A medium-high strength 7020 aluminum alloy profile with complex cross section and a preparation method thereof

Abstract

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

Description

TECHNICAL FIELD

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

[0002] The 7020 aluminum alloy belongs to medium-high strength Al-Zn-Mg alloy, has high performance strength, good welding performance and processing process performance, and is a main selected structural material for aerospace, high-end vehicles and high-end equipment. At present, there are few production related data of the 7020 aluminum alloy in the industry, the composition range of the 7020 in the standard is too wide, the effective alloy composition range cannot be determined to obtain the high strength 7020 aluminum alloy profile in the production process, in addition, the 7020 alloy is mostly used to prepare complex cross sections, and the mechanical properties of different thickness positions are greatly different, which easily leads to unqualified mechanical properties and low yield rate. Based on this, the present application provides a medium-high strength 7020 aluminum alloy profile and a preparation method thereof. SUMMARY

[0003] To solve the above technical problems, the present application provides a medium-high strength 7020 aluminum alloy profile with complex cross section and a preparation method thereof, which combines alloy composition and preparation process to obtain the 7020 aluminum alloy profile with high strength and small mechanical property difference of different thickness positions of cross section, and is suitable for preparing complex cross section aluminum alloy profile.

[0004] The technical scheme adopted by the present application is as follows:

[0005] The present application provides a medium-high strength 7020 aluminum alloy profile with complex cross section, which comprises the following mass percentage of alloy composition:

[0006] 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 inevitable impurities.

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

[0008] (1) according to the alloy composition, under the condition of 710-750℃, smelting 8-10h, adding 0.45-0.55% of the total mass of the furnace metal cover agent when the furnace temperature is 735℃, then refining the aluminum solution with the mixed gas of argon and chlorine with the volume ratio of 31-33.5:1, so that the hydrogen content in the solution is ≤0.25ml, maintaining for 50min; after smelting, casting to obtain 7020 aluminum alloy ingot;

[0009] (2) carrying out three-stage homogenization treatment on the 7020 aluminum alloy ingot in the homogenization furnace;

[0010] (3) using the reverse extrusion machine to extrude, the heating temperature of the aluminum rod is 400±5℃, the heating temperature of the die is 400±10℃ and the holding time is 3-8h, the heating temperature of the extrusion cylinder is 380±10℃, and the extrusion speed is 1.5±0.3m / min to obtain the extruded profile;

[0011] (4) carrying out online quenching on the extruded profile, and keeping the quenching intensity consistent at each position of the cross section of the extruded profile;

[0012] (5) stretching and sawing the extruded profile, and then artificially aging after sawing to obtain the 7020 aluminum alloy profile.

[0013] Further, the three-stage homogenization treatment process in step (2) is to maintain the temperature gradient of 200±10℃, 350±10℃ and 470±10℃ for at least 24h.

[0014] Further, the three-stage homogenization treatment process in step (2) is specifically:

[0015] First stage: heating to 200±10℃ at a heating rate of 3-5℃ / min and maintaining for 2-5h;

[0016] Second stage: heating to 350±10℃ at a heating rate of 2-4℃ / min and maintaining for 2-5h;

[0017] Third stage: heating to 470±10℃ at a heating rate of 1-3℃ / min and maintaining for 20-25h.

[0018] Further, the extrusion outlet temperature in step (3) is ≥430℃.

[0019] Further, the online quenching in step (4) adopts strong wind cooling+water mist cooling mixed quenching, water mist cooling is adopted at the wall thickness of 39-69mm, and strong wind cooling is adopted at the wall thickness of 12.2-38mm.

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

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

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

[0023] The present application provides a medium-high strength 7020 aluminum alloy profile with complex cross section and a preparation method thereof, by reducing the content of Si and Fe impurity phase, reducing the alloy fracture toughness, and increasing the content of Mg, Mn, Zn and Cr elements, the strength of the alloy is effectively improved, and by adding a small amount of Zr and Ti alloy, the recrystallization temperature can be significantly improved, the grain is refined, and the hardenability of the alloy is improved; in addition, the homogenization process, quenching process and aging process are optimized, wherein the homogenization process of the present application is three-stage homogenization, the first stage can effectively remove the residual stress of the casting organization, the second stage and the third stage 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 that the ideal organization morphology can be obtained; the quenching process adopts different quenching methods according to different wall thicknesses of the product, so that the quenching strength of each position of the extruded profile cross section tends to be consistent, and aging is carried out at low temperature for a long time, and according to different aging sequences, dispersed phase η ’ phase is obtained, and the mechanical properties of the alloy are improved. BRIEF DESCRIPTION OF DRAWINGS

[0024] In order to more clearly illustrate the technical solutions of the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed to be used in the embodiments or the prior art description. Obviously, the drawings described below are some embodiments of the present application, and other drawings can also be obtained by those skilled in the art without creative labor.

