A method for preparing bicycle frame pipes using raw materials containing more than 40% aluminum chips

Abstract

The present invention discloses a method for producing bicycle frame tubing using raw materials containing greater than 40% aluminum chips. The method involves smelting aluminum chips in an induction furnace, repeatedly adding material, and submerging the aluminum chips in the melt. The repeated addition and smelting process completely melts the aluminum chips. The aluminum chip melt is refined and filtered, then mixed with a bulk material melted in an industrial gas furnace. The mixed aluminum melt undergoes graphite rotor refining in the furnace, followed by dual-rotor online degassing and two-stage filtration to produce cast rods. The cast rods are then reverse-extruded to produce seamless bicycle frame tubing. After heat treatment, the tubing exhibits recrystallized grains in both the transverse and longitudinal directions, a tensile strength of 300 MPa or higher, a yield strength of 250 MPa or higher, an elongation of 13%, and weld micropores of 60 mm or less. Compared to existing technologies, the present invention achieves the production of high-strength, high-plasticity bicycle frame tubing using a high proportion of aluminum chips as raw material, achieving low-carbon, green manufacturing.

Description

Technical Field

[0001] The invention relates to the field of metal metallurgy and processing technology, and in particular to a method for preparing bicycle frame pipes by using raw materials with an aluminum scrap ratio greater than 40%. Background Art

[0002] Aluminum alloy bicycles, with their light weight, effortless riding, and excellent corrosion resistance, have become the preferred choice for everyday green travel. As the backbone and main body of a bicycle, the frame not only withstands the impact loads generated by the bicycle during travel but is also crucial for its comfortable and safe transport. Furthermore, with the increasing emphasis on fitness and racing functions, frame structures and styling are also emphasizing fashion and individuality. Ergonomically designed, lightweight, and aesthetically pleasing frames are increasingly favored by cyclists. The frame is the soul of a bicycle's lightness, coolness, greenness, and environmental friendliness.

[0003] Bicycle frames require alloys with high strength, as well as the ability to be extruded, bent, inflated, and welded. After anodizing, they must have an aesthetically pleasing appearance and a metallic sheen. To meet the comprehensive performance requirements of frame products, higher-purity electrolytic aluminum ingots are often selected as the raw material for frame tubing. A certain proportion of elements such as magnesium and silicon are added for aging toughening to ensure tubing performance. In recent years, with growing environmental awareness and increasing efforts to reduce carbon dioxide emissions, carbon dioxide emission reduction requirements have also been introduced for aluminum alloy raw materials used in bicycle production. The use of recycled aluminum and aluminum scrap, which have lower carbon dioxide emissions during production, is encouraged or prioritized for the production of lightweight, green vehicles.

[0004] In contrast, using high-purity aluminum ingots as raw material, the addition of aluminum chips, especially above a certain proportion, increases the content of metallic impurities and refractory Al₂O₃ oxides in the melt during the smelting process. These impurities are difficult to eliminate even after melt processing. Therefore, aluminum chips are strictly restricted as a raw material in the production of high-quality aluminum products, and there are no reports of using them in the production of aluminum alloy bicycle frames. However, aluminum chips are an inevitable byproduct of the cutting process in product production and have incorporated alloying elements essential for product performance, making them recyclable. Compared to electrolytic aluminum ingots, recycling aluminum chips is not only cost-effective but also significantly reduces carbon dioxide emissions, making them a recyclable low-carbon metal raw material. If the limitations on the use of aluminum chips can be overcome and their proportion can be increased in the production of bicycle frame tubing, this lightweight and convenient vehicle could simultaneously meet the environmental requirements of low-carbon manufacturing and green travel, thus having broad application value.

