Preparation process of 750mpa-grade ultra-high-strength aluminum alloy sheet

Abstract

The present application belongs to the technical field of aluminum alloy hot forming and heat treatment, and relates to a preparation process of 750MPa-grade ultra-high-strength aluminum alloy sheet. The composition of the aluminum alloy suitable for the process and the mass percentage of each component are as follows: Zn 11.5-13.5%, Mg 2.6-3.6%, Cu 0.5-1.5%, Mn 0.06-0.35%, Zr 0.10-0.20%, Ti 0.03-0.10%, impurity element Si ≤0.15%, Fe ≤0.25%, other impurities ≤0.05% individually, total amount ≤0.15%, and the balance being Al. After the aluminum alloy ingot within the above composition range is heated, hot rough rolling, hot finish rolling to the required thickness are carried out, and then uncoiling is performed to carry out solid solution quenching + pre-stretching + artificial aging treatment to the peak strength. The 700MPa strength grade aluminum alloy sheet prepared through the above process has the advantages of good surface quality, uniform microstructure and performance, good batch stability, and small residual stress. The process is suitable for the preparation of ultra-high-strength aluminum alloy sheet required in the fields of automobiles, mobile phones and the like.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy hot forming and heat treatment technology, specifically relating to a process for preparing 750MPa grade ultra-high strength aluminum alloy thin plates. Background Technology

[0002] Currently, the battery casings, armor plates, and crash beams of new energy vehicles mainly use aluminum alloys such as 3003, 6061, and 7075. These alloys have relatively low strength, resulting in a large structural weight and making it difficult to meet lightweight requirements. At present, the motherboard frames of mobile phones and the casings of VR devices use 6xxx series alloys, which also suffer from insufficient strength, leading to an overall heavy structure. With the continuous advancement of lightweight structural requirements in the new energy vehicle, mobile phone, and VR fields, the use of higher-strength aluminum alloys as the main structural material has become a current development trend. Some domestic units have produced aluminum alloy materials with a strength of 700MPa, but these materials are mostly thick plates and extruded materials, requiring significant machining removal when used in these fields, resulting in long cycles and high costs. Therefore, there is an urgent need to develop thin aluminum alloy plates (less than 3mm) with a strength of 750MPa or higher to meet the application requirements.

[0003] Increasing the alloy content is the main way to obtain higher strength aluminum alloys. However, as the alloy content increases, the casting and forming properties of the ingot deteriorate significantly. It is difficult to prepare large-sized ingots (ingot diameter greater than 600 mm) with high alloy content (total alloy content of 15% wt) using traditional casting methods. The ingots are also very prone to cracking during the casting process. Figure 1 b).

[0004] To achieve a strength of 750 MPa in aluminum alloy sheets, besides introducing sufficient high-alloying elements through compositional design to obtain a large number of precipitated strengthening phases, controlling the hot deformation process to maintain the deformed microstructure in the final sheet and further enhance the alloy's strength through deformation strengthening effects is also an important measure. However, with the increase of alloying elements, the resistance to hot deformation increases, and dynamic recrystallization or a high deformation energy can easily form during the hot rolling process of the sheet. This leads to significant static recrystallization during the subsequent solution treatment process, eliminating the strengthening effect of the deformed microstructure and causing a rapid decrease in the sheet's strength (e.g., ...). Figure 3 (as shown in b).

[0005] This invention addresses the current domestic demand for ultra-high-strength aluminum alloy thin plates in high-end civilian applications such as new energy vehicles and mobile phones, as well as the challenges in the industrial-scale preparation of 700MPa-grade aluminum alloy thin plates. The main issue is that existing industrial-scale preparation methods cannot meet the requirement of a room-temperature tensile strength ≥700MPa. Therefore, this invention provides a process for preparing 750MPa-grade ultra-high-strength aluminum alloy thin plates. Summary of the Invention

[0006] The purpose of this invention is to address the demand for 750MPa-grade ultra-high strength aluminum alloy thin plates in fields such as new energy vehicles and mobile phones, and to propose a method for preparing Al-Zn-Mg-Cu-X series ultra-high strength aluminum alloy thin plates. This method enables the alloy to maintain a tensile strength of over 750MPa even after being prepared into thin plates with a thickness of 1.5 to 3.0 mm, thus achieving industrial-scale mass production and application.

