A process for producing 6xxx aluminum alloy profiles for automotive applications

Abstract

This invention discloses a production process for 6xxx aluminum alloy profiles for automobiles, belonging to the field of aluminum alloy extrusion forming technology. This method optimizes the alloy composition, strictly controls the Fe and Mn content to suppress harmful brittle phases; employs a three-stage gradient heating homogenization treatment to eliminate ingot structural defects; implements high-temperature, low-speed extrusion to ensure full welding of internal ribs in complex cavities; utilizes an online three-stage gradient quenching process to effectively control cooling stress and deformation; and achieves an optimal balance between strength and corrosion resistance through a three-stage over-aging treatment. The aluminum alloy profiles produced by this invention exhibit excellent comprehensive performance, including tensile strength ≥306MPa, yield strength ≥278MPa, straightness ≤1mm / m, and a CASS test rating ≥9 after 48 hours. They also demonstrate good welding during low-magnification corrosion testing, fundamentally solving problems such as poor welding, large quenching deformation, and poor corrosion resistance.

Description

Technical Field

[0001] This invention belongs to the field of aluminum alloy extrusion molding technology, specifically relating to a production process for complex multi-cavity 6xxx series aluminum alloy profiles used in automotive lightweight structures. Background Technology

[0002] With the continuous advancement of automotive lightweighting, complex multi-cavity 6xxx series aluminum alloy profiles are widely used in vehicle body structural components due to their high strength and formability. However, in actual production, conventional high-speed extrusion processes are prone to insufficient welding problems—when the metal flow in the shunt holes and welding cavities fuses, if the flow rate is too fast or the temperature is not properly controlled, it will lead to a loose microstructure in the weld area and a significant reduction in mechanical properties. At the same time, severe quenching deformation is also a prominent problem. The large difference in cooling rates between thick and thin sections can easily generate uneven residual stress during online quenching, leading to geometric deviations such as bending and twisting, affecting assembly accuracy. In addition, although 6xxx series alloys themselves do not have stress corrosion tendency, if the composition is not properly controlled (such as high Fe and Cu impurities) or the aging treatment is insufficient, there is still a risk of intergranular corrosion or exfoliation corrosion, affecting service life. Summary of the Invention

[0003] This invention aims to overcome the shortcomings of existing technologies and provide a production process for 6xxx aluminum alloy profiles for automobiles. Through a complete process including synergistic optimization of composition design, three-stage gradient homogenization, high-temperature low-speed extrusion, three-stage gradient quenching, and three-stage over-aging, it fundamentally solves problems such as poor welding, severe quenching deformation, and insufficient corrosion resistance in the profiles.

[0004] To achieve the above objectives, the present invention adopts the following technical solution:

[0005] This invention provides a manufacturing process for 6xxx aluminum alloy profiles for automobiles, specifically including:

[0006] S1. Alloy casting: Melting and casting aluminum alloy ingots according to the set alloy composition range, wherein the alloy composition by weight percentage is: Si: 1.0-1.3%, Mg: 0.8-1.0%, Fe: ≤0.10%, Cu: 0.10-0.15%, Mn: 0.40-0.60%, Cr: 0.03-0.05%, Zn: ≤0.02%, Ti: 0.02-0.03%, individual impurities ≤0.05%, total impurities ≤0.15%, balance Al; S2. Homogenization treatment: Homogenizing the ingots with a three-stage gradient heating process; S3. Extrusion molding: Extruding the homogenized ingots after heating to obtain aluminum profiles; S4. Quenching and stretching straightening treatment: Quenching and stretching straightening treatment of the extruded aluminum profiles with online three-stage gradient cooling; S5. Aging treatment: Aging treatment of the quenched aluminum profiles with a three-stage over-aging process.

[0007] Furthermore, in step S1, the melting temperature is 730-750°C, and the melt is refined, degassed, filtered, purified, and cast to obtain an aluminum alloy ingot.

[0008] The process employs smelting at 730-750℃, combined with online rotary degassing and 30ppi ceramic plate filtration for deep purification, ensuring that the hydrogen content of the melt is ≤0.1 mL / 100g Al. This ensures that the melt is cast into high-quality round ingots of Φ370mm×950mm, providing a high-purity and high-plasticity material basis for subsequent processes.

