A method for recycling scrap aluminum into aluminum alloy ingots

Abstract

This invention relates to the field of aluminum alloy technology, specifically to a method for recycling and processing aluminum alloy ingots from waste aluminum, comprising the following steps performed in sequence: (1) graded pretreatment; (2) dual-chamber gradient melting; (3) composite modification coupled with intermittent ultrasonic purification; (4) time-series linkage spray degassing; (5) gradient filtration and controllable cooling. This invention solves the problems of rare earth and Te burn-off and acicular Fe phase runaway by core-shell slow-release modification, reconstructs the Fe-rich phase morphology by precisely controlling the Mn / Fe ratio, solves the problem of incomplete single degassing and impurity removal by bottom blowing-intermittent ultrasound-time-series spray triple purification, and solves the problems of inclusion residue and grain coarsening by gradient filtration and segmented phase transformation controlled cooling. Overall, it breaks through the industry bottleneck that high-impurity waste aluminum cannot be directly and stably prepared into high-end homogeneous aluminum alloy ingots. Under the conditions of zero primary aluminum dilution or low proportion of use, recycled aluminum alloy ingots with density, strong plasticity and uniform structure that meet the requirements of high-end castings can be obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, specifically to a method for recycling waste aluminum and processing it into aluminum alloy ingots. Background Technology

[0002] Recycled aluminum alloys, produced from recycled scrap aluminum, significantly reduce energy consumption and carbon emissions compared to primary aluminum production, making them an important aluminum source for the automotive, building materials, and general casting industries. However, scrap aluminum comes from a wide range of sources and fluctuates greatly from batch to batch. In addition to the target aluminum matrix, the raw materials often contain oil, paint, plastics, rubber, iron fasteners, alloying elements such as magnesium, zinc, and copper, as well as adsorbed water and surface hydroxyl groups. The difficulty of purifying the melt and controlling its microstructure is far greater than that of primary aluminum production. The industry's common practice is to use a process route of "crushing and sorting—flame or electric resistance furnace melting—inert gas rotary blowing degassing—single-layer foam ceramic filtration—natural cooling ingot casting." This process can maintain basic performance when using a low proportion of scrap aluminum, but it exposes a series of bottlenecks in scenarios with a high proportion or even all scrap aluminum recycling.

[0003] Firstly, the pretreatment process is rudimentary. Most production lines only perform crushing and magnetic separation, which is insufficient for removing oil, paint, adsorbed water, and surface hydroxyl groups. During smelting, hydrogen sources and organic cracking products are continuously released, resulting in a melt hydrogen content generally exceeding 0.12 mL / 100gAl. Consequently, the rate of pinholes and porosity defects remains high after casting. Although some companies have introduced alkaline washing and baking, the heating rate and holding time lack differentiated control. Highly contaminated materials and clean materials are treated the same, making it difficult to balance impurity removal efficiency and metal recovery rate.

[0004] Secondly, the methods for controlling impurity phases such as Fe are limited. The Fe mass fraction in scrap aluminum often exceeds 1%, easily leading to the precipitation of coarse needle-like α-Al+Fe+Si or β-Al5FeSi phases, which severely rupture the matrix and induce thermal cracking. Existing processes mostly rely on adding Mn to neutralize Fe, but the Mn / Fe mass ratio is poorly controlled. If it is too low, the needle-like phases are not eliminated; if it is too high, coarse Al6(Mn,Fe) phases are generated, which also impairs toughness. At the same time, a single Al-Ti-B grain refiner easily reacts with Fe and Mn in a high-impurity environment to generate ineffective phases, resulting in a diminished grain refinement effect and grain sizes often exceeding 80 μm.

[0005] Third, the burning loss and uneven distribution of the modified elements. When rare earth elements such as La, Ce and Te are directly added to the melt above 740℃, they suffer severe oxidation and burning loss, and the effective residual amount is difficult to stabilize. Te has a high vapor pressure and is easy to volatilize, and the utilization rate is low when added in a conventional way. The modification and rounding effect of eutectic silicon fluctuate greatly.

[0006] The aforementioned problems result in inconsistent mechanical properties of recycled aluminum alloy ingots, with pinholes and inclusions often exceeding the requirements of current standards for high-end ingots, making it difficult to stably supply the market for components that require a synergistic combination of high plasticity, density, and uniform microstructure. To address this situation, this invention provides a method for recycling and processing waste aluminum into aluminum alloy ingots. Summary of the Invention

[0007] The purpose of this invention is to provide a method for recycling and processing waste aluminum into aluminum alloy ingots.

[0008] To achieve the above objectives, the present invention provides the following technical solution: A method for recycling waste aluminum into aluminum alloy ingots includes the following steps performed sequentially: (1) Grading and pretreatment: The waste aluminum raw materials are graded and classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to be no more than 40mm. The materials are then sorted and cleaned, alkaline cleaning and thermal dehydroxylation treatment are performed to remove oil stains, surface inclusions, adsorbed water and hydroxyl impurities, and obtain qualified waste aluminum raw materials with low impurities. (2) Dual-chamber gradient melting: qualified scrap aluminum is preheated and melted in stages using a closed dual-chamber melting furnace to prepare a crude aluminum melt with uniform composition. Large particle inclusions are removed by static floating. (3) Composite modification coupled with intermittent ultrasonic purification: a core-shell structure composite modifier is added to the crude aluminum melt, the mass ratio of Mn / Fe in the melt is controlled to be 0.6~0.9, and argon bottom blowing at the furnace bottom is combined with intermittent high-energy ultrasound to achieve melt modification and purification. (4) Sequential linkage of jet degassing: Argon-chlorine mixture is jetted by a rotary nozzle. Through the sequential linkage of ultrasonic operation and rotary jet degassing, the oxide film is broken, fine inclusions are captured and hydrogen is removed in steps to achieve deep purification of the melt. (5) Gradient filtration and controllable cooling: Multi-level gradient preheated foam ceramic filter media is used to filter the melt in stages. After casting, segmented phase change temperature control cooling is used to obtain homogeneous low-defect aluminum alloy ingots. The core-shell structured composite modifier has a three-layer composite structure, consisting of an alloy core, a nano-SiO2 transition inner layer, and a rare earth-Te slow-release modifier outer layer from the inside out. The total mass of the double-layered shell accounts for 4% to 7% of the total mass of the modifier. The total mass of La and Ce in the modifier accounts for 0.8% to 1.6%, and the mass of Te accounts for 0.1% to 0.3%.

[0009] As a further technical solution, the specific process of the graded pretreatment in step (1) is as follows: After being crushed, the waste aluminum is sequentially subjected to magnetic separation to remove iron impurities and eddy current separation to remove non-metallic inclusions. It is then ultrasonically cleaned for 15-25 minutes at 35-45 kHz using a 3%-5% sodium hydroxide aqueous solution, followed by rinsing with deionized water until neutral. Under a nitrogen protective atmosphere, the temperature is raised to 350-400℃ at a rate of 5-8℃ / min, and thermally dehydroxylated for 25-40 minutes. After cooling, qualified waste aluminum with an iron content of ≤1.8% is obtained by screening. For highly polluted waste aluminum, the ultrasonic cleaning and thermal dehydroxylation times are extended to achieve differentiated impurity removal.

