A kind of ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace and its preparation method

Abstract

A super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use and a preparation method thereof. The present invention relates to a preparation method for a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use. The purpose of the present invention is to solve the problem that existing aluminum alloy ring forgings cannot meet the requirements of aerospace use. The aluminum alloy ring forging of the present invention is made of smelting raw materials of Cu, Mg, Zn, Zr, Cr, Ti and Al, and is manufactured through smelting, casting, homogenization annealing, hot forging, quenching, cold compression and aging. The present invention produces super-strong, high-toughness, corrosion-resistant aluminum alloy ring forgings through alloy composition optimization, ingot quality control, multi-stage homogenization treatment technology, forging molding technology, three-stage quenching and two-stage aging technology for toughening heat treatment. By controlling the cold compression amount and quenching water temperature, it is achieved to effectively reduce the residual stress of the ring forging and improve the fracture toughness of the ring forging. The present invention is applied to the field of preparation of aluminum alloy ring forgings.

Description

Technical Field

[0001] The invention relates to a super-strong, high-toughness, corrosion-resistant aluminum alloy annular forging for aerospace use and a preparation method thereof. Background Art

[0002] With the rapid development of my country's aerospace industry, more stringent requirements have been put forward for basic materials. While increasing the diameter and wall thickness of forged ring forgings, the forged ring forgings are required to have higher strength, toughness and corrosion resistance. It is necessary to develop tensile strength ≥ 600MPa, yield strength ≥ 570MPa, elongation ≥ 8%, fracture toughness ≥ 27KIC / MPa·m 1 / 2 , conductivity ≥ 37% IACS, exfoliation corrosion EB level or above, maximum wall thickness 115mm, maximum diameter 1500mm ring forgings, and form a stable production process. The existing aluminum alloy ring forging products are affected by the deformation mode, and the strength and toughness are lower than the extruded materials of the same material. The tensile strength is at the 500MPa level and the toughness is lower than 25KIC / MPa·m 1 / 2 , which is far from meeting the needs of aerospace users for forging materials. It is necessary to carry out better alloy composition combined with process control to achieve a comprehensive improvement in the performance of ring forging products and a coordinated match of multiple properties such as strength, toughness, corrosion resistance, and electrical conductivity. Summary of the invention

[0003] The purpose of the present invention is to solve the problem that the existing aluminum alloy ring forgings have low performance and cannot meet the development needs of the aerospace industry, to achieve comprehensive improvement in the performance of the ring forging products and coordinated matching of multiple properties such as strength, toughness, corrosion resistance, and electrical conductivity from the perspective of alloy ratio and process research, and to provide an ultra-strong, high-toughness, and corrosion-resistant aluminum alloy ring forging for aerospace use and a preparation method thereof.

[0004] The invention discloses a super-strong, high-toughness, corrosion-resistant aluminum alloy annular forging for aerospace use, which is composed of the following elements: Cu: 1.6%-3.0%, Mg: 1.8%-2.5%, Zn: 8.4%-9.7%, Zr: 0.10%-0.15%, Cr: 0.02%-0.04%, Ti: 0.015%-0.04% and the balance of Al.

[0005] A method for preparing a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use is carried out according to the following steps:

[0006] 1. Aluminum ingots, cathode copper, primary magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium master alloy ingots and aluminum-titanium wires are weighed according to the proportion of element mass percentage of Cu: 1.6%-3.0%, Mg: 1.8%-2.5%, Zn: 8.4%-9.7%, Zr: 0.10%-0.15%, Cr: 0.02%-0.04%, Ti: 0.015%-0.004% and the balance of Al to obtain raw materials, and then the raw materials are smelted in a smelting furnace at a smelting temperature of 720°C-760°C to obtain an aluminum alloy melt;

[0007] 2. Casting the aluminum alloy melt obtained in step 1 into a round ingot by semi-continuous casting;

[0008] 3. removing the casting oxide scale of the round ingot at room temperature to obtain the aluminum alloy round ingot with the oxide scale removed;

