High-performance aluminum alloy pipe and preparation method thereof

Abstract

The invention relates to the field of aluminum alloy pipe manufacturing, and discloses a high-performance aluminum alloy pipe and a preparation method thereof.The high-performance aluminum alloy pipe comprises, by mass, 1.2%-1.8% of Mg, 0.8%-1.2% of Si, 0.05%-0.15% of Sc, 0.08%-0.18% of Zr, 0.2%-0.4% of Cu, 0.1%-0.3% of Mn, impurities including smaller than or equal to 0.15% of Fe, smaller than or equal to 0.1% of Zn, smaller than or equal to 0.05% of Ti and the balance Al. According to the invention, a traditional single strengthening phase design thought is broken through, and a quaternary synergistic system of Mg-Si main strengthening, Sc-Zr grain refinement and Cu-Mn corrosion resistance regulation is provided, so that strength, corrosion resistance and toughness can be considered.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy tubing manufacturing technology, and more specifically, to a high-performance aluminum alloy tubing and its manufacturing method. Background Technology

[0002] Aluminum alloy tubing is widely used in structural components due to its lightweight and ease of processing. However, most current mainstream tubing is based on 6-series (Al-Mg-Si) or 7-series (Al-Zn-Mg) alloys, which presents the following technical drawbacks: Poor performance synergy: 6-series alloys (such as 6061) have a tensile strength of only 310-330MPa and a corrosion rate of 0.03-0.05mm / a in 1000h of neutral salt spray, which cannot meet the dual requirements of "high strength + high corrosion resistance" in high-end fields; although 7-series alloys have improved strength (tensile strength ≥500MPa), they have poor toughness (elongation ≤8%) and high cost, and insufficient resistance to intergranular corrosion.

[0003] Process limitations: The traditional preparation process adopts "single temperature homogenization → hot extrusion → offline quenching → single-stage aging", which easily leads to coarse ingot grains (≥50μm), uneven microstructure after extrusion, and offline quenching is prone to generating an oxide layer, affecting the surface quality of the pipe and subsequent processing performance.

[0004] Therefore, providing a high-performance aluminum alloy tube and its preparation method has become a technical problem that urgently needs to be solved by those skilled in the art. Summary of the Invention

[0005] In view of this, the present invention proposes a high-performance aluminum alloy tube, which aims to solve at least one of the problems in the background art.

[0006] This invention proposes a high-performance aluminum alloy tubing, comprising the following components by weight percentage: Mg: 1.2~1.8%, Si: 0.8~1.2%, Sc: 0.05~0.15%, Zr: 0.08~0.18%, Cu: 0.2~0.4%, Mn: 0.1~0.3%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance Al.

[0007] The present invention also provides a method for preparing the high-performance aluminum alloy tubing as described in claim 1, comprising the following preparation steps: Aluminum ingots, magnesium ingots, Al-Si master alloy, Al-Sc master alloy, Al-Zr master alloy, Al-Cu master alloy, and Al-Mn master alloy were weighed as raw materials according to the mass percentage of the high-performance aluminum alloy tubing composition. After heating and melting aluminum ingots, Al-Si, Al-Mn, and Al-Cu master alloys are added sequentially for the first stirring. After the first stirring, magnesium ingots and Al-Sc and Al-Zr master alloys are added for heat preservation treatment. Then, a refining agent is added, and after standing, the mixture is filtered to obtain the melt. The melt is cast to obtain an ingot. The ingot is then segmented and homogenized. After pretreatment, the homogenized ingot is extruded to obtain a coarse pipe. The coarse tube is quenched and then subjected to a three-stage aging treatment. After post-treatment, the high-performance aluminum alloy tube is obtained.

[0008] Preferably, the heating temperature is 740-760℃; the cooling temperature is 720-730℃; the stirring time of the first stirring is 15-20 minutes, and the stirring rate is 300 r / min.

[0009] Preferably, the casting temperature is 710-720℃, electromagnetic stirring is applied during casting, the stirring frequency of the electromagnetic stirring is 50-60Hz, the casting speed is 80-100mm / min, and the cooling rate is 15-20℃ / s.

[0010] Preferably, the segmented homogenization process specifically involves: holding the ingot at 420-430℃ for 4-5 hours for a first-stage homogenization; then raising the temperature to 480-490℃ and holding it for 8-10 hours for a second-stage homogenization; and finally cooling it to 300℃ with the furnace and then air-cooling it to room temperature.

[0011] Preferably, the pretreatment is as follows: removing a 2-3 cm thick outer skin from the homogenized ingot and preheating it to 480-500℃ and holding it for 2 hours.

[0012] Preferably, the extrusion molding is performed by preheating the mold to 500-520°C and extruding the pretreated ingot at a temperature of 500-520°C and a speed of 5-8 mm / s.

[0013] Preferably, the quenching is performed by water-air atomization cooling of the coarse pipe at a cooling rate of greater than or equal to 30°C / s.

