A method of melting and casting aerospace large size high metallurgical quality low segregation 7xxx aluminum alloy ingot

Abstract

The present disclosure relates to the technical field of aluminum alloy, and provides a melting and casting method of a large-size high-metallurgical-quality low-segregation 7xxx aluminum alloy ingot for aerospace, comprising the following steps: S1, covering the melt after melting of aluminum raw materials with a refining agent, and then adding copper raw materials, zinc raw materials, magnesium raw materials and the like; S2, subjecting the obtained melt to smelting furnace refining to obtain a melt; S3, adding Al-Ti alloy to the bottom of a holding furnace, transferring the obtained melt to the holding furnace, and starting electromagnetic stirring to perform holding furnace refining; S4, subjecting the obtained melt to grain refinement and ultrasonic treatment, and then performing online degassing and online filtration; and S5, subjecting the obtained melt to casting and ultrasonic treatment at the core of the casting. The melting and casting method provided by the present disclosure optimizes processes from multiple links such as raw materials, smelting processes, online treatment, casting processes and ultrasonic assistance, so that the internal metallurgical quality of the aluminum alloy ingot is improved, and the composition segregation is reduced.

Description

Technical Field

[0001] This disclosure relates to the field of aluminum alloy technology, and in particular to a casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications. Background Technology

[0002] 7xxx series aluminum alloys are widely used in the aerospace field due to their high strength, good toughness and excellent corrosion resistance. They are often used in components with high material strength requirements, such as aircraft frames, wing spars, landing gear and pressure-bearing components of rocket fuel tanks.

[0003] Based on industry experience and practical findings, certain quality issues still exist in the manufacturing process of 7xxx series aluminum alloys. The main problems are as follows:

[0004] (1) Particle aggregation

[0005] To improve ingot performance and refine the alloy grains during the as-cast state, a certain amount of Al-Ti master alloy, Al-Zr master alloy, and Al-Ti-B grain refiner are usually added to the alloy. However, if the master alloy and grain refiner are not properly adjusted, local enrichment of Ti, Zr, and B elements can easily occur, forming coarse intermetallic compounds (such as TiAl3, ZrAl3, etc.) and hard particles (TiB2 particles). These can lead to microcracks during subsequent alloy forging, resulting in the forging failing flaw detection.

[0006] (2) Loose

[0007] Porosity is generally classified into two types: shrinkage porosity, caused by insufficient liquid metal replenishment between matrix dendrites, and gas porosity, caused by unremoved gases (mainly hydrogen). In actual production, shrinkage porosity and gas porosity rarely occur alone; they are usually mixed types. Porosity mainly depends on the hydrogen content and feeding conditions (melt fluidity). Elements such as Cu, Zn, and Mg in 7xxx series alloys can cause the formation of wide, mushy zones during alloy casting, making melt feeding difficult and leading to porosity. Furthermore, many process details during casting can easily cause a significant increase in the hydrogen content of the melt, increasing the probability of porosity formation. Studies have shown that porosity disrupts the continuity of the metal matrix, becoming a source of component stress concentration when the forging is under stress, significantly reducing the mechanical properties of the forging. If porosity is not completely compacted and closed during forging, it can easily promote crack initiation and subsequent crack propagation, leading to non-compliance in flaw detection.

[0008] (3) Component segregation

[0009] Ingot compositional segregation is mainly caused by the different distribution coefficients of different alloying elements and the large differences in cooling rates at different locations on the ingot. For 7xxx series aluminum alloys, if the distribution of Cu, Zn, and Mg elements is uneven, the quantity and morphology of strengthening phases (such as MgZn2, Al2Mg3Zn3, etc.) will vary, weakening the age-hardening effect of the alloy and ultimately leading to inconsistent mechanical properties in different parts of the forging, which cannot meet the application requirements.

[0010] Currently, while the smelting process, refining and degassing, and ceramic foam filtration used in the preparation of 7xxx series aluminum alloys can improve melt purity to some extent, they lack specificity in addressing the agglomeration of alloying elements in actual production. While external field-assisted electromagnetic stirring and melt shear treatment-assisted casting can reduce porosity and segregation, they have inherent limitations. Electromagnetic fields exhibit a skin effect, with magnetic induction intensity rapidly decreasing from the edges to the center, leading to convection characteristics that are stronger at the outside and weaker at the inside. Furthermore, applying an electromagnetic field can cause liquid surface fluctuations. Convection induced by melt shear treatment-assisted casting also exhibits a characteristic of stronger convection at the inside and weaker at the outside, with limited depth of effect on large ingots and exacerbating the core-edge difference. Therefore, there is an urgent need to develop a systematic smelting and casting method to achieve stable production of high-metallurgical-quality, low-segregation 7xxx series aluminum alloy ingots. Summary of the Invention

[0011] The technical problem solved by this disclosure is to provide a casting method for 7xxx aluminum alloy ingots, which can improve the metallurgical quality of aluminum alloy ingots and reduce component segregation.

[0012] In view of this, this disclosure provides a casting method for high metallurgical quality, low segregation 7xxx aluminum alloy ingots, comprising the following steps:

[0013] S1. The melt after melting aluminum raw materials is covered with a refining agent, and then copper raw materials and zinc raw materials are added. When the temperature of the melt rises to 730~750℃, Al-Zr master alloy and magnesium raw materials are added, and then Al-Be master alloy is added.

