A production method of 6082 aluminum alloy hot top oil sliding hollow ingot

Abstract

The application discloses a production method of 6082 aluminum alloy hot top oil sliding hollow ingot, and relates to the technical field of aluminum alloy melting and casting. The method comprises the following steps: ingredient preparation, furnace charging and melting are carried out according to the target chemical composition of the 6082 aluminum alloy; the aluminum liquid is subjected to component detection and alloying material supplementing, and is subjected to smelting furnace refining and static furnace refining; online refining, online degassing and online filtering are sequentially carried out; the hollow ingot is formed by adopting the same horizontal hot top oil sliding semi-continuous casting mode, wherein the outer crystallizer and the initial solidification zone of the core are both provided with graphite rings, the lubricating oil film is formed by automatic internal and external oil supply, and the internal and external cooling water quantity and the casting speed are cooperatively controlled; and finally, homogenization treatment is carried out. The method can improve the purity of the aluminum liquid and the uniformity of the grain structure, reduce defects such as ingot cracking, layering, inner hole cracking, slag inclusion and oxidation film, reduce the thickness of the segregation layer on the surface of the ingot, and improve the forming stability and the surface quality of the large-size 6082 aluminum alloy hollow ingot.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy casting technology, and in particular to a production method for a 6082 aluminum alloy hot-top oil-lubricated hollow ingot. Background Technology

[0002] 6082 aluminum alloy, due to its good strength, corrosion resistance, and machinability, is widely used in pipes, cylinders, and load-bearing structural components. In pipe production, using hollow ingots as extrusion blanks reduces metal loss and machining steps caused by boring or piercing solid ingots. Therefore, the stable production of large-size, high-quality aluminum alloy hollow ingots is crucial for improving subsequent pipe processing efficiency and material utilization.

[0003] Traditional hollow aluminum alloy ingots are mostly cast using an open-top casting method. Open-top casting results in a longer effective crystallization zone, and the flow of molten aluminum is typically controlled using devices such as funnels. This leads to unstable liquid level control and inaccurate manual lubrication. The ingots are prone to surface defects such as tearing, delamination, and cracks, and also exhibit thick segregation layers and numerous internal oxide film defects. Hot-top oil-lubricated casting of hollow aluminum alloy ingots can mitigate these problems to some extent. Graphite rings are used for lubrication both inside and outside the ingot, enabling automatic oiling, precise control of lubrication frequency, and avoiding human intervention. This achieves smooth inner and outer surfaces of the ingot, meeting oil-lubricating standards. The segregation layer inside and outside the ingot can be reduced by more than 30% compared to open-top casting, reducing the amount of machining required for machining, significantly improving yield, and lowering costs.

[0004] In the prior art, CN102794416A discloses a semi-continuous casting crystallizer for hollow aluminum alloy ingots and its application. This method lubricates the inner and outer surfaces of the hollow ingot by setting lubricating oil channels in the outer crystallizer and the core, and employing a pulsed oil supply method. In an embodiment, this method is used to prepare 2A12 hollow ingots with a diameter of Φ272mm × Φ106mm, and the casting process is stabilized by controlling the lubricating oil pressure and supply frequency. However, with the development of demand for aluminum alloy tubing and large structural components, large-size hollow ingots are gradually becoming an application trend. When casting large-size 6082 aluminum alloy hollow ingots with a diameter exceeding φ650mm, the increased ingot cross-sectional size and extended melt feeding distance lead to significant differences in heat exchange conditions between the inner and outer crystallization regions. The lubrication parameters and crystallizer matching relationships established for small-size ingots are difficult to directly apply. Furthermore, different alloy systems require different solidification behaviors, segregation tendencies, and heat treatment requirements, necessitating the establishment of compatible melting and casting processes.

[0005] Therefore, it is particularly necessary to develop a production method for hot-top oil-lubricated hollow ingots that is compatible with large-size 6082 aluminum alloy hollow ingots, and to improve the internal and external quality of the ingots. Summary of the Invention

[0006] The purpose of this invention is to provide a production method for 6082 aluminum alloy hot-top oil-lubricated hollow ingots, addressing the problems of unstable lubrication, thick segregation layers, surface cracks, and large machining allowances encountered in the production of large-sized 6082 aluminum alloy hollow ingots (φ650mm and above). This invention achieves stable production of high-quality, large-sized hollow ingots by limiting the 6082 alloy composition, purifying and refining the melt for degassing, and matching the parameters of the hot-top oil-lubricated casting process. The invention involves batching, charging, and melting according to the target chemical composition of the 6082 aluminum alloy; component testing and alloying material replenishment of the molten aluminum; refining in the smelting furnace and refining and purifying in the settling furnace; sequential online refining, online degassing, and online filtration; and the formation of hollow ingots using a horizontal hot-top oil-lubricated semi-continuous casting method. Graphite rings are provided in the initial solidification zones of both the outer crystallizer and the core, forming a lubricating oil film through automatic internal and external oil supply, coordinated with the internal and external cooling water volume and casting speed; finally, homogenization treatment is performed. The method of the present invention can improve the purity and uniformity of aluminum liquid and grain structure, reduce defects such as ingot cracking, delamination, internal hole cracks, inclusions and oxide film, reduce the thickness of segregation layer on the surface of ingot, and improve the forming stability and surface quality of large-size 6082 aluminum alloy hollow ingots.

