Aluminum alloy cast bar production process based on microduct production

Abstract

The present application relates to the technical field of aluminum alloy cast bar production, and particularly relates to an aluminum alloy cast bar production process based on micro-tube production, which solves the problem of simple refining process of molten aluminum in the prior art, reduces the plasticity and uniformity of the subsequent formed cast bar, and through the refining link, a composite refining system containing nano-Al2O3, carbon nanotubes and nano-TiB2 is innovatively adopted, combined with ultrasonic assisted slagging, nucleation is strengthened; during casting, three-stage composite cooling and titanium boron wire grain refinement are used to control the grain size to 50-100 mu m, significantly improve the uniformity; scientific homogenization treatment releases residual stress, improves the elongation of the cast bar and improves its subsequent plasticity; the cast bar is adapted to the high-precision extrusion demand of the micro-tube, is significantly superior to the traditional process, provides reliable blank for the stable production of high-precision micro-tube, and has extremely strong industrial application value.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy casting rod production technology, and in particular to an aluminum alloy casting rod production process based on microtubes. Background Technology

[0002] Microchannel 3-series aluminum alloy, also known as microchannel 3-series aluminum alloy flat tube, refers to a flat tube made of 3-series aluminum alloy through an extrusion process, containing multiple tiny parallel channels inside, and is often used in high-efficiency heat exchange systems.

[0003] Chinese patent CN119592853A discloses a rare earth microalloyed aluminum alloy casting rod and its production process. During production, filtration, refining and electromagnetic treatment operations are combined. The ceramic filter plate filters out coarse inclusions, the controlled argon blowing conditions further purify the aluminum alloy melt, and the magnetic induction conditions are changed to promote nucleation and improve the nucleation rate.

[0004] Regarding the above-mentioned and existing related technologies, the inventors believe that the following defects often exist: the process only uses a single traditional refining agent composed of ZnCl2 and MgCl2 for refining, which has a limited effect on strengthening and purifying the nucleation in the aluminum melt. It is not easy to reduce the content of tiny impurities and gases in the aluminum melt. At the same time, the single refining operation and conventional slag removal operation make it difficult to completely separate small inclusions, which reduces the uniformity of the microstructure of the finished product in subsequent processes and makes it difficult to meet the high precision requirements of subsequent microtube extrusion processing. Therefore, there is room for improvement. Summary of the Invention

[0005] The technical problem to be solved by this invention is that the aluminum liquid refining process in the prior art is simple, which reduces the plasticity and uniformity of the subsequent forming of the cast rod. To this end, we propose an aluminum alloy casting rod production process based on micro-tube production.

[0006] To achieve the above objectives, this application adopts the following technical solution: an aluminum alloy casting rod production process based on microtubes, comprising the following steps: S1: Select 99.80% aluminum ingots as the base material, and combine them with Si7 master alloy, Mn10 master alloy and auxiliary materials to remove oxide scale and oil stains from the surface of all raw materials to obtain pretreated mixed raw materials. S2: The pretreated mixed raw materials are put into the furnace, the furnace temperature is controlled at 720-750℃, and electromagnetic stirring is started to melt them to obtain the initial aluminum liquid. S3: Raise the initial aluminum liquid temperature to 755-760℃, add sodium-free refining agent containing nano-Al2O3 particles into the furnace, refining for 15-20 minutes, refining bubble height ≤150mm, complete the first stage of refining, transfer the aluminum liquid to the holding furnace, control the furnace temperature to 734-745℃, add modified refining agent containing carbon nanotubes and nano-TiB2, refining for 20-25 minutes and simultaneously remove slag; S4: The refined aluminum liquid is fed into a multi-bladed rotor degassing device. The rotor speed is controlled at 330-450 rpm and the argon flow rate is 110-310 L / min for online degassing. The height of the degassing bubbles is ≤20 mm and the online degassing time is 25-35 min. The degassed aluminum liquid is then fed into a 40 PPI plate filter and deep bed filter system to intercept non-metallic inclusions and obtain refined and purified aluminum liquid. S5: The refined and purified aluminum liquid is fed into a high-precision wire feeder. Titanium boron wire is added online at a wire feeding speed of 416-460cm / min to refine the grains. The refined aluminum liquid is then introduced into a continuous casting equipment to obtain a casting rod. The finished product is sampled and tested at low magnification, and unqualified products are initially screened. S6: Put the qualified casting rod into the homogenization heat treatment furnace, heat it to 595-605℃ and hold it for 600-720 minutes. After the holding time, first air cool for 120 minutes, then water cool for 30-40 minutes, and finally blow water for 5 minutes to ensure that the elongation of the casting rod is ≥25% and obtain the homogenized casting rod. S7: The homogenized casting rod is fed into a precision saw with a water washing function and sawed according to the subsequent aluminum alloy micro-tube extrusion requirements, leaving a 5% length allowance, to obtain the sawn casting rod billet.

