Medium-high-strength 7020 aluminum alloy section with complex section and preparation method of medium-high-strength 7020 aluminum alloy section

Abstract

The invention discloses a medium-high strength 7020 aluminum alloy section with a complex section and a preparation method thereof. The section comprises the following alloy components in percentage by mass: less than or equal to 0.18% of Si, less than or equal to 0.25% of Fe, 0.10-0.20% of Cu, 0.3-0.5% of Mn, 1.2-1.4% of Mg, 0.25-0.35% of Cr, 4.6-5.0% of Zn, 0.04-0.06% of Ti, 0.10-0.15% of Zr, 0.15-0.20% of Zr + Ti and the balance of Al and inevitable impurities. The preparation method comprises the working procedures of casting, homogenization treatment, extrusion, online quenching, stretching, saw cutting, artificial aging and the like. Alloy components and a preparation process are combined, the 7020 aluminum alloy profile which is high in strength, good in toughness and small in mechanical property difference at different thickness positions of the cross section is obtained, and the preparation method is suitable for preparing the aluminum alloy profile with the complex cross section.

Description

Technical Field

[0001] The invention relates to the technical field of aluminum alloy profile preparation, and in particular to a medium-high strength 7020 aluminum alloy profile with a complex cross-section and a preparation method thereof. Background Art

[0002] 7020 aluminum alloy belongs to medium and high strength Al-Zn-Mg alloy, has high performance strength, good welding performance and processing technology performance, and is the main structural material for aerospace, high-end vehicles and high-end equipment. At present, there is little production-related information about 7020 aluminum alloy in the industry. The composition range of 7020 in the standard is too wide, and it is impossible to determine the effective alloy composition range in the production process to obtain high-strength 7020 aluminum alloy profiles. In addition, 7020 alloy is mostly used to prepare complex sections, and the mechanical properties at different thickness positions vary greatly, which easily leads to unqualified mechanical properties and low yield. Based on this, the present invention proposes a medium-high strength 7020 aluminum alloy profile and a preparation method thereof. Summary of the invention

[0003] In order to solve the above technical problems, the present invention provides a medium-to-high strength 7020 aluminum alloy profile with complex cross-section and a preparation method thereof. By combining the alloy composition with the preparation process, a 7020 aluminum alloy profile with high strength and small difference in mechanical properties at different thickness positions of the cross-section is obtained, which is suitable for preparing aluminum alloy profiles with complex cross-sections.

[0004] The technical solution adopted by the present invention is:

[0005] The present invention provides a medium-high strength 7020 aluminum alloy profile with a complex cross section, comprising the following alloy components in percentage by mass:

[0006] Si≤0.18%, Fe≤0.25%, Cu 0.10~0.20%, Mn 0.3~0.5%, Mg 1.2~1.4%, Cr0.25~0.35%, Zn 4.6~5.0%, Ti 0.04~0.06%, Zr 0.10~0.15%, and Zr+Ti 0.15~0.20%, and the balance is Al and unavoidable impurities.

[0007] The present invention also provides a method for preparing a medium-high strength 7020 aluminum alloy profile with a complex cross section, comprising the steps of:

[0008] (1) According to the alloy composition, the materials are prepared and smelted at 710° C. to 750° C. for 8 h to 10 h. When the furnace temperature is 735° C., a covering agent of 0.45% to 0.55% of the total mass of the metal in the furnace is added. Then, the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 31 to 33.5:1, so that the hydrogen content in the solution is ≤ 0.25 ml, and the mixture is kept for 50 min. After the smelting is completed, the 7020 aluminum alloy ingot is cast;

[0009] (2) subjecting the 7020 aluminum alloy ingot to a three-stage homogenization treatment in a homogenizing furnace;

[0010] (3) using a reverse extruder for extrusion, the aluminum rod is heated to 400±5°C, the mold is heated to 400±10°C and kept warm for 3 to 8 hours, the extrusion barrel is heated to 380±10°C, and the extrusion speed is 1.5±0.3m / min to obtain an extruded profile;

[0011] (4) The extruded profile is quenched online, and the quenching strength at each position of the extruded profile section is kept consistent;

[0012] (5) The extruded profile is stretched and sawed, and after the sawing is completed, artificial aging is performed to obtain a 7020 aluminum alloy profile.

[0013] Furthermore, in step (2), the three-stage homogenization process is carried out at a temperature gradient of 200±10°C, 350±10°C, and 470±10°C for a total of at least 24 hours.