[0007] To achieve the above objectives, the present invention adopts the following technical solution: This invention provides a method for producing 6082 aluminum alloy hot-top oil-lubricated hollow ingots, comprising the following steps: (1) Composition ratio, furnace loading and melting: The raw materials are prepared according to the target chemical composition of 6082 aluminum alloy; solid materials are used for furnace loading, and primary recycled materials, aluminum ingots and alloying materials are added in sequence for melting, and the temperature of the aluminum liquid is controlled not to exceed 760℃ during the melting process; (2) Refining and composition adjustment in the smelting furnace: The composition of the aluminum liquid obtained in step (1) is tested, and alloying materials are added according to the composition test results of the aluminum liquid to make the aluminum liquid reach the target chemical composition of the 6082 aluminum alloy; the first refining is carried out using high-purity argon and refining agent, and the slag is removed after the first refining is completed and the temperature of the aluminum liquid is adjusted. (3) Refining and purification in a static furnace: The aluminum liquid obtained in step (2) is transferred into a static furnace, and a refining agent is added by spraying powder for a second refining. After the second refining is completed, the slag is removed, argon gas is blown into the furnace bottom, and the temperature of the aluminum liquid is adjusted. (4) Online grain refinement, online degassing and online filtration: Online grain refinement is carried out using a grain refiner; then, online degassing is carried out on the aluminum liquid using a dual-rotor degassing device; finally, online filtration is carried out on the aluminum liquid using a two-stage filtration method. (5) Hot-top oil-lubricated hollow casting: The aluminum liquid after step (4) is processed by hot-top oil-lubricated semi-continuous casting method to form a hollow ingot and obtain a 6082 aluminum alloy hollow ingot. (6) Homogenization treatment: Homogenize the 6082 aluminum alloy hollow ingot to obtain a 6082 aluminum alloy hot-top oil-lubricated hollow ingot.

[0008] Preferably, the specifications of the 6082 aluminum alloy hot-top oil-lubricated hollow ingot are: outer diameter of 670mm and inner diameter of 305mm; it comprises the following components by mass percentage: Si 0.8-1.2%, Fe≤0.4%, Cu≤0.1%, Mn 0.5-0.9%, Mg0.7-1.1%, Cr≤0.2%, Ni≤0.05%, Zn≤0.2%, Ti≤0.1%, other individual elements: ≤0.05%, total of other elements: ≤0.15%, and the balance is Al.

[0009] Preferably, in step (1), the amount of primary recycled material added does not exceed 60% of the total mass of the furnace charge; and the amount of alloying material added does not exceed 80% of the mass of the aluminum ingot.

[0010] Preferably, in step (1), during the melting process, when the temperature of the molten aluminum exceeds 700°C, electromagnetic stirring is performed every 25-35 minutes, with each stirring lasting 8-12 minutes. This treatment can accelerate melting and prevent local overheating of the molten aluminum.

[0011] Preferably, in step (2), the specific steps for component detection are as follows: after stirring the aluminum liquid obtained in step (1) for 15-25 minutes, take samples before the furnace at 720-750℃ and detect the actual mass fraction of each alloying element by direct reading spectrometer; calculate the amount of alloying material to be added based on the difference between the detected actual mass fraction and the target chemical composition, combined with the total mass of aluminum liquid, the mass fraction of the corresponding element in the alloying material and the burn-off rate of the corresponding element.

[0012] As a preferred option, the specific steps for adding alloying materials in step (2) are as follows: first, remove the slag from the surface of the aluminum melt, control the melt temperature before adding the alloying materials to be 740-750℃, and add it to the aluminum melt under stirring conditions.

[0013] Preferably, in step (2), the refining temperature is 735-745℃ and the refining time is 30-40min during the first refining process; the refining agent is made by mixing MgCl2 and KCl in a mass ratio of 1:1 and the amount added is 1.5kg / tAl.

[0014] Preferably, in step (2), after removing the slag, the temperature of the aluminum liquid is controlled at 750-760℃ and the Ti content in the aluminum liquid is controlled at 0.02-0.03%.

[0015] Preferably, in step (3), during the second refining process, the refining agent is made by mixing MgCl2 and KCl in a mass ratio of 1:1, and the amount added is 1.0 kg / tAl; the refining temperature is 730-740℃ and the refining time is 30-40 min.

[0016] Preferably, in step (3), high-purity argon gas with a purity of ≥99.999% is used as the powder spraying carrier gas, and the carrier gas flow rate is 8-12L / min.

[0017] As a preferred option, in step (3), high-purity argon gas with a purity of ≥99.999% is used to blow gas into the furnace bottom for 30-40 minutes, the flow rate of argon gas into the furnace bottom is 35-45L / min, and the temperature of the aluminum liquid is adjusted to 745-755℃. After the bottom blowing is completed, the furnace bottom is left to stand for no less than 40 minutes.

[0018] Preferably, in step (4), the grain refiner is an Al-5Ti-1B aluminum-titanium-boron wire rod with a diameter of 9.5 mm.

[0019] As a preferred option, in step (4), during the online grain refinement process, two wire feeders are used to simultaneously feed the grain refiner into the molten aluminum from opposite directions. The feeding speed of each grain refiner is 160-200 cm / min; the flow rate of the molten aluminum is 11-12 t / h; and the amount of grain refiner added is 3.2-4 kg / tAl.

