A process for eliminating aluminum shavings on the surface of continuous extruded aluminum alloy flat tubes

Abstract

The present application relates to the process for eliminating the aluminum scraps on the surface of the continuous extruded aluminum alloy flat tube, by optimizing the aluminum alloy composition: Cu: 0.09-0.12%, Si: 0.03-0.05%, Fe: 0.12-0.17%, Fe: Si >= 3, Ti: 0.006-0.0075%, Ce and La mixed rare earth: 0.045-0.055%, the balance being Al, to improve the aluminum rod casting performance and the uniformity of the structure; at the same time, the refining process of adding rare earth in the furnace and adding aluminum titanium boron wire online is combined, so as to ensure that the porosity of the aluminum rod reaches 1 level. The ultra-high-speed online homogenization heat treatment is adopted, so that the chemical composition of the aluminum rod is homogenized in a very short time, and the intracrystalline segregation is eliminated. While improving the fluidity of the metal, the extrusion process parameters are optimized, the mold cooling process is changed, the extrusion temperature fluctuation is ensured to be in the minimum range, and constant temperature extrusion is realized; and the surface of the flat tube is treated online after the product is formed, and finally the technical purposes of eliminating the aluminum scraps on the surface of the aluminum flat tube and reducing the pressure pit defects are achieved.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy product processing technology, and in particular to a process method for eliminating aluminum chips on the surface of continuously extruded aluminum alloy flat tubes. Background Technology

[0002] The traditional production process for aluminum alloy flat tubes is as follows: raw material aluminum rods (smelted from aluminum ingots or molten aluminum, degassed and slag-removed, and cast and rolled into aluminum rods) → aluminum rod surface cleaning → extrusion die assembly → continuous extrusion → online water cooling → online air drying → tension adjustment → coiling → semi-finished product inspection → air leakage and water leakage inspection → blanking, length setting, finished product inspection, packaging and warehousing. The common alloy formula for aluminum alloy flat tubes is Cu: 0.05-0.15%, Si: 0.08-0.12%, Fe: 0.15-0.20%, with the balance being Al and unavoidable impurities. After simple surface cleaning, the aluminum rods are directly subjected to continuous extrusion. The extrusion process parameters are: extrusion roller surface temperature controlled at 400-420℃, extrusion speed 15-22 rpm, extrusion pressure 30-45MPa, and extrusion current 180-250A. Water cooling is used to control the die temperature, which is maintained at 380-450℃, but stabilizing the die temperature is difficult.

[0003] The existing manufacturing process for flat tubes is prone to quality problems such as aluminum shavings on the surface. Aluminum shavings or particles adhere to the surface of the flat tubes, forming aluminum shaving indentations during subsequent cutting and length processing. These defects account for approximately 30% of the total scrap, severely impacting the yield of finished flat tubes. Furthermore, some flat tubes with aluminum shavings on their surface are easily missed during inspection and end up with customers, leading to customer complaints and quality claims. These aluminum shavings or particles also affect the application of anti-corrosion coatings on the aluminum alloy surface, and the indentations caused by the particles can easily lead to corrosion and leakage, affecting the service life of the flat tubes. Therefore, it is necessary to eliminate aluminum shavings from the surface of aluminum alloy flat tubes during the manufacturing process. Summary of the Invention

[0004] (a) Technical problems to be solved

[0005] In view of the above-mentioned shortcomings and deficiencies of the prior art, the present invention provides a process method for eliminating aluminum chips on the surface of continuously extruded aluminum alloy flat tubes. By optimizing the aluminum alloy formula design and refining the grain size in and out of the furnace, the porosity of the aluminum alloy rod is guaranteed to reach level 1, improving the fluidity of the metal during extrusion and reducing the probability of aluminum chip generation.

[0006] Furthermore, improvements and innovations such as subjecting the aluminum rod to ultra-high temperature and high-speed heat treatment before continuous extrusion, optimizing continuous extrusion parameters and online cooling methods (to achieve near-constant temperature continuous extrusion), and adding a step to remove residual aluminum chips after extrusion molding reduce the amount of aluminum chips adhering to the surface of the aluminum alloy flat tube and the amount of scrap due to indentation defects, thereby improving the yield of aluminum alloy flat tubes.

