A high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and its preparation method

Abstract

The present invention discloses a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and a preparation method thereof. Industrial pure Mg, industrial pure Zn, industrial pure Al and master alloys are proportioned; the proportioned materials are subjected to vacuum melting to obtain an alloy liquid, and then the alloy liquid is refined; the refined molten raw materials are cast to obtain an aluminum alloy ingot, and the aluminum alloy ingot is subjected to homogenization treatment; the homogenized aluminum alloy ingot is subjected to surface milling treatment, and then the surface-milled aluminum alloy ingot is subjected to heat treatment. After heating and holding, the aluminum alloy ingot is hot-rolled to obtain an aluminum alloy sheet; the hot-rolled aluminum alloy sheet is subjected to solution quenching treatment; the solution-quenched aluminum alloy sheet is subjected to retrogression and re-aging treatment and post-treatment to obtain a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles. Through technical means such as alloy composition optimization, casting, hot rolling, retrogression and re-aging heat treatment, etc., a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles is prepared, effectively improving the corrosion resistance and fracture toughness of the aluminum alloy.

Description

Technical Field

[0001] The present invention belongs to the technical field of aluminum alloy processing, and particularly relates to a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and a preparation method thereof. Background Art

[0002] With the development of industrialization, the energy crisis has become increasingly prominent, and energy conservation and emission reduction have become important issues in the transportation industry (such as aviation, automobiles, and ships). Research shows that the self-weight of the vehicle body during driving is the main part of fuel consumption (about 70%), and for every 100 kg reduction in vehicle weight, the fuel consumption and the corresponding CO2 emissions per 100 km can be reduced by 0.4 L and 1 kg respectively. In this context, lightweight has gradually become the development trend of the transportation industry. After a large number of comparative studies and repeated experiments, it has been proven that a large amount of aluminum alloy materials is one of the effective ways to improve vehicle lightweight.

[0003] Currently, the aluminum alloys used in vehicles are mainly 5xxx series and 6xxx series aluminum alloys. Although both have good formability, their strength is relatively low, so a relatively thick thickness is used. While the high-strength 7xxx series aluminum alloy can still achieve a weight reduction of about 30% after increasing the strength and reducing the thickness.

[0004] The traditional Al-Mg-Zn alloy has good extrusion performance, can extrude thin-walled profiles with complex shapes, has good welding performance, and high weld quality, making it an ideal medium-strength welding structural material. However, its poor corrosion resistance limits its wide application. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and a preparation method thereof in view of the deficiencies in the above-mentioned prior art, so as to solve the technical problems of low strength and poor corrosion resistance of aluminum alloy sheets for vehicles.

[0006] The present invention adopts the following technical solutions:

[0007] A preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, which includes proportioning industrial pure Mg, industrial pure Zn, industrial pure Al, and intermediate alloys; performing vacuum melting on the proportioned materials to obtain alloy liquid, and then refining the alloy liquid; casting the refined molten raw materials to obtain an aluminum alloy ingot, and performing homogenization treatment on the aluminum alloy ingot; performing milling treatment on the homogenized aluminum alloy ingot, then performing heat treatment on the milled aluminum alloy ingot, and hot rolling the aluminum alloy ingot after heating and holding to obtain an aluminum alloy sheet; performing solution quenching treatment on the hot-rolled aluminum alloy sheet; performing regression re-aging treatment and post-treatment on the solution-quenched aluminum alloy sheet to obtain a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles.

[0008] Specifically, the mass percentages of commercially pure Mg, commercially pure Zn, commercially pure Al, and master alloys are as follows:

[0009] Commercially pure Zn accounts for 5.9% - 6.9%, commercially pure Mg accounts for 2.0% - 2.7%, Mn accounts for 0.1% - 0.2%, Ti accounts for 0.05% - 0.15%, Zr accounts for 0.05% - 0.15%, La accounts for 0.05% - 0.15%, Ce accounts for 0.05% - 0.10%, Y accounts for 0.10% - 0.15%, Sc accounts for 0.05% - 0.30%, Er accounts for 0.05% - 0.30%, the total amount of impurities ≤ 0.15%, and the balance is commercially pure Al.

[0010] Specifically, the melting temperature for vacuum melting is 730 - 760 °C, the melting time is 1 - 2 h, and master alloys AlMn10, AlTi5, AlZr5, AlLa20, AlCe10, AlV5, AlY10, AlSc2, and AlEr20 are added during the melting process.

[0011] Specifically, refining is carried out under a protective atmosphere, the refining temperature is 700 - 720 °C, and the time is 20 - 30 min.

[0012] Specifically, the casting temperature is 700 - 720 °C, the homogenization treatment temperature is 460 - 480 °C, and the holding time is 20 - 28 h.

[0013] Specifically, after facing treatment, the thickness of the aluminum alloy ingot is 20 - 30 mm, the heating temperature is 370 - 410 °C, and the holding time is 1 - 2 h.

[0014] Specifically, the hot rolling process uses 10 - 12 passes of rolling, with a 10 - minute holding time between passes, a rolling speed of 10 - 12 m / min. After hot rolling, the thickness of the sheet is 10 mm, the reduction per pass is 1 - 2 mm, the rolling speed is 13 m / s, and the final rolling temperature is 320 ± 10 °C to obtain an aluminum alloy sheet; the lubricant medium used during hot rolling is an emulsion, which is an oil-in-water lubricant composed of 4% - 4.5% Span, 15% - 17% detergent, and machine oil.

