Al-Mg-Si-Cu alloy and preparation method and application thereof

Abstract

The invention belongs to the field of alloys, and particularly discloses an Al-Mg-Si-Cu alloy and a preparation method and application thereof.The Al-Mg-Si-Cu alloy is composed of, by mass, 0.6%-1.0% of Mg, 1.3%-1.7% of Si, 0.2%-0.4% of Cu, 0.05%-0.1% of Mn, 0.05%-0.2% of Ti, 0.05%-0.2% of Zr, smaller than or equal to 0.02% of Cr, smaller than or equal to 0.15% of Fe, smaller than or equal to 0.15% of inevitable impurities and the balance Al. The aluminum alloy disclosed by the invention has relatively low quenching sensitivity, relatively high mechanical property and excellent welding property, and can meet the strength and use requirements of the rail transit or automobile field on aluminum alloy sections.

Description

Technical Field

[0001] The present invention belongs to the field of alloys, and in particular relates to an Al-Mg-Si-Cu alloy and a preparation method and application thereof. Background Art

[0002] 6xxx series aluminum alloy profiles offer advantages such as high strength, good toughness, and excellent corrosion resistance, and are widely used in industries such as rail transit and automobiles. The rapid development of high-speed rail and new energy vehicles has placed higher demands on the strength and toughness of 6xxx series aluminum alloy profiles.

[0003] Improving the alloying degree and microalloying of 6xxx aluminum alloys are important methods for enhancing the strength of 6xxx aluminum alloy profiles. Research has shown that increasing the content of the main alloying elements Mg and Si, or adding elements such as Cu, Mn, and Cr, can alter the nucleation and precipitation processes of 6xxx aluminum alloys. This significantly improves the strength of extruded profiles after quenching and aging treatments.

[0004] The conventional quenching method for 6xxx series aluminum alloy profiles is to place the extruded profile on a tray, heat it in a quenching furnace, and then, after reaching the required quenching temperature, use a lifting device to quickly lower the tray into a water pool below the quenching furnace to complete the quenching. This method is complex and energy-intensive. For the complex cross-sections and long, large hollow profiles required for high-speed trains and new energy vehicles, the lack of traction at both ends during the quenching process results in severe deformation of the profile after quenching, making it difficult to meet the required dimensional accuracy.

[0005] By utilizing the high temperature of the profile during extrusion to achieve solid solution, and then performing online quenching, it is beneficial to control the deformation of the profile while achieving energy conservation and consumption reduction. At present, the quenching sensitivity is relatively low, and the 6xxx series aluminum alloys that can achieve online quenching include 6063, 6005A, 6082, etc., which have the problem of low strength. The tensile strength after aging does not exceed 320MPa, which cannot meet the requirements of high-strength and lightweight structural parts. For 6xxx series aluminum alloys with high alloy composition, as the alloying element content increases, the quenching sensitivity increases. During the online quenching process, supersaturated solid solution precipitation will occur, and a coarse second phase will precipitate, which seriously affects the effect of subsequent aging treatment. Ultimately, it is difficult for the strength and fatigue performance of the profile to meet the requirements. Therefore, online quenching cannot be achieved on conventional production lines. Summary of the Invention

[0006] In order to overcome at least one technical problem existing in the above-mentioned prior art, one of the objects of the present invention is to provide an aluminum alloy having higher strength and toughness and lower quenching sensitivity, which can be used in the fields of rail transportation, automobiles, etc.

[0007] A second object of the present invention is to provide a method for preparing an aluminum alloy, which can realize online quenching and aging treatment when preparing the aluminum alloy, and can be used to prepare large-scale extruded profiles with complex cross-sections.

[0008] A third object of the present invention is to provide application of the above-mentioned aluminum alloy or the method for preparing the above-mentioned aluminum alloy in the field of rail transportation or automobile.