[0007] (II) Technical Solution

[0008] To achieve the above objectives, the main technical solutions adopted by the present invention include:

[0009] A process for eliminating aluminum chips from the surface of continuously extruded aluminum alloy flat tubes, comprising the following steps:

[0010] S1. The designed aluminum alloy composition is: Cu: 0.09-0.12%, Si: 0.03-0.05%, Fe: 0.12-0.17%, Fe:Si≥3, Ti: 0.006-0.0075%, Ce and La mixed rare earth: 0.045-0.055%, with the balance being Al and unavoidable impurities;

[0011] S2, Cast aluminum alloy rod

[0012] Aluminum material is melted in a smelting furnace. When the temperature drops to 770-790℃, Cu, Fe, and Si alloying materials are added, and the furnace is kept closed to ensure complete melting of the alloys. Then, Ce and La mixed rare earth elements are added, and the mixture is stirred for 10-20 minutes to begin refining, degassing, and slag removal. When the temperature of the molten aluminum drops to 735-760℃, aluminum rods are cast. Before casting the aluminum rods, Al-5Ti-B wire refiner is added to the casting channel to promote grain refinement. The alloy composition of the cast aluminum rods meets the alloy composition design of S1.

[0013] S3, Heat treatment before extrusion

[0014] The aluminum rod is cleaned and then subjected to homogenization heat treatment. The homogenization heat treatment method is: rapid heating, that is, heating at a rate of 195-205℃ / s for 2.5-3.5s, and then cooling to room temperature.

[0015] S4, Continuous extrusion

[0016] The aluminum rod is continuously extruded using an extrusion die assembled according to the flat tube specifications. The process parameters for continuous extrusion are as follows:

[0017] The temperature of the extrusion roller surface is controlled at 400-420℃;

[0018] The extrusion gap between the extrusion roller and the extrusion shoe satisfies: diverging gap = convergent gap + 0.8~1.0mm;

[0019] S5, Online Cooling

[0020] During continuous extrusion, liquid nitrogen is used to control the mold temperature, keeping it at 390℃±10℃ and controlling the mold temperature fluctuation within 3%.

[0021] S6. Remove residual aluminum shavings from the surface of the flat tube.

[0022] After the aluminum alloy flat tube is extruded, the residual aluminum shavings on the surface of the flat tube are removed by air knife blowing technology and scraping technology.

[0023] S7. Perform tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, material cutting, length setting, and obtain finished product.

[0024] According to a preferred embodiment of the present invention, in S1, the total content of Ce and La mixed rare earth elements in the aluminum alloy is 0.05%, and the content of Ce is 0.005%.

[0025] According to a preferred embodiment of the present invention, in step S2, when melting aluminum material in the melting furnace, the process includes: introducing high-temperature electrolytic aluminum molten material at a temperature of 830°C or higher into the melting furnace, and then adding 15% by mass of cold material to the high-temperature electrolytic aluminum molten material to lower the temperature of the aluminum molten material to 770-790°C; wherein the cold material is aluminum ingot at room temperature, recycled aluminum, or aluminum alloy. The addition of cold material and high-temperature electrolytic aluminum molten material for mixing and melting allows the cold material to cool the molten material and refine the grain size of the melt.

[0026] According to a preferred embodiment of the present invention, in S2, when the temperature of the molten aluminum in the smelting furnace drops to 770-790°C, Cu, Fe and Si alloy ingredients are added and the furnace is simmered for 15 minutes. Then Ce and La mixed rare earth are added and stirred for 15 minutes to start refining, degassing and slag removal.

[0027] According to a preferred embodiment of the present invention, in S3, the homogenization heat treatment involves rapidly heating the aluminum rod to above 600°C within 3 seconds using an induction heating furnace. Using an induction heating furnace offers the advantages of rapid heating and uniform heating.