[0007] Preferably, the weight fraction of the raw material components in S1 is 0.04-0.10% Si, 0.17-0.23% Fe, Cu≤0.01%, 0.34-0.40% Mn, 0.01-0.02% Cr, Ni≤0.01%, Zn≤0.01%, 0.01-0.03% Ti, V≤0.01%, with the remainder being Al and unavoidable impurities, the content of a single impurity ≤0.03%, and the total impurity content ≤0.15%.

[0008] Preferably, during the loading of raw materials into the furnace in S2, argon gas protection is used to prevent impurities from being mixed in. The argon gas purity is ≥99.99%, the argon gas flow rate is 18-22 L / min, and electromagnetic stirring is performed twice, with each stirring lasting 20-30 minutes. After stirring, the mixture is allowed to stand for 8-10 minutes before subsequent heating operations are performed.

[0009] Preferably, the sodium-free refining agent in S3 comprises: 40-50% KCl, 25-35% NaCl, 10-15% Na3AlF6, 5-8% CaF2, and 2-4% MgCl2, and 1-2% nano Al2O3 particles are added as nucleating agents. The nano Al2O3 particles have a particle size of 50-100 nm, a purity of ≥99.9%, and are dried at 120-150℃ for 2 hours to remove moisture before being added.

[0010] Preferably, the nano-modifying refining agent in S3 is based on a traditional refining agent with the addition of 0.5-1.0% carbon nanotubes and 1.0-2.0% nano-TiB2 particles. The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20-50 nm and a length of 1-5 μm. The nano-TiB2 particles have a particle size of 80-150 nm. Both are surface-modified. The modifier is a silane coupling agent KH550, and the addition amount is 0.3-0.5% of the total mass of carbon nanotubes and nano-TiB2.

[0011] Preferably, in step S3, the slag removal utilizes ultrasonic-assisted slag removal technology. The ultrasonic generator frequency is 20-40kHz, the ultrasonic probe is inserted into the molten aluminum to a depth of 100-150mm, a graphite slag removal spoon is used, the slag removal temperature is 755-760℃, the slag removal time for each batch is 8-10min, the surface temperature fluctuation of the molten aluminum is controlled to be ≤5℃ during the slag removal process, and there is no visible slag on the surface of the molten aluminum after slag removal.

[0012] Preferably, after online degassing in step S4, the hydrogen content in the molten aluminum is controlled at ≤0.12mL / 100gAl, and the degassing efficiency is ≥90%; the hydrogen content in the molten aluminum is monitored in real time using a hydrogen content detector, the degassing time is 25-35min, and the settling time is 25-35min.

[0013] Preferably, after the S5 grain refinement, the grain size of the cast rod formed by the solidification of aluminum liquid is controlled at 50-100μm, and the grain uniformity is ≥90%; the grain size is detected by metallographic microscope, and samples are taken according to the casting batch, with no less than 3 detection areas, and the detection area of ​​each area is ≥0.5mm². The product is qualified if there are no obvious coarse grain areas.

[0014] Preferably, in step S5, the casting temperature is controlled at 735-740℃, the front end temperature of the round bar casting is 700-715℃, the casting speed is 110-114mm / min, the cooling water volume is 210-230m³ / h, the cooling water temperature is 20-30℃, and a three-stage composite cooling method of air cooling, water cooling and mist cooling is adopted, wherein the air speed in the air cooling section is 4-6m / s, the water pressure in the water cooling section is 0.4-0.6MPa, and the droplet size in the mist cooling section is 10-20μm.

[0015] Preferably, during the S7 sawing process, the water washing temperature is controlled at 80-95℃, and a vacuum dust collection system is used to remove aluminum chips and dust. The perpendicularity error of the sawed end face is ≤0.015mm, the surface roughness Ra of the outer circle of the sawn casting billet is ≤0.8μm, the end face is free of burrs and chipping defects, the burr height is ≤0.02mm, the billet is stored in a dry and ventilated environment, the storage temperature is controlled at 15-30℃, the relative humidity is ≤60%, and a moisture-proof film is used to wrap the billet separately during storage to avoid surface oxidation. The billet is stored according to casting batch and is traceable throughout the process.

[0016] The technical effects and advantages of this invention are as follows: In this invention, 99.80% high-purity aluminum ingots are selected as raw materials, with strict control over the proportions of elements such as Si and Mn and the content of impurities. Combined with surface pretreatment, the purity of the material is ensured from the source. During the melting stage, high-purity argon gas is used for protection, along with electromagnetic stirring, to ensure uniform aluminum liquid composition. In the refining stage, an innovative composite refining system containing nano-Al2O3, carbon nanotubes, and nano-TiB2 is adopted, combined with ultrasonic-assisted slag removal to enhance nucleation. During casting, three-stage composite cooling and titanium-boron wire grain refinement control the grain size to 50-100μm, significantly improving uniformity. Scientific homogenization releases residual stress, increases the elongation of the cast rod, and enhances its subsequent plasticity. A multi-wing rotor degassing and dual filtration system effectively reduce hydrogen content and inclusions. Precision cutting and standardized storage ensure appearance accuracy and stability, making the cast rod suitable for the high-precision extrusion requirements of microtubes. This is significantly superior to traditional processes, providing reliable billets for the stable production of high-precision microtubes and possessing strong industrial application value. Attached Figure Description