[0015] Specifically, the solution temperature for solution quenching treatment is 465 - 470 °C, the holding time is 90 - 120 min, and the temperature of the cooling medium during quenching is 22 - 26 °C.

[0016] Specifically, the retrogression and re - aging treatment and post - treatment are as follows:

[0017] Heat from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min, hold for 24 - 26 h to complete pre-aging; heat from room temperature to 150 - 180 °C at a heating rate of 5 - 10 °C / min, hold for 60 - 80 min to complete reversion treatment; then heat from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min, hold for 24 - 26 h to complete re-aging; finally, a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles is prepared.

[0018] Another technical solution of the present invention is a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles.

[0019] Compared with the prior art, the present invention has at least the following beneficial effects:

[0020] A preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, through technical means such as alloy composition optimization, casting, hot rolling, reversion and re-aging heat treatment, prepares a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet, effectively improving the corrosion resistance and fracture toughness of the aluminum alloy, and successfully preparing an aluminum alloy sheet with optimized properties.

[0021] Furthermore, a high Zn / Mg ratio can improve the comprehensive mechanical properties of the aluminum alloy. Increasing the Zn content can increase the content of MgZn2, while reducing the proportion of the S (Al2CuMg) phase. The brittleness of the S phase is higher than that of the θ (Al2Cu) phase, which is beneficial to improving the strength and plastic toughness of the material at the same time. The Al3(Sc,Zr,Er) formed by the combination of Sc, Zr and Er has a better lattice and thermodynamic matching degree with the matrix. While refining the grains, it is beneficial to improve the welding performance and corrosion performance of the material. Ti can make the alloy have more excellent toughness and can form Al3Ti heterogeneous nucleation to refine the matrix grains. When La is added to the aluminum alloy during melting, the pinholes and gas holes in the sample are significantly reduced, making the ingot structure more uniform, having the effect of degassing and refining. After adding Ce, it can inhibit the formation of GP zones and θ″ phases, and is easy to form θ′ phases. And Ce will increase the lattice distortion of the matrix, making the system energy rise. For the system to reduce its own energy, θ′ phases are easily formed around Ce, increasing the tensile strength of the alloy. After adding Ce, it can inhibit the formation of GP zones and θ″ phases, and is easy to form θ′ phases. And Ce will increase the lattice distortion of the matrix, making the system energy rise. For the system to reduce its own energy, θ′ phases are easily formed around Ce, increasing the tensile strength of the alloy. An appropriate amount of Y can refine the grains and can form various compounds such as FeYAl8, Fe6AlY6, Fe4YAl8, SiYAl2, Si2YAl2, MnYAl8 with impurity elements Fe and Si. The formation of these compounds containing Fe, Si, etc. can purify the matrix.

[0022] Furthermore, in a vacuum melting furnace, nitrogen, hydrogen, oxygen, and carbon dissolved in the alloy can be easily removed to a level far lower than that achieved by smelting under normal pressure. At the same time, impurity elements whose vapor pressure is higher than that of the base metal at the melting temperature can be removed by volatilization, and the composition of active elements such as aluminum, titanium, boron, and zirconium that need to be added to the alloy can be easily controlled. Therefore, metal materials melted through vacuum induction melting can significantly improve various properties such as toughness, fatigue strength, corrosion resistance, and high-temperature creep. Setting the temperature between 730 and 760°C can prevent alloying element burnout, which in turn affects alloy properties.

[0023] Furthermore, refining is performed using a non-toxic and non-corrosive protective atmosphere of argon. When argon is introduced into the molten aluminum, the hydrogen partial pressure difference at the interface between the bubbles and the aluminum solution causes hydrogen to enter the bubbles and rise out of the molten aluminum. As the bubbles rise, they absorb impurities such as aluminum oxide, achieving a purification effect. The refining temperature is set at 700-720°C, which helps enhance hydrogen diffusion. During argon refining, argon concentrates on the surface of the aluminum bath, preventing the aluminum solution from reacting with external gases, resulting in better refining results.

[0024] Furthermore, the casting temperature is set between 700 and 720°C. This is primarily because high temperatures can easily burn the Mg element in the alloy, increase the alloy's air absorption, and easily produce pinholes and pores, reducing alloy quality. Low temperatures can lead to poor fluidity of the molten aluminum. The homogenization temperature is set between 460 and 480°C. This is primarily because high temperatures can cause overburning of the alloy, while low temperatures can lead to severe intragranular segregation within the matrix and uneven composition. Extensive calculations have shown that as homogenization time increases, the homogenization degree of Mg and Zn increases, while that of Sc, Ti, and Zr decreases. Furthermore, after 20 to 28 hours, the gap between the surface and core of the alloy decreases, resulting in a high degree of homogenization. Therefore, the optimal homogenization heat treatment process for this alloy is a hold at 460 to 480°C for 20 to 28 hours.

[0025] Furthermore, if the temperature is too high, coarse grains or melting of low-melting-point phases between grains are likely to occur, resulting in overheating or overburning of the ingot during heating, cracking during hot rolling, and failure to meet performance requirements; if the temperature is too low, it causes metal work hardening, increased energy consumption, incomplete recrystallization, and ultimately uneven grain size and poor performance.

[0026] Furthermore, the reduction per pass is set at 10-20% of the total reduction, mainly because the ingot has poor plasticity and limited bite, so a small reduction per pass can improve the product's shape and surface quality. Emulsion lubrication is used during the hot rolling process because the emulsion has high stability during storage, good separation at high temperatures, easy demulsification, no corrosion to the rolls and rolled parts, no residual ash or oil stains left after the lubricant burns, and a long service life. It has good washing properties, can wash away metal particles and other dirt on the rolls and metal surfaces, and reduce roll wear.