[0028] According to a preferred embodiment of the present invention, in S4, the extrusion roller speed is 17-20 rpm, the extrusion pressure is 50-55 MPa, the extrusion current is 130-150 A, the thickness of the aluminum layer working strip on the extrusion roller surface is 0.20 mm, and the width is 10 mm.

[0029] According to a preferred embodiment of the present invention, in S5, when liquid nitrogen is used to cool the die during the extrusion process, the liquid nitrogen pressure is 0.10-0.15 MPa and the flow rate is 0.8-1.0 m³ / s. 3 / h.

[0030] Further optimization involves using liquid nitrogen to cool the mold, ensuring that the temperature fluctuation of the mold is controlled within 2.5%.

[0031] According to a preferred embodiment of the present invention, in S6, the gap between the air knife nozzle and the surface of the flat tube is 0.3-0.5 mm, and the blowing pressure is 0.4-0.6 MPa; the scraping uses a scraping blade to remove the aluminum shavings remaining on the surface of the flat tube, and the elastic pressure of the scraping blade on the surface of the flat tube is 0.1-0.15 N.

[0032] (III) Beneficial Effects

[0033] The innovative aspects of this invention include:

[0034] (1) The formulation of the new aluminum alloy flat tube was optimized, improving the internal structure of the aluminum rod and facilitating metal extrusion fluidity, thereby fundamentally reducing the generation of aluminum chips from the perspective of formulation design. In the new aluminum alloy formulation, the casting performance of the aluminum rod is improved by controlling the iron-silicon ratio of the main impurity component in the melt to be no less than 3, thereby reducing internal cracks in the billet. Controlling the copper content within a certain range is mainly to ensure that the final strength performance of the product is not reduced after high-temperature homogenization treatment.

[0035] Furthermore, during the aluminum smelting process, adding 15% cold material to the high-temperature electrolytic aluminum molten metal can help cool the metal and refine its grain size.

[0036] (2) When casting aluminum alloy rods, Ce and La mixed rare earth elements are added to the furnace for stirring, refining, degassing, and slag removal; at the same time, Al-5Ti-B wire refiner is added to the flow channel. Therefore, this invention adopts a combination of in-furnace and out-of-furnace online grain refinement, which refines the aluminum alloy rod grains before the continuous extrusion process, ensuring that the porosity of the aluminum alloy rod reaches level 1, improving the fluidity of the metal during extrusion, and reducing the probability of aluminum chips.

[0037] (3) Before the aluminum rod enters continuous extrusion, the aluminum rod is subjected to online homogenization heat treatment. Specifically, an ultra-high speed heating method (about 200℃ / second, heating time is about 3 seconds) is used to heat the aluminum alloy rod to about 610℃ within 3 seconds, thereby achieving homogenization of the internal chemical composition of the aluminum rod and eliminating intracrystalline segregation (the chemical composition of the aluminum rod is homogenized in a very short time, which can eliminate intracrystalline segregation), greatly improving the metal fluidity of the aluminum alloy rod when it is extruded and reducing the probability of aluminum chips.

[0038] (4) During continuous extrusion, the present invention optimizes the extrusion gap parameters and the mold cooling method (liquid nitrogen) to control the temperature fluctuation of the mold and achieve continuous extrusion with near constant temperature, thereby fundamentally eliminating the mechanism of aluminum chip generation and the probability of aluminum chip adhesion (reducing the generation of indentation defects).

[0039] (5) After extrusion molding, an additional process of "air knife blowing + scraping" is added, which basically eliminates the aluminum chip defects remaining on the surface of the aluminum tube, further reduces aluminum chip particles and dent defects on the finished product, and improves the product qualification rate.

[0040] Through the above series of measures, the proportion of scrapped flat tubes with aluminum chip indentation defects on the surface has decreased from over 30% to about 5% of the total scrapped volume; the overall yield of flat tubes has increased by more than 3%; and the user's leak detection rate has been controlled within 1‰, meeting user requirements and improving product competitiveness. Detailed Implementation

[0041] To better explain and facilitate understanding of the present invention, the present invention will be described in detail below with reference to specific embodiments.

