High volume fraction aluminum matrix silicon carbide composite sheet and die forging-extrusion combined forming method thereof

Abstract

The application discloses a high-volume-fraction aluminum-based silicon carbide composite sheet and a die forging-extrusion combined forming method, which integrates semi-solid slurry preparation, high-pressure liquid die forging and near-liquidus continuous extrusion processes. The core innovation point is that a hard alloy die with a built-in self-lubricating phase is used to solve the lubrication problem of long-size continuous extrusion; through the "extrusion-replenishment" cycle process, new slurry is replenished when the extrusion amount reaches 2 / 3 of the single injection amount, breaking through the equipment stroke limit, and ultra-long components of more than 5m can be prepared. The process can simultaneously realize material densification, matrix grain refinement and SiC particle axial directional arrangement in one forming. The prepared sheet has a width of more than or equal to 200mm, a thickness of 3-10mm, no internal defects, SiC particles in streamline distribution, a plane thermal conductivity of more than or equal to 175W / (m*K), a tensile strength of more than or equal to 395MPa and an adjustable thermal expansion coefficient. The process is short, efficient and has a long die service life, and is suitable for batch production of large-size heat dissipation backplanes in the fields of 5G communication and high-performance computing.

Description

Technical fields:

[0001] This invention belongs to the field of metal matrix composite material preparation and precision plastic processing technology, specifically relating to a high volume fraction silicon carbide (SiC) particle-reinforced aluminum matrix composite thin plate and its near-net-shape manufacturing method. This method is particularly suitable for preparing heat dissipation backplates and support components for electronic devices requiring high thermal conductivity, low coefficient of thermal expansion, lightweight, and high reliability. Background technology:

[0002] With the rapid development of 5G mobile communication technology, high-performance computing (HPC), artificial intelligence (AI) chips, and high-power power electronic devices, their power density and heat flux density are rising sharply, placing unprecedentedly stringent requirements on the comprehensive performance of thermal management materials. An ideal heat dissipation material must simultaneously possess high thermal conductivity (for rapid heat dissipation), a low coefficient of thermal expansion matching the chip material (to reduce thermal stress), high specific strength / specific stiffness (for lightweight support), and good processability and reliability.

[0003] Aluminum-based silicon carbide (AlSiC) composites are considered ideal candidates for next-generation high-end thermal management materials due to their flexible thermophysical properties (achieved by adjusting the SiC volume fraction), excellent specific stiffness, good fatigue resistance, and relatively low cost. Among these, composites with a silicon carbide volume fraction of approximately 16%-18% exhibit high thermal conductivity (>175 W / (m·K)) and low coefficient of thermal expansion (11-13 × 10⁻⁶). -6 Achieving an optimal balance between / K) to meet the matching requirements of most semiconductor materials (such as silicon and gallium arsenide).

[0004] Currently, the mainstream technologies for preparing AlSiC composite sheets mainly include powder metallurgy and stir casting combined with subsequent plastic deformation methods (such as rolling, forging, and extrusion). However, these traditional methods face a series of bottlenecks in industrial applications: poor formability, making it difficult to prepare thin-walled, large-size parts; the high hardness and high volume fraction of SiC particles severely disrupt the continuity of the aluminum matrix, resulting in extremely high resistance to plastic rheology. Under conventional hot working temperatures, enormous forming forces are required, leading to abnormally severe die wear and a high susceptibility to defects such as cracks. Forming is particularly difficult for sheets with large aspect ratios and ultra-thin cross-sections.

[0005] Controlling microstructural defects is difficult: casting easily introduces porosity, shrinkage, and SiC particle agglomeration and segregation; although powder metallurgy can obtain a uniform microstructure, it is costly, complex, and may contain residual pores in the billet. Subsequent rolling or extrusion can achieve a certain degree of densification and microstructure improvement, but it is often difficult to completely eliminate microstructural defects, and the long process leads to high energy consumption and low yield.

