Light high-strength bicycle frame pipe and preparation method thereof

Abstract

The invention relates to the technical field of material preparation and processing, discloses a light high-strength bicycle frame pipe and a preparation method thereof and a preparation method of the light high-strength bicycle frame pipe, and aims at solving the problems that an existing aluminum alloy pipe is poor in strength and fatigue toughness, insufficient in mechanical uniformity and limited in minimum wall thickness, and the performance stability of a composite material is poor. The pipe and the preparation method thereof are characterized in that the chemical components of the pipe comprise silicon, magnesium, copper, manganese, iron, rare earth (lanthanum / cerium), strontium and aluminum according to a specific proportion, and the content ratio of the silicon to the magnesium to the iron to the manganese is controlled; the preparation method comprises the steps of smelting, casting, hot extrusion, T6 heat treatment and the like. According to the scheme, high strength, high plasticity and excellent fatigue welding performance are achieved, the minimum wall thickness can reach 0.5 mm, and the requirement for extreme light weight is met.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field of material preparation and processing, and specifically relates to a lightweight high-strength bicycle frame pipe and a preparation method thereof. BACKGROUND

[0002] With the increasing popularity of the concept of green travel and the popularization of a healthy lifestyle, the research and application of lightweight transportation tools have become an important trend in today's society. Under this background, as an efficient and environmentally friendly transportation and sports tool, the performance improvement of bicycles, especially the lightweight and high-strength of frame materials, is increasingly attracting widespread attention from the industry and consumers. As a core structural component that bears the weight of the rider, transmits driving force and withstands complex stress, the selection and preparation process of the material of the bicycle frame directly determines the riding experience, safety performance and service life of the whole vehicle. Therefore, the exploration and innovation of high-performance frame pipes have always been the focus of research in this field.

[0003] In the prior art, traditional bicycle frame pipes have long been mainly based on aluminum alloy materials. Specifically, 6061, 6069, 6066 and other series of aluminum alloys with silicon, magnesium and copper as the main alloying elements are widely used in the manufacture of bicycle frames due to their relatively excellent specific strength and good processing performance. This type of aluminum alloy can meet the basic needs of lightweight and strength of bicycles to some extent through hot extrusion forming and subsequent T6 heat treatment. The design principle is to reduce the weight of the frame by taking advantage of the low density characteristics of aluminum alloy, and to achieve material strengthening through alloying and heat treatment. However, although these aluminum alloys effectively solved the problem of lightweight bicycle frames in a certain historical period, their inherent technical limitations have become increasingly apparent. For example, when pursuing higher strength, the inherent low strength problem of traditional aluminum alloy frame pipes is difficult to overcome; at the same time, during the hot extrusion and subsequent heat treatment process, micro defects such as coarse grain rings and heterogeneous structures are prone to occur. These organizational defects not only affect the appearance of the material, but more fundamentally, they significantly reduce the fatigue performance and fracture toughness of the material as stress concentration sources, resulting in poor uniformity of the mechanical properties of the material, which in turn brings potential risks of fracture during riding, especially under high-frequency vibration and dynamic impact loads, the reliability and safety face serious challenges. To ensure structural integrity, the minimum wall thickness of such aluminum alloy pipes usually needs to be maintained at 0.8mm or more to ensure that the welded frame can pass the strict bench test, which undoubtedly limits the further development space in the field of extreme lightweight.

[0004] To break through the performance bottleneck of traditional metal materials, composite materials have been gradually introduced into the transportation field due to their high specific strength, high specific modulus, and designability, and have shown great application potential in the fields of aerospace and automobiles. In the field of bicycle frames, the application of composite materials is also expected to achieve more extreme lightweight, higher strength and modulus, and better uniformity. However, existing composite structural parts still have many deficiencies in preparation process and performance optimization, which seriously restrict their widespread popularity in the field of bicycle frames. Taking the manufacturing method of a snowmobile curved thin-walled composite structural part with publication number CN114619684B as an example, although the fiber-reinforced resin-based composite material is used to prepare a lightweight, high-strength, and customizable snowmobile curved structure, the technical solution mainly focuses on the forming process of the snowmobile curved structure, and the design and manufacturing process focuses more on the adaptability of the curved shape and the customization of the overall structure. This reveals a deep and non-obvious contradiction: although composite materials have excellent intrinsic properties, existing technologies face limitations at the principle level when effectively converting these properties into structural parts that meet the specific needs of bicycle frames. Specifically, the design focus of the snowmobile curved structure is on the coverage area and overall impact resistance, while bicycle frame tubes require high bending stiffness, torsional stiffness, and axial fatigue performance, especially under the premise of high modulus and extremely small wall thickness. To achieve these goals, the fiber arrangement, resin infiltration, and stress distribution after curing of the tube must achieve near-perfect uniformity and stability.

[0005] On this basis, the curing forming method adopted by the existing composite material technology, especially for complex geometric shapes and thin-walled pipes, often has difficulty in accurately controlling the micro stress distribution inside the material. This uneven internal stress distribution problem is not just a small flaw in manufacturing precision, it fundamentally affects the mechanical property stability of the final product, especially under the high-frequency vibration and dynamic load working conditions of the bicycle frame pipe, the material's fatigue resistance will face significant deficiencies. The reason is that the pipe is continuously subjected to bending, twisting and compression and other combined stresses during cycling, any micro-level unevenness can accumulate and evolve into macro cracks under long-term cyclic loading, resulting in structural failure. This "trade-off" between performance and convenience in forming certain macro shapes (such as snow car curves) may sacrifice the mechanical property uniformity and stability that is crucial in more precise and more complex pipe structures, making it difficult for existing composite material solutions to effectively meet the comprehensive needs of high modulus, extremely small wall thickness, and excellent fatigue performance of bicycle frames. Therefore, while improving the intrinsic properties of the material, the existing technology has not been able to provide a composite material preparation strategy that is universally applicable, process controllable, and effectively solves the problem of mechanical property stability and uniformity under the specific working conditions of bicycle frames.

[0006] The above problems show that both traditional aluminum alloy frame pipes and existing composite material structural components applied in other transportation fields have deep technical contradictions in preparation process, mechanical property stability, high modulus demand adaptability, and optimization design for special working conditions of bicycle frames. The core of this contradiction is that current technology cannot achieve extreme lightweight (i.e. extremely small wall thickness) while fully considering and significantly improving the inherent strength, fatigue resistance, and microstructure uniformity of the material to meet the growing demands of modern high-performance bicycle frames. SUMMARY

[0007] To achieve the above invention purpose, the present application provides a lightweight high-strength bicycle frame pipe and its preparation method, aiming to solve the problems of low strength, easy occurrence of coarse grain ring and heterogeneous structure, poor fatigue performance and fracture toughness, insufficient mechanical property uniformity, and limited minimum wall thickness of traditional aluminum alloy frame pipes in existing technology, while overcoming the deep contradictions of existing composite materials in terms of micro stress distribution difficulty in accurate control, insufficient mechanical property stability and uniformity when applied to thin-walled pipes, thereby providing a pipe solution for high-performance bicycles with extreme lightweight, excellent strength, high modulus, excellent fatigue performance, and good welding performance.