[0010] As a further technical solution, the specific process parameters for step (2) of the dual-chamber gradient melting are as follows: The charging chamber is preheated at 600~650℃ for 10~15 minutes, and the melting chamber is kept at 720~750℃ for 20~28 minutes to completely melt the waste aluminum. The melt is allowed to stand for 5~8 minutes to promote the separation of large particles. Nitrogen gas is maintained at a slightly positive pressure throughout the melting process to isolate the melt from air and prevent secondary oxidation and hydrogen absorption.

[0011] As a further technical solution, the core-shell structured composite modifier is prepared by the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 740~760℃ and completely melted. Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous. The mixture is then cast and sieved to obtain spherical alloy core particles with a particle size of 3~5mm. S2 double-layer coating molding: Two coating structures are sequentially constructed on the outer surface of alloy core particles. The inner layer is a dense transition layer of nano-SiO2 with a thickness of 0.05~0.1mm, and the outer layer is a rare earth-Te slow-release metamorphic shell with a thickness of 0.15~0.4mm. The total thickness of the composite shell is 0.2~0.5mm, thus obtaining a core-shell structure composite metamorphic agent.

[0012] As a further technical solution, the double-layered shell is prepared using a two-step process of sol-gel coupled argon-protected mechanical alloying, the specific steps of which are as follows: Preparation of transition layer using S11 sol-gel: Prepare silane hydrolysate by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2, and adjust the pH to 4.5 with hydrochloric acid; completely immerse the alloy core particles in the hydrolysate, ultrasonically impregnate for 20-30 minutes at 40 kHz, and cure at 120℃ for 30 minutes to form a dense barrier nano-SiO2 transition layer. S12 mechanical alloying coating: Sodium tetraborate decahydrate, Te powder, and zinc stearate are mixed at a mass ratio of 6~10:1~3:0.5 to obtain coating powder, which is dried at 80~90℃ and ≤-0.08MPa vacuum for 10~15min; the dried powder is mixed with particles with transition layer core at a mass ratio of 7~12:100, and ball-milled at argon protection, ball-to-material ratio of 8:1, and rotation speed of 220~260r / min for 40~60min. After sieving, it is vacuum sealed and stored to obtain the finished modifier.

[0013] As a further technical solution, the specific process parameters for ultrasonic purification and argon bottom blowing in step (3) are as follows: The amount of core-shell composite modifier added is 1.2%~2.0% of the total mass of crude aluminum melt; the purity of bottom-blown argon is ≥99.99%, the flow rate is 8~12L / min, and it is synchronously bottom-blown through multiple evenly distributed pores at the bottom of the furnace, with uniform flow rates at each pore; the ultrasonic frequency is 1.2~1.8kHz, the duration of a single ultrasonic treatment is 60~80s, the interval duration is 60~80s, the total ultrasonic treatment time is 10~18min, and the melt temperature is kept constant at 735~745℃ during the ultrasonic treatment stage.

[0014] As a further technical solution, the specific process parameters for step (4) of sequential linkage jet degassing are as follows: The volume fraction of Cl2 in the Ar-Cl2 mixture is 0.5%~1.5%; the rotational speed of the rotary nozzle is 280~360 r / min, and the total blowing time is 15~25 min; the operation sequence is as follows: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic treatment and then continue blowing for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final stage of continuous blowing; the final stage of blowing time accounts for 30%~40% of the total blowing time, and the melt temperature is kept constant at 710~720℃ during the blowing stage.

[0015] As a further technical solution, the specific process of gradient filtering in step (5) is as follows: High-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi, and 50ppi are used for step-by-step filtration. The filter plates are preheated to 680~700℃ and kept at a constant temperature for 20 minutes. The temperature fluctuation of the filter plates is ≤±5℃ throughout the filtration process. The melt flows through each level of filter plates at a constant flow rate of 1.2~1.8m / min, which separates and retains fine inclusions of different particle sizes.

[0016] As a further technical solution, the specific process of segmented controllable cooling in step (5) is as follows: After the melt is cast, it is first cooled by air cooling at room temperature at a speed of 3~5m / s for 10~15min. When the surface temperature of the ingot drops to the critical range of alloy phase transformation of 450~480℃, water mist spray cooling is switched. The water mist pressure is 0.2~0.4MPa and the water mist particle size is 20~50μm. The water mist evenly covers the surface of the ingot and sprays continuously for 8~12min to refine the grains and eliminate the internal stress of the ingot.

[0017] Compared with the prior art, the beneficial effects of the present invention are: 1. The technical solution of this invention employs a three-layer core-shell composite modifier consisting of an alloy core, a nano-SiO2 transition inner layer, and a rare earth-Te slow-release modifier outer layer. The total mass of the double-layered shell accounts for 4%~7% of the total modifier mass, La and Ce account for 0.8%~1.6%, and Te accounts for 0.1%~0.3%. The dense nano-SiO2 transition layer forms a physical barrier in the melt above 740℃, inhibiting the rare earth elements from being directly exposed to the oxidizing aluminum liquid and thus burned off. The outer layer... The slow-release shell gradually disintegrates under the thermal action of the melt, releasing La, Ce and Te, which continuously supplies the modified elements within the nucleation window. This transforms the eutectic silicon from needle-like to fibrous, improving its roundness. Furthermore, the crystal plane modification of the β-Al5FeSi phase by Te inhibits the growth of needle-like Fe-rich phases. At the same time, the melt Mn / Fe mass ratio is controlled within the range of 0.6 to 0.9, causing excess Fe to precipitate as the Chinese character-shaped Al6(Mn,Fe) phase instead of needle-like plates, thus eliminating the dominant defect source that cuts the matrix. By employing a combination of multi-point uniform argon bottom blowing at the furnace bottom and intermittent high-energy ultrasound at 1.2~1.8kHz, the bottom blowing creates a steady-state upward flow field that removes large inclusions and clustered hydrogen bubbles. Intermittent ultrasound, within each 60~80s interval, uses cavitation-induced microjets to break up oxide film clusters and induce heterogeneous nucleation. The 60~80s intervals prevent overheating and grain coarsening caused by continuous cavitation, thus achieving deep homogenization of the melt without introducing heterogeneous contamination. The Ar-Cl2 mixed gas rotary blowing and ultrasonic operation are time-coordinated with a sequence of "3 rounds of intermittent ultrasound, 5-minute stop of ultrasonic blowing, 2 rounds of intermittent ultrasound, and continuous blowing in the final stage," avoiding phase competition between the ultrasonic flow and the rotating bubble field. This ensures that oxide film fragments are captured and removed precisely at the upward floating window of the blowing bubbles after ultrasonic breakage. The continuous blowing in the final stage, lasting 30%~40% of the time, completes the deep removal of residual hydrogen, reducing the hydrogen content to the level of 0.08mL / 100gAl. Because it adopts a three-stage high-purity alumina foam ceramic gradient filtration system with 20ppi, 30ppi, and 50ppi, and the filter plate is kept at a constant temperature of 680~700℃ with fluctuations ≤±5℃ and a constant melting rate of 1.2~1.8m / min, impurities of different particle sizes are staged and intercepted rather than blocked all at once, resulting in stable filtration pressure drop and significantly improved capture rate.