[0009] Fourth, the aluminum alloy round ingot after the oxide scale is removed is kept at a temperature of 420°C to 440°C for 12 hours, then the temperature is raised to 470°C and kept for 60 hours, and after being taken out of the furnace, it is naturally cooled to room temperature to obtain an annealed round ingot;

[0010] 5. Put the annealed round ingot into a resistance heating furnace and heat it to 400°C to 450°C to obtain a hot forged ring forging blank;

[0011] 6. After the ingot is taken out of the furnace, the hot forged annular forging blank obtained in step 5 is forged into annular forging rough material by using a forging press under the condition that the air is naturally cooled to a surface temperature of 300° C. to 400° C., thereby obtaining a hot forged annular forging rough material;

[0012] 7. Rough machining the hot forged ring forging raw material to obtain a roughly processed ring forging raw material;

[0013] 8. Put the rough-machined ring forging raw material into a resistance heating furnace, keep it at 430-460℃ for 2h-4h, heat it to 470℃ for 4h-6h, and then heat it to 472℃-480℃ for 1h-3h before quenching. The water temperature before quenching is ≤19℃, and the water temperature after quenching is ≤21℃. The forging is immersed in water for 10min-20min.

[0014] 9. The rough-machined ring forging raw material processed in step 8 is subjected to cold compression stress relief treatment to obtain a stress-relieved rough-machined ring forging raw material;

[0015] 10. The rough-machined ring forging material after stress relief is placed in a resistance heating furnace and heated to a temperature of 115°C to 121°C. After heat preservation for 6h to 12h, the temperature is raised to 154°C to 165°C and heat preservation for 6h to 12h to obtain an over-aged ring forging;

[0016] 11. Process the aged ring forgings according to the finished product size to obtain finished ring forgings.

[0017] The present invention produces an aluminum alloy ring forging having high tensile strength, good fracture toughness and excellent corrosion resistance through alloy composition optimization, casting quality control, three-stage solid solution, low-temperature water quenching, cold compression control and two-stage aging. The ring forging manufactured by the present invention has a longitudinal tensile strength of 612N / mm according to the GB / T228 test. 2 ~635N / mm 2 , the non-proportional extension strength is specified to be 595N / mm 2 ~619N / mm 2 , elongation after fracture 9.2% ~ 12.3%; according to GB / T4161 test, the fracture toughness of the ring forging is 27.78MPa·m 1 / 2 ~33.73MPa·m 1 / 2 According to GB / T12966-2008 test conductivity is 37.23%IACS~37.68%IACS, according to HB5455 test exfoliation corrosion EB level. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] Figure 1 This is a schematic diagram of the forging process in step six of the present invention;

[0019] Figure 2 This is a low-magnification metallographic photograph of the round ingot as-cast of Example 2;

[0020] Figure 3 This is a high-magnification metallographic photograph of the as-cast round ingot of Example 2;

[0021] Figure 4 This is a low-magnification SEM photograph of the round ingot after homogenization annealing in Example 2;

[0022] Figure 5 This is a high-magnification SEM photograph of the round ingot after homogenization annealing in Example 2;

[0023] Figure 6 This is a low-magnification image of the metallographic structure of the raw material of the ring forging of Example 2;

[0024] Figure 7 This is a high-magnification image of the metallographic structure of the raw material of the ring forging of Example 2;

[0025] Figure 8 This is a low-magnification SEM photograph of the raw material of the annular forging of Example 2;

[0026] Fig. 9 This is a high-magnification SEM photo of the raw material of the ring forging of Example 2;

[0027] Fig.10This is a low-magnification SEM photograph of the ring forging after three-stage solid solution in Example 2;

[0028] Fig.11 This is a high-magnification SEM photograph of the ring forging after three-stage solid solution in Example 2;

[0029] Fig.12 TEM photos of solid solution structures at different deformation temperatures;

[0030] Fig.13 TEM microstructure of forgings after quenching at different water temperatures;

[0031] Fig.14 This is the TEM photo of the crystal after T6 peak aging;

[0032] Fig.15 This is the TEM picture of the grain boundary after T6 peak aging;

[0033] Fig.16 This is the intracrystalline TEM image of the ring forging after double-stage aging treatment;

[0034] Fig.17 This is the TEM photo of the grain boundary of the ring forging after double-stage aging treatment. DETAILED DESCRIPTION

[0035] The technical solution of the present invention is not limited to the specific implementation modes listed below, but also includes any combination of the specific implementation modes.

