A low-defect melting and casting method for aviation 7xxx aluminum alloy ingot

Abstract

The application discloses a low-defect smelting and casting method for 7xxx aluminum alloy ingot for aviation and belongs to the technical field of aluminum alloy preparation. The application proposes a smelting process in which Al-Zr intermediate alloy is preferentially added at 700-720 DEG C, Al-Ti intermediate alloy is dispersedly added at 735+ / -2 DEG C, Mg ingot and Al-Be intermediate alloy are respectively added at 745+ / -2 DEG C and 753+ / -2 DEG C stages, and a composite purification process is combined, such as RGI rotary gas refining, ultrasonic online degassing and impurity removal and multi-stage porous ceramic foam plate, so that Ti-Zr agglomeration, inclusion residue and hydrogen content are effectively controlled, a cast ingot with small grain size and high purity is obtained, the problem of performance reduction of aluminum alloy material caused by Ti-Zr agglomeration and other defects is solved, and meanwhile, a four-stage gradual heating homogenization heat treatment process is further adopted to improve the uniformity of the cast ingot structure, so that a high-performance aluminum alloy material suitable for fields such as aviation and aerospace is obtained.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy preparation technology, specifically to a low-defect melting and casting method for 7xxx aluminum alloy ingots for aerospace applications. Background Technology

[0002] 7xxx series (Al-Zn-Mg-Cu) aluminum alloys are widely used in aerospace structural components, ship frames, and high-end transportation equipment manufacturing due to their high specific strength, good corrosion resistance, and excellent welding and heat treatment properties. Among them, 7150 aluminum alloy, with its high static strength, excellent fracture toughness, and good resistance to stress corrosion, has become a typical representative of the third-generation high-strength and high-toughness 7xxx alloys.

[0003] However, serious quality control challenges still exist in the industrial casting of 7150 and similar 7xxx alloys, mainly including the following typical problems:

[0004] (1) Ti-Zr element aggregation

[0005] To refine ingot grains and promote uniform nucleation, it is common practice to introduce grain refiners such as Al-Ti and Al-Zr into the alloy. However, if the order of addition, timing of addition, and timing of melt stirring are not properly controlled, Ti and Zr elements can easily accumulate locally and form coarse intermetallic compounds (such as Al3Ti, Al3Zr, Al3(Ti,Zr)). These phases are often distributed at grain boundaries or in local segregation zones, becoming sources of microcrack initiation. It is worth noting that Ti-Zr agglomerates usually exist as submicron dispersed phases when they do not undergo significant enrichment, making them difficult to identify with optical metallographic microscopy. Once local enrichment occurs and coarse intermetallic compounds are formed, they can only be observed as dark gray or bright white phases under metallographic conditions. Further analysis using scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS) is required to confirm their composition and distribution. Moreover, their presence has an adverse effect on the uniformity of subsequent heat treatment and the stability of mechanical properties.

[0006] (2) High hydrogen content

[0007] Hydrogen is the primary source of gaseous inclusions in molten aluminum. It typically dissolves in the melt and precipitates during solidification, forming volume defects such as pinholes and white spots. The main causes of abnormally high hydrogen content include poor furnace lid sealing, residual wetting agents, insufficient degassing time, or uneven gas distribution. Studies have shown that when the hydrogen content exceeds 0.20 ml / 100 g, the hot working cracking tendency and fatigue performance of the ingot significantly decrease, severely impacting the material's service reliability.

[0008] (3) Non-metallic inclusions

[0009] Inclusions mainly originate from magnesium oxide (MgO), aluminum oxide (Al2O3), intermetallic compounds (such as Al3Fe), and reaction film fragments generated during the smelting process. If these inclusions are not effectively removed during transfer, casting, or other processes, they will serve as potential crack sources inside the ingot, affecting not only the material's plasticity but also potentially inducing surface quality problems such as warping and edge cracking during subsequent extrusion molding.

[0010] While conventional methods such as rotary degassing combined with static refining and ceramic foam filtration are widely used in industry to improve melt purity, problems remain in practice, including insufficient targeting of purification methods and a single mechanism of action. This is particularly true when dealing with complex defects involving Ti-Zr agglomeration and gas inclusions, where existing processes struggle to simultaneously achieve grain refinement and ingot microstructure uniformity. Therefore, a systematic melting and purification method is urgently needed to achieve multi-dimensional and precise control of defects in 7xxx series aluminum alloy ingots. Summary of the Invention

[0011] To address the aforementioned technical problems, this invention provides a low-defect melting and casting method for 7xxx series aluminum alloy ingots used in aviation, which can solve problems such as Ti-Zr element agglomeration, excessive hydrogen content, and non-metallic inclusion residues that exist in the melting and casting process of 7xxx series aluminum alloys.