[0014] Preferably, the three-stage aging treatment is as follows: the quenched coarse pipe is held at 120-130℃ for 4-6 hours for pre-aging, then the temperature is raised to 180-190℃ and held for 8-10 hours for main aging, and finally the temperature is lowered to 60-70℃ and held for 12-15℃ for low-temperature aging.

[0015] Preferably, the post-processing is as follows: straightening the aged coarse pipe and then chemically polishing it.

[0016] Compared with the prior art, the beneficial effects of the present invention are as follows: This invention breaks through the traditional single-strengthening phase design concept and provides a quaternary synergistic system of "Mg-Si main strengthening + Sc-Zr grain refinement + Cu-Mn corrosion resistance regulation", which enables the invention to take into account strength, corrosion resistance and toughness.

[0017] This invention employs a "segmented homogenization + online quenching + three-stage aging" process to achieve precise control of the microstructure throughout the entire process from ingot to finished product, greatly improving process stability. Detailed Implementation

[0018] Various exemplary embodiments of the present invention will now be described in detail. This detailed description should not be considered as a limitation of the present invention, but rather as a more detailed description of certain aspects, features, and embodiments of the present invention. It should be understood that the terminology used in this invention is merely for describing particular embodiments and is not intended to limit the present invention.

[0019] Furthermore, regarding the numerical ranges in this invention, it should be understood that each intermediate value between the upper and lower limits of the range is also specifically disclosed. Every smaller range between any stated value or intermediate value within a stated range, and any other stated value or intermediate value within said range, is also included within this invention. The upper and lower limits of these smaller ranges may be independently included or excluded from the range.

[0020] Unless otherwise stated, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art. While only preferred methods and materials have been described herein, any methods and materials similar or equivalent to those described herein may be used in the implementation or testing of this invention. All references to this specification are incorporated by way of citation to disclose and describe methods and / or materials associated with those references. In the event of any conflict with any incorporated reference, the content of this specification shall prevail.

[0021] Various modifications and variations can be made to the specific embodiments described in this specification without departing from the scope or spirit of the invention, as will be apparent to those skilled in the art. Other embodiments derived from this specification will also be apparent to those skilled in the art. This specification and embodiments are merely exemplary.

[0022] The terms “include,” “including,” “have,” “contain,” etc., used in this article are all open-ended terms, meaning that they include but are not limited to.

[0023] This invention provides a high-performance aluminum alloy tubing, comprising the following components by weight percentage: Mg: 1.2~1.8%, Si: 0.8~1.2%, Sc: 0.05~0.15%, Zr: 0.08~0.18%, Cu: 0.2~0.4%, Mn: 0.1~0.3%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance Al.

[0024] Specifically, the functions of each metallic element are as follows: Al: A matrix element that ensures the basic toughness of the material; Mg (1.2~1.8%): forms the Mg2Si strengthening phase with Si, which improves strength; if the content is less than 1.2%, the strengthening is insufficient, and if it is greater than 1.8%, it is easy to form the β-Mg2Si brittle phase; Si (0.8~1.2%): forms a reinforcing phase in synergy with Mg. The Si / Mg molar ratio is controlled at 0.6-0.8 to avoid the decrease in toughness caused by free Si. Sc (0.05~0.15%): It synergistically forms L12 type Al3(Sc,Zr) phase with Zr, which refines the ingot grains and increases the recrystallization temperature; if the content is greater than 0.15%, the cost will increase dramatically, and if it is less than 0.05%, the refining effect will be insufficient. Zr (0.08~0.18%): Reduces the amount of Sc used, while inhibiting grain growth during extrusion and improving thermal stability; Cu (0.2~0.4%): forms Al-Cu-Mg-Si quaternary precipitates, improving the aging strengthening effect; if the content is less than 0.2%, the strengthening is limited, and if it is greater than 0.4%, it is easy to form CuAl2 phase, which reduces corrosion resistance; Mn (0.1~0.3%): forms the Al6Mn phase, inhibits intergranular corrosion, and refines recrystallized grains to improve toughness; content greater than 0.3% is prone to producing coarse inclusions. Impurities (Fe≤0.15%, Zn≤0.1%, Ti≤0.05%): Control the total amount of impurities to ≤0.3% to avoid the formation of brittle inclusions such as FeAl3.

[0025] Understandably, this invention breaks through the traditional single-strengthening phase design concept and provides a quaternary synergistic system of "Mg-Si main strengthening + Sc-Zr grain refinement + Cu-Mn corrosion resistance regulation", which enables this invention to take into account strength, corrosion resistance and toughness.

[0026] This invention also provides a method for preparing high-performance aluminum alloy tubing, comprising the following preparation steps: Aluminum ingots, magnesium ingots, Al-Si master alloy, Al-Sc master alloy, Al-Zr master alloy, Al-Cu master alloy, and Al-Mn master alloy were weighed as raw materials according to the mass percentage of the high-performance aluminum alloy tubing composition. After heating and melting aluminum ingots, Al-Si, Al-Mn, and Al-Cu master alloys are added sequentially for the first stirring. After the first stirring, magnesium ingots and Al-Sc and Al-Zr master alloys are added for heat preservation treatment. Then, a refining agent is added, and after standing, the mixture is filtered to obtain the melt. The melt is cast to obtain an ingot. The ingot is then segmented and homogenized. After pretreatment, the homogenized ingot is extruded to obtain a coarse pipe. The coarse tube is quenched and then subjected to a three-stage aging treatment. After post-treatment, the high-performance aluminum alloy tube is obtained.