[0018] 2. In the technical solution of this invention, the dual-chamber melting is carried out in stages with preheating at 600~650℃ and melting at 720~750℃, and nitrogen micro-positive pressure protection is used to suppress secondary oxidation and hydrogen absorption, providing a low oxygen potential substrate for deterioration and purification; the core-shell deterioration releases active elements in the melt at a constant temperature window of 735~745℃, and pins and refines the nucleation of inclusions in sync with bottom blowing and ultrasonication; the time-linked degassing ends at 710~720℃, and hydrogen and fine inclusions migrate out simultaneously; gradient filtration retains submicron residues that were not removed by the previous stage; and segmented controlled cooling locks in the fine grain structure.

[0019] 3. In summary, this invention addresses the issues of rare earth and Te burn-off and uncontrolled needle-like Fe phase through core-shell slow-release metamorphism, reconstructs the Fe-rich phase morphology through precise Mn / Fe ratio control, solves the problem of incomplete degassing and impurity removal through bottom blowing-intermittent ultrasound-timed jetting triple purification, and solves the problems of inclusion residue and grain coarsening through gradient filtration and segmented phase transformation controlled cooling. Overall, it breaks through the industry bottleneck that high-impurity waste aluminum cannot be directly and stably used to prepare high-end homogeneous aluminum alloy ingots. Under conditions of zero primary aluminum dilution or low proportion of use, recycled aluminum alloy ingots with density, strength, plasticity and microstructure uniformity that meet the requirements of high-end castings can be obtained, improving the product level and added value of waste aluminum resource utilization, and conforming to the development direction of low-carbonization and high-value-added recycled aluminum. Detailed Implementation

[0020] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0021] This invention provides a method for recycling and processing waste aluminum into aluminum alloy ingots, comprising the following steps: (1) Grading and pretreatment: The waste aluminum raw materials are graded and classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to be no more than 40mm. The materials are then sorted and cleaned, alkaline cleaning and thermal dehydroxylation treatment are performed to remove oil stains, surface inclusions, adsorbed water and hydroxyl impurities, and obtain qualified waste aluminum raw materials with low impurities. (2) Dual-chamber gradient melting: qualified scrap aluminum is preheated and melted in stages using a closed dual-chamber melting furnace to prepare a crude aluminum melt with uniform composition. Large particle inclusions are removed by static floating. (3) Composite modification coupled with intermittent ultrasonic purification: a core-shell structure composite modifier is added to the crude aluminum melt, the mass ratio of Mn / Fe in the melt is controlled to be 0.6~0.9, and argon bottom blowing at the furnace bottom is combined with intermittent high-energy ultrasound to achieve melt modification and purification. (4) Sequential linkage of jet degassing: Argon-chlorine mixture is jetted by a rotary nozzle. Through the sequential linkage of ultrasonic operation and rotary jet degassing, the oxide film is broken, fine inclusions are captured and hydrogen is removed in steps to achieve deep purification of the melt. (5) Gradient filtration and controllable cooling: Multi-level gradient preheated foam ceramic filter media is used to filter the melt in stages. After casting, segmented phase change temperature control cooling is used to obtain homogeneous low-defect aluminum alloy ingots.

[0022] In step (1), the present invention classifies waste aluminum raw materials according to material grade and surface contamination level. In this invention, the waste aluminum raw materials preferably include one or more of the following: automotive dismantling aluminum, architectural aluminum profile scraps, aluminum alloy processing waste, and waste aluminum alloy castings; they can be obtained using recycling and classification methods well known to those skilled in the art or through commercial purchase. After crushing, the maximum particle size is controlled to be no greater than 40 mm, preferably no greater than 30 mm.

[0023] In this invention, the preferred specific process for the graded pretreatment in step (1) is as follows: after crushing, the waste aluminum is sequentially subjected to magnetic separation to remove iron impurities and eddy current separation to remove non-metallic inclusions; a 3%~5% sodium hydroxide aqueous solution is used for ultrasonic cleaning at 35~45kHz for 15~25min, followed by rinsing with deionized water until neutral; under a nitrogen protective atmosphere, the temperature is raised to 350~400℃ at 5~8℃ / min, and thermal dehydroxylation is performed at a constant temperature for 25~40min; after cooling, qualified waste aluminum with an iron content ≤1.8% is obtained by screening; for highly polluted waste aluminum, the ultrasonic cleaning and thermal dehydroxylation times are extended accordingly to achieve differentiated impurity removal. More preferably, a 4% sodium hydroxide aqueous solution is used for ultrasonic cleaning at 40kHz for 20min, followed by thermal dehydroxylation at 6℃ / min under a nitrogen protective atmosphere for 30min.

[0024] In step (2), the present invention uses a closed double-chamber smelting furnace to preheat and melt qualified scrap aluminum in stages at high temperature. In the present invention, the double-chamber smelting furnace is preferably a gas-heated or resistance-heated closed double-chamber furnace, and the charging chamber and the melting chamber are connected by a guide channel. Commercially available equipment known to those skilled in the art can be used.

[0025] In this invention, the preferred process parameters for the dual-chamber gradient melting in step (2) are: preheating the charging chamber at 600~650℃ for 10~15min, and constant-temperature melting at 720~750℃ in the melting chamber for 20~28min to completely melt the waste aluminum; allowing the melt to stand for 5~8min to promote the floating and separation of large particle inclusions; maintaining a slight positive pressure of nitrogen throughout the melting process to isolate the melt from air and prevent secondary oxidation and hydrogen absorption. More preferably, the parameters are: preheating the charging chamber at 620℃ for 12min, constant-temperature melting at 740℃ in the melting chamber for 24min, allowing the melt to stand for 6min, and a slight positive pressure of nitrogen of 0.02~0.05MPa.

[0026] The nitrogen gas has a slight positive pressure of 10 Pa.

[0027] In step (3), the present invention adds a core-shell structured composite modifier to the crude aluminum melt, controls the Mn / Fe mass ratio of the melt to be 0.6~0.9, and simultaneously uses bottom blowing of argon gas from the furnace bottom combined with intermittent high-energy ultrasound to achieve melt modification and purification. In the present invention, the core-shell structured composite modifier is a three-layer composite structure, consisting of an alloy core, a nano-SiO2 transition inner layer, and a rare earth-Te slow-release modifier outer layer from the inside out; the total mass of the double-layered shell accounts for 4%~7% of the total mass of the modifier; the total mass of La and Ce in the modifier accounts for 0.8%~1.6%, and the mass of Te accounts for 0.1%~0.3%.

[0028] In this invention, the core-shell composite modifier is preferably prepared by the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 740~760℃ and completely melted, and Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B, and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous, and then cast and sieved to obtain spherical alloy core particles with a particle size of 3~5mm; S2 Double-layer coating molding: Two coating structures are sequentially constructed on the outer surface of the alloy core particles. The inner layer is a dense transition layer of nano-SiO2 with a thickness of 0.05~0.1mm, and the outer layer is a rare earth-Te slow-release modifier shell with a thickness of 0.15~0.4mm. The total thickness of the composite shell is 0.2~0.5mm, thus obtaining the core-shell composite modifier. More preferably, the alloy core is prepared at a temperature of 750°C, with a core particle size of 4 mm; the inner nano-SiO2 transition layer has a thickness of 0.08 mm, the outer rare earth-Te slow-release metamorphic shell has a thickness of 0.25 mm, and the total thickness of the composite shell is 0.33 mm.

