A 6-series high-toughness medium-high-strength aluminum alloy and a production process thereof

Abstract

The application relates to the technical field of aluminum alloy production and processing, and discloses a 6-series high-toughness medium-high-strength alloy and a production process thereof. Through optimization of alloy components and cooperation with a two-stage homogenization and rapid cooling process, the 6-series aluminum alloy is realized in the three aspects of strength, good toughness and low cost. The 6-series high-toughness medium-high-strength alloy prepared by the application has the alloy components as follows: Si 0.59-0.63%, Fe<=0.15%, Cu 0.02-0.10%, Mn 0.22-0.30%, Mg 0.62-0.67%, Cr 0.05-0.1%, Zn<=0.03%, Ti<=0.04%, and the balance of Al, and the content is in percentage by weight; the tensile strength is >=290MPa, the yield strength is >=255Mpa, and the bending angle is >=100 degrees.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy production and processing technology, specifically to a 6-series high-efficiency, high-toughness, medium-high strength alloy and its production process. Background Technology

[0002] Aluminum alloys are widely used in aerospace, automotive manufacturing, and construction industries due to their lightweight, high strength, good corrosion resistance, and machinability. Among them, 6-series aluminum alloys, with their excellent overall performance, are widely used in the manufacture of components such as battery trays and automotive door sills. As these fields continue to develop, the performance requirements for aluminum alloys are constantly increasing, making it a challenge to balance production efficiency with strength and toughness.

[0003] In existing technologies, improving the performance of aluminum alloys is usually achieved by adding more alloying elements such as Mn and Cr. However, high Mn and high Cr content significantly increases the deformation resistance of aluminum rods (the hardness of aluminum rods can reach about 60 HV), resulting in low extrusion production efficiency. This is especially true for profiles with complex cavity structures, where the extrusion breakthrough pressure is high, the discharge speed is limited, and the production cost is high.

[0004] In terms of homogenization processes, traditional single-stage homogenization processes and slow cooling methods after homogenization are insufficient to effectively suppress the growth and coarsening of the second phase at high temperatures. The coarse second phase cannot be fully dissolved in the aluminum matrix during subsequent extrusion processes, affecting not only the mechanical properties of the profile but also forming wide non-precipitation bands at grain boundaries, significantly reducing the profile's bending toughness and resulting in a lower bending angle, making it difficult to meet the stringent high toughness requirements of automotive structural components.

[0005] To address these challenges, researchers have been exploring new aluminum alloy formulations and manufacturing processes. However, traditional methods often suffer from drawbacks such as complex operations, low efficiency, and high costs. Therefore, developing a novel manufacturing process for 6-series aluminum alloys that simultaneously achieves strength, good toughness, and low cost has become a key focus and challenge in current research. This requires not only optimizing the alloy composition ratios but also combining innovations in various stages of the processing technology to achieve an efficient and stable production process and superior product performance. Summary of the Invention

[0006] The purpose of this invention is to provide a production process for low-alloyed, high-strength, and high-toughness 6-series aluminum alloys; and to solve one or more technical problems in the prior art, to provide at least one beneficial option or create conditions.

[0007] To achieve the above objectives, the present invention adopts the following technical solution.

[0008] A manufacturing process for 6-series high-toughness, medium-high-strength aluminum alloys includes the following steps:

[0009] 1) Melting and casting: Add the prepared aluminum alloy raw materials to the melting furnace to melt into aluminum liquid at a melting temperature of 700-760℃, and stir evenly using an electromagnetic stirring device for 25-40 minutes; use a refining agent to refine 2-3 times, each refining time for 20-30 minutes; let stand for 30-60 minutes, then degas online and filter by plate; finally cast the aluminum liquid into aluminum alloy ingots at a casting temperature of 690-730℃, a casting speed of 50-80 mm / min, and a cooling water flow rate of 3000-4000 L / min.

