Aluminum alloy profile and its on-line spray quenching production method

Abstract

The application provides an aluminum alloy profile and an online spray quenching production method thereof. The method comprises the following steps: (1) heating an aluminum alloy ingot to 440-490 DEG C for extrusion, and controlling the temperature of the aluminum alloy profile at the outlet of the extrusion die to be 435-445 DEG C; (2) making the profile obtained in step (1) enter a spray zone, and receiving the spray quenching of the cooling liquid from the top, the side and the bottom of a spraying device; and (3) performing online stretch straightening on the quenched profile obtained in step (2). Through the accurate control of the extrusion outlet temperature, the adoption of the asymmetric spraying strategy to compensate the gravity influence, and the integration of the quenching and the stretch straightening, the application can inhibit the coarse grain ring, reduce the quenching deformation, shorten the production cycle, and make the mechanical properties of the profile meet the aviation standards.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy heat treatment technology, specifically to an aluminum alloy profile and its online spray quenching production method, which is particularly suitable for direct quenching treatment of 2A12 aluminum alloy profiles after extrusion. Background Technology

[0002] 2A12 aluminum alloy (corresponding to US standard 2024) is a typical Al-Cu-Mg series high-strength aerospace structural material. Its excellent mechanical properties rely on the strengthening phases such as Al2CuMg (S phase) precipitated during aging after solution quenching. In the traditional manufacturing process, 2A12 profiles often use offline quenching: after extrusion forming, the profile is transferred to a heating furnace for reheating to the solution temperature (usually 490-495℃) and held at that temperature, and then quickly transferred to a water tank or spray device for quenching. This "extrusion → cooling → reheating → quenching" process consists of multiple discontinuous steps, resulting in disadvantages such as long production cycle, high energy consumption, prominent coarse grain ring problems, and severe quenching deformation.

[0003] Online quenching technology utilizes the residual heat from extrusion for direct quenching, eliminating the need for secondary heating and theoretically offering significant advantages in process simplification, energy efficiency, and high performance. However, for alloys like 2A12 with stringent strength requirements, achieving online quenching faces significant challenges: the extrusion exit temperature is difficult to stably control within the solution treatment temperature range; ensuring uniform cooling of complex cross-section profiles is challenging; and there is a lack of differentiated cooling designs for different wall thicknesses. Currently, a mature, mass-producible online spray quenching solution that simultaneously optimizes microstructure, achieves strength targets, and controls deformation has not yet been developed. Summary of the Invention

[0004] After long-term research, it was unexpectedly discovered that the online spray quenching process for aluminum alloy profiles, which involves the following steps, achieves continuous production of high-performance profiles with no coarse grain rings, low deformation, and integrated online stretching and straightening by precisely controlling the extrusion exit temperature, differentiating spray cooling, and online stretching and straightening.

[0005] Therefore, based on the above findings, in a first aspect, the present invention provides an online spray quenching production method for aluminum alloy profiles, comprising the following steps: (1) Heat the aluminum alloy ingot to 440-490℃ for extrusion, and control the temperature of the aluminum alloy profile at the extrusion die outlet to 435-445℃; (2) The profile obtained in step (1) is brought into the spray zone to receive coolant spray quenching from the top, side and bottom of the spray device; (3) The quenched profile obtained in step (2) is subjected to online tensile straightening.

[0006] In some implementations, the aluminum alloy is a 2-series aluminum alloy.

[0007] In some embodiments, the aluminum alloy is 2A12 aluminum alloy.

[0008] In some implementations, in step (1), the extrusion speed is 0.2-0.6 mm / s.

[0009] In some embodiments, in step (1), the extrusion speed is 0.2 mm / s, 0.3 mm / s, 0.4 mm / s, 0.5 mm / s, or 0.6 mm / s.

[0010] In some implementations, in step (2), the coolant spray intensity at the bottom is 100% of the baseline value, and the coolant spray intensity at the top and sides is 70-85% of the baseline value.