[0009] In order to achieve the above object, the technical solution adopted by the present invention is:

[0010] A first aspect of the present invention provides an aluminum alloy, which is composed of the following elements in the following mass percentages: Mg 0.6-1.0%, Si 1.3-1.7%, Cu 0.2-0.4%, Mn 0.05-0.1%, Ti 0.05-0.2%, Zr 0.05-0.2%, Cr≤0.02%, Fe≤0.15%, the total amount of unavoidable impurities ≤0.15%, and Al as the balance.

[0011] In some embodiments of the present invention, the mass percentage of Mg may be selected from any one of 0.6%, 0.7%, 0.8%, 0.9%, 1.0%, or a range formed by any two of them.

[0012] In some embodiments of the present invention, the mass percentage of Si can be selected from any one of 1.3%, 1.4%, 1.5%, 1.6%, 1.7%, or a range formed by any two of them.

[0013] In the aluminum alloy of the present invention, Mg and Si are the main alloying elements, which form the Mg2Si phase in the aluminum alloy. By controlling the Mg and Si contents, the Mg2Si content is controlled to 0.95% to 1.58%, and the excess silicon content is controlled to 0.8% to 1.2%. The present invention primarily enhances the strength of the aluminum alloy through excess silicon and Mg2Si, ensuring the strength of the aluminum alloy. Too little excess silicon reduces the strengthening effect on the aluminum alloy; too much excess silicon forms a coarse second phase with elements such as Al, Fe, and Mn, affecting the strengthening effect and material toughness.

[0014] In some embodiments of the present invention, the mass percentage of Cu can be selected from any of 0.2%, 0.3%, and 0.4%, or a range formed by any two of these. The Cu element can improve the age hardening properties of the material and the strength of the final material. However, excessive Cu content can increase the quenching sensitivity of the alloy. Therefore, the present invention controls the Cu content to 0.2 to 0.4%.

[0015] In some embodiments of the present invention, the mass percentage of Mn can be selected from any one of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, or a range formed by any two of them.

[0016] In some embodiments of the present invention, the mass percentage of Ti is any one of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, or 0.2%, or a range formed by any two of these. Ti significantly refines the as-cast grain structure of the alloy. When the Ti content is too low, the cast structure is coarse; when the Ti content is too high, the ingot tends to become microporous, reducing the density of the aluminum alloy.

[0017] In some embodiments of the present invention, the mass percentage of Zr is any one of 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.1%, 0.11%, 0.12%, 0.13%, 0.14%, 0.15%, 0.16%, 0.17%, 0.18%, 0.19%, or 0.2%, or a range formed by any two of these. The Zr element can refine the as-cast grain structure of the alloy and inhibit the formation of coarse recrystallized structure after extrusion. Excessive Zr content can easily lead to the formation of microscopic pinholes in the ingot. Therefore, the present invention controls the Zr content to 0.05 to 0.2%.

[0018] In some embodiments of the present invention, the mass percentage of Cr is any one of 0%, 0.01%, 0.02%, or a range formed by any two of them.

[0019] Although Mn and Cr can inhibit the formation of coarse recrystallized structures during extrusion, they can increase quenching sensitivity. The present invention controls the Mn content to 0.05-0.1% and the Cr content to below 0.02%. Furthermore, excessive Mn content can form an AlMnSi phase with Si, reducing the strength of the alloy.

[0020] In some embodiments of the present invention, the mass percentage of Fe is any one of 0%, 0.01%, 0.02%, 0.03%, 0.04%, 0.05%, 0.06%, 0.07%, 0.08%, 0.09%, 0.10%, 0.11%, 0.12%, 0.13%, 0.14%, and 0.15%, or a range formed by any two of them. Fe is an impurity element in the present invention and forms coarse and insoluble intermetallic compounds with other elements. Excessive Fe will form excessive second phases, reducing the mechanical properties, toughness, and fatigue properties of the material. Therefore, its content needs to be controlled below 0.15%.

[0021] In some embodiments of the present invention, the mass percentage of a single impurity element in the unavoidable impurities is ≤0.05%.

