A 6-series aluminum alloy and a method of manufacturing the same

Abstract

This invention provides a 6-series aluminum alloy, comprising, by mass percentage: Mg 1-1.8%, Si 0.8-1.6%, Mn 0.5-1.0%, Zr 0.08-0.2%, Cr 0.1-0.3%, Nb 0.1-0.4%, with the balance being Al. This application also provides a method for preparing the 6-series aluminum alloy. The aluminum alloy provided in this application, through the introduction of reinforcing phases, is beneficial for improving strength. Furthermore, the two-stage homogenization and high extrusion exit temperature processes in the preparation method enable the production of aluminum alloy extruded profiles with a tensile strength greater than 440 MPa.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, and in particular to a 6-series aluminum alloy and its preparation method. Background Technology

[0002] Lightweighting of new energy vehicles is a major trend in current automotive development. Aluminum alloys are the main material for lightweighting automobiles. Therefore, developing high-performance, efficient, and low-cost aluminum alloys is key to automotive lightweighting. Currently, the main types of aluminum alloys used in automobiles include aluminum alloy die castings, aluminum alloy sheet stampings, and aluminum alloy extrusions. Although aluminum alloy extrusions account for only about 10%, they are used in critical parts such as anti-collision beams and main structural beams, and have the highest requirements for comprehensive performance.

[0003] The tensile strength of existing high-strength 6xxx series aluminum alloys is typically below 400 MPa, and requires offline quenching to achieve this. The latest international advancements in high-strength 6xxx series alloys are as follows: Alcoa has developed the A210 ExtruStrong alloy with a tensile strength ≥390 MPa in T6 temper (offline quenching); Kennametal has developed the HSA6420 alloy with a tensile strength ≥430 MPa in T6 temper (offline quenching). However, 6xxx series alloys that can be quenched online typically achieve a tensile strength of around 300 MPa. Compared to online quenching, offline quenching significantly increases costs and is more complex. Therefore, existing 6xxx series aluminum alloys still cannot meet the demands of lightweight new energy vehicles for high-strength, high-efficiency, and low-cost manufacturing.

[0004] To address the aforementioned issues, aluminum alloys with a tensile strength greater than 440MPa for the main structural beams of new energy vehicles, belonging to the 6xxx series, are currently in the research and development stage. Therefore, developing a high-strength, high-efficiency, low-cost 6xxx series aluminum alloy suitable for online quenching is of great significance. Summary of the Invention

[0005] The technical problem solved by this invention is to provide a 6-series aluminum alloy, which has high strength.

[0006] In view of this, this application provides a 6-series aluminum alloy comprising, by mass percentage: Mg 1-1.8%, Si 0.8-1.6%, Mn 0.5-1.0%, Zr 0.08-0.2%, Cr 0.1-0.3%, Nb 0.1-0.4%, with the balance being Al.

[0007] Preferably, the Nb content is 0.2–0.3 wt%; and / or, the Mg content is 1.2–1.6 wt%; and / or, the Si content is 1.0–1.4 wt%.

[0008] This application also provides a method for preparing the aforementioned 6-series aluminum alloy, comprising the following steps:

[0009] S1) The raw materials are prepared according to the composition ratio of 6-series aluminum alloy, and then smelted to obtain molten aluminum;

[0010] S2) Cast the molten aluminum to obtain a 6-series aluminum alloy ingot;

[0011] S3) The 6-series aluminum alloy ingot is subjected to homogenization treatment by first heating it to 300-500℃ and holding it for 10-15 hours, then raising the temperature to 500-600℃ and holding it for 15-25 hours.

[0012] S4) The 6-series aluminum alloy ingot obtained in step S3) is extruded, and the extrusion outlet temperature is 520-550°C to obtain an extruded profile.

[0013] S5) The extruded profile is quenched online and then aged.

[0014] Preferably, the smelting step specifically includes:

[0015] Aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are heated and melted. Magnesium ingots are added using a magnesium-adding frame when the melt temperature reaches 725-745℃. Before adding magnesium, 0.0010% beryllium is added and then refined.