[0027] Further, the solution treatment temperature is set to 465 - 470 °C, the holding time is 90 - 120 min, and then quenching is carried out, so that alloying elements can be fully dissolved into the matrix to obtain a supersaturated solid solution, preparing for the subsequent heat treatment. If the solution treatment temperature is too high, overburning of alloying elements will occur, thus affecting the alloy properties. If the temperature is too low, the alloying elements cannot be fully dissolved, and the alloy properties cannot be fully exerted.

[0028] Further, regression re-aging can endow the sheet with the strength of a single-stage peak aging state and the corrosion resistance of a double-stage aging state, that is, the alloy can obtain good stress corrosion resistance and fracture toughness after regression heat treatment aging.

[0029] In summary, through technical means such as alloy composition optimization, casting, hot rolling, and regression re-aging heat treatment, the present invention prepares a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, effectively improving the corrosion resistance and fracture toughness of the aluminum alloy.

[0030] Next, through the accompanying drawings and embodiments, the technical solutions of the present invention will be further described in detail. Description of the Drawings

[0031] Figure 1 It is a schematic diagram of the hot rolling process of the present invention;

[0032] Figure 2 It is a physical diagram of 5 hot-rolled samples of the high-strength and corrosion-resistant 7xxx series aluminum alloy for vehicles of the present invention;

[0033] Figure 3 It is an Euler diagram of the alloy hot-rolled plate of Example 1 of the present invention;

[0034] Figure 4 It is an Euler diagram of the alloy hot-rolled plate of Example 2 of the present invention;

[0035] Figure 5 It is an Euler diagram of the alloy hot-rolled plate of Example 3 of the present invention;

[0036] Figure 6 It is an Euler diagram of the alloy hot-rolled plate of Example 4 of the present invention;

[0037] Figure 7 It is an Euler diagram of the alloy hot-rolled plate of Example ⑤ of the present invention. Specific Embodiments

[0038] Next, the technical solutions of the present invention will be described clearly and completely. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present invention without creative efforts shall fall within the protection scope of the present invention.

[0039] In the present invention, unless otherwise specified, all the embodiments and preferred implementation methods mentioned herein can be combined with each other to form a new technical solution.

[0040] In the present invention, unless otherwise specified, all the technical features and preferred features mentioned herein can be combined with each other to form a new technical solution.

[0041] In the present invention, unless otherwise specified, the percentage (%) or part refers to the weight percentage or weight part relative to the composition.

[0042] In the present invention, unless otherwise specified, the various components or their preferred components involved can be combined with each other to form a new technical solution.

[0043] In the present invention, unless otherwise stated, the numerical range "a to b" represents an abbreviated representation of any real number combination between a and b, where a and b are both real numbers. For example, the numerical range "6 to 22" means that all real numbers between "6 to 22" have been fully listed herein, and "6 to 22" is only an abbreviated representation of these numerical combinations.

[0044] The "range" disclosed in the present invention can be in the form of one or more lower limits and one or more upper limits, respectively.

[0045] In the present invention, the term "and / or" used herein refers to any combination and all possible combinations of one or more of the associated listed items, and includes these combinations.

[0046] In the present invention, unless otherwise specified, each reaction or operation step can be carried out sequentially or in order. Preferably, the reaction methods herein are carried out sequentially.

[0047] Unless otherwise specified, the professional and scientific terms used herein have the same meaning as those familiar to persons skilled in the art. In addition, any method or material similar or equivalent to the described content can also be applied to the present invention.

[0048] The present invention provides a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and a preparation method thereof, which refine grains through micro-alloying elements, optimize the preparation process of the alloy sheet, and improve the corrosion resistance and comprehensive mechanical properties.

[0049] Please refer to Figure 1 , a preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles according to the present invention, comprising the following steps:

[0050] S1. Batching

[0051] Ingredients are prepared by mixing commercially pure Mg, commercially pure Zn, commercially pure Al, and master alloys according to the designed mass percentages, including: commercially pure Zn accounts for 5.9% - 6.9%, commercially pure Mg accounts for 2.0% - 2.7%, Mn accounts for 0.1% - 0.2%, Ti accounts for 0.05% - 0.15%, Zr accounts for 0.05% - 0.15%, La accounts for 0.05% - 0.15%, Ce accounts for 0.05% - 0.10%, Y accounts for 0.10% - 0.15%, Sc accounts for 0.05% - 0.30%, Er accounts for 0.05% - 0.30%, Fe accounts for 0.05% - 0.10%, Si accounts for 0.05% - 0.10%, the total amount of impurities ≤ 0.15%, and the balance is commercially pure Al.

[0052] S2. Melting

[0053] Put the ingredients obtained in step S1 into a vacuum melting furnace. During the melting process, control the melting temperature at 730 - 760 °C and the melting time at 1 - 2 h. During the melting process, add master alloys AlMn10, AlTi5, AlZr5, AlLa20, AlCe10, AlV5, AlY10, AlSc2, and AlEr20.

[0054] S3. Refining

[0055] Refine the alloy liquid obtained in step S2. During the refining process, control the temperature at 700 - 720 °C, and use a protective atmosphere for refining to obtain the raw material in a molten state. The refining time is 20 - 30 min.

[0056] The protective atmosphere is degassing using hexachloroethane and argon.

[0057] S4. Casting

[0058] Cast the alloy liquid obtained after standing in step S3. During the casting process, control the pouring temperature at 700 - 720 °C.