[0009] Furthermore, the three-stage gradient heating homogenization process in step S2 specifically involves:

[0010] First stage: Increase the temperature to 440-460℃ at a rate of 75-85℃ / h, and hold for 1-3 hours;

[0011] Second stage: Increase the temperature to 520-540℃ at a rate of 55-65℃ / h, and hold for 3-5 hours;

[0012] The third stage: raise the temperature to 565-575℃ at a rate of 35-45℃ / h and hold for 5-7 hours;

[0013] The total heat preservation time is 9-15 hours. After completion, the product is removed from the oven and air-cooled to room temperature.

[0014] By optimizing the composition and using a three-stage gradient homogenization process to eliminate dendritic segregation and brittle phases in the ingot, a billet with a uniform microstructure is provided for extrusion. Then, by using a high-temperature, low-speed extrusion method, the residence time of the metal flow in the high-temperature, high-pressure welding cavity is greatly extended, which promotes the full diffusion of interface atoms and achieves complete metallurgical fusion. This fundamentally avoids defects such as incomplete welding, inclusions, and microcracks, and ensures that the welding interface is consistent with the microstructure of the matrix.

[0015] The homogenization process, through slow, stepwise heating, promotes full diffusion of elements, effectively eliminates dendrite segregation, and fosters the growth of coarse second phases (such as...). The process fully re-dissolves the material and significantly reduces micropores, resulting in high-quality extruded billets with highly uniform structure and low-magnification defects (slag ≤ grade 1, very few pores).

[0016] Furthermore, in step S3, the ingot head heating temperature is 525-530℃, the middle heating temperature is 515-525℃, and the tail heating temperature is 510-515℃, with the head temperature being higher than the middle temperature and the tail temperature being higher; the extrusion cylinder temperature is 455-465℃; the die preheating temperature is 500-510℃; and the extrusion speed is controlled at 1.2-1.6 m / min.

[0017] Higher temperature settings improve metal fluidity, while lower extrusion speeds significantly extend the residence time and pressure holding time of the metal in the mold welding cavity, ensuring that the metal flow can fully fuse in multi-cavity structures, especially in the inner rib areas, thereby obtaining a dense, defect-free welding interface.

[0018] Furthermore, the three-stage gradient cooling quenching in step S4 specifically involves:

[0019] First stage air cooling: Use an air speed of 20m / s-30m / s to cool for 15-25 seconds, so that the profile temperature drops to 390-410℃;

[0020] The second stage is water mist cooling: water mist cooling at a pressure of 0.3-0.5 MPa is used for 20-30 seconds to reduce the profile temperature to 140-160℃;

[0021] The third stage is spray cooling: water with a pressure of 0.1 to 0.2 MPa is used as the medium for uniform spray cooling for 20-30 seconds, so that the final cooling temperature of the profile is ≤50℃.

[0022] This gradient quenching process achieves precise control of the cooling rate of complex cross sections through the path of "slow cooling (buffering thermal shock) → intermediate cooling (ensuring solid solution) → uniform cooling (minimizing stress)," which greatly reduces thermal stress and warping deformation caused by uneven cooling.

[0023] Furthermore, in the stretching and straightening step S4, the stretching amount of the profile is controlled to be 0.5 to 1.0%.

[0024] This is to further correct micro-deformation and improve the straightness of the profile.

[0025] Furthermore, the three-level over-age processing in step S5 specifically includes:

[0026] First stage: Heat to 100-110℃ and keep warm for 3-5 hours;

[0027] Second stage: Heat to 150-160℃ and keep warm for 5-7 hours;

[0028] Third stage: Heat to 245-255℃ and keep warm for 5-7 hours;

[0029] After the third stage is completed, the product is removed from the oven and allowed to cool naturally to room temperature.