[0014] S2. Refine the obtained melt in a smelting furnace to obtain a melt;

[0015] S3. Add Al-Ti alloy to the bottom of the holding furnace, transfer the melt obtained in step S2 to the holding furnace, and at the same time turn on the electromagnetic stirring of the holding furnace for holding furnace refining.

[0016] S4. The melt obtained in step S3 is introduced into the flow channel. A grain refiner is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Ultrasonic treatment is performed on the flow channel behind the grain refiner addition point, followed by online degassing and online filtration.

[0017] S5. The melt obtained in step S4 is cast and the core of the casting is ultrasonically treated to obtain a 7xxx aluminum alloy ingot. The casting speed is 15~45mm / min and the water flow rate is 40~150m³ / min. 3 / h;

[0018] The 7xxx aluminum alloy ingot comprises, by mass percentage: Zn 6.10~6.50%, Mg 2.00~2.30%, Cu 2.00~2.30%, Zr 0.10~0.15%, Ti 0.018~0.030%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, Be 0.0005~0.002%, with the balance being Al.

[0019] In some specific embodiments, in step S1, the purity of the aluminum raw material is ≥99.9%, and / or the temperature of the melt after the aluminum raw material is melted is ≤760℃, and / or the amount of refining agent used is 0.5~1.5kg / t·Al.

[0020] In some specific embodiments, in step S1, electromagnetic stirring is started simultaneously with the addition of copper and zinc raw materials, and the electromagnetic stirring time is 10-30 minutes.

[0021] In some specific embodiments, in step S2, the refining temperature in the smelting furnace is 730~750℃, the time is 20~40min, and the settling time after refining is ≥20min.

[0022] In some specific embodiments, step S2 further includes sampling after refining in the smelting furnace. If the chemical composition of the melt obtained from the refining in the smelting furnace meets the composition ratio, then proceed to step S3. If the chemical composition of the melt obtained from the refining in the smelting furnace does not meet the composition ratio, then dilution or feeding is performed until the composition ratio is met.

[0023] In some specific embodiments, in step S3, the temperature of the transfer to the holding furnace is 730~750℃, and / or the refining time in the holding furnace is 20~40min, the settling temperature of the refining in the holding furnace is 730~750℃, and the settling time of the refining in the holding furnace is ≥20min.

[0024] In some specific embodiments, in step S4, the grain refiner includes Al-Ti-B wire; and / or, the insertion depth of the ultrasonic treatment is 50~150mm, and the power is 1200~1800W.

[0025] In some specific embodiments, in step S5, the initial casting temperature is 740~750℃, and / or the casting adopts a bottom-laying process, and / or the temperature of the molten aluminum at the end of the casting pan is 685~695℃.

[0026] In some specific embodiments, in step S5, the insertion depth of the ultrasonic treatment is 200~600mm, and the power is 400~1200W.

[0027] In some specific embodiments, the specifications of the 7xxx aluminum alloy ingot are Ф600~Ф1100mm.

[0028] This disclosure provides a casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications. By strictly limiting the Si and Fe content of the aluminum alloy ingots, harmful phases are prevented from forming during casting. The limiting of the Al-Zr master alloy addition temperature allows for rapid dissolution, forming fine and uniformly distributed ZrAl3 dispersed phases, which refine grains and inhibit recrystallization. The online grain refiner addition location and the introduction of ultrasonic treatment accelerate the dispersed distribution of TiAl3 and TiB2 particles, breaking down particle agglomeration, increasing the number of nucleation cores, and refining grains. Simultaneously, increasing the casting speed and casting water flow rate during casting accelerates the core solidification rate and reduces... The core of the ingot is shrinkage and porosity. Ultrasonic-assisted casting is used in the ingot core, where the acoustic flow effect stirs the melt, homogenizing temperature and solute distribution, improving feeding conditions, and suppressing porosity. Through the cavitation effect, ultrasound generates cavitation bubbles, which, upon collapse, produce high-temperature, high-pressure pulses, locally causing supercooling, refining the core grains, and reducing core shrinkage and porosity. Furthermore, by increasing the casting speed and casting water flow rate, the ingot cavity becomes shallower, the solidification transition zone narrows, and the diffusion paths and times of Zn, Mg, and Cu elements in the liquid phase are shortened. The acoustic flow effect of ultrasound stirs the melt, uniformly and dispersedly distributing primary crystal nuclei, improving microstructure homogeneity and reducing segregation. Therefore, the casting method for 7xxx aluminum alloy ingots provided in this disclosure optimizes aspects such as raw materials, smelting process, online processing, casting process, and ultrasonic assistance, improving the metallurgical quality of the aluminum alloy ingots and reducing component segregation. Attached Figure Description

[0029] Figure 1 The fracture morphology and scanning electron microscope image of the TiB2 agglomeration defect in the 7050 aluminum alloy ring forging produced in Comparative Example 1 of this disclosure are shown.

[0030] Figure 2 Table 1 shows the flaw detection results of the 7050 aluminum alloy ring forging produced as Comparative Example 1 of this disclosure;

[0031] Figure 3Table 2 shows the flaw detection results of the 7050 aluminum alloy ring forging produced as Comparative Example 1 of this disclosure;

[0032] Figure 4 This is a data table of flaw detection results for the 7050 aluminum alloy ring forging produced in Embodiment 1 of this disclosure;

[0033] Figure 5 This is a data table of flaw detection results for the 7050 aluminum alloy ring forging produced in Embodiment 2 of this disclosure. Detailed Implementation

[0034] To further understand this disclosure, preferred embodiments of this disclosure are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of this disclosure and are not intended to limit the scope of the claims of this disclosure.