[0012] The technical solution adopted in this invention is as follows:

[0013] A low-defect melting and casting method for 7xxx aluminum alloy ingots for aerospace applications, comprising the following steps:

[0014] (1) Weigh out aluminum ingots, zinc ingots, magnesium ingots, copper plates, and Al-Ti, Al-Zr, and Al-Be master alloys according to the following mass percentages: Zn 6.30~6.70%, Mg 1.90~2.20%, Cu 2.10~2.50%, Zr 0.12~0.15%, Ti 0.07~0.13%, Mn≤0.02%, Cr≤0.01%, Si≤0.05%, Fe≤0.04%, with the balance being Al, and use them as raw materials for later use.

[0015] (2) Add the raw materials prepared in step (1) into the smelting furnace for smelting. The order of adding each raw material during the smelting process is as follows: first add aluminum ingots, copper plates, zinc ingots and primary waste and heat them to fully melt them; when the temperature rises to 700~720℃, add Al-Zr master alloy and maintain the temperature to dissolve Al-Zr master alloy; then continue heating to 735±2℃ and maintain it for 15~20min, then add Al-Ti master alloy at this temperature and simultaneously turn on electromagnetic stirring for 5~10min; then continue heating to 745±2℃ and add magnesium ingots. After the magnesium ingots are completely melted, continue heating; when the temperature rises to 753±2℃, add Al-Be master alloy. After the Al-Be master alloy is completely melted, aluminum alloy melt is obtained.

[0016] (3) Transfer the aluminum alloy melt from step (2) to a holding furnace and refine the aluminum alloy melt at 740±5℃ using a mixture of argon and chlorine gas. Set the rotor speed to 320±20rpm, the argon flow rate to 210±5slpm, and the refining time to 30~35min. After refining, remove the slag and let it stand for 20min~30min.

[0017] (4) The refined aluminum alloy melt from step (3) is introduced into the flow tank, and ultrasonic treatment is performed in the flow tank for 5 to 10 minutes. Then, online degassing is performed, Al-Ti-B wire is added to refine the grains, and finally, online filtration is performed to remove impurities.

[0018] (5) The aluminum alloy melt after filtration and impurity removal in step (4) is cast using a semi-continuous casting process to obtain aluminum alloy ingots. During the casting stage, the melt temperature is adjusted to 750±5℃, and the initial casting temperature is set to 750±5℃, the steady-state casting temperature is set to 705±5℃, and the casting speed is set to 33±2mm / min.

[0019] (6) The aluminum alloy ingot was homogenized by a four-stage homogenization process to obtain homogenized 7xxx aluminum alloy ingot.

[0020] In the above technical solution of the present invention, the order of addition and the temperature of each raw material during smelting in step (2) are crucial, especially the order of addition of Al-Zr master alloy, Al-Ti master alloy, Mg ingot, and Al-Be master alloy. Specifically, in the present invention, after the basic alloying elements are melted, Al-Zr master alloy is added first at 700~720℃. At this temperature, it can dissolve well and promote the uniform distribution of Zr atoms in the aluminum liquid, ensuring that a fine and uniformly distributed Al3Zr dispersed phase is formed during subsequent solidification, which plays a role in grain refinement and inhibiting recrystallization. However, if the temperature is too low, the dissolution will be incomplete, and if the dissolution temperature is too high, it will easily lead to oversaturation of Al3Zr coarsening and loss of the refining effect. After the Al-Zr master alloy dissolves, the temperature is raised to 735±2℃, and the Al-Ti master alloy is added simultaneously with electromagnetic stirring. At this temperature, the temperature is slightly higher than when Zr is added, ensuring rapid dissolution and dispersion of the Al-Ti master alloy. The electromagnetic stirring, combined with the addition, ensures uniform dispersion of Al3Ti particles, preventing agglomeration. Furthermore, during subsequent solidification, Al3Ti particles act as heterogeneous nucleation sites, improving grain refinement. In this invention, Zr is added before Ti to avoid undesirable interactions between Ti and Zr (such as the formation of coarse Al3(Zr,Ti) phases), ensuring a grain refinement effect. Regarding the addition of Mg ingots, due to Mg's low melting point and susceptibility to oxidation and combustion, it must be added only after the aluminum liquid has been completely melted and refined to prevent Mg oxidation and burn-off, and to avoid oxide film and MgO inclusions. Additionally, the Mg ingots are added at 745℃, a sufficiently high temperature for rapid melting and uniform distribution, but not so high as to cause excessive Mg volatilization. For Al-Be master alloys, Be is used in very small amounts in aluminum alloys, but plays a crucial role. Be can significantly reduce hydrogen content, inhibit the formation of oxide inclusions, and improve the fluidity and purification effect of molten aluminum. Moreover, Be must be added after all major alloying elements have dissolved, otherwise it is easy to combine with oxide products in the melt and become consumed and ineffective. In addition, adding Be at a high temperature of 753℃ can also ensure that Be dissolves quickly and acts fully, improving the cleanliness of molten aluminum.

[0021] Furthermore, in step (1), the aluminum ingot is an electrolytic aluminum ingot with a purity ≥99.99%; and the total content of Ti and Zr elements does not exceed 0.25%, and the total content of Mn and Cr elements does not exceed 0.07%.