[0006] Risk of harmful interfacial reactions: At processing temperatures above the melting point of aluminum, molten aluminum and SiC particles are prone to interfacial reactions, forming a brittle, needle-like Al4C3 phase. This phase not only reduces the mechanical properties of the material but also affects the long-term reliability of devices due to hygroscopic reactions. Although surface coating of SiC particles (such as SiO2 or Al2O3) can effectively suppress this reaction, how to fully utilize and protect this coating layer in efficient, high-temperature forming processes remains a technical challenge.

[0007] Limitations of a single process: Liquid forging (or extrusion casting) can produce high-density near-net-shape parts, but the solidification structure is relatively coarse and the particle orientation is random, which is not conducive to the isotropic optimization of thermal conductivity and strength; while hot extrusion alone can refine grains and achieve oriented particle arrangement, but it requires high billet density, is difficult to directly form complex cross sections, and is limited by the length of the extrusion cylinder, making it impossible to continuously produce ultra-long components.

[0008] Lubrication challenges in continuous processing: In the continuous extrusion of long components, traditional external lubricants (such as graphite emulsion and boron nitride) are difficult to replenish evenly and in a timely manner, which can easily lead to lubrication failure, resulting in mold damage, deterioration of product surface quality, and dimensional fluctuations.

[0009] Therefore, developing a short-process, high-efficiency, and low-cost composite molding method that can integrate material preparation and molding, achieve high density, fine grains, oriented particle arrangement, and fabricate ultra-long thin-walled parts, and fundamentally solve the problem of continuous extrusion lubrication, is of great significance for promoting the large-scale application of high-performance AlSiC composite materials in the high-end electronics field. Summary of the Invention:

[0010] The purpose of this invention is to overcome the technical defects in existing AlSiC composite material preparation and molding technologies, such as long process, difficult molding, difficulty in preparing long thin parts, uneven microstructure and properties, and difficulty in continuous lubrication, and to provide an integrated, short-process, and highly efficient aluminum-based silicon carbide composite material thin plate and its die forging and extrusion composite molding method.

[0011] To achieve the above objectives, the present invention adopts the following technical solution:

[0012] In a first aspect, the present invention provides a method for die forging and extrusion composite forming of aluminum-based silicon carbide composite sheet, the method comprising the following steps performed sequentially:

[0013] S1. Vacuum / protective atmosphere stirring and semi-solid slurry preparation:

[0014] Under a vacuum or inert gas (such as argon) protective atmosphere, molten aluminum alloy (such as 6061, 6063, 6351, etc.) is heated to a fully molten state (e.g., 660-700℃). Subsequently, preheated (e.g., 300-450℃) and surface-coated (with SiO2, Al2O3, or a composite layer) silicon carbide (SiC) particles are added to the melt in batches. The SiC particles are uniformly dispersed in the molten aluminum using mechanical stirring, electromagnetic stirring, or a combination of both, resulting in a homogeneous liquid aluminum-based composite material. This liquid composite material is then rapidly introduced into a cooling shearing device (such as a spiral shear rheostat, inclined cooling plate, etc.). By precisely controlling the cooling rate and shear strength, a semi-solid slurry with thixotropic properties is prepared. The solid volume fraction of the semi-solid slurry is controlled at 50%-60%, and the temperature range is maintained at 590-640℃. This temperature range ensures that the slurry has good fluidity to facilitate subsequent filling, while also containing enough solid particles to suppress SiC particle sedimentation and agglomeration, and creates conditions for subsequent near-liquidline extrusion.

[0015] S2. Rapid Slurry Transfer and Forging-Extrusion Composite Molding: The semi-solid slurry prepared in S1 is rapidly transferred through an insulated delivery pipe or a metering pump into the cavity of a dedicated high-temperature extrusion die preheated to 380-450℃. The core features of this die are: firstly, a movable carbide plug driven by hydraulic or mechanical means is provided at the die exit end; secondly, the critical forming section (die opening area) of the die is made of self-lubricating carbide material.

