Aluminum alloy profile for rocket stringer and preparation method of aluminum alloy profile

Abstract

The invention discloses an aluminum alloy profile for a rocket stringer and a preparation method of the aluminum alloy profile. The aluminum alloy profile for the rocket stringer consists of the following elements in percentage by weight: 2.2-2.4% of Cu, 2.9-3.4% of Mg, 7.3-7.9% of Zn, 0.05-0.15% of Zr, less than or equal to 0.05% of Fe, less than or equal to 0.1% of Si and the balance of Al. The preparation method comprises the steps of extrusion, solid solution heat treatment, stretch straightening, aging heat treatment and the like. The advantages of high purity, high strength, high rigidity, high safety and the like of the 7050-8 aluminum alloy material are utilized, development of the 7050-8 aluminum alloy profile product for the launch vehicle stringer is developed, core technologies such as mold design, extrusion forming, heat treatment strengthening and finishing treatment are overcome in the development process, the launch vehicle structure efficiency in China is improved, and the production cost is reduced. The prepared profile meets the application requirements of a new-generation carrier rocket structure, and application and iteration of a new aluminum alloy material are promoted.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy profile processing, and in particular to an aluminum alloy profile for a rocket long stringer and a preparation method thereof. Background Art

[0002] As an important preparation material for launch vehicles, launch vehicle profiles play different roles in different parts of the rocket. The performance of these profiles directly affects the strength, stiffness, weight, corrosion resistance, reliability and safety of the launch vehicle. In order to successfully send the spacecraft into the predetermined orbit, the launch vehicle needs to overcome the effects of various forces such as the earth's gravity, which requires the rocket profile to have sufficient strength. At the same time, in order to improve the carrying capacity of the rocket, the profile must be as light as possible to reduce its own weight in the total weight of the rocket. In addition, during the launch and flight of the rocket, it will experience different temperature environments. For example, during the launch phase, the rocket engine will produce high-temperature flames, and in the space environment it will face extremely low temperatures, so the rocket profile needs to be able to withstand these extreme temperature changes. Moreover, whether it is stored on the ground or during flight, the rocket profile may be exposed to various corrosive substances, so good corrosion resistance is a prerequisite for ensuring the structural integrity and performance stability of the rocket.

[0003] The rocket stringer serves as the longitudinal support structure of the rocket, which can ensure the structural integrity and stability of the rocket during flight. The rocket stringer, skin and frame ring together constitute the shell structure of the rocket, similar to the bamboo strips in a lantern and the gauze cover outside. During flight, the rocket stringer participates in the overall force of the wing, and bears part of the axial force caused by the wing bending moment and the local aerodynamic force of the skin, ensuring that the rocket will not be deformed or damaged during high-speed flight. This requires that the profiles used to prepare the rocket stringer have high mechanical properties and light weight. However, the ordinary profiles currently used to prepare the rocket stringer are generally heavy, and lack strength and rigidity. They are easily deformed when subjected to large external forces, and are not very safe.

[0004] With the rapid development of the aviation manufacturing industry, the demand for high-strength and tough aluminum materials in the aviation field is becoming more and more urgent. How to master key technologies to achieve industrialization, further improve the structural efficiency of my country's new launch vehicles, drive the application of new aluminum alloy materials, meet the structural application needs of launch vehicles, and promote the iteration of new aluminum alloy materials has become a technical problem that needs to be solved urgently. Research shows that 7050-8 aluminum alloy is a high-strength heat-treatable alloy with good low-temperature performance, high specific strength and specific stiffness, good fatigue toughness, good resistance to exfoliation corrosion and stress corrosion cracking. Its main alloying element is zinc. By adding magnesium to form MgZn2 with significant strengthening effect, the heat treatment effect of the alloy can be far better than that of aluminum-zinc binary alloy. Therefore, it is urgent to use 7050-8 aluminum alloy instead of ordinary alloys and apply it in the long stringer structure of the launch vehicle as the longitudinal support to increase the strength and stiffness of the rocket. Summary of the invention

[0005] The present invention provides an aluminum alloy profile for a rocket long stringer and a preparation method thereof. The purpose is to utilize the advantages of 7050-8 aluminum alloy material such as high purity, high strength, high rigidity and high safety, to carry out the research and development of 7050-8 aluminum alloy profile products for a new generation of launch vehicles, and to promote the iteration of new materials.