[0042] According to the analysis, the reasons for the adhesion of aluminum shavings on the surface of flat tubes include: (1) Currently, ordinary electrical round aluminum rods are used to produce flat tubes. The aluminum rod grain refinement process is not up to standard, the porosity is poor, and it has not undergone homogenization heat treatment. The chemical composition is uneven (there is intracrystalline segregation). It is difficult to directly extrude into aluminum flat tubes. The extrusion process is difficult to control, the mold temperature fluctuates greatly, and there are no subsequent surface treatment measures, resulting in a lot of aluminum shavings on the tube surface and a low yield. (2) Due to the unreasonable chemical composition ratio of the raw material aluminum rod and the unscientific grain refinement process, the porosity of the aluminum rod is greater than level 1. At the same time, the aluminum rod has not undergone homogenization treatment, and its intracrystalline composition is severely segregated. These problems make the fluidity of the metal worse during the extrusion forming process. When the metal is split during extrusion, it is difficult to flow, which easily causes local extrusion temperature rise and large fluctuations, resulting in low product strength and performance, thus producing aluminum shavings.

[0043] To address the low yield caused by excessive aluminum shavings on the surface of aluminum alloy flat tubes produced by existing processes, this invention presents a new aluminum alloy flat tube manufacturing process, with the following steps:

[0044] S1: The designed aluminum alloy composition is: Cu: 0.09-0.12%, Si: 0.03-0.05%, Fe: 0.12-0.17%, Fe:Si≥3, Ti: 0.006-0.0075%, Ce and La mixed rare earth: 0.045-0.055%, with the balance being Al and unavoidable impurities;

[0045] S2: Cast aluminum alloy rod

[0046] Aluminum material is melted in a smelting furnace. When the temperature drops to 770-790℃, Cu, Fe, and Si alloying materials are added, and the furnace is simmered to ensure complete melting of the alloys. Then, Ce and La mixed rare earth elements are added, and the mixture is stirred for 10-20 minutes to begin refining, degassing, and slag removal. When the temperature of the molten aluminum drops to 735-760℃, aluminum rods are cast. Before casting the aluminum rods, Al-5Ti-B wire refiner is added to the casting channel to promote grain refinement. The alloy composition of the cast aluminum rods meets the alloy composition designed in step S1.

[0047] S3: Heat treatment before extrusion

[0048] The aluminum rod is surface cleaned and then subjected to homogenization heat treatment. The homogenization heat treatment method is: rapid heating, that is, heating at a rate of 195-205℃ / s for 2.5-3.5s, heating to above 600℃, preferably to 610℃, and then cooling to room temperature for extrusion.

[0049] S4: Continuous extrusion

[0050] The aluminum rod is continuously extruded using an extrusion die assembled according to the flat tube specifications. The process parameters for continuous extrusion are as follows:

[0051] The extrusion roller surface temperature is controlled at 400-420℃; the gap between the extrusion roller and the extrusion shoe satisfies: diverging gap = convergent gap + 0.8~1mm (preferably 0.9mm).

[0052] S5: Online Cooling

[0053] During continuous extrusion, liquid nitrogen is used to control the mold temperature, keeping it at 390℃±10℃ and controlling the mold temperature fluctuation within 3%.

[0054] S6: Remove residual aluminum shavings from the surface of the flat tube.

[0055] After the aluminum alloy flat tube is extruded, the residual aluminum shavings on the surface of the flat tube are removed by air knife blowing technology and scraping technology.

[0056] S7: Perform tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, material cutting, length setting, and obtain finished product.

[0057] Among them, steps S3 and S6 are new steps added on the existing technology, and S2, S4 and S5 are optimization steps based on the existing technology; step S1 is the composition design of the aluminum alloy flat tube optimized by the present invention; step S7 is not limited and can be an existing conventional step.