[0016] After the composition is qualified, continue refining at a temperature of 740-760℃ for 20-40 minutes. After each refining, let it stand for 20-40 minutes and then remove the slag. After the last standing and slag removal, pour the melt from the melting furnace into the holding furnace through the trough. During the furnace pouring process, turn on the permeable brick for refining. The pressure of the permeable brick is 650-950 kPa and the flow rate is 50-80 L / min.

[0017] Preferably, the casting is a semi-continuous direct cooling casting, the casting speed is 25-50 mm / min, and the water flow rate is 100-150 m³ / min. 3 / h.

[0018] Preferably, the heating rate of the homogenization process is 15–25 °C / h.

[0019] Preferably, the initial heating temperature is 340–400°C, and the temperature for further heating is 540–570°C.

[0020] Preferably, the extrusion temperature is 500–520°C, and the temperature is maintained for 2–4 hours.

[0021] Preferably, the water immersion temperature for online quenching is 520–550°C.

[0022] Preferably, the aging temperature is 170–200°C, and the holding time is 6–12 hours.

[0023] This application provides a 6-series aluminum alloy comprising: Mg 1–1.8%, Si 0.8–1.6%, Mn 0.5–1.0%, Zr 0.08–0.2%, Cr 0.1–0.3%, Nb 0.1–0.4%, with the balance being Al. The 6-series aluminum alloy provided in this application introduces Mg, Nb, Zr, and Mn to form the main age-hardening phase Mg2Si and the non-age-hardening phases Al3Nb, Al3Zr, Al3Cr, and Al6Mn, among other reinforcing phases. Simultaneously, a new reinforcing phase, L12-Al3Nb, is introduced to supplement the reinforcement, thereby contributing to the improvement of the strength of the 6-series aluminum alloy.

[0024] Furthermore, this application provides a method for preparing 6-series aluminum alloys, which includes sequentially performing batching, melting, casting, homogenization, extrusion, online quenching, and aging. This application achieves the preparation of extruded aluminum alloy profiles with tensile strength greater than 440 MPa and capable of online quenching by combining slow two-stage homogenization and high extrusion outlet temperature online quenching processes. Detailed Implementation

[0025] To further understand the present invention, preferred embodiments of the present invention are described below in conjunction with examples. However, it should be understood that these descriptions are only for further illustrating the features and advantages of the present invention, and not for limiting the scope of the claims of the present invention.

[0026] Given the difficulty in achieving tensile strengths greater than 440 MPa in existing online quenching processes for 6-series aluminum alloys, this application provides a 6-series aluminum alloy and its preparation method. Based on research into the strengthening and refining mechanism of L12-Al3Nb in aluminum alloys, it proposes a high-strength online quenchable process enhanced by non-aging precipitation strengthening phases, thus realizing the preparation of a high-strength 6-series aluminum alloy capable of online quenching. Specifically, this invention discloses a 6-series aluminum alloy, comprising, by mass percentage: Mg 1–1.8%, Si 0.8–1.6%, Mn 0.5–1.0%, Zr 0.08–0.2%, Cr 0.1–0.3%, Nb 0.1–0.4%, with the balance being Al.

[0027] In the 6-series aluminum alloys provided in this application, Mg affects the strength, and its content is more specifically 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, 1.6wt%, 1.7wt%, or 1.8wt%. When the Mg content is less than 1wt%, the alloy's strength performance is relatively low.

[0028] Si also affects strength, and its content is more specifically 0.8wt%, 0.9wt%, 1.0wt%, 1.1wt%, 1.2wt%, 1.3wt%, 1.4wt%, 1.5wt%, or 1.6wt%. If the Si content is less than 0.8wt%, the alloy's strength properties will be lower.

[0029] Mn can precipitate the strengthening phase Al6Mn to improve the strength of aluminum alloys, with its content being more specifically 0.5wt%, 0.6wt%, 0.7wt%, 0.8wt%, 0.9wt%, or 1.0wt%.

[0030] Zr can precipitate a strengthening phase, Al3Zr, which, as a non-aging strengthening phase, is beneficial to improving strength. Its content is more specifically 0.08wt%, 0.09wt%, 0.10wt%, 0.11wt%, 0.12wt%, 0.13wt%, 0.14wt%, 0.15wt%, 0.16wt%, 0.17wt%, 0.18wt%, 0.19wt%, or 0.20wt%.