[0022] In some embodiments of the present invention, the aluminum alloy contains 0.95% to 1.58% by mass of Mg2Si; in some embodiments of the present invention, the mass percentage of Mg2Si in the aluminum alloy is 0.95%, 1.0%, 1.05%, 1.1%, 1.15%, 1.2%, 1.25%, 1.3%, 1.35%, 1.4%, 1.45%, 1.5%, 1.55%, 1.58%, or a range formed by any two of the values.

[0023] In some embodiments of the present invention, the aluminum alloy contains excess silicon in an amount of 0.8% to 1.2% by mass; in some embodiments of the present invention, the excess silicon in the aluminum alloy has an amount of 0.8%, 0.9%, 1.0%, 1.1%, 1.2% by mass, or a range formed by any two of these amounts. Excess silicon is the amount of Si remaining after all Mg in the aluminum alloy forms the Mg2Si phase with Si, and is in the range of 0.8% to 1.2%. Excess silicon can significantly improve the fluidity of the aluminum alloy during hot extrusion and enhance its thermoplasticity, thereby meeting the requirements of high-speed extrusion. In addition, a higher excess silicon content can enhance the aging effect, shorten the aging time, and improve production efficiency. In addition, excess silicon can reduce the adverse effects of Fe on welding.

[0024] A second aspect of the present invention provides a method for preparing the aluminum alloy according to the first aspect of the present invention, comprising the following steps:

[0025] S1: melting and refining the raw materials for preparing the aluminum alloy, and then casting the aluminum alloy rods by vertical semi-continuous casting;

[0026] S2: subjecting the aluminum alloy rod to homogenization heat treatment, cooling the rod, and then extruding the rod to obtain an aluminum alloy profile;

[0027] S3: placing the aluminum alloy profile into a cooling device for online quenching, and then performing aging treatment to obtain the aluminum alloy;

[0028] The temperature of the aluminum alloy profile in step S2 is 540-560°C;

[0029] The temperature of the aluminum alloy profile when entering the cooling equipment is ≥530°C.

[0030] In some embodiments of the present invention, the melting temperature is 720-760°C; in some embodiments of the present invention, the melting temperature is any one of 720°C, 725°C, 730°C, 735°C, 740°C, 745°C, 750°C, 755°C, and 760°C, or a range formed by any two of the values.

[0031] In some embodiments of the present invention, the refining step comprises: introducing an inert gas carrying a refining agent into the melt, skimming off the slag, and allowing the melt to stand.

[0032] In some embodiments of the present invention, the standing time is 20 to 60 minutes.

[0033] In some embodiments of the present invention, the temperature during the vertical semi-continuous casting is 730-750°C; in some embodiments of the present invention, the temperature during the vertical semi-continuous casting is any one of 730°C, 735°C, 740°C, 745°C, 750°C or a range formed by any two of them.

[0034] In some embodiments of the present invention, the casting speed during the vertical semi-continuous casting is 130-150 mm / min; in some embodiments of the present invention, the casting speed during the vertical semi-continuous casting is any one of 130 mm / min, 135 mm / min, 140 mm / min, 145 mm / min, 150 mm / min or a range formed by any two of them.

[0035] In some embodiments of the present invention, the cooling rate during the vertical semi-continuous casting is 5 to 10 K / s; in some embodiments of the present invention, the cooling rate during the vertical semi-continuous casting is any one of 5 K / s, 6 K / s, 7 K / s, 8 K / s, 9 K / s, and 10 K / s, or a range formed by any two of them.

[0036] In some embodiments of the present invention, the pressure of the cooling water during the vertical semi-continuous casting is 90-110 kPa; in some embodiments of the present invention, the pressure of the cooling water during the vertical semi-continuous casting is any one of 90 kPa, 95 kPa, 100 kPa, 105 kPa, 110 kPa or a range formed by any two of them.