[0036] Specific implementation method 1: In this implementation method, an ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use is composed of the following elements in percentage by mass: Cu: 1.6% to 3.0%, Mg: 1.8% to 2.5%, Zn: 8.4% to 9.7%, Zr: 0.10% to 0.15%, Cr: 0.02% to 0.04%, Ti: 0.015% to 0.04% and the remainder Al.

[0037] Specific implementation method 2: This implementation method is a method for preparing an ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use, which is carried out according to the following steps:

[0038] 1. Aluminum ingots, cathode copper, primary magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium master alloy ingots and aluminum-titanium wires are weighed according to the proportion of element mass percentage of Cu: 1.6%-3.0%, Mg: 1.8%-2.5%, Zn: 8.4%-9.7%, Zr: 0.10%-0.15%, Cr: 0.02%-0.04%, Ti: 0.015%-0.004% and the balance of Al to obtain raw materials, and then the raw materials are smelted in a smelting furnace at a smelting temperature of 720°C-760°C to obtain an aluminum alloy melt;

[0039] 2. Casting the aluminum alloy melt obtained in step 1 into a round ingot by semi-continuous casting;

[0040] 3. removing the casting oxide scale of the round ingot at room temperature to obtain the aluminum alloy round ingot with the oxide scale removed;

[0041] Fourth, the aluminum alloy round ingot after the oxide scale is removed is kept at a temperature of 420°C to 440°C for 12 hours, then the temperature is raised to 470°C and kept for 60 hours, and after being taken out of the furnace, it is naturally cooled to room temperature to obtain an annealed round ingot;

[0042] 5. Put the annealed round ingot into a resistance heating furnace and heat it to 400°C to 450°C to obtain a hot forged ring forging blank;

[0043] 6. After the ingot is taken out of the furnace, the hot forged annular forging blank obtained in step 5 is forged into annular forging rough material by using a forging press under the condition that the air is naturally cooled to a surface temperature of 300° C. to 400° C., thereby obtaining a hot forged annular forging rough material;

[0044] 7. Rough machining the hot forged ring forging raw material to obtain a roughly processed ring forging raw material;

[0045] 8. Put the rough-machined ring forging raw material into a resistance heating furnace, keep it at 430-460℃ for 2h-4h, heat it to 470℃ for 4h-6h, and then heat it to 472℃-480℃ for 1h-3h before quenching. The water temperature before quenching is ≤19℃, and the water temperature after quenching is ≤21℃. The forging is immersed in water for 10min-20min.

[0046] 9. The rough-machined ring forging raw material processed in step 8 is subjected to cold compression stress relief treatment to obtain a stress-relieved rough-machined ring forging raw material;

[0047] 10. The rough-machined ring forging material after stress relief is placed in a resistance heating furnace and heated to a temperature of 115°C to 121°C. After heat preservation for 6h to 12h, the temperature is raised to 154°C to 165°C and heat preservation for 6h to 12h to obtain an over-aged ring forging;

[0048] 11. Process the aged ring forgings according to the finished product size to obtain finished ring forgings.

[0049] Specific embodiment 3: This embodiment is different from specific embodiment 1 or 2 in that: the aluminum alloy ring forging is made of aluminum ingots, cathode copper, primary magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium intermediate alloy ingots and aluminum-titanium wires as raw materials according to the mass percentage of elements Cu: 2.2%, Mg: 2.2%, Zn: 9.2%, Zr: 0.11%, Cr: 0.02%, Ti: 0.022% and the balance Al. Others are the same as specific embodiment 1 or 2.