[0016] The molding process is divided into two consecutive stages:

[0017] High-pressure liquid forging (densification and preforming) stage: First, the drive block seals the mold outlet. Then, a high pressure of 80-120 MPa is applied to the upper pressure head (or punch), which is transmitted through the pressure head to the semi-solid slurry within the cavity. This high pressure is maintained for 5-15 seconds. The high hydrostatic pressure in this stage forces the slurry to completely fill the cavity corners and causes it to solidify (or partially solidify) under high pressure, resulting in an extremely dense preform free of shrinkage cavities and porosity. Simultaneously, the high-pressure environment strengthens the interfacial bonding between SiC particles and the aluminum matrix.

[0018] Near-liquidline continuous extrusion (deformation and microstructure optimization) stage: After the holding pressure is completed, the outlet plug is quickly removed. At this time, the indenter pressure is maintained or slightly adjusted (e.g., reduced to 70-100 MPa), and the semi-solid / partially solidified material flows under pressure through a self-lubricating forming section with a specific cross-sectional shape (e.g., a flat rectangle), and is extruded into a sheet. During extrusion, the material temperature remains in the near-liquidline range of 590-640℃.

[0019] Continuous pressurized feeding mechanism: To prepare ultra-long sheet materials, this invention designs a unique feeding mode. When the volume of material extruded from the die reaches 2 / 3 of the initial slurry volume injected into the die cavity, as monitored by a displacement sensor or flow meter, the control system automatically executes the following cycle: a) stop extrusion; b) raise the pressure head to a certain height (e.g., 30-80mm) to make room for feeding; c) under vacuum or a protective atmosphere, rapidly replenish the die cavity with an equal amount of semi-solid slurry identical to the preparation parameters of S1 (the feeding time is strictly controlled within 3-5 seconds to prevent excessive drop in slurry temperature); d) lower the pressure head, reapply extrusion pressure, and continue the extrusion process. This "extrusion-monitoring-stop feeding-continue extrusion" cycle is repeated until a continuous extruded part of the target length is obtained. This "2 / 3 volume" trigger point design ensures that sufficient material is always retained in the die cavity as a "headstock," preventing air entrapment and pressure interruption, and achieving continuity and stability in the extrusion process.

[0020] S3. Follow-up processing:

[0021] The elongated sheet material continuously extruded from the die is immediately subjected to online quenching (e.g., high-pressure air mist cooling, cooling rate ≥50℃ / s) to fix the fine-grained structure formed by extrusion and create conditions for subsequent age hardening. After quenching, the sheet material is tension-wound to eliminate residual stress and ensure the flatness of the sheet. Finally, it undergoes age heat treatment (e.g., T6 treatment: holding at 170-180℃ for 8-12 hours) to fully precipitation strengthen the aluminum alloy matrix, thereby obtaining the final high-performance composite material sheet.

[0022] Preferably, the silicon carbide particles have an average particle size of 5-15 micrometers and a volume fraction of 16%-18%.

[0023] Preferably, the forming section of the self-lubricating cemented carbide mold is prepared by uniformly adding 3%-8% (by mass) of a solid self-lubricating phase to a high wear-resistant cemented carbide matrix (such as YG) using a powder metallurgy method. The self-lubricating phase is selected from one or more of molybdenum disulfide (MoS2), tungsten disulfide (WS2), or graphite. These self-lubricating phases can continuously release and form an effective solid lubricating film at extrusion working temperatures of 380-450℃, achieving self-lubrication without requiring additional machine stoppages for lubricant application.

[0024] Preferably, in step S2, only before the initial injection of slurry into the mold cavity for liquid forging, a very small amount of water-based graphite release agent may be sprayed onto the cavity surface to assist in initial demolding. In all subsequent continuous feeding extrusion processes, lubrication is achieved entirely through the self-lubricating function of the mold itself, without the application of any external lubricant.