[0008] To achieve the above-mentioned object, the present application provides a light-weight and high-strength bicycle frame tube. The chemical composition of the tube contains, in percentage by mass, 2.5% to 3.5% of silicon, 0.5% to 0.7% of magnesium, 0.2% to 0.4% of copper, 0.15% to 0.30% of manganese, 0.12% to 0.20% of iron, 0.01% to 0.05% of rare earth elements (lanthanum or cerium), 0.004% to 0.008% of strontium, and the balance of aluminum and unavoidable impurities. The total amount of the unavoidable impurities is less than or equal to 0.10%. The present application precisely controls the content of alloying elements and their mutual ratio, optimizes the microstructure of the material and the strengthening mechanism, so as to achieve the comprehensive performance indicators required by the high-performance frame tube.

[0009] As a preferred embodiment of the present application, the chemical composition of the light-weight and high-strength bicycle frame tube has a specific element content ratio. Specifically, the ratio of the content of silicon to the content of magnesium is 4 to 8. This ratio range aims to precisely control the formation and distribution of Mg2Si strengthening phase in the aluminum alloy matrix, and inhibit the generation of coarse silicon phase, so as to ensure sufficient precipitation strengthening effect while avoiding the decrease in plasticity and the appearance of brittle phase caused by excessive silicon content. At the same time, the ratio of the content of iron to the content of manganese is 1.25 to 2.5. This ratio range aims to optimize the synergistic effect of iron and manganese elements in the alloy, so as to form fine and dispersed Al-Fe-Mn-Si type compounds instead of harmful coarse needle-shaped or flaky iron-rich phases. These fine and dispersed compounds act as heterogeneous nucleation sites, which help to refine the grains and effectively pin the grain boundaries, thereby inhibiting recrystallization and improving the strength, toughness and uniformity of the material.

[0010] As a preferred embodiment of the present application, the rare earth element is one or both of lanthanum or cerium. The addition amount of the lanthanum or cerium is 0.01% to 0.05%. The rare earth element lanthanum or cerium plays a significant role in refining the α-Al phase during the solidification of the aluminum alloy, and inhibits grain growth by segregating at the grain boundaries. In addition, the rare earth element can also combine with impurity elements (such as iron) in the alloy to form stable rare earth compounds, thereby reducing the formation of harmful coarse iron phases, purifying the matrix, and further improving the strength and plasticity of the material. The addition amount of strontium is 0.004% to 0.008%. Strontium acts as an important modifier in aluminum-silicon alloys, which changes the growth pattern of eutectic silicon, and promotes the transformation of eutectic silicon from coarse flaky or needle-shaped structure to fine and round fibrous or granular structure. This non-equilibrium solidification eutectic silicon modification treatment significantly improves the plasticity, toughness and fatigue performance of the alloy, and effectively reduces the stress concentration effect caused by the sharp edges of the silicon phase.

[0011] As a preferred embodiment of the present application, the lightweight high-strength bicycle frame tube has a tensile strength of 500 MPa or more, a yield strength of 320 MPa or more, and an elongation of 10% or more at room temperature after hot extrusion and T6 treatment. The realization of the above mechanical properties indicates that the present application maintains excellent plasticity while ensuring high strength, thereby significantly improving the reliability and safety of the tube under complex stress conditions and effectively solving the contradiction between strength and plasticity of existing aluminum alloy frame tubes. In addition, the product of the tensile strength and the elongation (the product of the tensile strength and the elongation) of the tube is greater than 5 GPa·%. This value is better than the product of the tensile strength and the elongation of traditional 6061 aluminum alloy, reflecting the significant improvement in the balance between strength and plasticity of the alloy, which is crucial for bicycle frame tubes that need to withstand high-frequency vibrations and dynamic impact loads.

[0012] As a preferred embodiment of the present application, the minimum wall thickness of the lightweight high-strength bicycle frame tube can reach 0.5 mm after hot extrusion. The realization of this technical index enables the bicycle frame to achieve more extreme lightweight while ensuring structural integrity and safety. The frame made of the alloy tube of the present application has a significantly lower weight than the frame made of traditional aluminum alloy (such as 6061 aluminum alloy), and after welding and forming, it can successfully pass strict bench tests, ensuring its long-term reliability in service.

[0013] The present application also provides a method for preparing a lightweight high-strength aluminum alloy tube for bicycle frames. This method precisely controls key process parameters such as alloy melting, casting, hot extrusion, cold deformation, and heat treatment to ensure the obtainment of the high-performance tube. The preparation method comprises the following steps: Step S1: Preparation of aluminum alloy liquid.

[0014] This step uses high-purity electrolytic aluminum liquid or pure aluminum ingot as the base material. The purity of the electrolytic aluminum liquid or pure aluminum ingot should be 99.7% or more. The base material is heated to a temperature range of 750-800°C to ensure that the aluminum is fully melted and has good fluidity. The following alloying elements are precisely added per 1000 kg of aluminum liquid: Crystalline silicon: the addition amount is 25-35 kg. The purity of the crystalline silicon should be 99.5% or more. The addition of silicon is aimed at forming Mg2Si strengthening phase and cooperating with other elements to control the fluidity and solidification characteristics of the alloy.

[0015] High-carbon ferromanganese alloy: the addition amount is 3-5 kg. The manganese content of the high-carbon ferromanganese alloy is 65-75%. The addition of manganese is aimed at forming Al-Fe-Mn-Si type compounds with iron, refining grains, and inhibiting the formation of harmful coarse iron-rich phases.

[0016] Magnesium ingot: 5.5 kg to 7.5 kg of addition. The purity of the magnesium ingot should reach or exceed 99.8%. The addition of magnesium element is mainly used to form Mg2Si strengthening phase, providing precipitation strengthening effect.

[0017] Copper plate: 2 kg to 4 kg of addition. The purity of the copper plate should reach or exceed 99.9%. The addition of copper element aims to enhance the solid solution strengthening and precipitation strengthening effect, and improve the mechanical properties of the alloy.