[0035] To address the internal quality issues of large-size 7xxx aluminum alloy ingots in existing technologies, this disclosure provides a casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications. The process flow includes: raw material preparation – melting – alloy element addition – refining in a smelting furnace – refining in a holding furnace – online processing – casting. In this casting method, process optimization is implemented across multiple stages, including raw materials, smelting process, online processing, casting process, and ultrasonic assistance, thereby improving the internal metallurgical quality of the aluminum alloy ingot and reducing compositional segregation. Specifically, this disclosure provides a casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications, comprising the following steps:

[0036] S1. The melt after melting aluminum raw materials is covered with a refining agent, and then copper raw materials and zinc raw materials are added. When the temperature of the melt rises to 730~750℃, Al-Zr master alloy and magnesium raw materials are added, and then Al-Be master alloy is added.

[0037] S2. Refine the obtained melt in a smelting furnace to obtain a melt;

[0038] S3. Add Al-Ti alloy to the bottom of the holding furnace, transfer the melt obtained in step S2 to the holding furnace, and at the same time turn on the electromagnetic stirring of the holding furnace for holding furnace refining.

[0039] S4. The melt obtained in step S3 is introduced into the flow channel. A grain refiner is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Ultrasonic treatment is performed on the flow channel behind the grain refiner addition point, followed by online degassing and online impurity removal.

[0040] S5. The melt obtained in step S4 is cast and the core of the casting is ultrasonically treated to obtain a 7xxx aluminum alloy ingot. The casting speed is 15~45mm / min and the water flow rate is 40~150m³ / min. 3 / h;

[0041] The 7xxx aluminum alloy ingot comprises, by mass percentage: Zn 6.10~6.50%, Mg 2.00~2.30%, Cu 2.00~2.30%, Zr 0.10~0.15%, Ti 0.018~0.030%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, Be 0.0005~0.0020%, with the balance being Al.

[0042] In the casting method for high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots, in step S1, the molten aluminum raw material is covered with a refining agent, and then copper and zinc raw materials are added. When the molten temperature rises to 730~750℃, Al-Zr master alloy and magnesium raw materials are added, followed by Al-Be master alloy. During this process, the raw materials are first prepared according to the composition of the aluminum alloy ingot. In this disclosure, the raw materials are selected from high-purity aluminum ingots, Al-Ti master alloy wire, Al-Zr master alloy wire, Al-Be master alloy, zinc ingots, magnesium ingots, and copper plates. The purity of the high-purity aluminum ingot is ≥99.9%, and in a specific embodiment, the purity is 99.95%. First, the high-purity aluminum ingot is placed in a melting furnace and heated to melt. During the melting process, the molten temperature is ≤760℃, specifically 700~750℃, and more specifically, 730~740℃. After the pure aluminum ingots are leveled, they are mechanically stirred at least twice in an "N" shape using a stirring rake. After stirring, slag is skimmed off the surface slag and moved into the slag box. Once the melt is completely melted, a refining agent is applied to the surface of the melt, followed by the addition of copper plates and zinc ingots. Simultaneously, electromagnetic stirring is activated for 10-30 minutes. When the melt temperature reaches 730-750°C, Al-Zr master alloy wire and magnesium ingots are added, with the magnesium ingots being melted in a magnesium frame. The melt temperature is maintained at 730-750°C until the master alloy and magnesium ingots are completely dissolved, and then Al-Be master alloy is added. In the above process, the amount of refining agent added is 0.5-1.5 kg / t Al. In specific embodiments, the amount of refining agent added is 0.8-1.0 kg / t Al. In some specific embodiments, the stirring time is 15-20 minutes. In some specific embodiments, the melt temperature is 735-740°C.

[0043] In the above steps, high-grade aluminum ingots are preferred, with Si ≤ 0.04% and Fe ≤ 0.03% strictly limited to prevent the formation of harmful phases, such as Al7Cu2Fe, during subsequent casting. Due to the "microstructure inheritance effect," large particles in the aluminum master alloy can directly enter the aluminum melt, easily forming particle agglomerates. These agglomerates form hard spots during casting, leading to non-compliance in forging inspection. Therefore, Al-Zr and Al-Ti master alloy wires are preferred. This reduces the particle size in the master alloy and accelerates its dissolution rate, allowing TiAl3 and ZrAl3 particles to quickly disperse into the aluminum melt, preventing agglomeration. Simultaneously, the addition temperature and time of the Al-Zr master alloy are limited to ensure rapid dissolution and the formation of fine and uniformly distributed ZrAl3 dispersed phases, refining grains and inhibiting recrystallization. In some specific embodiments, after adding the Al-Be master alloy, mechanical stirring is performed at least twice, depending on the melting of the alloying elements, to ensure sufficient diffusion of the alloying elements and uniform melt composition and temperature.

[0044] In step S2, the melt is refined in a smelting furnace, that is, the melt obtained in step S1 is refined in a smelting furnace to obtain a melt. During this process, the refining and settling slag removal is performed at least 4 times. The temperature of the smelting furnace refining is 730~750℃, the time is 20~40min, and the settling time after refining is ≥20min. Specifically, the temperature of the smelting furnace refining is 735~745℃, the time is 25~35min, and the settling time after refining is 25~30min.