[0025] Preferably, the extrusion ratio (the ratio of the cross-sectional area of ​​the die cavity to the cross-sectional area of ​​the extruded sheet) in step S2 is 8:1 to 15:1, which can be designed according to different requirements for the microstructure and properties of the sheet.

[0026] Preferably, the aging heat treatment regime in step S3 is optimized according to the selected aluminum alloy grade. For example, for 6061 aluminum alloy, 175℃×10h can be used.

[0027] Secondly, the present invention provides a high volume fraction aluminum-based silicon carbide composite material thin plate prepared by the above method. The thin plate is characterized in that:

[0028] Composition and structure: The volume fraction of silicon carbide particles is 16%-18%, uniformly dispersed in the aluminum alloy matrix. The sheet is free of defects such as pores and shrinkage porosity on a macroscopic scale.

[0029] Microstructure: Under the action of extrusion shear force, SiC particles exhibit a distinct directional streamlined arrangement along the extrusion direction (i.e., the length direction of the sheet). The aluminum alloy matrix grains are significantly refined.

[0030] Size specifications: The width of the sheet is ≥200mm, and the thickness is 3-10mm (typically 6mm). Its length can be flexibly adjusted by the number of continuous feeding cycles. Theoretically, it is only limited by equipment and space, and can achieve continuous preparation of 5 meters, 10 meters or even longer.

[0031] Overall Performance: Benefiting from the high density, fine-grained matrix, and oriented SiC particles, this sheet exhibits excellent thermal conductivity (≥175 W / (m·K)) and high tensile strength (≥395 MPa) in a plane parallel to the extrusion direction. It also possesses a low coefficient of thermal expansion (typically 11-13 × 10⁻⁶) that is well-matched to semiconductor chips. -6 / K).

[0032] Beneficial effects: Compared with the prior art, the present invention has the following outstanding advantages:

[0033] The revolutionary shortened process flow results in significant efficiency and cost advantages: integrating multiple traditional independent processes such as "melting and compounding - semi-solid preparation - densification molding - plastic deformation - microstructure optimization" into a single continuous process unit, achieving near-net-shape forming in a "one-step" process. This significantly reduces production steps, equipment investment, energy consumption, and material turnover, improving production efficiency and material utilization while lowering overall costs.

[0034] Synergistic optimization and enhancement of microstructure and performance: "Pre-high pressure die forging" ensures that the material is formed at near-theoretical density, completely eliminating casting defects and establishing a strong and tough particle / matrix interface; "Post-near-liquidline extrusion" introduces intense shear deformation, which not only significantly refines the aluminum matrix grains but also causes high-volume-fraction SiC particles to be highly oriented along the extrusion direction. This unique "dense + fine-grained + oriented" composite microstructure enables the material to simultaneously achieve excellent thermal conductivity (oriented arrangement facilitates heat flow conduction), high mechanical strength (fine-grained strengthening and interface strengthening), and controllable thermal expansion anisotropy, perfectly meeting the application requirements of high-end heat dissipation backplates.

[0035] Overcoming the core lubrication challenges of continuous extrusion to ensure stable production and extended die life: A specially designed self-lubricating carbide die is employed. Its built-in self-lubricating phase stably and continuously supplies lubricating components to the friction interface at extrusion temperatures, forming an effective solid lubricating film. This design fundamentally solves the technical bottleneck of uneven lubricant application and difficulty in timely replenishment in traditional long-distance continuous extrusion, making ultra-long-distance continuous extrusion possible. Simultaneously, it significantly reduces frictional resistance and die wear during extrusion, extending die life (up to five times that of traditional dies) and ensuring a smooth surface and dimensional stability of the extruded sheet.

