New energy vehicle high-conductivity aluminum profile and preparation method thereof

Abstract

The application relates to the field of aluminum alloy material processing, and particularly relates to a high-conductivity aluminum profile for new energy vehicles and a preparation method thereof. The components and the weight percentages of the components in the profile are as follows: the Si content is 0.015-0.055%; the Fe content is 0.08-0.14%; the Cu content is 0.002-0.006%; the B content is 0.005-0.02%; the total content of (Mn+Cr+Ti+V) is less than or equal to 0.018%; the total content of other impurity elements is less than or equal to 0.02%; and the balance is Al. The yield strength of the profile is greater than or equal to 27 MPa, the tensile strength is greater than or equal to 56 MPa, the elongation is greater than or equal to 40%, and the conductivity is greater than or equal to 62.9% IACS.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy material processing, specifically to a high-conductivity aluminum profile for new energy vehicles and its preparation method. Background Technology

[0002] With the rapid development of new energy vehicles, the proportion of high-current high-voltage wiring harnesses used in automobiles is increasing, and the requirements for the conductivity of high-voltage wiring harnesses are also increasing. Aluminum alloys have high conductivity and low price, and replacing wiring harnesses with high-voltage aluminum profiles has become a research hotspot. At present, high-conductivity aluminum profiles with continuous extrusion can be produced by simply covering the shielding layer and the insulation layer and then performing a three-dimensional bending process, which eliminates the aluminum rod coiling and unwinding process of continuous casting and rolling. At present, the high-conductivity aluminum profile products of car manufacturers have strict performance requirements. The specific standards are: yield strength (25-40) MPa, tensile strength (50-70) MPa, elongation (≥25)%, conductivity (≥61.9%) IACS and Vickers hardness (21±4) HV. Since the material needs to be coiled afterward, the strength must strictly meet the standard requirements.

[0003] Currently, to improve electrical conductivity, rare earth elements are typically added to purify the melt, and aluminum alloys undergo heat treatments such as billet homogenization, artificial aging, and annealing to enhance conductivity. However, the addition of rare earth elements and heat treatment processes increases production costs and complicates the process. Furthermore, the introduction of rare earth elements and drawing processes increases mechanical properties and reduces elongation, leading to increased difficulty in subsequent coiling. This increases residual stress within the coiled profile, negatively impacting subsequent automotive aluminum profile wiring harnesses. Currently, the demand for new energy vehicles is increasing, but research on high-conductivity aluminum profiles for new energy vehicles is extremely limited. There are almost no products that can simultaneously achieve a yield strength of 27-40 MPa, a tensile strength of 56-70 MPa, an electrical conductivity of 62.9% IACS, and an elongation of 25%.

[0004] In summary, there is an urgent need for a high-conductivity aluminum profile for new energy vehicles that combines excellent mechanical strength, conductivity, and elongation, as well as its preparation method. Summary of the Invention

[0005] The present invention aims to solve the technical problem of how to provide a high-conductivity aluminum profile for new energy vehicles with excellent mechanical strength, conductivity and elongation, and the preparation method thereof.

[0006] To achieve the above objectives, the first aspect of the present invention provides a high-conductivity aluminum profile for new energy vehicles, wherein the components and their weight percentages in the profile are as follows: The Si content is 0.015-0.055%; The Fe content is 0.08-0.14%; The Cu content is 0.002-0.006%; The content of B is 0.005-0.02%; The total content of (Mn+Cr+Ti+V) is ≤0.018%; The total content of other impurity elements is ≤0.02%; The balance is Al.

[0007] A second aspect of the present invention provides a method for preparing the above-mentioned high-conductivity aluminum profile for new energy vehicles, characterized in that the method includes: Melting, casting, extrusion; The casting conditions include: heating the raw material to 720-740℃, holding it at that temperature for 5-6 hours, adding Al-B and Al-Fe alloys until melting, degassing and refining, removing slag, letting it stand for 30-45 minutes, and then carrying out semi-continuous casting at an aluminum melt temperature of 710-730℃. The cooling water flow rate is 60-200 L / min, the cooling water temperature is 20-30℃, the casting speed is 90-180 mm / min, the ingot cooling rate is 10-30℃ / s, and the ingot grain size is greater than 900 μm. The preparation method of the profile does not include homogenization treatment, aging treatment, or annealing.