[0045] In this disclosure, after refining in the smelting furnace, it is preferable to take a sample of the obtained melt to test the chemical composition of the melt. If the chemical composition of the melt meets the composition ratio of the aluminum alloy ingot, it proceeds to the next process. If the chemical composition of the melt does not meet the composition ratio of the aluminum alloy ingot, the melt is diluted or replenished until the chemical composition of the melt meets the composition ratio.

[0046] According to this disclosure, after refining in the smelting furnace, the melt is transferred to a holding furnace for further refining. In step S3, an Al-Ti alloy is added to the bottom of the holding furnace, and the melt obtained in step S2 is transferred to the holding furnace. Simultaneously, the electromagnetic stirring of the holding furnace is activated for holding furnace refining. During the above process, the slag on the surface of the molten aluminum is thoroughly removed before the melt is transferred. The transfer temperature is 730~750℃, and in some specific embodiments, the transfer temperature is 735~745℃. The Al-Ti alloy is added in the form of wire. The Al-Ti alloy wire is added to the bottom of the holding furnace before the melt is transferred, and the electromagnetic stirring of the holding furnace is activated throughout the transfer process. The timing of adding the Al-Ti alloy wire reduces the timing of its addition and its residence time in the melt. Adding it during the transfer process ensures rapid dissolution and dispersion of the Al-Ti intermediate alloy. Simultaneous activation of the electromagnetic stirring accelerates the dispersion and distribution of TiAl3 particles and prevents agglomeration. Reducing its residence time in the molten aluminum avoids coarsening and accumulation of TiAl3 particles, ensuring a refining effect. The refining time in the holding furnace is 20-40 minutes; in some specific embodiments, the refining time is 25-35 minutes. The settling temperature for refining in the holding furnace is 730-750°C; in some specific embodiments, the settling temperature is 740-745°C. The settling time for refining in the holding furnace is ≥20 minutes; in some specific embodiments, the settling time is 25-30 minutes. In some specific embodiments, the time from when the melt is poured into the holding furnace to when casting begins is controlled to be ≤3.0 hours; specifically, the time from when the melt is poured into the holding furnace to when casting begins is controlled to be 2.0-2.5 hours.

[0047] After refining in the holding furnace, the melt enters an online processing stage, which includes online grain refinement, online degassing, and online filtration. In step S4, the melt obtained in step S3 is introduced into a flow channel. A grain refiner is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Ultrasonic treatment is then performed in the flow channel behind the grain refiner addition point, followed by online degassing and online filtration. In this process, the grain refiner includes Al-Ti-B wire, added at a rate of 60-70 cm / min, specifically 65-70 cm / min. The online ultrasonic treatment in the flow channel behind the Al-Ti-B wire addition point accelerates the dispersion and distribution of TiAl3 and TiB2 particles, breaks up particle agglomeration, increases the number of nucleation cores, and refines the grains. The ultrasonic treatment promotes the precipitation and upward floating of hydrogen gas inside the melt, reducing the hydrogen content of the melt and thus reducing the probability of gas porosity in the ingot. The ultrasonic treatment has an insertion depth of 50-150 mm and a power of 1200-1800 W. Specifically, the ultrasonic treatment has an insertion depth of 80-120 mm and a power of 1300-1500 W. The online degassing is carried out sequentially in the degassing box, and the online filtration is carried out in the filtration box.

[0048] In step S5, the melt obtained in step S4 is cast and ultrasonically treated in the casting core to obtain a 7xxx aluminum alloy ingot. The casting speed is 15~45 mm / min and the water flow rate is 40~150 m³ / min. 3 / h; This step refers to the casting process. During the casting process described above, the initial casting temperature is 740~750℃. The casting adopts a bottom-laying process to ensure the temperature of the molten aluminum at the end of the casting pan is 685~695℃. Specifically, the initial casting temperature is 745~750℃, and the temperature of the molten aluminum at the end of the casting pan is 690~695℃. Further, the casting speed is 15~45mm / min, and the water flow rate is 40~150m³ / min. 3 Specifically, the casting speed is 24~40 mm / min, and the water flow rate is 60~120 m³ / h. 3 More specifically, the casting speed is 26~35 mm / min, and the water flow rate is 70~93 m³ / h. 3 More specifically, the casting speed is 28~30 mm / min, and the water flow rate is 78~90 m³ / h. 3 / h. Ultrasonic treatment is performed on the cast core, wherein the insertion depth of the ultrasonic treatment is 200~600mm and the power is 400~1200W, specifically, the insertion depth is 300~500mm and the power is 500~1000W, more specifically, the insertion depth is 400~450mm and the power is 600~900W. In the aforementioned casting process, optimizing casting parameters and ultrasonic-assisted casting are beneficial for improving internal metallurgical quality. Firstly, by appropriately increasing the casting speed and casting water flow rate, the core solidification rate is accelerated, reducing core shrinkage and porosity. Simultaneously, ultrasonic-assisted casting in the ingot core generates a stirring effect in the melt through acoustic flow, uniformizing temperature and solute distribution, improving feeding conditions, and suppressing porosity. Through cavitation, ultrasound can generate cavitation bubbles, producing high-temperature, high-pressure pulses when these bubbles collapse, resulting in localized supercooling, refining core grains, and reducing core shrinkage and porosity. Furthermore, ultrasound has a certain degassing effect, reducing the hydrogen content within the melt and further reducing gas porosity. Simultaneously, optimizing casting parameters and ultrasonic-assisted casting helps reduce component segregation in the ingot. Specifically, by appropriately increasing the casting speed and casting water flow rate, the ingot cavity becomes shallower, the solidification transition zone narrows, and the diffusion paths and times of Zn, Mg, and Cu elements in the liquid phase are shortened. Meanwhile, the ultrasonic flow effect generates a stirring effect in the melt, which uniformly and disperses the primary crystal nuclei in the melt, improving the uniformity of the structure and reducing segregation.