[0010] The aluminum alloy raw material is designed with low Mn and controlled Cr content, specifically in the following proportions: Si 0.59~0.63%, Fe≤0.15%, Cu 0.02~0.10%, Mn 0.22~0.30%, Mg 0.62~0.67%, Cr 0.05~0.1%, Zn≤0.03%, Ti≤0.04%, with the balance being Al, by weight percentage. This aluminum alloy raw material, while maintaining the strength of 6-series alloys, exhibits lower deformation resistance, resulting in better production efficiency and lower production costs compared to high Mn (>0.30wt%) and high Cr (>0.10wt%) alloys. The added small amounts of Mn and Cr effectively suppress grain coarsening in extruded profiles while avoiding excessively high content that could increase the deformation resistance of aluminum alloy castings. Excessive Cu may form a brittle Cu-containing phase, posing a certain risk to toughness; therefore, it is preferable to control the Cu content to less than 0.10%.

[0011] 2) Homogenization: A two-stage homogenization process is used to homogenize the aluminum alloy casting obtained in step 1). The casting is held at 450–460℃ for 2–3 hours to dissolve the low-melting-point phase and achieve initial homogenization. Then, it is held at 550–560℃ for 8–9 hours to eliminate micro-segregation and promote the spheroidization and dispersion of the Mg2Si phase, resulting in a fine and uniform grain structure and a dispersed second phase. After homogenization, rapid cooling with water mist is used, controlling the cooling time to below 100℃ to within 60 minutes. Rapid cooling effectively inhibits the growth of the second phase at high temperatures, thus avoiding the appearance of coarse, unsolvable second phases in subsequent extrusion processes.

[0012] 3) Extrusion: The homogenized aluminum alloy ingot is extruded to obtain aluminum alloy profiles. The extrusion ingot temperature is 475~500℃, the discharge speed is 5~8m / min, and the discharge port temperature is 535~550℃, which maximizes the dissolution of Mg2Si into the aluminum matrix. The cooling method after extrusion is water spray cooling. The profile temperature after exiting the water tank is <40℃. Rapid cooling inhibits the precipitation of coarse phases at grain boundaries, forming narrow precipitation-free zones and improving bending performance.

[0013] 4) Aging: The extruded aluminum alloy profiles are subjected to a two-stage aging process. First, they are held at 140-60℃ for 1-3 hours to allow uniform and fine metastable phases to precipitate preferentially (the low temperature section promotes the formation of GP regions / atomic clusters, providing more nucleation sites for subsequent precipitation). Then, they are held at 170-190℃ for 4-8 hours to ensure that the precipitated phases are small in size and dispersed in distribution, thus achieving a good match between strength and toughness.

[0014] The aforementioned two-stage aging parameters can be flexibly selected within the specified range: the low-temperature stage (140–160°C) mainly promotes uniform nucleation of GP regions / clusters, while the high-temperature stage (170–190°C) controls β″ phase growth and moderate over-aging. Because this invention uses a low Mn composition and combines two-stage homogenization with rapid water mist cooling to form a narrow, non-precipitation zone, the matrix is ​​insensitive to fluctuations in aging temperature and time. Therefore, comprehensive properties such as tensile strength ≥290MPa, yield strength ≥255MPa, and bending angle ≥100° can be obtained within a relatively wide aging window. It exhibits high process tolerance and is easy to control stably in industrial applications.

[0015] On the other hand, the present invention also provides a 6-series high-toughness, medium-high-strength aluminum alloy, which is produced using a production process for a 6-series high-toughness, medium-high-strength aluminum alloy as described in the claims.

[0016] Through actual production verification, the present invention has at least the following beneficial effects:

[0017] I. Significantly Reduced Deformation Resistance and Lower Production Costs: Due to the low-Mn and controlled-Cr composition design, the hardness of the aluminum alloy casting is controlled at around 43HV. Compared to a high Mn / Cr ratio, the extrusion breakthrough pressure is reduced (by approximately 5%). The significantly reduced hardness of the aluminum alloy casting improves extrusion fluidity, allowing for a discharge speed of 5-8 m / min and a substantial increase in production efficiency. This is particularly suitable for the high-efficiency extrusion production of profiles with more than 10 complex small-cavity structures. Simultaneously, the low-alloy design reduces the amount of alloying elements such as Mn and Cr, lowering the hardness of the aluminum alloy casting by approximately 28%. The process flow is more rational and controllable, resulting in a better overall production cost compared to traditional high-alloy schemes, demonstrating significant economic benefits.