[0027] Specifically, the raw materials used are: 99.97% high-purity aluminum ingots, magnesium ingots (99.95%), Al-Si master alloy (Si content 20wt%), Al-Sc master alloy (Sc content 2wt%), Al-Zr master alloy (Zr content 5wt%), Al-Cu master alloy (Cu content 30wt%), and Al-Mn master alloy (Mn content 10wt%).

[0028] Specifically, the melting equipment is a graphite dry boiler (the inner wall is coated with boron nitride to prevent Al from reacting with graphite).

[0029] Specifically, during the melting process of raw materials, an argon-nitrogen mixture (volume ratio 7:3) is introduced at a flow rate of 5L / min to ensure that the oxygen content in the furnace is ≤0.5% (monitored in real time by an oxygen content detector) to prevent the melt from oxidizing. Specifically, after adding magnesium ingots and Al-Sc and Al-Zr master alloys, keep stirring for 10 minutes, then stop stirring and keep warm for 20-25 minutes (to allow the alloying elements to dissolve fully).

[0030] Specifically, the refining agent is Al-5Ti-B refining agent, and the amount added is 0.1wt (calculated according to the total mass of the melt, such as 0.1kg for 100kg melt). After adding Al-5Ti-B refining agent, stir for 5 minutes and let stand for 10 minutes (to allow the refining agent to be evenly distributed and to allow the inclusions to float). Filter the melt using a 100-mesh ceramic filter plate.

[0031] It is understandable that the present invention adopts the process of "segmented homogenization + online quenching + three-stage aging" to achieve precise control of the microstructure from ingot to finished product throughout the entire process, which greatly improves the stability of the process.

[0032] In this invention, the preferred temperature for heating is 740-760℃; the preferred temperature for cooling is 720-730℃; the preferred stirring time for the first stirring is 15-20 minutes, and the preferred stirring rate is 300 r / min.

[0033] Specifically, the alloy melting operation is as follows: All high-purity aluminum ingots are added to a graphite crucible furnace, the furnace door is closed, and the temperature is increased to 740-760℃ at a rate of 10℃ / min (too rapid a heating rate can easily cause localized overheating and burning of the aluminum ingots) until the aluminum ingots are completely melted (confirmed through the furnace door observation window that no solid aluminum blocks remain). During this process, an argon-nitrogen mixture (volume ratio 7:3) is introduced at a flow rate of 5L / min to ensure that the oxygen content in the furnace is ≤0.5% (monitored in real time by an oxygen content detector) to prevent oxidation of the melt. After the aluminum ingots are completely melted, Al-Si (melting point 610℃), Al-Mn (melting point 658℃), and Al-Cu (melting point 640℃) master alloys are added sequentially, and mechanical stirring is started (300r / min, stirring depth equal to the melt height). Add 2 / 3 of the Mg ingot and stir for 15-20 minutes (to ensure uniform diffusion of alloying elements). After stirring, lower the furnace temperature to 720-730℃ (Mg melting point 650℃, this temperature can reduce Mg burn-off rate ≤3%). Add Mg ingot and Al-Sc (melting point 630℃) and Al-Zr (melting point 660℃) master alloys. Continue stirring for 10 minutes, then stop stirring and hold for 20-25 minutes (to allow alloying elements to fully dissolve). Add 0.1wt% Al-5Ti-B refining agent (calculated based on the total mass of the melt, e.g., 0.1kg for 100kg melt). Stir manually for 5 minutes, then let stand for 10 minutes. Use a 100-mesh ceramic filter plate to collect the filtered melt into a heat-insulating crucible (heat-insulating temperature 710-720℃) for later use.

[0034] In this invention, the casting temperature is preferably 710-720℃, electromagnetic stirring is applied during casting, the stirring frequency of the electromagnetic stirring is preferably 50-60Hz, the casting speed is preferably 80-100mm / min, and the cooling rate is preferably 15-20℃ / s.

[0035] Specifically, the casting process involves heating the crystallizer to 300-320℃ (to avoid the cold crystallizer causing quenching of the melt and resulting in surface cracks), holding it at that temperature for 30 minutes, and then pouring the melt at 710-720℃ from the holding crucible into the crystallizer. When the melt level in the crystallizer reaches 2 / 3 of the crystallizer height (monitored by a level sensor), the traction device is activated to cast the ingot at a speed of 80-100 mm / min. During this process, an electromagnetic stirrer at a frequency of 50-60 Hz is activated, and water mist cooling is simultaneously activated to cool the ingot to between 300-350℃ by controlling the water temperature and pressure at a cooling rate of 15-20℃ / s.