[0018] All alloying elements are slowly added to the aluminum liquid under stirring conditions to ensure their complete dissolution and uniform distribution. After the addition of all alloying elements is completed, the melt temperature is maintained and stirring is continued until all additives are completely dissolved, obtaining the aluminum alloy liquid according to the present application.

[0019] Step S2: Refining and degassing.

[0020] After the preparation of the aluminum alloy liquid is completed, it is subjected to refining and degassing treatment to remove hydrogen and non-metallic inclusions in the melt, ensuring the compactness and uniformity of the cast rod. This step is carried out at a precisely controlled temperature. Specifically, for every 1000 kg of the alloy liquid of the present application, sodium-free refining agent is added for floating method refining and degassing. The components of the sodium-free refining agent are usually potassium chloride, sodium chloride and fluoride composite salt, without sodium element harmful to the environment. The addition amount of the refining agent is related to the surface area and contamination level of the aluminum liquid, and is usually 0.1% to 0.3% of the mass of the aluminum liquid. The floating method refining is carried out by injecting the refining agent or inert gas (such as high-purity argon or nitrogen) through a porous plug or a rotating nozzle into the bottom of the melt, so that the refining agent particles or gas bubbles combine with hydrogen and non-metallic inclusions during the rising process and are carried out to the surface of the melt to form dross. The process lasts for 10 to 20 minutes, and the melt temperature is maintained at 720°C to 760°C. After the refining and degassing are completed, the content of inclusions in the melt is evaluated by K-mode inspection, which is required to reach level 1, and the gas content in the melt is determined by reduced pressure solidification method, which is required to be less than or equal to 0.05 ml / 100 g. The above refining and degassing operation ensures the purity of the alloy cast rod, laying a foundation for the subsequent preparation of high-performance pipe.

[0021] Step S3: Modification and cast rod.

[0022] After the completion of the refining and degassing, the temperature of the alloy melt is precisely adjusted to the range of 710°C to 750°C. At this temperature, a modification treatment is carried out to further optimize the microstructure of the alloy. Specifically, 0.5 kg to 1.5 kg of aluminum foil-coated lanthanum-cerium alloy and 0.4 kg to 0.6 kg of aluminum-10 strontium master alloy are added per 1000 kg of aluminum alloy melt. The content of rare earth elements (lanthanum or cerium) in the aluminum foil-coated lanthanum-cerium alloy is 10% to 20%. The purpose of using aluminum foil coating is to prevent the oxidation of rare earth elements with oxygen in the air during the addition process, thereby increasing the yield of rare earth elements and ensuring their more uniform dispersion in the melt. The strontium content of the aluminum-10 strontium master alloy is 10%. Both master alloys are added under stirring conditions and ensure sufficient dissolution and uniform dispersion in the alloy melt. The stirring time is usually 5 minutes to 10 minutes.

[0023] After the completion of the modification treatment, continuous casting of the ingot is immediately carried out. The continuous casting process uses vertical or horizontal casting equipment to obtain an ingot with uniform structure, fine grains, and no macrosegregation by precisely controlling the casting speed, cooling rate, and mold design. The casting speed is adjusted according to the diameter of the ingot and the type of alloy, usually 50 mm / min to 150 mm / min. The cooling rate is precisely controlled by the water cooling system to ensure the formation of fine equiaxed crystals during rapid cooling and to inhibit the formation of coarse eutectic phases. The diameter of the ingot is usually determined according to the size requirements of the subsequent extrusion equipment. The continuous casting process aims to minimize casting defects such as shrinkage, porosity, and coarse grains, etc., to provide high-quality raw materials for the subsequent hot extrusion process.

[0024] Step S4: homogenization treatment, hot extrusion, and cold deformation.

[0025] After the completion of the ingot, the homogenization treatment is first carried out. The homogenization treatment aims to eliminate the chemical composition inhomogeneity produced during the solidification of the ingot, especially dendritic segregation, and to dissolve the soluble phase into the aluminum matrix. The ingot is heated to a homogenization temperature of 480°C to 520°C and held for 8 hours to 12 hours. After the holding period ends, it is cooled to room temperature at a controlled rate to avoid the formation of new segregation or the premature precipitation of coarse phases.

[0026] The homogenized bar stock is then hot-extruded. The homogenized bar stock is reheated to 460°C to 500°C to ensure uniform heating before extrusion. It is then fed into a hot extruder to produce bicycle frame tubing of various specifications with wall thicknesses ranging from 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, and 2.0 mm. The extrusion ratio is controlled between 20 and 60 to ensure sufficient plastic deformation, thereby refining the grains and eliminating casting structures. The extrusion speed is controlled between 4 m / s and 15 m / s. During hot extrusion, the dimensional accuracy and surface quality of the tubing are controlled by optimizing the extrusion die design and lubrication conditions. Immediately after extrusion, the tubing is water-quenched to maximize the retention of solid solution elements in the matrix, laying the foundation for subsequent age hardening.

[0027] After hot extrusion, the pipes can be selectively subjected to cold deformation treatment based on the dimensional accuracy and mechanical property requirements of the final product. This cold deformation typically employs cold stretching or cold rolling processes to further reduce the pipe wall thickness or diameter, improve dimensional accuracy, and introduce work hardening, thereby enhancing the pipe's strength and surface finish. The amount of cold deformation is controlled between 10% and 30%. If the amount of cold deformation is large, intermediate annealing can be performed to restore plasticity.

[0028] Step S5: Weld the frame and perform T6 treatment.

[0029] The hot-extruded and cold-deformed tubing is then welded into a bicycle frame using welding methods such as argon arc welding, laser welding, or high-frequency induction welding. During the welding process, high-strength welding wire with a chemical composition similar to or specially designed for the tubing should be preferred to minimize the degradation of mechanical properties in the weld area.

[0030] After welding, the chassis undergoes T6 heat treatment. T6 heat treatment includes two stages: solution treatment and artificial aging treatment.

[0031] Solution treatment: The welded frame is heated to a temperature range of 515°C to 530°C and held for 1 to 4 hours. This temperature and time are designed to allow soluble phases in the alloy (such as Mg2Si and Al2Cu) to fully dissolve in the aluminum matrix, forming a supersaturated solid solution. After solution treatment, water quenching or polymer quenching is performed immediately. The quenching rate should ensure that the frame temperature is reduced to below 80°C within 5 seconds to maximize the retention of solid solution elements and inhibit their premature precipitation.

[0032] Artificial aging treatment: The quenched chassis undergoes artificial aging treatment. The chassis is heated to a temperature range of 170°C to 195°C and held for 8 to 16 hours. This aging treatment temperature and time are designed to induce the precipitation of solute atoms in the supersaturated solid solution as fine, dispersed precipitates, such as GP zones and Mg2Si phases, thereby significantly improving the material's hardness and strength. After the aging treatment, the chassis is cooled to room temperature in the furnace.