[0005] However, current bicycle frame tubing manufacturing technology demonstrates strict raw material selection and control, with no breakthroughs in the selection and application of low-carbon raw materials such as aluminum scrap. Patent CN102392157A discloses a method for preparing aluminum alloy rods for electric bicycle frame tubing. The raw materials used to prepare the alloy are electrolytically pure aluminum ingots, pure magnesium ingots, and aluminum-silicon master alloy ingots. Electrolytic aluminum ingots emit significant amounts of carbon dioxide during production, making them high-carbon raw materials. Patent CN103484728A discloses an aluminum alloy for bicycle frame tubing and its preparation method. Addressing the issue of insufficient tube strength, the company discloses an aluminum alloy containing Er and Zr, achieving a tube strength exceeding 450 MPa. However, this alloy has high requirements for impurity elements and their content, making it unsuitable for production using aluminum scrap as raw material. Patent CN105838940A discloses an aluminum alloy material for bicycle frame manufacturing and its production process. However, this material primarily utilizes raw aluminum ingots and alloy ingots, with strict restrictions on the main alloying elements and impurity elements, including the aluminum scrap content. Patent CN106498202A discloses a method for recycling wrought aluminum alloy scrap. Using scrap aluminum as raw material, this patent optimizes the composition of the scrap aluminum raw material to directly regenerate high-value-added wrought aluminum alloy products. The method is suitable for various pressure-forming processes, including extrusion, rolling, and forging. This method uses only a small amount of aluminum scrap as raw material and places strict restrictions on other recycled aluminum types, resulting in high raw material selection and production costs. Based on the currently disclosed patents, it is difficult to produce bicycle frame tubing with high strength, high elongation, and excellent weldability using raw materials containing more than 40% aluminum scrap. Summary of the Invention

[0006] The purpose of the present invention is to provide a method for preparing bicycle frame pipes using raw materials with an aluminum scrap ratio greater than 40%, thereby preparing aluminum alloy frame pipes with high elongation and excellent welding performance, thereby achieving the goal of low-carbon production of aluminum alloy bicycle frames.

[0007] To achieve the above objectives, the production process of the present invention is implemented through the following technical solutions and steps:

[0008] (1) Raw material composition: Aluminum alloy scraps and scraps generated during the aluminum processing process, as well as aluminum alloy products used in the process, are selected as raw materials. The raw material composition and mass percentage are as follows: 40% to 60% 6××× aluminum alloy chips, 20% to 30% machining scraps or recycled aluminum products, etc., and the balance is 10% to 20% pure aluminum ingots and intermediate alloy ingots. The raw materials are configured into aluminum alloy for vehicle frames. The types and mass percentages of each element are as follows: Si: 0.6-1.3%; Fe: 0.1-0.3%; Mg: 0.8-1.5%; Cu: 0.1-0.3%; Mn: 0.07-0.25%; Zn: ≤0.08%; Cr: 0.05-0.3%; V: 0.05-0.20%; the balance is Al, and the remaining elements are considered impurities.

[0009] (2) Induction furnace melting aluminum chips process: Aluminum chips are melted in an electromagnetic induction furnace. First, large pieces of aluminum raw materials that account for no more than 5% of the total weight of the raw materials are placed in a medium frequency furnace and melted into liquid. Then, aluminum chips are slowly and continuously added to the medium frequency liquid melt, and the liquid aluminum melt is completely immersed in the added aluminum chips. The medium frequency furnace is turned on and off again. The induction heat and melt stirring function of the medium frequency furnace are used to mix the added aluminum chips with the aluminum melt and melt them all into liquid under the action of induction heat. Then, solid aluminum chips are added to the liquid aluminum melt in the medium frequency furnace again. After the aluminum melt in the furnace is completely immersed in the aluminum chips, the medium frequency furnace is turned on again. This process is repeated several times until all the aluminum chips in the raw materials are added to the induction furnace and melted into liquid. During the aluminum chip smelting process, the temperature range of the aluminum alloy melt in the furnace is: 650℃~730℃, and the temperature difference at various positions in the induction furnace is ≤60℃. The aluminum chip raw materials used in the present invention are all smelted in the induction furnace in this way, which can control the burn-off amount during the aluminum chip melting process to less than 3% and significantly reduce the formation of refractory Al2O3 oxides.