[0006] To achieve its purpose, the present invention adopts the following technical solution: A method for preparing an aluminum alloy profile for a rocket long stringer, wherein the aluminum alloy profile is composed of the following elements in weight percentage: Cu 2.2-2.4%, Mg 2.9-3.4%, Zn 7.3-7.9%, Zr 0.05-0.15%, Fe ≤ 0.05%, Si ≤ 0.1%, and the balance is Al; the preparation method comprises the following steps: (1) Extrusion: Under the conditions of an extrusion barrel temperature of 465-485°C, an ingot temperature of 480-495°C, a reverse extrusion speed of 0.4-0.9 mm / s, and an extrusion ratio of 20.0-50.0, a 7050-8 aluminum alloy ingot is extruded into a profile with an inverted T-shaped cross section, and air-cooled to room temperature; (2) Solution heat treatment: the extruded profile of step (1) is heated to 488-491°C after pre-finishing, kept at this temperature for 4-8 hours, and then solution heat treated; (3) Tensile straightening: the profile after solution heat treatment in step (2) is first tension straightened within 8 hours, and then sent to a roller straightening machine for twisting and bending straightening; (4) Aging heat treatment: The straightened profile in step (3) is heated to 165-170°C, kept at this temperature for 48 hours, and then taken out of the furnace and cooled naturally to obtain a 7050-8 aluminum alloy profile for rocket long stringers.

[0007] Furthermore, the extruder in step (1) is a 25MN double-acting reverse extruder.

[0008] Furthermore, the ingot in step (1) is an aluminum alloy solid cylindrical ingot with an outer diameter of 255 mm.

[0009] Furthermore, in step (2), a 22 m vertical quenching furnace is used for the solution heat treatment of the extruded profile.

[0010] Furthermore, in step (3), a tension straightening machine is used for straightening the profile.

[0011] Furthermore, the stretching rate during tension straightening in step (3) is 3.0-3.5%.

[0012] Furthermore, in step (4), an 18 m horizontal aging furnace is used for the aging heat treatment.

[0013] The 7050-8 aluminum alloy profile for rocket long stringer prepared by the above preparation method has a nominal thickness of ≤25mm, a tensile strength of ≥690MPa, a specified non-proportional elongation strength of ≥660MPa, an elastic modulus of ≥90GPa, and an elongation after fracture of ≥10%.

[0014] The beneficial effects of the present invention are as follows: 1. The present invention makes full use of the advantages of 7050-8 aluminum alloy materials such as high purity, high strength, high rigidity and high safety, and develops 7050-8 aluminum alloy profile products for launch vehicles. During the development process, core technologies such as mold design, extrusion molding, heat treatment strengthening and finishing treatment were mastered, which improved the structural efficiency of my country's launch vehicles. The profiles meet the structural application needs of the new generation of launch vehicles, drive the application of new materials, and promote the iteration of new materials.

[0015] 2. The profile of the present invention selects reverse extrusion, pre-finishing, solution heat treatment, stretch straightening and aging heat treatment steps during preparation. There is a strict logical relationship between each step, and each step sets specific process parameters. After a large number of experiments and comparative studies, it is found that compared with 7050 aluminum alloy, 7050-8 aluminum alloy has very low Si and Fe contents. Since the Fe element will reduce the corrosion resistance and alloy strength of the material, and the Si element will reduce the alloy strength and plasticity, reducing the content of Fe and Si impurity elements can effectively improve the plastic strength of the material, and the elongation (A50.8mm) can be controlled above 9%, meeting the requirements of the use conditions.