[0008] The beneficial effects of this invention are as follows: By controlling the alloy composition and using a specific casting process, the aluminum alloy profiles provided by this invention have a yield strength ≥27MPa, tensile strength ≥56MPa, elongation ≥40%, and electrical conductivity ≥62.9%IACS. Furthermore, the specific extrusion process, combined with the working zone thickness of each part of the extrusion die, controls the flow rate of the molten metal, eliminating product cracking and chatter defects, resulting in aluminum alloy profiles with smooth surfaces, thus making the aluminum alloy profiles perform better. In addition, the profile preparation process does not require heat treatment such as billet homogenization, artificial aging, and annealing, effectively reducing carbon emissions and energy consumption. Attached Figure Description

[0009] Figure 1 The grain sizes are those of Example 1 and Comparative Example 4; Figure 2 This is a schematic diagram of the working zone of the extrusion die. Detailed Implementation

[0010] The endpoints and any values ​​of the ranges disclosed herein are not limited to the precise ranges or values, and these ranges or values ​​should be understood to include values ​​close to these ranges or values. For numerical ranges, the endpoint values ​​of the various ranges, the endpoint values ​​of the various ranges and individual point values, and individual point values ​​can be combined with each other to obtain one or more new numerical ranges, which should be considered as specifically disclosed herein.

[0011] The first aspect of this invention provides a high-conductivity aluminum profile for new energy vehicles, wherein the components and their weight percentages in the profile are as follows: The Si content is 0.015-0.055%; The Fe content is 0.08-0.14%; The Cu content is 0.002-0.006%; The content of B is 0.005-0.02%; The total content of (Mn+Cr+Ti+V) is ≤0.018%; The total content of other impurity elements is ≤0.02%; The balance is Al.

[0012] In this invention, the elements Cr, V, Mn, Ti, and Mg in aluminum alloys have a significant impact on their conductivity; the higher the content, the lower the conductivity. Elements such as Si, Fe, and Cu have a smaller impact. Therefore, for high-conductivity aluminum alloy profiles used in automobiles, the content of transition elements (Mn+Cr+Ti+V) and alkali metal Mg should be strictly controlled. Thus, the content of (Mn+Cr+Ti+V) elements is limited, and Mg elements are not added. The addition of element B can purify the aluminum alloy. It can form solid particles with a density higher than aluminum in the aluminum melt with the transition elements (Mn+Cr+Ti+V) and alkali metal Mg in the alloy. These particles can be separated from the melt by methods such as filtration, precipitation, or centrifugation, thereby effectively removing impurities and purifying the aluminum alloy.

[0013] According to the present invention, the profile has a yield strength ≥27MPa, a tensile strength ≥56MPa, and an elongation ≥40%.

[0014] According to the present invention, the conductivity of the profile is ≥62.9% IACS.

[0015] A second aspect of the present invention provides a method for preparing the above-mentioned high-conductivity aluminum profile for new energy vehicles, characterized in that the method includes: Melting, casting, extrusion; The casting conditions include: heating the raw material to 720-740℃, holding it at that temperature for 5-6 hours, adding Al-B and Al-Fe alloys until melting, degassing and refining, removing slag, letting it stand for 30-45 minutes, and then carrying out semi-continuous casting at an aluminum melt temperature of 710-730℃. The cooling water flow rate is 60-200 L / min, the cooling water temperature is 20-30℃, the casting speed is 90-180 mm / min, the ingot cooling rate is 10-30℃ / s, and the ingot grain size is greater than 900 μm. The preparation method of the profile does not include homogenization treatment, aging treatment, or annealing.

[0016] In this invention, the inventors discovered that the cooling rate of the casting rod changes according to the cooling water flow rate and casting speed. When the cooling water flow rate is below 60 L / min and the casting speed is above 180 mm / min, the cooling rate of the casting rod is below 10℃ / s. However, excessively low cooling water flow rate and excessively fast casting speed can lead to aluminum leakage in semi-continuous casting, causing casting accidents. When the cooling water flow rate is above 200 L / min and the casting speed is below 90 mm / min, the cooling rate of the casting rod is above 30℃ / s. Excessively fast casting rod cooling rate can make the casting rod grains finer. In industrial production, fine-grained aluminum alloy casting rods are often sought because, according to genetic characteristics, the product grains will be smaller after extrusion deformation, and the mechanical properties will be improved. However, the smaller the aluminum alloy grains, the more grain boundaries there are per unit area, resulting in more scattering of electrons when they pass through, increasing resistivity, and thus reducing the conductivity of the aluminum alloy product.