[0049] In this disclosure, the 7xxx aluminum alloy ingot, by mass percentage, comprises: Zn 6.10~6.50%, Mg 2.00~2.30%, Cu 2.00~2.30%, Zr 0.10~0.15%, Ti 0.018~0.030%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, with the balance being Al; specifically, the Zn content is 6.15%, 6.20%, 6.25%, 6.30%, 6.35%, and 6.40%; the Mg content is 2.05%, 2.10%, 2.15%, 2.20%, 2.25%, and 2.30%; the Cu content is 2.05%, 2.10%, 2.15%, 2.20%, and 2.25%; the Zr content is 0.11%, 0.12%, 0.13%, and 0.14%; and the Ti content is 0. 0.019%, 0.020%, 0.021%, 0.022%, 0.023%, 0.024%, 0.025%, 0.026%, 0.027%, 0.028%, 0.029%; The addition of Be can prevent ingot cracking, but the amount added needs to be controlled, and its specific content is 0.0006%, 0.0007%, 0.0008%, 0.0009%, 0.0010%, 0.0011%, 0.0012%, 0.0013%, 0.0014%, 0.0015%, 0.0016%, 0.0017%, 0.0018%, 0.0018%.

[0050] The high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingot casting method disclosed herein is applicable to large-size aluminum alloy ingots (Ф600~Ф1100mm). The compositional characteristics of this 7xxx aluminum alloy, combined with the large-size requirements, increase the difficulty of production, making the control of metallurgical quality and compositional segregation a key challenge. The casting method disclosed herein optimizes multiple aspects, including raw materials, smelting process, online treatment, casting process, and ultrasonic-assisted casting, and has the following advantages: It reduces the agglomeration of TiAl3, ZrAl3, and TiB2 particles in the melt, and the use of a dual degassing box and ultrasonic online treatment can greatly reduce the hydrogen content in the melt, improve melt purity, reduce the probability of gas porosity formation, and significantly improve the subsequent forging flaw detection pass rate, and ring forgings with a diameter of 5m or more can achieve flaw detection pass rate; it reduces the segregation of Zn, Mg, and Cu elements in casting, so that the amount of strengthening phases (such as MgZn2, Al2Mg3Zn3, etc.) precipitated reaches the expected target, achieving the alloy aging strengthening effect.

[0051] To further understand this disclosure, the following detailed description of the casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications provided by this disclosure is provided in conjunction with embodiments. The scope of protection of this disclosure is not limited to the following embodiments.

[0052] Example 1

[0053] A casting method for improving compositional segregation in 7050 aluminum alloy ingots with a diameter of Ф830mm for aerospace forgings includes the following steps:

[0054] Step 1: The chemical composition of the aluminum alloy ingot, by mass percentage, is: Zn 6.20%, Mg 2.10%, Cu 2.10%, Zr 0.13%, Ti 0.022%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, Be 0.0010%, with the balance being Al; according to the composition of the target alloy, weigh out 99.95% high-purity aluminum ingots, Al-Ti alloy wire, Al-Zr alloy wire, Al-Be master alloy, zinc ingots, magnesium ingots, and copper plates as raw materials;

[0055] Step 2: Weigh the 99.95% high-purity aluminum ingots according to the batching calculation and put them into the melting furnace. Start heating and melting. During the melting process, the melt temperature is controlled to be ≤760℃.

[0056] Step 3: After the material has leveled, use a stirring rake to mechanically stir it back and forth in an "N" shape twice. After stirring, remove the slag from the surface of the molten aluminum into the slag box.

[0057] Step 4: After the melt is completely melted, cover it with a refining agent of 1.0 kg / t Al, then add copper plates and zinc ingots, and start electromagnetic stirring for 20 minutes. When the melt temperature rises to 740℃, add Al-Zr alloy wire and magnesium ingots. The magnesium ingots are scalded in a magnesium frame to prevent them from floating on the surface of the melt and burning. Maintain this temperature until the alloy wire and magnesium ingots are completely melted. Then add Al-Be master alloy.

[0058] Step 5: Based on the melting of the alloying elements, mechanical stirring should be performed ≥2 times to ensure that the alloying elements diffuse fully and that the melt composition and temperature are uniform.

[0059] Step 6: After the ingredients are mixed, they are refined in the smelting furnace. The slag is removed 4 times during the refining and settling process. The refining and settling temperature is 740℃ and the refining time is 25 minutes. The refining operation is strictly controlled to ensure no dead corners. After the refining is completed, the mixture is settling for 30 minutes.

[0060] Step 7: Take a sample from the melt obtained in Step 6 and test the alloy chemical composition. If it meets the requirements, proceed to the next process. If it does not meet the requirements, dilute or add material.

