall thickness of the main body structure.

3. The thin-walled high-strength automotive structural member according to claim 1, characterized by: The main body structure is formed with a closed multi-chamber structure in a key stress area.

4. The thin-walled high-strength automotive structural member according to claim 3, characterized by: The application further relates to a preparation method of the high-strength and high-toughness aluminum alloy automobile structure.

5. A method for producing a thin-walled high-strength automobile structural member, the thin-walled high-strength automobile structural member being produced as claimed in any one of claims 1 to 4, characterized by, S1. Melting and refining: aluminum alloy raw materials are melted and subjected to rotary degassing refining, so that the hydrogen content of the melt is less than or equal to 0.08 ml / 100 g Al; S2. Ultra-vacuum die casting: a vacuum degree of less than or equal to 30 mbar is established in a die casting cavity, and the aluminum liquid obtained in S1 is injected into a mold under the condition that the injection speed is 4.5-5.5 m / s and the pressurized pressure is 75-85 MPa; S3. In-mold quenching: after die casting, the mold is subjected to point cooling tube forced water cooling in the pressure maintaining stage, so that the casting is cooled from the solidus temperature to below 200 DEG C within 8 seconds; S4. T5 heat treatment: the casting is subjected to aging treatment at 190-210 DEG C for 2.5-3.5 hours, and after the treatment is completed, a high-strength automobile structure is obtained. In the S2, the inner gate speed of the mold is 45-55 m / s.

6. The method of claim 5, wherein the method further comprises: Before the S2, a water-based nano ceramic coating is sprayed on the mold cavity, and the spraying amount of the coating is 30-50 ml / m2.

7. The method of claim 5, wherein the method further comprises: In the S3, the cooling water temperature of the in-mold quenching is 15-25 DEG C, and the water flow speed is 8-12 L / min. ​ 8. The method of claim 5, wherein the method further comprises: After the S4, a post-processing step of laser cleaning and local shape correction is further included. ​ 9. The method of claim 5, wherein the method further comprises: The laser cleaning uses a pulsed fiber laser with a wavelength of 1064 nm to process the gate, overflow tank residues and flash burrs; the local shape correction uses a robot clamping solid-state high-frequency induction heating equipment to locally and instantaneously heat, and after the material becomes soft, a precise correction force (50-300 N) is applied and maintained for a short time (2-10 seconds). ​ 10. The method of claim 9, wherein the method further comprises: ​ ​