[0017] The preparation method provided by this invention requires strict control of the semi-continuous casting process, matching the cooling water flow rate and casting speed, thereby strictly controlling the casting rate and ultimately controlling the grain size of the cast rod, which can be higher than 900 μm. If the casting rate is too fast, the grain size will be lower than 900 μm, which will lead to a decrease in the conductivity of the extruded product.

[0018] In this invention, no homogenization treatment is performed. Impurity elements in the alloy are removed by using element B, and the grain size of the cast rod is reasonably controlled to be higher than 900μm. Therefore, the strength of the cast rod is low, thereby improving the extrudability of the alloy. Thus, extrusion deformation can be performed without homogenization treatment and the performance will not be reduced.

[0019] According to the present invention, powder spraying is used for degassing and refining, and 99.9% pure argon gas is used in conjunction with granular refining grade for refining.

[0020] According to the present invention, the online purification system includes a graphite rotor degasser with a degassing efficiency of ≥50%, and is equipped with a two-stage filtration device, which includes a foam ceramic filter plate of 30ppi + 50ppi.

[0021] According to the present invention, the extrusion conditions include: the relationship between the thickness of the working zone of the extrusion die and the thickness A of the extruded profile is: C=0.38+0.2(AB), in mm, where A is the thickness of the extruded profile, 2mm≤A≤8mm; B is the thickness of the working zone at the longest plane of the profile; C is the thickness of the working zone at the corner of the profile, A>B>C.

[0022] According to the present invention, the extrusion conditions include: the relationship between the length D of the connection between the profile plane and the corner and the thickness of the working zone of the extrusion die is: D=|(BC) / tan10°|, in mm, where B is the thickness of the working zone at the longest plane of the profile; and C is the thickness of the working zone at the corner of the profile.

[0023] In this invention, the inventors discovered that the frictional resistance of the aluminum alloy at the working zone can adjust the metal flow rate. Under the condition that the shape and size of the die's guide chamber and diversion chamber are fixed, rationally designing unequal working zone lengths can effectively improve the uniformity of metal flow rate in various parts of the profile cross-section, preventing defects such as cracking and chattering in the extruded profile. Because the aluminum alloy used in this invention has a low alloying content, chattering defects are easily generated on the profile surface during extrusion deformation. Research has shown that changing the working zone length according to different profile thicknesses can effectively reduce chattering and achieve a smooth profile surface. Simultaneously, because the deformation is large at profile corners, the working zone thickness at these locations should be reduced to decrease friction and promote metal flow. The thickness of the extrusion die's working zone and the thickness of the extruded profile are limited to the formula mentioned above to ensure smooth metal flow at the profile plane and corner connections. By rationally matching the working zone thickness at various parts of the extrusion die and controlling the molten metal flow rate, the generation of product cracking and chattering defects can be eliminated.

[0024] According to the present invention, the extrusion conditions include: an extrusion die temperature of 450-475°C, a casting rod heating temperature of 350-370°C, an extrusion speed of 9-12 m / min, cooling to 190-210°C at a cooling rate of 0.4-0.6°C / s, and then cooling to 22-28°C at a cooling rate of 1.3-1.7°C / s.

[0025] In this invention, a slower cooling rate allows the grains of the extruded aluminum alloy profile to recrystallize and grow from a fibrous state, thereby improving its conductivity.

[0026] According to the present invention, the diameter of the casting rod is 80-198 mm.

[0027] Test methods Room temperature tensile mechanical property test: The test was conducted in accordance with the relevant provisions of GB / T 228.1-2021 ≪Metallic materials, tensile testing - Part 1: Room temperature test method ≫, and the test equipment was AG-X 100kN electronic universal testing machine.