[0036] In this invention, the segmented homogenization process is preferably performed by holding the ingot at 420-430°C for 4-5 hours for a first-stage homogenization, then raising the temperature to 480-490°C and holding it for 8-10 hours for a second-stage homogenization, and finally cooling it to 300°C with the furnace and then air-cooling it to room temperature.

[0037] Specifically, the ingot is placed in a box-type resistance furnace and heated to 420-430°C at a rate of 5°C / min, and held at that temperature for 4-5 hours for a first stage of homogenization. After that, the temperature is increased to 480-490°C at a rate of 3°C / min and held for 8-10 hours for a second stage of homogenization. After that, the ingot is cooled to 300°C with the furnace and then the furnace door is opened for air cooling to room temperature.

[0038] Understandably, the purpose of the first-stage homogenization is to dissolve the fine Mg2Si metastable phase precipitated in the ingot, so as to avoid abnormal grain growth during subsequent high-temperature heating. The purpose of the second-stage homogenization is to completely dissolve the residual second phase, while promoting the uniform precipitation of Al3(Sc, Zr) phase, so as to provide a fine-grained basis for subsequent extrusion.

[0039] In this invention, the pretreatment is preferably as follows: removing a 2-3 cm thick outer skin from the homogenized ingot and preheating it to 480-500℃ and holding it therefore for 2 hours.

[0040] Specifically, a CNC lathe is used to machine the outer diameter of the homogenized ingot to remove the skin, with a thickness of 2-3 mm (to remove the surface oxide layer and possible inclusions, ensuring that the die is not scratched during extrusion). The machined ingot is then placed in an induction heating furnace and heated to 480-500℃ at a rate of 10℃ / min, and held at that temperature for 2 hours (the purpose is to make the ingot temperature uniform and reduce the extrusion resistance). In this invention, the extrusion molding is preferably performed by preheating the mold to 500-520°C and extruding the pretreated ingot at a temperature of 500-520°C and a speed of 5-8 mm / s.

[0041] In this invention, the quenching is performed by water-air atomization cooling of the coarse pipe at a cooling rate of greater than or equal to 30°C / s.

[0042] Specifically, select the desired mold, place the mold in a mold heating furnace, heat it to 500-520℃, and hold it for 3 hours (too low a mold temperature will cause the surface of the extruded pipe to be rough, while too high a temperature will shorten the mold life). Apply graphite lubricant to the working surface of the mold (to form a lubricating film at high temperature and reduce friction). Feed the preheated ingot into the extruder barrel, start the extruder, and extrude the ingot from the mold at a pressure of 250-300MPa and a speed of 5-8mm / s. After extrusion, immediately enter the water-air atomization cooling device for online quenching and cooling to ensure a cooling rate of ≥30℃ / s.

[0043] In this invention, the preferred three-stage aging process is as follows: the quenched coarse pipe is pre-aged by holding it at 120-130°C for 4-6 hours, then the temperature is raised to 180-190°C and held for 8-10 hours for main aging, and finally the temperature is lowered to 60-70°C and held for 12-15°C for low-temperature aging.

[0044] Specifically, the preferred aging equipment for the three-stage aging process is a hot air circulating aging furnace.

[0045] Specifically, the three-stage time-sensitive processing steps are as follows: Hang the quenched pipes on the rack inside the furnace, close the furnace door, and turn on the hot air circulation system; The furnace is heated to 120-130℃ at a rate of 5℃ / min and held for 4-6 hours for pre-aging. Then, it is heated to 180-190℃ at a rate of 3℃ / min and held for 8-9 hours for main aging. Finally, it is cooled to 60-70℃ at a rate of 2℃ / min and held for 12-15 hours for low-temperature aging. After the process is completed, the heating device is turned off, hot air is kept circulating, and the furnace is allowed to cool naturally to below 100℃. Then, the furnace door is opened and the furnace is allowed to air-cool to room temperature.

[0046] Understandably, pre-aging promotes uniform nucleation in the GP region, which is the core for subsequent precipitation of the β'-Mg2Si phase. Uniform nucleation can prevent the subsequent precipitates from being coarse. The purpose of main aging is to form the main strengthening phase. Holding at 180-190℃ for 8-10 hours transforms the GP region into a fine β'-Mg2Si phase with a size ≤10nm, which is the main strengthening phase. The purpose of low-temperature aging is to eliminate the internal stress generated by main aging and to finely adjust the distribution of the GP region and the β' phase, thereby improving toughness.

[0047] In this invention, the post-processing is as follows: straightening the aged coarse pipe and then chemically polishing it.

[0048] Specifically, after aging, the coarse pipe is sent to a straightening machine for straightening, then immersed in polishing liquid for 10 minutes, turning it over every 2 minutes to ensure uniform polishing of the surface. After the process, the pipe is taken out and rinsed with deionized water 3 times for 1 minute each time, and then placed in an 80°C drying oven for 30 minutes.

[0049] Specifically, the polishing solution is formulated as follows: 80% phosphoric acid (mass fraction), 15% sulfuric acid, and 5% nitric acid (prepared in advance in an acid-resistant tank at a temperature of 60-70°C, controlled by a constant temperature water bath). The main purpose of the post-treatment is to remove the oxide layer and improve the surface quality.