[0061] Step 8: Transfer the melt to the holding furnace. Before pouring, thoroughly remove the slag from the surface of the molten aluminum. The pouring temperature is 750℃. Before pouring, add Al-Ti alloy wire to the bottom of the holding furnace. After adding, turn on the electromagnetic stirring of the holding furnace during the entire pouring process.

[0062] Step 9: Refine in the holding furnace, remove slag twice during the refining and settling period, the refining and settling temperature is 740℃, the refining time is 25min, after the refining is completed, settling for 30min, and control the time from pouring the melt into the holding furnace to the start of casting is 2.5h.

[0063] Step 10: After refining and settling the melt in the holding furnace and removing slag, the molten aluminum alloy is introduced into the flow channel. Al-Ti-B wire is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Online ultrasonic treatment is then performed in the flow channel behind the Al-Ti-B wire addition point. Subsequently, the melt undergoes online degassing through two degassing boxes, and finally, online filtration to remove impurities. Specifically:

[0064] In the first stage, Al-Ti-B wires are added between the outlet of the heat preservation furnace and the inlet of the degassing box to refine the grains, with an addition rate of 65±5cm / min.

[0065] In the second stage, online ultrasonic treatment is performed in the flow channel at the rear end of the Al-Ti-B wire insertion position. The insertion depth is 80mm and the power is 1500W. This accelerates the dispersion and distribution of TiAl3 and TiB2 particles, breaks up particle agglomeration, and promotes the precipitation and floating of hydrogen inside the melt.

[0066] The third stage uses two degassing boxes for online degassing. Both degassing boxes use dual rotating rotors. Degassing box #2 uses vacuum degassing to improve the gas removal efficiency in the aluminum alloy melt.

[0067] The fourth stage uses bipolar porous ceramic foam boards for online filtration. The mesh size of the filter board is 60+60ppi, which improves the filtration efficiency of impurities in the melt.

[0068] Step 11: Cast the melt obtained in Step 10, controlling the initial casting temperature at 750℃, using a bottom-laying casting process to ensure the temperature of the molten aluminum at the end of the casting pan is 690℃, obtaining an aluminum alloy ingot with a diameter of Ф830mm; the casting speed is 24mm / min, and the water flow rate is 90m³ / min. 3 / h; and each cast core is ultrasonically treated, with an insertion depth of 300mm and a power of 900W;

[0069] Step 12: The aluminum alloy ingot obtained in Step 11 is homogenized, machined, and then forged to obtain the final finished ring forging.

[0070] Example 2

[0071] A casting method for improving compositional segregation in 7050 aluminum alloy ingots with a diameter of Ф830mm for aerospace forgings includes the following steps:

[0072] Step 1: The chemical composition of the aluminum alloy, by mass percentage, is: Zn 6.30%, Mg 2.15%, Cu 2.15%, Zr 0.12%, Ti 0.025%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, Be 0.0011%, with the balance being Al. Based on the composition of the target alloy, weigh out 99.95% high-purity aluminum ingots, Al-Ti alloy wires, Al-Zr alloy wires, Al-Be master alloy, zinc ingots, magnesium ingots, and copper plates as raw materials.

[0073] Step 2: Weigh the 99.95% high-purity aluminum ingots according to the batching calculation and put them into the melting furnace. Start heating and melting. During the melting process, the melt temperature is controlled to be ≤760℃.

[0074] Step 3: After the material has leveled, use a stirring rake to mechanically stir it back and forth in an "N" shape twice. After stirring, remove the slag from the surface of the molten aluminum into the slag box.

[0075] Step 4: After the melt is completely melted, cover it with a refining agent of 1.0 kg / t Al, then add copper plates and zinc ingots, and start electromagnetic stirring for 20 minutes. When the melt temperature rises to 735℃, add Al-Zr alloy wire and magnesium ingots. The magnesium ingots are scalded in a magnesium frame to prevent them from floating on the surface of the melt and burning. Maintain this temperature until the alloy wire and magnesium ingots are completely melted. Then add Al-Be master alloy.

[0076] Step 5: Based on the melting of the alloying elements, mechanical stirring should be performed ≥2 times to ensure that the alloying elements diffuse fully and that the melt composition and temperature are uniform.

[0077] Step 6: After the ingredients are mixed, they are refined in the smelting furnace. The slag is removed 4 times during the refining and settling process. The refining and settling temperature is 735℃ and the refining time is 20 minutes. The refining operation is strictly controlled to ensure no dead corners. After the refining is completed, the mixture is settling for 25 minutes.

[0078] Step 7: Take a sample from the melt and test the alloy chemical composition. If it meets the requirements, proceed to the next process. If it does not meet the requirements, dilute or add material.

[0079] Step 8: Transfer the melt to the holding furnace. Before pouring the melt, thoroughly remove the slag from the surface of the aluminum liquid. The pouring temperature is 745℃. Before pouring, add Al-Ti alloy wire to the bottom of the holding furnace. After adding, turn on the electromagnetic stirring of the holding furnace during the entire pouring process.

[0080] Step 9: Refine in the holding furnace, remove slag twice during the refining and settling process, the refining and settling temperature is 745℃, the refining time is 20min, after the refining is completed, settling is performed for 25min, and the time from pouring the melt into the holding furnace to the start of casting is controlled to 2.0h.