[0059] S5. Homogenization treatment

[0060] Conduct homogenization treatment on the ingot obtained in step S4 at a temperature of 460 - 480 °C and hold for 20 - 28 h.

[0061] S6. Milling

[0062] Mill the 7xxx series aluminum alloy ingot after homogenization treatment in step S5, remove 20 mm from the bottom of the casting gate, with a single - side milling amount greater than 10 mm, remove the surface oxide scale and the coarsely grained part, and the thickness of the milled aluminum alloy ingot is 20 - 30 mm.

[0063] S7. Heating

[0064] Place the milled aluminum alloy ingot in a heating furnace and heat it. The temperature of the heating furnace is 370 - 410 °C, and the holding time is 1 - 2 h.

[0065] S8. Hot rolling

[0066] Take out the ingot after heating and holding for hot rolling. The thickness of the plate after hot rolling is 10 mm, the reduction per pass is 1 - 2 mm, the rolling speed is 13 m / s, and the final rolling temperature is 320 ± 10 °C to obtain an aluminum alloy plate. Finally, place the hot-rolled plate horizontally on the ground and air-cool it to room temperature.

[0067] The hot rolling process uses 10 - 12 passes of rolling, with a 10-minute hold between passes and a rolling speed of 10 - 12 m / min.

[0068] The lubricating medium used during hot rolling is emulsion, with the emulsion concentration being 4% - 4.5% and the pH value being 8 - 8.5.

[0069] Under the condition of following the same rolling process, increase the measurement frequency to find the difference between the roll gap value and the actual thickness and the difference between the head, middle, and tail of the plate, so as to accurately set the roll gap value and precisely control the thickness.

[0070] S9. Solution heat treatment and quenching

[0071] Conduct solution heat treatment and quenching on the hot-rolled aluminum alloy plate. The solution temperature is 465 - 470 °C, the holding time is 80 - 90 min, and then quench.

[0072] After solution treatment, transfer it to the cooling medium for quenching within 5 s. During quenching, the temperature of the cooling medium is 22 - 26 °C.

[0073] S10. Aging

[0074] Conduct regression re-aging treatment on the solution heat-treated and quenched plate. The steps are as follows:

[0075] S101. Pre-aging: Raise the temperature from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min and hold for 24 - 26 h;

[0076] S102. Regression treatment: Raise the temperature from room temperature to 150 - 180 °C at a heating rate of 5 - 10 °C / min and hold for 60 - 80 min;

[0077] S103. Re-aging: Raise the temperature from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min and hold for 24 - 26 h.

[0078] S11. Post-treatment

[0079] Saw the aluminum alloy plate after regression re-aging heat treatment into finished product specifications.

[0080] A high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles according to the present invention, by mass percentage, includes: Zn accounts for 5.9% - 6.9%, Mg accounts for 2.0% - 2.7%, Mn accounts for 0.1% - 0.2%, Ti accounts for 0.05% - 0.15%, Zr accounts for 0.05% - 0.15%, La accounts for 0.05% - 0.15%, Ce accounts for 0.05% - 0.10%, Y accounts for 0.10% - 0.15%, Sc accounts for 0.05% - 0.30%, Er accounts for 0.05% - 0.30%, the total amount of impurities ≤ 0.15%, and the balance is Al.

[0081] Please refer to Figure 2 , which is a schematic diagram of the rolled sample. After mechanical property testing, its strength reaches 600 - 650 Mpa, the elongation rate reaches 7 - 15%, and the stress corrosion sensitivity is E loss is 0.1 - 0.2, indicating that the regression re-aging treatment can enable the alloy to obtain good stress corrosion resistance while obtaining a relatively high strength.

[0082] The Zn / Mg ratio in the alloy is increased. Increasing the Zn content can increase the content of MgZn2, thereby increasing the strength of the alloy; Cu is reduced to 0, eliminating the Al2Cu phase and the Al2CuMg phase. The compressive strength of these two phases is higher than that of MgZn2. At the same time, Ti is added to make the alloy have better toughness. And Ti can form Al3Ti with Al, hinder the migration of grain boundaries, effectively refine the as-cast structure, and increase the recrystallization temperature. The single-pass reduction amount during the rolling process of the alloy is 10% of the total reduction amount, improving the tissue uniformity and the strength of the sheet in the thickness direction. The regression re-aging treatment system adopted in the present invention can effectively improve the corrosion resistance of the alloy while ensuring a relatively high strength.

[0083] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present invention. Obviously, the described embodiments are some, but not all, of the embodiments of the present invention. Usually, the components described and shown in the accompanying drawings here can be arranged and designed in various different configurations. Therefore, the following detailed description of the embodiments of the present invention provided in the drawings is not intended to limit the scope of the claimed present invention, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the scope of protection of the present invention.

[0084] Example 1

[0085] The present invention discloses a preparation method for a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, including the following steps:

[0086] Calculated based on the total alloy mass of 100%: Zn: 5.9%, Mg: 2.0%, Mn: 0.1%, Ti: 0.05%, Zr: 0.05%, Sc: 0.05%, Er: 0.05%, La: 0.05%, Ce: 0.05%, Y: 0.10%, total impurities ≤ 0.15%, and the balance is Al.