[0031] Cr can precipitate a strengthening phase Al3Cr, which, as a non-aging strengthening phase, is beneficial to improving strength. Its content is more specifically 0.1wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.20wt%, 0.21wt%, 0.23wt%, 0.25wt%, 0.28wt%, or 0.30wt%.

[0032] Nitrogen (Nb) can precipitate the strengthening phase Al3Nb, which acts as a second-phase strengthening agent. Furthermore, Al3Nb, as a high-temperature precipitate, is independent of the quenching-aging precipitation process, significantly improving strength after online quenching. Nb has little effect on the alloy's quenching sensitivity and is beneficial for the precipitation of the main strengthening phase after online quenching. Excessive Nb content increases the alloy's quenching sensitivity, affecting the precipitation of the Mg2Si main strengthening phase and reducing the strength improvement effect. Specifically, Nb content should be 0.10wt%, 0.12wt%, 0.15wt%, 0.18wt%, 0.20wt%, 0.23wt%, 0.26wt%, 0.28wt%, 0.30wt%, 0.32wt%, 0.33wt%, 0.36wt%, 0.38wt%, or 0.40wt%.

[0033] This application also provides a method for preparing 6-series aluminum alloys, including the following steps:

[0034] S1) The raw materials are prepared according to the composition ratio of 6-series aluminum alloy, and then smelted to obtain molten aluminum;

[0035] S2) Cast the molten aluminum to obtain a 6-series aluminum alloy ingot;

[0036] S3) The 6-series aluminum alloy ingot is first heated to 300-500℃ and held for 10-15 hours, then heated to 500-600℃ and held for 15-25 hours for homogenization treatment.

[0037] S4) The 6-series aluminum alloy ingot obtained in step S3) is extruded, and the extrusion outlet temperature is 520-550°C to obtain an extruded profile.

[0038] S5) The extruded profile is quenched online and then aged.

[0039] The preparation method provided for 6-series aluminum alloys first involves batching raw materials according to the composition ratio of 6-series aluminum alloys. Specific raw materials may include aluminum ingots, magnesium ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys. These raw materials are then mixed according to the specified ratio and smelted to obtain molten aluminum. In this application, the smelting specifically involves:

[0040] Aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are heated and melted. Magnesium ingots are added using a magnesium-adding frame when the melt temperature reaches 725-745℃. Before adding magnesium, 0.0010% beryllium is added and then refined.

[0041] After the composition is qualified, continue refining at a temperature of 740-760℃ for 20-40 minutes. After each refining, let it stand for 20-40 minutes and then remove the slag. After the last standing and slag removal, pour the melt from the melting furnace into the holding furnace through the trough. During the furnace pouring process, turn on the permeable brick for refining. The pressure of the permeable brick is 650-950 kPa and the flow rate is 50-80 L / min.

[0042] In the above-mentioned smelting process, aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are first added to the smelting furnace and heated to melt. To avoid premature addition of magnesium ingots and resulting losses, they are added at 725–745°C. Refining is then carried out, and after settling and slag removal, samples are taken for analysis. If the composition is unqualified, it is adjusted. Once the composition is qualified, refining continues using a refining agent. This refining agent is well known to those skilled in the art, and this application does not impose any special limitations on it. The refining temperature is 740–760°C, and the time is 20–40 minutes; more specifically, the refining temperature is 745–755°C, and the time is 25–35 minutes.

[0043] The obtained aluminum liquid is then cast, and the casting is a technique well known to those skilled in the art. More specifically, the casting involves introducing the aluminum liquid into a crystallizer via a flow channel for semi-continuous direct cooling casting. The casting speed is 25–50 mm / min, and the water flow rate is 100–150 m³ / min. 3Specifically, the casting speed is 30–45 mm / min, and the water flow rate is 110–130 m³ / h. 3 / h.