[0018] II. Excellent mechanical properties and significantly improved toughness: The aluminum alloy profiles obtained by this invention have a tensile strength ≥290MPa and a yield strength ≥255MPa, achieving a comprehensive mechanical property level of medium to high strength, meeting the requirements for automotive structural components; and this effect remains stable within a wide aging window of 140~160℃×1~3h+170~190℃×4~8h, showing good tolerance to fluctuations in aging parameters and easy industrial-scale stable control; furthermore, the aluminum alloy profiles obtained by this invention have a bending angle of up to 107°, exhibiting outstanding bending forming performance. Detailed Implementation

[0019] The specific embodiments of the present invention will be further described below to make the technical solution and its beneficial effects clearer and more explicit. The embodiments described below are exemplary and intended to explain the present invention, and should not be construed as limiting the present invention.

[0020] Additional aspects and advantages of the invention will become apparent in the following description or may be learned by practice of the invention.

[0021] Example 1.

[0022] A production process for 6-series high-toughness, medium-high-strength aluminum alloys, comprising the following steps:

[0023] 1) Melting and casting: The prepared aluminum alloy raw materials are added to the melting furnace and melted into aluminum liquid at a melting temperature of 730℃. The mixture is stirred evenly using an electromagnetic stirring device for 30 minutes. The mixture is then refined three times with a refining agent, with each refining time being 20 minutes. After standing for 45 minutes, the mixture is degassed online and filtered through a plate filter. Finally, the aluminum liquid is cast into aluminum alloy rods at a casting temperature of 700℃, a casting speed of 60 mm / min, and a cooling water flow rate of 3000 L / min.

[0024] The alloy composition of the aluminum alloy raw material is: Si 0.598%, Fe 0.112%, Cu 0.023%, Mn 0.223%, Mg 0.63%, Cr 0.065%, Zn 0.012%, Ti 0.017%, with the balance being Al, by weight percentage.

[0025] 2) Homogenization: A two-stage homogenization process is adopted, holding at 450℃ for 2.5 hours, and then directly raising the temperature to 560℃ and holding for 9 hours. After homogenization, water mist cooling is used for rapid cooling, controlling the time for the aluminum alloy casting to cool to below 100℃ within 60 minutes.

[0026] 3) Extrusion: Extrusion bar temperature 490℃, discharge speed 5.5m / min, discharge outlet temperature 540℃, cooling method is water spray cooling.

[0027] 4) Aging: The aging process is 160℃×1.5h+175℃×5h. Holding at 160℃ for 1.5h allows the profile to preferentially precipitate uniform and fine metastable phases, and then holding at 175℃ for 5h ensures the strength of the alloy.

[0028] Example 2.

[0029] A manufacturing process for 6-series high-toughness, medium-high-strength aluminum alloys includes the following steps:

[0030] 1) Melting and casting: The prepared aluminum alloy raw materials are added to the melting furnace and melted into aluminum liquid at a melting temperature of 700℃. The mixture is stirred evenly using an electromagnetic stirring device for 40 minutes. The mixture is then refined twice with a refining agent, with each refining time being 20 minutes. After standing for 60 minutes, the mixture is degassed online and filtered through a plate filter. Finally, the aluminum liquid is cast into aluminum alloy rods at a casting temperature of 690℃, a casting speed of 50 mm / min, and a cooling water flow rate of 3000 L / min.

[0031] The alloy composition of the aluminum alloy raw material is: Si 0.625%, Fe 0.111%, Cu 0.029%, Mn 0.286%, Mg 0.661%, Cr 0.092%, Zn 0.0122%, Ti 0.032%, with the balance being Al, by weight percentage.

[0032] 2) Homogenization: A two-stage homogenization process is adopted, holding at 460℃ for 2 hours, and then directly raising the temperature to 560℃ and holding for 8 hours. After homogenization, water mist cooling is used for rapid cooling, controlling the time for the aluminum alloy casting to cool to below 100℃ within 60 minutes.

[0033] 3) Extrusion: Extrusion bar temperature 500℃, discharge speed 7.5m / min, discharge outlet temperature 550℃, cooling method is water spray cooling.