[0010] The aluminum chips melted in the induction furnace are transferred to a crucible for melt refining at a temperature of 700°C to 720°C. The refining unit utilizes a graphite rotor. Granular refining agents are continuously ejected from the bottom of the rotor. The rotor stirs and flows the melt, refining the entire crucible. Refining is performed one to three times, with each refining cycle lasting 20 to 40 minutes. The refining agent is granular and is added at a rate of 0.85 to 1.15 kg per ton of aluminum. After refining, the crucible melt is filtered through a 30-mesh filter plate and then continuously poured into a gas-fired melting furnace to mix with the melt from the bulk material. If the total weight of the aluminum chips exceeds the capacity of the induction furnace, this melting and melt refining process is repeated until all the aluminum chips are melted in the induction furnace. After refining and filtering, the chips are transferred to an industrial gas-fired furnace to mix with the bulk material.

[0011] (3) Melting aluminum raw materials in industrial gas furnaces: Industrial gas furnaces are used to melt large aluminum raw materials that do not contain aluminum chips, including machining waste, recycled large aluminum products, and metal aluminum ingots, alloy ingots, etc. These raw materials are dried at a temperature of 200℃~300℃ and placed in the furnace body. After melting to a semi-solid state, aluminum chips melt that has been refined and filtered is continuously injected into the gas-fired smelting furnace. When the aluminum melt submerges the semi-solid aluminum material, the gas burner is turned on again. The large aluminum raw materials are melted under the heating effect of the gas and aluminum chips melt. During the smelting process in the furnace, the surface of the large aluminum raw materials in the gas furnace is partially or completely covered by the processed aluminum chips melt, forming a semi-solid melt. The melting is accelerated by the heat conduction of the aluminum melt and the thermal corrosion of the flame. At this stage, because the liquid aluminum chips melt is mixed in first, compared with direct smelting in the smelting furnace, the surface of the raw materials is covered by the aluminum melt, which not only accelerates heat transfer but also plays a role in isolating the air and preventing oxidation, avoiding the generation of a large amount of oxides, which brings difficulties to the refining and filtration of the melt.

[0012] When the solid material in the smelting furnace is completely melted and the melt temperature reaches the range of 650-700℃, the electromagnetic stirrer at the bottom of the furnace is turned on to make the temperature and chemical composition of the entire melt in the furnace gradually uniform under the action of the electromagnetic stirrer. When all the aluminum chips melt is transferred to the gas-fired smelting furnace and the melt temperature in the furnace reaches the range of 700-750℃, the melt in the furnace is refined using a rotary nozzle refining equipment and a granular refining agent. The addition amount is 0.85-1.25 kg / ton of aluminum, the number of refining times is 1-3, and the refining time for each refining is 10-40 minutes. After refining, the total inclusion content of the melt is ≤0.35 mm2 / kg, and the number of oxide films on the fracture is ≤3. Finally, the aluminum melt after refining in the gas furnace is put into the casting plate after online degassing and online filtration. Continuous oil-gas lubrication is used to prepare cast rods with a diameter of 100mm~Ф200mm. The micro grain size of the cast rod is level 1, and the segregation layer thickness is ≤0.6mm.

[0013] (4) Reverse extrusion seamless pipe: The ingot is extruded into a seamless pipe with a wall thickness ranging from 1.5mm to 3.5mm by reverse extrusion. For pipes with diameters and wall thicknesses that cannot be directly prepared by reverse extrusion, the wall thickness and size requirements of the product can be achieved by extruding a pipe of similar specifications and then performing 1 to 3 cold working deformations by pipe drawing. The entire cross section of the seamless pipe has no weld seams and a layered structure. The microscopic grains along the extrusion direction and perpendicular to the extrusion direction are all nearly spherical recrystallized grains with a grain size of ≤90μm and a pipe elongation of ≥15% to ensure the process requirements for subsequent bulging of the frame pipe. Welding performance: The welding performance of the pipe is tested by MIG welding. The tensile strength of the weld is not less than 70% of the body strength, and the microscopic size of the micropores at the weld is ≤60μm. Mechanical properties of pipes: After solution and aging heat treatment, the seamless pipes extruded by this process have a tensile strength of ≥300Mpa, a yield strength of ≥250Mpa, an elongation of ≥13%, and micropores at the weld of ≤60μm. Beneficial effects

[0014] The method described in the present invention uses raw materials with an aluminum chip ratio greater than 40%. Compared with existing aluminum alloy frame tube processing technology, the present invention realizes the application of using high-proportion aluminum chip raw materials to prepare high-performance frame tubes. By separately smelting aluminum chips and other aluminum raw materials, purifying them separately, and then re-mixing them, a reverse extrusion method is used to prepare tubes with recrystallized equiaxed grains in both the transverse and longitudinal directions and without weld seams. The tubes can be inflated or plastically deformed and have high tensile strength, thereby realizing green manufacturing of lightweight bicycle frame tube structural components. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 The figure is a flow chart for preparing the frame tube of the present invention.