[0022] Furthermore, after the aluminum ingots, zinc ingots, magnesium ingots, copper plates and Al-Ti, Al-Zr and Al-Be intermediate alloys are weighed in step (1), they are subjected to vacuum drying and compressed air purging.

[0023] Furthermore, in step (2), the total smelting time is controlled to be ≤9h.

[0024] Furthermore, in step (4), the ultrasonic power is 200~400kW.

[0025] Furthermore, in step (4), the online degassing adopts an SNIF degassing device, which uses an argon-chlorine mixed gas for degassing, and the flow rate of argon is 240±10 slpm.

[0026] Furthermore, in step (4), the Al-Ti-B filament is added by a filament feeder at a feeding speed of 90±5cm / min, and the Al-Ti-B filament is added within a flow channel length range of 20~30% from the starting point of the flow channel.

[0027] Furthermore, in step (4), the filter includes at least two stages of porous ceramic foam boards, and the pore size of the porous ceramic foam boards decreases progressively along the flow direction of the aluminum alloy melt.

[0028] Furthermore, in step (5), the cooling water temperature during the casting stage is 20±3℃, and the cooling water flow rate is 37±3m³. 3 / h.

[0029] Furthermore, the four-stage homogenization process in step (6) specifically includes:

[0030] First stage homogenization: the holding temperature is 440±1℃, the holding time is 6h, and the heating rate is 20℃ / h.

[0031] Second-stage homogenization: The holding temperature is 460±1℃, the holding time is 8h, and the heating rate is 20℃ / h.

[0032] Third-stage homogenization: The holding temperature is 475±1℃, the holding time is 12h, and the heating rate is 5℃ / h;

[0033] Fourth stage homogenization: The holding temperature is 480±1℃, the holding time is 12~18h, and the heating rate is 5℃ / h.

[0034] The beneficial effects of this invention are as follows:

[0035] This invention provides a low-defect melting and casting method for 7xxx aluminum alloy ingots used in aerospace applications. By optimizing the order and temperature of raw material addition during the melting process, a melting process is proposed that prioritize the addition of Al-Zr master alloy, disperse the addition of Al-Ti master alloy at 735±2℃, and add Mg ingot and Al-Be master alloy at 745±2℃ and 753±2℃ respectively. Combined with RGI rotating gas refining, ultrasonic online degassing and impurity removal, and multi-stage porous ceramic foam board composite purification processes, the method effectively controls Ti-Zr agglomeration, MgO aggregation, silicate refractory inclusion residues, and hydrogen content, resulting in ingots with fine grains and high purity, minimizing the reduction in aluminum alloy material performance caused by defects. This invention also optimizes the homogenization process by adopting a four-stage gradually increasing homogenization heat treatment process to further improve the uniformity of the ingot microstructure. The aluminum alloy ingots prepared by this method are suitable for manufacturing structural components in aerospace, high-speed rail transportation, and other fields where material purity and reliability requirements are extremely high. Attached Figure Description

[0036] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0037] Figure 1 The image shows the metallographic structure of the aluminum alloy ingot prepared in Example 1 of this invention.

[0038] Figure 2 A metallographic photograph of the aluminum alloy ingot prepared in Comparative Example 1 of this invention;

[0039] Figure 3 The images shown are SEM images and EDS energy dispersive spectroscopy images of fatigue fracture region I of the aluminum alloy forging of Comparative Example 1 of the present invention. Among them, (a) is an SEM image of fatigue fracture region I, (b) is an EDS energy dispersive spectroscopy image of Zr element distribution in fatigue fracture region I, and (c) is an EDS energy dispersive spectroscopy image of Ti element distribution in fatigue fracture region I.

[0040] Figure 4 The images shown are SEM images and EDS energy dispersive spectroscopy images of fatigue fracture region II of the aluminum alloy forging of Comparative Example 1 of the present invention. Among them, (a) is an SEM image of fatigue fracture region II, (b) is an image of the O element distribution in fatigue fracture region II obtained by EDS energy dispersive spectroscopy, and (c) is an image of the Mg element distribution in fatigue fracture region II obtained by EDS energy dispersive spectroscopy.

[0041] Figure 5 This is a metallographic photograph of the aluminum alloy ingot prepared in Comparative Example 5 of the present invention. Detailed Implementation

[0042] This invention provides a low-defect melting and casting method for 7xxx aluminum alloy ingots used in aviation. To make the objectives, technical solutions, and effects of this invention clearer and more explicit, the invention is further described in detail below. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention.

[0043] Example 1

[0044] This embodiment prepares a low-defect 7150 aluminum alloy ingot for aerospace applications. The alloy composition is as follows: Zn 6.30%, Mg 2.20%, Cu 2.30%, Zr 0.12%, Ti 0.11%, Mn 0.01%, Cr 0.01%, Si 0.05%, Fe 0.04%, with the balance being aluminum and unavoidable impurities. The content of a single impurity element does not exceed 0.015%, and the total content of Mn and Cr impurity elements does not exceed 0.07%.