[0029] In this invention, the double-layered shell is preferably prepared using a two-step process of sol-gel coupled argon-protected mechanical alloying, and the specific steps are preferably as follows: Preparation of transition layer using S11 sol-gel: Prepare silane hydrolysate by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2, and adjust the pH to 4.5 with hydrochloric acid; completely immerse the alloy core particles in the hydrolysate, ultrasonically impregnate for 20-30 minutes at 40 kHz, and cure at 120℃ for 30 minutes to form a dense barrier nano-SiO2 transition layer. S12 mechanical alloying coating: Sodium tetraborate decahydrate, Te powder, and zinc stearate are mixed at a mass ratio of 6~10:1~3:0.5 to obtain a coating powder, which is dried at 80~90℃ and ≤-0.08MPa vacuum for 10~15min. The dried powder is then mixed with core particles with a transition layer at a mass ratio of 7~12:100 and ball-milled at 220~260r / min under argon protection, a ball-to-particle ratio of 8:1, and a rotation speed of 40~60min. After sieving, the mixture is vacuum-sealed and stored to obtain the finished modifier. More preferably, the mass ratio of sodium tetraborate decahydrate, Te powder, and zinc stearate is 8:2:0.5, the drying temperature is 85℃, the drying time is 12min, the powder-to-core particle mass ratio is 10:100, the ball-milling speed is 240r / min, and the ball-milling time is 50min. The present invention does not impose any special restrictions on the sources of the tetraethyl orthosilicate, ethanol, sodium tetraborate decahydrate, Te powder, and zinc stearate, and any commercially available products well known to those skilled in the art can be used; in a preferred embodiment of the present invention, the tetraethyl orthosilicate is provided by Sinopharm Chemical Reagent Co., Ltd., and is of AR grade; the Te powder is provided by Zhongnuo New Materials Technology Co., Ltd., and has a purity of ≥99.9%.

[0030] In this invention, the preferred process parameters for ultrasonic purification and argon bottom blowing in step (3) are: the amount of core-shell composite modifier added is 1.2%~2.0% of the total mass of crude aluminum melt; the purity of bottom blowing argon is ≥99.99%, the flow rate is 8~12L / min, and it is synchronously bottom blown through multiple evenly distributed pores at the bottom of the furnace, with uniform flow rates at each pore; the ultrasonic frequency is 1.2~1.8kHz, the duration of a single ultrasonic wave is 60~80s, the interval duration is 60~80s, the total ultrasonic treatment time is 10~18min, and the melt temperature is constant at 735~745℃ during the ultrasonic treatment stage. More preferably, the modifier added is 1.5%, the bottom blowing argon flow rate is 10L / min, the ultrasonic frequency is 1.5kHz, the duration of a single ultrasonic wave is 70s, the interval duration is 70s, the total ultrasonic treatment time is 14min, and the melt temperature is constant at 740℃.

[0031] In step (4), the present invention uses a rotary nozzle to spray an argon-chlorine mixture. Through the sequential coordination of ultrasonic operation and rotary spraying, the oxide film is broken, fine inclusions are captured and hydrogen is removed in steps, thereby achieving deep purification of the melt.

[0032] In this invention, the preferred process parameters for the sequential linkage blowing degassing in step (4) are: the volume fraction of Cl2 in the Ar-Cl2 mixture is 0.5%~1.5%; the rotational speed of the rotary nozzle is 280~360 r / min, and the total blowing time is 15~25 min; the operation sequence is: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic treatment and continue blowing for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final continuous blowing stage; the final blowing time accounts for 30%~40% of the total blowing time, and the melt temperature is constant at 710~720℃ during the blowing stage. More preferably, the volume fraction of Cl2 is 1.0%, the rotational speed of the rotary nozzle is 320 r / min, the total blowing time is 20 min, the final blowing time accounts for 35%, and the melt temperature is constant at 715℃. This invention does not have any special restrictions on the source of the rotary nozzle, and commercially available products known to those skilled in the art can be used.

[0033] In step (5), the present invention uses multi-level gradient preheated foam ceramic filter media to filter the melt in stages, and after casting, it uses segmented phase change temperature control cooling to obtain homogeneous low-defect aluminum alloy ingots.

[0034] In this invention, the gradient filtration process in step (5) is preferably as follows: high-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi, and 50ppi are used for step-by-step gradient filtration; the filter plates are preheated to 680~700℃ and kept at a constant temperature for 20min, with the filter plate temperature fluctuation ≤±5℃ throughout the filtration process; the melt flows through each level of filter plate at a constant flow rate of 1.2~1.8m / min, retaining fine inclusions of different particle sizes in stages. More preferably, the filter plate is preheated to 690℃ and kept at a constant temperature for 20min, with a melt flow rate of 1.5m / min. This invention does not impose any special restrictions on the source of the high-purity alumina foam ceramic filter plates; commercially available products known to those skilled in the art can be used. In the preferred embodiment of this invention, the filter plate material is 99% alumina, with specifications of 20ppi, 30ppi, and 50ppi, respectively.

[0035] In this invention, the preferred specific process for the segmented controllable cooling in step (5) is as follows: after the melt is cast, it is first cooled by ambient air at a speed of 3-5 m / s for 10-15 min; when the surface temperature of the ingot drops to the critical range of alloy phase transformation of 450-480℃, water mist spray cooling is switched; the water mist pressure is 0.2-0.4 MPa, the water mist particle size is 20-50 μm, and it uniformly covers the surface of the ingot, spraying continuously for 8-12 min to refine the grains and eliminate the internal stress of the ingot. More preferably, the air cooling rate is 4 m / s, the air cooling time is 12 min, the switching temperature is 460℃, the water mist pressure is 0.3 MPa, the water mist particle size is 35 μm, and the spraying time is 10 min. This invention does not have any special restrictions on the source of the water mist spraying equipment, and commercially available products known to those skilled in the art can be used.

[0036] This invention provides a method for recycling and processing waste aluminum into aluminum alloy ingots. The method involves removing oil and hydroxyl impurities through graded pretreatment, followed by dual-chamber gradient melting to prepare a homogeneous coarse aluminum melt. The slow-release modification effect of a core-shell composite modifier, coupled with intermittent ultrasonic purification and argon bottom blowing, achieves deep impurity removal and microstructure refinement of the melt. The segmented synergistic effect of time-linked jet degassing further removes hydrogen and fine inclusions. Gradient filtration and segmented phase-change temperature-controlled cooling yield a homogeneous, low-defect, high-quality aluminum alloy ingot. Compared with existing technologies, this invention solves problems such as incomplete impurity removal, high hydrogen content in the melt, coarse grain structure, and unstable mechanical properties during waste aluminum recycling. It achieves efficient and clean recycling and high-value utilization of waste aluminum resources, resulting in aluminum alloy ingots with low hydrogen content, high density, fine and uniform grain structure, and excellent mechanical properties.

[0037] To further illustrate the present invention, the following embodiments will be described in detail.