[0016] 3. η phase (MgZn2) and T phase (Al2Mg2Zn3) are the main strengthening phases in 7050 alloy, and their solubility at eutectic temperature is about 25%, which can effectively improve the strength of the alloy. Compared with 7050 aluminum alloy, the Mg content of 7050-8 aluminum alloy is increased by 0.8%, and the Zn content is increased by 1.1%, which further improves the aging strengthening effect. The yield strength of the existing 7050T6 aluminum alloy is about 600MPa. The yield strength of the 7050-8T6 aluminum alloy treated by the method of the present invention is increased to more than 660MPa, and the yield strength is greatly increased. In addition, under the T6 heat treatment state, the tensile strength of the 7050-8 aluminum alloy is increased to more than 690MPa, which effectively enhances the strength of the alloy.

[0017] 4. In step (1) of the preparation method of the present invention, the Zn content of the 7050-8 alloy is 7.3-7.9%, and the Mg content is 2.9-3.4%. The high content of Zn and Mg elements increases the difficulty of extrusion molding, so it is difficult to produce profiles using traditional extrusion processing technology. In addition, the extrusion flow rate will be uneven during the extrusion process, resulting in defects such as cracks on the surface of the product, extrusion mold blockage and extrusion breakage. Based on this, the present invention has found through a large number of experiments and comparative studies that when extruding, the extrusion barrel temperature is set to 465-485°C, the ingot temperature is set to 480-495°C, the reverse extrusion speed is set to 0.4-0.9mm / s, the extrusion ratio is set to 20.0-50.0, and the extrusion die is reasonably designed to control the metal flow rate ratio and reduce the metal shear stress and axial stress, so that the profile of the required specification can be extruded.

[0018] 5. Steps (2) and (3) of the preparation method of the present invention are solution heat treatment and tensile straightening, respectively. Since the 7050-8 high-strength and high-rigidity aluminum alloy profile is placed at room temperature after solution heat treatment, surface hardening will occur, resulting in the tensile straightening surface being brittle and sensitive, prone to breakage, and unable to be straightened by twisting and bending. Therefore, the time interval between the solution heat treatment and tensile straightening process is controlled at 2-8 hours, and a pre-finishing process is added before the solution heat treatment to straighten the bending and twisting defects of the profile to prevent the defects from being further amplified after the solution heat treatment. After the solution heat treatment, tension straightening + roller straightening are performed to ensure that the profile size is qualified. The straightened profile is transported to manual aging heat treatment. The aging temperature is selected at 165-170°C and kept warm for 48 hours. Under the condition of ensuring plasticity, the strength and stiffness reach the peak value, meeting the requirements for the use of rocket long trusses. BRIEF DESCRIPTION OF THE DRAWINGS

[0019] Figure 1 This is a cross-sectional view of the aluminum alloy profile used for the rocket long stringer in Example 1 of the present invention; Figure 2 This is a product picture of the aluminum alloy profile used for the rocket long stringer in Example 1 of the present invention. DETAILED DESCRIPTION

[0020] The present invention will be further described below in conjunction with embodiments: In the following embodiments of the present invention, the extruder is a 25MN double-acting reverse extruder, the ingots required for extrusion are all solid cylindrical ingots of aluminum alloy with an outer diameter of 255mm, a 22m vertical quenching furnace is used for solution heat treatment, and an 18m horizontal aging furnace is used for aging heat treatment. The room temperature mechanical properties of the aluminum alloy profile for rocket long girders of the present invention should meet the standards shown in Table 1: Table 1 Room temperature mechanical properties standards of profiles