[0033] After undergoing T6 heat treatment, the frame can be subjected to various surface treatments, such as anodizing, sandblasting, painting, or electroplating, to enhance its corrosion resistance, wear resistance, and aesthetics. The manufacturing method described in this invention ensures excellent performance in terms of mechanical properties, microstructure uniformity, dimensional accuracy, and surface quality of the final tubing and frame through precise control of each process step.

[0034] The lightweight, high-strength bicycle frame tubing and its preparation method provided by this invention have significant advantages over existing technologies: 1. Excellent casting fluidity and dense, uniform ingot microstructure: The alloy composition of this invention is optimized, particularly the precise ratio of silicon to magnesium content and the addition of rare earth elements and strontium, which significantly improves the fluidity of the alloy melt and reduces the tendency for hot cracking. During continuous casting, through strict control of solidification conditions and modification treatment, a dense ingot microstructure with fine grains, uniform distribution, and no macroscopic shrinkage porosity or central segregation is obtained. This high-quality casting microstructure forms the basis for the subsequent production of high-performance tubing, effectively avoiding the microstructural defects common in traditional aluminum alloy ingots.

[0035] 2. Excellent Strength-Plasticity Balance: After T6 treatment, the room temperature tensile strength of the frame tubing of this invention reaches or exceeds 500 MPa, the yield strength reaches or exceeds 320 MPa, while the elongation remains above 10%. Its strength-plasticity product is greater than 5 GPa·%, significantly higher than that of traditional 6061 aluminum alloy (approximately 4 GPa·%). This excellent strength-plasticity balance allows the tubing to withstand high-intensity loads while possessing sufficient toughness and impact resistance, greatly improving the safety and reliability of the bicycle frame under complex working conditions.

[0036] 3. High Strength and Extreme Lightweight: The alloy material and manufacturing process of this invention enable the tubing to achieve extremely low wall thickness while maintaining mechanical properties. The minimum wall thickness of the hot-extruded tubing can reach 0.5 mm, far lower than the minimum wall thickness of traditional 6061 aluminum alloy frame tubing (typically 0.8 mm to 1.2 mm). Bicycle frames welded using the 0.5 mm wall thickness tubing of this invention have significantly reduced weight while still meeting and passing rigorous bench tests, making it possible to pursue high-performance bicycles with extreme lightweight design. For example, compared to frames using traditional aluminum alloys weighing 1.4 to 1.6 kg, this invention can reduce frame weight by more than 20%. 4. Excellent Weldability: The alloy tubing of this invention exhibits excellent weldability and can be joined using various advanced welding processes such as argon arc welding, laser welding, and high-frequency induction welding. After welding, the mechanical property degradation rate in the weld area is controlled within 5% to 10%, significantly better than the weld performance degradation rate of traditional 6061 aluminum alloy (typically 15% to 20%). This is due to the precise control of the alloy composition, especially the optimization of the Mg2Si phase and rare earth elements, which effectively suppresses grain coarsening and the formation of harmful phases in the weld heat-affected zone, thereby ensuring the uniformity and reliability of the overall mechanical properties of the frame structure.

[0037] 5. Significantly Improved Fatigue Performance: Through the synergistic effect of rare earth elements and strontium, the α-Al grains of the alloy of this invention are effectively refined, and the eutectic silicon morphology changes from lamellar to fine, rounded fibrous or granular. Simultaneously, precise control of hot extrusion and T6 heat treatment processes results in the formation of fine, dispersed, and uniformly distributed reinforcing phases within the alloy matrix. These microstructural features effectively reduce stress concentration sources, significantly improving the fatigue strength and fatigue life of the material. This makes the bicycle frame less prone to fatigue fracture under long-term, high-frequency vibration and dynamic loads, thereby extending the product's service life.

[0038] 6. Uniformity and Stability of Mechanical Properties: The series of processes employed in this invention, including refining and degassing, modification treatment, and homogenization treatment, ensures a high degree of uniformity in the microstructure of the cast ingot. Subsequent hot extrusion and T6 heat treatment processes have also been rigorously optimized, guaranteeing high uniformity and stability of the microstructure and mechanical properties within the tube in all directions and across different cross-sections. This completely solves the problem of uneven performance caused by microstructural defects in traditional aluminum alloys and overcomes the limitations of existing composite materials in precisely controlling internal stress distribution in thin-walled structures, thereby ensuring the consistency and reliability of the bicycle frame during actual riding.

[0039] In summary, this invention, through unique alloy composition design and systematic optimization of the preparation process, provides a bicycle frame tube that combines extreme lightweight, ultra-high strength, excellent plasticity, superior fatigue performance, and good weldability. Its comprehensive performance is significantly better than existing technologies, and it can meet the stringent material requirements of modern high-performance bicycles, thus having broad application prospects. Attached Figure Description

[0040] Figure 1 This is a schematic diagram of the preparation method of a lightweight and high-strength bicycle frame tube according to the present invention.

[0041] The attached figures are labeled as follows: S1, preparation of aluminum alloy liquid; S2, refining and degassing; S3, modification treatment and casting of rods; S4, homogenization treatment, hot extrusion and cold deformation; S5, welding of the frame and T6 treatment. Detailed Implementation

[0042] This invention provides a lightweight, high-strength bicycle frame tube and its manufacturing method. To enable those skilled in the art to better understand and implement this invention, it will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that the given embodiments are for illustrative purposes only and are not intended to limit the scope of the invention. Those skilled in the art can make various modifications and variations to this invention without departing from its principles and scope.

[0043] The lightweight, high-strength bicycle frame tubing disclosed in this invention features a precisely designed and optimized chemical composition aimed at achieving a significant improvement in overall mechanical properties, particularly in balancing lightweight and high strength. The tubing's chemical composition, by mass percentage, comprises 2.5% to 3.5% silicon, 0.5% to 0.7% magnesium, 0.2% to 0.4% copper, 0.15% to 0.30% manganese, 0.12% to 0.20% iron, 0.01% to 0.05% rare earth elements (lanthanum or cerium), 0.004% to 0.008% strontium, with the balance being aluminum and unavoidable impurities. The total amount of these unavoidable impurities is strictly controlled to be less than or equal to 0.10%. Through precise control of these elements, especially their proportional relationships and their mechanisms of action in the microstructure, this invention effectively optimizes the alloy's solidification characteristics, solid solution strengthening effect, precipitation strengthening effect, and grain refinement.