[0038] The waste aluminum raw materials used in the following embodiments of the present invention mainly include aluminum from dismantled automobiles, scrap aluminum profiles from buildings, and aluminum alloy processing waste. After sorting, the iron content is 1.2%~1.6% by mass. The industrial pure aluminum used is provided by China Aluminum Shandong Co., Ltd., with the grade Al99.70. The Al-10Mn master alloy used is provided by Xuzhou Alloy Materials Co., Ltd. The Al-20La and Al-15Ce master alloys used are provided by Hunan Rare Earth Metal Materials Research Institute. The Al-5Ti-B master alloy used is provided by Beijing General Research Institute of Nonferrous Metals, with the model Al-5Ti-1B. The Al-3Te master alloy used is provided by Zhongnuo New Materials Technology Co., Ltd. The tetraethyl orthosilicate used is provided by Sinopharm Chemical Reagent Co., Ltd., with the model AR grade. The sodium tetraborate decahydrate used is provided by Tianjin Bodi Chemical Co., Ltd. The Te powder used is provided by Zhongnuo New Materials Technology Co., Ltd., with a purity ≥99.9%. The zinc stearate used is provided by Hangzhou Oil & Fat Chemical Co., Ltd.

[0039] Example 1: (1) Graded pretreatment: The waste aluminum raw materials are graded and classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to 30 mm. The iron impurities are removed by magnetic separation and the non-metallic inclusions are removed by eddy current separation. The waste aluminum raw materials are then ultrasonically cleaned with a 3% sodium hydroxide aqueous solution at 35 kHz for 15 min and rinsed with deionized water until neutral. The temperature is raised to 350℃ at 5℃ / min under nitrogen protection and the heat is kept constant for 25 min to remove hydroxyl groups. After cooling, qualified waste aluminum materials with an iron content of 1.5% are obtained by screening.

[0040] (2) Dual-chamber gradient melting: Qualified scrap aluminum is added to a closed dual-chamber melting furnace. The feeding chamber is preheated at 600℃ for 10 minutes, and the melting chamber is kept at 720℃ for 20 minutes to completely melt the scrap aluminum. The melt is left to stand for 5 minutes to promote the separation of large particles. Nitrogen gas is maintained at a slight positive pressure of 0.02MPa throughout the melting process.

[0041] (3) Composite modification coupled with intermittent ultrasonic purification: A core-shell structure composite modifier is added to the crude aluminum melt at a rate of 1.2% of the total mass of the crude aluminum melt, and the mass ratio of Mn / Fe in the melt is controlled to be 0.6; the purity of bottom blowing argon gas is 99.99%, the flow rate is 8L / min, and it is blown synchronously through multiple evenly distributed gas holes at the bottom of the furnace; the ultrasonic frequency is 1.2kHz, the duration of a single ultrasonic treatment is 60s, the duration of the interval is 60s, the total ultrasonic treatment time is 10min, and the melt temperature is kept constant at 735℃ during the ultrasonic treatment stage.

[0042] The core-shell structured composite modifier is prepared according to the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 740℃ and completely melted. Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous. The mixture is then cast and sieved to obtain spherical alloy core particles with a particle size of 3mm. S2 Double-Layer Coating Molding: A silane hydrolysate was prepared by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2. The pH was adjusted to 4.5 with hydrochloric acid. The alloy core particles were completely immersed in the hydrolysate and ultrasonically impregnated at 40kHz for 20 minutes. The mixture was then cured at 120℃ for 30 minutes to form a dense transition layer of nano-SiO2 with a thickness of 0.05 mm. Sodium tetraborate decahydrate, Te powder, and zinc stearate were mixed in a mass ratio of 6:1:0.5 to obtain the coating powder. The powder was dried at 80℃ and ≤-0.08MPa vacuum for 10 minutes. The dried powder was mixed with the core particles with the transition layer in a mass ratio of 7:100. The mixture was ball-milled for 40 minutes under argon protection, a ball-to-material ratio of 8:1, and a rotation speed of 220 r / min. After sieving, the mixture was vacuum-sealed and stored to obtain the finished modifier. The total thickness of the composite shell was 0.2 mm, the total mass percentage of La and Ce was 0.8%, and the mass percentage of Te was 0.1%.

[0043] (4) Sequential spraying degassing: A rotating nozzle is used to spray Ar-Cl2 mixed gas with a Cl2 volume fraction of 0.5%, a rotating nozzle speed of 280 r / min, and a total spraying time of 15 min. The operation sequence is as follows: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic and continue spraying for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final continuous spraying stage. The final spraying time accounts for 30% of the total spraying time, and the melt temperature is kept constant at 710℃ during the spraying stage.

[0044] (5) Gradient filtration and controllable cooling: High-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi and 50ppi are used for step-by-step gradient filtration. The filter plates are preheated to 680℃ and kept at a constant temperature for 20min. The temperature fluctuation of the filter plates during the entire filtration process is ≤±5℃. The melt flows through each level of filter plates at a constant flow rate of 1.2m / min. After casting, the ingot is first cooled by room temperature air cooling at 3m / s for 10min. When the surface temperature of the ingot drops to 450℃, water mist spray cooling is switched. The water mist pressure is 0.2MPa and the water mist particle size is 20μm. The spraying is continued for 8min to obtain a homogeneous aluminum alloy ingot with low defects.

[0045] Example 2: (1) Grading and pretreatment: The waste aluminum raw materials are graded and classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to be 30 mm. The iron impurities are removed by magnetic separation and the non-metallic inclusions are removed by eddy current separation. The waste aluminum raw materials are then ultrasonically cleaned with a mass concentration of 5% sodium hydroxide aqueous solution at 45 kHz for 25 min and rinsed with deionized water until neutral. The temperature is raised to 400℃ at 8℃ / min under nitrogen protection atmosphere and the heat is kept constant for 40 min to remove hydroxyl groups. After cooling, qualified waste aluminum materials with an iron content of 1.4% are obtained by screening.

[0046] (2) Dual-chamber gradient melting: Qualified scrap aluminum is added to a closed dual-chamber melting furnace. The charging chamber is preheated at 650℃ for 15 minutes, and the melting chamber is kept at 750℃ for 28 minutes to completely melt the scrap aluminum. The melt is left to stand for 8 minutes to promote the separation of large particles. Nitrogen gas is maintained at a slight positive pressure of 0.05MPa throughout the melting process.

[0047] (3) Composite modification coupled with intermittent ultrasonic purification: A core-shell structure composite modifier is added to the crude aluminum melt at a rate of 2.0% of the total mass of the crude aluminum melt, and the mass ratio of Mn / Fe in the melt is controlled to be 0.9; the purity of bottom blowing argon gas is 99.99%, the flow rate is 12L / min, and it is blown synchronously through multiple evenly distributed gas holes at the bottom of the furnace; the ultrasonic frequency is 1.8kHz, the duration of a single ultrasonic treatment is 80s, the duration of the interval is 80s, the total ultrasonic treatment time is 18min, and the melt temperature is kept constant at 745℃ during the ultrasonic treatment stage.