[0016] Figure 2 Microstructure diagram of cast rod.

[0017] Figure 3 Microscopic grain morphology of seamless pipe along the extrusion direction and perpendicular to the extrusion direction.

[0018] Figure 4 Microscopic grain morphology of seamless pipe along the extrusion direction and perpendicular to the extrusion direction.

[0019] Figure 5 This is the pore morphology at the weld position. Implementation Method

[0020] In order to enable those skilled in the art to better understand the present invention and to make the above-mentioned objects, features and advantages of the present invention more obvious and understandable, the present invention is further described in detail below with reference to the embodiments. Example

[0021] 7 tons of 6´´´ aluminum alloy chips, 5 tons of 6061 alloy machining waste, 3 tons of consumer aluminum products and a small amount of pure aluminum ingots and aluminum-based master alloy ingots were selected as raw materials, and the alloying element composition ratio after melting met the following requirements: Si: 0.6-1.3%; Fe: 0.1-0.3%; Mg: 0.8-1.5%; Cu: 0.1-0.3%; Mn: 0.07-0.15%; Zn: ≤0.08%; Cr: 0.05-0.3%; V: 0.05-0.20%.

[0022] First, 4.8 tons of machined scrap and 3 tons of aluminum products were dried at 200-300°C and then heated and melted in a 15-ton industrial gas furnace until the solid aluminum material melted and the melt temperature reached the range of 600-650°C. During this process, the remaining 200kg of machined aluminum scrap was placed in an induction furnace and melted until it became liquid. Then, 200kg of dried aluminum chips were slowly added to a 2-ton medium-frequency induction furnace. After the liquid aluminum melt in the induction furnace completely submerged the added aluminum chips, the medium-frequency furnace was restarted to begin the melting process. When the materials in the furnace were completely melted and the melt temperature rose to 670°C, the medium-frequency furnace was closed again and 500kg of dried aluminum chips were continuously added to the furnace. After the melt in the furnace completely submerged the aluminum chips, the medium-frequency furnace was reopened to melt the materials in the furnace until the aluminum chips were completely melted under the electromagnetic induction stirring and heating of the medium-frequency furnace. The above aluminum chip addition and melting process was repeated until the melt capacity in the medium frequency furnace reached 2 tons. During this melting process, the temperature of the aluminum melt in the furnace was controlled within the range of 680°C to 700°C. After melting, the temperature difference at various locations in the induction furnace was ±20°C. The total burn-off loss of aluminum chips during this melting process was measured to be 2.3%.

[0023] The aluminum melt in the induction furnace is heated to 740°C and poured into a preheated, insulated crucible. A graphite rotor degassing device is used to refine the aluminum melt in the crucible. At 720°C, the crucible undergoes a primary refining process using 12 kg of Perico granular refining agent for 25 minutes. After refining, the crucible is raked to remove all surface slag. The crucible is then tilted and filtered through a 30-mesh plate filter before slowly flowing into a 15-ton industrial melting furnace. During this stage, the aluminum chips gradually submerge the surface of the machined scrap and aluminum products already in the furnace. The furnace's regenerative burner is then activated, introducing flames to melt the semi-solid aluminum melt. The heating from the aluminum chips and flames accelerates the melting of the machined scrap and aluminum products. After the solid material in the smelting furnace is completely melted into liquid form, the electromagnetic stirrer at the bottom of the furnace is turned on to homogenize the melt composition and maintain the melt temperature within the range of 690℃~700℃. The aluminum chips melt that has been refined and filtered is then transferred to the smelting furnace again, and the electromagnetic stirrer is turned on to homogenize the melt in the furnace. This process is repeated until all the aluminum chips melt is transferred to the industrial-grade smelting furnace.