[0087] In Example 1, a total of 70 kg of alloy was cast, and the detailed preparation steps are as follows:

[0088] The first step

[0089] Charge various alloy ingredients according to the designed ratio, including adding 4.13 kg of pure Zn, 1.4 kg of pure Mg, 0.7 kg of AlMn10, 0.7 kg of AlTi5, 0.7 kg of AlZr5, 1.75 kg of AlSc2, 0.175 kg of AlEr20, 0.175 kg of AlLa20, 0.3 kg of AlCe10, 0.7 kg of AlY10, and 59.27 kg of pure Al;

[0090] The second step

[0091] Put the ingredients obtained in the first step into a vacuum melting furnace for melting, with a melting temperature of 730 °C and a melting time of 1 h;

[0092] Refining: Refine the alloy liquid obtained in the second step. Control the temperature at 700 °C during the refining process, use a protective atmosphere for refining to obtain the raw materials in a molten state, with a refining time of 20 min, and conduct combined refining by introducing argon, hexachloroethane, and a solvent;

[0093] Casting: After allowing the molten raw materials to stand for 30 min, pour them into a mold at a pouring temperature of 700 °C to obtain an aluminum alloy ingot;

[0094] Homogenization treatment: Subject the cast ingot to homogenization treatment at a temperature of 460 °C for 20 h;

[0095] Facing: Face the aluminum alloy ingot after homogenization treatment, remove 20 mm from the bottom of the casting gate, with a single-sided milling amount greater than 10 mm, remove the surface oxide scale and the coarser part of the grains, and the thickness of the milled ingot is 20 mm;

[0096] Heating: Place the milled aluminum alloy ingot in a heating furnace for heating, with the heating furnace temperature at 370 ± 10 °C and a holding time of 1 h;

[0097] Hot rolling: The ingot after heating and heat preservation is taken out of the furnace for hot rolling. After hot rolling, the thickness of the plate is 16 mm, the reduction per pass is 0.4 mm, the rolling speed is 10 m / min, and the final rolling temperature is 320 ± 10 °C to obtain an aluminum alloy plate. Finally, the hot-rolled plate is placed horizontally on the ground and air-cooled to room temperature;

[0098] Solution quenching: The hot-rolled aluminum alloy plate is subjected to solution quenching treatment. The solution temperature is 465 ± 10 °C, the holding time is 90 min, and then quenching is carried out;

[0099] Aging: The solution-quenched plate is subjected to regression re-aging treatment, and the steps are as follows:

[0100] Pre-aging: Raise the temperature from room temperature to 100 °C at a heating rate of 5 - 10 °C / min and hold for 24 h;

[0101] Regression treatment: Raise the temperature from room temperature to 150 °C at a heating rate of 5 - 10 °C / min and hold for 60 min;

[0102] Re-aging: Raise the temperature from room temperature to 100 °C at a heating rate of 5 - 10 °C / min and hold for 24 h;

[0103] Post-treatment: The aluminum alloy plate after regression re-aging heat treatment is sawed into finished product specifications.

[0104] Please refer to Figure 3 , finally, the performance of the plate is good, with high strength, plasticity and toughness, and good corrosion resistance (strength: 600 MPa, elongation: 8%, E loss : 0.12).

[0105] Example 2

[0106] The present invention discloses a preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy plate for vehicles, including the following steps:

[0107] Calculated based on the total alloy mass of 100%: Zn: 6.9%, Mg: 2.7%, Mn: 0.2%, Ti: 0.15%, Zr: 0.15%, Sc: 0.15%, Er: 0.30%, La: 0.15%, Ce: 0.10%, Y: 0.15%, the total amount of impurities ≤ 0.15%, and the balance is Al.

[0108] A total of 70 kg of alloy is cast in Example 2, and the detailed preparation steps are as follows:

[0109] The first step

[0110] Charge various alloy ingredients in accordance with the designed ratios, including 4.83 kg of pure Zn, 1.89 kg of pure Mg, 1.4 kg of AlMn10, 2.1 kg of AlTi5, 2.1 kg of AlZr5, 5.25 kg of AlSc2, 1.05 kg of AlEr20, 0.525 kg of AlLa20, 0.7 kg of AlCe10, 1.05 kg of AlY10, and 49.105 kg of pure Al;

[0111] The second step

[0112] Put the ingredients obtained in the first step into a vacuum melting furnace for melting at a melting temperature of 760 °C for 2 hours;

[0113] Refining: Refine the alloy liquid obtained in the second step. Control the temperature at 720 °C during the refining process, use a protective atmosphere for refining to obtain the raw materials in a molten state. The refining time is 20 minutes, and argon, hexachloroethane, and a solvent are used for combined refining;

[0114] Casting: After the raw materials in the molten state are left standing for 30 minutes, pour them into a mold at a pouring temperature of 720 °C to obtain an aluminum alloy ingot;

[0115] Homogenization treatment: Carry out homogenization treatment on the cast ingot at a temperature of 480 °C for 28 hours;

[0116] Facing: Carry out facing on the aluminum alloy ingot after homogenization treatment. Remove 20 mm from the bottom of the casting gate, with a single-sided milling amount greater than 10 mm, remove the surface oxide scale and the coarsely grained part, and the thickness of the milled ingot is 30 mm;

[0117] Heating: Place the aluminum alloy ingot after facing in a heating furnace for heating. The temperature of the heating furnace is 410 ± 10 °C, and the holding time is 2 hours;

[0118] Hot rolling: Take the ingot out of the furnace for hot rolling after heating and holding. The thickness of the hot-rolled sheet is 16 mm, the reduction per pass is 0.4 mm, the rolling speed is 10 m / min, and the final rolling temperature is 320 ± 10 °C to obtain an aluminum alloy sheet. Finally, place the hot-rolled sheet horizontally on the ground and air-cool it to room temperature;