[0025] Figure 1 The cross-sectional view of the 7020 aluminum alloy profile prepared in Example 1 of the present application. DETAILED DESCRIPTION

[0026] The present application 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 application more clear and definite, the present application will be further described in detail below. It should be understood that the specific embodiments described herein are only used to explain the present application and are not used to limit the present application.

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

[0028] 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 being Al and unavoidable impurities.

[0029] The application can effectively improve the strength of the alloy by reducing the content of Si and Fe impurities, reducing the fracture toughness of the alloy, and increasing the content of Mg, Mn, Zn and Cr elements, and a small amount of Zr and Ti alloy can significantly improve the recrystallization temperature, refine the grain, and improve the hardenability of the alloy.

[0030] The application also provides a preparation method of the middle-high strength 7020 aluminum alloy profile with complex cross section, comprising the following steps:

[0031] (1) according to the alloy composition, the alloy is dosed, and is smelted at 710-750 DEG C for 8-10 h, 0.45-0.55% of the total mass of the metal in the furnace is added as a covering agent when the temperature in the furnace is 735 DEG C, then the aluminum solution is refined by using the mixed gas of argon and chlorine with a volume ratio of 31-33.5:1, so that the hydrogen content in the solution is ≤0.25 ml, and the solution is maintained for 50 min; after the smelting is completed, the 7020 aluminum alloy ingot is obtained by casting;

[0032] (2) the 7020 aluminum alloy ingot is subjected to three-stage homogenization treatment in a homogenization furnace; the three-stage homogenization treatment process is as follows: according to a temperature gradient of 200±10 DEG C, 350±10 DEG C and 470±10 DEG C, the total temperature is maintained for at least 24 hours, and the specific process is as follows:

[0033] first stage: the temperature is raised to 200±10 DEG C at a temperature raising rate of 3-5 DEG C / min, and is maintained for 2-5 h;

[0034] second stage: the temperature is raised to 350±10 DEG C at a temperature raising rate of 2-4 DEG C / min, and is maintained for 2-5 h;

[0035] third stage: the temperature is raised to 470±10 DEG C at a temperature raising rate of 1-3 DEG C / min, and is maintained for 20-25 h;

[0036] (3) the reverse extrusion machine is used for extrusion, the heating temperature of the aluminum rod is 400±5 DEG C, the heating temperature of the die is 400±10 DEG C and is maintained for 3-8 h, the heating temperature of the extrusion cylinder is 380±10 DEG C, the extrusion speed is 1.5±0.3 m / min during the extrusion, and the extruded profile is obtained, and the extrusion outlet temperature is ≥430 DEG C;

[0037] (4) the extruded section is quenched on line, and at the wall thickness of 39-69 mm, water mist cooling is used, and at the wall thickness of 12.2-38 mm, strong wind cooling is used, so as to ensure that the quenching strength of each position of the cross section of the extruded section is consistent;

[0038] (5) the extruded section is stretched and sawed, the stretching rate is 0.8-1.0%, the cutting head amount is at least 800 mm, and the cutting tail amount is at least 500 mm; after the sawing is completed, artificial aging is carried out, the artificial aging system is 121±5℃*24h, and the 7020 aluminum alloy section is obtained.

[0039] In the preparation process of the above-mentioned 7020 aluminum alloy section, the homogenization process, the quenching process and the aging process are mainly optimized. Among them, the homogenization process of the application is three-stage homogenization, the first stage can effectively remove the residual stress of the casting organization, the second stage and the third stage 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 that the ideal organization morphology can be obtained; the quenching process uses different quenching methods according to different wall thicknesses of products, so that the quenching strength of each position of the cross section of the extruded section tends to be consistent, low-temperature long-time aging is used, and according to different aging sequences, η ’ phase is obtained, and the mechanical properties of the alloy are improved.