[0017] The disclosure of this invention is illustrated with reference to the accompanying drawings. It should be understood that the drawings are for illustrative purposes only and are not intended to limit the scope of protection of this invention. In the drawings, the same reference numerals are used to refer to the same parts: Figure 1 This is a flowchart illustrating the overall steps of the present invention; Figure 2 This is a flowchart illustrating the preparation process of the aluminum alloy casting rod of the present invention. Detailed Implementation

[0018] It is readily understood that, based on the technical solution of this invention, those skilled in the art can propose various interchangeable structural methods and implementations without altering the essential spirit of the invention. Therefore, the following detailed embodiments and accompanying drawings are merely illustrative examples of the technical solution of this invention and should not be considered as the entirety of the invention or as limitations or restrictions on the technical solution of this invention.

[0019] Example 1 Reference Figure 1 and Figure 2The production process of aluminum alloy casting rods based on microtubes includes the following steps: S1. Raw material pretreatment: 99.80% aluminum ingots were selected as the base material, combined with Si7 master alloy, Mn10 master alloy and auxiliary materials, and the total raw material preparation amount was controlled to be 29,000 kg; the raw material composition by weight fraction was: 0.07% Si, 0.20% Fe, 0.008% Cu, 0.37% Mn, 0.015% Cr, 0.006% Ni, 0.005% Zn, 0.02% Ti, 0.007% V, with the remainder being Al and unavoidable impurities. The content of a single impurity was ≤0.025%, and the total impurity content was ≤0.12%. Mechanical grinding combined with organic solvent cleaning was used to remove all oxide scale and oil stains from the surface of the raw materials to obtain the pretreated mixed raw materials; S2. Melting treatment: The pretreated mixed raw materials are put into the furnace. During the feeding process, 99.99% pure argon gas is introduced for protection at a flow rate of 20L / min. The furnace temperature is controlled at 735℃. The electromagnetic stirring is started twice, with each stirring lasting 25 minutes. After stirring, the mixture is allowed to stand for 9 minutes to obtain the initial aluminum liquid. S3. Refining Process: The initial molten aluminum is heated to 758℃, and a sodium-free refining agent containing nano-Al2O3 particles is added. The agent's composition is 45% KCl, 30% NaCl, 12% Na3AlF6, 6% CaF2, 3% MgCl2, and 4% nano-Al2O3 particles. The nano-Al2O3 particles have a diameter of 80nm and a purity of 99.9%. The aluminum was dried at 135℃ for 2 hours before addition. The refining time is 18 minutes, and the refining bubble height is 130mm, completing the first stage of refining. The molten aluminum is then transferred to a settling furnace, and the furnace temperature is controlled at 740℃. A nano-modified refining agent is then added. Based on traditional refining agents, 0.8% multi-walled carbon nanotubes and 1.5% nano-TiB2 particles were added. The carbon nanotubes had a diameter of 35nm and a length of 3μm, and the nano-TiB2 particles had a diameter of 120nm. Both were surface-modified with 0.4% silane coupling agent KH550. The refining time was 22 minutes, and slag was removed simultaneously. Slag removal was carried out using ultrasonic-assisted technology with an ultrasonic generator frequency of 30kHz and a probe inserted into the molten aluminum to a depth of 120mm. A graphite slag removal spoon was used, and the slag removal temperature was 758℃ for 9 minutes. The surface temperature fluctuation of the molten aluminum was controlled to be ≤3℃. After slag removal, there was no visible slag on the surface of the molten aluminum. S4. Degassing and Filtration: The refined aluminum liquid is passed into a multi-bladed rotor degassing device, with the rotor speed controlled at 390 rpm and the argon flow rate at 210 L / min. The online degassing time is 30 min, followed by 30 min of settling. The hydrogen content of the aluminum liquid is monitored in real time using a hydrogen content detector. The hydrogen content in the aluminum liquid is controlled at ≤0.12 mL / 100 gAl, and the degassing efficiency is ≥90%. The degassed aluminum liquid is then passed sequentially into a 40 PPI plate filter system and a deep bed filter system to intercept non-metallic inclusions, resulting in refined and purified aluminum liquid. S5. Grain Refinement and Casting: The refined and purified molten aluminum is fed into a high-precision wire feeder, and titanium boron wire is added online at a feeding speed of 438 cm / min to refine the grains. The refined molten aluminum is then introduced into a continuous casting equipment, with the casting temperature controlled at 737℃, the front-end temperature of the round bar casting at 708℃, the casting speed at 112 mm / min, and the cooling water volume at 220 m³ / min. 3 The cooling water temperature is 25℃, employing a three-stage composite cooling method. The air-cooling section has a wind speed of 5 m / s, the water-cooling section has a water pressure of 0.5 MPa, and the mist-cooling section has a droplet size of 15 μm. After casting, the cast rods are sampled and inspected at low magnification to screen out qualified rods. The grain size of the cast rods formed by the solidification of aluminum melt is controlled between 50-100 μm, with a grain uniformity ≥90%. The grain size is inspected using a metallographic microscope, with sampling taken from each casting, and at least three inspection areas, each with an area ≥0.5 mm². 2 The absence of obvious coarse grain areas indicates a qualified product. S6. Homogenization treatment: Put the qualified casting rod into the homogenization heat treatment furnace, heat it to 600℃ and hold it for 660 min. After the holding period, first air cool for 120 min, then water cool for 35 min, and finally blow water for 5 min. After tensile test, the casting rod elongation rate is ≥25%, and the qualified casting rod is obtained. S7. Precision Cutting and Storage: The homogenized casting rods are fed into a precision saw with a water washing function. A 5% length allowance is reserved according to the subsequent micro-tube extrusion requirements. During the sawing process, the water washing temperature is controlled at 88℃, and the vacuum dust collection system is turned on to remove aluminum chips and dust. The surface roughness Ra of the sawn casting rod billet is Ra≤0.8μm, and there are no burrs or chipping defects on the end face. The burr height is ≤0.02mm. The billet is stored in a dry and ventilated environment with the storage temperature controlled at 15-30℃ and the relative humidity ≤60%. During the storage process, it is wrapped with a moisture-proof film to avoid surface oxidation. The billet is stored in a classified stack according to the casting batch and is traceable throughout the process.