[0048] The core-shell structured composite modifier is prepared according to the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 760℃ and completely melted. Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous. The mixture is then cast and sieved to obtain spherical alloy core particles with a particle size of 5mm. S2 Double-Layer Coating Molding: A silane hydrolysate was prepared by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2. The pH was adjusted to 4.5 with hydrochloric acid. The alloy core particles were completely immersed in the hydrolysate and ultrasonically impregnated at 40 kHz for 30 min, followed by constant-temperature curing at 120 °C for 30 min to form a dense transition layer of nano-SiO2 with a thickness of 0.1 mm. Sodium tetraborate decahydrate, Te powder, and zinc stearate were mixed in a mass ratio of 10:3:0.5 to obtain the coating powder, which was dried at 90 °C and ≤-0.08 MPa vacuum for 15 min. The dried powder was mixed with the core particles with the transition layer in a mass ratio of 12:100 and ball-milled for 60 min under argon protection, a ball-to-material ratio of 8:1, and a rotation speed of 260 r / min. After sieving, the mixture was vacuum-sealed and stored to obtain the finished modifier. The total thickness of the composite shell was 0.5 mm, the total mass percentage of La and Ce was 1.6%, and the mass percentage of Te was 0.3%.

[0049] (4) Sequential spraying degassing: A rotating nozzle is used to spray Ar-Cl2 mixed gas with a Cl2 volume fraction of 1.5%, a rotating nozzle speed of 360 r / min, and a total spraying time of 25 min. The operation sequence is as follows: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic and continue spraying for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final stage of continuous spraying. The final stage of spraying time accounts for 40% of the total spraying time, and the melt temperature is kept constant at 720℃ during the spraying stage.

[0050] (5) Gradient filtration and controllable cooling: High-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi and 50ppi are used for step-by-step gradient filtration. The filter plates are preheated to 700℃ and kept at a constant temperature for 20min. The temperature fluctuation of the filter plates during the entire filtration process is ≤±5℃. The melt flows through each level of filter plates at a constant flow rate of 1.8m / min. After casting, the ingot is first cooled by ambient air cooling at 5m / s for 15min. When the surface temperature of the ingot drops to 480℃, water mist spray cooling is switched. The water mist pressure is 0.4MPa and the water mist particle size is 50μm. The spraying is continued for 12min to obtain a homogeneous aluminum alloy ingot with low defects.

[0051] Example 3: (1) Grading and pretreatment: The waste aluminum raw materials are graded and classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to 30 mm. The iron impurities are removed by magnetic separation and the non-metallic inclusions are removed by eddy current separation. The waste aluminum raw materials are then ultrasonically cleaned with a mass concentration of 4% sodium hydroxide aqueous solution at 40 kHz for 20 min and rinsed with deionized water until neutral. The temperature is raised to 380℃ at 6℃ / min under nitrogen protection atmosphere and dehydroxylated by constant temperature thermal desorption for 30 min. After cooling, qualified waste aluminum materials with an iron content of 1.3% are obtained by screening.

[0052] (2) Dual-chamber gradient melting: Qualified scrap aluminum is added to a closed dual-chamber melting furnace. The charging chamber is preheated at 620℃ for 12 minutes, and the melting chamber is kept at 740℃ for 24 minutes to completely melt the scrap aluminum. The melt is left to stand for 6 minutes to promote the floating and separation of large particles. Nitrogen gas is maintained at a slight positive pressure of 0.03MPa throughout the melting process.

[0053] (3) Composite modification coupled with intermittent ultrasonic purification: A core-shell structure composite modifier is added to the crude aluminum melt at a rate of 1.5% of the total mass of the crude aluminum melt, and the mass ratio of Mn / Fe in the melt is controlled to be 0.75; the purity of bottom blowing argon gas is 99.99%, the flow rate is 10L / min, and it is blown synchronously through multiple evenly distributed gas holes at the bottom of the furnace; the ultrasonic frequency is 1.5kHz, the duration of a single ultrasonic treatment is 70s, the duration of the interval is 70s, the total ultrasonic treatment time is 14min, and the melt temperature is kept constant at 740℃ during the ultrasonic treatment stage.

[0054] The core-shell structured composite modifier is prepared according to the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 750℃ and completely melted. Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous. The mixture is then cast and sieved to obtain spherical alloy core particles with a particle size of 4mm. S2 Double-Layer Coating Molding: A silane hydrolysate was prepared by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2. The pH was adjusted to 4.5 with hydrochloric acid. The alloy core particles were completely immersed in the hydrolysate and ultrasonically impregnated at 40kHz for 25 minutes. The mixture was then cured at 120℃ for 30 minutes to form a dense transition layer of nano-SiO2 with a thickness of 0.08 mm. Sodium tetraborate decahydrate, Te powder, and zinc stearate were mixed in a mass ratio of 8:2:0.5 to obtain the coating powder. The powder was dried at 85℃ and ≤-0.08MPa vacuum for 12 minutes. The dried powder was mixed with the core particles with the transition layer in a mass ratio of 10:100. The mixture was ball-milled for 50 minutes under argon protection, a ball-to-material ratio of 8:1, and a rotation speed of 240 r / min. After sieving, the mixture was vacuum-sealed and stored to obtain the finished modifier. The total thickness of the composite shell was 0.33 mm, and the total mass percentage of La and Ce was 1.2%, while the mass percentage of Te was 0.2%.

[0055] (4) Sequential spraying degassing: A rotating nozzle is used to spray Ar-Cl2 mixed gas with a Cl2 volume fraction of 1.0%, a rotating nozzle speed of 320 r / min, and a total spraying time of 20 min. The operation sequence is as follows: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic and continue spraying for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final stage of continuous spraying. The final stage of spraying time accounts for 35% of the total spraying time, and the melt temperature is kept constant at 715℃ during the spraying stage.

[0056] (5) Gradient filtration and controllable cooling: High-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi and 50ppi are used for step-by-step gradient filtration. The filter plates are preheated to 690℃ and kept at a constant temperature for 20min. The temperature fluctuation of the filter plates is ≤±5℃ throughout the filtration process. The melt flows through each level of filter plates at a constant flow rate of 1.5m / min. After casting, the ingot is first cooled by room temperature air cooling at 4m / s for 12min. When the surface temperature of the ingot drops to 460℃, water mist spray cooling is switched. The water mist pressure is 0.3MPa and the water mist particle size is 35μm. The spraying is continued for 10min to obtain a homogeneous aluminum alloy ingot with low defects.

[0057] Comparative Example 1: The treatment method provided in Example 3 is adopted, except that: in step (3), no core-shell composite modifier is added, the Mn / Fe mass ratio is not adjusted, and only bottom blowing argon gas and intermittent ultrasonic treatment are used. The remaining steps and parameters are the same as in Example 3.

[0058] Comparative Example 2: The processing method provided in Example 3 is adopted, except that: the modifier used in step (3) is a single-layer uncoated Al-5Ti-B intermediate alloy modifier, and the amount added is 1.5% of the total mass of crude aluminum melt. The core-shell structure composite modifier is not used. The remaining steps and parameters are the same as in Example 3.

[0059] Comparative Example 3: The processing method provided in Example 3 is adopted, except that: in step (4), the sequential linkage spraying degassing is not used, but the rotary nozzle spraying degassing is performed separately after the ultrasonic treatment. The volume fraction of Cl2 is 1.0%, the rotation speed of the rotary nozzle is 320 r / min, the spraying time is 20 min, the melt temperature is constant at 715℃, and the remaining steps and parameters are the same as in Example 3.

[0060] Comparative Example 4: The processing method provided in Example 3 is adopted, except that: in step (5), gradient filtration is not used, but only a single specification 30ppi foam ceramic filter plate is used for filtration. The filter plate is preheated to 690℃ and kept at a constant temperature for 20min. The melt flows through the filter plate at a flow rate of 1.5m / min. The cooling method is changed to natural cooling to room temperature after casting. The remaining steps and parameters are the same as in Example 3.