[0007] To solve this technical problem, the technical solution of the present invention is as follows:

[0008] A process for preparing 750MPa grade ultra-high strength aluminum alloy thin plates is provided, targeting 7XXX series aluminum alloys; the pre-treated aluminum alloy slab is placed in a furnace for heating, then taken out for hot rough rolling, and after reaching the predetermined thickness, it is transferred to a hot precision rolling equipment for hot precision rolling into coils; after the hot precision rolled coils are uncoiled, they are subjected to solution treatment + pre-stretching + artificial aging treatment to the peak state.

[0009] The aluminum alloy for which the process is particularly suitable has the following composition and mass percentage of each component: Zn 11.5-13.5%, Mg 2.6-3.6%, Cu 0.5-1.5%, Mn 0.06-0.35%, Zr 0.10-0.20%, Ti 0.02-0.08%, Sc 0.03-0.16%, impurity elements Si≤0.15%, Fe≤0.25%, other impurities ≤0.05% individually, total ≤0.15%, with the balance being Al.

[0010] The process steps are as follows:

[0011] Step 1: Preparation of aluminum alloy rolled slab: The ingot is homogenized, hot-pressed and compacted, and forged to form a rolled slab.

[0012] The homogenization process for aluminum alloy ingots involves holding at 380–420℃ for 4–8 hours, then heating in the furnace to 465–472℃, holding for 24–40 hours, and finally removing from the furnace and cooling to room temperature.

[0013] The temperature of the ingot and mold during hot pressing is 390-450℃, the pressure is not less than 100MPa, and the holding time after the pressure reaches the peak is not less than 5min.

[0014] Forging is carried out using a high-temperature followed by a low-temperature process: during high-temperature forging, the material temperature is 400℃~450℃, the die temperature is not lower than 350℃, and the final forging temperature is not lower than 320℃. The forging deformation in this process accounts for 70~85% of the total forging deformation. During low-temperature forging, the material temperature is 270℃~310℃, the die temperature is not lower than 290℃, and the final forging temperature is not lower than 220℃. The forging deformation in this process accounts for 15~30% of the total forging deformation.

[0015] Step 2, Plate Rolling: The slab processed in Step 1 is heated, and then hot rough rolling and hot finish rolling are performed to obtain a hot finish coil to a specific thickness;

[0016] The slab heating temperature is 440℃~460℃, and the heat preservation process is to keep the slab at the set temperature for 4~6 hours after the surface temperature of the rolled slab reaches the set temperature.

[0017] Hot rough rolling process involves rolling a slab into a plate with a thickness of 15-25mm through multiple passes. The deformation per rolling pass is in the range of 5-30%. After rough rolling, the surface temperature of the plate must not be lower than 360℃.

[0018] The hot finishing rolling process involves rolling the hot rough-rolled sheet into a coil after finishing rolling, and then rolling it to 1.5-3.0 mm using a high-speed, large-reduction method. The rolling speed is not less than 150 m / min, the deformation per pass is not less than 20%, and the surface temperature of the sheet after final rolling is not less than 300℃.

[0019] Step 3, heat treatment of sheet metal: The hot-rolled coils processed in Step 2 are treated to peak strength by solution quenching + pre-stretching + aging treatment.

[0020] During solution quenching, different process parameters are adopted depending on whether the hot-rolled coil is rolled into a whole or unrolled coil, specifically:

[0021] When hot-rolled coils are solution quenched, heating is carried out in a zoned heating manner. The heating zones of the air cushion furnace are usually divided into 1 to 12 zones according to their position. The heating temperature of the first and second zones is 500 to 515℃, and the heating temperature of the subsequent zones is 470 to 480℃. The total heating time shall not be less than 8 minutes. After online quenching, a pre-stretching deformation operation of 0.5% to 1.5% is carried out.

[0022] When hot-rolled coils are uncoiled and sliced, and then subjected to solution quenching, the heating temperature is 470-475℃, the heating time is not less than 20 minutes, the quenching method is room temperature water quenching, the quenching transfer time is not more than 12 seconds, and after quenching, a pre-stretch deformation of 0.8-1.6% is performed.