[0020] Example 2 Reference Figure 1 and Figure 2 The production process of aluminum alloy casting rods based on microtubes includes the following steps: S1. Raw material pretreatment: 99.80% aluminum ingots were selected as the base material, combined with Si7 master alloy, Mn10 master alloy and auxiliary materials, and the total raw material preparation amount was controlled to be 29,000 kg; the raw material composition by weight fraction was: 0.05% Si, 0.20% Fe, 0.008% Cu, 0.35% Mn, 0.015% Cr, 0.006% Ni, 0.005% Zn, 0.015% Ti, 0.007% V, with the remainder being Al and unavoidable impurities. The content of a single impurity was ≤0.025%, and the total impurity content was ≤0.12%. Mechanical grinding combined with organic solvent cleaning was used to remove all oxide scale and oil stains from the surface of the raw materials to obtain the pretreated mixed raw materials; S2. Melting treatment: The pretreated mixed raw materials are put into the furnace. During the feeding process, 99.99% pure argon gas is introduced for protection at a flow rate of 20L / min. The furnace temperature is controlled at 735℃. The electromagnetic stirring is started twice, with each stirring lasting 25 minutes. After stirring, the mixture is allowed to stand for 9 minutes to obtain the initial aluminum liquid. S3. Secondary Refining Process: The initial molten aluminum is heated to 756℃, and a sodium-free refining agent containing nano-Al2O3 particles is added. The agent's composition is 45% KCl, 30% NaCl, 12% Na3AlF6, 6% CaF2, 3% MgCl2, and 4% nano-Al2O3 particles. The nano-Al2O3 particles have a diameter of 60nm and a purity of 99.9%. The aluminum was dried at 135℃ for 2 hours before addition. The refining time is 16 minutes, and the refining bubble height is 130mm, completing the primary refining. The molten aluminum is then transferred to a settling furnace, and the furnace temperature is controlled at 740℃. A nano-modified refining agent is then added. The process involves adding 0.8% multi-walled carbon nanotubes and 1.5% nano-TiB2 particles to the traditional refining agent. The carbon nanotubes have a diameter of 20 nm and a length of 3 μm, while the nano-TiB2 particles have a diameter of 80 nm. Both are surface-modified with 0.4% silane coupling agent KH550. The refining time is 22 min, and slag is removed simultaneously. The slag removal is performed using ultrasonic-assisted technology with an ultrasonic generator frequency of 30 kHz and a probe inserted into the molten aluminum to a depth of 120 mm. A graphite slag removal spoon is used, and the slag removal temperature is 758℃ for 9 min. The surface temperature fluctuation of the molten aluminum is controlled to be ≤3℃. After slag removal, there is no visible slag on the surface of the molten aluminum. S4. Degassing and Filtration: The refined aluminum liquid is passed into a multi-bladed rotor degassing device, with the rotor speed controlled at 390 rpm and the argon flow rate at 210 L / min. The online degassing time is 30 min, followed by 30 min of settling. The hydrogen content of the aluminum liquid is monitored in real time using a hydrogen content detector. The hydrogen content in the aluminum liquid is controlled at ≤0.12 mL / 100 gAl, and the degassing efficiency is ≥90%. The degassed aluminum liquid is then passed sequentially into a 40 PPI plate filter system and a deep bed filter system to intercept non-metallic inclusions, resulting in refined and purified aluminum liquid. S5. Grain Refinement and Casting: The refined and purified molten aluminum is fed into a high-precision wire feeder, and titanium boron wire is added online at a feeding speed of 438 cm / min to refine the grains. The refined molten aluminum is then introduced into a continuous casting equipment, with the casting temperature controlled at 737℃, the front-end temperature of the round bar casting at 708℃, the casting speed at 112 mm / min, and the cooling water volume at 220 m³ / min. 3 The cooling water temperature is 25℃, employing a three-stage composite cooling method. The air-cooling section has a wind speed of 5 m / s, the water-cooling section has a water pressure of 0.5 MPa, and the mist-cooling section has a droplet size of 15 μm. After casting, the cast rods are sampled and inspected at low magnification to screen out qualified rods. The grain size of the cast rods formed by the solidification of aluminum melt is controlled between 50-100 μm, with a grain uniformity ≥90%. The grain size is inspected using a metallographic microscope, with sampling taken from each casting, and at least three inspection areas, each with an area ≥0.5 mm². 2 The absence of obvious coarse grain areas indicates a qualified product. S6. Homogenization treatment: Put the qualified casting rod into the homogenization heat treatment furnace, heat it to 598℃ and hold it for 630 minutes. After the holding period, first air cool for 120 minutes, then water cool for 32 minutes, and finally blow water for 5 minutes. After tensile testing, the casting rod elongation rate is ≥25%, and the qualified casting rod is obtained. S7. Precision Cutting and Storage: The homogenized casting rods are fed into a precision saw with a water washing function. A 5% length allowance is reserved according to the subsequent micro-tube extrusion requirements. During the sawing process, the water washing temperature is controlled at 88℃, and the vacuum dust collection system is turned on to remove aluminum chips and dust. The surface roughness Ra of the sawn casting rod billet is Ra≤0.8μm, and there are no burrs or chipping defects on the end face. The burr height is ≤0.02mm. The billet is stored in a dry and ventilated environment with the storage temperature controlled at 15-30℃ and the relative humidity ≤60%. During the storage process, it is wrapped with a moisture-proof film to avoid surface oxidation. The billet is stored in a classified stack according to the casting batch and is traceable throughout the process.