[0030] This composite overaging process, through prolonged holding at different temperature stages, promotes the uniform precipitation of strengthening phases (β″, β′, etc.) in a coarser and more stable morphology. It not only provides sufficient strengthening effect within the grains to maintain high strength, but also significantly reduces the electrochemical activity of grain boundaries by optimizing the precipitated phases at the grain boundaries, thereby achieving an excellent balance between strength and corrosion resistance.

[0031] Beneficial Effects: The production process of 6xxx aluminum alloy profiles for automobiles proposed in this invention, through synergistic optimization of composition design, three-level gradient homogenization, high-temperature low-speed extrusion, three-level gradient quenching, and three-level over-aging process, produces complex multi-cavity aluminum alloy profiles with excellent comprehensive performance, including tensile strength ≥306MPa, yield strength ≥278MPa, straightness ≤1mm / m, CASS test rating ≥9 after 48h, and good welding during low-magnification corrosion inspection. This fundamentally solves the problems of poor welding, large quenching deformation, and poor corrosion resistance. Detailed Implementation

[0032] The embodiments of the present invention will be described in further detail below with reference to examples, comparative examples, and accompanying tables. The following examples are for illustrative purposes only and should not be construed as limiting the scope of the invention.

[0033] Example 1

[0034] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon) and filtered through a 30ppi ceramic foam filter, and then cast into ingots of Φ370mm × 950mm.

[0035] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0036] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0037] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0038] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0039] Example 2

[0040] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0041] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 440℃ at a rate of 75℃ / h, held for 3 hours, then heated to 520℃ at a rate of 55℃ / h, held for 5 hours, and finally heated to 565℃ at a rate of 35℃ / h, held for 7 hours, for a total holding time of 15 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0042] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0043] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0044] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0045] Example 3

[0046] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0047] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 460℃ at a rate of 85℃ / h, held for 1 hour, then heated to 540℃ at a rate of 65℃ / h, held for 3 hours, and finally heated to 575℃ at a rate of 45℃ / h, held for 5 hours, for a total holding time of 9 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0048] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0049] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0050] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0051] Example 4

[0052] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0053] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0054] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 525℃, the middle temperature at 515℃, and the tail temperature at 510℃. The extrusion barrel temperature is set at 455℃, and the die (flat flow divider die) is preheated to 500℃. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.2 m / min, with an extrusion ratio of 35.

[0055] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0056] The aging process involves first heating the furnace to 105℃ and holding for 4 hours, then heating it to 155℃ and holding for 6 hours, and finally heating it to 250℃ and holding for 6 hours. The furnace is then removed and air-cooled to room temperature.

[0057] Example 5

[0058] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0059] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0060] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 530℃, the middle temperature at 525℃, and the tail temperature at 515℃. The extrusion barrel temperature is set at 465℃, and the die (flat flow divider die) is preheated to 510℃. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.6 m / min, with an extrusion ratio of 35.

[0061] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0062] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0063] Example 6

[0064] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0065] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0066] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0067] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 15 seconds with strong airflow at a speed of 20 m / s, reducing the surface temperature to approximately 410°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.3 MPa for 20 seconds, reducing the temperature to approximately 160°C. Finally, they are cooled to below 50°C with uniform water curtain spray at a pressure of 0.1 MPa. Afterward, the profiles undergo 0.5% tensile straightening on a tension straightening machine.

[0068] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0069] Example 7

[0070] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0071] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0072] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0073] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 25 seconds with strong airflow at a speed of 30 m / s, reducing the surface temperature to approximately 390°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.5 MPa for 30 seconds, reducing the temperature to approximately 140°C. Finally, they are cooled to below 50°C with uniform water curtain spray at a pressure of 0.2 MPa. Afterward, the profiles undergo 1.0% tensile straightening on a tension straightening machine.

[0074] Aging: First, heat the furnace to 105℃ and hold for 4 hours, then heat to 155℃ and hold for 6 hours, and finally heat to 250℃ and hold for 6 hours. Remove from the furnace and air cool to room temperature.

[0075] Example 8

[0076] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0077] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0078] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0079] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0080] Aging: First, heat the furnace to 100℃ and hold for 5 hours, then heat to 150℃ and hold for 7 hours, and finally heat to 245℃ and hold for 7 hours. Remove from the furnace and air cool to room temperature.