[0023] The aging process is carried out at 115-125℃ for 20-26 hours. After aging is completed, the product is removed from the furnace and cooled to room temperature.

[0024] The process of this invention combines spray deposition forming ingot casting with a densification process to achieve the goal of preparing high-alloy slabs with high metallurgical quality and excellent thermal processing performance. Combined with the slab hot rolling process, parameters such as rolling temperature, rolling speed, and deformation per pass are controlled to prepare thin plates of 1.5–3 mm thickness. Heat treatment, cold deformation, and artificial aging further enhance the mechanical properties of the thin plates, achieving high material strength. Ultimately, thin plates with performance requirements and thicknesses of 1.5–3.0 mm can be produced.

[0025] Preferably, the homogenization treatment of the ingot in step one is cooled by air cooling or wind cooling.

[0026] Preferably, the ingot in step one is prepared by spray deposition.

[0027] In step one, the hot pressing and densification of the ingot is carried out on a large extrusion press or a forging press equipped with a densification die.

[0028] In step two, the slab heating is carried out in an air-circulating furnace.

[0029] In step three, when the hot-rolled coil is solution quenched as a whole, it is carried out in an air cushion furnace; when the hot-rolled coil is unwound and sliced ​​for solution quenching, it is carried out in a salt bath furnace or a box-type air-circulating heating furnace.

[0030] Step 3, aging treatment, is carried out in an air-circulating furnace, followed by air cooling after aging.

[0031] In step three, the pre-stretching deformation is achieved through a tension roller.

[0032] The beneficial effects of this invention are:

[0033] This invention addresses the issue of large-size aluminum alloy composition range (750MPa) for thin plates with a thickness of 1.5–3.0 mm. It also addresses the difficulty in forming large-size ingots of high-alloy aluminum alloys (prone to cracking during casting) by employing a spray deposition combined with hot pressing densification process to obtain large-size aluminum alloy ingots with excellent metallurgical quality. To fully realize the deformation strengthening effect of the hot-deformation structure and avoid the weakening effect of dynamic recrystallization and static recrystallization during subsequent solution treatment, a high-low temperature variable-temperature forging method followed by high-temperature heating is used to eliminate the grain boundary structure characteristics formed by the original spray deposition, resulting in a slab with excellent thermal processing properties. Then, by precisely controlling process parameters such as temperature, deformation per pass, and rolling speed during hot roughing and finishing rolling, sufficient dynamic recovery occurs while preventing dynamic recrystallization during rolling, thereby eliminating deformation energy storage during hot deformation and obtaining thin plates with typical deformation structures. Finally, the desired properties of the thin plate are obtained through online solution quenching / slice solution quenching + pre-stretching + artificial aging. Specifically, it has the following advantages:

[0034] 1. The process is simple and feasible. All processes in this invention can be implemented on existing industrial aluminum alloy production equipment, making it suitable for large-scale industrial production.

[0035] 2. Outstanding performance. The 7xxx series aluminum alloy sheet prepared by the method of this invention has a thickness range of 1.5 to 3.0 mm and a tensile strength of over 750 MPa. Compared with ordinary 6xxx series aluminum alloys, the strength is increased by 87%, which well meets the requirements of structural weight reduction.

[0036] 3. The process of this invention can process high-alloy ingots with a diameter greater than 600mm, which is larger than the large-size high-alloy ingots (300mm in diameter) prepared by conventional processes. Attached Figure Description

[0037] To more clearly illustrate the technical solutions implemented in this invention, the accompanying drawings used in the embodiments of this invention will be briefly explained below. Obviously, the drawings described below are merely some embodiments of this invention. Those skilled in the art can obtain other drawings based on these drawings without any creative effort.

[0038] Figure 1 The ingots prepared using the components of the present invention and the conventionally prepared flat ingots are described, wherein (a) is a round ingot prepared by spray deposition method and (b) is a flat ingot prepared by conventional DC casting.