[0011] In some implementations, in step (2), the distance between the spray zone and the extrusion die outlet is within 1 m, and the transfer time of the profile from the extrusion die outlet to entering the spray zone is within 15 s.

[0012] In some implementations, in step (3), the permanent deformation after stretching and straightening is 1-3%.

[0013] In another aspect of the invention, an aluminum alloy profile is provided, which is produced using the above-described production method.

[0014] The method of the present invention has at least one of the following beneficial effects: (1) Uniform and refined structure: By precisely controlling the extrusion outlet temperature in the high temperature range of 435-445℃, the profile is ensured to be in a fully solid solution state when entering the quenching zone. Combined with rapid spray cooling, a highly supersaturated solid solution is obtained. At the same time, secondary heating is avoided, and the formation of coarse grain rings is suppressed from the source. The thickness of the surface coarse grain rings can be controlled to below 0.5 mm or even completely eliminated.

[0015] (2) Uniform cooling and small deformation: The bottom-reinforced asymmetric spraying strategy is adopted to compensate for the downward flow effect of water caused by gravity, so as to achieve uniform cooling of the profile in the circumference and significantly reduce the internal stress and warping deformation during quenching.

[0016] (3) Integrated process and high efficiency: The extrusion, online quenching and online stretching and straightening are integrated into a continuous process, eliminating the need for offline reheating, heat preservation, transfer and separate straightening. The production cycle is shortened from more than 5 days to 1 day, and energy consumption is greatly reduced.

[0017] (4) Excellent mechanical properties: After online quenching and T4 aging, the tensile strength is ≥410 MPa, the yield strength is ≥295 MPa, and the elongation is ≥10%, which meets or exceeds the requirements of aviation standards. Attached Figure Description

[0018] To clearly illustrate the technical solutions in this invention or related technologies, the accompanying drawings used in describing this invention or related technologies will be briefly introduced below. Obviously, the drawings in the following description only relate to some embodiments of this invention. For those skilled in the art, other drawings can be obtained based on these drawings without any inventive effort.

[0019] Figure 1 These are low-magnification microstructure comparison photographs of the profiles prepared in Example 1 (the present invention) and Comparative Example 3 (offline quenching), where a is the sample of Example 1 and b is the sample of Comparative Example 3. Figure 2 This is a photograph of the surface cracks caused by excessive extrusion speed in Comparative Example 2. Detailed Implementation

[0020] To better illustrate the technical means and effects of the present invention, the invention is further described below with reference to non-limiting examples. The embodiments of the present invention (including the descriptions provided in the embodiments) are intended to illustrate the embodiments of the invention and are not intended to limit the scope of any claim. According to the present invention, those skilled in the art will understand that many changes can be made to the disclosed embodiments without departing from the spirit and scope of the invention, and the same or similar results can still be obtained.

[0021] Unless otherwise stated, the terms used in this specification and claims have the following meanings.

[0022] In this document, the term "2-series aluminum alloys" refers to a series of aluminum alloys with copper as the main alloying element, including 2A12 aluminum alloy (corresponding to US Standard 2024), which is a key structural material in the aerospace field. In this invention, 2A12 aluminum alloy is preferred, and its typical composition by mass percentage includes: Cu 3.8-4.9%, Mg 1.2-1.8%, Mn 0.3-0.9%, with the balance being Al and unavoidable impurities.

[0023] In this article, the term "online spray quenching" refers to the method in which, after the profile leaves the extrusion die outlet in the extrusion production line, it directly enters the spray cooling device for quenching treatment without cooling and reheating.

[0024] In this article, the term "online tension straightening" refers to a process in which profiles, after quenching and before fully cooling to room temperature, are directly fed into a tension straightening machine by a traction device, and a tensile force exceeding the material's yield strength is applied to induce plastic deformation (the amount of permanent deformation is usually 1-3%), thereby eliminating residual quenching stress and correcting straightness.

[0025] In this document, the term "spray intensity" refers to the volume or mass of coolant sprayed onto a unit surface area of ​​the profile per unit time. In this invention, the spray intensity at the bottom is taken as 100% of the baseline value, and the spray intensity at other locations is expressed as a percentage of the baseline value.