[0028] Conductivity test: According to GB / T 12966-2022 "Eddy current test method for conductivity of aluminum and aluminum alloy", the test equipment is Sigmates 2.069 conductivity meter.

[0029] Grain size testing: According to GB / T3246.1-2012 "Methods for testing the microstructure of wrought aluminum and aluminum alloy products - Part 1: Microstructure testing methods", the testing equipment was an AXIO universal research-grade inverted materials microscope.

[0030] Vickers hardness test: According to GB / T 4340.1-2024 "Metallic materials Vickers hardness test - Part 1: Test method", the test equipment is Q10M micro Vickers hardness tester.

[0031] The technical solution of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Obviously, the embodiments described herein are only some embodiments of the present invention and are not intended to limit the present invention. All other embodiments implemented by those skilled in the art based on the embodiments of the present invention without creative improvements are within the protection scope of the present invention.

[0032] Example 1 The chemical composition of the aluminum alloy profile is Si: 0.02%, Fe: 0.10%, Cu: 0.004%, B: 0.015%, (Mn+Cr+Ti+V) ≤ 0.018%; the balance is Al.

[0033] Melting and casting: Pure aluminum and other raw materials are placed in a melting furnace and heated to 720℃. After melting, the temperature is maintained for 5 hours. Al-B and Al-Fe master alloys are added, and the mixture is maintained at 730℃ until fully melted. The mixture is then stirred uniformly and degassed using powder spraying (99.9% pure argon + granular refining grade), followed by slag removal. The mixture is allowed to stand for 30 minutes. Semi-continuous casting is then performed when the aluminum melt temperature reaches 710℃. The online purification system includes a graphite rotor degasser (degassing efficiency ≥50%) and a dual-stage filtration device (30ppi + 50ppi foam ceramic filter plates). The casting rod diameter is 120mm, the cooling water flow rate is set to 60L / min, the water temperature is 25℃, and the casting speed is 180mm / min. The cooling water flow rate and casting speed are strictly controlled to ensure a casting rod cooling rate of 10℃ / s. Extrusion: Select a die with a wall thickness of 2mm, a working strip thickness of 0.9mm at the longest plane, a working strip thickness of 0.6mm at the corner of the profile, a connection length of 1.7mm between the profile plane and the corner, and a profile thickness of 2mm; The extrusion die temperature is 460℃, the aluminum alloy casting rod heating temperature is 360℃, the extrusion speed is 11m / min, and the extrusion is followed by segmented air cooling. First, the profile is cooled to 200℃ at a rate of 0.4℃ / s, and then the profile is cooled to 25℃ at a rate of 1.5℃ / s. Aluminum alloy profile A1 was obtained.

[0034] Example 2 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the chemical composition of the aluminum alloy profiles was Si: 0.015%, Fe: 0.08%, Cu: 0.002%, B: 0.005%, (Mn+Cr+Ti+V) ≤ 0.018%; the balance was Al.

[0035] Aluminum alloy profile A2 was obtained.

[0036] Example 3 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the chemical composition of the aluminum alloy profiles was Si: 0.055%, Fe: 0.14%, Cu: 0.006%, B: 0.02%, (Mn+Cr+Ti+V) ≤ 0.018%; the balance was Al.

[0037] Aluminum alloy profile A3 was obtained.

[0038] Example 4 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the diameter of the cast rod was 80 mm.

[0039] Aluminum alloy profile A4 was obtained.

[0040] Example 5 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the diameter of the cast rod was 198 mm.

[0041] Aluminum alloy profile A5 was obtained.

[0042] Example 6 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the cooling water flow rate was 200 L / min, the casting speed was 90 mm / min, and the casting rod cooling rate was 30 °C / s.

[0043] Aluminum alloy profile A6 was obtained.

[0044] Example 7 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that a mold with a wall thickness of 5 mm was selected, the working strip thickness at the longest plane was 1.5 mm, the working strip thickness at the corner of the profile was 1.08 mm, the connection length between the profile plane and the corner was 2.39 mm, and the profile thickness was 5 mm.

[0045] Aluminum alloy profile A7 was obtained.