[0061] test: Experiment 1: Test of hydrogen content and inclusion content in melt; Hydrogen content test in melt: The dissolved hydrogen content in the melt was determined using a boiling depressurization hydrogen analyzer (model: HYSCANII, LECO Corporation, USA) at a test temperature of 720℃. Each sample was tested three times and the average value was taken. The instrument detection accuracy was ±0.01mL / 100gAl.

[0062] Inclusion content test: Samples were taken from the aluminum alloy ingots obtained in each example and comparative example. After grinding and polishing, the inclusion area fraction was statistically analyzed using image analysis (Image-ProPlus 6.0 software). Ten fields of view (100× objective lens) were randomly selected for each sample, with each field of view having an area of ​​0.25 mm². 2 The average area fraction of inclusions was calculated. Simultaneously, the total amount of inclusions in the melt was determined using vacuum filtration extraction according to JB / T7946.1-2017 standard. The results are as follows: Table 1

[0063] As shown in Table 1, the hydrogen content of the melts in Examples 1-3 is ≤0.08 mL / 100 g Al, the area fraction of inclusions is ≤0.12%, and the total amount of inclusions is ≤1.8 × 10⁻⁶. -4 The wt% results were significantly better than those of the comparative examples. Comparative Example 1, lacking the addition of a core-shell composite modifier, suffered from a lack of rare earth-Te slow-release modifier effect and Mn / Fe ratio regulation, resulting in ineffective suppression of Fe element segregation in the melt, inclusion aggregation and growth, and increased hydrogen content. Comparative Example 2, using a single-layer uncoated Al-5Ti-B modifier, experienced severe loss of modifier elements, insufficient nucleation density, and reduced inclusion capture efficiency. Comparative Example 3, lacking the sequential coordination of ultrasound and blowing, failed to effectively break up the oxide film in the melt during the ultrasonic intervals, resulting in insufficient capture of fine inclusions and incomplete hydrogen removal. Comparative Example 4, using only a single-size filter plate instead of gradient filtration, failed to classify and retain large and small inclusions, and natural cooling led to secondary gas precipitation during solidification, carrying with it inclusions, significantly increasing the inclusion content.

[0064] Experiment 2: Mechanical property testing; Samples were taken from the aluminum alloy ingots obtained in the various embodiments and comparative examples, and tensile specimens were prepared in accordance with GB / T228.1-2021 "Metallic materials - Tensile testing - Part 1: Test at room temperature". The gauge length was 10 mm in diameter and 50 mm in length. The room temperature tensile test was carried out using an electronic universal testing machine (model: Instron 5982, INSTRON Corporation, USA) with a loading rate of 2 mm / min. Three parallel specimens were tested for each sample and the average value was taken. The tensile strength Rm and yield strength Rp0.2 were determined.

[0065] Hardness testing: A Brinell hardness tester (model: HB-3000, Laizhou Huayin Testing Instrument Co., Ltd.) was used. The test force was 29400 N (3000 kgf), the indenter diameter was 10 mm, and the holding time was 30 s. Five points were tested for each sample, and the average value was taken. The results are as follows: Table 2

[0066] As shown in Table 2, the tensile strength of Examples 1-3 is ≥285MPa, the yield strength is ≥235MPa, and the Brinell hardness is ≥92HB, indicating significantly better mechanical properties than the comparative examples. Comparative Example 1, lacking the core-shell composite modifier and the slow-release modification effect of rare earth-Te, suffered from insufficient grain refinement and Fe segregation forming coarse, brittle phases, resulting in a significant decrease in strength and hardness. Comparative Example 2, using a single-layer uncoated Al-5Ti-B modifier, experienced severe burn-off of modifier elements in the melt, resulting in insufficient effective nucleation sites, grain coarsening, and reduced mechanical properties. Comparative Example 3, lacking the sequential coordination of ultrasonication and blowing, resulted in incomplete melt purification, leaving residual fine inclusions as stress concentration sources, reducing the material's load-bearing capacity and plastic deformation coordination. Comparative Example 4, without gradient filtration and natural cooling, had low inclusion retention efficiency, leading to gas precipitation during solidification, forming micropore defects, coarse grains, and internal stress concentration, resulting in a comprehensive decline in mechanical properties.

[0067] Experiment 3: Grain size and microstructure uniformity test; Samples were taken from the central region of the aluminum alloy ingots obtained in each embodiment and comparative example. After being sanded to 2000 grit with sandpaper, the samples were mechanically polished and etched with Graff Sargent reagent (15 mL HF + 45 mL HCl + 15 mL HNO3 + 25 mL H2O) for 10-15 seconds. The microstructure was observed under an optical microscope (model: Axio Imager M2m, ZEISS GmbH, Germany). The average grain size was determined by the truncation method. Eight fields of view (50× objective lens) were randomly selected for each sample, and no less than 50 grains were measured in each field of view. The average value was taken.

[0068] Tissue homogeneity assessment: The standard deviation σ and coefficient of variation CV = σ / d̄ × 100% of the grain size for each sample in eight fields of view were calculated using image analysis software (Image-ProPlus 6.0). A smaller coefficient of variation indicates better tissue homogeneity. Simultaneously, the morphology and distribution characteristics of grain boundary precipitates were observed using a scanning electron microscope (model: JSM-7800F, JEOL Ltd., Japan). The accelerating voltage was 15kV and the working distance was 10mm. The results are as follows: Table 3

[0069] As shown in Table 3, the average grain size of Examples 1-3 is ≤68μm, the grain size variation coefficient is ≤12.5%, and the density of grain boundary precipitates is ≤1850 / mm. 2The microstructure uniformity of Comparative Example 1 was significantly better than that of the Comparative Example 2, with fine and dispersed grain boundary precipitates. Comparative Example 1, lacking the synergistic rare earth-Te refining effect due to the absence of a core-shell composite modifier, exhibited coarse grains with uneven size distribution and a coefficient of variation as high as 24.6%, with a large amount of coarse end-cap compounds precipitating at the grain boundaries. Comparative Example 2 used a single-layer uncoated Al-5Ti-B modifier, where Ti-B nucleation cores agglomerated, grew, and burned off in the melt, reducing the effective nucleation rate and limiting the grain refining effect. Comparative Example 3, lacking sequential spray degassing, allowed residual hydrogen in the melt to precipitate during solidification, forming pores. Fine inclusions were not fully captured and removed, acting as heterogeneous nucleation cores and resulting in uneven grain size distribution. Comparative Example 4, lacking gradient filtration and relying on natural cooling, suffered from low filtration efficiency leading to numerous inclusions, and the slow natural cooling rate allowed for sufficient grain growth, resulting in the worst microstructure uniformity.

[0070] The preferred embodiments of the present invention disclosed above are merely illustrative of the invention. These preferred embodiments do not exhaustively describe all details, nor do they limit the invention to the specific implementations described. Clearly, many modifications and variations can be made based on the content of this specification. This specification selects and specifically describes these embodiments to better explain the principles and practical applications of the invention, thereby enabling those skilled in the art to better understand and utilize the invention. The invention is limited only by the claims and their full scope and equivalents.