[0058] This invention's production process optimizes the proportions of key chemical components within the furnace, controlling copper, iron, and silicon within a specific range while ensuring a certain iron-silicon ratio. This improves the casting performance of aluminum rods, reduces internal cracks in the billet, and enhances the uniformity of the microstructure. Controlling the copper content within a certain range ensures that the final strength of the product does not decrease after high-temperature homogenization treatment. The process employs a refinement technique combining in-furnace rare earth element addition and online addition of aluminum-titanium-boron wire to ensure the aluminum rod achieves a porosity of Grade 1. The process utilizes a novel high-temperature and ultra-high-speed online homogenization heat treatment process, enabling the aluminum rod to homogenize its chemical composition in a very short time and eliminating intracrystalline segregation. This invention improves metal fluidity while optimizing extrusion process parameters and modifying the die cooling process to minimize extrusion temperature fluctuations (within 3%), achieving near-constant temperature extrusion. Furthermore, after product forming, the surface of the flat tube undergoes online treatment to ultimately eliminate aluminum chips from the aluminum flat tube surface.

[0059] To further illustrate the technical effects of the present invention, the following are specific embodiments of the present invention.

[0060] Example 1

[0061] This embodiment provides a process for eliminating aluminum chips from the surface of continuously extruded aluminum alloy flat tubes, which includes the following steps:

[0062] (1) Cast aluminum alloy rod

[0063] Raw materials were prepared according to the pre-designed alloy composition. High-temperature electrolytic aluminum molten metal at 850℃ was introduced into the melting furnace, followed by 15% cold material (room-temperature aluminum ingots). The aluminum molten metal temperature was lowered to 770℃, and the proportions of Cu, Fe, and Si were adjusted within the furnace. The furnace was then simmered for 15 minutes. Ce and La mixed rare earth elements were added and stirred for 15 minutes, followed by refining, degassing, and slag removal. When the aluminum molten metal temperature reached 750℃, aluminum rods were cast. An Al-5Ti-B wire refiner was added online into the casting channel, resulting in aluminum rods 1m long and 9.5mm in diameter.

[0064] The alloy composition of the aluminum rod was determined to be: Cu: 0.12%, Si: 0.04%, Fe: 0.15%, Fe:Si = 3.75, Ti: 0.0075%, Ce and La mixed rare earth (10% Ce): 0.05%, with the balance being Al and unavoidable impurities.

[0065] (2) Heat treatment before extrusion

[0066] The aluminum rod is surface cleaned and then subjected to homogenization heat treatment. The homogenization heat treatment method is as follows: the Φ9.5mm aluminum rod is heated to 610℃ in 3 seconds in a 1-meter-long circular induction heating furnace, and then cooled to room temperature.

[0067] (3) Continuous extrusion

[0068] Assemble the extrusion die according to the flat tube specifications, and continuously extrude the aluminum rod. The continuous extrusion process parameters are: extrusion speed 20 rpm, extrusion pressure 50 MPa, extrusion current 140 A, and the gap between the extrusion shoe and the extrusion roller meets the following requirements: divergence gap = convergence gap + 0.9 mm; the working zone thickness of the aluminum layer on the extrusion roller surface is 0.20 mm, and the width is 10 mm. The temperature of the extrusion roller surface is controlled at 400-420℃.

[0069] (4) Online cooling

[0070] During continuous extrusion, liquid nitrogen is used to control the die temperature, maintaining it consistently between 380-400℃ and limiting temperature fluctuations to within 3%. The liquid nitrogen cooling pressure is 0.15 MPa, and the flow rate is 0.9 m³ / s. 3 / h.

[0071] (5) Remove residual aluminum shavings from the surface of the flat tube.

[0072] After the aluminum alloy flat tube is extruded, residual aluminum shavings on the surface of the flat tube are removed using air knife blowing and scraping techniques. The gap between the air knife tip and the surface of the flat tube is 0.5 mm, and the blowing pressure is 0.5 MPa. Scraping uses scraper blades to remove residual aluminum shavings from the surface of the flat tube, with an elastic pressure of 0.12 N applied by the scraper blades to the surface of the flat tube.

[0073] (6) Perform tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, material cutting, length setting, and obtain finished product.