[0020] Preferably, in step (4), the dual-rotor degassing device uses a graphite rotor with a rotor speed of 250-400 r / min, and the working gas is high-purity argon with a purity ≥99.999% and a working gas flow rate of 2-6 m³ / min. 3 / h, control the height of bubbles on the surface of the aluminum liquid to not exceed 30 mm; the hydrogen content in the aluminum liquid after online degassing is less than 0.13 mL / 100g Al.

[0021] Preferably, in step (4), the two-stage filtration method uses a 30ppi ceramic foam filter plate and a 50ppi ceramic foam filter plate, which are arranged sequentially along the flow direction of the molten aluminum, with the 30ppi ceramic foam filter plate located upstream and the 50ppi ceramic foam filter plate located downstream; the filter box is electrically heated before filtration, and the preheating time is not less than 30 minutes.

[0022] Preferably, in step (5), the hot-top oil-lubricated semi-continuous casting includes the following steps: (a) Casting preparation: A horizontal hot-top oil-lubricated semi-continuous casting method is adopted. Porous high-purity graphite rings are installed in the initial solidification zones of both the outer crystallizer and the core. The scum in the degassing box is cleaned, and the rotors of the dual-rotor degassing device are in operation. The settling furnace is tilted to allow the molten aluminum to flow into the flow channel, and the online grain refinement device is started. After the molten aluminum enters the casting tray, a false bottom material layer is laid on the ingot head. When the molten aluminum level in the annular casting cavity reaches 50-70 mm above the transfer plate 2, the casting machine, the cooling water system of the outer crystallizer, and the core, as well as the lubrication system, are simultaneously started. The casting speed is 25-35 mm / min, and the lubrication system is 55-65 m / min. 3 / h external crystallizer cooling water volume and 25-35m 3 Casting begins under the condition of a core cooling water volume of / h; (b) Stabilizing casting: When the ingot length reaches 150mm, adjust the casting speed to 40-45mm / min and the cooling water flow rate of the external crystallizer to 95-105m³. 3 / h, the core cooling water volume is 45-55m³ 3 / h, while controlling the temperature of the molten aluminum at the tail end of the casting pan to 700-710℃; (c) Casting completion: When the end of the ingot descends to 20-30mm below the graphite ring, stop the aluminum liquid supply and stop the machine, and then turn off the cooling water.

[0023] Furthermore, in step (a), the height of the high-purity graphite rings is 30 mm; lubricating oil is supplied to the core graphite ring and the outer crystallizer graphite ring at a delivery pressure of 40-50 bar, and the oil is supplied in a pulse manner; wherein, the single pulse oil supply volume is 0.02-0.05 mL / time, the oil supply interval is 15-30 s, the average supply flow rate of lubricating oil for the outer crystallizer graphite ring is 0.15-0.30 mL / min, the average supply flow rate of lubricating oil for the core graphite ring is 0.08-0.18 mL / min, and the pulse oil supply operates in a cycle of 5 s supply and 20 s stop.

[0024] Furthermore, in step (a), 50-70 seconds after casting begins, the core is driven to reciprocate along the circumferential direction by the core manipulation mechanism, with an amplitude of 10-15 mm and an oscillation frequency of 10-15 times / min. This operation can prevent the initial billet shell from sticking to the core.

[0025] Furthermore, in step (b), the core cooling water volume is synchronously adjusted to 50% of the outer crystallizer cooling water volume, and the casting speed and cooling water volume are adjusted within ±5% of their respective set values.

[0026] Preferably, in step (6), before homogenization treatment, the head 100-200mm and the tail 160-200mm of the 6082 aluminum alloy hollow ingot are removed; then the temperature is raised to 550±5℃ in 350-400min and held at 550±5℃ for 16-20h; after the holding period, the ingot is cooled to below 250℃ by a combination of forced air cooling and water mist cooling at an average cooling rate of not less than 200℃ / h and then taken out of the furnace and allowed to cool naturally to room temperature.

[0027] The beneficial effects of this invention are: This invention involves batching, charging, and melting of 6082 aluminum alloy according to its target chemical composition; component analysis and replenishment of alloying materials in the molten aluminum; sequential refining in the smelting furnace and refining in the settling furnace; online refining using Al-5Ti-1B grain refiner, online degassing using a dual-rotor degassing device, and online filtration using a two-stage filtration system; subsequently, hollow ingots are formed using a horizontal hot-top oil-lubricated semi-continuous casting method, wherein high-purity graphite rings are set in the initial solidification zones of the outer crystallizer and the core, and a lubricating oil film is formed through automatic internal and external oil supply, which is coordinated with the internal and external cooling water volume and casting speed; finally, the resulting hollow ingots are homogenized.

[0028] The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingots of the present invention can improve the purity of aluminum liquid and the uniformity of grain structure, reduce defects such as ingot cracking, delamination, internal hole cracks, slag inclusions and oxide film, reduce the thickness of segregation layer on the surface of ingots, and improve the forming stability and surface quality of large-size 6082 aluminum alloy hollow ingots. It is suitable for the continuous and stable production of large-size 6082 aluminum alloy hollow ingots of Φ670 mm / Φ305 mm. Attached Figure Description

[0029] Figure 1 Image of the end face of the large-size 6082 aluminum alloy hollow ingot obtained in Example 1 of this invention; Figure 2 Low-magnification microstructure image of the large-size 6082 aluminum alloy hollow ingot obtained in Example 1 of this invention; Figure 3 : Schematic diagram of the structure of the hollow ingot core and the outer crystallizer used in this invention; In the diagram, 1-heating top, 2-adapter plate, 3-graphite ring. Detailed Implementation

[0030] It should be noted that the following detailed descriptions are illustrative and intended to provide further explanation of this application. Unless otherwise specified, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application pertains.