[0044] According to the present invention, the ingot is then subjected to homogenization treatment. Specifically, the homogenization treatment involves first heating to 300–500°C, holding at that temperature for 10–15 hours, then raising the temperature to 500–600°C and holding for 15–25 hours for homogenization. More specifically, the homogenization treatment involves first heating to 340–400°C, then holding at 340–400°C for 10–15 hours, and then raising the temperature to 540–570°C and holding for 15–25 hours. Even more specifically, the homogenization treatment involves first heating to 360–380°C, then holding at 360–380°C for 11–15 hours, and then raising the temperature to 550–560°C and holding for 18–20 hours. The heating rate of the homogenization treatment is 15–25°C / min, specifically 18–23°C / min. The slow, two-stage homogenization process is more conducive to improving tensile strength.

[0045] This application then applies an extrusion procedure to the homogenized ingot. The extrusion is performed in a manner well-known to those skilled in the art. Specifically, the extrusion temperature is 500–520°C, and the holding time is 2–4 hours; more specifically, the extrusion temperature is 505–515°C, and the holding time is 2.5–3.5 hours. The extrusion speed is 3–6°C / min; more specifically, the extrusion speed is 4–5°C / min. The extrusion outlet temperature is 520–550°C; more specifically, the extrusion outlet temperature is 530–540°C.

[0046] Finally, this application undergoes online quenching and aging. The online quenching water temperature is 520–550℃, more specifically, the water temperature is 530–540℃. The aging temperature is 170–200℃, and the holding time is 6–12 hours; more specifically, the aging temperature is 180–190℃, and the holding time is 8–10 hours.

[0047] This invention provides a 6-series aluminum alloy and its preparation method. It employs a compositional design scheme that enhances the main age-hardening phase Mg2Si and the non-age-hardening phases Al3Nb, Al3Zr, Al3Cr, and Al6Mn through multi-phase reinforcement. A new strengthening phase, L12-Al3Nb, is introduced to supplement the reinforcement. Through this chemical composition design, combined with a subsequent slow, two-stage homogenization process and a high extrusion exit temperature online quenching process, aluminum alloy extruded profiles with tensile strength greater than 440 MPa and capable of online quenching are achieved. This provides a new approach for achieving lightweight and low-cost manufacturing of main structural beams in new energy vehicles, balancing strength and online quenching requirements.

[0048] To further understand the present invention, the following detailed description of the 6-series aluminum alloy and its preparation method provided by the present invention is provided in conjunction with embodiments. The scope of protection of the present invention is not limited by the following embodiments.

[0049] Example 1

[0050] A high-strength 6xxx aluminum alloy capable of online quenching and its preparation method, with an ingot diameter of Φ380mm, includes the following steps:

[0051] Step 1: The chemical composition of the aluminum alloy by mass percentage is: 1.2% Mg, 1% Si, 0.7% Mn, 0.15% Zr, 0.2% Cr, 0.3% Nb, with the balance being Al; according to the composition of the target alloy, weigh aluminum ingots, master alloys, and pure metals as raw materials.

[0052] Step 2: The above-mentioned aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are put into the melting furnace and heated to melt. Magnesium ingots are added using a magnesium-adding frame when the melt temperature reaches 740℃, and 0.0010% beryllium is added before adding magnesium. Then, refining is carried out with a refining agent. After settling and removing slag, samples are taken for analysis, and the composition is adjusted if necessary. After the composition is qualified, refining is continued with a refining agent. The refining temperature is 745℃, the refining time is 25 minutes, and the slag is removed after each refining settling for 30 minutes. After the last settling and slag removal, the melt is poured from the melting furnace into the holding furnace through a trough. During the furnace pouring process, the permeable brick is turned on for refining. The pressure of the permeable brick is 720 kPa, and the flow rate of the permeable brick is 60 L / min.

[0053] Step 3: The high-purity aluminum liquid, after degassing and slag removal, is introduced into a Φ380mm crystallizer via a flow channel for semi-continuous direct cooling casting. The casting speed is 35mm / min, and the water flow rate is 120m³ / min. 3 / h;

[0054] Step 4: The ingot is sent into a homogenizing furnace for homogenization. The ingot is heated to 380°C at a heating rate of 15°C / h, and then held at 380°C for 15h. Then the temperature is increased to 560°C and held for 20h.

[0055] Step 5: Heat the ingot to 510℃, hold it for 3 hours, and then send it to the extrusion press for extrusion. The extrusion speed is 5m / min and the extrusion outlet temperature is 540℃.