[0050] Specific embodiment 4: This embodiment is different from the specific embodiments 1 to 3 in that the heating temperature of the round ingot in step 5 is 430° C. The rest is the same as the specific embodiments 1 to 3.

[0051] Specific embodiment 5: This embodiment differs from specific embodiments 1 to 4 in that in step 6, after the ingot is heated, the air is naturally cooled to a surface temperature of 350° C., before forging begins. The rest is the same as specific embodiments 1 to 4.

[0052] Specific embodiment 6: This embodiment is different from specific embodiments 1 to 5 in that the forging process in step 6 is: according to the forging material with a diameter-to-height ratio of 0.40 to 0.45, it is longitudinally compressed three times, circumferentially deformed and stretched, and finally longitudinally compressed to a pancake shape, and ring forged after center punching. The rest is the same as specific embodiments 1 to 5.

[0053] Specific embodiment 7: This embodiment is different from specific embodiments 1 to 6 in that: in step 8, in a resistance heating furnace, the temperature is kept at 450°C for 2 hours, the temperature is raised to 470°C for 5 hours, and then the temperature is raised to 475°C for 1 hour before quenching, the water temperature before quenching is 16°C, the water temperature after quenching is ≤18°C, and the forging is immersed in water for 10 minutes to 20 minutes. Others are the same as specific embodiments 1 to 6.

[0054] Specific embodiment 8: This embodiment is different from specific embodiments 1 to 7 in that the stress relief treatment is performed by low-temperature water quenching and cold compression in step 9. The rest is the same as specific embodiments 1 to 7.

[0055] Specific implementation method 9: This implementation method is different from specific implementation methods 1 to 8 in that the stress relief compression amount in step 9 is controlled at 1-3%. Other aspects are the same as specific implementation methods 1 to 8.

[0056] Specific embodiment 10: This embodiment differs from specific embodiments 1 to 9 in that the stress relief compression amount in step 9 is controlled at 2%. The rest is the same as specific embodiments 1 to 9.

[0057] Specific embodiment 11: This embodiment differs from specific embodiments 1 to 10 in that in step 10, the temperature is heated to 118°C, kept for 9 hours, then raised to 162°C, kept for 11 hours, and subjected to aging treatment. The rest is the same as specific embodiments 1 to 10.

[0058] The following examples are used to verify the beneficial effects of the present invention:

[0059] Embodiment 1: The preparation method of a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use in this embodiment is carried out according to the following steps:

[0060] 1. Aluminum ingots, cathode copper, primary magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium master alloy ingots and aluminum-titanium wires are weighed as raw materials according to the proportion of element mass percentage of Cu: 2.4%, Mg: 2.3%, Zn: 9.4%, Zr: 0.14%, Cr: 0.03%, Ti: 0.027% and the balance of Al, and then the raw materials are smelted in a smelting furnace to obtain aluminum alloy melt;

[0061] 2. Casting the aluminum alloy melt obtained in step 1 into a round ingot by semi-continuous casting;

[0062] 3. removing the casting oxide scale of the round ingot at room temperature to obtain the aluminum alloy round ingot with the oxide scale removed;

[0063] Fourth, the aluminum alloy round ingot after the oxide scale is removed is kept at a temperature of 440°C for 12 hours, then the temperature is raised to 470°C and kept for 60 hours, and after being taken out of the furnace, it is naturally cooled to room temperature to obtain an annealed round ingot;

[0064] 5. Put the annealed round ingot into an induction heating furnace and heat it to 435°C to obtain a hot forged ring forging blank;

[0065] 6. After the ingot is taken out of the furnace, the hot forged annular forging blank obtained in step 5 is forged into annular forging rough material by using a forging press under the condition that the air is naturally cooled to a surface temperature of 352° C., thereby obtaining annular forging rough material;

[0066] 7. Rough machining the hot forged ring forging raw material to obtain a roughly processed ring forging raw material;

[0067] 8. Put the rough-machined ring forging raw material into the resistance heating furnace, keep it at 450℃ for 2h, heat it to 470℃ for 5h, and then heat it to 473℃ for 2h before quenching. The water temperature before quenching is 15℃, and the water temperature after quenching is 17℃. The forging is immersed in water for 15min.