[0026] In this article, the term "offline quenching" refers to the process of cooling the extruded profile to room temperature, then re-inserting it into a heating furnace for solution treatment, followed by quenching.

[0027] In this paper, the term "coarse grain ring" refers to a coarse recrystallized structure layer in the surface region of an aluminum alloy extruded profile, in which the grain size is significantly larger than the internal matrix grains. Its depth is usually measured from the profile surface toward the center.

[0028] In this paper, the term "asymmetric flow distribution" refers to setting different spray intensities at different circumferential positions (top, side, bottom) of the profile within the same spray cooling zone to compensate for the uneven cooling caused by factors such as gravity.

[0029] In this paper, the term "permanent deformation stretching" refers to a straightening method that applies a tensile force exceeding the yield strength to a quenched profile, causing it to undergo plastic deformation (typically 1%-3% elongation) to eliminate residual stress.

[0030] In this article, the term "T4 state" refers to the state of an aluminum alloy after solution quenching and natural aging until it is basically stable.

[0031] The following uses 2A12 aluminum alloy from the 2-series aluminum alloys as an example to illustrate the online spray quenching production method of the present invention.

[0032] In some embodiments, the 2A12 alloy ingot is heated to 440-490°C, for example, to 440°C, 445°C, 450°C, 455°C, 460°C, 465°C, 470°C, 475°C, 480°C, 485°C, or 490°C, preferably 480°C, and extruded by controlling the extrusion speed to 0.2-0.6 mm / s, for example, to 0.2 mm / s, 0.3 mm / s, 0.4 mm / s, 0.5 mm / s, or 0.6 mm / s, and the temperature of the profile at the die exit is stably controlled at 435-445°C, for example, within a window of 435°C, 436°C, 437°C, 438°C, 439°C, 440°C, 441°C, 442°C, 443°C, 444°C, or 445°C, preferably 440°C. To ensure that the profile remains above the sufficient solution temperature when entering the quenching zone, the temperature range used is higher than that known in conventional processes. This provides a prerequisite for obtaining a highly supersaturated solid solution and achieves a "seamless temperature relay" from extrusion to quenching. At the same time, to avoid excessively high temperatures that could lead to reduced plasticity or surface quality issues, a lower extrusion speed is selected to ensure material dimensions and surface quality.

[0033] In some implementations, an online spray zone is set immediately after the extrusion die exit. This zone is equipped with independently controlled top, side, and bottom spray arrays. An "asymmetric flow distribution" strategy is employed, setting the bottom spray intensity as a baseline (100%), while the top and side spray intensities are set to 70-85% of the baseline, for example, 70%, 71%, 72%, 73%, 74%, 75%, 76%, 77%, 78%, 79%, 80%, 81%, 82%, 83%, 84%, or 85%, preferably 80%. This design is based on the effect of gravity on water flow distribution, compensating for the cooling intensity reduction caused by the natural downward flow of water by enhancing bottom cooling, thereby achieving uniform circumferential cooling of the profile and effectively avoiding warping deformation caused by uneven cooling.

[0034] In addition, the distance between the spray zone and the extrusion die outlet is set to within 1 m, for example, it can be set to 0.9 m, 0.8 m, 0.7 m, 0.6 m, 0.5 m, 0.4 m, 0.3 m, 0.2 m, or 0.1 m; the transfer time of the profile from the extrusion die outlet to entering the spray zone is within 15 s, for example, the transfer time can be 14 s, 13 s, 12 s, 11 s, 10 s, 9 s, 8 s, 7 s, 6 s, 5 s, 4 s, 3 s, 2 s, or 1 s.