[0037] In some embodiments of the present invention, the temperature of the cooling water during the vertical semi-continuous casting is 10-30°C; in some embodiments of the present invention, the temperature of the cooling water during the vertical semi-continuous casting is any one of 10°C, 15°C, 20°C, 25°C, 30°C or a range formed by any two of them.

[0038] In some embodiments of the present invention, the temperature of the aluminum alloy profile in step S2 is any one of 540°C, 545°C, 550°C, 555°C, and 560°C, or a range formed by any two of them.

[0039] In some embodiments of the present invention, the temperature of the homogenization heat treatment is 550°C to 570°C; in some embodiments of the present invention, the temperature of the homogenization heat treatment is any one of 550°C, 555°C, 560°C, 565°C, and 570°C, or a range formed by any two of them.

[0040] In some embodiments of the present invention, the holding time of the homogenization heat treatment is 6 to 10 hours; in some embodiments of the present invention, the holding time of the homogenization heat treatment is any one of 6 hours, 7 hours, 8 hours, 9 hours, and 10 hours, or a range formed by any two of them.

[0041] In some embodiments of the present invention, the cooling step comprises cooling the aluminum alloy rod to a temperature of 20-40° C. by air cooling or water mist cooling. The cooling step allows the second phase in the aluminum alloy to be fully dissolved, preventing premature precipitation, and ensuring that the total amount of the second phase in the aluminum alloy is ≤3%.

[0042] In some embodiments of the present invention, the temperature during the extrusion molding is 490-510°C.

[0043] In some embodiments of the present invention, the extrusion speed during the extrusion molding is 6 to 8 m / min.

[0044] In some embodiments of the present invention, the extrusion molding step is: heating the aluminum alloy round rod after homogenization heat treatment and then extruding it into a hollow profile, and the temperature of the hollow profile at the outlet of the extrusion die is 540-560°C.

[0045] In some embodiments of the present invention, the aluminum alloy profile enters a cooling device for online quenching within 15 seconds after extrusion forming.

[0046] In some embodiments of the present invention, the temperature of the aluminum alloy profile when it comes out of the cooling device is ≤100°C; in some embodiments of the present invention, the temperature of the aluminum alloy profile when it comes out of the cooling device is any one of 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C, 70°C, 80°C, 90°C, 100°C, or a range formed by any two of them.

[0047] In some embodiments of the present invention, the temperature of the coolant in the cooling device is ≤60°C; in some embodiments of the present invention, the temperature of the coolant in the cooling device is any value of 0°C, 10°C, 20°C, 30°C, 40°C, 50°C, 60°C or a range formed by any two of them.

[0048] In some embodiments of the present invention, the cooling device is a water tank or a water pool.

[0049] In some embodiments of the present invention, the cooling liquid is water.

[0050] In some embodiments of the present invention, the temperature of the aging treatment is 170-200°C; in some embodiments of the present invention, the temperature of the aging treatment is any one of 170°C, 175°C, 180°C, 185°C, 190°C, 195°C, and 200°C, or a range formed by any two of the values.

[0051] In some embodiments of the present invention, the holding time of the aging treatment is 8 to 15 hours; in some embodiments of the present invention, the holding time of the aging treatment is any one of 8 hours, 9 hours, 10 hours, 11 hours, 12 hours, 13 hours, 14 hours, and 15 hours, or a range formed by any two of the values.

[0052] In some embodiments of the present invention, the time interval between the online quenching and the aging treatment is ≤48 hours.

[0053] The third aspect of the present invention provides the application of the aluminum alloy described in the first aspect of the present invention or the method for preparing the aluminum alloy described in the second aspect of the present invention in the field of rail transportation or automobiles.

[0054] The beneficial effects of the present invention are: the aluminum alloy in the present invention has low quenching sensitivity, high mechanical properties and excellent welding performance, specifically: tensile strength of 390-420 MPa, yield strength of 370-390 MPa, elongation of 14-16%, fatigue limit of 170-180 MPa, and tensile strength of the welded joint after welding of 339-370 MPa, which can meet the strength and usage requirements of aluminum alloy profiles in the rail transit or automotive fields.