[0044] Specifically, the silicon content is controlled within the range of 2.5% to 3.5%, aiming to provide sufficient silicon source for the formation of the important Mg2Si strengthening phase, while avoiding excessive silicon content that could lead to the precipitation of coarse primary silicon crystals, thus affecting the material's plasticity and toughness. The magnesium content is controlled within the range of 0.5% to 0.7%, its main role being to form the Mg2Si phase with silicon, serving as the primary precipitated strengthening phase and significantly improving the alloy's strength. The copper content is 0.2% to 0.4%, forming a solid solution in the aluminum matrix and precipitating strengthening phases such as Al2Cu, further enhancing the alloy's solid solution strengthening and precipitation strengthening effects. The manganese content is 0.15% to 0.30%, primarily forming Al-Fe-Mn-Si type compounds in the alloy. These compounds exist in a fine, dispersed form, effectively pinning grain boundaries, inhibiting grain growth, and thus refining the grain size. The iron content is 0.12% to 0.20%. Iron is a common impurity element in aluminum alloys, usually forming coarse needle-like or lamellar iron-rich phases, which have a detrimental effect on mechanical properties. In this invention, through synergistic action with manganese, iron is promoted to form fine Al-Fe-Mn-Si type compounds, thereby passivating its detrimental effects. Rare earth elements, specifically lanthanum or cerium, are added at a level of 0.01% to 0.05%. Rare earth elements play a grain-refining role in aluminum alloys. By segregating at grain boundaries and influencing the growth mode of the solidification front, they effectively inhibit the growth of α-Al grains. At the same time, they can also form stable rare earth compounds with impurity elements such as iron, reducing the formation of harmful iron phases, purifying the matrix, and further improving the strength and plasticity of the material. The addition of strontium ranges from 0.004% to 0.008%. As an important modifier, strontium can alter the growth pattern of eutectic silicon during the solidification process of aluminum-silicon alloys, transforming it from a coarse, stress-concentrating lamellar or needle-like structure into a fine, rounded fibrous or granular structure. This modification of eutectic silicon is crucial for improving the alloy's plasticity, toughness, and fatigue properties.

[0045] In a preferred embodiment of the present invention, the chemical composition of the lightweight, high-strength bicycle frame tubing is further optimized by adjusting the elemental content ratios. Specifically, the silicon to magnesium ratio is controlled between 4 and 8. This ratio range has been verified through extensive experiments and aims to precisely control the formation kinetics and precipitation distribution of the Mg2Si strengthening phase, while effectively suppressing the formation of coarse silicon phases, ensuring sufficient precipitation strengthening while maintaining good material plasticity. When the silicon-magnesium ratio is below 4, magnesium is relatively excessive, which may lead to the formation of other intermetallic compounds that are detrimental to strengthening or to underutilize the strengthening potential of silicon; when the silicon-magnesium ratio is above 8, silicon is relatively excessive, which easily leads to the formation of coarse primary silicon crystals, reducing the material's plasticity and toughness. Another key ratio is the iron to manganese ratio, controlled between 1.25 and 2.5. This ratio aims to optimize the synergistic effect of iron and manganese in the alloy, promoting the formation of fine, dispersed Al-Fe-Mn-Si type compounds, rather than harmful coarse needle-like or plate-like iron-rich phases. These fine, dispersed compounds not only serve as heterogeneous nucleation sites to promote grain refinement, but also effectively pin grain boundaries and inhibit recrystallization, thereby comprehensively improving the strength, toughness, and microstructure uniformity of the material. When the Fe / Mn ratio deviates from this range, it easily leads to the formation of coarse, iron-rich phases, or insufficient passivation of iron by manganese, thus impairing the mechanical properties of the material.

[0046] Through optimized chemical composition and refined manufacturing processes, the lightweight, high-strength bicycle frame tubing of this invention exhibits excellent overall balance of mechanical properties at room temperature after hot extrusion and T6 treatment. Specifically, its tensile strength reaches or exceeds 500 MPa, its yield strength reaches or exceeds 320 MPa, while its elongation remains above 10%. These performance indicators demonstrate that this invention maintains excellent plasticity while ensuring high material strength, thereby significantly improving the reliability and safety of the tubing under complex stress conditions. Furthermore, the strength-ductility product of the tubing, i.e., the product of tensile strength and elongation, is greater than 5 GPa·%. The strength-ductility product is an important indicator for measuring the balance between material strength and plasticity; a higher value indicates better overall performance in withstanding high-load deformation, which has significant application advantages for bicycle frame tubing that needs to withstand high-frequency vibration and dynamic impact loads.

[0047] In addition to its excellent mechanical properties, the lightweight, high-strength bicycle frame tubing described in this invention also possesses the potential for extreme weight reduction. After hot extrusion, its minimum wall thickness can reach 0.5 mm. This achievement allows for a significant reduction in overall weight while maintaining structural integrity and safety. Traditional aluminum alloy frame tubing, limited by material strength and processing technology, typically has a minimum wall thickness that is difficult to lower than 0.8 mm. Frames made using the 0.5 mm wall thickness alloy tubing of this invention can be significantly lighter than frames made with traditional aluminum alloys, and after welding, they can successfully pass rigorous bench tests, fully verifying their long-term reliability and safety.

[0048] This invention also provides a method for preparing lightweight, high-strength bicycle frame tubing. This method ensures the production of the aforementioned high-performance tubing by precisely controlling a series of key process parameters, including alloy smelting, casting, hot extrusion, cold deformation, and heat treatment. The entire preparation process can be systematically divided into five main steps, whose logical connections and process transitions together constitute the key to achieving high-quality tubing.

[0049] Step S1: Prepare aluminum alloy liquid.