Claims

1. A method for recycling and processing waste aluminum into aluminum alloy ingots, characterized in that, This includes the following steps performed sequentially: (1) Graded pretreatment: The waste aluminum raw materials are classified according to the material grade and surface contamination degree. After crushing, the maximum particle size is controlled to be no more than 40mm. They are then subjected to sorting and impurity removal, alkaline cleaning, and thermal dehydroxylation treatment to remove oil stains, surface inclusions, adsorbed water and hydroxyl impurities, and obtain qualified waste aluminum raw materials with low impurities. (2) Dual-chamber gradient melting: qualified scrap aluminum is preheated and melted in stages using a closed dual-chamber melting furnace to prepare a crude aluminum melt with uniform composition. Large particle inclusions are removed by static floating. (3) Composite modification coupled with intermittent ultrasonic purification: a core-shell structure composite modifier is added to the crude aluminum melt, and the mass ratio of Mn / Fe in the melt is controlled to be 0.6~0.

9. Simultaneously, bottom blowing of argon gas from the furnace bottom is combined with intermittent high-energy ultrasound. (4) Sequentially linked jet degassing: Argon-chlorine mixture is jetted by a rotary nozzle. The oxide film is broken, fine inclusions are captured and hydrogen is removed in steps by the sequential linkage of ultrasonic operation and rotary jet degassing. (5) Gradient filtration and controllable cooling: Multi-level gradient preheated foam ceramic filter media is used to filter the melt in stages. After casting, segmented phase change temperature control cooling is used to obtain homogeneous low-defect aluminum alloy ingots. The core-shell structured composite modifier has a three-layer composite structure, consisting of an alloy core, a nano-SiO2 transition inner layer, and a rare earth-Te slow-release modifier outer layer from the inside out. The total mass of the double-layered shell accounts for 4% to 7% of the total mass of the modifier. The total mass of La and Ce in the modifier accounts for 0.8% to 1.6%, and the mass of Te accounts for 0.1% to 0.3%.

2. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process of the graded pretreatment in step (1) is as follows: After being crushed, the scrap aluminum is sequentially subjected to magnetic separation to remove iron impurities and eddy current separation to remove non-metallic inclusions. It is then ultrasonically cleaned with a 3%~5% sodium hydroxide aqueous solution at 35~45kHz for 15~25min, and rinsed with deionized water until neutral. Under a nitrogen protective atmosphere, the temperature is raised to 350~400℃ at 5~8℃ / min, and the aluminum is thermally dehydroxylated at a constant temperature for 25~40min. After cooling, qualified scrap aluminum with an iron content ≤1.8% is obtained by screening.

3. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process parameters for step (2) dual-chamber gradient melting are as follows: The charging chamber is preheated at 600~650℃ for 10~15 minutes, and the melting chamber is kept at 720~750℃ for 20~28 minutes to completely melt the waste aluminum. The melt is allowed to stand for 5~8 minutes to promote the separation of large particles. Nitrogen gas is maintained at a slightly positive pressure throughout the melting process to isolate the melt from air and prevent secondary oxidation and hydrogen absorption.

4. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The core-shell structured composite modifier is prepared by the following steps: S1 Preparation of alloy core: Industrial pure aluminum is heated to 740~760℃ and completely melted. Al-10Mn, Al-20La, Al-15Ce, Al-5Ti-B and Al-3Te intermediate alloys are added in sequence. The mixture is stirred at a constant temperature until the composition is homogeneous. The mixture is then cast and sieved to obtain spherical alloy core particles with a particle size of 3~5mm. S2 double-layer coating molding: Two coating structures are sequentially constructed on the outer surface of alloy core particles. The inner layer is a dense transition layer of nano-SiO2 with a thickness of 0.05~0.1mm, and the outer layer is a rare earth-Te slow-release metamorphic shell with a thickness of 0.15~0.4mm. The total thickness of the composite shell is 0.2~0.5mm, thus obtaining a core-shell structure composite metamorphic agent.

5. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 4, characterized in that, The double-layered shell is prepared using a two-step process of sol-gel coupled argon-protected mechanical alloying. The specific steps are as follows: Preparation of transition layer using S11 sol-gel: Prepare silane hydrolysate by mixing tetraethyl orthosilicate, ethanol, and deionized water in a mass ratio of 1:4:2, and adjust the pH to 4.5 with hydrochloric acid; completely immerse the alloy core particles in the hydrolysate, ultrasonically impregnate for 20-30 minutes at 40 kHz, and cure at 120℃ for 30 minutes to form a dense barrier nano-SiO2 transition layer. S12 mechanical alloying coating: Sodium tetraborate decahydrate, Te powder, and zinc stearate are mixed at a mass ratio of 6~10:1~3:0.5 to obtain coating powder, which is dried at 80~90℃ and ≤-0.08MPa vacuum for 10~15min; the dried powder is mixed with particles with transition layer core at a mass ratio of 7~12:100, and ball-milled at argon protection, ball-to-material ratio of 8:1, and rotation speed of 220~260r / min for 40~60min. After sieving, it is vacuum sealed and stored to obtain the finished modifier.

6. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process parameters for step (3) ultrasonic purification and argon bottom blowing are as follows: The amount of core-shell composite modifier added is 1.2%~2.0% of the total mass of crude aluminum melt; the purity of bottom-blown argon is ≥99.99%, the flow rate is 8~12L / min, and it is synchronously bottom-blown through multiple evenly distributed pores at the bottom of the furnace, with uniform flow rates at each pore; the ultrasonic frequency is 1.2~1.8kHz, the duration of a single ultrasonic treatment is 60~80s, the interval duration is 60~80s, the total ultrasonic treatment time is 10~18min, and the melt temperature is kept constant at 735~745℃ during the ultrasonic treatment stage.

7. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process parameters for step (4) time-linked pulse-jet degassing are as follows: The volume fraction of Cl2 in the Ar-Cl2 mixture is 0.5%~1.5%; the rotational speed of the rotary nozzle is 280~360 r / min, and the total blowing time is 15~25 min; the operation sequence is as follows: first complete 3 complete ultrasonic intermittent cycles, pause the ultrasonic treatment and then continue blowing for 5 min, then complete 2 complete ultrasonic intermittent cycles, and finally enter the final stage of continuous blowing; the final stage of blowing time accounts for 30%~40% of the total blowing time, and the melt temperature is kept constant at 710~720℃ during the blowing stage.

8. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process for gradient filtering in step (5) is as follows: High-purity alumina foam ceramic filter plates with pore sizes of 20ppi, 30ppi, and 50ppi are used for step-by-step filtration. The filter plates are preheated to 680~700℃ and kept at a constant temperature for 20 minutes. The temperature fluctuation of the filter plates is ≤±5℃ throughout the filtration process. The melt flows through each level of filter plates at a constant flow rate of 1.2~1.8m / min, which separates and retains fine inclusions of different particle sizes.

9. The method for recycling and processing waste aluminum into aluminum alloy ingots according to claim 1, characterized in that, The specific process for segmented controllable cooling in step (5) is as follows: After the melt is cast, it is first cooled by air cooling at 3~5m / s for 10~15min. When the surface temperature of the ingot drops to the critical range of alloy phase transformation of 450~480℃, water mist spray cooling is switched. The water mist pressure is 0.2~0.4MPa and the water mist particle size is 20~50μm. The water mist evenly covers the surface of the ingot and sprays continuously for 8~12min.

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