[0014] Furthermore, the three-stage homogenization process in step (2) is specifically as follows:

[0015] Stage 1: Heat to 200±10℃ at a rate of 3-5℃ / min and keep warm for 2-5h;

[0016] Stage 2: Heat to 350±10℃ at a rate of 2-4℃ / min and keep warm for 2-5h;

[0017] Stage 3: Heat to 470±10℃ at a rate of 1-3℃ / min and keep warm for 20-25h.

[0018] Furthermore, in step (3), the extrusion outlet temperature is ≥ 430°C.

[0019] Furthermore, in the step (4), the online quenching adopts a mixed quenching of strong air cooling + water mist cooling, where the wall thickness is 39 to 69 mm, water mist cooling is adopted, and strong air cooling is adopted where the wall thickness is 12.2 to 38 mm.

[0020] Furthermore, in the step (5), the stretching rate is controlled to be 0.8-1.0% during the stretching process.

[0021] Furthermore, the artificial aging system in step (5) is 121±5°C*24h.

[0022] The beneficial effects of the present invention are:

[0023] The present invention provides a medium-high strength 7020 aluminum alloy profile with complex cross-section and a preparation method thereof. The alloy strength is effectively improved by reducing the content of Si and Fe impurity phases, reducing the alloy fracture toughness, and increasing the content of Mg, Mn, Zn, and Cr elements. A small amount of Zr and Ti alloys can be added to significantly increase the recrystallization temperature, refine the grains, and improve the hardenability of the alloy. In addition, the present invention also optimizes the homogenization process, the quenching process, and the aging process. The homogenization process of the present invention is a three-stage homogenization process. The first stage can effectively remove the residual stress of the casting structure. The second and third stages effectively control the non-equilibrium phase solid solution and the supersaturated phase decomposition, so that the second phase is spheroidized, aggregated, or phase-changed, thereby obtaining an ideal organizational morphology. The quenching process adopts different quenching methods according to the different wall thicknesses of the products, so that the quenching strength of each position of the extruded profile section tends to be consistent, and low temperature and long-term aging are used to obtain a dispersed phase η according to different aging sequences. ’ phase, improving the mechanical properties of the alloy. BRIEF DESCRIPTION OF THE DRAWINGS

[0024] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[0025] Figure 1 This is a cross-sectional view of the 7020 aluminum alloy profile prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The present invention provides a medium-high strength 7020 aluminum alloy profile with complex cross section and a preparation method thereof. In order to make the purpose, technical scheme and effect of the present invention clearer and more specific, the present invention is further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present invention and are not used to limit the present invention.

[0027] The present invention provides a medium-high strength 7020 aluminum alloy profile with a complex cross section, comprising the following alloy components in percentage by mass:

[0028] Si≤0.18%, Fe≤0.25%, Cu 0.10~0.20%, Mn 0.3~0.5%, Mg 1.2~1.4%, Cr0.25~0.35%, Zn 4.6~5.0%, Ti 0.04~0.06%, Zr 0.10~0.15%, and Zr+Ti 0.15~0.20%, and the balance is Al and unavoidable impurities.

[0029] The present invention can effectively improve the strength of the alloy by reducing the content of Si and Fe impurity phases, reducing the fracture toughness of the alloy, and increasing the content of Mg, Mn, Zn, and Cr elements. Adding a small amount of Zr and Ti alloy can significantly increase the recrystallization temperature, refine the grains, and improve the hardenability of the alloy.

[0030] The present invention also provides a method for preparing a medium-high strength 7020 aluminum alloy profile with a complex cross section, comprising the steps of:

[0031] (1) According to the alloy composition, the materials are prepared and smelted at 710° C. to 750° C. for 8 h to 10 h. When the furnace temperature is 735° C., a covering agent of 0.45% to 0.55% of the total mass of the metal in the furnace is added. Then, the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 31 to 33.5:1, so that the hydrogen content in the solution is ≤ 0.25 ml, and the mixture is kept for 50 min. After the smelting is completed, the 7020 aluminum alloy ingot is cast;

[0032] (2) The 7020 aluminum alloy ingot is subjected to a three-stage homogenization treatment in a homogenization furnace; the three-stage homogenization treatment process is to keep the temperature at 200±10℃, 350±10℃, and 470±10℃ for at least 24 hours, specifically:

[0033] Stage 1: Heat to 200±10℃ at a rate of 3-5℃ / min and keep warm for 2-5h;

[0034] Stage 2: Heat to 350±10℃ at a rate of 2-4℃ / min and keep warm for 2-5h;

[0035] Stage 3: Heat to 470±10℃ at a rate of 1-3℃ / min and keep warm for 20-25h;

[0036] (3) Extrusion is performed using a reverse extruder, the aluminum rod is heated to 400±5°C, the mold is heated to 400±10°C and kept warm for 3 to 8 hours, the extrusion barrel is heated to 380±10°C, the extrusion speed is 1.5±0.3m / min, and an extruded profile is obtained, and the extrusion outlet temperature is ≥430°C;

[0037] (4) The extruded profile is quenched online, and water mist cooling is used at the wall thickness of 39-69 mm, and strong air cooling is used at the wall thickness of 12.2-38 mm to ensure that the quenching strength at each position of the extruded profile section remains consistent;

[0038] (5) The extruded profile is stretched and sawed, with a stretching rate of 0.8-1.0%, a head cut of at least 800 mm, and a tail cut of at least 500 mm; after the sawing is completed, artificial aging is performed, and the artificial aging system is 121±5℃*24h to obtain a 7020 aluminum alloy profile.

[0039] In the preparation process of the above-mentioned 7020 aluminum alloy profile, the present invention mainly optimizes the homogenization process, quenching process and aging process. Among them, the homogenization process of the present invention is a three-stage homogenization process, the first stage can effectively remove the residual stress of the casting structure, the second and third stages can effectively control the non-equilibrium phase solid solution and the decomposition of the supersaturated phase, so that the second phase is spheroidized, aggregated or phase-changed, so as to obtain the ideal structure morphology; the quenching process adopts different quenching methods according to the different wall thickness of the product, so that the quenching strength of each position of the extruded profile section tends to be consistent, and low temperature and long time aging are used to obtain the dispersed phase η according to different aging sequences. ’ phase, improving the mechanical properties of the alloy.

[0040] Example 1

[0041] This embodiment prepares a 7020 aluminum alloy profile, whose cross-sectional shape is as follows Figure 1 As shown, its width is 129mm, the maximum wall thickness is 69mm, and the minimum wall thickness is 12.2mm.

[0042] The 7020 aluminum alloy profile includes the following alloy components in mass percentage:

[0043] Si 0.15%, Fe 0.24%, Cu 0.20%, Mn 0.48%, Mg 1.4%, Cr 0.33%, Zn 5.0%, Ti 0.06%, Zr 0.14%, and the balance is Al and inevitable impurities.

[0044] The preparation method of the 7020 aluminum alloy profile is as follows:

[0045] (1) According to the alloy composition, the materials are prepared and smelted at 750° C. for 8 h. When the furnace temperature is 735° C., a covering agent of 0.55% of the total mass of the metal in the furnace is added, and then the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 33.5:1 to make the content in the solution ≤ 0.25 ml, and the mixture is kept for 50 min. After the smelting is completed, the aluminum alloy is cast to obtain a 7020 aluminum alloy ingot;

[0046] (2) The 7020 aluminum alloy ingot is subjected to a three-stage homogenization treatment in a homogenizing furnace; the three-stage homogenization treatment process is specifically as follows:

[0047] Stage 1: Heating to 200°C at a rate of 3°C / min and keeping warm for 2h;

[0048] The second stage: heating to 350℃ at a heating rate of 2.5℃ / min and keeping the temperature for 2h;

[0049] Stage 3: Heating to 470°C at a rate of 2°C / min and keeping at this temperature for 20h;

[0050] (3) using a 60MN reverse extruder for extrusion, the aluminum rod was heated to 403°C, the mold was heated to 405°C and kept warm for 5 hours, the extrusion barrel was heated to 380°C, and the extrusion speed was 1.5 m / min to obtain an extruded profile;

[0051] (4) The extruded profile is quenched online, and water mist cooling is used at the wall thickness of 39-69 mm, and strong air cooling is used at the wall thickness of 12.2-38 mm to ensure that the quenching strength at each position of the extruded profile section remains consistent;

[0052] (5) The extruded profile is stretched and sawed, with a stretching rate of 1.0%, a head cut of 800 mm, and a tail cut of 500 mm; after the sawing is completed, artificial aging is performed, and the artificial aging system is 121±5℃*24h to obtain a 7020 aluminum alloy profile.