[0039] Figure 2 for Figure 1 (a) Morphology of jet-deposited ingots after densification;

[0040] Figure 3 The images show the high-magnification microstructure of the thin plate prepared by the present invention and the microstructure of the thin plate prepared by the comparative process. (a) shows the deformed fiber strip microstructure of the 1.5 mm thin plate prepared by the high-temperature rapid rolling process of the present invention, and (b) shows the recrystallized blocky microstructure of the thin plate prepared by the comparative process 2. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of the embodiments of the present invention clearer, the technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some, not all, of the embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0042] The features of various aspects of the embodiments of the present invention will now be described in detail. In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, it will be apparent to those skilled in the art that the invention can also be practiced without these specific details. The following description of the embodiments is merely intended to provide a better understanding of the invention by illustrating examples. The invention is not limited to any specific setups and methods provided below, but covers all improvements, substitutions, etc., to product structures and methods without departing from the spirit of the invention.

[0043] In the various accompanying drawings and the following description, well-known structures and techniques are not shown in order to avoid unnecessarily obscuring the invention.

[0044] Example 1

[0045] A thin plate with a cross-sectional dimension of δ1.5×1200mm was prepared using the 750MPa aluminum alloy thin plate preparation method involved in this invention. First, a Φ650mm round ingot (e.g., with an alloy composition of Zn 13.0%, Mg 3.2%, Cu 1.0%, Mn 0.15%, Ti 0.03%, Zr 0.12%, Sc 0.05%, impurity elements Si 0.08%, Fe 0.10%, and the balance Al) was prepared by spray deposition. Figure 1 As shown in a, Figure 1 b represents the crack morphology of a flat ingot prepared using traditional casting technology. After homogenization at 400℃ / 6h + 470℃ / 28h and peeling, it is placed in a circular mold with a diameter of 850mm for densification. The mold temperature is 420℃, the material temperature is 430℃, and the maximum pressure is 150MPa. After the pressure head stops moving, the pressure is maintained for 10min, and then the ingot is removed from the furnace and air-cooled to room temperature. Figure 2 (As shown). The billet is then reheated in the furnace to 430°C, with the die temperature at 400°C. After axial elongation, upsetting, reverse elongation, and upsetting, it is squared into a billet with a thickness of 200mm, a width of 1230mm, and a length of 2300mm. The final forging temperature is 350°C. After cooling to room temperature, it is reheated in the furnace to 280°C, then forged in the furnace with the die temperature at 300°C. It is forged downwards along the thickness direction to 160mm, and after shaping, it is air-cooled to room temperature.

[0046] After forging, the slab is placed in an air-circulating furnace and heated until the metal temperature reaches 460℃. It is then held at this temperature for 5 hours, followed by hot rough rolling to 15mm and coiling. The deformation per pass is within the range of 10% to 30%, and the final rolling temperature is 400℃. The sheet is then rolled on a hot finishing mill at a speed of 160m / min, with a deformation per pass ranging from 25% to 40%, to 1.5mm. The final forging temperature is 330℃.

[0047] After hot rolling, the coiled sheet is uncoiled and cut into sheets with a length of 6000mm. Then, it is placed in a box-type air circulation furnace for solution treatment. The heating temperature is 475℃, and the temperature is held for 30 minutes. After that, it is taken out of the furnace for quenching. The quenching water temperature is 25℃, and the transfer time is 8s. After quenching, it is subjected to 1.3% pre-stretch deformation on a thin plate stretching machine.

[0048] After pre-stretching, the sheet material was placed in an air-circulating furnace for artificial aging treatment at 120℃ for 20 hours, followed by air cooling to room temperature. Samples were taken from the aged sheet material to measure longitudinal and transverse tensile properties and observe the high-magnification microstructure of the longitudinal section. The results were compared with those of the same specifications prepared using the same composition, same billet process, and same heat treatment process, but with a different rolling process (rolling process 2: hot roughing at 420℃, finishing at 360℃, hot finishing at 80m / min, and finishing at 280℃). The results are shown in Table 1. Figure 3 As shown.