[0034] 4) Aging: The aging process is 140℃×3h+190℃×4h. Holding at 140℃ for 3h allows the profile to preferentially precipitate uniform and fine metastable phases, and then holding at 190℃ for 4h ensures the alloy strength.

[0035] Example 3.

[0036] A manufacturing process for 6-series high-toughness, medium-high-strength aluminum alloys includes the following steps:

[0037] 1) Melting and casting: The prepared aluminum alloy raw materials are added to the melting furnace and melted into aluminum liquid at a melting temperature of 760℃. The mixture is stirred evenly using an electromagnetic stirring device for 25 minutes. The mixture is then refined three times with a refining agent, with each refining time being 20 minutes. After standing for 30 minutes, the mixture is degassed online and filtered through a plate filter. Finally, the aluminum liquid is cast into aluminum alloy rods at a casting temperature of 730℃, a casting speed of 80 mm / min, and a cooling water flow rate of 3000 L / min.

[0038] The alloy composition of the aluminum alloy raw material is: Si 0.598%, Fe 0.112%, Cu 0.023%, Mn 0.223%, Mg 0.63%, Cr 0.065%, Zn 0.012%, Ti 0.017%, with the balance being Al, by weight percentage.

[0039] 2) Homogenization: A two-stage homogenization process is adopted, which involves holding the temperature at 450℃ for 3 hours, and then directly raising the temperature to 550℃ and holding it for 9 hours. After homogenization, water mist cooling is used for rapid cooling, and the time for the aluminum alloy casting to cool to below 100℃ is controlled within 60 minutes.

[0040] 3) Extrusion: Extrusion bar temperature 480℃, discharge speed 6.5m / min, discharge outlet temperature 540℃, cooling method is water spray cooling.

[0041] 4) Aging: The aging process is 140℃×2h+175℃×5h. Holding at 140℃ for 2h can promote uniform nucleation of GP regions / atomic clusters, providing sufficient nucleation sites for subsequent precipitation. Then, holding at 175℃ for 5h ensures the strength of the alloy.

[0042] Example 4.

[0043] A manufacturing process for 6-series high-toughness, medium-high-strength aluminum alloys includes the following steps:

[0044] 1) Melting and casting: The prepared aluminum alloy raw materials are added to the melting furnace and melted into aluminum liquid at a melting temperature of 720℃. The mixture is stirred evenly using an electromagnetic stirring device for 35 minutes. The mixture is then refined three times with a refining agent, with each refining time being 25 minutes. After standing for 50 minutes, the mixture is degassed online and filtered through a plate filter. Finally, the aluminum liquid is cast into aluminum alloy rods at a casting temperature of 700℃, a casting speed of 60 mm / min, and a cooling water flow rate of 4000 L / min.

[0045] The alloy composition of the aluminum alloy raw material is: Si 0.598%, Fe 0.112%, Cu 0.023%, Mn 0.223%, Mg 0.63%, Cr 0.065%, Zn 0.012%, Ti 0.017%, with the balance being Al, by weight percentage.

[0046] 2) Homogenization: A two-stage homogenization process is adopted, which involves holding the aluminum alloy casting at 450℃ for 2.5 hours and then directly raising the temperature to 550℃ and holding it for 8 hours. After homogenization, water mist cooling is used for rapid cooling, and the time for the aluminum alloy casting to cool to below 100℃ is controlled within 60 minutes.

[0047] 3) Extrusion: Extrusion bar temperature 500℃, discharge speed 7.5m / min, discharge outlet temperature 550℃, cooling method is water spray cooling.

[0048] 4) Aging: The aging process is 155℃×2h+188℃×5h. Holding at 155℃ for 2h allows the profile to preferentially precipitate uniform and fine metastable phases, and then holding at 188℃ for 4h ensures the alloy strength.

[0049] Comparative Example 1.

[0050] This comparative example is basically the same as Example 1, except that it adopts a high Mn and high Cr design, with Mn > 0.30% and Cr > 0.10%.

[0051] Comparative Example 2.

[0052] This comparative example is basically the same as Example 1, except that the alloy composition of the aluminum alloy raw material is different. The alloy composition of this comparative example is: Si 0.544%, Fe 0.213%, Cu 0.229%, Mn 0.366%, Mg 0.553%, Cr 0.168%, Zn 0.008%, Ti 0.019%, with the balance being Al, by weight percentage.