[0081] Example 9

[0082] Composition and casting: The raw materials were batched according to the following ratio: Si: 1.2%, Mg: 0.9%, Fe: 0.08%, Cu: 0.12%, Mn: 0.50%, Cr: 0.04%, Zn: 0.01%, Ti: 0.025%, other impurities totaling 0.12%, with Al as the balance. The mixture was smelted at 740℃, degassed by rotary jet (argon), and filtered through a 30ppi ceramic foam filter before casting into ingots of Φ370mm × 950mm.

[0083] Homogenization treatment: The ingot was fed into a homogenizing furnace and heated to 450℃ at a rate of 80℃ / h, held for 2 hours, then heated to 530℃ at a rate of 60℃ / h, held for 4 hours, and finally heated to 570℃ at a rate of 40℃ / h, held for 6 hours, for a total holding time of 12 hours. After being removed from the furnace, it was cooled to room temperature by strong air. Samples were taken for low-magnification microstructure examination, and the results showed that the microstructure was uniform, without coarse crystals, and no visible pores were found.

[0084] Extrusion: After the ingot is rolled into a sheet, it is heated in an induction furnace, with the bar head temperature controlled at 528°C, the middle temperature at 520°C, and the tail temperature at 513°C. The extrusion barrel temperature is set at 460°C, and the die (flat flow divider die) is preheated to 505°C. Extrusion is carried out on a 2500-ton extruder at a main bar speed of 1.4 m / min, with an extrusion ratio of 35.

[0085] Quenching and Tensile Straightening: After demolding, the profiles immediately enter the online quenching system. First, they are cooled for 20 seconds with strong airflow at a speed of 25 m / s, reducing the surface temperature to approximately 400°C. Then, they enter a water mist chamber where they are cooled with water mist sprayed at a pressure of 0.4 MPa for 25 seconds, reducing the temperature to approximately 150°C. Finally, they are cooled to below 40°C with uniform water curtain spray at a pressure of 0.15 MPa. Afterward, the profiles undergo 0.8% tensile straightening on a tension straightening machine.

[0086] Aging: First, heat the furnace to 110℃ and hold for 3 hours, then heat to 160℃ and hold for 5 hours, and finally heat to 255℃ and hold for 5 hours. Remove from the furnace and air cool to room temperature.

[0087] Comparative Example 1

[0088] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the homogenization treatment was performed by directly placing them in a furnace at 570°C for 10 hours and then air-cooling them.

[0089] Comparative Example 2

[0090] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the quenching and tension straightening were performed by directly spraying 0.4MPa water mist to cool to 40°C, and then the profiles were tension straightened by 0.8% on a tension straightening machine.

[0091] Comparative Example 3

[0092] 6xxx aluminum profiles were produced according to the production process of Example 1, except that the aging process used was conventional T6 aging: 175℃ for 8 hours, followed by air cooling.

[0093] Comparative Example 4

[0094] 6xxx aluminum profiles were produced according to the production process of Example 1, except for the homogenization treatment: the ingots were fed into a homogenizing furnace, heated to 430°C at a rate of 70°C / h and held for 3 hours, then heated to 510°C at a rate of 50°C / h and held for 5 hours, and finally heated to 560°C at a rate of 30°C / h and held for 7 hours, for a total holding time of 15 hours. After being removed from the furnace, the profiles were cooled to room temperature by strong air.

[0095] Comparative Example 5

[0096] 6xxx aluminum profiles were produced according to the production process of Example 1, except for the homogenization treatment: the ingots were fed into a homogenizing furnace, heated to 470°C at a rate of 90°C / h and held for 1 hour, then heated to 550°C at a rate of 70°C / h and held for 3 hours, and finally heated to 580°C at a rate of 50°C / h and held for 5 hours, for a total holding time of 9 hours. After being removed from the furnace, the profiles were cooled to room temperature by strong air.