[0045] The specific preparation steps are as follows:

[0046] (1) Weigh out electrolytic aluminum ingots (purity ≥ 99.99%), zinc ingots, magnesium ingots, copper plates and Al-Ti, Al-Zr and Al-Be according to the above alloy composition ratio. After weighing, perform vacuum drying and compressed air purging to prepare them as raw materials.

[0047] (2) Add the raw materials prepared in step (1) into the melting furnace for melting. The order of adding each raw material during the melting process is as follows: first add electrolytic aluminum ingots, copper plates, zinc ingots and 7xxx aluminum alloy grade 1 scrap and heat them to fully melt them; when the temperature rises to 700℃, add Al-Zr master alloy and maintain the temperature to dissolve Al-Zr master alloy; then continue heating to 735℃ and maintain it for 15 minutes, add Al-Ti master alloy at this temperature, and simultaneously turn on electromagnetic stirring for 5 minutes; then continue heating to 745℃ and add magnesium ingots. After the magnesium ingots are completely melted, continue heating; when the temperature rises to 753℃, add Al-Be master alloy. After the Al-Be master alloy is completely melted, take a sample for analysis and test the composition to be qualified to obtain aluminum alloy melt; the total melting time is 8 hours.

[0048] (3) Transfer the aluminum alloy melt from step (2) to a holding furnace and pass an argon-chlorine mixed gas through it at 740°C to perform RGI refining. Set the rotor speed to 320 rpm, the argon-chlorine mixing ratio to 5:1, the argon flow rate to 210 slpm, and the refining time to 35 minutes, ensuring that Na≤0.00015% and Ca≤0.0008%. After refining, remove the slag and let it stand for 25 minutes.

[0049] (4) The refined aluminum alloy melt from step (3) is introduced into a flow channel, and an ultrasonic treatment device, an online degassing device, an Al-Ti-B wire addition point, and an online filtration device are sequentially installed from the head to the tail of the flow channel. A composite purification process is used to further purify the melt, specifically:

[0050] In the first stage, a high-power ultrasonic transducer is used to perform ultrasonic treatment for 10 minutes in the initial section of the flow channel. The ultrasonic power is 300kW, which promotes the floating of inclusions, hydrogen evolution, and the breaking of fine agglomerates.

[0051] In the second stage, an online degassing device is used. The SNIF degassing device uses a dual-nozzle linkage and uses an argon-chlorine mixed gas for degassing. The argon to chlorine mixing ratio is 5:1 and the argon flow rate is 240 slpm, which improves the removal efficiency of free hydrogen and harmful gases in the aluminum alloy melt and reduces gas entrainment.

[0052] In the third stage, within a flow channel length area of ​​25% from the starting point of the flow channel, Al-Ti-B wire is added by a servo-controlled wire feeder to refine the grains, with a wire feeding speed of 90±5cm / min.

[0053] In the fourth stage, two-stage porous ceramic foam boards are used for online filtration and impurity removal. The outer porous ceramic foam board has a pore size of 40ppi, and the inner layer has a pore size of 20ppi, which improves the capture capacity and filtration efficiency of impurities.

[0054] (5) The aluminum alloy melt after filtration and impurity removal in step (4) is cast using a direct cooling semi-continuous casting process to obtain an aluminum alloy round ingot with a diameter of 600 mm. Specifically, during the casting stage, the melt temperature is adjusted to 752℃, and the initial casting temperature is set to 750℃, the steady-state casting temperature is set to 705℃, the casting speed is set to 33 mm / min, the cooling water temperature is set to 20℃, and the cooling water flow rate is set to 37 m³ / min. 3 / h;

[0055] (6) A four-stage homogenization process is used to homogenize the aluminum alloy ingot to improve the internal structure uniformity and stress release effect, resulting in a homogenized 7150 aluminum alloy ingot. The four-stage homogenization process is as follows:

[0056] First stage homogenization: the holding temperature is 440±1℃, the holding time is 6h, and the heating rate is 20℃ / h.

[0057] Second-stage homogenization: The holding temperature is 460±1℃, the holding time is 8h, and the heating rate is 20℃ / h.

[0058] Third-stage homogenization: The holding temperature is 475±1℃, the holding time is 12h, and the heating rate is 5℃ / h;

[0059] Fourth stage homogenization: The holding temperature is 480±1℃, the holding time is 12h, and the heating rate is 5℃ / h;

[0060] After the fourth stage of homogenization and heat preservation is completed, the ingot is air-cooled to 250°C in the cooling chamber to ensure the stability of the ingot structure, and then naturally cooled to room temperature.

[0061] Throughout the entire homogenization process described above, the direction of the circulating air inside the furnace is controlled to be consistent with the direction of the ingot stacking to ensure uniform temperature distribution, with the maximum temperature difference controlled within ±1℃. Furthermore, in this embodiment, the temperature of the fourth-stage homogenization needs to be achieved by controlling the homogenization temperature, time, and heating rate of each stage, and ensuring that the strengthening phase does not overburn during homogenization at this temperature in order to guarantee a good homogenization effect.