[0055] The preparation method of the present invention can realize online quenching of aluminum alloy, reduce production difficulty, reduce the deformation rate of profiles, and realize large-scale production of large-sized aluminum alloy profiles with complex cross-sections. BRIEF DESCRIPTION OF THE DRAWINGS

[0056] Figure 1 Schematic diagram of the cross-section of the hollow alloy profile obtained after extrusion in step (4) of Example 1.

[0057] Figure 2 This is the SEM image of the alloy cast rod obtained in step (2) of Example 1.

[0058] Figure 3 This is the SEM image of the hollow alloy profile obtained after extrusion in step (4) of Example 1. DETAILED DESCRIPTION

[0059] The specific implementation of the present invention will be further described in detail below in conjunction with the accompanying drawings and examples, but the implementation and protection of the present invention are not limited thereto. It should be noted that if there are any processes that are not particularly described in detail below, they can be implemented or understood by those skilled in the art with reference to the prior art. The reagents or instruments used that do not indicate the manufacturer are all conventional products that can be purchased commercially.

[0060] The raw material information used in the following examples and comparative examples is as follows:

[0061] In the AlSi20 master alloy, the mass percentage of Si is 20% and the mass percentage of Al is 80%;

[0062] In the AlMn10 master alloy, the mass percentage of Mn is 10% and the mass percentage of Al is 90%;

[0063] In the AlCu50 master alloy, the mass percentage of Cu is 50% and the mass percentage of Al is 50%.

[0064] In the AlTi10 master alloy, the mass percentage of Ti is 10% and the mass percentage of Al is 90%;

[0065] In AlZr10 alloy, the mass percentage of Zr is 10% and the mass percentage of Al is 90%;

[0066] Example 1

[0067] This example provides an Al-Mg-Si-Cu alloy, the composition and mass percentage of which are shown in Table 1 below.

[0068] This example also provides a method for preparing an Al-Mg-Si-Cu alloy, comprising the following steps:

[0069] (1) According to the composition and proportion of the alloy in Example 1 in Table 1, aluminum ingots with a purity of 99.85%, AlSi20 master alloy, AlMn10 master alloy, and AlCu50 master alloy are added to a gas-heated melting furnace for melting. Cr and Fe are impurity elements in the raw materials and do not need to be added separately. It is only necessary to control their content within the scope of the present invention. When the melt temperature reaches 740°C, Mg ingots with a purity of 99.9% and AlTi10 master alloy are added to the melting furnace in sequence for melting, and the melt is then stirred uniformly. AlZr10 alloy is then added, and after stirring uniformly again, the melt is refined using high-purity nitrogen and a commercially available aluminum alloy refining agent. After refining, the slag is removed and the melt is allowed to stand for 30 minutes before semi-continuous casting begins.

[0070] (2) During casting, the melt temperature in the furnace was 740°C, the cooling water pressure was 100 kPa, the cooling water temperature was 25°C, the casting speed was 140 mm / min, the cooling rate of the cast rod was 7 K / s, and a cast rod with a diameter of 127 mm was prepared.

[0071] (3) The cast rod prepared in step (2) is subjected to homogenization heat treatment, and the specific process is: heating to 560°C, keeping the temperature for 5 hours, and then cooling to room temperature by water mist cooling.

[0072] (4) The cast rods in step (3) are cut into extruded ingots, which are rapidly heated to 500° C. in an induction heating furnace, and extruded into hollow profiles with a hollow rectangular cross-section at an extrusion speed of 7 m / min, wherein the width of the hollow profile is 50 mm, the height is 20 mm, one wall thickness in the width direction is 2 mm, and the other wall thickness in the width direction is 4 mm. The specific dimensions of the cross section of the hollow profile are as follows: Figure 1 The temperature of the hollow profile at the die outlet is 550°C, and then it enters the online quenching water tank (the water tank length is about 2m) within 15 seconds. The temperature of the hollow profile when entering the water tank is 510°C, and the temperature when leaving the water tank is about 80°C.