[0053] Comparative Example 3.

[0054] This comparative example is basically the same as Example 1, except that the homogenization process is different. A single-stage homogenization process is used, and the temperature is directly kept at 560°C for 9 hours (without passing through the 450°C low-temperature section). After homogenization, it is first cooled by strong air for 2 hours, and then cooled to room temperature by water mist.

[0055] Comparative Example 4.

[0056] This comparative example is basically the same as Example 1, except that the Cu content is 0.30 wt%.

[0057] Comparative Example 5.

[0058] This comparative example is basically the same as Example 1, except that the Cu content is 0.005 wt%.

[0059] Comparative Example 6.

[0060] This comparative example is basically the same as Example 1, except that the content of Mn is 0.50wt%.

[0061] Comparative Example 7.

[0062] This comparative example is basically the same as Example 1, except that the content of Mn is 0.10wt%.

[0063] Comparative Example 8.

[0064] This comparative example is basically the same as Example 1, except that the Cr content is 0.18wt%.

[0065] Comparative Example 9.

[0066] This comparative example is basically the same as Example 1, except that the Cr content is 0.02wt%.

[0067] To better demonstrate the technological advancements of this invention, the performance of the aluminum alloys obtained in Examples 1-4 and Comparative Examples 1-9 was tested, and the results are shown in Table 1.

[0068] Table 1. Comparison of the properties of aluminum alloys prepared in Examples 1-4 and Comparative Examples 1-9.

[0069]

[0070] As shown in Table 1, the aluminum alloys obtained in each embodiment of the present invention have tensile strength ≥290MPa, yield strength ≥255MPa, bending angle ≥103°, extrusion breakthrough pressure ≤28.5MPa, and aluminum alloy casting rod hardness ≤45HV. The comprehensive mechanical properties reach a high toughness and medium-high strength level, meeting the requirements for automotive structural parts. Moreover, this effect remains stable within a wide aging window of 140~160℃×1~3h+170~190℃×4~8h, showing good tolerance to fluctuations in aging parameters and easy industrial-scale stable control. At the same time, the low hardness of the aluminum alloy casting rod improves extrusion fluidity, and the discharge speed can reach 5~8m / min, greatly improving production efficiency. It is especially suitable for the efficient extrusion production of profiles with more than 10 complex small cavities.

[0071] As can be seen from Comparative Examples 1 and 2, when the Mn and Cr contents significantly exceed the maximum values ​​defined in this invention (Comparative Example 1), the extrusion breakthrough pressure and the hardness of the aluminum alloy casting rod both increase significantly, and the bending angle decreases significantly; moreover, this change is not affected by reducing the Si and Mg contents (Comparative Example 2).

[0072] Comparative Example 3 shows that when a single-stage homogenization process is used and rapid cooling is not performed after homogenization, the tensile strength, elongation, and bending angle of the resulting aluminum alloy all decrease significantly. This may be because the two-stage homogenization + water mist rapid cooling process effectively suppresses the coarsening of the second phase, forming a narrow, precipitation-free zone.

[0073] Comparative Examples 4-9 show that: when Cu is too high (Comparative Example 4), the bending angle drops sharply to 92°; when Cu is too low (Comparative Example 5), the tensile strength is only 284.6 MPa, which is below standard, and the yield strength is only 251.3 MPa, which is also below standard. When Mn is too high (Comparative Example 6), the hardness of the aluminum alloy casting increases to 52 HV, the extrusion breakthrough pressure increases to 29.2 MPa, and the bending angle drops to 96°; when Mn is too low (Comparative Example 7), the bending angle is 99°, which is below standard, and the tensile strength is 287.2 MPa, which is also below standard. When Cr is too high (Comparative Example 8), the bending angle drops to 94°, and the hardness increases to 50 HV; when Cr is too low (Comparative Example 9), the tensile strength is 285.8 MPa, and the yield strength is 252.7 MPa, which are both below standard.