[0081] Step 10: After refining and settling the melt in the holding furnace and removing slag, the molten aluminum alloy is introduced into the flow channel. Al-Ti-B wire is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Online ultrasonic treatment is then performed in the flow channel behind the Al-Ti-B wire addition point. Subsequently, the melt undergoes online degassing through two degassing boxes, and finally, online filtration to remove impurities. Specifically:

[0082] In the first stage, Al-Ti-B wires are added between the outlet of the heat preservation furnace and the inlet of the degassing box to refine the grains, with an addition rate of 65±5cm / min.

[0083] In the second stage, online ultrasonic treatment is performed in the flow channel at the rear end of the Al-Ti-B wire insertion position. The insertion depth is 50mm and the power is 1200W to accelerate the dispersion and distribution of TiAl3 and TiB2 particles, break up particle agglomeration, and promote the precipitation and floating of hydrogen inside the melt.

[0084] The third stage uses two degassing boxes for online degassing. Both degassing boxes use dual rotating rotors. Degassing box #2 uses vacuum degassing to improve the gas removal efficiency in the aluminum alloy melt.

[0085] The fourth stage uses bipolar porous ceramic foam boards for online filtration. The mesh size of the filter board is 60+60ppi, which improves the filtration efficiency of impurities in the melt.

[0086] Step 11: Cast the melt obtained in Step 10, controlling the initial casting temperature at 745℃, using a bottom-laying casting process to ensure the temperature of the molten aluminum at the end of the casting pan is 690℃, obtaining an aluminum alloy ingot with a diameter of Ф830mm; the casting speed is 26mm / min, and the water flow rate is 93m³ / min. 3 / h; and each cast core is ultrasonically treated, with an insertion depth of 400mm and a power of 1000W;

[0087] Step 12: The aluminum alloy ingot obtained in Step 11 is homogenized, machined, and then forged to obtain the final finished ring forging.

[0088] Two furnaces of Φ830mm diameter 7050 ingots were produced using the above-mentioned casting technology. The finished product testing results all met the customer's internal metallurgical quality requirements. After forging, this batch of ingots produced 15 3.5m ring forgings, 14 of which met Class A flaw detection standards. Only one piece was scrapped due to a single defect exceeding the standard. Some flaw detection results are shown below. Figure 2 As shown.

[0089] Comparative Example 1

[0090] A conventional melting and casting method for a Φ830mm 7050 aluminum alloy ingot includes the following steps:

[0091] Step 1: The chemical composition of the aluminum alloy, by mass percentage, is: Zn 6.35%, Mg 2.40%, Cu 2.35%, Zr 0.12%, Ti 0.035%, Mn≤0.05%, Cr≤0.02%, Si≤0.10%, Fe≤0.10%, Be 0.0010%, with the balance being Al; based on the composition of the target alloy, weigh out 99.90% high-purity aluminum ingots, Al-Ti, Al-Zr, Al-Be master alloys, zinc ingots, magnesium ingots, and copper plates as raw materials;

[0092] Step 2: Weigh out the 99.90% high-purity aluminum ingot and intermediate alloy according to the batching calculation and put them into the melting furnace. Start heating and melting. During the melting process, the melt temperature is controlled to be ≤760℃.

[0093] Step 3: After the material has leveled, use a stirring rake to mechanically stir it back and forth in an "N" shape twice. After stirring, remove the slag from the surface of the molten aluminum into the slag box.

[0094] Step 4: After the melt is completely melted, cover it with a refining agent of 1.0 kg / t Al, then add copper plates and zinc ingots, and start electromagnetic stirring at the same time for 20 minutes; scald the magnesium ingots in a magnesium frame to prevent the magnesium ingots from floating on the surface of the melt and burning, and maintain this temperature until the magnesium ingots are completely melted.

[0095] Step 5: Based on the melting of the alloying elements, mechanical stirring should be performed ≥2 times to ensure that the alloying elements diffuse fully and that the melt composition and temperature are uniform.

[0096] Step 6: After the ingredients are mixed, they are refined in the smelting furnace. The slag is removed 3 times during the refining and settling process. The refining and settling temperature is 735~745℃ and the refining time is 20 minutes. The refining operation is strictly controlled to ensure no dead corners. After the refining is completed, the mixture is settling for 30 minutes.

[0097] Step 7: Take a sample from the melt obtained in Step 6 and test the alloy chemical composition. If it meets the requirements, proceed to the next process. If it does not meet the requirements, dilute or add material.

[0098] Step 8: Transfer the melt obtained in step 7 to the holding furnace. Before pouring the melt, thoroughly remove the slag from the surface of the aluminum liquid. The pouring temperature is 745℃.

[0099] Step 9: Refine in a holding furnace, remove slag twice during the refining and settling period, the refining and settling temperature is 735~745℃, the refining time is 20min, and after refining, settling period is 30min.

[0100] Step 10: After refining and settling the melt in the holding furnace and removing slag, the molten aluminum alloy is introduced into the flow channel. Al-Ti-B wire is added between the outlet of the holding furnace and the inlet of the degassing box for grain refinement. Then, it passes through two degassing boxes for online degassing, and finally through a filter box for online filtration to remove impurities. Specifically:

[0101] In the first stage, Al-Ti-B wires are added between the outlet of the heat preservation furnace and the inlet of the degassing box to refine the grains, with an addition rate of 65±5cm / min.