[0050] Example 1 Pipe composition design: Mg: 1.5%, Si: 1%, Sc: 0.1%, Zr: 0.13%, Cu: 0.3%, Mn: 0.2%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance is Al.

[0051] Preparation method: S1. Weigh out 99.97% high-purity aluminum ingots, magnesium ingots (99.95%), Al-Si master alloy (Si content 20wt%), Al-Sc master alloy (Sc content 2wt%), Al-Zr master alloy (Zr content 5wt%), Al-Cu master alloy (Cu content 30wt%), and Al-Mn master alloy (Mn content 10wt%) as raw materials according to the designed composition. S2. Add all the high-purity aluminum ingots to the graphite crucible furnace, close the furnace door, and heat to 740-760℃ at a rate of 10℃ / min until the aluminum ingots are completely melted. During this process, argon-nitrogen mixed gas (volume ratio 7:3) is introduced at a flow rate of 5L / min. After the aluminum ingots are completely melted, Al-Si, Al-Mn and Al-Cu master alloys are added in sequence. Mechanical stirring is started at a rate of 300r / min for 18min. After the stirring is completed, the furnace temperature is reduced to 720-730℃. Magnesium ingots and Al-Sc and Al-Zr master alloys are added. Stirring is continued for 10min. Stirring is stopped and the temperature is held for 23min. 0.1wt% Al-5Ti-B refining agent is added. The mixture is manually stirred for 5min and then allowed to stand for 10min. The filtered melt is collected using a 100-mesh ceramic filter plate and kept at a temperature of 710-720℃ for later use. S3. Heat the crystallizer to 300-320℃ and hold for 30 minutes. Pour the melt at 710-720℃ from the holding crucible into the crystallizer. When the melt level in the crystallizer reaches 2 / 3 of the crystallizer height, start the traction device to cast at a speed of 90mm / min. During this period, turn on the electromagnetic stirring at a frequency of 55Hz and turn on the water mist cooling. Cool the ingot to between 300-350℃ by controlling the water temperature and water pressure at a cooling rate of 18℃ / s. S4. Place the ingot into a box-type resistance furnace and heat it to 420-430℃ at a rate of 5℃ / min. Hold it at that temperature for 4.5 hours to perform a first stage of homogenization. After that, raise the temperature to 480-490℃ at a rate of 3℃ / min and hold it for 9 hours to perform a second stage of homogenization. After that, cool it down to 300℃ with the furnace and then open the furnace door to air cool to room temperature. S5. Using a CNC lathe, the outer diameter of the homogenized ingot is machined to remove the skin, with a thickness of 2-3mm. The machined ingot is then placed in an induction heating furnace and heated to 480-500℃ at a rate of 10℃ / min. It is then held at that temperature for 2 hours for later use. S6. Place the mold in the mold heating furnace, heat it to 500-520℃, keep it at that temperature for 3 hours, apply graphite lubricant to the working surface of the mold, feed the ingot after heat preservation into the extruder barrel, start the extruder, and extrude the ingot from the mold at a speed of 7mm / s with a pressure of 280MPa to obtain a coarse pipe. Immediately put the extruded coarse pipe into the water-air atomization cooling device for online quenching and cooling, ensuring a cooling rate ≥30℃ / s. S7. Hang the quenched coarse pipe on the rack inside the hot air circulation aging furnace, close the furnace door, turn on the hot air circulation system, raise the temperature to 120-130℃ at a rate of 5℃ / min, hold for 5 hours for pre-aging, then raise the temperature to 180-190℃ at a rate of 3℃ / min, hold for 9 hours for main aging, and finally lower the temperature to 60-70℃ at a rate of 2℃ / min, hold for 13 hours for low-temperature aging. After completion, turn off the heating device, keep the hot air circulating, and let it cool naturally to below 100℃, then open the furnace door and let it air cool to room temperature. S8. After the aging of the coarse pipe is straightened by a straightening machine, it is immersed in polishing liquid for 10 minutes, turning it over every 2 minutes to ensure uniform polishing of the surface. After the immersion, the pipe is taken out and rinsed with deionized water 3 times for 1 minute each time. Then it is placed in an 80℃ drying oven for 30 minutes to obtain high-performance aluminum alloy pipe.

[0052] Example 2 Pipe composition design: Mg: 1.2%, Si: 0.8%, Sc: 0.05%, Zr: 0.08%, Cu: 0.2%, Mn: 0.1%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance is Al.