[0021] Example 3 Reference Figure 1 and Figure 2 The production process of aluminum alloy casting rods based on microtubes includes the following steps: S1. Raw material pretreatment: 99.80% aluminum ingots were selected as the base material, combined with Si7 master alloy, Mn10 master alloy and auxiliary materials, and the total raw material preparation amount was controlled to be 29,000 kg; the raw material composition by weight fraction was: 0.09% Si, 0.20% Fe, 0.008% Cu, 0.39% Mn, 0.015% Cr, 0.006% Ni, 0.005% Zn, 0.025% Ti, 0.007% V, with the remainder being Al and unavoidable impurities. The content of a single impurity was ≤0.025%, and the total impurity content was ≤0.12%. Mechanical grinding combined with organic solvent cleaning was used to remove all oxide scale and oil stains from the surface of the raw materials to obtain the pretreated mixed raw materials; S2. Melting treatment: The pretreated mixed raw materials are put into the furnace. During the feeding process, 99.99% pure argon gas is introduced for protection at a flow rate of 20L / min. The furnace temperature is controlled at 735℃. The electromagnetic stirring is started twice, with each stirring lasting 25 minutes. After stirring, the mixture is allowed to stand for 9 minutes to obtain the initial aluminum liquid. S3. Secondary Refining Process: The initial molten aluminum is heated to 759℃, and a sodium-free refining agent containing nano-Al2O3 particles is added. The agent's composition is 45% KCl, 30% NaCl, 12% Na3AlF6, 6% CaF2, 3% MgCl2, and 4% nano-Al2O3 particles. The nano-Al2O3 particles have a diameter of 90nm and a purity of 99.9%. The aluminum was dried at 135℃ for 2 hours before addition. The refining time is 19 minutes, and the refining bubble height is 130mm, completing the primary refining. The molten aluminum is then transferred to a settling furnace, and the furnace temperature is controlled at 740℃. A nano-modified refining agent is then added. It adds 0.8% multi-walled carbon nanotubes and 1.5% nano-TiB2 particles to the traditional refining agent; the carbon nanotubes have a diameter of 50nm and a length of 3μm, and the nano-TiB2 particles have a diameter of 150nm. Both are surface modified with 0.4% silane coupling agent KH550. The refining time is 22min and slag is removed simultaneously. The slag removal adopts ultrasonic-assisted technology, with an ultrasonic generator frequency of 30kHz and a probe inserted into the aluminum liquid to a depth of 120mm. A graphite slag removal spoon is used, the slag removal temperature is 758℃, and the time is 9min. The surface temperature fluctuation of the aluminum liquid is controlled to be ≤3℃. After slag removal, there is no visible slag on the surface of the aluminum liquid. S4. Degassing and Filtration: The refined aluminum liquid is passed into a multi-bladed rotor degassing device, with the rotor speed controlled at 390 rpm and the argon flow rate at 210 L / min. The online degassing time is 30 min, followed by 30 min of settling. The hydrogen content of the aluminum liquid is monitored in real time using a hydrogen content detector. The hydrogen content in the aluminum liquid is controlled at ≤0.12 mL / 100 gAl, and the degassing efficiency is ≥90%. The degassed aluminum liquid is then passed sequentially into a 40 PPI plate filter system and a deep bed filter system to intercept non-metallic inclusions, resulting in refined and purified aluminum liquid. S5. Grain Refinement and Casting: The refined and purified molten aluminum is fed into a high-precision wire feeder, and titanium boron wire is added online at a feeding speed of 438 cm / min to refine the grains. The refined molten aluminum is then introduced into a continuous casting equipment, with the casting temperature controlled at 737℃, the front-end temperature of the round bar casting at 708℃, the casting speed at 112 mm / min, and the cooling water volume at 220 m³ / min. 3 The cooling water temperature is 25℃, employing a three-stage composite cooling method. The air-cooling section has a wind speed of 5 m / s, the water-cooling section has a water pressure of 0.5 MPa, and the mist-cooling section has a droplet size of 15 μm. After casting, the cast rods are sampled and inspected at low magnification to screen out qualified rods. The grain size of the cast rods formed by the solidification of aluminum melt is controlled between 50-100 μm, with a grain uniformity ≥90%. The grain size is inspected using a metallographic microscope, with sampling taken from each casting, and at least three inspection areas, each with an area ≥0.5 mm². 2 The absence of obvious coarse grain areas indicates a qualified product. S6. Homogenization treatment: Put the qualified casting rod into the homogenization heat treatment furnace, heat it to 603℃ and hold it for 690 min. After the holding period, first air cool for 120 min, then water cool for 38 min, and finally blow water for 5 min. After tensile test, the casting rod elongation rate is ≥25%, and the qualified casting rod is obtained. S7. Precision Cutting and Storage: The homogenized casting rods are fed into a precision saw with a water washing function. A 5% length allowance is reserved according to the subsequent micro-tube extrusion requirements. During the sawing process, the water washing temperature is controlled at 88℃, and the vacuum dust collection system is turned on to remove aluminum chips and dust. The surface roughness Ra of the sawn casting rod billet is Ra≤0.8μm, and there are no burrs or chipping defects on the end face. The burr height is ≤0.02mm. The billet is stored in a dry and ventilated environment with the storage temperature controlled at 15-30℃ and the relative humidity ≤60%. During the storage process, it is wrapped with a moisture-proof film to avoid surface oxidation. The billet is stored in a classified stack according to the casting batch and is traceable throughout the process.