[0031] As described in the background art, when casting large-sized 6082 aluminum alloy hollow ingots with a diameter exceeding φ650mm, the increased ingot cross-sectional size and extended melt feeding distance result in significant differences in heat exchange conditions between the inner and outer crystallization regions. Consequently, the lubrication parameters and crystallizer matching relationships established for small-sized ingots are difficult to apply directly.

[0032] Based on this, the present invention provides a method for producing 6082 aluminum alloy hot-top oil-lubricated hollow ingots. Through component proportioning, in-furnace aluminum liquid purification, online refining, online purification, online degassing, casting, and homogenization treatment, the optimal process is determined by the reasonable connection of each process step and process parameter control, thus solving ingot appearance defects and ensuring its forming stability. A schematic diagram of the hollow ingot core and outer crystallizer structure used in the casting process is shown below. Figure 3 As shown. Specifically: 1. This invention upgrades the traditional single-stage, simple in-furnace treatment into a tiered, interconnected system of two-stage refining + bottom blowing and settling + three-stage online purification. Specifically: powder refining (refining agent + high-purity argon carrier) is performed once in the smelting furnace and once in the settling furnace. After refining, slag is removed, and bottom argon blowing is initiated for 30-40 minutes, with a settling time of at least 40 minutes. Furthermore, in the casting flow channel, online grain refinement + dual-rotor online degassing + 30ppi + 50ppi dual-stage ceramic filter plates are connected in series to establish a complete tiered purification chain, thereby improving internal quality and enhancing microstructure uniformity.

[0033] (1) Two-stage in-furnace refining + bottom blowing and settling Powdered Refining: A refining agent, carried by high-purity argon gas, is injected deep into the molten aluminum. Its chloride salt system combines with oxide inclusions in the molten aluminum through chemical adsorption, forming large slag clumps. Argon Bubble Flotation: Numerous bubbles generated by the carrier argon gas rise to the surface. On one hand, the partial pressure difference "absorbs" dissolved hydrogen into the bubbles and carries it to the surface; on the other hand, it physically floats the aforementioned large slag clumps to the surface for removal by the slag skimming process. Bottom Blowing + Settling (Sedimentation Separation): Bottom blowing creates full-area convection, ensuring thorough purification. Forced settling for at least 40 minutes after refining allows residual micro-inclusions to gradually rise to the surface and separate from the molten aluminum, further achieving deep purification.

[0034] (2) Online degassing combined with dual-stage filtration forms a three-stage online purification + crystal refinement Dual-rotor online degassing (mesoscopic purification): At the final stage before casting, a high-speed rotating graphite rotor (250-400 rpm) shears high-purity argon gas into countless tiny, dispersed bubbles. This significantly increases the contact area between the gas and liquid phases, efficiently reducing the dissolved hydrogen content to below the metallurgical safety threshold of 0.13 mL / 100g Al. This is crucial to preventing pinholes formed during ingot solidification due to hydrogen precipitation. 30ppi + 50ppi dual-stage filtration (microscopic purification): The initial 30ppi coarse filter intercepts large particles or flocculent slag that may accidentally detach from upstream, protecting the subsequent stage. The subsequent 50ppi fine filter specifically captures and intercepts micron-sized inclusions (10-50 μm) that could become sources of fatigue cracks in the material. This tiered configuration of "coarse protecting fine" ensures filtration accuracy while preventing the fine filter layer from clogging too quickly, ensuring stability during long-term casting. Synergistic effect of purification and grain refinement: The addition of the Al-5Ti-1B wire rod at this stage releases TiB2 particles, which serve as ideal heterogeneous nucleation sites during aluminum solidification. This high-purity melt environment ensures the surface cleanliness of the TiB2 particles, enabling them to exert their grain refinement effect. Purification is a prerequisite for refinement, which in turn solidifies the advantages of the high-purity melt into a dense, as-cast equiaxed grain structure.

[0035] This step helps reduce oxide film inclusions and pinhole defects inside the ingot, providing a high-purity billet base for subsequent high-performance extruded materials. After the high-purity and refined melt solidifies, a fine and uniform as-cast structure is obtained, avoiding the difference in core and surface properties caused by coarse grains and impurity enrichment, thereby improving internal quality and improving the uniformity of the structure.

[0036] 2. The large-scale hot-top casting process with synchronous internal and external automatic oil lubrication in this invention further establishes a differentiated automatic oil supply and cooling-lubrication synergistic control process suitable for large-scale 6082 aluminum alloy hollow ingots with internal and external characteristics, specifically: double-sided automatic oil lubrication, with both the outer crystallizer and the inner core equipped with high-purity graphite rings 3 and independent automatic oil supply systems, using Mobil 230 fully synthetic high-temperature lubricating oil, and precise oil supply in a pulse mode (e.g., 5 seconds on, 20 seconds off). Differentiated parameter settings for "internal and external": The differentiated oil supply amounts for the outer crystallizer (0.15-0.30 mL / min) and the inner core (0.08-0.18 mL / min) are determined, and the lubricating oil pressure is maintained at 40-50 bar. The "speed-water volume" coordinated control model establishes the core principle of adjusting the core cooling water volume in conjunction with 50% of the crystallizer water volume, and is combined with dynamic programs for the start-up stage (low speed and low water volume) and the steady-state operation stage (speeding up to 40-45 mm / min and increasing water volume).