[0050] This step is the starting point of the entire preparation process and has a decisive impact on the performance of the final pipe. First, high-purity electrolytic aluminum liquid or pure aluminum ingots are selected as the base material, with a purity of 99.7% or higher to ensure the purity of the alloy matrix and reduce the influence of harmful impurities. The base material is fed into a medium-frequency induction furnace or resistance furnace and heated to a temperature range of 750°C to 800°C. This temperature range ensures that the aluminum liquid is fully melted, has good fluidity, facilitates the uniform dissolution of alloying elements, and avoids excessively high temperatures that could lead to aluminum oxidation and increased gas absorption. After the melt reaches the specified temperature, alloying elements are precisely added. For example, 25 kg to 35 kg of crystalline silicon is added per 1000 kg of aluminum liquid, with a purity of 99.5% or higher. The addition of silicon, besides serving as a component of the Mg2Si strengthening phase, also moderately improves the fluidity of the melt. Next, 3 kg to 5 kg of high-carbon ferromanganese alloy with a manganese content of 65% to 75% is added. The addition of the ferromanganese alloy aims to introduce manganese to refine the grains and passivate the harmful effects of iron. Subsequently, 5.5 kg to 7.5 kg of magnesium ingots, with a purity of 99.8% or higher, are added. The addition of magnesium primarily serves to form the Mg₂Si precipitation strengthening phase. Finally, 2 kg to 4 kg of copper plates, with a purity of 99.9% or higher, are added. The addition of copper primarily serves to enhance both solid solution strengthening and precipitation strengthening effects. All alloying elements must be slowly added to the molten aluminum under stirring conditions, typically using mechanical or electromagnetic stirring at a rate controlled at 50 to 100 rpm, to ensure complete dissolution and uniform distribution in the melt. After all alloying elements have been added, the melt temperature is maintained within the aforementioned range, and stirring continues for at least 30 minutes to ensure complete dissolution of all additives, forming a homogeneous molten aluminum alloy as described in this invention. During this process, a thin oxide film will form on the surface of the melt, requiring periodic slag removal to maintain the cleanliness of the melt.

[0051] Step S2: Refining and degassing.

[0052] After the aluminum alloy liquid is prepared, it must be refined and degassed to remove dissolved hydrogen and non-metallic inclusions from the melt, ensuring the density and uniformity of the subsequent cast rod microstructure. This step is crucial because hydrogen and inclusions are the main causes of casting defects and decreased mechanical properties. The refining and degasing process is carried out at precisely controlled temperatures, typically using a rotor degasser or a porous plug degasser. Specifically, for every 1000 kg of the alloy liquid of this invention, a sodium-free refining agent is added for flotation refining and degasing. The sodium-free refining agent is typically composed of a complex salt of potassium chloride, sodium chloride, and fluoride, and is strictly free of environmentally harmful sodium to avoid the potential negative impact of sodium contamination on alloy properties. The amount of refining agent added is assessed based on the surface area and degree of contamination of the aluminum liquid, typically ranging from 0.1% to 0.3% of the aluminum liquid mass. In the flotation refining process, refining agent particles, high-purity argon (≥99.999%), or high-purity nitrogen (≥99.99%) are injected into the bottom of the melt through a porous plug or rotary nozzle. As the gas or refining agent particles rise in the molten aluminum, they combine with hydrogen and non-metallic inclusions in the melt to form scum, which is carried to the surface of the melt. The rotational speed of the rotary nozzle is typically controlled at 200 to 600 rpm, and the gas flow rate is controlled at 1 to 5 liters per minute to ensure sufficient contact between the gas or refining agent and the melt. This degassing process lasts for 10 to 20 minutes, during which the melt temperature is maintained at 720°C to 760°C. Degassing within this temperature range ensures good melt fluidity, which is beneficial for the floating of inclusions and gases, while avoiding accelerated oxidation caused by excessively high temperatures. After refining and degassing, the inclusion content in the melt is assessed using the K-mold test, requiring it to meet the national standard's Grade 1 requirement (no macroscopic inclusions visible to the naked eye). Simultaneously, the gas content in the melt is determined using the reduced-pressure solidification method, requiring it to be less than or equal to 0.05 ml / 100 g of molten aluminum. These stringent quality control measures ensure the high purity of the alloy casting, laying a solid material foundation for the subsequent preparation of high-performance tubing.

[0053] Step S3: Modification treatment and casting.

[0054] After refining and degassing, the temperature of the molten alloy is immediately and precisely adjusted to a range of 710°C to 750°C to facilitate modification treatment and subsequent casting. This temperature range was determined by comprehensively considering the dissolution efficiency of rare earth elements and strontium, the modification effect, and the stability of the casting process. At this temperature, modification treatment aimed at optimizing the microstructure of the alloy is carried out. Specifically, based on 1000 kg of molten aluminum alloy, 0.5 kg to 1.5 kg of aluminum foil-coated lanthanum-cerium alloy and 0.4 kg to 0.6 kg of aluminum-10 strontium master alloy are added. The rare earth element (lanthanum or cerium) content in the aluminum foil-coated lanthanum-cerium alloy is 10% to 20%, and the foil coating thickness is typically 0.1 mm to 0.2 mm. The purpose of using aluminum foil to coat the rare earth alloy is to effectively prevent the rare earth elements from undergoing a violent oxidation reaction with oxygen in the air during the addition process, thereby significantly improving the yield of rare earth elements and ensuring that they can be more uniformly dispersed and dissolved in the melt. The aluminum-10 strontium master alloy has a strontium content of 10%. Both master alloys must be slowly added to the molten aluminum under stirring conditions, typically for 5 to 10 minutes, to ensure that the master alloys are fully dissolved and uniformly dispersed in the alloy liquid. During this stage, the stirring intensity must be precisely controlled to avoid re-entry of gas.

[0055] After the modification treatment, continuous casting of ingots is immediately carried out. This continuous casting process typically employs vertical or horizontal semi-continuous casting equipment. The casting process requires precise control of the casting speed, cooling rate, and crystallizer design to obtain ingots with uniform microstructure, fine grains, and no macroscopic segregation. The casting speed is adjusted according to the ingot diameter and alloy type, typically ranging from 50 mm / min to 150 mm / min. Slower casting speeds promote grain growth and the formation of solidification defects, while excessively high speeds may lead to casting instability. The cooling rate is precisely controlled through a direct water cooling system within the ingot crystallizer and a secondary cooling zone spray water flow, ensuring the formation of fine equiaxed grains during rapid cooling and effectively suppressing the formation of coarse eutectic phases. The crystallizer is typically made of graphite or copper alloy, and its surface requires a special coating treatment to ensure the surface quality and dimensional accuracy of the ingot. The ingot diameter is usually determined by the size requirements of the subsequent extrusion equipment, with a common diameter range of 150 mm to 300 mm. The entire continuous casting process aims to minimize casting defects such as shrinkage cavities, porosity, cold shuts, and coarse grains, providing high-quality raw materials for subsequent hot extrusion processes and ensuring the stability and reliability of the final pipe performance. The molten metal passes through a ceramic foam filter before casting to further remove residual inclusions.

[0056] Step S4: Homogenization, hot extrusion and cold deformation.