[0036] Breaking through equipment limitations, this technology enables the flexible fabrication of ultra-long components: The innovative "2 / 3 volume trigger, continuous pressure feeding" mechanism is like adding an "unlimited refill" function to the extrusion process. It cleverly bypasses the fundamental constraint of traditional extruders being limited by the length of the extrusion cylinder, allowing for the continuous fabrication of sheets of any target length through multiple feedings. This provides an efficient solution to meet the demand for long-sized heat dissipation components in the large-scale and integrated development of electronic products, offering extremely high production flexibility.

[0037] The process temperature window is perfectly compatible with particle coating technology: the entire composite molding process is carried out in the near-liquidline temperature range of 590-640℃, which is lower than the conventional pure liquid processing temperature but higher than the traditional hot extrusion temperature. This temperature window ensures that the material has good molding fluidity while effectively reducing the risk of thermal shock and damage to the protective layer (such as SiO2) on the surface of SiC particles. This allows the advantages of particle coating technology in suppressing interfacial reactions to be fully utilized, resulting in a cleaner and more stable interface and improving the long-term reliability of the material. Attached image description:

[0038] Figure 1 This is a process flow diagram of the forging-extrusion composite forming method described in this invention.

[0039] Figure 2This is a schematic diagram of the structure of the composite molding die used in this invention (where 2a is the state of liquid forging with the block closed; 2b is the state of extrusion with the block open).

[0040] Figure 2 In section a: 1-Pressure head; 2-Extrusion barrel; 3-Heating element; 4-Semi-solid slurry; 5-Self-lubricating carbide forming section of extrusion die; 6-Movable block.

[0041] Figure 2 In b: 1-Pressure head 2-Extrusion barrel 3-Heating element 4-Semi-solid slurry 5-Self-lubricating carbide forming section of extrusion die 6-All-solid composite material slab.

[0042] Figure 3 This is a schematic diagram showing the timing and state of the continuous pressurization and feeding step of the present invention, wherein... Figure 3 a) is the stage of stopping the machine, raising the pressure head, and replenishing the new slurry. Figure 3 b represents the continued extrusion process after material replenishment.

[0043] Figure 3 a. 7 - Pouring spoon. Detailed implementation method:

[0044] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described in detail below through six specific embodiments. However, the scope of protection of this invention is not limited to the following embodiments.

[0045] Example 1 This example describes the fabrication of a large-size heat dissipation backplate for a 5G macro base station power amplifier unit.

[0046] Raw materials: The matrix is ​​6061 aluminum alloy; the reinforcement is α-SiC particles with an average particle size of 8μm and a target volume fraction of 17.5%. The SiC particles are pre-coated with an amorphous SiO2 layer of about 50nm thickness on their surface by the sol-gel method.

[0047] Semi-solid slurry preparation: 6061 aluminum alloy was melted and superheated to 680°C in an argon-protected mechanically stirred melting furnace. Preheated SiC-coated particles (preheated to 400°C) were added in batches, and the melt temperature was controlled at 650°C. The mixture was vigorously stirred at 600 rpm for 20 minutes to ensure thorough wetting and uniform dispersion of the particles. Subsequently, the homogeneous composite melt was introduced into a twin-helix shear rheostat, and cooling and shear parameters were precisely controlled to obtain a homogeneous semi-solid slurry with a temperature of 620°C and a solid content of approximately 55% at the rheostat outlet.

[0048] Forging-Extrusion Composite Molding:

[0049] Mold: Used as Figure 2The mold shown is a specialized mold. The mold cavity dimensions are designed to be 250mm (width) × 80mm (thickness) × 300mm (length). The forming section (mold opening) is made of a special self-lubricating cemented carbide (composition: cemented carbide matrix + 5wt.% MoS2). The exit dimensions are designed to be 222mm × 6.3mm (width × thickness), taking into account material cooling shrinkage. The entire mold is preheated to 400℃.

[0050] First forging: Close the hydraulically driven carbide plug. Inject a semi-solid slurry at 620°C into the die cavity within 5 seconds using a metering pump. Immediately activate the main pressure cylinder, apply a pressure of 100MPa, and hold the pressure for 10 seconds to complete high-pressure densification.