[0053] Preparation method: S1. Weigh out 99.97% high-purity aluminum ingots, magnesium ingots (99.95%), Al-Si master alloy (Si content 20wt%), Al-Sc master alloy (Sc content 2wt%), Al-Zr master alloy (Zr content 5wt%), Al-Cu master alloy (Cu content 30wt%), and Al-Mn master alloy (Mn content 10wt%) as raw materials according to the designed composition. S2. Add all the high-purity aluminum ingots to the graphite crucible furnace, close the furnace door, and heat to 740-760℃ at a rate of 10℃ / min until the aluminum ingots are completely melted. During this process, argon-nitrogen mixed gas (volume ratio 7:3) is introduced at a flow rate of 5L / min. After the aluminum ingots are completely melted, Al-Si, Al-Mn and Al-Cu master alloys are added in sequence. Mechanical stirring is started at a rate of 300r / min for 15min. After the stirring is completed, the furnace temperature is reduced to 720-730℃. Magnesium ingots and Al-Sc and Al-Zr master alloys are added. Stirring is continued for 10min. Stirring is stopped and the temperature is held for 20min. 0.1wt% Al-5Ti-B refining agent is added. The mixture is manually stirred for 5min and then allowed to stand for 10min. The filtered melt is collected into a holding crucible using a 100-mesh ceramic filter plate and held at a temperature of 710-720℃ for later use. S3. Heat the crystallizer to 300-320℃ and hold for 30 minutes. Pour the melt at 710-720℃ from the holding crucible into the crystallizer. When the melt level in the crystallizer reaches 2 / 3 of the crystallizer height, start the traction device to cast at a speed of 80mm / min. During this period, turn on the electromagnetic stirring at a frequency of 50Hz and turn on the water mist cooling. Cool the ingot to between 300-350℃ by controlling the water temperature and water pressure at a cooling rate of 15℃ / s. S4. Place the ingot into a box-type resistance furnace and heat it to 420-430℃ at a rate of 5℃ / min. Hold it at that temperature for 4 hours to perform a first stage of homogenization. After that, raise the temperature to 480-490℃ at a rate of 3℃ / min and hold it for 8 hours to perform a second stage of homogenization. After that, cool it to 300℃ with the furnace and then open the furnace door to air cool to room temperature. S5. Using a CNC lathe, the outer diameter of the homogenized ingot is machined to remove the skin, with a thickness of 2-3mm. The machined ingot is then placed in an induction heating furnace and heated to 480-500℃ at a rate of 10℃ / min. It is then held at that temperature for 2 hours for later use. S6. Place the mold in the mold heating furnace, heat it to 500-520℃, keep it at that temperature for 3 hours, apply graphite lubricant to the working surface of the mold, feed the ingot after heat preservation into the extruder barrel, start the extruder, and extrude the ingot from the mold at a speed of 5mm / s with a pressure of 250MPa to obtain a coarse pipe. Immediately put the extruded coarse pipe into the water-air atomization cooling device for online quenching and cooling, ensuring a cooling rate ≥30℃ / s. S7. Hang the quenched coarse pipe on the rack inside the hot air circulation aging furnace, close the furnace door, turn on the hot air circulation system, raise the temperature to 120-130℃ at a rate of 5℃ / min, hold for 4 hours for pre-aging, then raise the temperature to 180-190℃ at a rate of 3℃ / min, hold for 8 hours for main aging, and finally lower the temperature to 60-70℃ at a rate of 2℃ / min, hold for 12 hours for low-temperature aging. After completion, turn off the heating device, keep the hot air circulating, and let it cool naturally to below 100℃. Then open the furnace door and let it air cool to room temperature. S8. After the aging of the coarse pipe is straightened by a straightening machine, it is immersed in polishing liquid for 10 minutes, turning it over every 2 minutes to ensure uniform polishing of the surface. After the immersion, the pipe is taken out and rinsed with deionized water 3 times for 1 minute each time. Then it is placed in an 80℃ drying oven for 30 minutes to obtain high-performance aluminum alloy pipe.

[0054] Example 3 Pipe composition design: Mg: 1.8%, Si: 1.2%, Sc: 0.15%, Zr: 0.18%, Cu: 0.4%, Mn: 0.3%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance is Al.