[0057] After the casting is completed, the casting is first homogenized. This homogenization process is a crucial heat treatment step, designed to eliminate chemical composition inhomogeneities generated during ingot solidification, particularly dendritic segregation, and to allow soluble phases (such as Mg₂Si) to dissolve in the aluminum matrix, providing sufficient solute atoms for subsequent age hardening. The casting is placed in a homogenization furnace and uniformly heated to a homogenization temperature of 480°C to 520°C, and held at this temperature for 8 to 12 hours. The homogenization temperature must be selected to ensure sufficient dissolution of the soluble phase while avoiding overheating. The holding time must be determined to ensure ideal uniformity of element diffusion. After holding, the casting is cooled to room temperature at a controlled rate. Controlling the cooling rate aims to prevent the formation of new segregations or premature precipitation of coarse phases during cooling, which could affect the subsequent heat treatment effect. Typically, the cooling rate is controlled between 10°C and 50°C per hour.

[0058] The homogenized bar stock is then hot-extruded. Before extrusion, the homogenized bar stock is reheated to 460°C to 500°C to ensure uniform heating and achieve good plastic deformation capacity. It is then fed into a horizontal or vertical hot extrusion press for extrusion molding. During extrusion, by optimizing the extrusion die design (e.g., using a split-flow combination die), coating the die surface with graphite-based lubricant, and precisely controlling lubrication conditions, bicycle frame tubing with wall thicknesses ranging from 0.5 mm, 0.6 mm, 0.8 mm, 1.0 mm, 1.2 mm, 1.5 mm, and 2.0 mm is produced. The extrusion ratio (the ratio of the cross-sectional area of ​​the cast bar before extrusion to the cross-sectional area of ​​the extruded tubing) is strictly controlled between 20 and 60 to ensure sufficient plastic deformation, thereby effectively refining the grains and eliminating macroscopic defects in the casting structure. The extrusion speed is controlled between 4 m / s and 15 m / s. Excessively low extrusion speeds lead to low production efficiency and accelerated die wear, while excessively high extrusion speeds can cause excessive heat accumulation, resulting in rough pipe surfaces, dimensional deviations, or thermal cracking. After extrusion, the pipes are immediately subjected to water quenching, with quenching water temperatures typically ranging from 20°C to 40°C. The quenching speed should be as fast as possible to maximize the retention of solid solution elements in the matrix, forming a supersaturated solid solution, which lays the microstructural foundation for subsequent aging strengthening.

[0059] After hot extrusion, the pipes can be selectively subjected to cold deformation treatment based on the dimensional accuracy and mechanical performance requirements of the final product. This cold deformation typically employs cold stretching or cold rolling processes to further reduce the pipe wall thickness or diameter, improve dimensional accuracy, and introduce work hardening, thereby enhancing the pipe's strength and surface finish. The amount of cold deformation (section reduction rate) is controlled between 10% and 30%. If the amount of cold deformation is large, to prevent the pipe from breaking due to excessive work hardening, intermediate annealing can be performed to restore plasticity. The annealing temperature is typically 300℃ to 350℃, held for 1 to 2 hours.

[0060] Step S5: Weld the frame and perform T6 treatment.

[0061] The hot-extruded and cold-deformed tubing is a high-quality raw material for manufacturing high-performance bicycle frames. These tubings are cut to specific lengths and precisely welded into bicycle frames using various advanced welding methods, such as inert gas shielded tungsten inert gas (TIG), laser welding, or high-frequency induction welding. During welding, high-strength welding wire with a chemical composition similar to or specially designed for the tubing should be preferred to minimize the degradation of mechanical properties in the weld area. For example, in TIG welding, a pulsed current mode is typically used, with a current range between 100A and 250A, and high-purity argon as the shielding gas, with a flow rate controlled at 10 to 15 liters per minute. Laser welding uses a high-energy-density laser beam to achieve welding with small deformation and a narrow heat-affected zone.

[0062] After welding, the chassis must undergo T6 heat treatment to fully realize the strengthening potential of the alloy. T6 heat treatment includes two stages: solution treatment and artificial aging treatment.

[0063] Solution treatment: The welded chassis is heated to a temperature range of 515°C to 530°C. This temperature range is designed to allow soluble phases in the alloy (such as Mg₂Si and Al₂Cu) to fully dissolve in the aluminum matrix, forming a homogeneous supersaturated solid solution. The holding time for solution treatment is 1 to 4 hours to ensure complete dissolution. After holding, the chassis is immediately subjected to water quenching or polymer quenching. The quenching speed is crucial for solution treatment; the chassis temperature should be rapidly reduced from the solution temperature to below 80°C within 5 seconds to maximize the retention of dissolved elements and inhibit premature precipitation of coarse phases during cooling. Water quenching is the most common quenching medium, with the water temperature controlled between 20°C and 40°C.

[0064] Artificial aging treatment: The quenched chassis undergoes artificial aging treatment. The chassis is heated to a temperature range of 170°C to 195°C and held at this temperature for 8 to 16 hours. The precise control of the temperature and time in this aging treatment aims to promote the precipitation of solute atoms in the supersaturated solid solution as fine, dispersed precipitates, primarily GP zones and Mg2Si phases, thereby significantly improving the material's hardness and strength and optimizing its fatigue performance. Excessively high or low aging temperatures, or excessively long or short aging times, can lead to under-aging or over-aging, affecting the final mechanical properties. After the aging treatment, the chassis is cooled to room temperature in the furnace.

[0065] After undergoing T6 heat treatment, the chassis can be subjected to various surface treatments, such as anodizing, sandblasting, painting, or electroplating, to enhance its corrosion resistance, wear resistance, aesthetics, or provide additional protection. The preparation method described in this invention, through precise control of each process step, from alloy liquid preparation to final heat treatment, ensures the superior performance of the final tubing and chassis in terms of mechanical properties, microstructure uniformity, dimensional accuracy, and surface quality.

Claims

1. A lightweight, high-strength bicycle frame tube, characterized in that, Its chemical composition, by mass percentage, includes: silicon 2.5% to 3.5%, magnesium 0.5% to 0.7%, copper 0.2% to 0.4%, manganese 0.15% to 0.30%, iron 0.12% to 0.20%, rare earth elements 0.01% to 0.05%, wherein the rare earth elements are selected from one or two of lanthanum or cerium, strontium 0.004% to 0.008%, and the balance being aluminum and unavoidable impurities, wherein the total amount of unavoidable impurities is less than or equal to 0.10%.

2. The lightweight, high-strength bicycle frame tubing according to claim 1, characterized in that, The chemical composition of the pipe has a silicon to magnesium ratio of 4 to 8, which aims to precisely control the formation and distribution of the Mg2Si strengthening phase in the aluminum alloy matrix and suppress the formation of coarse silicon phases while maintaining good material plasticity; and an iron to manganese ratio of 1.25 to 2.5, which aims to optimize the synergistic effect of iron and manganese elements in the alloy, promoting the formation of fine and dispersed Al-Fe-Mn-Si type compounds, rather than harmful coarse needle-like or plate-like iron-rich phases.