[0046] Example 8 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that a mold with a wall thickness of 8 mm was selected, the working strip thickness at the longest plane was 2.2 mm, the working strip thickness at the corner of the profile was 1.54 mm, the connection length between the profile plane and the corner was 3.75 mm, and the profile thickness was 8 mm.

[0047] Aluminum alloy profile A8 was obtained.

[0048] Example 9 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the heating temperature of the aluminum alloy casting rod was 350°C, the extrusion speed was 12 m / min, and the extrusion was followed by segmented air cooling. First, the profile was cooled to 190°C at a rate of 0.6°C / s, and then the profile was cooled to 25°C at a rate of 1.3°C / s.

[0049] Aluminum alloy profile A9 was obtained.

[0050] Example 10 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the heating temperature of the aluminum alloy casting rod was 370°C, the extrusion speed was 9 m / min, and segmented air cooling was used after extrusion. First, the profile was cooled to 210°C at a rate of 0.4°C / s, and then the profile was cooled to 25°C at a rate of 1.7°C / s.

[0051] Aluminum alloy profile A10 was obtained.

[0052] Comparative Example 1 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the chemical composition of the aluminum alloy profiles was Si: 0.01%, Fe: 0.07%, Cu: 0.001%, B: 0.004%, (Mn+Cr+Ti+V) ≥ 0.018%; the balance was Al.

[0053] Aluminum alloy profile DA1 was obtained.

[0054] Comparative Example 2 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the chemical composition of the aluminum alloy profiles was Si: 0.06%, Fe: 0.15%, Cu: 0.007%, B: 0.03%, (Mn+Cr+Ti+V) ≥ 0.018%; the balance was Al.

[0055] Aluminum alloy profile DA2 was obtained.

[0056] Comparative Example 3 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the cooling water flow rate was 50 L / min, the casting speed was 190 mm / min, and the casting rod cooling rate was 8 °C / s.

[0057] Aluminum alloy profile DA3 was obtained.

[0058] Comparative Example 4 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the cooling water flow rate was 210 L / min, the casting speed was 190 mm / min, and the casting rod cooling rate was 32 °C / s.

[0059] Aluminum alloy profile DA4 was obtained.

[0060] Comparative Example 5 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that a mold with a wall thickness of 2 mm was selected, the working strip thickness at the longest plane was 0.5 mm, the working strip thickness at the corner of the profile was 0.3 mm, the connection length between the profile plane and the corner was 1.02 mm, and the profile thickness was 2 mm.

[0061] Aluminum alloy profile DA5 was obtained.

[0062] Comparative Example 6 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that a mold with a wall thickness of 8mm was selected, the working strip thickness at the longest plane was 5mm, the working strip thickness at the corner of the profile was 5mm, the connection length between the profile plane and the corner was 2mm, and the profile thickness was 8mm.

[0063] Aluminum alloy profile DA6 was obtained.

[0064] Comparative Example 7 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that the extruded profiles were cooled to 25°C at a rate of 0.3°C / s.

[0065] Aluminum alloy profile DA7 was obtained.

[0066] Comparative Example 8 Aluminum alloy profiles were prepared according to the processing method of Example 1, except that in the extrusion process, the extruded profiles were cooled to 25°C at a rate of 1.8°C / s.

[0067] Aluminum alloy profile DA8 was obtained.

[0068] Performance tests were performed on A1-A10 and DA1-DA8, as shown in Table 1. Table 1 By comparing the embodiments and comparative examples, it can be seen that the high conductivity aluminum profile for new energy vehicles provided by the present invention combines certain strength, high elongation and high conductivity, and the profile surface is smooth without cracks or defects.

[0069] Specifically, in Comparative Examples 3 and 4, after changing the cooling water flow rate and casting speed, a slower cooling rate of the cast ingot led to aluminum leakage during semi-continuous casting; an excessively fast cooling rate caused the grains to become smaller, resulting in decreased conductivity. In Comparative Examples 5 and 6, due to the failure to design the thickness of each part of the mold working zone according to the patent, defects such as cracking or chattering appeared in the profile. In Comparative Example 7, reducing the cooling rate of the profile caused the crystals to grow, resulting in the mechanical properties not meeting the requirements. In Comparative Example 8, increasing the cooling rate of the profile caused its conductivity to not meet the requirements.