[0053] Example 2

[0054] In this embodiment, a 7020 aluminum alloy profile is prepared, and its cross-sectional shape is the same as that of Embodiment 1.

[0055] The 7020 aluminum alloy profile includes the following alloy components in mass percentage:

[0056] Si 0.10%, Fe 0.18%, Cu 0.16%, Mn 0.41%, Mg 1.3%, Cr 0.30%, Zn 4.8%, Ti 0.05%, Zr 0.12%, and the balance is Al and inevitable impurities.

[0057] The preparation method of the 7020 aluminum alloy profile is as follows:

[0058] (1) According to the alloy composition, the materials are prepared and smelted at 720° C. for 10 h. When the furnace temperature is 735° C., a covering agent of 0.5% of the total mass of the metal in the furnace is added, and then the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 32:1 to make the content in the solution ≤ 0.25 ml, and the mixture is kept for 50 min. After the smelting is completed, the aluminum alloy is cast to obtain a 7020 aluminum alloy ingot;

[0059] (2) The 7020 aluminum alloy ingot is subjected to a three-stage homogenization treatment in a homogenizing furnace; the three-stage homogenization treatment process is specifically as follows:

[0060] Stage 1: Heating to 210°C at a rate of 4°C / min and keeping warm for 2h;

[0061] Stage 2: Heating to 360°C at a rate of 3°C / min and keeping warm for 2h;

[0062] Stage 3: Heating to 480°C at a rate of 2°C / min and keeping at this temperature for 20h;

[0063] (3) using a 60MN reverse extruder for extrusion, the aluminum rod is heated to 405°C, the mold is heated to 410°C and kept warm for 8 hours, the extrusion barrel is heated to 390°C, and the extrusion speed is 1.6 m / min to obtain an extruded profile;

[0064] (4) The extruded profile is quenched online, and water mist cooling is used at the wall thickness of 39-69 mm, and strong air cooling is used at the wall thickness of 12.2-38 mm to ensure that the quenching strength at each position of the extruded profile section remains consistent;

[0065] (5) The extruded profile is stretched and sawed, with a stretching rate of 1.0%, a head cut of 800 mm, and a tail cut of 500 mm; after the sawing is completed, artificial aging is performed, and the artificial aging system is 121±5℃*24h to obtain a 7020 aluminum alloy profile.

[0066] Example 3

[0067] This embodiment prepares a 7020 aluminum alloy profile, and its cross-sectional shape is the same as that of Embodiment 1.

[0068] The 7020 aluminum alloy profile includes the following alloy components in mass percentage:

[0069] Si 0.09%, Fe 0.10%, Cu 0.12%, Mn 0.32%, Mg 1.23%, Cr 0.26%, Zn 4.6%, Ti 0.05%, Zr 0.10%, and the balance is Al and inevitable impurities.

[0070] The preparation method of the 7020 aluminum alloy profile is as follows:

[0071] (1) According to the alloy composition, the materials are smelted at 730° C. for 9 hours, and when the furnace temperature is 735° C., a covering agent of 0.5% of the total mass of the metal in the furnace is added, and then the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 31:1, so that the content in the solution is ≤0.25 ml, and the mixture is kept for 50 minutes; after the smelting is completed, the 7020 aluminum alloy ingot is cast;

[0072] (2) The 7020 aluminum alloy ingot is subjected to a three-stage homogenization treatment in a homogenizing furnace; the three-stage homogenization treatment process is specifically as follows:

[0073] Stage 1: Heating to 195°C at a rate of 3°C / min and keeping warm for 2h;

[0074] Stage 2: Heating to 340°C at a rate of 2.5°C / h and keeping warm for 2h;

[0075] Stage 3: Heating to 460°C at a rate of 2°C / h and keeping warm for 24h;

[0076] (3) using a 60MN reverse extruder for extrusion, the aluminum rod is heated to 400°C, the mold is heated to 405°C and kept warm for 8 hours, the extrusion barrel is heated to 380°C, and the extrusion speed is 1.4 m / min to obtain an extruded profile;

[0077] (4) The extruded profile is quenched online, and water mist cooling is used at the wall thickness of 39-69 mm, and strong air cooling is used at the wall thickness of 12.2-38 mm to ensure that the quenching strength at each position of the extruded profile section remains consistent;

[0078] (5) The extruded profile is stretched and sawed, with a stretching rate of 0.9%, a head cut of 800 mm, and a tail cut of 500 mm; after the sawing is completed, artificial aging is performed, and the artificial aging system is 121±5℃*24h to obtain a 7020 aluminum alloy profile.