[0022] The following table compares the core process parameters in Examples 1-3:

[0023] Comparative Example 1: Based on Example 3, S3 was made without adding nano-Al2O3 particles and nano-modifying refining agents.

[0024] Comparative Example 2: Based on Example 3, the homogenization heating temperature in S6 was changed to 580℃ and the holding time was 500min.

[0025] Comparative Example 3: Based on Example 3, the casting cooling method in S5 is water cooling only.

[0026] The following performance tests were performed on Examples 1-3 and Comparative Examples 1-3: Metallurgical microscopy was used to observe three detection areas, each with a detection area ≥ 0.5 mm². 2 Statistical analysis of grain size and uniformity.

[0027] Hydrogen content was measured using a hydrogen content analyzer, and the average value of the three groups of samples was taken.

[0028] Tensile tests were conducted according to the standard GB / T228.1-2010 to measure the elongation.

[0029] The content of inclusions was determined by observing with a metallographic microscope.

[0030] The surface roughness Ra of the outer circle of the cast bar billet was detected by a roughness tester, and the end face perpendicularity error and burr height were detected by a laser diameter gauge.

[0031] Cast rod blanks were used for extrusion of φ3mm×0.3mm micro-tubes. The number of qualified products out of 1000 products was counted. The products were required to be free of cracks and have a wall thickness deviation of ≤0.05mm.

[0032] The performance test results of Examples 1-3 and Comparative Examples 1-3 are compared in the following table:

[0033] As can be seen from the table above, among Examples 1-3, Example 3 has the best data, which can meet the extrusion molding requirements of microtubes and has the highest product qualification rate. The working principle of Example 3 is as follows: using 99.80% aluminum ingots as the base material, after pretreatment according to the appropriate composition ratio of Si 0.09%, Mn 0.39%, and Ti 0.025%, it is melted twice by electromagnetic stirring under argon protection at 735℃ and then allowed to stand. First, it is refined at 759℃ with a sodium-free refining agent containing 90nm nano Al2O3 for 19 minutes to complete the first-stage purification nucleation, and then transferred to a 740℃ settling furnace for further processing. The aluminum melt is refined for 22 minutes with a modified refining agent containing 50nm carbon nanotubes and 150nm nano TiB2. Inclusions are thoroughly removed by slag removal with the assistance of 30kHz ultrasonic waves. The melt is then deeply purified by a 390rpm rotor, online degassing with 210L / min argon gas for 30 minutes, and double filtration. Titanium boron wire is added at a wire feeding speed of 438cm / min to refine the grains. The melt is then cast using a three-stage composite cooling process of air cooling, water cooling, and mist cooling at 737℃. Finally, the melt undergoes homogenization treatment at 603℃ for 690 minutes and water cooling for 38 minutes to release residual stress. The final product is then precisely cut to obtain the cast rod.