[0051] Continuous extrusion and feeding: After the pressure holding period, the blockage retracts rapidly within 0.5 seconds. The main cylinder pressure is maintained at 95 MPa, and the material begins to be extruded from the die, with an exit speed of approximately 30 mm / s and an actual extrusion ratio of approximately 12.7:1. When the displacement sensor detects that the extruded sheet length reaches 800 mm (the volume of extruded material corresponding to this length is exactly 2 / 3 of the initial slurry volume injected into the die cavity), the control system automatically executes: a) stopping the main cylinder; b) raising the pressure head by 50 mm; c) injecting the same amount (same temperature, same composition) of semi-solid slurry into the die cavity through the rapid feeding valve under an argon atmosphere (takes 4 seconds); d) lowering the pressure head and re-establishing the 95 MPa pressure to continue extrusion. This feeding-extrusion cycle is repeated 3 times.

[0052] Subsequent processing: The extruded continuous sheet immediately enters a high-pressure air mist quenching chamber (air pressure 0.6MPa, water mist flow rate 2L / min), with a measured cooling rate of approximately 65℃ / s. After cooling to room temperature, tension straightening is performed. Finally, standard T6 heat treatment is carried out: aging at 175℃ for 10 hours.

[0053] Results: A thin AlSiC composite sheet with dimensions of 220 mm (width) × 6.0 mm (thickness) × 3200 mm (length) was obtained, exhibiting a smooth surface and excellent flatness. Performance tests showed that the thermal conductivity in the planar direction (parallel to the sheet surface and perpendicular to the extrusion direction) was 185 W / (m·K); the coefficient of thermal expansion (20-100℃) was 11.5 × 10⁻⁶. -6 / K; room temperature tensile strength is 410MPa. Metallographic and SEM analyses show that the SiC particles are uniformly distributed, exhibiting a distinct banded streamline distribution along the extrusion direction; the matrix is ​​dense with no visible pores; the interface is clear, and no needle-like Al4C3 harmful phases were found. After continuous operation, the surface of the self-lubricating forming section of the mold only shows a slight shine, and the wear is negligible.

[0054] Example 2 This example mainly examines the influence of molding temperature on the process and performance.

[0055] The preparation and molding temperature of the semi-solid slurry were adjusted to 600℃ (at which point the solid fraction increased to approximately 60%). The forging pressure was correspondingly increased to 110MPa, and held for 12 seconds to compensate for the decrease in fluidity. During continuous extrusion, the exit speed was adjusted to 25mm / s to maintain stable flow.

[0056] Results: The molding process was smooth and no jamming occurred. Properties of the obtained sheet: thermal conductivity 180 W / (m·K), coefficient of thermal expansion 11.8 × 10⁻⁶. -6 / K, tensile strength 425MPa. Analysis shows that the matrix grains are finer at lower temperatures, resulting in increased strength; however, the particle orientation and thermal conductivity are slightly inferior to Example 1, leading to a slight decrease in thermal conductivity. Mold wear is further reduced by approximately 15% compared to Example 1.

[0057] Example 3 This example investigates the effect of liquid forging pressure on the performance of the product.

[0058] The liquid forging pressure was adjusted to 85 MPa and held for 8 seconds. For simplicity, only two consecutive material replenishments were performed, resulting in a final sheet length of 2400 mm. All other parameters were the same as in Example 1.

[0059] Results: The properties of the obtained sheet material are: thermal conductivity 182 W / (m·K), coefficient of thermal expansion 11.7 × 10⁻⁶. -6 / K, tensile strength 398MPa. Compared with Example 1, the reduced forging pressure resulted in a slight decrease in densification and interfacial bonding, leading to a minor decline in mechanical properties, but with little impact on thermal conductivity. The sheet exhibited good performance uniformity from start to finish, with a deviation ≤3%.