[0035] In some implementations, the quenched profile is immediately fed into a tension straightener by a traction machine for 1-3% permanent deformation stretching, for example, 1%, 2%, or 3%. This invention performs 1-3% permanent deformation stretching immediately after quenching via a traction machine. This step effectively eliminates residual stress generated during quenching. Furthermore, this step is completed continuously online, avoiding the straightening process after quenching found in traditional processes. Compared to traditional processes, this integrated process significantly shortens the production cycle, reduces equipment investment and energy consumption, and shortens the time for transferring profiles after quenching. Faster straightening better ensures the straightness and geometric accuracy of the profile, guaranteeing high strength and low deformation product quality. By precisely controlling the stretching amount and temperature, this invention overcomes the difficulties in traditional straightening processes, ensuring that 2A12 aluminum alloy profiles do not generate secondary stress during straightening while maintaining good mechanical properties.

[0036] In summary, the online spray quenching method of this invention effectively shortens the production process and significantly improves the performance and production efficiency of aluminum profiles through the process route of heating-extrusion-spray water cooling-on-line stretching. Compared with traditional offline quenching, this invention can avoid coarse grain ring defects, reduce grain coarsening, and eliminate the need for subsequent large-scale straightening, thus reducing costs and energy consumption.

[0037] The online spray quenching production system for aluminum alloys used in this invention includes: an extrusion device comprising an extrusion die with an outlet; a spray device located after the outlet of the extrusion die of the extrusion device, comprising a top spray array, a side spray array, and a bottom spray array; a control device connected to each spray array (capable of zoned adjustment) to control at least one parameter among the flow rate, pressure, and temperature of the coolant; an online traction and tension straightening device located at the rear end of the spray array; and a sensing and closed-loop control unit for collecting the die outlet temperature, profile temperature, and traction speed (capable of achieving "seamless temperature relay" and dynamic adjustment of spray parameters). The extrusion device is equipped with a control unit to control the profile temperature at the extrusion die outlet to be between 435-445°C, for example, 435°C, 436°C, 437°C, 438°C, 439°C, 440°C, 441°C, 442°C, 443°C, 444°C, or 445°C; the distance between the extrusion die outlet and the spraying device is within 1 m, for example, 0.9 m, 0.8 m, 0.7 m, 0.6 m, 0.5 m, 0.4 m, 0.3 m, 0.2 m, or 0.1 m; the distance between the spraying device and the traction and tension straightening device is within 20 m, for example, less than or equal to 15 m, 10 m, 9 m, 8 m, 7 m, 6 m, or 5 m.

[0038] The present invention also provides an aluminum alloy profile produced using the above-described production method of the present invention, wherein the coarse grain ring thickness of the surface layer of the aluminum alloy profile is ≤0.5 mm; and the specified straightness tolerance can be met without offline heating and straightening process in the factory condition.

[0039] Example

[0040] Example 1

[0041] 2A12 aluminum alloy ingots were used, with a composition conforming to GB / T 3190 standard. The ingots were heated to 480℃ and hot-extruded at an extrusion speed of 0.3 mm / s, with the profile temperature at the die exit controlled at approximately 435℃. Immediately after leaving the die, the profile entered an online spraying zone. The spraying configuration was: 100% intensity at the bottom, and 80% intensity each at the top and sides. After quenching, the profile was immediately fed into a tension straightener by a traction machine for 2% permanent deformation tensile testing. Performance was tested after T4 natural aging.

[0042] Example 2

[0043] The 2A12 aluminum alloy profile was produced in the same manner as in Example 1, except that the outlet temperature of the profile was controlled at 440°C.

[0044] Comparative Example 1 (Lower Outlet Temperature)

[0045] The 2A12 aluminum alloy profiles were produced in the same manner as in Example 1, except that the ingots were heated to 460°C and the exit temperature of the profiles was controlled at 430°C.

[0046] Comparative Example 2 (Extrusion speed too fast)

[0047] 2A12 aluminum alloy profiles were produced in the same manner as in Example 1, except that the extrusion speed was increased to 0.8 mm / s and the exit temperature was controlled at 450°C.

[0048] Comparative Example 3 (Offline Quenching)

[0049] The ingot was heated to 440°C, extruded at a speed of 0.8 mm / s, and exited at 380°C. After extrusion, the profile was cooled to room temperature and then solution-treated at 490°C for 35 min in a vertical quenching furnace, followed by water quenching.