[0062] The homogenized 7150 aluminum alloy ingot is machined, the head and tail of the ingot are cut off and the skin is peeled off to obtain the finished 7150 aluminum alloy ingot.

[0063] The microstructure of the aforementioned 7150 aluminum alloy ingot was analyzed, and the ingot was forged into forgings. The mechanical and fatigue properties of the forgings were then tested. The results are shown in Table 1 below. The metallographic structure is as follows: Figure 1 As shown.

[0064] Table 1. Performance indicators of 7150 aluminum alloy ingots and forgings in Example 1

[0065]

[0066] Combined with Table 1 and Figure 1 It can be seen that the aluminum alloy ingot prepared in this embodiment has fine and uniform grains, no Ti-Zr agglomerates, and low hydrogen and inclusion content, indicating that the ingot prepared by the method of this embodiment has high purity. In addition, the forgings prepared by the ingot of this invention not only have high strength and high elongation, but also have a certain toughness, and their fatigue life exceeds 10. 6 Second-rate.

[0067] Example 2

[0068] This embodiment prepares a low-defect 7150 aluminum alloy ingot for aerospace applications. The alloy composition ratio is: Zn 6.70%, Mg 2.10%, Cu 2.50%, Zr 0.12%, Ti 0.10%, Mn 0.01%, Si 0.03%, Fe 0.02%, with the balance being aluminum and unavoidable impurities, and the content of a single impurity element not exceeding 0.015%.

[0069] The specific preparation steps are as follows:

[0070] (1) Weigh out electrolytic aluminum ingots (purity ≥ 99.99%), zinc ingots, magnesium ingots, copper plates and Al-Ti, Al-Zr and Al-Be according to the above alloy composition ratio. After weighing, perform vacuum drying and compressed air purging to prepare them as raw materials.

[0071] (2) Add the raw materials prepared in step (1) into the melting furnace for melting. The order of adding each raw material during the melting process is as follows: first add electrolytic aluminum ingots, copper plates, zinc ingots and 7xxx aluminum alloy grade 1 scrap and heat them to fully melt them; when the temperature rises to 720℃, add Al-Zr master alloy and maintain the temperature to dissolve Al-Zr master alloy; then continue heating to 735℃ and maintain for 20 minutes, then add Al-Ti master alloy at this temperature and simultaneously turn on electromagnetic stirring for 5 minutes; then continue heating to 745℃ and add magnesium ingots. After the magnesium ingots are completely melted, continue heating; when the temperature rises to 753℃, add Al-Be master alloy. After the Al-Be master alloy is completely melted, take a sample for analysis and test the composition to be qualified to obtain aluminum alloy melt; the total melting time is 9 hours.

[0072] (3) Transfer the aluminum alloy melt from step (2) to a holding furnace and refine it at 740°C. Set the rotor speed to 320 rpm, the argon to chlorine mixing ratio to 5:1, the argon flow rate to 210 slpm, and the refining time to 35 minutes, ensuring that Na≤0.00015% and Ca≤0.0008%. After refining, remove the slag and let it stand for 25 minutes.

[0073] (4) The refined aluminum alloy melt from step (3) is introduced into a flow channel, and an ultrasonic treatment device, an online degassing device, an Al-Ti-B wire addition point, and an online filtration device are sequentially installed from the head to the tail of the flow channel. A composite purification process is used to further purify the melt, specifically:

[0074] In the first stage, a high-power ultrasonic transducer is used to perform ultrasonic treatment for 5 minutes in the initial section of the flow channel. The ultrasonic power is 300kW, which promotes the floating of inclusions, hydrogen evolution, and the breaking of fine agglomerates.

[0075] In the second stage, an online degassing device is used. The SNIF degassing device uses a dual-nozzle linkage and uses an argon-chlorine mixed gas for degassing. The argon to chlorine mixing ratio is 5:1 and the argon flow rate is 235 slpm, which improves the removal efficiency of free hydrogen and harmful gases in the aluminum alloy melt and reduces gas entrainment.

[0076] In the third stage, within a flow channel length area of ​​25% from the starting point of the flow channel, Al-Ti-B wire is added by a servo-controlled wire feeder to refine the grains, with a wire feeding speed of 90±5cm / min.

[0077] In the fourth stage, a three-stage porous ceramic foam board is used for online filtration and impurity removal. The pore sizes are 50ppi, 40ppi, and 30ppi respectively along the flow direction of the aluminum alloy melt, which improves the capture capacity and filtration efficiency of inclusions.