[0056] Step 6: Using a water-passing process, the extruded profiles are continuously passed through a quenching water tank, and the temperature of the extruded profiles before entering the water is controlled at 540℃;

[0057] Step 7: After online quenching, aging is performed at 180℃ for 10 hours.

[0058] Example 2

[0059] A high-strength 6xxx aluminum alloy capable of online quenching and its preparation method, with an ingot diameter of Φ380mm, includes the following steps:

[0060] Step 1: The chemical composition of the aluminum alloy by mass percentage is: 1.4% Mg, 1.2% Si, 0.5% Mn, 0.15% Zr, 0.2% Cr, 0.3% Nb, with the balance being Al. Weigh aluminum ingots, master alloys, and pure metals as raw materials according to the composition of the target alloy.

[0061] Step 2: The above-mentioned aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are put into the melting furnace and heated to melt. Magnesium ingots are added using a magnesium-adding frame when the melt temperature reaches 740℃, and 0.0010% beryllium is added before adding magnesium. Then, refining is carried out with a refining agent. After settling and removing slag, samples are taken for analysis, and the composition is adjusted if necessary. After the composition is qualified, refining is continued with a refining agent. The refining temperature is 745℃, the refining time is 25 minutes, and the slag is removed after each refining settling for 30 minutes. After the last settling and slag removal, the melt is poured from the melting furnace into the holding furnace through a trough. During the furnace pouring process, the permeable brick is turned on for refining. The pressure of the permeable brick is 720 kPa, and the flow rate of the permeable brick is 60 L / min.

[0062] Step 3: The high-purity aluminum liquid, after degassing and slag removal, is introduced into a Φ380mm crystallizer via a flow channel for semi-continuous direct cooling casting. The casting speed is 35mm / min, and the water flow rate is 120m³ / min. 3 / h;

[0063] Step 4: The ingot is sent into a homogenizing furnace for homogenization. The ingot is heated to 380°C at a heating rate of 15°C / h, and then held at 380°C for 15h. Then the temperature is increased to 560°C and held for 20h.

[0064] Step 5: Heat the ingot to 510℃, hold it for 3 hours, and then send it to the extrusion press for extrusion. The extrusion speed is 5m / min and the extrusion outlet temperature is 540℃.

[0065] Step 6: Using a water-passing process, the extruded profiles are continuously passed through a quenching water tank, and the temperature of the extruded profiles before entering the water is controlled at 540℃;

[0066] Step 7: After online quenching, aging is performed at 180℃ for 10 hours.

[0067] Comparative Example 1

[0068] The preparation method is the same as in Example 1, except that: 1.2% Mg, 1% Si, 0.7% Mn, 0.15% Zr, 0.2% Cr, with the balance being Al, and no Nb is added.

[0069] Comparative Example 2

[0070] The preparation method is the same as in Example 1, except that the homogenization is carried out using conventional processes: only heat treatment at 560℃ for 20 hours.

[0071] Comparative Example 3

[0072] The preparation method is the same as in Example 1, except that the extrusion outlet temperature is 510°C.

[0073] Comparative Example 4

[0074] The preparation method is the same as in Example 1, except that: 0.8% Mg, 1% Si, 0.7% Mn, 0.15% Zr, 0.2% Cr, 0.3% Nb, and the balance is Al.

[0075] Comparative Example 5

[0076] The preparation method is the same as in Example 1, except that: 1.2% Mg, 0.6% Si, 0.7% Mn, 0.15% Zr, 0.2% Cr, 0.3% Nb, and the balance is Al.

[0077] Comparative Example 6

[0078] The preparation method is the same as in Example 1, except that: 1.2% Mg, 1% Si, 0.7% Mn, 0.15% Zr, 0.2% Cr, 0.6% Nb, and the balance being Al and impurities.

[0079] The following table compares the performance of extruded profiles prepared using the alloy composition ratios and homogenization and extrusion processes of the embodiments of the present invention with those prepared using the comparative process.