[0037] In large-size (Φ670 / Φ305) hollow ingots, the core is completely surrounded by high-temperature molten aluminum, resulting in extremely poor heat dissipation. This causes the inner shell to be inherently thinner than the outer shell, with higher temperature and lower strength. This is the fundamental reason why the inner hole of large-size hollow ingots is prone to cracking and aluminum leakage. This invention addresses this problem in forming large-size inner holes by adjusting the cooling water volume of the core and the outer crystallizer. This prevents the inner shell from being excessively cooled, causing rapid contraction and thickening, and prematurely generating a huge clamping force that holds it to the core. Thus, the inner shell remains within a temperature range with good plasticity during demolding, preventing brittle fracture. Differential lubrication is then applied based on the different stress states of the inner and outer holes. The outer shell cools strongly, resulting in significant inward contraction and high normal pressure on the graphite ring 3, thus requiring more lubricating oil to form an effective oil film. The inner hole cools weakly, resulting in less outward contraction and lower normal pressure; excessive lubricating oil can cause defects due to vaporization, thus requiring less lubricating oil. By employing differentiated oil supply with "less oil inside and more oil outside," a stable and balanced hydrodynamic lubrication film is established simultaneously inside and outside, enabling smooth and synchronous demolding under low frictional resistance. The slow cooling effect of the oil film reduces the segregation layer: the oil film seeping through the pores of the graphite ring forms a controllable thermal resistance layer at high temperatures. This slows down the rapid cooling rate of the aluminum liquid upon contact with the crystallizer wall, thereby suppressing the driving force of reverse segregation of solute elements (i.e., compositional segregation and a coarse precipitate enrichment layer) on the surface caused by rapid supercooling.

[0038] This operation successfully achieved stable mass production of 6082 aluminum alloy hollow ingots with Φ670 / Φ305 specifications, effectively reducing defects such as tearing, delamination, and internal cracks leading to aluminum leakage, and improving surface quality and material utilization. Specifically, the surface finish of the ingots reached an oily smooth standard that required no surface treatment, and appearance defects were significantly reduced; the thickness of the segregation layer inside and outside the ingots was reduced by more than 30% compared to open-top casting, and the uniformity of the microstructure was significantly improved.

[0039] To enable those skilled in the art to better understand the technical solution of the present invention, the technical solution of the present invention will be described in detail below with reference to specific embodiments.

[0040] The experimental materials used in the embodiments of this invention are all conventional experimental materials in the art and can be purchased through commercial channels.

[0041] In this invention, the primary recycled material is clean recycled material generated during the production of 6082 aluminum alloy, including the head and tail cuttings of qualified ingots and the extrusion residue and head and tail cuttings of profiles. The alloying materials are purchased from intermediate alloy manufacturers, including aluminum-based intermediate alloys and pure magnesium ingots. The lubricating oil is Mobil 230 fully synthetic high-temperature lubricating oil, with a kinematic viscosity of 200-220 mm² / s at 40°C, an open-cup flash point ≥255°C, and a viscosity index ≥145; the refining agent is prepared by mixing MgCl2 and KCl in a 1:1 mass ratio.

[0042] Examples 1-3 and Comparative Examples 1-3: Production methods of 6082 aluminum alloy hot-top oil-lubricated hollow ingots with specifications of φ670 / φ305 mm (1) Composition ratio, furnace loading and melting: Target composition: The target chemical composition of the 6082 aluminum alloys in Examples 1-3 and Comparative Examples 1-3 is shown in Table 1.

[0043] Table 1 Target chemical composition of 6082 aluminum alloys in Examples 1-3 and Comparative Examples 1-3 Charging and melting of the smelting furnace: Solid materials are used for charging. First-grade recycled material that has been dried and is free of oil is added, and the first-grade recycled material shall not exceed 60% of the total mass of the furnace charge. Then aluminum ingots are added, and alloying materials are added according to the target chemical composition of 6082 aluminum alloy, and their mass shall not exceed 80% of the mass of pure aluminum ingots. After the furnace charge is added, melting is carried out, and the temperature of the molten aluminum is controlled not to exceed 760℃ during the melting process. Once the temperature of the molten aluminum exceeds 700°C, electromagnetic stirring is initiated every 30 minutes for 10 minutes each time to promote the melting of solid charge and reduce the risk of localized overheating of the molten aluminum.

[0044] (2) Refining and composition adjustment in the smelting furnace: The aluminum liquid obtained in step (1) was subjected to compositional analysis. The specific steps were as follows: After the solid material in the furnace was completely melted, the aluminum liquid was stirred to make the composition of the aluminum liquid uniform in each area of ​​the furnace. Before each sampling, mechanical stirring was performed for 10 minutes, followed by electromagnetic stirring for 10 minutes. The temperature of the aluminum liquid was controlled at 720-750℃. One aluminum liquid sample was taken from the middle of the furnace and another from the edge about 0.5m from the furnace wall. The sampling depth was about 1 / 2 of the total depth of the melt. After the obtained sample was cooled, its surface condition was checked. The sample was required to be free of obvious cracks, slag inclusions and pores. For samples that did not meet the requirements, resampling was performed. The sample was analyzed by direct reading spectrometer before the furnace to obtain the actual mass fraction of each alloying element in the aluminum liquid.