[0078] (5) The aluminum alloy melt after filtration and impurity removal in step (4) is cast using a direct cooling semi-continuous casting process to obtain an aluminum alloy round ingot with a diameter of 600 mm. Specifically, during the casting stage, the melt temperature is adjusted to 752℃, and the initial casting temperature is set to 7501℃, the steady-state casting temperature is set to 708℃, the casting speed is 35 mm / min, the cooling water temperature is 19℃, and the cooling water flow rate is 37 m³ / min. 3 / h;

[0079] (6) A four-stage homogenization process is used to homogenize the aluminum alloy ingot to improve the internal structure uniformity and stress release effect, resulting in a homogenized 7150 aluminum alloy ingot. The four-stage homogenization process is as follows:

[0080] First stage homogenization: the holding temperature is 440±1℃, the holding time is 6h, and the heating rate is 20℃ / h.

[0081] Second-stage homogenization: The holding temperature is 460±1℃, the holding time is 8h, and the heating rate is 20℃ / h.

[0082] Third-stage homogenization: The holding temperature is 475±1℃, the holding time is 12h, and the heating rate is 5℃ / h;

[0083] Fourth stage homogenization: The holding temperature is 480±1℃, the holding time is 18h, and the heating rate is 5℃ / h;

[0084] After the fourth stage of homogenization and heat preservation is completed, allow it to cool naturally to room temperature;

[0085] Throughout the entire homogenization process, the direction of the circulating air inside the furnace is controlled to be consistent with the direction of the ingot stacking to ensure uniform temperature distribution, and the maximum temperature difference can be controlled within ±1℃.

[0086] The homogenized 7150 aluminum alloy ingot is machined, the head and tail of the ingot are cut off and the skin is peeled off to obtain the finished 7150 aluminum alloy ingot.

[0087] The microstructure of the 7150 aluminum alloy ingot was tested, and the ingot was forged to obtain forgings. The mechanical properties and fatigue properties of the forgings were tested, and the test results are shown in Table 2 below.

[0088] Table 2 Performance indicators of 7150 aluminum alloy ingots and forgings in Example 2

[0089]

[0090] Analysis of the test results in Table 2 above shows that the aluminum alloy ingots prepared in this embodiment have fine and uniform grains, no Ti-Zr agglomerates, and low hydrogen and inclusion content, indicating that the ingots prepared by the method of this embodiment have high purity. Furthermore, the forgings prepared using the ingots of this invention not only have high strength and high elongation, but also possess a certain degree of toughness, with a fatigue life exceeding 10 years. 6 Second-rate.

[0091] Comparative Example 1

[0092] This comparative example prepares an aerospace-grade 7150 aluminum alloy ingot, which differs from Example 1 in the smelting process, specifically:

[0093] In this comparative example, the order of adding each raw material during the smelting process is as follows: electrolytic aluminum ingots, copper plates, zinc ingots, large scrap pieces, Al-Ti and Al-Zr master alloys are added to the smelting furnace in order from large to small materials. After all the furnace materials have melted, the melt temperature is measured and the slag is removed. Then, when the furnace materials are leveled and the melt temperature reaches 700℃, the electromagnetic stirring is turned on. Then, when the temperature is continued to rise to 735℃, Mg ingots and Al-Be master alloys are added. The Al-Be master alloy is added at the inlet of the holding furnace or at the furnace door. At the same time, the melt temperature is not allowed to exceed 745℃ during the entire smelting process.

[0094] The homogenized 7150 aluminum alloy ingot is machined, the head and tail of the ingot are cut off and the skin is peeled off to obtain the finished 7150 aluminum alloy ingot.

[0095] The microstructure of the aforementioned 7150 aluminum alloy ingot was analyzed, and the ingot was forged into forgings. The mechanical and fatigue properties of the forgings were then tested. The results are shown in Table 3 below. The metallographic structure is as follows: Figure 2 As shown, the fatigue fracture surface was examined using a scanning electron microscope, as follows. Figure 3 , Figure 4 As shown.

[0096] Table 3 Performance Indicators of 7150 Aluminum Alloy Ingots and Forgings in Comparative Example 1

[0097]

[0098] Combined with Table 3 and Figure 2 , Figure 4 , Figure 5 It can be seen that the aluminum alloy ingot prepared in this comparative example has Ti-Zr agglomeration and MgO inclusions, with high inclusion and hydrogen content. In this comparative example, the order and temperature of adding each raw material were not controlled during the smelting process, resulting in defects such as Ti-Zr agglomeration and MgO inclusions. Moreover, the presence of these defects not only affects the mechanical properties but also the fatigue life.

[0099] Comparative Example 2

[0100] This comparative example prepares an aerospace-grade 7150 aluminum alloy ingot, which differs from Example 1 in the smelting process, specifically:

[0101] In this comparative example, the order of adding raw materials during the smelting process was as follows: first, electrolytic aluminum ingots, copper plates, zinc ingots, and 7xxx aluminum alloy grade 1 scrap were added and heated to fully melt them; when the temperature reached 700℃, Al-Ti master alloy was added, and then the temperature was continued to 735℃ and held for 15 minutes; then, Al-Zr master alloy was added at this temperature, and electromagnetic stirring was started simultaneously for 5 minutes; then, when the temperature was continued to rise to 745℃, magnesium ingots were added, and heating continued after the magnesium ingots were completely melted; when the temperature reached 753℃, Al-Be master alloy was added, and after the Al-Be master alloy was completely melted, samples were taken for analysis, and after passing the test, aluminum alloy melt was obtained; the total smelting time was 8 hours.