[0074] Example 2

[0075] This embodiment provides a process for eliminating aluminum chips from the surface of continuously extruded aluminum alloy flat tubes, which includes the following steps:

[0076] (1) Cast aluminum alloy rod

[0077] Raw materials were prepared according to the pre-designed alloy composition. High-temperature electrolytic aluminum molten metal at 850℃ was introduced into the melting furnace, followed by 15% cold material (room-temperature aluminum ingots). The temperature of the molten aluminum was reduced to 770℃, and the proportions of Cu, Fe, and Si were mixed in the furnace. The furnace was then simmered for 15 minutes. Ce and La mixed rare earth elements were added and stirred for 15 minutes, followed by refining, degassing, and slag removal. When the temperature of the molten aluminum reached 740℃, aluminum rods were cast. Al-5Ti-B wire refiner was added online in the casting channel. After casting, aluminum rods with a length of 1m and a diameter of 9.5mm were obtained.

[0078] The alloy composition of the aluminum rod was determined to be: Cu: 0.11%, Si: 0.04%, Fe: 0.16%, Fe:Si=4, Ti: 0.0068%, Ce and La mixed rare earth (10% Ce): 0.047%, with the balance being Al and unavoidable impurities.

[0079] (2) Heat treatment before extrusion

[0080] The aluminum rod is surface cleaned and then subjected to homogenization heat treatment. The homogenization heat treatment method is as follows: the Φ9.5mm aluminum rod is heated to 614℃ in 3 seconds in a 1-meter-long circular induction heating furnace, and then cooled to room temperature.

[0081] (3) Continuous extrusion

[0082] Assemble the extrusion die according to the flat tube specifications, and continuously extrude the aluminum rod. The continuous extrusion process parameters are: extrusion speed 20 rpm, extrusion pressure 55 MPa, extrusion current 150 A, and the gap between the extrusion shoe and the extrusion roller meets the following requirements: divergence gap = convergence gap + 0.9 mm; the working zone thickness of the aluminum layer on the extrusion roller surface is 0.20 mm, and the width is 10 mm. The temperature of the extrusion roller surface is controlled at 400-420℃.

[0083] (4) Online cooling

[0084] During continuous extrusion, liquid nitrogen is used to control the die temperature, maintaining it consistently between 380-400℃ and limiting temperature fluctuations to within 3%. The liquid nitrogen cooling pressure is 0.10 MPa, and the flow rate is 1.0 m³ / min. 3 / h.

[0085] (5) Remove residual aluminum shavings from the surface of the flat tube.

[0086] After the aluminum alloy flat tube is extruded, residual aluminum shavings on the surface of the flat tube are removed using air knife blowing and scraping techniques. The gap between the air knife tip and the flat tube surface is 0.4 mm, and the blowing pressure is 0.5 MPa. Scraping uses scraper blades to remove residual aluminum shavings from the flat tube surface, with an elastic pressure of 0.15 N applied by the scraper blades to the flat tube surface.

[0087] (6) Perform tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, material cutting, length setting, and obtain finished product.

[0088] Example 3

[0089] This embodiment provides a process for eliminating aluminum chips on the surface of continuously extruded aluminum alloy flat tubes. Based on Embodiment 1, the conditions of step (1) are changed as follows: Casting aluminum alloy rods: Prepare raw materials according to the pre-designed alloy composition, introduce high-temperature electrolytic aluminum liquid at 850°C into the melting furnace, and add 15% cold material (room temperature aluminum ingot). The temperature of the aluminum liquid drops to 775°C, and the proportions of Cu, Fe, and Si are carried out in the furnace. The furnace is then simmered for 15 minutes. Ce and La mixed rare earth are added and stirred for 15 minutes. After refining, degassing and slag removal are performed. When the temperature of the aluminum liquid reaches 750°C, aluminum rods are cast. Al-5Ti-B wire refiner is added online in the flow channel. After casting, an aluminum rod with a length of 1m and a diameter of 9.5mm is obtained. The alloy composition of the aluminum rod was determined to be: Cu: 0.10%, Si: 0.05%, Fe: 0.17%, Fe:Si = 3.4, Ti: 0.0070%, Ce and La mixed rare earth (10% Ce): 0.051%, with the balance being Al and unavoidable impurities. All other conditions and procedures were the same as in Example 1.