[0073] (5) The profile obtained in step (4) is cut to a predetermined length and then placed in an aging furnace for treatment at an aging temperature of 180° C. for 10 h. The profile is then removed from the furnace and air-cooled to obtain the Al-Mg-Si-Cu alloy in this example.

[0074] The SEM images of the aluminum alloy cast rod (i.e., cast state) obtained in step (2) and the hollow profile (i.e., extruded state) obtained in step (4) were respectively measured using a scanning electron microscope. Figure 2 and Figure 3 As shown. Figure 2 and Figure 3 It can be seen that in the cast state, the precipitated phase is distributed along the grain boundaries in a network shape; in the extruded state, the precipitated phase is spheroidized.

[0075] Examples 2 to 6

[0076] The compositions and mass percentages of the Al-Mg-Si-Cu alloys in Examples 2 to 6 are shown in Table 1 below.

[0077] The Al-Mg-Si-Cu alloys in Examples 2 to 6 were prepared by referring to the preparation method in Example 1.

[0078] Comparative Examples 1 to 9

[0079] The components and mass percentages of the aluminum alloys in Comparative Examples 1 to 9 are shown in Table 1 below.

[0080] The aluminum alloys in Comparative Examples 1 to 9 were prepared by referring to the preparation method in Example 1.

[0081] Table 1 Composition ratio of the aluminum alloys in Examples 1 to 6 and Comparative Examples 1 to 9

[0082]

[0083]

[0084] Comparative Example 10

[0085] The composition of the aluminum alloy in this example is 6061 aluminum alloy; the preparation method of the aluminum alloy in this example is different from that in Example 1 only in that: during casting, the cooling rate of the cast rod is adjusted to 10°C / s by adjusting the cold water pressure, temperature, and casting speed. The specific parameters are: adjusting the cold water pressure to 135 kPa, the cold water temperature to 3.2°C, and the casting speed to 197 mm / min.

[0086] Comparative Example 11

[0087] The composition of the aluminum alloy in this example is 6082 aluminum alloy; the preparation method of the aluminum alloy in this example is different from that in Example 1 only in that: in step (3) of this example, after the homogenization heat treatment, the ingot is cooled to room temperature by air cooling.

[0088] Comparative Example 12

[0089] The composition and content of the aluminum alloy in this example are the same as those in Example 1. The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that during extrusion in step (4), the temperature of the hollow profile at the die outlet is 520°C. The temperature of the hollow profile entering the water tank at the extrusion outlet is 512°C.

[0090] Comparative Example 13

[0091] The composition and content of the aluminum alloy in this example are the same as those in Example 1. The only difference between the preparation method of the aluminum alloy in this example and that in Example 1 is that in step (4) of this example, during extrusion, the temperature of the hollow profile at the die outlet is 580°C, and the temperature of the hollow profile when entering the water tank at the extrusion outlet is 550°C.

[0092] Performance Testing

[0093] Samples were taken from the hollow aluminum alloy profiles prepared in Examples 1 to 6 and Comparative Examples 1 to 13 for room temperature mechanical property testing. The mechanical properties of the products were tested in accordance with GB / T228.1-2021 "Tensile test of metallic materials - Part 1: Room temperature test method". The fatigue limit of the product was tested in accordance with GB / T3075-2021 "Axial force control method for fatigue test of metallic materials". The test equipment was a high-frequency fatigue testing machine, the test load waveform was a sine wave, the test frequency was about 90 Hz, the stress ratio R was -1, and the fatigue limit specified number of cycles was 10. 7 The test results are shown in Table 2.