[0040] Example 1

[0041] This embodiment prepares a 7020 aluminum alloy section, the cross-sectional shape of which is as shown in Figure 1 , the width of which is 129 mm, the maximum wall thickness of which is 69 mm, and the minimum wall thickness of which is 12.2 mm.

[0042] The 7020 aluminum alloy section 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 unavoidable impurities.

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

[0045] (1) according to the alloy component, the alloy component is dosed, and the molten aluminum solution is refined by adding a mixed gas of argon and chlorine with a volume ratio of 33.5:1 at a total mass of 0.55% of the total mass of the metal in the furnace at a temperature of 735℃ in the furnace, so that the content in the solution is ≤0.25ml, and the solution is maintained for 50min; after the melting is completed, the 7020 aluminum alloy ingot is obtained by casting;

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

[0047] First stage: heating to 200℃ at a heating rate of 3℃ / min, and keeping for 2h;

[0048] Second stage: heating to 350℃ at a heating rate of 2.5℃ / min, and keeping for 2h;

[0049] Third stage: heating to 470℃ at a heating rate of 2℃ / min, and keeping for 20h;

[0050] (3) the extrusion is performed by using a 60MN reverse extrusion machine, the heating temperature of the aluminum rod is 403℃, the heating temperature of the die is 405℃ and the temperature is kept for 5h, the heating temperature of the extrusion cylinder is 380℃, and the extrusion speed is 1.5m / min during the extrusion to obtain an extruded profile;

[0051] (4) the extruded profile is subjected to online quenching, and at the wall thickness of 39-69mm, water mist cooling is adopted, and at the wall thickness of 12.2-38mm, strong wind cooling is adopted, so as to ensure that the quenching intensity of each position of the cross section of the extruded profile is consistent;

[0052] (5) the extruded profile is subjected to stretching and sawing, the stretching rate is 1.0%, the cutting head amount is 800mm, and the cutting tail amount is 500mm; after the sawing is completed, artificial aging is performed, the artificial aging system is 121±5℃*24h, and the 7020 aluminum alloy profile is obtained.

[0053] Example 2

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

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

[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 of Al and inevitable impurities.

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

[0058] (1) the alloy components are proportioned, the melting is performed at 720℃ for 10h, the covering agent with a total mass of 0.5% of the total mass of the metal in the furnace is added when the temperature in the furnace is 735℃, then the aluminum solution is refined by using the mixed gas of argon and chlorine with a volume ratio of 32:1, so that the content in the solution is ≤0.25ml, and the solution is kept for 50min; after the melting is completed, the 7020 aluminum alloy ingot is obtained by casting;

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

[0060] first stage: heating to 210℃ at a heating rate of 4℃ / min, and keeping for 2h;

[0061] second stage: heating to 360℃ at a heating rate of 3℃ / min, and keeping for 2h;

[0062] third stage: heating to 480℃ at a heating rate of 2℃ / min, and keeping for 20h;

[0063] (3) the extrusion is performed by using a 60MN reverse extrusion machine, the heating temperature of the aluminum rod is 405℃, the heating temperature of the die is 410℃ and keeping for 8h, the heating temperature of the extrusion cylinder is 390℃, and the extrusion speed is 1.6m / min during the extrusion to obtain an extruded profile;

[0064] (4) the extruded profile is subjected to online quenching, and at the wall thickness of 39-69mm, water mist cooling is adopted, and at the wall thickness of 12.2-38mm, strong wind cooling is adopted, so as to ensure that the quenching intensities of different positions of the cross section of the extruded profile are consistent;

[0065] (5) the extruded profile is subjected to stretching and sawing, the stretching rate is 1.0%, the cutting head amount is 800mm, and the cutting tail amount is 500mm; after the sawing is completed, artificial aging is performed, the artificial aging system is 121±5℃*24h, and the 7020 aluminum alloy profile is obtained.

[0066] Example 3

[0067] In this example, a 7020 aluminum alloy profile is prepared, and the cross-sectional shape is the same as that of Example 1.

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

[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 of Al and inevitable impurities.

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

[0071] (1) According to the alloy composition, melt at 730℃ for 9 hours. When the furnace temperature is 735℃, add 0.5% of the total mass of metal in the furnace as a covering agent. Then, refine the aluminum solution with a mixed gas of argon and chlorine in a volume ratio of 31:1 to make the content in the solution ≤0.25ml and keep it for 50min. After the melting is completed, cast to obtain 7020 aluminum alloy ingot.