[0021] In Table 1, the nominal thickness ≤ 25 indicates that the aluminum alloy profile is lightweight. After application, it can reduce the proportion of its own weight in the total weight of the rocket and improve the carrying capacity of the rocket. The tensile strength is the maximum tensile stress that the profile can withstand before tensile fracture. The specified non-proportional elongation strength (Rp0.2) refers to the stress value corresponding to the plastic elongation of the material reaching 0.2% in the tensile test. Therefore, when the tensile strength of the aluminum alloy profile is ≥ 690MPa and the specified non-proportional elongation strength is ≥ 660MPa, it means that the prepared aluminum alloy profile meets the high-strength requirements of aluminum alloy profiles for rocket girders. The elastic modulus reflects the stiffness of the aluminum alloy profile. The elastic modulus ≥ 90GMP indicates that the prepared aluminum alloy profile meets the high stiffness requirements of aluminum alloy profiles for rocket girders.

[0022] Example 1 An aluminum alloy profile for rocket long stringer, the cross-sectional shape of which is as follows Figure 1 As shown, the aluminum alloy profile is composed of the following elements in weight percentage: Cu 2.32%, Mg 3.10%, Zn 7.85%, Zr 0.12%, Fe 0.03%, Si 0.02%, and the balance is Al; the preparation method thereof comprises the following steps: (1) Extrusion: The ingot was extruded into Figure 1 The cross-sectional shape shown is an inverted T-shaped profile and is air-cooled to room temperature; (2) Solution heat treatment: the extruded profile of step (1) is heated to 489°C after pre-finishing, kept at this temperature for 6 hours, and then solution heat treated; (3) Tensile straightening: The profile after solution heat treatment in step (2) for 6 hours is first sent to a tension straightening machine with a stretching rate of 3.3% for tension straightening, and then sent to a roller straightening machine to straighten the twisted bend; (4) Aging heat treatment: The straightened profile in step (3) is heated to 167°C, kept at this temperature for 48 hours, and then taken out of the furnace and cooled naturally to obtain the following Figure 2 The rocket boom shown is made of 7050-8 aluminum alloy profile, which has a smooth, flat surface without burrs and meets the use requirements.

[0023] The head and tail ends of the obtained profile were cut by 600 mm respectively to obtain mechanical property samples and low-magnification samples. The mechanical properties were measured as shown in Table 2. Analysis shows that the high- and low-magnification microstructure and mechanical property tests of the samples are qualified. The produced 7050-8 aluminum alloy profiles meet the high strength and high stiffness requirements of aluminum alloy profiles for rocket long girders shown in Table 1.

[0024] Table 2 Mechanical properties of profiles at room temperature

[0025] Example 2 An aluminum alloy profile for a rocket long stringer is composed of the following elements in weight percentage: Cu 2.38%, Mg 3.05%, Zn 7.85%, Zr 0.15%, Fe 0.02%, Si 0.04%, and the balance is Al; the preparation method thereof comprises the following steps: (1) Extrusion: The ingot was extruded into Figure 1 The cross-sectional shape shown is an inverted T-shaped profile and is air-cooled to room temperature; (2) Solution heat treatment: the extruded profile of step (1) is heated to 488°C after pre-finishing, kept at this temperature for 4 hours, and then solution heat treated; (3) Tensile straightening: The profile after solution heat treatment in step (2) for 5 hours is first sent to a tension straightening machine with a stretching rate of 3.5% for tension straightening, and then sent to a roller straightening machine to straighten the twisted bend; (4) Aging heat treatment: The straightened profile in step (3) is heated to 165°C, kept at this temperature for 48 hours, taken out of the furnace, and cooled naturally to obtain a 7050-8 aluminum alloy profile for rocket long stringers.

[0026] The head and tail ends of the obtained profile were cut by 600 mm respectively to obtain mechanical property samples and low-magnification samples. The mechanical properties were measured as shown in Table 3. Analysis shows that the high- and low-magnification microstructure and mechanical property tests of the samples are qualified. The produced 7050-8 aluminum alloy profiles meet the high strength and high stiffness requirements of aluminum alloy profiles for rocket long girders as shown in Table 1.