[0024] By adding a small amount of aluminum-silicon master alloy ingots and pure magnesium ingots, the melt in the smelting furnace was adjusted to an alloy composition by weight of: Si 0.85%; Fe: 0.19%; Mg: 0.92%; Cu: 0.24%; Mn: 0.11%; Zn: 0.05%; Cr: 0.12%; V: 0.12%; the remaining elements being Al. The melt temperature range during the smelting process was 730°C to 740°C, and the temperature gradient within the furnace was ±16°C. In order to improve the purity of the melt in the furnace and remove oxide inclusions, the furnace melt is refined by a graphite rotor refining equipment. The melt temperature during the refining operation is 710°C. A granular environmentally friendly refining agent is selected and sent to the bottom of the melt by the graphite rotor refining equipment. During the continuous rotation of the rotor, the refining agent is dispersed in the entire furnace melt by the melt flow, and is heated and liquefied by the melt temperature during the floating process to form droplets, which serves the purpose of adsorbing particulate impurities in the melt and purifying the melt. The entire refining process lasts for 20 minutes. Since the rotation of the graphite rotor drives the melt in the furnace to form a periodic flow, the entire furnace melt is refined and purified. After the refining is completed, the liquid slag measurement method is used to detect the residual inclusion content in the melt, which is 0.27mm 2 / Kg, the number of oxide films detected by V-shaped solidification specimen fracture is 1.

[0025] After the refining of the melt in the smelting furnace is completed, all the melt in the furnace is transferred to a static furnace. After the melt is statically treated for 45 minutes according to the standard process flow, it is degassed using a dual-rotor online degassing device and a 30-mesh + 50-mesh plate filter. After completion, the casting plate is continuously lubricated with oil and gas to prepare cast rods with a diameter of Ф178mm. Figure 2 The following is a photo of the cast rod and its microstructure. The micro grain size is level 1 and the thickness of the segregation layer of the cast rod product is 0.5 mm.

[0026] The cut short ingots are extruded into φ50mmX2.2mm seamless pipes at 480℃ by reverse extrusion. After two pipe drawing passes, the process specification is φ50mmX2.0mm pipes. Figure 2 The microscopic grain morphology of the tube along the cross-section perpendicular to the extrusion direction (cross section) and the longitudinal section along the extrusion direction is shown. The internal grains of the tube are fully recrystallized, with an average grain size of 60 μm. The tensile strength of the tube in the F state was 189 MPa, the yield strength was 98 MPa, and the elongation was 26%. The weldability of the tube was tested using MIG welding. The tensile strength at the weld was 160 MPa, 84% of the parent material strength, and the micropore size was 30-40 μm, meeting the weldability requirements. After solution treatment at 540°C for 1.5 hours and aging at 180°C for 5 hours, the mechanical properties of the tube are shown in Table 1. The average tensile strength was 329 MPa, the average yield strength was 294 MPa, and the average elongation was 15%, meeting the performance requirements for vehicle frame tubing, with high yield strength and good elongation.

[0027] Table 1 Mechanical properties of frame tubes

[0028] Example

[0029] 10 tons of aluminum chip briquettes, 6 tons of machined scraps, 8 tons of recycled architectural aluminum formwork, and a small amount of metal aluminum ingots and alloy ingots totaling 25 tons were selected as raw materials to prepare frame aluminum tubes, and the alloy composition range of the tubes was made to meet the following requirements: Si: 0.6-1.3%; Fe: 0.1-0.3%; Mg: 0.8-1.5%; Cu: 0.1-0.3%; Mn: 0.07-0.15%; Zn: ≤0.08%; Cr: 0.05-0.3%; V: 0.05-0.20%.

[0030] First, 150 kg of scrap was melted in a 2-ton medium-frequency induction furnace. Simultaneously, 5.8 tons of machined scrap and architectural aluminum formwork were melted in a 25-ton gas-fired furnace. The induction furnace was powered on. Once the scrap had completely melted and the melt temperature reached 680°C, the furnace was turned off. Approximately 200 kg of preheated, dried aluminum chips were slowly added to the furnace. Once the molten aluminum partially submerged the briquettes, the furnace was turned on again to restart the melting process. Once the added aluminum chips had completely melted and the melt temperature had risen to 685°C, the furnace was turned off again. The addition of briquettes and the immersion of the chips in the molten aluminum were repeated. Once the molten aluminum had submerged the chips, the induction furnace was restarted. This process was repeated until the molten aluminum reached 2 tons and was completely melted.