[0045] Based on the aluminum liquid composition test results, alloying materials are added to achieve the target chemical composition of the 6082 aluminum alloy. The specific steps are as follows: The amount of alloying material to be added is calculated based on the difference between the actual mass fraction obtained from the test and the target chemical composition, combined with the total mass of the aluminum liquid, the mass fraction of the corresponding element in the alloying material, and the burn-off rate of the corresponding element. Specifically, the formula for calculating the mass of a single element to be added is: Required element content = Aluminum liquid weight × (Target value of alloying element - Pre-analyzed measured value of alloying element); the formula for calculating the mass of alloying material to be added is: Required alloy weight = Required element mass ÷ Mass fraction of the corresponding element in the alloy × (1 + Burn-off coefficient). Before adding material, the slag on the surface of the aluminum liquid is removed, the aluminum liquid temperature is controlled at 740-750℃, and the weighed corresponding alloying material is evenly added to the aluminum liquid to avoid localized accumulation of the alloy material. After adding the alloying elements, the molten aluminum is stirred thoroughly to ensure uniform dispersion. Samples are taken again before the furnace and direct-reading spectrometers are then used for analysis. Based on the results, necessary minor adjustments are made until the content of each element reaches the target chemical composition range of 6082 aluminum alloy.

[0046] The first refining was carried out using high-purity argon and refining agent. After the first refining, the scum was removed, the temperature of the aluminum liquid was adjusted to 750-760℃, and the Ti content in the aluminum liquid was controlled to be 0.02-0.03%. The refining time and the amount of refining agent are shown in Table 2.

[0047] (3) Refining and purification in a settling furnace: The aluminum liquid obtained in step (2) is transferred into a static furnace. A powder spraying machine is used, and high-purity argon gas with a purity of not less than 99.999% is used as the carrier gas. The carrier gas flow rate is controlled at 8-12L / min. Under the condition that the aluminum liquid temperature is 730-740℃, a refining agent is added at a dosage of 1.0 kg / tAl for a second refining. During the second refining process, the refining temperature is 730-740℃ and the refining time is 30-40 minutes. After the second refining, the surface slag of the aluminum liquid is removed, and the furnace bottom is turned on for high-purity argon blowing for 30-40 minutes. The furnace bottom argon blowing flow rate is controlled at 35-45 L / min. During the blowing process, the aluminum liquid temperature is adjusted to 745-755℃, and the aluminum liquid is kept at a constant temperature for no less than 40 minutes, as shown in Table 2.

[0048] (4) Online aeration, online degassing, and online filtration: Online grain refinement was performed using Al-5Ti-1B aluminum-titanium-boron wire rods with a diameter of 9.5 mm. During the online grain refinement process, two wire feeders simultaneously fed the Al-5Ti-1B aluminum-titanium-boron wire rods into the molten aluminum from opposite directions. The feeding speed of each grain refiner was 160-200 cm / min; the flow rate of the molten aluminum was 11-12 t / h; and the amount of Al-5Ti-1B aluminum-titanium-boron wire rod added was 3.2-4 kg / tAl. A dual-rotor degassing device is used for online degassing of molten aluminum; the rotor is a graphite rotor with a rotation speed of 250-400 r / min; the working gas is high-purity argon with a purity ≥99.999% and a flow rate of 2-6 m³ / min. 3 / h, and ensure that the bubble height on the liquid surface does not exceed 30mm. The dissolved hydrogen content of the aluminum liquid before casting is monitored using a quantitative hydrogen analyzer and kept below 0.13 mL / 100 g Al; Ceramic foam filter plates are used for online filtration of molten aluminum. The specifications of the ceramic foam filter plates are shown in Table 2. The 30ppi ceramic foam filter plate and the 50ppi ceramic foam filter plate are arranged sequentially along the flow direction of the molten aluminum, with the 30ppi ceramic foam filter plate located upstream and the 50ppi ceramic foam filter plate located downstream; the filter box is electrically heated before filtration, and the preheating time is not less than 30 minutes.

[0049] Table 2. Melt treatment parameters for 6082 aluminum alloy hot-top oil-lubricated hollow ingots in Examples 1-3 and Comparative Examples 1-3. (5) Using a hot-top oil-lubricating semi-continuous casting method, the aluminum liquid treated in step (4) is formed into a hollow ingot to obtain a 6082 aluminum alloy hollow ingot with an outer diameter of 670 mm and an inner diameter of 305 mm; the specific steps are as follows: Casting preparation: The same level hot top oil-lubricated semi-continuous casting is adopted. Porous high-purity graphite rings 3 with a height of 30mm are set in the initial solidification zone of the outer crystallizer and the core. Before casting, clean the slag from the degassing box and put the rotor into working condition. Tilt the settling furnace to allow the molten aluminum to flow into the flow channel. Start wire feeding. After the molten aluminum enters the casting tray, lay a false bottom material layer on the ingot head. When the liquid level in the annular casting cavity reaches 50-70 mm above the transfer plate 2, simultaneously start the casting machine, internal and external cooling water, and lubrication system. Lubricating oil is delivered to the core graphite ring 3 and the outer crystallizer graphite ring 3 at a delivery pressure of 40-50 bar, and supplied in a pulse manner. The single pulse oil supply is 0.02-0.05 mL / time, the oil supply interval is 15-30 s, the average lubricating oil supply flow rate of the outer crystallizer graphite ring 3 is 0.15-0.30 mL / min, and the average lubricating oil supply flow rate of the core graphite ring 3 is 0.08-0.18 mL / min. The pulse oil supply operates in a cycle of 5 seconds of supply and 20 seconds of stop. When starting the casting machine, adjust the casting speed to 30. The speed is mm / min, and the cooling water volume of the external crystallizer is 60m³. 3 / h, core cooling water volume is 30m³ 3 Casting is carried out at a rate of / h; and, 50-70s after casting starts, the core is driven to reciprocate in a circumferential direction via a core manipulation mechanism, with an amplitude of 10-15mm and a frequency of 10-15 times / min. This operation prevents the initial billet shell from sticking to the core; Stabilize casting: Once the ingot length reaches 150mm, adjust the casting speed to 40-45mm / min and the cooling water flow rate of the external crystallizer to 96-102m³. 3 / h, the core cooling water volume is 45-55m³ 3 / h; During the casting process, the casting speed and cooling water volume are allowed to be finely adjusted within ±5% of the set values. At the same time, the temperature of the molten aluminum at the tail end of the casting pan is controlled at 700-710℃.