[0094] Table 2 Room temperature mechanical properties and fatigue limit of aluminum alloys

[0095]

[0096]

[0097] As can be seen from Table 2, compared with Comparative Examples 1 to 13, the mechanical properties and fatigue limits of the aluminum alloys prepared in Examples 1 to 6 at room temperature are significantly improved, specifically: tensile strength is 398 to 412 MPa, yield strength is 371 to 381 MPa, elongation is 14.1 to 15.8%, and fatigue limit is 173 to 179 MPa.

[0098] According to the national standard GB / T 2651-2008 "Welded Joint Tensile Test Method", the aluminum alloys in Examples 1 to 6 and Comparative Examples 1 to 13 were processed and welded respectively. The welding wire was commercially available ER5R59 welding wire, and the welding method was MIG welding. Then, the welds were tested according to the flat plate welding weld tensile test. The specific test results are shown in Table 3.

[0099] Table 3 Welding joint strength test results

[0100]

[0101]

[0102] As shown in Table 3, compared with comparative examples 1 to 13, the tensile strength of the welded joints of the aluminum alloys in Examples 1 to 6 is significantly improved after welding, and the value is 339 to 367 MPa, which further shows that the aluminum alloy in the present invention has good welding performance.

[0103] While the embodiments of the present invention have been described in detail above, the present invention is not limited to the embodiments described above. Various modifications may be made within the scope of knowledge possessed by a person skilled in the art without departing from the spirit of the present invention. Furthermore, the embodiments of the present invention and the features thereof may be combined with one another unless there is a conflict.

Claims

1. An aluminum alloy, characterized in that: The aluminum alloy is composed of the following elements in mass percentage: Mg 0.6-1.0%, Si 1.3-1.7%, Cu 0.2-0.4%, Mn 0.05-0.1%, Ti 0.05-0.2%, Zr 0.05-0.2%, Cr≤0.02%, Fe≤0.15%, the total amount of inevitable impurities≤0.15%, and Al is the balance.

2. The aluminum alloy according to claim 1, wherein: Among the unavoidable impurities, the mass percentage of a single impurity element is ≤0.05%.

3. The aluminum alloy according to claim 1, wherein: The aluminum alloy contains Mg2Si in a mass percentage of 0.95% to 1.58%.

4. The aluminum alloy according to claim 1, wherein: The aluminum alloy contains 0.8% to 1.2% by mass of excess silicon.

5. The method for preparing the aluminum alloy according to any one of claims 1 to 4, characterized in that: The following steps are involved: S1: melting and refining the raw materials for preparing the aluminum alloy, and then casting the aluminum alloy rods by vertical semi-continuous casting; S2: subjecting the aluminum alloy rod to homogenization heat treatment, cooling the rod, and then extruding the rod to obtain an aluminum alloy profile; S3: placing the aluminum alloy profile into a cooling device for online quenching, and then performing aging treatment to obtain the aluminum alloy; The temperature of the aluminum alloy profile in step S2 is 540-560°C; The temperature of the aluminum alloy profile when entering the cooling equipment is ≥530°C.

6. The method for preparing the aluminum alloy according to claim 5, wherein: The temperature of the homogenization heat treatment is 550°C to 570°C; And / or, the holding time of the homogenization heat treatment is 6 to 10 hours.

7. The method for preparing the aluminum alloy according to claim 5, wherein: The cooling step comprises: cooling the aluminum alloy rod to a temperature of 20-40° C. by air cooling or water mist cooling.

8. The method for preparing the aluminum alloy according to claim 5, wherein: The temperature of the aluminum alloy profile when it comes out of the cooling device is ≤100°C; And / or, the temperature of the coolant in the cooling device is ≤ 60°C.

9. The method for preparing the aluminum alloy according to claim 5, wherein: The aging treatment temperature is 170-200°C; And / or, the holding time of the aging treatment is 8 to 15 hours; And / or, the time interval between the online quenching and the aging treatment is ≤48h.

10. Use of the aluminum alloy according to any one of claims 1 to 4 or the method for preparing the aluminum alloy according to any one of claims 5 to 9 in the field of rail transportation or automobiles.

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