[0102] The second stage uses two degassing boxes for online degassing. Both degassing boxes use dual rotating rotors. Degassing box #2 uses vacuum degassing to improve the gas removal efficiency in the aluminum alloy melt.

[0103] The third stage uses bipolar porous ceramic foam board for online filtration. The filter board mesh count is 60+60ppi, which improves the filtration efficiency of impurities in the melt.

[0104] Step 11: Cast the melt obtained in Step 10, controlling the initial casting temperature at 735~745℃, using a bottom-laying casting process to ensure the temperature of the molten aluminum at the end of the casting pan is 685~690℃, obtaining an aluminum alloy ingot with a diameter of Ф830mm; the casting speed is 20mm / min, and the water flow rate is 81m³ / min. 3 / h;

[0105] Step 12: The aluminum alloy ingot obtained in Step 11 is homogenized, machined, and then forged to obtain the final finished ring forging.

[0106] Combined with the metallographic image of the defective microstructure of the forging in Comparative Example 1 (e.g.) Figure 1 ), and the flaw detection results of the aluminum alloy ring forgings prepared in Examples 1, 2 and Comparative Example 1 (e.g. Figure 2 , Figure 3 , Figure 4 , Figure 5 This disclosure achieves (1) reducing the aggregation of oxides and TiAl3, ZrAl3, and TiB2 particles inside the ingot; and (2) enabling the production of ring forgings that meet the requirements of Class A flaw detection after forging from self-produced ingots.

[0107] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of this disclosure. It should be noted that those skilled in the art can make several improvements and modifications to this disclosure without departing from the principles of this disclosure, and these improvements and modifications also fall within the protection scope of the claims of this disclosure.

[0108] The above description of the disclosed embodiments enables those skilled in the art to make or use this disclosure. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of this disclosure. Therefore, this disclosure is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A casting method for large-size, high-metallurgical-quality, low-segregation 7xxx aluminum alloy ingots for aerospace applications, comprising the following steps: S1. The melt after melting aluminum raw materials is covered with a refining agent, and then copper raw materials and zinc raw materials are added. When the temperature of the melt rises to 730~750℃, Al-Zr master alloy and magnesium raw materials are added, and then Al-Be master alloy is added. S2. Refine the obtained melt in a smelting furnace to obtain a melt; S3. Add Al-Ti alloy to the bottom of the holding furnace, transfer the melt obtained in step S2 to the holding furnace, and at the same time turn on the electromagnetic stirring of the holding furnace for holding furnace refining. S4. The melt obtained in step S3 is introduced into the flow channel. A grain refiner is added between the outlet of the holding furnace and the inlet of the degassing box to refine the grains. Ultrasonic treatment is performed on the flow channel behind the grain refiner addition point, followed by online degassing and online filtration. S5. The melt obtained in step S4 is cast and the core of the casting is ultrasonically treated to obtain a 7xxx aluminum alloy ingot. The casting speed is 15~45mm / min and the water flow rate is 40~150m³ / min. 3 / h; The 7xxx aluminum alloy ingot comprises, by mass percentage: Zn 6.10~6.50%, Mg 2.00~2.30%, Cu 2.00~2.30%, Zr 0.10~0.15%, Ti 0.018~0.030%, Mn≤0.03%, Cr≤0.02%, Si≤0.04%, Fe≤0.03%, Be 0.0005~0.002%, with the balance being Al.

2. The casting method according to claim 1, characterized in that, In step S1, the purity of the aluminum raw material is ≥99.9%, and / or the temperature of the melt after the aluminum raw material is melted is ≤760℃, and / or the amount of refining agent used is 0.5~1.5kg / t·Al.

3. The casting method according to claim 1, characterized in that, In step S1, the electromagnetic stirring is started simultaneously with the addition of copper and zinc raw materials, and the electromagnetic stirring time is 10-30 minutes.

4. The casting method according to claim 1, characterized in that, In step S2, the refining temperature in the smelting furnace is 730~750℃, the time is 20~40min, and the settling time after refining is ≥20min.

5. The casting method according to any one of claims 1 to 4, characterized in that, In step S2, after refining in the smelting furnace, sampling is also included. If the chemical composition of the melt obtained from the refining in the smelting furnace meets the composition ratio, then proceed to step S3. If the chemical composition of the melt obtained from the refining in the smelting furnace does not meet the composition ratio, then dilution or feeding is performed until the composition ratio is met.

6. The casting method according to claim 5, characterized in that, In step S3, the temperature of the transfer to the holding furnace is 730~750℃, and / or the refining time in the holding furnace is 20~40min, the settling temperature of the refining in the holding furnace is 730~750℃, and the settling time of the refining in the holding furnace is ≥20min.

7. The casting method according to claim 5, characterized in that, In step S4, the grain refiner includes Al-Ti-B wire; and / or, the insertion depth of the ultrasonic treatment is 50~150mm, and the power is 1200~1800W.

8. The casting method according to claim 5, characterized in that, In step S5, the initial casting temperature is 740~750℃, and / or the casting adopts the bottom-laying process, and / or the temperature of the molten aluminum at the end of the casting pan is 685~695℃.

9. The casting method according to claim 5 or 8, characterized in that, In step S5, the insertion depth of the ultrasonic treatment is 200~600mm, and the power is 400~1200W.

10. The casting method according to claim 5, characterized in that, The specifications of the 7xxx aluminum alloy ingots are Ф600~Ф1100mm.

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