[0027] Table 3 Mechanical properties of profiles at room temperature

[0028] Example 3 An aluminum alloy profile for a rocket long stringer is composed of the following elements in weight percentage: Cu 2.33%, Mg 2.9%, Zn 7.88%, Zr 0.07%, Fe 0.03%, Si 0.03%, and the balance is Al; the preparation method thereof comprises the following steps: (1) Extrusion: The ingot was extruded into Figure 1 The cross-sectional shape shown is an inverted T-shaped profile and is air-cooled to room temperature; (2) Solution heat treatment: the extruded profile of step (1) is heated to 491°C after pre-finishing, kept at this temperature for 8 hours, and then solution heat treated; (3) Tensile straightening: The profile after solution heat treatment in step (2) for 5 hours is first sent to a tension straightening machine with a stretching rate of 3.0% for tension straightening, and then sent to a roller straightening machine to straighten the twisted bend; (4) Aging heat treatment: The straightened profile in step (3) is heated to 170°C, kept at this temperature for 48 hours, taken out of the furnace, and cooled naturally to obtain a 7050-8 aluminum alloy profile for rocket long stringers.

[0029] The head and tail ends of the obtained profile were cut by 600 mm respectively to obtain mechanical property samples and low-magnification samples. The mechanical properties were measured as shown in Table 4. Analysis shows that the high- and low-magnification microstructure and mechanical property tests of the samples are qualified. The produced 7050-8 aluminum alloy profiles meet the high strength and high stiffness requirements of aluminum alloy profiles for rocket long girders shown in Table 1.

[0030] Table 4 Mechanical properties of profiles at room temperature

Claims

1. A method for preparing an aluminum alloy profile for a rocket long stringer, characterized in that: The aluminum alloy profile is composed of the following elements in weight percentage: Cu 2.2-2.4%, Mg 2.9-3.4%, Zn 7.3-7.9%, Zr 0.05-0.15%, Fe ≤ 0.05%, Si ≤ 0.1%, and the balance is Al; the preparation method comprises the following steps: (1) Extrusion: Under the conditions of an extrusion barrel temperature of 465-485°C, an ingot temperature of 480-495°C, a reverse extrusion speed of 0.4-0.9 mm / s, and an extrusion ratio of 20.0-50.0, a 7050-8 aluminum alloy ingot is extruded into a profile with an inverted T-shaped cross section, and air-cooled to room temperature; (2) Solution heat treatment: the extruded profile of step (1) is heated to 488-491°C after pre-finishing, kept at this temperature for 4-8 hours, and then solution heat treated; (3) Tensile straightening: the profile after solution heat treatment in step (2) is first tension straightened within 8 hours, and then sent to a roller straightening machine for twisting and bending straightening; (4) Aging heat treatment: The straightened profile in step (3) is heated to 165-170°C, kept at this temperature for 48 hours, and then taken out of the furnace and cooled naturally to obtain a 7050-8 aluminum alloy profile for rocket long stringers.

2. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 1, characterized in that: The extruder in step (1) is a 25MN double-acting reverse extruder.

3. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 2, characterized in that: The ingot in step (1) is an aluminum alloy solid cylindrical ingot with an outer diameter of 255 mm.

4. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 3, characterized in that: In step (2), a 22 m vertical quenching furnace is used for solution heat treatment of the extruded profile.

5. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 4, characterized in that: In step (3), a tension straightening machine is used for straightening the medium-sized material.

6. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 5, characterized in that: The elongation during tension straightening in step (3) is 3.0-3.5%.

7. The method for preparing an aluminum alloy profile for a rocket long stringer according to claim 6, characterized in that: In step (4), an 18m horizontal aging furnace is used for aging heat treatment.

8. A 7050-8 aluminum alloy profile for rocket long stringer made by the preparation method according to any one of claims 1 to 7, characterized in that: The profile has a nominal thickness of ≤25mm, a tensile strength of ≥690MPa, a specified non-proportional elongation strength of ≥660MPa, an elastic modulus of ≥90GPa, and an elongation after fracture of ≥10%.

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