[0068] 9. The rough-machined ring forging blank processed in step 8 is subjected to cold compression stress relief treatment to obtain the rough-machined ring forging blank after stress relief. The stress relief cold compression amount is controlled at 2%. The low-temperature water quenching and cold compression stress relief treatment are performed to achieve the purpose of both improving the fracture toughness of the ring forging and effectively reducing the residual stress of the ring forging.

[0069] 10. The rough-machined ring forging material after stress relief is placed in a resistance heating furnace and heated to 118°C. After heat preservation for 8 hours, the temperature is raised to 157°C and heat preservation for 12 hours to obtain an over-aged ring forging;

[0070] 11. The aged ring forging is precisely machined according to the finished product size to obtain a finished ring forging.

[0071] In this embodiment, the forging process of step six is ​​as follows: Figure 1 As shown, according to the forging material with a diameter-to-height ratio of 0.40 to 0.45, it is repeatedly subjected to longitudinal compression three times, circumferential deformation and elongation, and finally longitudinally compressed to a pancake shape, and ring forging is performed after center punching.

[0072] This embodiment produces ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forgings by optimizing alloy composition, controlling ingot quality, using multi-stage homogenization technology, forging technology, and strengthening and toughening heat treatment technology. The ring forgings manufactured in this embodiment have a longitudinal tensile strength of 618-635N / mm according to the GB / T228 test. 2 , non-proportional extension strength is specified to be 601-619N / mm 2 , elongation after fracture 9.5-12.3%; according to GB / T4161 test, the fracture toughness of the ring forging is 29.14~33.73MPa·m 1 / 2 According to GB / T12966-2008 test conductivity is 37.35~37.68% IACS, and according to HB5455 test exfoliation corrosion EB level.

[0073] Example 2: An industrialized preparation method of an ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use is carried out according to the following steps:

[0074] 1. Aluminum ingots, cathode copper, native magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium intermediate alloy ingots and aluminum-titanium wires are weighed as raw materials according to the proportion of element mass percentage of Cu: 2.2%, Mg: 2.2%, Zn: 9.2%, Zr: 0.11%, Cr: 0.02%, Ti: 0.022% and the balance Al, and then the raw materials are smelted in a smelting furnace at a temperature of 760°C for 6 hours to obtain an aluminum alloy melt.

[0075] 2. Casting the aluminum alloy melt obtained in step 1 into a round ingot by semi-continuous casting;

[0076] 3. removing the casting oxide scale of the round ingot at room temperature to obtain the aluminum alloy round ingot with the oxide scale removed;

[0077] Fourth, the aluminum alloy round ingot after the oxide scale is removed is kept at a temperature of 430°C for 12 hours, then the temperature is raised to 470°C and kept for 60 hours, and after being taken out of the furnace, it is naturally cooled to room temperature to obtain an annealed round ingot;

[0078] 5. Put the annealed round ingot into an induction heating furnace and heat it to 430°C to obtain a hot forged ring forging blank;

[0079] 6. After the ingot is taken out of the furnace, the hot forged annular forging blank obtained in step 5 is forged into annular forging rough material under the condition that the air is naturally cooled to a surface temperature of 350° C., thereby obtaining annular forging rough material;

[0080] 7. Rough machining the hot forged ring forging raw material to obtain a roughly processed ring forging raw material;

[0081] 8. Put the rough-machined ring forging raw material into the resistance heating furnace, keep it at 450℃ for 2h, heat it to 470℃ for 5h, and then heat it to 475℃ for 1h before quenching. The water temperature before quenching is 16℃, and the water temperature after quenching is ≤18℃. The forging is immersed in water for 15min.