[0090] Comparative Example 1

[0091] Comparative Example 1 uses an existing alloy formula to cast an aluminum alloy rod. The alloy composition of the rod was determined to be: Cu: 0.05%, Si: 0.12%, Fe: 0.18%, with the balance being Al and unavoidable impurities. All other conditions and procedures were the same as in Example 1.

[0092] Comparative Example 2

[0093] Comparative Example 2 is based on Example 1, but step (2) is changed to: placing the aluminum alloy rod in a box furnace and holding it at 580°C for 10 hours, then air cooling it after removing it from the furnace. All other conditions and steps are the same as in Example 1.

[0094] Comparative Example 3

[0095] Comparative Example 3 is based on Example 1, with step (3) modified as follows: the extrusion roller surface temperature is controlled at 400-420℃, the extrusion speed is 16 rpm, the extrusion pressure is 40 MPa, and the extrusion current is 240 A. Other conditions and steps are the same as in Example 1.

[0096] Comparative Example 4

[0097] Comparative Example 4 is based on Example 1, but step (4) is changed to: water cooling is used to control the mold temperature, and the temperature fluctuation range of the mold is 380-450℃. Other conditions and steps are the same as in Example 1.

[0098] Comparative Example 5

[0099] Comparative Example 5 is based on Example 1, except that step (5) is removed. All other conditions and steps are the same as in Example 1.

[0100] Comparative Example 6

[0101] Comparative Example 6 describes the preparation of aluminum alloy flat tubes using existing conventional processes. The alloy composition of the aluminum alloy flat tubes is Cu: 0.05%, Si: 0.12%, Fe: 0.18%, with the balance being Al and unavoidable impurities. After simple surface cleaning, the aluminum rods are placed in a box furnace and held at 580℃ for 10 hours, then air-cooled before continuous extrusion. The extrusion process parameters are: extrusion roller surface temperature controlled at 400-420℃, extrusion speed 16 rpm, extrusion pressure 40 MPa, and extrusion current 200 A. Water cooling is used to control the die temperature, with a fluctuation range of 380-450℃. After extrusion forming, tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, blanking, length setting, and the finished product are obtained.

[0102] In the flat tube production workshop of Hunan Hengjia New Materials Co., Ltd., production tests of aluminum alloy flat tubes were conducted using the schemes of Examples 1-3 and Comparative Examples 1-6, respectively. Under the same lighting conditions, the quantity of aluminum shavings and indentations was visually inspected. The results confirmed that the quantity and distribution density of residual aluminum shavings and indentations on the surface of the aluminum alloy flat tubes produced in Examples 1-3 were significantly less than those in Comparative Examples 1-6. In particular, compared with Comparative Example 6, the quantity of residual aluminum shavings and indentations on the surface of the aluminum alloy flat tubes produced in Examples 1-3 was only about 1 / 4 to 1 / 5 of that in Comparative Example 6.

[0103] Furthermore, compared with the current conventional aluminum alloy flat tube production process (see background art), the aluminum alloy flat tubes produced by the applicant company using the process of the invention have reduced the proportion of scrapped tubes with aluminum chip indentation defects from over 30% to about 5%; the overall yield of flat tubes has increased by more than 3%, and the leak detection rate is controlled within 1‰. Precisely because the invention has achieved such excellent technical effects in practice, this patent application is hereby filed to obtain patent protection.