[0102] The microstructure of the 7150 aluminum alloy ingot was tested, and the ingot was forged to obtain forgings. The mechanical properties and fatigue properties of the forgings were tested, and the test results are shown in Table 4 below.

[0103] Table 4 Performance Indicators of 7150 Aluminum Alloy Ingots and Forgings in Comparative Example 2

[0104]

[0105] Analysis of the test results in Table 3 above: Ti-Zr agglomeration exists in the aluminum alloy ingot prepared in this comparative example. In this comparative example, Al-Ti master alloy was added first and then Al-Zr master alloy during the melting process. Although stirring was carried out when adding Al-Zr master alloy, the temperature was relatively high when Al-Zr master alloy was added later, which led to the formation of supersaturated Al3Zr coarsening phase during the dissolution of Al-Zr master alloy. At the same time, coarse Al3(Zr,Ti) phase was formed between Ti and Zr, resulting in defects such as Ti-Zr agglomeration. The presence of these defects not only affects the mechanical properties, but also affects its fatigue life.

[0106] Comparative Example 3

[0107] This comparative example prepares an aerospace-grade 7150 aluminum alloy ingot, which differs from Example 1 in the smelting process, specifically:

[0108] The order of adding raw materials during the smelting process is as follows: first, add electrolytic aluminum ingots, copper plates, zinc ingots, and large pieces of scrap and heat them to fully melt them; when the temperature reaches 730℃, add Al-Zr master alloy, and then continue heating to 735℃ and hold for 15 minutes; then add Al-Ti master alloy at this temperature and simultaneously start electromagnetic stirring for 5 minutes; then continue heating to 745℃ and add magnesium ingots, and continue heating after the magnesium ingots have completely melted; when the temperature reaches 753℃, add Al-Be master alloy, and after the Al-Be master alloy has completely melted, take samples for analysis and, if the test is qualified, obtain the aluminum alloy melt; the entire smelting process takes 9 hours.

[0109] Table 5 Performance indicators of 7150 aluminum alloy ingots and forgings in Comparative Example 3

[0110]

[0111] Analysis of the test results in Table 5 above reveals that Ti-Zr agglomeration exists in the aluminum alloy ingot prepared in this comparative example. Although Al-Zr master alloy was added first and then Al-Ti master alloy during the smelting process, the temperature was relatively high when Al-Zr master alloy was added, which led to the formation of a supersaturated Al3Zr coarsened phase during the dissolution of Al-Zr master alloy. When Al-Ti master alloy was added subsequently, the presence of coarse Al3Zr phase easily led to adverse interactions between Ti and Zr, generating coarse Al3(Zr,Ti) phase, thus resulting in defects such as Ti-Zr agglomeration. The presence of these defects not only affects mechanical properties but also its fatigue life.

[0112] Comparative Example 4

[0113] This comparative example prepares an aerospace-grade 7150 aluminum alloy ingot, which differs from Example 1 in the aluminum alloy melt purification process, specifically:

[0114] In this comparative example, the ultrasonic treatment power was 300W when the aluminum alloy melt was purified in the flow channel.

[0115] Table 6 Performance Indicators of 7150 Aluminum Alloy Ingots and Forgings in Comparative Example 4

[0116]

[0117] Analysis of the test results in Table 6 above shows that the aluminum alloy ingot prepared in this comparative example has high hydrogen content and high inclusion content. This is because although ultrasonic treatment was performed in the flow channel in this comparative example, the ultrasonic treatment power was low, which only played a certain role in degassing and had little effect on breaking up agglomerated phases.

[0118] Comparative Example 5

[0119] This comparative example prepares an aerospace-grade 7150 aluminum alloy ingot, which differs from Example 1 in the homogenization process; this comparative example uses a three-stage homogenization process. Specifically:

[0120] First stage homogenization: the holding temperature is 440±1℃, the holding time is 6h, and the heating rate is 20℃ / h.

[0121] Second-stage homogenization: The holding temperature is 460±1℃, the holding time is 8h, and the heating rate is 20℃ / h.

[0122] The third stage of homogenization: the holding temperature is 475±1℃, the holding time is 12h, and the heating rate is 5℃ / h.

[0123] The microstructure of the aforementioned 7150 aluminum alloy ingot was analyzed, and the ingot was forged into forgings. The mechanical and fatigue properties of the forgings were then tested. The results are shown in Table 7 below. The metallographic structure is as follows: Figure 5 As shown.