[0082] 9. The rough-machined ring forging blank processed in step 8 is subjected to cold compression stress relief treatment to obtain a rough-machined ring forging blank after stress relief, and the stress relief compression amount is controlled at 1.5%;

[0083] 10. The rough-machined ring forging material after stress relief is placed in a resistance heating furnace and heated to 118°C. After keeping the temperature for 9 hours, the temperature is raised to 162°C and kept for 11 hours to obtain an over-aged ring forging.

[0084] 11. The aged ring forging is precisely machined according to the finished product size to obtain a finished ring forging.

[0085] In the forging process of step six of the present embodiment, the forging material with a diameter-to-height ratio of 0.40 to 0.45 is subjected to longitudinal compression three times repeatedly, followed by circumferential deformation and elongation, and finally longitudinal compression to a pancake shape, followed by ring forging after center punching.

[0086] The annular forging manufactured in this embodiment has a longitudinal tensile strength of 612N / mm according to GB / T228 test. 2 ~624N / mm 2 , the non-proportional extension strength is specified to be 595N / mm 2 ~610N / mm 2, elongation after fracture 9.2% ~ 12.0%; according to GB / T4161 test, the fracture toughness of the ring forging is 27.78MPa·m 1 / 2 ~31.92MPa·m 1 / 2 According to GB / T12966-2008 test conductivity is 37.23~37.45%IACS, according to HB5455 test exfoliation corrosion EB level.

[0087] The metallographic photograph of the aluminum alloy round ingot in this embodiment is as follows: Figure 2 and 3 As shown by Figure 2 and 3 It can be seen that the cast structure of the alloy is a typical dendrite structure, the coarse primary solidification precipitate phase is segregated at the grain boundary, and there are also a large number of fine precipitates near the grain boundary in the crystal. The high-magnification structure photo shows that there is an obvious lamellar structure at the grain boundary. The AlZnMgCu quaternary phase formed during the solidification process forms a continuous network of lamellar eutectic structure distribution grain boundaries with the α (Al) phase. The fine second phase precipitated along the grain boundary in the matrix is ​​the MgZn2 phase. The grain size is relatively uniform overall.

[0088] The purpose of homogenization treatment of 7000 series alloy is to promote the dissolution of coarse primary solidification precipitate phase. In addition, it is necessary to promote the dispersion and precipitation of Al3Zr particles at high temperature. This phase can pin the grain boundary during subsequent deformation and heat treatment, inhibit recrystallization, and improve the alloy performance. The temperature range with a higher nucleation rate of Al3Zr is 420-450℃. Therefore, in order to take into account both the dispersion and precipitation of Al3Zr particles and the dissolution of the primary solidification phase, a first-stage homogenization annealing treatment is carried out at 420℃-440℃ for 12h, followed by a high-temperature treatment at 470℃ for 60h. After being taken out of the furnace, it is naturally cooled to room temperature. The SEM photograph of the round ingot after homogenization annealing is shown in the figure. Figure 4 and 5 As can be seen from the figure, after homogenization treatment, the precipitated phase in the organization is fully dissolved, the lamellar eutectic structure of the cast alloy completely disappears, and only sporadic white phases remain. Energy spectrum analysis shows that it is an Fe-rich phase. The amount and distribution of the Fe-rich phase do not change significantly with the extension of the homogenization time. After homogenization annealing, the grain size of the alloy does not change significantly.

[0089] Metallographic structure observation of the longitudinal section of the aluminum alloy ring forging rough material ( Figure 6 and 7 ). It can be found that the metallographic structure has obvious streamline characteristics, and there are densely distributed and fine-sized Mg(Zn,Cu,Al)2 phases in the alloy, and Fe-containing phases are also observed. SEM image of the raw material of the aluminum alloy ring forging ( Figure 8 and Fig. 9), it can be seen that most of the residual phase is Mg(Zn,Cu,Al)2 phase, which is finely fragmented and distributed along the deformation direction, and only contains a small amount of Fe-containing phase.