3. The lightweight, high-strength bicycle frame tubing according to claim 1 or 2, characterized in that, The rare earth elements play a role in refining the α-Al phase during the solidification process of aluminum alloys. They inhibit the growth of α-Al grains by segregating at grain boundaries and combine with impurity elements in the alloy to form stable rare earth compounds, thereby purifying the matrix. The strontium, as an important modifier, changes the growth mode of eutectic silicon, causing the eutectic silicon to transform from a coarse, stress-concentrating lamellar or needle-like structure into a fine, round fibrous or granular structure.

4. The lightweight, high-strength bicycle frame tubing according to claim 1, characterized in that, After hot extrusion and T6 heat treatment, the pipe has a tensile strength of 500 MPa or more, a yield strength of 320 MPa or more, and an elongation of more than 10% at room temperature; and the strength-ductility product of the pipe is greater than 5 GPa·%, which is an important indicator for measuring the balance between strength and plasticity of a material.

5. The lightweight, high-strength bicycle frame tubing according to claim 1, characterized in that, After hot extrusion, the minimum wall thickness of the tubing can reach 0.5 mm, thus enabling the bicycle frame to achieve extreme lightweighting while ensuring structural integrity and safety.

6. A method for preparing a lightweight, high-strength bicycle frame tube, characterized in that, The method includes the following steps:

1. Preparation of aluminum alloy liquid (S1) includes using electrolytic aluminum liquid or pure aluminum ingot with a purity of 99.7% or higher as the base material, melting it in a temperature range of 750°C to 800°C, and precisely adding specific alloying elements to form the aluminum alloy liquid; 2. Refining and degassing (S2) includes refining and degassing the aluminum alloy liquid to remove dissolved hydrogen and non-metallic inclusions, ensuring the dense and uniform structure of the cast rod. III. Modification treatment and casting (S3) includes modifying the refined and degassed aluminum alloy liquid at a temperature of 710°C to 750°C to further optimize the microstructure, and using a continuous casting process to obtain a casting rod with uniform structure, fine grains and no macro segregation. IV. Homogenization, hot extrusion and cold deformation (S4) includes homogenizing the cast rod to eliminate solidification segregation and dissolve the soluble phase in the aluminum matrix, followed by hot extrusion into a tube, and selectively performing cold deformation according to the dimensional accuracy and mechanical property requirements of the final product. V. Welding the frame and T6 treatment (S5), which includes connecting the hot-extruded and cold-deformed tubing into a bicycle frame by welding, and subjecting the frame to T6 heat treatment to fully utilize the strengthening potential of the alloy and significantly improve hardness and strength.

7. The preparation method according to claim 6, characterized in that: In step S1, the base material is heated to 750°C to 800°C. For every 1000 kg of molten aluminum, 25 kg to 35 kg of crystalline silicon with a purity of 99.5% or higher, 3 kg to 5 kg of high-carbon ferromanganese alloy with a manganese content of 65% to 75%, 5.5 kg to 7.5 kg of magnesium ingots with a purity of 99.8% or higher, and 2 kg to 4 kg of copper plates with a purity of 99.9% or higher are added. All alloying elements are slowly added to the molten aluminum under stirring conditions, while maintaining the melt temperature and continuously stirring until all additives are completely dissolved, forming a homogeneous molten aluminum alloy. In step S2, the refining and degassing process involves adding a sodium-free refining agent to every 1000 kg of the molten aluminum alloy for flotation refining and degassing. The sodium-free refining agent consists of a complex salt of potassium chloride, sodium chloride, and fluoride, and is added at 0.1% to 0.3% of the mass of the molten aluminum. High-purity argon or high-purity nitrogen is injected during the process. The degassing process lasts for 10 to 20 minutes, and the melt temperature is maintained at 720°C to 760°C. After the refining and degassing process is completed, the inclusions in the melt are assessed using a K-mold test to determine that they reach level 1, and the gas content in the melt is determined to be less than or equal to 0.05 ml / 100 g using a reduced pressure solidification method. In step S3, the temperature of the alloy liquid is adjusted to 710°C to 750°C for modification treatment. For every 1000 kg of the aluminum alloy liquid, 0.5 kg to 1.5 kg of aluminum foil-coated rare earth element alloy and 0.4 kg to 0.6 kg of aluminum-10 strontium master alloy are added. The rare earth element content in the aluminum foil-coated rare earth element alloy is 10% to 20%, and the strontium content in the aluminum-10 strontium master alloy is 10%. Both master alloys are added under stirring conditions to ensure they are fully dissolved and uniformly dispersed in the alloy liquid. The continuous casting process has a casting speed of 50 mm / min to 150 mm / min, and the cooling rate is precisely controlled by a water cooling system to ensure that the casting rod forms fine equiaxed crystals during rapid cooling and to suppress the formation of coarse eutectic phases.

8. The preparation method according to claim 6, characterized in that: In step S4, the homogenization treatment involves heating the cast rod to a homogenization temperature of 480°C to 520°C and holding it at that temperature for 8 to 12 hours. After holding, the rod is cooled to room temperature at a controlled rate of 10°C to 50°C / hour to avoid the formation of new segregation or premature precipitation of coarse phases. The hot extrusion involves reheating the homogenized rod to 460°C to 500°C and then feeding it into a hot extrusion press for extrusion molding. The extrusion ratio is controlled between 20 and 60, and the extrusion speed is controlled between 4 m / s and 15 m / s. After extrusion, the rod is immediately water-quenched to maximize the retention of solid solution elements in the matrix, laying the foundation for subsequent age hardening. The cold deformation typically employs cold stretching or cold rolling processes, with the cold deformation amount controlled between 10% and 30%. In step S5, the welded frame is connected using methods such as argon arc welding, laser welding, or high-frequency induction welding. The T6 heat treatment includes: solution treatment, heating the welded frame to a temperature range of 515°C to 530°C and holding it at that temperature for 1 to 4 hours, followed immediately by water quenching or polymer quenching. The quenching speed ensures that the frame temperature is reduced to below 80°C within 5 seconds to maximize the retention of solid solution elements and inhibit their premature precipitation; and artificial aging treatment, heating the quenched frame to a temperature range of 170°C to 195°C and holding it at that temperature for 8 to 16 hours, aiming to promote the precipitation of solute atoms in the supersaturated solid solution as fine and dispersed precipitates, thereby significantly improving the hardness and strength of the material. After the aging treatment, the frame is cooled to room temperature in the furnace.

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