[0079] The above examples 1-3 were sampled and tested, and their mechanical properties are shown in Table 1 below.

[0080] Table 1

[0081] Tensile strength / MPa Yield strength / MPa Elongation / % Sampling location Example 1 456 399 14.0 Wall thickness 69mm Example 1 454 398 15.0 Wall thickness 39mm Example 1 460 402 14.0 Wall thickness 12.2mm Example 2 458 400 14.5 Wall thickness 69mm Example 3 449 388 15.5 Wall thickness 69mm Standard requirements 350 290 10.0 -

[0082] It can be seen from the test data in Table 1 that the mechanical properties of the 7020 alloy profiles prepared in the above Examples 1-3 are much higher than the standard requirements, and have high elongation while maintaining medium-to-high strength, that is, they have both strength and toughness and have excellent mechanical properties; and the mechanical properties at different wall thickness positions are basically consistent.

[0083] It should be noted that some parts not described in the present invention can be implemented by adopting or drawing on existing technologies.

[0084] Of course, the above description is not a limitation of the present invention, and the present invention is not limited to the above examples. Changes, modifications, additions or substitutions made by technicians in this technical field within the essential scope of the present invention should also fall within the protection scope of the present invention.

Claims

1. A medium-high strength 7020 aluminum alloy profile with complex cross section, characterized in that: The alloy components include the following mass percentages: Si≤0.18%, Fe≤0.25%, Cu 0.10~0.20%, Mn 0.3~0.5%, Mg 1.2~1.4%, Cr 0.25~0.35%, Zn 4.6~5.0%, Ti 0.04~0.06%, Zr 0.10~0.15%, and Zr+Ti 0.15~0.20%, and the balance is Al and unavoidable impurities.

2. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 1, characterized in that: Includes steps: (1) According to the alloy composition, the materials are prepared and smelted at 710° C. to 750° C. for 8 h to 10 h. When the furnace temperature is 735° C., a covering agent of 0.45% to 0.55% of the total mass of the metal in the furnace is added, and then the aluminum solution is refined with a mixed gas of argon and chlorine in a volume ratio of 31 to 33.5:1 to make the content in the solution ≤ 0.25 ml, and the mixture is kept for 50 min. After the smelting is completed, the aluminum alloy is cast to obtain a 7020 aluminum alloy ingot; (2) subjecting the 7020 aluminum alloy ingot to a three-stage homogenization treatment in a homogenizing furnace; (3) using a reverse extruder for extrusion, the aluminum rod is heated to 400±5°C, the mold is heated to 400±10°C and kept warm for 3 to 8 hours, the extrusion barrel is heated to 380±10°C, and the extrusion speed is 1.5±0.3m / min to obtain an extruded profile; (4) The extruded profile is quenched online, and the quenching strength at each position of the extruded profile section is kept consistent; (5) The extruded profile is stretched and sawed, and after the sawing is completed, artificial aging is performed to obtain a 7020 aluminum alloy profile.

3. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 2, characterized in that: The three-stage homogenization process in step (2) is to keep the temperature at a gradient of 200±10°C, 350±10°C, and 470±10°C for at least 24 hours.

4. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 3, characterized in that: The three-stage homogenization process in step (2) is specifically as follows: Stage 1: Heat to 200±10℃ at a rate of 3-5℃ / min and keep warm for 2h; Stage 2: Heat to 350±10℃ at a rate of 2-4℃ / min and keep warm for 2h; Stage 3: Heat to 470±10℃ at a rate of 1-3℃ / min and keep warm for 20-25h.

5. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 2, characterized in that: In the step (3), the extrusion outlet temperature is ≥430°C.

6. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 2, characterized in that: In the step (4), the online quenching adopts a mixed quenching of strong air cooling + water mist cooling. Water mist cooling is adopted when the wall thickness is 39 to 69 mm, and strong air cooling is adopted when the wall thickness is 12.2 to 38 mm.

7. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 2, characterized in that: In the step (5), the stretching rate is controlled to be 0.8-1.0% during the stretching process.

8. The method for preparing a medium-high strength 7020 aluminum alloy profile with complex cross-section according to claim 2, characterized in that: The artificial aging system in step (5) is 121±5°C*24h.

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