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

[0073] First stage: Heat to 195℃ at a heating rate of 3℃ / min and hold for 2 hours;

[0074] Second stage: Heat to 340℃ at a heating rate of 2.5℃ / h and hold for 2 hours;

[0075] Level 3: Heat to 460℃ at a rate of 2℃ / h and hold for 24 hours;

[0076] (3) Extrusion was carried out using a 60MN reverse extrusion press. The aluminum rod was heated to 400℃, the die was heated to 405℃ and kept at that temperature for 8 hours, the extrusion cylinder was heated to 380℃, and the extrusion speed was 1.4m / min to obtain the extruded profile.

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

[0078] (5) The extruded profile is stretched and sawn with a stretching rate of 0.9%, a head cutting amount of 800 mm, and a tail cutting amount of 500 mm. After sawing, artificial aging is carried out with an artificial aging regime of 121±5℃*24h to obtain 7020 aluminum alloy profile.

[0079] The mechanical properties of samples taken from Examples 1-3 above were tested and are shown in Table 1 below.

[0080] Table 1

[0081] Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa 456 399 14.0 Tensile strength / MPa Tensile strength / MPa 454 398 15.0 Tensile strength / MPa Tensile strength / MPa 460 402 14.0 Tensile strength / MPa Tensile strength / MPa 458 400 14.5 Tensile strength / MPa Tensile strength / MPa 449 388 15.5 Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa Tensile strength / MPa 350 290 10.0 -

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

[0083] It should be noted that any parts not mentioned in this invention can be achieved by using or referencing existing technologies.

[0084] Of course, the above description is not a limitation on the present application, and the present application is not limited to the above examples. Changes, modifications, additions or substitutions made by those skilled in the art within the spirit and scope of the present application should also be included in the protection scope of the present application.

Claims

1. A method of producing a sectionally complex medium-high strength 7020 aluminium alloy profile, characterised in that, The 7020 aluminum alloy profile includes alloy components with 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 of Al and inevitable impurities; The preparation method includes the following steps: (1) according to the alloy component, the alloy is dosed, and is smelted at 710~750℃ for 8~10h, and then 0.45%~0.55% of the total mass of the metal in the furnace is added as a covering agent when the temperature in the furnace is 735℃, and then the aluminum solution is refined by using a mixed gas of argon and chlorine with a volume ratio of 31~33.5:1, so that the content in the solution is ≤0.25ml, and the solution is maintained for 50min; after the smelting is completed, the 7020 aluminum alloy ingot is obtained by casting; (2) the 7020 aluminum alloy ingot is subjected to three-stage homogenization treatment in a homogenization furnace; (3) the reverse extrusion machine is used for extrusion, the heating temperature of the aluminum rod is 400±5℃, the heating temperature of the die is 400±10℃ and is maintained for 3~8h, the heating temperature of the extrusion cylinder is 380±10℃, and the extrusion speed is 1.5±0.3m / min during extrusion, so as to obtain the extruded profile; (4) the extruded profile is subjected to online quenching, and the quenching intensity of each position of the cross section of the extruded profile is kept consistent; (5) the extruded profile is subjected to stretching and sawing, and after the sawing is completed, artificial aging is performed, so as to obtain the 7020 aluminum alloy profile; In the step (4), the online quenching adopts strong air cooling+water mist cooling mixed quenching, water mist cooling is adopted at the position with a wall thickness of 39~69mm, and strong air cooling is adopted at the position with a wall thickness of 12.2~38mm; In the step (2), the three-stage homogenization treatment process is as follows: First stage: the temperature is raised to 200±10℃ at a temperature raising rate of 3~5℃ / min, and is maintained for 2h; Second stage: the temperature is raised to 350±10℃ at a temperature raising rate of 2~4℃ / min, and is maintained for 2h; Third stage: the temperature is raised to 470±10℃ at a temperature raising rate of 1~3℃ / min, and is maintained for 20~25h.

2. The method of claim 1, wherein the method is characterized by: In the step (3), the extrusion outlet temperature is ≥430℃.

3. The method of claim 1, wherein the method is characterized by: In the step (5), the stretching rate is controlled to be 0.8~1.0% during the stretching process.

4. The method of claim 1, wherein the method is characterized by: In the step (5), the artificial aging system is 121±5℃*24h.

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