[0049] Table 1 Performance test results of the 2.0 mm thick sheet prepared according to the present invention

[0050]

[0051] Example 2

[0052] A thin plate with a cross-sectional dimension of δ3.0×1300mm was prepared using the 750MPa aluminum alloy thin plate preparation method involved in this invention. First, a Φ800mm round ingot prepared by spray deposition method with an alloy composition of Zn 11.8%, Mg 2.9%, Cu 1.3%, Mn 0.10%, Ti 0.04%, Zr 0.16%, and Sc 0.04%, impurity elements Si 0.10%, Fe 0.12%, and the balance being Al was homogenized at 380℃ / 8h + 472℃ / 36h and peeled. Then, it was placed in a circular mold with a diameter of 1350mm for densification treatment. The mold temperature was 430℃, the material temperature was 410℃, the maximum pressure was 180MPa, and after the pressure head stopped moving, the pressure was held for 15min. After being removed from the furnace, it was air-cooled to room temperature. The billet is then reheated in the furnace to 420°C, with the die temperature at 410°C. It is then forged into a square billet with a thickness of 330mm, a width of 1360mm, and a length of 3300mm by radial drawing, upsetting, reverse drawing, and upsetting, with a final forging temperature of 360°C. After cooling to room temperature, it is reheated in the furnace to 290°C, then forged with the die temperature at 320°C, and forged downwards along the thickness direction to 260mm. After shaping, it is air-cooled to room temperature.

[0053] After forging, the slab is placed in an air-circulating furnace for heating. Once the furnace gas temperature reaches 480℃, it is then placed into the furnace and held at 450℃ for 6 hours. Afterward, it is hot-rolled to 12mm and coiled, with a deformation per pass ranging from 15% to 30%, and a final rolling temperature of 420℃. The sheet is then rolled on a hot finishing mill at a speed of 180m / min, with a deformation per pass ranging from 20% to 38%, to 3.0mm, and a final forging temperature of 325℃.

[0054] After hot finishing, the coiled sheet is uncoiled and cut into sheets with a length of 5000mm. Then, it is placed in a salt bath furnace for solution treatment. The heating temperature is 473℃, and the temperature is held for 25 minutes. After that, it is taken out of the furnace for quenching. The quenching water temperature is 23℃, and the transfer time is 10s. After quenching, it is subjected to 1.5% pre-stretch deformation on a thin plate stretching machine.

[0055] After pre-stretching, the sheet material was placed in an air-circulating furnace for artificial aging treatment at 125℃ for 22 hours, and then air-cooled to room temperature. Samples were taken from the aging sheet material, and the longitudinal and transverse tensile properties were measured. The results are shown in Table 2.

[0056] Table 2 Performance test results of the 3.0 mm thick sheet prepared according to the present invention

[0057]

[0058] Table 1 shows that the hot rolling process parameters of the hot roughing and hot finishing rolling adopted in this invention are very important. Different hot rolling process parameters affect the mechanical properties of the thin plate. A suitable hot rolling process can make the tensile strength of the thin plate greater than 750 MPa. Table 2 shows that the longitudinal and transverse mechanical properties of the thin plate are uniform. The thin plate prepared by the process of this invention has the superior strength of 750 MPa, uniform microstructure and properties, and can be prepared under industrial conditions, making it suitable for automobiles, mobile phones and other fields.

[0059] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, but the protection scope of the present invention is not limited thereto. Any person skilled in the art can easily conceive of various equivalent modifications or substitutions within the technical scope disclosed in the present invention, and these modifications or substitutions should be covered within the protection scope of the present invention.