[0104] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, and not to limit them; although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A process for eliminating aluminum chips from the surface of continuously extruded aluminum alloy flat tubes, characterized in that, Including the following steps: S1. The designed aluminum alloy composition is: Cu: 0.09-0.12%, Si: 0.03-0.05%, Fe: 0.12-0.17%, Fe:Si≥3, Ti: 0.006-0.0075%, Ce and La mixed rare earth: 0.045-0.055%, with the balance being Al and unavoidable impurities; S2, Cast aluminum alloy rod Aluminum material is melted in a smelting furnace. When the temperature drops to 770-790℃, Cu, Fe, and Si alloying materials are added, and the furnace is kept closed to ensure complete melting of the alloys. Then, Ce and La mixed rare earth elements are added, and the mixture is stirred for 10-20 minutes to begin refining, degassing, and slag removal. When the temperature of the molten aluminum drops to 735-760℃, aluminum rods are cast. Before casting the aluminum rods, Al-5Ti-B wire refiner is added to the casting channel to promote grain refinement. The alloy composition of the cast aluminum rods meets the alloy composition design of S1. S3, Heat treatment before extrusion The aluminum rod is surface cleaned and then subjected to homogenization heat treatment. The homogenization heat treatment method is: rapid heating, that is, heating at a rate of 195-205℃ / s for 2.5-3.5s. S4, Continuous extrusion Assemble the extrusion die according to the flat tube specifications, and continuously extrude the aluminum rod. The process parameters for continuous extrusion are: the temperature of the extrusion roller surface is controlled at 400-420℃. The extrusion gap between the extrusion roller and the extrusion shoe satisfies: diverging gap = convergent gap + 0.8~1.0mm; S5, Online Cooling During continuous extrusion, liquid nitrogen is used to control the mold temperature, keeping it at 390℃±10℃ and controlling the mold temperature fluctuation within 3%. S6. Remove residual aluminum shavings from the surface of the flat tube. After the aluminum alloy flat tube is extruded, the residual aluminum shavings on the surface of the flat tube are removed by air knife blowing technology and scraping technology. S7, tension adjustment, winding, semi-finished product inspection, air and water leakage inspection, material feeding, length setting, and finished product.

2. According to the process method described in claim 1, in S1, the total content of Ce and La mixed rare earth elements in the aluminum alloy is 0.05%, and the content of Ce is 0.005%.

3. The process method according to claim 1, wherein S2, when melting aluminum material in the smelting furnace, includes: High-temperature electrolytic aluminum molten metal at a temperature above 830℃ is introduced into the smelting furnace, and then 15% by mass of cold material is added to lower the temperature of the molten aluminum to 770-790℃. The cold material is aluminum ingots at room temperature or recycled aluminum. The cold material and high-temperature electrolytic aluminum molten metal are mixed and smelted together. The cold material plays the role of cooling down and refining the melt grains.

4. According to the process method described in claim 1, in S2, when the temperature of the molten aluminum in the melting furnace drops to 770-790℃, Cu, Fe and Si alloy ingredients are added and the furnace is simmered for 15 minutes. Then Ce and La mixed rare earth are added and stirred for 15 minutes to start refining, degassing and slag removal.

5. In the process method according to claim 1, in S3, the homogenization heat treatment is to use an induction heating furnace to rapidly heat the aluminum rod to above 600°C within 3 seconds.

6. In the process method according to claim 1, in S4, the extrusion roller speed is 17-20 rpm, the extrusion pressure is 50-55 MPa, the extrusion current is 130-150 A, the thickness of the aluminum layer working strip on the extrusion roller surface is 0.20 mm, and the width is 10 mm.

7. In the process method according to claim 1, in S5, when liquid nitrogen is used to cool the mold during the extrusion process, the liquid nitrogen pressure is 0.10-0.15 MPa and the flow rate is 0.8-1.0 m³ / s. 3 / h.

8. In the process method according to claim 1, in S5, when liquid nitrogen is used to cool the mold, the temperature fluctuation of the mold is controlled within 2.5%.

9. In the process method according to claim 1, in S6, the gap between the air knife nozzle and the surface of the flat tube is 0.3-0.5 mm, and the blowing pressure is 0.4-0.6 MPa; the scraping uses a scraping blade to remove the aluminum shavings remaining on the surface of the flat tube, and the elastic pressure of the scraping blade on the surface of the flat tube is 0.1-0.15 N.