[0034] As shown in the table above, Examples 1-3 used a composite refining agent containing nano-Al2O3, carbon nanotubes, and nano-TiB2, combined with titanium boron wire grain refinement, controlling the grain size to 68-82 μm and uniformity ≥91%. Utilizing the complementary particle size distributions of nano-Al2O3, carbon nanotubes, and nano-TiB2, the wettability with molten aluminum was significantly improved after modification, preventing nanoparticle agglomeration and allowing uniform dispersion in the molten aluminum. The titanium boron wire rapidly decomposes in the molten aluminum to generate micron-sized TiB2 particles, forming a multi-level nucleation system of micron and nanometer-sized particles with the nano-TiB2, further improving the density and uniformity of nucleation sites. Simultaneously, Ti element optimizes the solidification kinetics of the molten aluminum, slowing down grain growth. During solidification, the dispersed nanoparticles adsorb at grain boundaries, and the high hardness and stability of the nanoparticles hinder grain boundary migration, further suppressing excessive grain growth and ensuring stable grain size within a small range. In contrast, Comparative Example 1 did not use nano-Al2O3 particles or nano-modified refining agent. The additives increased the grain size to 142 μm, but the uniformity was only 78%, indicating that the nucleation effect of nanoparticles can significantly refine the grains, effectively inhibit grain growth, and promote uniform grain precipitation. The elongation of Examples 1-3 was ≥25.8%, meeting the plasticity requirements for microtube extrusion. However, Comparative Example 2 reduced the homogenization temperature and holding time, resulting in insufficient uniformity of the internal structure of the cast rod and insufficient release of residual stress, with the elongation dropping to 23.5%. Insufficient plasticity made it easy to crack during subsequent processing and extrusion. Examples 1-3 used three-stage composite cooling, which resulted in high grain uniformity and achieved stable cooling during the solidification process of aluminum liquid, effectively avoiding the problem of excessive temperature gradient caused by a single cooling method. In contrast, Comparative Example 3 used single water cooling, which increased the grain size to 126 μm, with a uniformity of 82%, and an extrusion pass rate of only 89.3%. The microtube extrusion pass rate of Examples 1-3 was ≥97.2%, which was much higher than the 82.3%-89.3% of the comparative examples, indicating that the cast rod prepared by the process of this invention can effectively ensure the production quality of subsequent microtubes.

[0035] The technical scope of this invention is not limited to the content described above. Those skilled in the art can make various modifications and variations to the above embodiments without departing from the technical concept of this invention, and all such modifications and variations should fall within the protection scope of this invention.

Claims

1. A process for producing aluminum alloy casting rods based on microtubes, characterized in that, Includes the following steps: S1: Select 99.80% aluminum ingots as the base material, and combine them with Si7 master alloy, Mn10 master alloy and auxiliary materials to remove oxide scale and oil stains from the surface of all raw materials to obtain pretreated mixed raw materials. S2: The pretreated mixed raw materials are put into the furnace, the furnace temperature is controlled at 720-750℃, and electromagnetic stirring is started to melt them to obtain the initial aluminum liquid. S3: Raise the initial aluminum liquid temperature to 755-760℃, add sodium-free refining agent containing nano-Al2O3 particles into the furnace, refining for 15-20 minutes, refining bubble height ≤150mm, complete the first stage of refining, transfer the aluminum liquid to the holding furnace, control the furnace temperature to 734-745℃, add modified refining agent containing carbon nanotubes and nano-TiB2, refining for 20-25 minutes and simultaneously remove slag; S4: The refined aluminum liquid is fed into a multi-bladed rotor degassing device. The rotor speed is controlled at 330-450 rpm and the argon flow rate is 110-310 L / min for online degassing. The height of the degassing bubbles is ≤20 mm and the online degassing time is 25-35 min. The degassed aluminum liquid is then fed into a 40 PPI plate filter and deep bed filter system to intercept non-metallic inclusions and obtain refined and purified aluminum liquid. S5: The refined and purified aluminum liquid is fed into a high-precision wire feeder. Titanium boron wire is added online at a wire feeding speed of 416-460cm / min to refine the grains. The refined aluminum liquid is then introduced into a continuous casting equipment to obtain a casting rod. The finished product is sampled and tested at low magnification, and unqualified products are initially screened. S6: Put the qualified casting rod into the homogenization heat treatment furnace, heat it to 595-605℃ and hold it for 600-720 minutes. After the holding time, first air cool for 120 minutes, then water cool for 30-40 minutes, and finally blow water for 5 minutes to ensure that the elongation of the casting rod is ≥25% and obtain the homogenized casting rod. S7: The homogenized casting rod is fed into a precision saw with a water washing function and sawed according to the subsequent aluminum alloy micro-tube extrusion requirements, leaving a 5% length allowance, to obtain the sawn casting rod billet.

2. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: The raw material components in S1 have the following weight fractions: 0.04-0.10% Si, 0.17-0.23% Fe, Cu≤0.01%, 0.34-0.40% Mn, 0.01-0.02% Cr, Ni≤0.01%, Zn≤0.01%, 0.01-0.03% Ti, V≤0.01%, with the remainder being Al and unavoidable impurities. The content of a single impurity is ≤0.03%, and the total impurity content is ≤0.15%.

3. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: During the loading of the raw materials into the furnace in S2, argon gas protection is used to prevent impurities from being mixed in. The argon gas purity is ≥99.99%, the argon gas flow rate is 18-22 L / min, and electromagnetic stirring is performed twice, with each stirring lasting 20-30 minutes. After stirring, the mixture is allowed to stand for 8-10 minutes before subsequent heating operations are carried out.

4. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: The sodium-free refining agent in S3 comprises: 40-50% KCl, 25-35% NaCl, 10-15% Na3AlF6, 5-8% CaF2, and 2-4% MgCl2, and adds 1-2% nano Al2O3 particles as nucleating agents. The nano Al2O3 particles have a particle size of 50-100nm, a purity of ≥99.9%, and are dried at 120-150℃ for 2 hours to remove moisture before addition.

5. The aluminum alloy casting rod production process based on microtube production as described in claim 1, characterized in that: The nano-modified refining agent in S3 is based on a traditional refining agent with the addition of 0.5-1.0% carbon nanotubes and 1.0-2.0% nano-TiB2 particles. The carbon nanotubes are multi-walled carbon nanotubes with a diameter of 20-50 nm and a length of 1-5 μm. The nano-TiB2 particles have a particle size of 80-150 nm. Both are surface-modified using silane coupling agent KH550, and the amount added is 0.3-0.5% of the total mass of carbon nanotubes and nano-TiB2.

6. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: In step S3, slag removal utilizes ultrasonic-assisted slag removal technology. The ultrasonic generator frequency is 20-40kHz, the ultrasonic probe is inserted into the molten aluminum to a depth of 100-150mm, a graphite slag removal spoon is used, the slag removal temperature is 755-760℃, the slag removal time for each batch is 8-10min, the surface temperature fluctuation of the molten aluminum is controlled to be ≤5℃ during the slag removal process, and there is no visible slag on the surface of the molten aluminum after slag removal.

7. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: After online degassing via S4, the hydrogen content in the molten aluminum is controlled at ≤0.12mL / 100gAl, and the degassing efficiency is ≥90%. The hydrogen content in the molten aluminum is monitored in real time using a hydrogen content detector. The degassing time is 25-35min, and the settling time is 25-35min.

8. The aluminum alloy casting rod production process based on microtube production as described in claim 1, characterized in that: After the S5 grain refinement, the grain size of the cast rod formed by the solidification of aluminum liquid is controlled at 50-100μm, and the grain uniformity is ≥90%. The grain size is detected by metallographic microscope. Sampling is done by casting, and the detection area is no less than 3 places. The detection area of ​​each place is ≥0.5mm². The product is qualified if there is no obvious coarse grain area.

9. The aluminum alloy casting rod production process based on microtubes as described in claim 1, characterized in that: In the S5, the casting temperature is controlled at 735-740℃, the front end temperature of the round bar casting is 700-715℃, the casting speed is 110-114mm / min, the cooling water volume is 210-230m³ / h, the cooling water temperature is 20-30℃, and a three-stage composite cooling method of air cooling, water cooling and mist cooling is adopted. The air cooling section has a wind speed of 4-6m / s, the water cooling section has a water pressure of 0.4-0.6MPa, and the mist cooling section has a droplet size of 10-20μm.

10. The aluminum alloy casting rod production process based on microtube production as described in claim 1, characterized in that: During the S7 sawing process, the water washing temperature is controlled at 80-95℃, and a vacuum dust collection system is used to remove aluminum chips and dust. The perpendicularity error of the sawed end face is ≤0.015mm, the surface roughness Ra of the outer circle of the sawn casting billet is ≤0.8μm, the end face is free of burrs and chipping defects, the burr height is ≤0.02mm, the billet is stored in a dry and ventilated environment, the storage temperature is controlled at 15-30℃, the relative humidity is ≤60%, and a moisture-proof film is used to wrap the billet individually during storage to avoid surface oxidation. The billet is stored according to casting batch and is traceable throughout the process.

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