[0074] If the content of any of the elements Cu, Mn, and Cr deviates from the range defined in this invention, at least one of the indicators of strength, toughness, or deformation resistance will fail to meet the standard. In particular, when Mn exceeds the range, whether it is too high or too low, it will lead to a decrease in bending angle. The synergistic ratio of Cu (0.02-0.10%), Mn (0.22-0.30%), and Cr (0.05-0.1%), which is "low but not lacking", is a necessary condition for this invention to achieve the comprehensive performance of tensile strength ≥290MPa, yield strength ≥255MPa, bending angle ≥100°, and low deformation resistance.

[0075] Based on the above description of the principles, those skilled in the art should understand that this invention is not limited to the specific embodiments described above. Improvements and substitutions made using techniques known in the art based on this invention all fall within the scope of protection of this invention, which should be defined by the claims and their equivalents. Parts not described in the specific embodiments are all prior art or common knowledge.

Claims

1. A production process for 6-series high-toughness, medium-high strength aluminum alloys, characterized in that, Includes the following steps: 1) Melting and casting: The prepared aluminum alloy raw materials are melted and cast into aluminum alloy ingots. The composition ratio of the aluminum alloy raw materials is: Si 0.59~0.63%, Fe≤0.15%, Cu 0.02~0.10%, Mn 0.22~0.30%, Mg 0.62~0.67%, Cr 0.05~0.1%, Zn≤0.03%, Ti≤0.04%, and the balance is Al, by weight percentage. 2) Homogenization: The aluminum alloy casting obtained in step 1) is subjected to a two-stage homogenization process. The low-melting-point phase is dissolved and initially homogenized at 450-460℃ for 2-3 hours. Then, the aluminum alloy casting is kept at 550-560℃ for 8-9 hours to eliminate microsegregation and promote the spheroidization and dispersion of the Mg2Si phase, resulting in a fine and uniform grain structure and a dispersed second phase. After homogenization, the aluminum alloy casting is rapidly cooled to below 100℃ within 60 minutes. 3) Extrusion: The homogenized aluminum alloy casting rod is extruded to obtain aluminum alloy profiles, and the extruded aluminum alloy profiles are cooled by water spraying. 4) Aging: The extruded aluminum alloy profiles are subjected to a two-stage aging process. The first stage of aging causes the aluminum alloy profiles to preferentially precipitate uniform and fine metastable phases, and the second stage of aging ensures that the precipitated phases are small in size and dispersed in distribution.

2. The production process of a 6-series high-toughness, medium-high strength aluminum alloy according to claim 1, characterized in that, In step 1), the prepared aluminum alloy raw materials are added to the melting furnace to melt into aluminum liquid, and then cast into aluminum alloy rods after stirring, refining, degassing and filtering.

3. The production process of a 6-series high-toughness, medium-high strength aluminum alloy according to claim 2, characterized in that, In step 1), the melting and casting process, the melting temperature is 700-760℃; the stirring time is 25-40 min; the refining process is 2-3 times, with each refining time being 20-30 min; the settling and degassing time is 30-60 min; the casting temperature is 690-730℃; the casting speed is 50-80 mm / min; and the cooling water flow rate is 3000-4000 L / min.

4. The production process of a 6-series high-toughness, medium-high strength aluminum alloy according to claim 1, characterized in that, In step 2), the homogenization step is cooled by water mist cooling.

5. The production process of a 6-series high-toughness, medium-high strength aluminum alloy according to claim 1, characterized in that, In step 3), the extrusion bar temperature is 475-500℃, the discharge speed is 5-8m / min, and the discharge port temperature is 535-550℃; the temperature of the aluminum alloy profile after water cooling in the water tank is <40℃.

6. The production process of a 6-series high-toughness, medium-high strength aluminum alloy according to claim 1, characterized in that, In step 4), the aging process is carried out at a temperature of 140-60℃ for 1-3 hours and at a temperature of 170-190℃ for 4-8 hours.

7. A 6-series high-toughness, medium-high strength aluminum alloy, characterized in that, It is prepared using the production process of a 6-series high-toughness, medium-high strength aluminum alloy as described in any one of claims 1-6.

8. A 6-series high-toughness, medium-high strength aluminum alloy according to claim 7, characterized in that, Tensile strength ≥290MPa, yield strength ≥255MPa and bending angle ≥100°.

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