[0050] The tensile strength, yield strength, elongation, coarse grain ring condition, and processing cycle of the aluminum alloy profiles produced in Examples 1-2 and Comparative Examples 1-3 are summarized in Table 1 below.

[0051] Table 1. Performance of aluminum alloy profiles in Examples 1-2 and Comparative Examples 1-3

[0052] Note: For online quenching, the quenching temperature refers to the profile temperature at the extrusion die exit (the profile at the extrusion die exit will immediately enter the online spray quenching system, so the quenching temperature is considered to be equal to the profile temperature at the extrusion die exit). For offline quenching, the quenching temperature is the solution temperature.

[0053] A comprehensive performance comparison of Examples 1-2 and Comparative Examples 1-3 shows that Examples 1 and 2, employing the online spray quenching method of the present invention, both achieved the absence of coarse-grained ring structures under extrusion exit temperatures of 435℃ and 440℃, respectively (see...). Figure 1 a) The production cycle is only 1 day, and the mechanical properties are excellent (Example 1: tensile strength 466 MPa, yield strength 296 MPa, elongation 18%; Example 2: tensile strength 485 MPa, yield strength 319 MPa, elongation 18%). In contrast, Comparative Example 1 suffered from insufficient solution treatment due to the low extrusion exit temperature (430℃), resulting in a decrease in tensile strength to 432 MPa, yield strength to 270 MPa, and a slight decrease in elongation (17.5%). Although Comparative Example 2 achieved good mechanical properties (tensile strength 485 MPa, yield strength 322 MPa, elongation 18%), the excessively high extrusion speed (0.8 mm / s) caused surface cracks, resulting in a substandard product (see [link to product description]). Figure 2 Comparative Example 3, using a traditional offline quenching process, achieved slightly higher tensile strength (490 MPa) and yield strength (335 MPa) than the embodiments of the present invention. However, its processing cycle was as long as 5 days, and the profile exhibited severe bending and torsion, accompanied by obvious coarse grain rings (see...). Figure 1 (b) The elongation (16.5%) is also lower than that of the present invention. The above comparison shows that the online spray quenching process of the present invention can maintain excellent comprehensive mechanical properties while significantly shortening the production cycle, eliminating coarse grain rings and quenching deformation, thus achieving the goal of high-efficiency and high-quality production.

[0054] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features; and these modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the various embodiments of the present invention.

Claims

1. An online spray quenching production method for aluminum alloy profiles, characterized in that, include: (1) Heat the aluminum alloy ingot to 440-490℃ for extrusion, and control the temperature of the aluminum alloy profile at the extrusion die outlet to 435-445℃; (2) The profile obtained in step (1) is brought into the spray zone to receive coolant spray quenching from the top, side and bottom of the spray device; (3) The quenched profile obtained in step (2) is subjected to online tensile straightening.

2. The method according to claim 1, characterized in that, The aluminum alloy is a 2-series aluminum alloy.

3. The method according to claim 2, characterized in that, The aluminum alloy is 2A12 aluminum alloy.

4. The method according to claim 1, characterized in that, In step (1), the extrusion speed is 0.2-0.6 mm / s.

5. The method according to claim 1, characterized in that, In step (1), the extrusion speed is 0.2 mm / s, 0.3 mm / s, 0.4 mm / s, 0.5 mm / s or 0.6 mm / s.

6. The method according to claim 1, characterized in that, In step (2), the coolant spray intensity at the bottom is taken as 100% of the baseline value, and the coolant spray intensity at the top and the side is taken as 70-85% of the baseline value.

7. The method according to claim 1, characterized in that, In step (2), the distance between the spray zone and the extrusion die outlet is within 1 m, and the transfer time of the profile from the extrusion die outlet to the spray zone is within 15 s.

8. The method according to claim 1, characterized in that, In step (3), the permanent deformation after stretching and straightening is 1-3%.

9. An aluminum alloy profile, characterized in that, Produced using the production method described in any one of claims 1 to 8.

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