[0050] Casting completion: When casting enters the completion stage and the end of the ingot descends to 20-30mm below the graphite ring 3, stop the aluminum liquid supply and stop the machine. Then turn off the cooling water to prevent the end face of the ingot from being directly impacted by water.

[0051] Table 3 Casting parameters of 6082 aluminum alloy hot-top oil-lubricated hollow ingots in Examples 1-3 and Comparative Examples 1-3 (6) Homogenization treatment: First, cut off the head 150mm and tail 180mm of the 6082 aluminum alloy hollow ingot; then raise the temperature to 550±5℃ in 360min and keep it at 550±5℃ for 18h; after the heat preservation is completed, use a combination of forced air cooling and water mist cooling to cool the ingot to below 250℃ at an average cooling rate of not less than 200℃ / h before taking it out of the furnace, and then let it cool naturally to room temperature after taking it out of the furnace.

[0052] Experimental Example 1: The grain size (GB / T 3246.2-2012), cleanliness (GB / T 32186-2015), fracture surface (GB / T26492.1-2011), segregation layer thickness (GB / T 3246.2-2012), hydrogen content (GB / T 32186-2015), and presence of oxide film of the low-magnification specimens of the 6082 aluminum alloy hot-top oil-lubricated hollow ingots prepared in Examples 1-3 and Comparative Examples 1-3 were tested, and the results are shown in Table 4. In addition, the end face and low-magnification microstructure images of the large-size 6082 aluminum alloy hollow ingot prepared in Example 1 are shown in Table 4. Figure 1-2 As shown.

[0053] Table 4. Test results of 6082 aluminum alloy hot-top oil-lubricated hollow ingots prepared in Examples 1-3 and Comparative Examples 1-3 As shown in Table 4, the 6082 aluminum alloy hollow ingots prepared in Examples 1-3 of this invention all achieved Grade I low-magnification grain size, with no inclusions, metallurgical defects, or oxide films observed. The segregation layer thickness was only 4-5 mm, indicating good overall ingot quality. In contrast, Comparative Example 1 showed inclusion defects, while the segregation layer thicknesses in Comparative Examples 2 and 3 increased to 10 mm and 9 mm, respectively. This demonstrates that this invention, through the synergistic combination of multi-stage melt purification and internal and external hot-top oil-lubricating casting, can effectively reduce the segregation layer thickness while ensuring ingot cleanliness and microstructure uniformity, thereby improving the forming quality and stability of large-size 6082 aluminum alloy hollow ingots.

[0054] The above description is merely a preferred embodiment of this application and is not intended to limit this application. Various modifications and variations can be made to this application by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of this application should be included within the protection scope of this application.

Claims

1. A method for producing a 6082 aluminum alloy hot-top oil-lubricated hollow ingot, characterized in that, Includes the following steps: (1) Composition ratio, furnace loading and melting: The raw materials are prepared according to the target chemical composition of 6082 aluminum alloy; Solid materials are used for furnace loading. Primary recycled materials, aluminum ingots and alloying materials are added in sequence for melting. The temperature of the molten aluminum is controlled not to exceed 760℃ during the melting process. (2) Refining and composition adjustment in the smelting furnace: The composition of the aluminum liquid obtained in step (1) is tested, and alloying materials are added according to the composition test results of the aluminum liquid to make the aluminum liquid reach the target chemical composition of the 6082 aluminum alloy; the first refining is carried out using high-purity argon and refining agent, and the slag is removed after the first refining is completed and the temperature of the aluminum liquid is adjusted. (3) Refining and purification in a static furnace: The aluminum liquid obtained in step (2) is transferred into a static furnace, and a refining agent is added by spraying powder for a second refining. After the second refining is completed, the slag is removed, argon gas is blown into the furnace bottom, and the temperature of the aluminum liquid is adjusted. (4) Online grain refinement, online degassing and online filtration: Online grain refinement is carried out using a grain refiner; Subsequently, a dual-rotor degassing device was used to degas the molten aluminum online; finally, a two-stage filtration method was used to filter the molten aluminum online. (5) Hot-top oil-lubricated hollow casting: The aluminum liquid after step (4) is processed by hot-top oil-lubricated semi-continuous casting method to form a hollow ingot and obtain a 6082 aluminum alloy hollow ingot. (6) Homogenization treatment: Homogenize the 6082 aluminum alloy hollow ingot to obtain a 6082 aluminum alloy hot-top oil-lubricated hollow ingot.

2. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, The specifications of the 6082 aluminum alloy hot-top oil-lubricated hollow ingot are: outer diameter 670mm, inner diameter 305mm; it comprises the following components by mass percentage: Si 0.8-1.2%, Fe≤0.4%, Cu≤0.1%, Mn 0.5-0.9%, Mg 0.7-1.1%, Cr≤0.2%, Ni≤0.05%, Zn≤0.2%, Ti≤0.1%, other individual elements: ≤0.05%, total other elements: ≤0.15%, balance Al.

3. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (1), the amount of primary recycled material added shall not exceed 60% of the total mass of the furnace charge; the amount of alloying material added shall not exceed 80% of the mass of the aluminum ingot.

4. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (2), during the first refining process, the refining temperature is 735-745℃ and the refining time is 30-40min; the refining agent is made by mixing MgCl2 and KCl in a mass ratio of 1:1, and its addition amount is 1.5kg / tAl; after removing the slag, the temperature of the aluminum liquid is controlled at 750-760℃ and the Ti content in the aluminum liquid is controlled at 0.02-0.03%.

5. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (3), during the second refining process, the refining agent is made by mixing MgCl2 and KCl in a mass ratio of 1:1, and the amount added is 1.0 kg / tAl; the refining temperature is 730-740℃ and the refining time is 30-40 min; high-purity argon gas with a purity of ≥99.999% is used to blow gas into the furnace bottom for 30-40 min, the flow rate of argon gas into the furnace bottom is 35-45 L / min, and the temperature of the aluminum liquid is adjusted to 745-755℃. After the bottom gas blowing is completed, the furnace bottom is left to stand for no less than 40 min.

6. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (4), the grain refiner is Al-5Ti-1B aluminum titanium boron wire rod, and its addition amount is 3.2-4 kg / tAl; The dual-rotor degassing device uses a graphite rotor with a rotor speed of 250-400 r / min. The working gas is high-purity argon with a purity ≥99.999% and a working gas flow rate of 2-6 m³ / min. 3 / h, control the height of bubbles on the surface of the aluminum melt to not exceed 30 mm; the hydrogen content in the aluminum melt after online degassing is less than 0.13 mL / 100gAl; The two-stage filtration method uses a 30ppi ceramic foam filter plate and a 50ppi ceramic foam filter plate.

7. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (5), the hot-top oil-lubricated semi-continuous casting includes the following steps: (a) Using the same level hot-top oil-lubricated semi-continuous casting, porous high-purity graphite rings are set in the initial solidification zones of the outer crystallizer and the core. The scum in the degassing box is cleaned, and the rotors of the dual-rotor degassing device are in working condition. The tilting of the settling furnace allows the molten aluminum to flow into the flow channel, and the online grain refinement device is started. After the molten aluminum enters the casting tray, a false bottom material layer is laid on the ingot head. When the molten aluminum level in the annular casting cavity reaches 50-70mm above the transfer plate 2, the casting machine, the cooling water system of the outer crystallizer and the core, and the lubrication system are started simultaneously. The casting speed is 25-35mm / min, and the lubrication system is 55-65m / min. 3 / h external crystallizer cooling water volume and 25-35m 3 Casting begins under the condition of a core cooling water volume of / h; (b) When the ingot length reaches 150mm, adjust the casting speed to 40-45mm / min and the cooling water flow rate of the external crystallizer to 95-105m³. 3 / h, the core's cooling water volume is 45-55m³ / h. 3 / h, while controlling the temperature of the molten aluminum at the tail end of the casting pan to 700-710℃; (c) When the tail end of the ingot descends to 20-30mm below the graphite ring, stop the aluminum liquid supply and stop the machine, and then turn off the cooling water.

8. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 7, characterized in that, In step (a), the height of the high-purity graphite rings is 30 mm. Lubricating oil is supplied to the core graphite ring and the outer crystallizer graphite ring at a delivery pressure of 40-50 bar, and the oil is supplied in a pulse manner. The single pulse oil supply volume is 0.02-0.05 mL / time, the oil supply interval is 15-30 s, the average supply flow rate of lubricating oil for the outer crystallizer graphite ring is 0.15-0.30 mL / min, and the average supply flow rate of lubricating oil for the core graphite ring is 0.08-0.18 mL / min. The pulse oil supply operates in a cycle of 5 s supply and 20 s stop.

9. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 7, characterized in that, In step (a), 50-70 seconds after the casting starts, the core is driven to swing back and forth along the circumference by the core manipulation mechanism, with an swing amplitude of 10-15 mm and a swing frequency of 10-15 times / min.

10. The production method of 6082 aluminum alloy hot-top oil-lubricated hollow ingot as described in claim 1, characterized in that, In step (6), before homogenization, the head of the 6082 aluminum alloy hollow ingot is cut off by 100-200 mm and the tail by 160-200 mm; then the temperature is raised to 550±5℃ in 350-400 min and held at 550±5℃ for 16-20 h; after the holding is completed, the ingot is cooled to below 250℃ by a combination of forced air cooling and water mist cooling at an average cooling rate of not less than 200℃ / h and then taken out of the furnace. After taking out of the furnace, it is naturally cooled to room temperature.

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