[0080] Table 1. Performance Comparison Data of Examples and Comparative Examples

[0081]

[0082]

[0083] As shown in Table 1, the preparation process of the present invention can meet the requirement of tensile strength greater than 440 MPa. However, the composition of aluminum alloy or the relevant parameters in the preparation process are not within the scope of this application, and the tensile strength, yield strength and elongation will be affected.

[0084] The above description of the embodiments is only for the purpose of helping to understand the method and core ideas of the present invention. It should be noted that those skilled in the art can make several improvements and modifications to the present invention without departing from the principles of the present invention, and these improvements and modifications also fall within the protection scope of the claims of the present invention.

[0085] The above description of the disclosed embodiments enables those skilled in the art to make or use the invention. Various modifications to these embodiments will be readily apparent to those skilled in the art, and the general principles defined herein may be implemented in other embodiments without departing from the spirit or scope of the invention. Therefore, the invention is not to be limited to the embodiments shown herein, but is to be accorded the widest scope consistent with the principles and novel features disclosed herein.

Claims

1. A 6-series aluminum alloy, comprising, by weight percentage: Mg 1.4~1.6%, Si 0.8~1.6%, Mn 0.5~1.0%, Zr 0.08~0.2%, Cr 0.1~0.3%, Nb 0.1~0.4%, balance Al; The preparation method of the 6-series aluminum alloy includes the following steps: S1) The raw materials are prepared according to the composition ratio of 6-series aluminum alloy, and then smelted to obtain molten aluminum; S2) Cast the molten aluminum to obtain a 6-series aluminum alloy ingot; S3) The 6-series aluminum alloy ingot is first heated to 340~400℃ and held for 10~15h, then heated to 540~570℃ and held for 15~25h for homogenization treatment. S4) The 6-series aluminum alloy ingot obtained in step S3) is extruded, and the extrusion outlet temperature is 520~550℃ to obtain an extruded profile; S5) The extruded profile is quenched online and then aged.

2. The 6-series aluminum alloy according to claim 1, characterized in that, The Nb content is 0.2~0.3wt%; and / or, the Si content is 1.0~1.4wt%.

3. The method for preparing the 6-series aluminum alloy according to claim 1, comprising the following steps: S1) The raw materials are prepared according to the composition ratio of 6-series aluminum alloy, and then smelted to obtain molten aluminum; S2) Cast the molten aluminum to obtain a 6-series aluminum alloy ingot; S3) The 6-series aluminum alloy ingot is first heated to 340~400℃ and held for 10~15h, then heated to 540~570℃ and held for 15~25h for homogenization treatment. S4) The 6-series aluminum alloy ingot obtained in step S3) is extruded, and the extrusion outlet temperature is 520~550℃ to obtain an extruded profile; S5) The extruded profile is quenched online and then aged.

4. The preparation method according to claim 3, characterized in that, The specific steps of the smelting process are as follows: Aluminum ingots, aluminum-silicon master alloys, aluminum-manganese master alloys, aluminum-zirconium master alloys, aluminum-chromium master alloys, and aluminum-niobium master alloys are heated and melted. Magnesium ingots are added using a magnesium-adding frame when the melt temperature reaches 725~745℃. Before adding magnesium, 0.0010% beryllium is added and then refined. After the composition is qualified, continue refining at a temperature of 740~760℃ for 20~40 minutes. After each refining, let it stand for 20~40 minutes and then remove the slag. After the last standing and slag removal, pour the melt from the melting furnace into the holding furnace through the trough. During the furnace pouring process, turn on the permeable brick for refining. The pressure of the permeable brick is 650~950KPa and the flow rate is 50~80L / min.

5. The preparation method according to claim 3, characterized in that, The casting is a semi-continuous direct cooling casting, with a casting speed of 25~50 mm / min and a water flow rate of 100~150 m³ / min. 3 / h.

6. The preparation method according to claim 3, characterized in that, The heating rate of the homogenization process is 15~25℃ / h.

7. The preparation method according to claim 3, characterized in that, The extrusion temperature is 500~520℃, and the temperature is maintained for 2~4 hours.

8. The preparation method according to claim 3, characterized in that, The water immersion temperature for online quenching is 520~550℃.

9. The preparation method according to claim 3, characterized in that, The aging temperature is 170~200℃, and the holding time is 6~12h.

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