[0031] Two tons of molten aluminum from the induction furnace were poured into a preheated, insulated crucible. When the crucible's temperature reached 720°C, a rotor-type degassing device was used to refine and degas the molten aluminum. 10 kg of Perico granular refining flux was added, and the refining process lasted 25 minutes. After refining, the molten aluminum was allowed to stand for 15 minutes, and all surface slag was removed. The molten aluminum was then filtered through a 30-mesh plate filter using a tilting mechanism. The molten aluminum was then continuously transferred to a 25-ton gas-fired melting furnace, which had been filled with machined scraps and template material at the bottom. As the molten aluminum from the insulated crucible was introduced, the molten aluminum gradually submerged the solid material surface. The gas burner was then turned on, and the solid aluminum material began to melt.

[0032] During the melting of lump aluminum raw materials in a 25-ton gas-fired furnace, the process of adding aluminum chips and smelting them in a 2-ton induction furnace is repeated. The smelted aluminum melt is then repeatedly introduced into a crucible, refined, filtered, and continuously introduced into the 25-ton gas-fired furnace. After the 10-ton aluminum chips are completely melted and the filtered aluminum chips melt is fully introduced into the gas-fired furnace, the aluminum chips melt and the lump material melt are mixed in the furnace. Under the action of electromagnetic stirring at the furnace bottom, the chemical composition and temperature of the melt in the entire 25-ton gas-fired furnace gradually converge to a uniform temperature. The temperature difference of the melt in the furnace is within ±15°C.

[0033] A small amount of aluminum-silicon master alloy and commercially pure magnesium ingots were added to a gas-fired smelting furnace to create an alloy melt with the following composition: Si 0.91%, Fe 0.23%, Mg 0.89%, Cu 0.21%, Mn 0.09%, Cr 0.11%, V 0.09%, and Zn 0.05%, with Al as the remaining element. After the composition was adjusted, the melt temperature was raised to 710°C. The melt was then automatically refined and purified using a granular refining agent and an in-furnace graphite rotor refining device to remove oxides and inclusions.

[0034] The graphite rotor-type refining equipment in the furnace continuously injects granular refining agents into the bottom of the melt with a temperature range of 720~730℃. Under the continuous rotation of the rotor, the refining agent reacts with the high-temperature melt and quickly liquefies. Under the forced flow of the melt, it is gradually dispersed throughout the melt in the furnace. As the refining agent floats up, it reacts with the entire melt in the furnace and achieves the refining and purification of the entire melt in the furnace. Compared with traditional straight tube refining, the use of rotor-type refining equipment can disperse the refining agent more evenly throughout the melt, avoiding the phenomenon of tube-type direct blowing refining and insufficient refining of the melt in the furnace, and has better refining and purification effects. After 25 minutes of refining treatment, the residual inclusion content in the melt was detected by a slag meter and was 0.22mm 2 / Kg, the number of oxide films detected by V-type solidification sample fracture is 0.

[0035] The refined aluminum melt was transferred to a tilting static furnace and allowed to stand at 720°C for 30 minutes to allow fine particles and oxide inclusions in the melt to float and sink. After the static period, the melt was degassed in a dual-rotor degassing box and filtered through a 40-mesh + 50-mesh plate filter. The hydrogen content of the melt after treatment was 0.13 ml / 100 g. Cast rods with a diameter of 127 mm were produced using 56 horizontal oil-air lubricated casting plates at a casting temperature of 690-710°C. Analysis of the cast rods revealed a microscopic grain size of Class 1 and a segregation layer thickness of 0.3 mm.