[0119] Solution quenching: Carry out solution quenching treatment on the hot-rolled aluminum alloy sheet. The solution temperature is 470 ± 10 °C, the holding time is 120 minutes, and then quench;

[0120] Aging: Carry out regression re-aging treatment on the sheet after solution quenching, and the steps are as follows:

[0121] Pre-aging: Raise the temperature from room temperature to 120 °C at a heating rate of 5 - 10 °C / min and hold for 26 hours;

[0122] Regression treatment: Heat from room temperature to 180°C at a heating rate of 5 - 10°C / min and hold for 800 min;

[0123] Re-aging: Heat from room temperature to 120°C at a heating rate of 5 - 10°C / min and hold for 26 h;

[0124] Post-treatment: Saw the aluminum alloy sheet after regression and re-aging heat treatment into finished product specifications.

[0125] Please refer to Figure 4 , finally the sheet has good properties, high strength, plasticity and toughness, and good corrosion resistance (strength: 650 MPa, elongation: 7.5%, E loss : 0.13).

[0126] Example 3

[0127] The present invention discloses a preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, comprising the following steps:

[0128] Calculated based on the total alloy mass of 100%: Zn: 6.9%, Mg: 2.2%, Mn: 0.1%, Ti: 0.10%, Zr: 0.3%, Sc: 0.3%, Er: 0.3%, La: 0.05%, Ce: 0.05%, Y: 0.10%, total impurities ≤ 0.15%, and the balance is Al.

[0129] A total of 70 kg of alloy was cast in Example 3, and the preparation steps are as follows:

[0130] The first step

[0131] Mix various alloy ingredients according to the designed ratio, including adding 4.83 kg of pure Zn, 1.54 kg of pure Mg, 0.7 kg of AlMn10, 1.4 kg of AlTi5, 4.2 kg of AlZr5, 10.5 kg of AlSc2, 1.05 kg of AlEr20, 0.175 kg of AlLa20, 0.35 kg, AlCe10, 0.7 kg of AlY10, and 44.56 kg of pure Al;

[0132] The second step

[0133] Put the ingredients obtained in the first step into a vacuum melting furnace for melting, with a melting temperature of 750°C and a melting time of 2 h;

[0134] Refining: Refine the alloy liquid obtained in the second step. Control the temperature at 720°C during the refining process, use a protective atmosphere for refining to obtain the molten raw materials, with a refining time of 20 min, and introduce argon, hexachloroethane, and a solvent for composite refining;

[0135] Casting: After the molten raw material is allowed to stand for 30 minutes, it is cast into a mold at a casting temperature of 700°C to obtain an aluminum alloy ingot;

[0136] Homogenization treatment: The cast ingot is homogenized at 470°C for 26 hours;

[0137] Milling: Mill the aluminum alloy ingot after homogenization treatment, remove 20mm from the bottom of the pouring mouth, and the single-side milling amount is greater than 10mm to remove the surface oxide scale and coarse grains. The thickness of the ingot after milling is 20mm.

[0138] Heating: Place the milled aluminum alloy ingot in a heating furnace and heat it at a temperature of 390±10℃ for 1 hour;

[0139] Hot rolling: The ingot after heating and insulation is taken out of the furnace and hot rolled. The thickness of the plate after hot rolling is 16mm, the single-pass reduction is 0.4mm, the rolling speed is 10m / min, and the final rolling temperature is 340±10℃ to obtain the aluminum alloy plate. Finally, the hot-rolled plate is placed horizontally on the ground and air-cooled to room temperature;

[0140] Solution quenching: The hot-rolled aluminum alloy plate is subjected to solution quenching treatment at a solution temperature of 465±10℃ and a holding time of 90min, followed by quenching;

[0141] Aging: The plate after solution quenching is subjected to regression and aging treatment. The steps are as follows:

[0142] Pre-aging: from room temperature to 110℃, heating rate 5-10℃ / min, keep warm for 24h;

[0143] Regression treatment: heating from room temperature to 180℃, heating rate 5-10℃ / min, keeping warm for 60min;

[0144] Re-aging: from room temperature to 110℃, heating rate 5-10℃ / min, keep warm for 24h;

[0145] Post-processing: The aluminum alloy sheets after the regression and aging heat treatment are sawn into finished product specifications.

[0146] See also Figure 5 Finally, the plate has good performance, high strength, high toughness and good corrosion resistance (strength: 615MPa, elongation: 9.5%, E loss :0.16).

[0147] Example 4

[0148] The present invention discloses a method for preparing a high-strength and corrosion-resistant 7xxx series aluminum alloy plate for vehicles, the preparation method comprising the following steps:

[0149] Calculated based on the total mass of the alloy being 100%: Zn: 5.9%, Mg: 2.0%, Mn: 0.1%, Ti: 0.10%, Zr: 0.15%, Sc: 0.15%, Er: 0.15%, La: 0.05%, Ce: 0.05%, Y: 0.10%, total impurities ≤ 0.15%, the balance being Al. A total of 70 kg of the alloy was cast in Example 4, and the detailed preparation steps are as follows:

[0150] Step 1: Weigh various alloy ingredients according to the designed proportions, including 4.13 kg of pure Zn, 1.4 kg of pure Mg, 0.7 kg of AlMn10, 1.4 kg of AlTi5, 2.1 kg of AlZr5, 5.25 kg of AlSc2, 0.525 kg of AlEr20, 0.175 kg of AlLa20, 0.35 kg of AlCe10, 0.7 kg of AlY10, and 53.27 kg of pure Al;