[0124] Table 7 Performance Indicators of 7150 Aluminum Alloy Ingots and Forgings in Comparative Example 5

[0125]

[0126] Analysis of the test results in Table 7 above shows that the aluminum alloy ingot prepared in this comparative example, after three-stage homogenization, has a slightly larger average grain size, and its strength, elongation, and fatigue life are all lower than those of Example 1. This indicates that the fourth-stage homogenization process in this invention has a significant impact on the performance of 7150 aluminum alloy.

[0127] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0128] Of course, the above description is not intended to limit the present invention, and the present invention is not limited to the examples given above. Any changes, modifications, additions or substitutions made by those skilled in the art within the scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A low-defect melting and casting method for 7xxx aluminum alloy ingots for aerospace applications, characterized in that, Including the following steps: (1) Weigh out aluminum ingots, zinc ingots, magnesium ingots, copper plates, and Al-Ti, Al-Zr, and Al-Be master alloys according to the following mass percentages: Zn 6.30~6.70%, Mg 1.90~2.20%, Cu 2.10~2.50%, Zr 0.12~0.15%, Ti 0.07~0.13%, Mn≤0.02%, Cr≤0.01%, Si≤0.05%, Fe≤0.04%, with the balance being Al, and use them as raw materials for later use. (2) Add the raw materials prepared in step (1) into the smelting furnace for smelting. The order of adding each raw material during the smelting process is as follows: first add aluminum ingots, copper plates, zinc ingots and primary waste and heat them to fully melt them; when the temperature rises to 700~720℃, add Al-Zr master alloy and maintain the temperature to dissolve Al-Zr master alloy; then continue heating to 735±2℃ and maintain it for 15~20min, then add Al-Ti master alloy at this temperature and simultaneously turn on electromagnetic stirring for 5~10min; then continue heating to 745±2℃ and add magnesium ingots. After the magnesium ingots are completely melted, continue heating; when the temperature rises to 753±2℃, add Al-Be master alloy. After the Al-Be master alloy is completely melted, aluminum alloy melt is obtained. (3) Transfer the aluminum alloy melt from step (2) to a holding furnace and refine the aluminum alloy melt at 740±5℃ using a mixture of argon and chlorine gas. Set the rotor speed to 320±20rpm, the argon flow rate to 210±5slpm, and the refining time to 30~35min. After refining, remove the slag and let it stand for 20min~30min. (4) The refined aluminum alloy melt from step (3) is introduced into the flow tank, and ultrasonic treatment is performed in the flow tank for 5 to 10 minutes. Then, online degassing is performed, Al-Ti-B wire is added to refine the grains, and finally, online filtration is performed to remove impurities. (5) The aluminum alloy melt after filtration and impurity removal in step (4) is cast using a semi-continuous casting process to obtain aluminum alloy ingots. During the casting stage, the melt temperature is adjusted to 750±5℃, and the initial casting temperature is set to 750±5℃, the steady-state casting temperature is set to 705±5℃, and the casting speed is set to 33±2mm / min. (6) The aluminum alloy ingot was homogenized by a four-stage homogenization process to obtain homogenized 7xxx aluminum alloy ingot.

2. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (1), the aluminum ingot is an electrolytic aluminum ingot with a purity ≥99.99%; and the total content of Ti and Zr elements does not exceed 0.25%, and the total content of Mn and Cr elements does not exceed 0.07%.

3. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, After the aluminum ingots, zinc ingots, magnesium ingots, copper plates and Al-Ti, Al-Zr and Al-Be intermediate alloys are weighed in step (1), they are subjected to vacuum drying and compressed air purging.

4. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (2), the total smelting time is controlled to be ≤9h.

5. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (4), the ultrasonic power is 200~400kW.

6. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (4), the online degassing uses an SNIF degassing device, which uses an argon-chlorine mixture for degassing. The flow rate of the argon gas is 240±10 slpm.

7. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (4), the Al-Ti-B filament is added by a filament feeder at a feeding speed of 90±5cm / min. The Al-Ti-B filament is added within a flow channel length range of 20~30% from the starting point of the flow channel.

8. The method for low-defect melting and casting of 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (4), the filter includes at least two stages of porous ceramic foam boards, and the pore size of the porous ceramic foam boards decreases progressively along the flow direction of the aluminum alloy melt.

9. A low-defect melting and casting method for 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, In step (5), the cooling water temperature during the casting stage is 20±3℃, and the cooling water flow rate is 37±3m³. 3 / h.

10. A low-defect melting and casting method for 7xxx aluminum alloy ingots for aviation applications according to claim 1, characterized in that, The four-stage homogenization process in step (6) is specifically as follows: First stage homogenization: the holding temperature is 440±1℃, the holding time is 6h, and the heating rate is 20℃ / h. Second-stage homogenization: The holding temperature is 460±1℃, the holding time is 8h, and the heating rate is 20℃ / h. Third-stage homogenization: The holding temperature is 475±1℃, the holding time is 12h, and the heating rate is 5℃ / h; Fourth stage homogenization: The holding temperature is 480±1℃, the holding time is 12~18h, and the heating rate is 5℃ / h.

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