[0090] The three-stage quenching process is adopted. The first stage has a lower solution temperature, which can release more deformation energy storage, reduce the recrystallization driving force of high-temperature solution treatment, and make the ring forging retain a higher proportion of deformation structure. The second stage adopts a higher temperature treatment to ensure that most of the second phase of the alloy is dissolved back into the matrix and increase the overburning temperature of the material. The third stage treatment chooses a short-term treatment close to the overburning temperature to maximize the second phase dissolution and provide the largest space for the strength and toughness matching of the alloy. Fig.10 and 11 It can be seen that after the three-stage solid solution treatment, the second phase is fully dissolved, and only a small amount of Fe-rich second phase remains, and the size is also relatively small. Fig.12 TEM photos of the solution structure at different deformation temperatures; b and d are at 320°C and a and c are at 400°C. After solution treatment, the MgZn2 phase in the deformed structure dissolves back, dislocations disappear, and clear and straight subgrain boundaries are formed, as shown by the white arrows in (a) and (b). In addition, nano-scale Al3Zr phases are also found in the solution structure, as shown by the white dashed arrows in (c) and (d). The Al3Zr phase in the 7xxx series aluminum alloy is precipitated during the homogenization heat treatment, and has a pinning and dragging effect on dislocations and grain boundaries during deformation and solution treatment, which inhibits recrystallization and grain growth.

[0091] The quenching water temperature control of the ring forging is the key to improving its fracture toughness. The TEM images of the alloy after quenching at different water temperatures are compared. Fig.13 ; a is 20℃, b is 40℃, and c is 60℃; As can be seen from the figure, with the increase of quenching cooling temperature, the size of the dissolution precipitation phase gradually increases. After quenching at 20℃ water temperature, the size of the grain boundary precipitation phase is only 8nm, and the size of the dissolution precipitation phase at the grain boundary is significantly smaller than that of other samples, and there is no PFZ at the grain boundary position; at 40℃, the grain boundary phase grows to 17nm, and PFZ begins to appear; at 60℃, the grain boundary phase increases to 19nm, and obvious PFZ appears. The size and distribution of the precipitate phase have a significant effect on the strength and fracture toughness of the alloy. The grain boundary precipitation phase and the grain boundary non-precipitation zone have a significant effect on the fracture toughness of the alloy, especially the coarse grain boundary precipitation phase is easy to become a crack source during the stress process, which is very unfavorable to the fracture toughness of the alloy. During the quenching process after the solution treatment, the quenching temperature is high, and the alloy precipitation process is more obvious. Compared with low-temperature quenching, the quenching precipitation phase produced at the grain boundary during high-temperature quenching is larger in size, which will significantly weaken the grain boundary strength and reduce the fracture toughness of the alloy. Therefore, for materials with higher fracture toughness requirements, low-temperature quenching must be used. Therefore, the conventional forging quenching water temperature of 30°C to 80°C cannot be used for the forgings of the present invention.

[0092] The 7000 series aluminum alloy is a typical precipitation-strengthened alloy and one of the main structural materials in the aerospace industry. After T6 peak aging treatment of the 7000 series aluminum alloy, the precipitation phases in the grain are fine GP zones and η′ phases. After aging for 24 hours, the size of the precipitated phases is concentrated in the range of 2nm to 5nm, and the number of unit nano-sized precipitated phases accounts for about 30%, achieving the maximum strengthening effect. However, after reaching the peak value, fine semi-coherent dispersed phases precipitate in the alloy crystals, and coarse continuous chain particles are distributed at the grain boundaries. This grain boundary structure is very sensitive to stress corrosion and exfoliation corrosion, and it is difficult to exert its comprehensive performance in practical applications. The organization photo is shown in FIG. Fig.14 and 15 In order to overcome the shortcomings of low corrosion resistance and fracture toughness of T6 treatment, solve the contradiction between strength and stress corrosion resistance, and take into account the conductivity and fracture toughness of the ring forging, the present invention adopts the traditional semi-continuous casting method to obtain uniform grain structure, adopts appropriate forging temperature and process, forges the ring forging, and adopts three-stage solid solution after machining. Low temperature cold quenching process improves the fracture toughness of the material, and cooperates with the appropriate two-stage aging process (the structure photo after two-stage aging treatment is shown in Figure 2). Fig.16 and 17 ), so that the precipitated phase is distributed discontinuously on the grain boundary, improving the corrosion resistance of the forging, while ensuring the control of the size and distribution state of the precipitated phase within the grain, achieving the ideal matching effect of mechanical properties and fracture toughness, so as to meet the service conditions with higher comprehensive requirements.