[0055] Preparation method: S1. Weigh out 99.97% high-purity aluminum ingots, magnesium ingots (99.95%), Al-Si master alloy (Si content 20wt%), Al-Sc master alloy (Sc content 2wt%), Al-Zr master alloy (Zr content 5wt%), Al-Cu master alloy (Cu content 30wt%), and Al-Mn master alloy (Mn content 10wt%) as raw materials according to the designed composition. S2. Add all the high-purity aluminum ingots to the graphite crucible furnace, close the furnace door, and heat to 740-760℃ at a rate of 10℃ / min until the aluminum ingots are completely melted. During this process, argon-nitrogen mixed gas (volume ratio 7:3) is introduced at a flow rate of 5L / min. After the aluminum ingots are completely melted, Al-Si, Al-Mn and Al-Cu master alloys are added in sequence. Mechanical stirring is started at a rate of 300r / min for 20min. After the stirring is completed, the furnace temperature is reduced to 720-730℃. Magnesium ingots and Al-Sc and Al-Zr master alloys are added. Stirring is continued for 10min. Stirring is stopped and the temperature is held for 25min. 0.1wt% Al-5Ti-B refining agent is added. The mixture is manually stirred for 5min and then allowed to stand for 10min. The filtered melt is collected into a holding crucible using a 100-mesh ceramic filter plate and held at a temperature of 710-720℃ for later use. S3. Heat the crystallizer to 300-320℃ and hold for 30 minutes. Pour the melt at 710-720℃ from the holding crucible into the crystallizer. When the melt level in the crystallizer reaches 2 / 3 of the crystallizer height, start the traction device to cast at a speed of 100mm / min. During this period, turn on the electromagnetic stirring at a frequency of 60Hz and turn on the water mist cooling. Cool the ingot to between 300-350℃ by controlling the water temperature and water pressure at a cooling rate of 20℃ / s. S4. Place the ingot into a box-type resistance furnace and heat it to 420-430℃ at a rate of 5℃ / min. Hold it at that temperature for 5 hours to perform a first stage of homogenization. After that, raise the temperature to 480-490℃ at a rate of 3℃ / min and hold it for 10 hours to perform a second stage of homogenization. After that, cool it to 300℃ with the furnace and then open the furnace door to air cool to room temperature. S5. Using a CNC lathe, the outer diameter of the homogenized ingot is machined to remove the skin, with a thickness of 2-3mm. The machined ingot is then placed in an induction heating furnace and heated to 480-500℃ at a rate of 10℃ / min. It is then held at that temperature for 2 hours for later use. S6. Place the mold in the mold heating furnace, heat it to 500-520℃, and keep it at that temperature for 3 hours. Apply graphite lubricant to the working surface of the mold. Feed the ingot after heat preservation into the extruder barrel, start the extruder, and extrude the ingot from the mold at a speed of 8mm / s with a pressure of 300MPa to obtain a coarse pipe. Immediately put the extruded coarse pipe into the water-air atomization cooling device for online quenching and cooling to ensure a cooling rate ≥30℃ / s. S7. Hang the quenched coarse pipe on the rack inside the hot air circulation aging furnace, close the furnace door, turn on the hot air circulation system, raise the temperature to 120-130℃ at a rate of 5℃ / min, hold for 6 hours for pre-aging, then raise the temperature to 180-190℃ at a rate of 3℃ / min, hold for 9 hours for main aging, and finally lower the temperature to 60-70℃ at a rate of 2℃ / min, hold for 15 hours for low-temperature aging. After completion, turn off the heating device, keep the hot air circulating, and let it cool naturally to below 100℃, then open the furnace door and let it air cool to room temperature. S8. After the aging of the coarse pipe is straightened by a straightening machine, it is immersed in polishing liquid for 10 minutes, turning it over every 2 minutes to ensure uniform polishing of the surface. After the immersion, the pipe is taken out and rinsed with deionized water 3 times for 1 minute each time. Then it is placed in an 80℃ drying oven for 30 minutes to obtain high-performance aluminum alloy pipe.

[0056] Effect test Test sample The high-performance aluminum alloy tube prepared in Example 1 of this invention has a specification of Φ50×5mm; 6-series alloy: The mainstream industrial 6061-T6 aluminum alloy tubing (Al-Mg-Si series, standard heat-treated state) is selected, with a specification of Φ50×5mm, and is marked as "6061-T6"; 7-series alloys: High-strength 7075-T6 aluminum alloy tubing (Al-Zn-Mg-Cu series, standard heat-treated state), with specifications of Φ50×5mm, designated as "7075-T6".

[0057] Experimental standard prediction equipment (as shown in Table 1) Table 1 Test Standards and Equipment

[0058] Experimental steps Sample pretreatment: All pipes were straightened (multi-roller straightener, accuracy 0.5mm / m) and surface cleaned (chemical polishing, Ra≤0.8μm) according to the same process to ensure consistent testing standards; Mechanical property testing: The tensile specimens were plate-shaped (5 mm thick, 50 mm gauge length), and the impact specimens were U-notched (10 × 10 × 55 mm in size). The average value of 5 tests was taken. Corrosion resistance test: After salt spray test, weigh and calculate corrosion rate (weight loss method), and observe whether corrosion cracks appear in metallographic structure after intergranular corrosion; Process adaptability test: Measure the thickness of the oxide layer on the surface of the extruded pipe (online quenching vs. offline quenching), and calculate the performance variation coefficient of 20 samples in the same batch (fluctuation range = variation coefficient × 100%).

[0059] The experimental results are shown in Table 2-4: Table 2 Mechanical property test data

[0060] Table 3 Corrosion Resistance Test Data

[0061] Table 4 Process adaptability test data

[0062] It is evident that, in terms of mechanical properties, the high-performance aluminum alloy tubing prepared by this invention exhibits superior strength compared to the 6-series and significantly higher toughness than the 7-series: the tensile strength (392 MPa) of the alloy of this invention is 22.5% higher than that of 6061-T6, resolving the "insufficient strength" problem of the 6-series; simultaneously, the elongation (16.2%) is 2.1 times that of 7075-T6, and the impact toughness (48 J / cm²) is also significantly higher. 2 It is 1.9 times that of the 7075-T6, making up for the 7 Series' shortcoming of "embrittlement risk"; Regarding corrosion resistance, the corrosion rate of the alloy of this invention over 1000 hours (0.008 mm / a) is only 19% of that of 6061-T6 and 32% of that of 7075-T6, which can extend its service life by 3-5 times in marine engineering (such as offshore platform pipelines). 7075-T6 is prone to intergranular corrosion due to its high Cu content (1.2-2.0wt%). However, the alloy of this invention, through the synergistic regulation of Cu (0.3wt%) and Mn (0.2wt%), exhibits no cracks in intergranular corrosion after 168 hours and can replace the 7 series for use in humid / corrosive environments (such as marine hydraulic pipelines).