[0060] Example 4 This example studies the effect of a higher extrusion ratio.

[0061] The exit dimensions of the forming section of the mold were modified to 222mm × 4.5mm, increasing the extrusion ratio to approximately 17.8:1. Maintaining the initial mold cavity volume and feed volume unchanged, a sheet with a thickness of 4.5mm and a length of 3200mm was ultimately obtained.

[0062] Results: A higher extrusion ratio resulted in stronger shear deformation. The sheet properties were as follows: longitudinal (extrusion direction) tensile strength significantly increased to 435 MPa; planar thermal conductivity also increased to 190 W / (m·K), attributed to a more significant particle orientation effect optimizing the heat conduction path. The sheet surface roughness Ra ≤ 0.8 μm, indicating excellent quality.

[0063] Example 5 This example verifies the applicability of different coating layers and self-lubricating phases.

[0064] SiC particles were coated with Al2O3 (approximately 80 μm thick). The die forming section used a cemented carbide with 6 wt.% WS2 self-lubricating phase. The forming process parameters were the same as in Example 1, with four consecutive feeding cycles to obtain a sheet with a length of 4000 mm. Results: Sheet properties: thermal conductivity 188 W / (m·K), coefficient of thermal expansion 11.6 × 10⁻⁶. -6 / K, tensile strength 405MPa. The Al2O3 coating layer also effectively isolates the aluminum-carbon reaction. The WS2 self-lubricating phase exhibits more stable lubrication performance at high temperatures, and the die wear is reduced by about 20% compared with the MoS2 die in Example 1, and the pressure curve of the continuous extrusion process is more stable.

[0065] Example 6 This example demonstrates the application of different aluminum alloy substrates. 6351 aluminum alloy is used as the substrate.

[0066] The process was adjusted accordingly: the semi-solid slurry preparation temperature was set to 615℃, and the die forging extrusion temperature was set to 610℃. The die forming section used cemented carbide with 4 wt.% graphite self-lubricating phase. The die forging pressure was 105 MPa, and the holding time was 10 seconds. Three consecutive feeding cycles were performed to obtain a sheet material with a length of 3200 mm.

[0067] Results: Benefiting from the higher strength potential of 6351 aluminum alloy, the composite material achieved a tensile strength of 445 MPa. The thermal conductivity was 175 W / (m·K), and the coefficient of thermal expansion was 11.4 × 10⁻⁶. -6 / K. The graphite self-lubricating phase forms a continuous and stable lubricating film on the mold surface, resulting in a smooth and quiet extrusion process.

[0068] Comparative Example: A comparative sample was prepared using a traditional powder metallurgy hot extrusion process. Powders of the same composition (6061Al + 17.5 vol.% SiC) were mixed, cold isostatically pressed, and vacuum sintered to prepare billets. The billets were heated to 480°C and hot-extruded in a standard cemented carbide die (extrusion ratio approximately 12:1). During the extrusion process, boron nitride lubricant was applied intermittently by hand. The final product was a short plate measuring 220 mm × 6 mm × 800 mm, which was then subjected to the same T6 heat treatment.

[0069] Results: The extrusion process was exceptionally difficult, resulting in high equipment load and periodic scratches on the sheet surface. The die experienced severe wear, with the wear after a single extrusion being approximately five times that of the die in Example 1 after continuous production. Performance tests: Thermal conductivity 170 W / (mK), tensile strength 380 MPa. Microstructural analysis revealed locally incompletely closed micropores and slight particle agglomeration.

[0070] Conclusion: The above embodiments fully demonstrate that the aluminum-based silicon carbide composite sheet and its die forging and extrusion composite molding method provided by this invention can stably and efficiently produce large-size, thin-walled, ultra-long, and high-performance AlSiC composite sheet materials. This method innovatively solves two major industry challenges: continuous extrusion lubrication and long part preparation. It significantly surpasses traditional processes in terms of product density, microstructure, thermal conductivity, mechanical strength, and production economy, providing a practical and advanced technical solution for the large-scale, low-cost, and high-quality manufacturing of heat dissipation backplates for high-end electronic devices.