Claims

1. A method for preparing an ultra-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use, characterized in that The preparation method is carried out according to the following steps:

1. Aluminum ingots, cathode copper, primary magnesium ingots, zinc ingots, aluminum-zirconium alloy ingots, aluminum-chromium intermediate alloy ingots and aluminum-titanium wires are weighed according to the proportion of element mass percentage of Cu: 2.4%, Mg: 2.3%, Zn: 9.4%, Zr: 0.14%, Cr: 0.03%, Ti: 0.027% and the balance of Al to obtain raw materials, and then the raw materials are smelted in a smelting furnace at a smelting temperature of 720°C to 760°C to obtain an aluminum alloy melt; 2. Casting the aluminum alloy melt obtained in step 1 into a round ingot by semi-continuous casting; 3. removing the casting oxide scale of the round ingot at room temperature to obtain the aluminum alloy round ingot with the oxide scale removed; Fourth, the aluminum alloy round ingot after the oxide scale is removed is kept at a temperature of 420°C to 440°C for 12 hours, then the temperature is raised to 470°C and kept for 60 hours, and after being taken out of the furnace, it is naturally cooled to room temperature to obtain an annealed round ingot; 5. Put the annealed round ingot into a resistance heating furnace and heat it to 400°C~450°C to obtain a hot forged ring forging blank; 6. After the ingot is taken out of the furnace, the hot forged annular forging blank obtained in step 5 is forged into annular forging rough material by using a forging press under the condition that the air is naturally cooled to a surface temperature of 300°C to 400°C, thereby obtaining a hot forged annular forging rough material; 7. Rough machining the hot forged ring forging raw material to obtain a roughly processed ring forging raw material; 8. Put the rough-machined ring forging raw material into the resistance heating furnace, keep it at 450℃ for 2h, heat it to 470℃ for 5h, and then heat it to 475℃ for 1h before quenching. The water temperature before quenching is 16℃, and the water temperature after quenching is ≤18℃. The forging is immersed in water for 10min~20min.

9. The rough-machined ring forging raw material processed in step 8 is subjected to cold compression stress relief treatment to obtain a stress-relieved rough-machined ring forging raw material; The compression is controlled at 1-3%; 10. The rough-machined ring forging material after stress relief is placed in a resistance heating furnace and heated to a temperature of 115°C to 121°C. After heat preservation for 6h to 12h, the temperature is raised to 154°C to 165°C and heat preservation for 6h to 12h to obtain an over-aged ring forging; 11. Processing the aged ring forgings according to the finished product size to obtain finished ring forgings.

2. The method for preparing a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use according to claim 1, characterized in that In step 5, the heating temperature of the round ingot is 430°C.

3. The method for preparing a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use according to claim 1, characterized in that In step 6, after the ingot is heated and the air is naturally cooled to a surface temperature of 350°C, forging begins.

4. The method for preparing a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use according to claim 1, characterized in that The forging process of step six is: according to the forging material with a diameter-to-height ratio of 0.40 to 0.45, longitudinal compression is repeated three times, circumferential deformation and elongation are performed, and finally longitudinal compression is performed to a pancake shape, and ring forging is performed after center punching.

5. The method for preparing a super-strong, high-toughness, corrosion-resistant aluminum alloy ring forging for aerospace use according to claim 1, characterized in that In step 10, the temperature is heated to 118° C., kept at this temperature for 9 hours, then raised to 162° C., kept at this temperature for 11 hours, and then subjected to aging treatment.

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