Claims

1. A process for preparing 750MPa grade ultra-high strength aluminum alloy thin plates, characterized in that, The pre-treated aluminum alloy slab is heated in a furnace and then hot-rolled to the predetermined thickness. It is then transferred to a hot finishing rolling mill for hot finishing rolling into coils. After uncoiling, the hot-finished coils undergo solution treatment, pre-stretching, and artificial aging to reach their peak condition. The process steps are as follows: Step 1: Preparation of aluminum alloy rolled slab: The ingot is homogenized, hot-pressed and compacted, and then forged to prepare a rolled slab. The homogenization process for aluminum alloy ingots involves holding at 380~420℃ for 4~8 hours, then heating in the furnace to 465~472℃, holding for 24~40 hours, and finally removing from the furnace and cooling to room temperature. The temperature of the ingot and mold during hot pressing is 390~450℃, the pressure is not less than 100MPa, and the holding time after the pressure reaches the peak is not less than 5min. Forging is performed using a high-temperature followed by a low-temperature process: During high-temperature forging, the material temperature is 400-450℃, the die temperature is no lower than 350℃, and the final forging temperature is no lower than 320℃. The forging deformation during this process accounts for 70-85% of the total forging deformation. During low-temperature forging, the material temperature is 270-310℃, the die temperature is no lower than 290℃, and the final forging temperature is no lower than 220℃. The forging deformation during this process accounts for 15-30% of the total forging deformation. Step 2, Plate Rolling: The slab processed in Step 1 is heated, and then hot rough rolling and hot finish rolling are performed to obtain a hot finish coil to a specific thickness; The slab heating temperature is 440~460℃, and the heat preservation process is to keep the slab at the set temperature for 4~6 hours after the surface temperature of the rolled slab reaches the set temperature. Hot rough rolling process involves rolling a slab into a plate with a thickness of 15-25mm through multiple passes. The deformation per rolling pass is in the range of 5-30%. After rough rolling, the surface temperature of the plate must not be lower than 360℃. The hot finishing rolling process involves rolling the hot rough-rolled sheet into a coil after finishing rolling, and then rolling it to 1.5~3.0mm using a high-speed, large-reduction method. The rolling speed is not less than 150m / min, the deformation per pass is not less than 20%, and the surface temperature of the sheet after final rolling is not less than 300℃. Step 3, heat treatment of sheet metal: The hot-rolled coils processed in Step 2 are treated to peak strength by solution quenching + pre-stretching + aging treatment. During solution quenching, different process parameters are adopted depending on whether the hot-rolled coil is rolled into a whole or unrolled coil, specifically: When the hot-rolled coil is solution quenched in the air cushion furnace, the heating is carried out in a zone heating method. The heating temperature of the first and second zones is 500~515℃, and the heating temperature of the subsequent zones is 470~480℃. The total heating time shall not be less than 8 minutes. After the online quenching is completed, a pre-stretching deformation operation of 0.5~1.5% is carried out. When hot-rolled coils are uncoiled and sliced, and then subjected to solution quenching in a salt bath furnace or a box-type air-circulating heating furnace, the heating temperature is 470~475℃, the heating time is not less than 20min, the quenching method is room temperature water quenching, the quenching transfer time is not more than 12s, and 0.8~1.6% pre-stretch deformation is performed after quenching. The aging process is 115~125℃ / 20~26h. After aging is completed, the product is removed from the furnace and cooled to room temperature. The aluminum alloy for which the process is applicable has the following composition and mass percentage of each component: Zn 11.5-13.5%, Mg 2.6-3.6%, Cu 0.5-1.5%, Mn 0.06-0.35%, Zr 0.10-0.20%, Ti 0.02-0.08%, Sc 0.03-0.16%, impurity elements Si≤0.15%, Fe≤0.25%, other impurities ≤0.05% individually, total ≤0.15%, with the balance being Al.

2. The process according to claim 1, characterized in that: The process is applicable to sheet thicknesses of 1.5~3.0mm.

3. The process according to claim 1, characterized in that: The homogenization treatment of the ingot in step one is cooled by air cooling or wind cooling.

4. The process according to claim 1, characterized in that: In step one, the hot pressing and densification of the ingot is carried out on a large extrusion press or a forging press equipped with a densification die.

5. The process according to claim 1, characterized in that: In step one, the ingot is prepared using a spray deposition method.

6. The process according to claim 1, characterized in that: In step two, the slab heating is carried out in an air-circulating furnace.

7. The process according to claim 1, characterized in that: Step 3, aging treatment, is carried out in an air-circulating furnace, followed by air cooling after aging.

8. The process according to claim 1, characterized in that: In step three, when the hot-rolled coil is solution quenched as a whole, it is carried out in an air cushion furnace; when the uncoiled and sliced ​​coil is solution quenched, it is carried out in a salt bath furnace or a box-type air-circulating heating furnace.

9. The process according to claim 1, characterized in that: In step three, the pre-stretching deformation is achieved through a tension roller.

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