[0063] In terms of process adaptability, the high-performance aluminum alloy tube prepared by this invention has a thin oxide layer and low processing cost. Online quenching makes the oxide layer thickness (3μm) of this invention only 37.5% of that of 6061-T6 (8μm) and 30% of that of 7075-T6 (10μm), and the cost of subsequent oxide layer removal processes is reduced by 20-30%. 7075-T6 is prone to cracking during bending, welding and other processing due to its poor toughness (elongation ≤8%). In contrast, the invented alloy has an elongation ≥15%, and the processing scrap rate can be controlled below 5%, making it suitable for complex pipe forming needs (such as special-shaped conduits for high-end equipment).

[0064] 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 it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the specific implementation of the present invention. Any modifications or equivalent substitutions that do not depart from the spirit and scope of the present invention should be covered within the scope of protection of the claims of the present invention.

Claims

1. A high-performance aluminum alloy tube, characterized in that, Including the following ingredients by weight percentage: Mg: 1.2~1.8%, Si: 0.8~1.2%, Sc: 0.05~0.15%, Zr: 0.08~0.18%, Cu: 0.2~0.4%, Mn: 0.1~0.3%, impurities: Fe≤0.15%, Zn≤0.1%, Ti≤0.05%, balance Al.

2. A method for preparing the high-performance aluminum alloy tubing as described in claim 1, characterized in that, The preparation steps include the following: Aluminum ingots, magnesium ingots, Al-Si master alloy, Al-Sc master alloy, Al-Zr master alloy, Al-Cu master alloy, and Al-Mn master alloy were weighed as raw materials according to the mass percentage of the high-performance aluminum alloy tubing composition. After heating and melting aluminum ingots, Al-Si, Al-Mn, and Al-Cu master alloys are added sequentially for the first stirring. After the first stirring, magnesium ingots and Al-Sc and Al-Zr master alloys are added for heat preservation treatment. Then, a refining agent is added, and after standing, the mixture is filtered to obtain the melt. The melt is cast to obtain an ingot. The ingot is then segmented and homogenized. After pretreatment, the homogenized ingot is extruded to obtain a coarse pipe. The coarse tube is quenched and then subjected to a three-stage aging treatment. After post-treatment, the high-performance aluminum alloy tube is obtained.

3. The method for preparing high-performance aluminum alloy tubing according to claim 2, characterized in that, The heating temperature is 740-760℃; the cooling temperature is 720-730℃; the stirring time of the first stirring is 15-20 minutes, and the stirring rate is 300 r / min.

4. The method for preparing high-performance aluminum alloy tubing according to claim 3, characterized in that, The casting temperature is 710-720℃, and electromagnetic stirring is applied during casting. The stirring frequency of the electromagnetic stirring is 50-60Hz, the casting speed is 80-100mm / min, and the cooling rate is 15-20℃ / s.

5. The method for preparing high-performance aluminum alloy tubing according to claim 4, characterized in that, The segmented homogenization process specifically involves: holding the ingot at 420-430℃ for 4-5 hours for the first stage of homogenization; then raising the temperature to 480-490℃ and holding it for 8-10 hours for the second stage of homogenization; and finally cooling it to 300℃ with the furnace and then air-cooling it to room temperature.

6. The method for preparing high-performance aluminum alloy tubing according to claim 5, characterized in that, The pretreatment is as follows: remove a 2-3 cm thick outer skin from the homogenized ingot and preheat it to 480-500℃ and hold it for 2 hours.

7. The method for preparing high-performance aluminum alloy tubing according to claim 6, characterized in that, The extrusion molding process involves preheating the mold to 500-520℃ and extruding the pretreated ingot at a temperature of 500-520℃ and a speed of 5-8mm / s.

8. The method for preparing high-performance aluminum alloy tubing according to claim 7, characterized in that, The quenching process involves cooling the coarse pipe material with water-air atomization at a cooling rate of 30°C or higher.

9. The method for preparing high-performance aluminum alloy tubing according to claim 8, characterized in that, The three-stage aging process is as follows: the quenched coarse pipe is held at 120-130℃ for 4-6 hours for pre-aging, then the temperature is raised to 180-190℃ and held for 8-10 hours for main aging, and finally the temperature is lowered to 60-70℃ and held for 12-15℃ for low-temperature aging.

10. The method for preparing high-performance aluminum alloy tubing according to claim 9, characterized in that, The post-processing involves straightening the aged coarse pipe and then chemically polishing it.

Images