[0070] The above description is merely a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any equivalent substitutions or modifications made by those skilled in the art within the scope of the technology disclosed in the present invention, based on the technical solution and inventive concept of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A high-conductivity aluminum profile for new energy vehicles, characterized in that, The components and their weight percentages in the profile are as follows: The Si content is 0.015-0.055%; The Fe content is 0.08-0.14%; The Cu content is 0.002-0.006%; The content of B is 0.005-0.02%; The total content of (Mn+Cr+Ti+V) is ≤0.018%; The total content of other impurity elements is ≤0.02%; The balance is Al; The method for preparing the profile includes: Melting, casting, extrusion; The casting conditions include: heating the raw material to 720-740℃, holding it at that temperature for 5-6 hours, adding Al-B and Al-Fe alloys until melting, degassing and refining, removing slag, letting it stand for 30-45 minutes, and then carrying out semi-continuous casting at an aluminum melt temperature of 710-730℃. The cooling water flow rate is 60-200 L / min, the cooling water temperature is 20-30℃, the casting speed is 90-180 mm / min, the ingot cooling rate is 10-30℃ / s, and the ingot grain size is greater than 900 μm. The preparation method of the profile does not include homogenization treatment, aging treatment, or annealing. The extrusion conditions include: the relationship between the thickness of the working zone of the extrusion die and the thickness A of the extruded profile is: C=0.38+0.2(AB), in mm, where A is the thickness of the extruded profile, 2mm≤A≤8mm; B is the thickness of the working zone at the longest plane of the profile; C is the thickness of the working zone at the corner of the profile, A>B>C; The extrusion conditions include the following: the relationship between the length D of the profile plane and corner connection and the thickness of the working zone of the extrusion die is: D=|(BC) / tan10°|, in mm, where B is the thickness of the working zone at the longest plane of the profile; C is the thickness of the working zone at the corner of the profile; The extrusion conditions include: extrusion die temperature of 450-475℃, casting rod heating temperature of 350-370℃, extrusion speed of 9-12m / min, cooling to 190-210℃ at a cooling rate of 0.4-0.6℃ / s, and then cooling to 22-28℃ at a cooling rate of 1.3-1.7℃ / s.

2. The profile according to claim 1, characterized in that, The profile has a yield strength ≥27MPa, a tensile strength ≥56MPa, and an elongation ≥40%.

3. The profile according to claim 1, characterized in that, The conductivity of the profile is ≥62.9% IACS.

4. A method for preparing a high-conductivity aluminum profile for new energy vehicles according to any one of claims 1-3, characterized in that, The method includes: Melting, casting, extrusion; The casting conditions include: heating the raw material to 720-740℃, holding it at that temperature for 5-6 hours, adding Al-B and Al-Fe alloys until melting, degassing and refining, removing slag, letting it stand for 30-45 minutes, and then carrying out semi-continuous casting at an aluminum melt temperature of 710-730℃. The cooling water flow rate is 60-200 L / min, the cooling water temperature is 20-30℃, the casting speed is 90-180 mm / min, the ingot cooling rate is 10-30℃ / s, and the ingot grain size is greater than 900 μm. The preparation method of the profile does not include homogenization treatment, aging treatment, or annealing. The extrusion conditions include: the relationship between the thickness of the working zone of the extrusion die and the thickness A of the extruded profile is: C=0.38+0.2(AB), in mm, where A is the thickness of the extruded profile, 2mm≤A≤8mm; B is the thickness of the working zone at the longest plane of the profile; C is the thickness of the working zone at the corner of the profile, A>B>C; The extrusion conditions include the following: the relationship between the length D of the profile plane and corner connection and the thickness of the working zone of the extrusion die is: D=|(BC) / tan10°|, in mm, where B is the thickness of the working zone at the longest plane of the profile; C is the thickness of the working zone at the corner of the profile; The extrusion conditions include: extrusion die temperature of 450-475℃, casting rod heating temperature of 350-370℃, extrusion speed of 9-12m / min, cooling to 190-210℃ at a cooling rate of 0.4-0.6℃ / s, and then cooling to 22-28℃ at a cooling rate of 1.3-1.7℃ / s.

5. The method according to claim 4, characterized in that, The diameter of the casting rod is 80-198mm.

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