[0036] After the cast rod is homogenized at 460℃ for 12h, the homogenized aluminum ingot is extruded into φ50mm´2.1mm seamless pipes by reverse extrusion. Figure 3 The micro grains in the vertical extrusion direction (cross section) and along the extrusion direction (longitudinal section) after the pipe is extruded are uniform and fine, with no residual micro linear or granular inclusions. The internal grain structure of the pipe is completely recrystallized grains with an average grain size of 50μm. The tensile strength of the pipe in the F state after extrusion is 172MPa, the yield strength is 88MPa, and the elongation is 27%. The welding performance of the pipe is tested by MIG welding. Figure 5 The weld microstructure and micropore morphology show that the weld tensile strength is 138 MPa, reaching 80% of the parent material strength, and the micropore size is 20-30 μm, meeting the welding performance requirements. After solution treatment at 540°C for 1.5 hours and aging at 180°C for 5 hours, the tensile strength of the three selected pipes is shown in Table 2. The average tensile strength is 328 MPa, the average yield strength is 294 MPa, and the average elongation is 15%, meeting the mechanical performance requirements for vehicle frame pipes.

[0037] Table 2 Mechanical properties of frame tubes

[0038]

Claims

1. A method for preparing bicycle frame pipes using raw materials containing more than 40% aluminum chips, characterized in that: The following steps are involved: (1) Aluminum alloy waste, scraps generated in the aluminum processing process and aluminum alloy products in use are selected as raw materials, with the composition and mass percentage being: 40% to 60% of 6××× aluminum alloy chips, 20% to 30% of machining waste or recycled aluminum products, and the balance being 10% to 20% of pure aluminum ingots and intermediate alloy ingots, to be configured into an aluminum alloy, with the type and mass percentage of each element being: Si: 0.6-1.3%; Fe: 0.1-0.3%; Mg: 0.8-1.5%; Cu: 0.1-0.3%; Mn: 0.07-0.25%; Zn: ≤0.08%; Cr: 0.05-0.3%; V: 0.05-0.20%; the balance is Al, and the remaining elements are considered impurities and their content is less than 0.1%; (2) Induction furnace melting aluminum chips: Aluminum chips are melted in an induction furnace. The aluminum chips are immersed in the melt by adding materials, and then aluminum chips are added to the melt again. The aluminum chips are immersed in the melt again to control the melting process and the burning of the aluminum chips. The aluminum chip melt is transferred to a crucible furnace, and after refining and filtering, it is continuously injected into an industrial gas melting furnace and mixed with the melt in the melting furnace; (3) Melting of bulk aluminum raw materials in industrial gas furnaces: Using gas furnaces to melt bulk aluminum raw materials, including metal aluminum ingots and alloy ingots, machining waste, and recycled bulk aluminum products, after melting to semi-solid state, aluminum chips melt is continuously injected into the melting furnace, and the aluminum chips melt is immersed in the semi-solid aluminum material until the raw materials in the furnace are completely mixed and melted; after melting, the melt in the furnace is refined in the furnace using a granular refining agent in a graphite rotor refining equipment, and then prepared into extruded cast rods after online degassing and filtration; (4) Reverse extrusion seamless pipe: The ingot is extruded into a seamless pipe with a wall thickness ranging from 1.5 mm to 3.5 mm by reverse extrusion.

2. The method for preparing bicycle frame pipes using raw materials containing more than 40% aluminum chips according to claim 1, characterized in that: In step (2), during the smelting process of adding aluminum chips, the aluminum chips need to be added to the melt that has already melted in the induction furnace. After the aluminum melt in the furnace completely immerses the aluminum chips, the smelting process is started again. The aluminum chips are added repeatedly and smelted repeatedly until the aluminum chips are completely melted into the melt. During the aluminum chip smelting process, the aluminum chip burn loss is no more than 3%.

3. The method for preparing bicycle frame pipes using raw materials containing aluminum chips greater than 40% according to claim 1, characterized in that: In step (3), the aluminum chip melt and the aluminum block melt are mixed in the smelting furnace. After the melt purification treatment is completed, the total inclusion content is ≤0.35mm 2 / Kg, the number of oxide films on the fracture surface is ≤3.

4. The method for preparing bicycle frame pipes using raw materials containing aluminum chips greater than 40% according to claim 1, characterized in that: In step (4), the microscopic grains along the extrusion direction and the vertical extrusion direction are all recrystallized grains with a grain size of ≤90 μm. After heat treatment of the pipe, the tensile strength is ≥300 MPa, the yield strength is ≥250 MPa, the elongation is ≥13%, and the microscopic pores at the weld are ≤60 μm.

Images