[0151] Step 2: Put the ingredients obtained in Step 1 into a vacuum melting furnace for melting. The melting temperature is 750 °C and the melting time is 2 h;

[0152] Refining: Refine the alloy liquid obtained in Step 2. Control the temperature at 720 °C during the refining process, use a protective atmosphere for refining to obtain the raw material in a molten state. The refining time is 20 min, and argon, hexachloroethane, and a solvent are used for combined refining;

[0153] Casting: After allowing the molten raw material to stand for 30 min, pour it into a mold at a pouring temperature of 700 °C to obtain an aluminum alloy ingot;

[0154] Homogenization treatment: Subject the cast ingot to homogenization treatment at a temperature of 465 °C for 24 h;

[0155] Facing: Face the aluminum alloy ingot after homogenization treatment. Remove 20 mm from the bottom of the casting gate, with a single-sided milling amount greater than 1 mm, remove the surface oxide scale and the coarsely grained part, and the thickness of the milled ingot is 20 mm;

[0156] Heating: Place the milled aluminum alloy ingot in a heating furnace for heating. The temperature of the heating furnace is 410 ± 10 °C and the holding time is 1 h;

[0157] Hot rolling: Take the ingot out of the furnace for hot rolling after heating and holding. The thickness of the rolled sheet is 16 mm, the single-pass reduction is 0.4 mm, the rolling speed is 10 m / min, and the final rolling temperature is 360 ± 10 °C to obtain an aluminum alloy sheet. Finally, place the hot-rolled sheet horizontally on the ground and air-cool it to room temperature;

[0158] Solution quenching: The hot-rolled aluminum alloy sheet is subjected to solution quenching treatment. The solution temperature is 465 ± 10 °C, the holding time is 90 min, and then quenching is carried out;

[0159] Aging: The solution-quenched sheet is subjected to regression re-aging treatment, and the steps are as follows:

[0160] Pre-aging: Raise the temperature from room temperature to 115 °C at a heating rate of 5 - 10 °C / min and hold for 22 h;

[0161] Regression treatment: Raise the temperature from room temperature to 180 °C at a heating rate of 5 - 10 °C / min and hold for 60 min;

[0162] Re-aging: Raise the temperature from room temperature to 115 °C at a heating rate of 5 - 10 °C / min and hold for 22 h;

[0163] Post-treatment: The aluminum alloy sheet after regression re-aging heat treatment is sawn into finished product specifications.

[0164] Please refer to Figure 6 , finally, the sheet has good properties, high strength, plasticity and toughness, and good corrosion resistance (strength: 625 MPa, elongation: 10.5%, E loss : 0.16).

[0165] Example 5

[0166] The present invention discloses a preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, and the preparation method includes the following steps:

[0167] Calculated based on the total mass of the alloy being 100%: Zn: 5.9%, Mg: 2.5%, Mn: 0.1%, Ti: 0.10%, Zr: 0.30%, Sc: 0.15%, Er: 0.30%, La: 0.05%, Ce: 0.05%, Y: 0.10%, total impurities ≤ 0.15%, and the balance is Al.

[0168] A total of 70 kg of alloy is cast in Example 5, and the detailed preparation steps are as follows:

[0169] First step: Charge various alloy ingredients according to the designed ratio, including 4.13 kg of pure Zn, 1.75 kg of pure Mg, 0.7 kg of AlMn10, 1.4 kg of AlTi5, 4.2 kg of AlZr5, 5.25 kg of AlSc2, 1.05 kg of AlEr20, 0.175 kg of AlLa20, 0.35 kg, AlCe10, 0.7 kg of AlY10, and 50.295 kg of pure Al;

[0170] Second step: Put the ingredients obtained in the first step into a vacuum melting furnace for melting, with a melting temperature of 750 °C and a melting time of 2 h;

[0171] Refining: The alloy liquid obtained in Step 2 is refined. The temperature during the refining process is controlled at 720 °C, and a protective atmosphere is used for refining to obtain the raw materials in a molten state. The refining time is 20 min, and argon, hexachloroethane, and a solvent are used for combined refining;

[0172] Casting: After the raw materials in a molten state are allowed to stand for 30 min, they are poured into a mold at a pouring temperature of 700 °C to obtain an aluminum alloy ingot;

[0173] Homogenization treatment: The cast ingot is subjected to homogenization treatment at a temperature of 465 °C for 24 h;

[0174] Facing: The aluminum alloy ingot after homogenization treatment is faced. 20 mm is removed from the bottom of the casting gate, and the single-pass milling amount is greater than 10 mm to remove the surface oxide scale and the coarsened grain part. The thickness of the milled ingot is 20 mm;

[0175] Heating: The aluminum alloy ingot after facing is placed in a heating furnace for heating. The temperature of the heating furnace is 450 ± 10 °C, and the holding time is 1 h;

[0176] Hot rolling: The ingot after heating and holding is taken out of the furnace for hot rolling. The thickness of the hot-rolled sheet is 16 mm, the single-pass reduction is 0.4 mm, the rolling speed is 10 m / min, and the final rolling temperature is 400 ± 10 °C to obtain an aluminum alloy sheet. Finally, the hot-rolled sheet is placed horizontally on the ground and air-cooled to room temperature;

[0177] Solution quenching: The hot-rolled aluminum alloy sheet is subjected to solution quenching treatment. The solution temperature is 465 ± 10 °C, the holding time is 90 min, and then quenching is carried out;

[0178] Aging: The sheet after solution quenching is subjected to regression re-aging treatment, and the steps are as follows:

[0179] Pre-aging: Raise the temperature from room temperature to 120 °C at a heating rate of 5 - 10 °C / min and hold for 25 h;

[0180] Regression treatment: Raise the temperature from room temperature to 170 °C at a heating rate of 5 - 10 °C / min and hold for 70 min;

[0181] Re-aging: Raise the temperature from room temperature to 120 °C at a heating rate of 5 - 10 °C / min and hold for 25 h;

[0182] Post-treatment: The aluminum alloy sheet after regression re-aging heat treatment is sawn into finished product specifications.