Claims

1. A method for die forging and extrusion composite forming of a high volume fraction aluminum-based silicon carbide composite sheet, characterized in that, Includes the following steps: S1. Semi-solid slurry preparation: Under a protective atmosphere, molten aluminum alloy is uniformly mixed with surface-coated silicon carbide (SiC) particles to obtain a liquid composite material; subsequently, the liquid composite material is cooled and sheared to prepare a semi-solid slurry with a solid volume fraction of 50%-60% and a temperature of 590-640℃; S2. Die forging-extrusion composite molding and continuous feeding: The semi-solid slurry obtained in S1 is transferred to an extrusion die cavity preheated to 380-450℃. The die has an openable and closable plug at the outlet end, and the forming section of the die is made of self-lubricating hard alloy; first, the plug is closed, and the cavity is... The slurry is subjected to a pressure of 80-120 MPa for liquid forging, and the pressure is held for 5-15 seconds; then the block is opened, and the material is extruded from the self-lubricating forming section under a pressure of 70-100 MPa; when the volume of the extruded material reaches 2 / 3 of the slurry volume injected into the mold cavity in a single operation, a feeding cycle is executed: stop extrusion and raise the pressure head → replenish the cavity with an equal amount of semi-solid slurry consistent with the preparation parameters in S1 → lower the pressure head and restore the extrusion pressure to continue extrusion; repeat the feeding cycle until the extruded sheet of the target length is obtained; S3. Post-processing: the extruded sheet is subjected to online quenching, straightening and aging heat treatment.

2. The method according to claim 1, characterized in that: The silicon carbide particles have an average particle size of 5-15 micrometers and a volume fraction of 16%-18%, and their surface coating is SiO2, Al2O3 or a composite layer thereof.

3. The method according to claim 1, characterized in that: The aluminum alloy is 6061, 6063, or 6351 aluminum alloy; the cooling and shearing treatment is achieved by a spiral shear rheostat or an inclined cooling plate.

4. The method according to claim 1, characterized in that: The forming section of the self-lubricating cemented carbide mold has a self-lubricating phase with a mass fraction of 3%-8% uniformly dispersed in the cemented carbide matrix. The self-lubricating phase is selected from one or more of MoS2, WS2, and graphite.

5. The method according to claim 1 or 4, characterized in that: Throughout the continuous feeding extrusion process in step S2, no external lubricant is applied; lubrication is achieved solely through the self-lubricating function of the self-lubricating carbide mold.

6. The method according to claim 1, characterized in that: In step S2, the extrusion ratio for extrusion molding is 8:1 to 15:1; in the replenishment cycle, the replenishment of slurry is completed within 3-5 seconds.

7. The method according to claim 1, characterized in that: In step S3, the online quenching is performed using high-pressure gas mist cooling with a cooling rate of not less than 50°C / second; the aging heat treatment is performed by holding at 170-180°C for 8-12 hours.

8. A high volume fraction aluminum-based silicon carbide composite material thin plate prepared by the method according to any one of claims 1 to 7, characterized in that: The thin plate has a silicon carbide volume fraction of 16%-18%, a width of ≥200mm, a thickness of 3-10mm, and a length of not less than 3 meters; the thin plate has no macroscopic pores inside, and the silicon carbide particles are oriented along the extrusion direction.

9. The aluminum-based silicon carbide composite material thin plate according to claim 8, characterized in that: Its planar thermal conductivity is ≥175W / (m·K), and its room temperature tensile strength is ≥395MPa.

10. A heat dissipation backplate for electronic devices, characterized in that: It is made of aluminum-based silicon carbide composite sheet as described in claim 8 or 9.

Images