[0183] Please refer to Figure 7 , finally, the performance of the sheet is good, with high strength, plasticity, toughness, and good corrosion resistance (strength: 620 Mpa, elongation: 8.5%, E loss: 0.15).

[0184] In summary, for a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles and its preparation method according to the present invention, the control of impurity elements is more stringent, which can greatly remove the formation of impurity phases such as Al3Fe and Mg2Si, facilitating the improvement of the elongation of the material and enhancing the corrosion resistance and comprehensive mechanical properties of the alloy sheet; the addition of trace alloy elements Sc and Er can form Al3(Sc, Zr, Er) particles with Zr, which refine the as-cast grains to 20 - 40 nm, can prevent the growth of recrystallized grains, and improve the welding performance and corrosion performance of the alloy.

[0185] Finally, it should be noted that: the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it; although the present invention has been described in detail with reference to the foregoing embodiments, those of ordinary skill in the art should understand that: they can still modify the technical solutions recorded in the foregoing embodiments, or perform equivalent replacements on some or all of the technical features; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A preparation method of a high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles, characterized in that, Ingredient the industrial pure Mg, industrial pure Zn, industrial pure Al and master alloys; conduct vacuum melting on the ingredients to obtain alloy liquid, and then refine the alloy liquid; cast the refined molten raw materials to obtain aluminum alloy ingots, and conduct homogenization treatment on the aluminum alloy ingots; conduct milling on the homogenized aluminum alloy ingots, and then conduct heat treatment on the milled aluminum alloy ingots, and hot-roll the aluminum alloy ingots after heating and holding to obtain aluminum alloy sheets; conduct solution quenching treatment on the hot-rolled aluminum alloy sheets; conduct reversion re-aging treatment and post-treatment on the solution-quenched aluminum alloy sheets to obtain high-strength and corrosion-resistant 7xxx series aluminum alloy sheets for vehicles; The mass percentages of industrial pure Mg, industrial pure Zn, industrial pure Al and master alloys are specifically as follows: Industrial pure Zn accounts for 5.9% - 6.9%, industrial pure Mg accounts for 2.0% - 2.7%, Mn accounts for 0.1% - 0.2%, Ti accounts for 0.05% - 0.15%, Zr accounts for 0.05% - 0.15%, La accounts for 0.05% - 0.15%, Ce accounts for 0.05% - 0.10%, Y accounts for 0.10% - 0.15%, Sc accounts for 0.05% - 0.30%, Er accounts for 0.05% - 0.30%, the total amount of impurities ≤ 0.15%, and the balance is industrial pure Al; The hot-rolling process adopts 10 - 12 passes of rolling, with an inter-pass holding time of 10 min, a rolling speed of 10 - 12 m / min, the thickness of the hot-rolled sheet is 10 mm, the reduction per pass is 1 - 2 mm, the rolling speed is 13 m / s, and the final rolling temperature is 320 ± 10 °C to obtain aluminum alloy sheets; the lubricating medium used during hot rolling is emulsion, and the emulsion is an oil-in-water lubricant composed of 4% - 4.5% Span, 15 - 17% detergent and machine oil; The solution temperature for solution quenching treatment is 465 - 470 °C, the holding time is 90 - 120 min, and the temperature of the cooling medium during quenching is 22 - 26 °C; The reversion re-aging treatment and post-treatment are specifically as follows: Raise the temperature from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min, hold for 24 - 26 h to complete pre-aging; raise the temperature from room temperature to 150 - 180 °C at a heating rate of 5 - 10 °C / min, hold for 60 - 80 min to complete reversion treatment; Then raise the temperature from room temperature to 100 - 120 °C at a heating rate of 5 - 10 °C / min, hold for 24 - 26 h to complete re-aging; finally, prepare high-strength and corrosion-resistant 7xxx series aluminum alloy sheets for vehicles.

2. The preparation method of the high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles according to claim 1, characterized in that, The melting temperature for vacuum melting is 730 - 760 °C, the melting time is 1 - 2 h, and master alloys AlMn10, AlTi5, AlZr5, AlLa20, AlCe10, AlV5, AlY10, AlSc2 and AlEr20 are added during the melting process.

3. The preparation method of the high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicle use according to claim 1, wherein Refine using a protective atmosphere, with a refining temperature of 700 - 720 °C and a time of 20 - 30 min.

4. The preparation method of the high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles according to claim 1, characterized in that, The casting temperature is 700 - 720 °C, the temperature for homogenization treatment is 460 - 480 °C, and the holding time is 20 - 28 h.

5. The preparation method of the high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles according to claim 1, characterized in that, The thickness of the aluminum alloy ingot after milling treatment is 20 - 30 mm, the heating temperature is 370 - 410 °C, and the holding time is 1 - 2 h.

6. A high-strength and corrosion-resistant 7xxx series aluminum alloy sheet for vehicles prepared by the method according to any one of claims 1 to 5.

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