[0097] Comparative Example 6

[0098] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the extrusion process involved: after the ingot was rolled into a sheet, it was heated in an induction furnace, with the head temperature controlled at 520°C, the middle temperature at 510°C, and the tail temperature at 505°C. The extrusion barrel temperature was set to 450°C, and the die (flat flow divider die) was preheated to 490°C. Extrusion was carried out on a 2500-ton extruder at a main bar speed of 1 m / min, with an extrusion ratio of 35.

[0099] Comparative Example 7

[0100] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the extrusion process involved: after the ingot was rolled into a sheet, it was heated in an induction furnace, with the head temperature controlled at 535°C, the middle temperature at 530°C, and the tail temperature at 520°C. The extrusion barrel temperature was set to 470°C, and the die (flat flow divider die) was preheated to 520°C. Extrusion was carried out on a 2500-ton extruder at a main bar speed of 1 m / min, with an extrusion ratio of 35.

[0101] Comparative Example 8

[0102] The 6xxx aluminum profiles were produced according to the production process of Example 1, with the difference being in the quenching and tensile straightening: After the profiles were demolded, they immediately entered the online quenching system. First, they were cooled for 25 seconds with a strong wind at a speed of 15 m / s, reducing the surface temperature to approximately 420°C. Then, they entered a water mist chamber and were cooled for 30 seconds with water mist sprayed at a pressure of 0.2 MPa, reducing the temperature to approximately 170°C. Finally, they were cooled to below 60°C with uniform water curtain spray at a pressure of 0.05 MPa. Afterward, the profiles were subjected to 0.4% tensile straightening on a tension straightening machine.

[0103] Comparative Example 9

[0104] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the quenching and tensile straightening were performed as follows: After the profiles were demolded, they immediately entered the online quenching system. First, they were cooled for 15 seconds with a strong wind at a speed of 35 m / s, reducing the surface temperature to approximately 380°C. Then, they entered a water mist chamber and were cooled with water mist sprayed at a pressure of 0.6 MPa for 30 seconds, reducing the temperature to approximately 170°C. Finally, they were cooled to below 40°C with uniform water curtain spray at a pressure of 0.3 MPa. Afterward, the profiles were stretched and straightened by 0.4% on a tension straightening machine.

[0105] Comparative Example 10

[0106] 6xxx aluminum profiles were produced according to the production process of Example 1, except that the aging process was as follows: the temperature was first raised to 90°C and held for 5 hours in the aging furnace, then raised to 140°C and held for 7 hours, and finally raised to 240°C and held for 7 hours. The profiles were then air-cooled to room temperature after being taken out of the furnace.

[0107] Comparative Example 11

[0108] The 6xxx aluminum profiles were produced according to the production process of Example 1, except that the aging process was as follows: the temperature was first raised to 115°C and held for 3 hours in the aging furnace, then raised to 170°C and held for 5 hours, and finally raised to 260°C and held for 5 hours. The profiles were then air-cooled to room temperature after being taken out of the furnace.

[0109] Table 1 Performance Comparison

[0110]

[0111] By comparing the examples and comparative examples, it can be seen that the 6xxx aluminum alloy profiles prepared in Examples 1-9 can significantly improve corrosion performance and welding quality while ensuring stable yield strength and straightness performance, and achieve consistent performance control between batches through online monitoring and dynamic parameter adjustment.

[0112] Comparative Example 1, using a traditional homogenization process, resulted in microcracks in the internal ribs of the profile, uneven microstructure, and substandard internal defects. Comparative Example 2, using traditional quenching and tensile straightening, showed a decrease in yield strength and severe quenching deformation, failing to meet standards. Comparative Example 3, using a traditional aging process, exhibited excellent welding performance but significantly reduced corrosion resistance. Comparative Examples 4-11, by changing the process control, resulted in aluminum alloy profiles with varying mechanical properties, straightness, corrosion resistance, and welding quality, failing to meet product requirements.

[0113] 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 manufacturing process for 6xxx aluminum alloy profiles for automobiles, characterized in that, Includes the following steps: S1. Alloy melting and casting: Melting and casting the alloy into ingots according to the set alloy composition range, wherein the alloy composition by weight percentage is: Si: 1.0~1.3%, Mg: 0.8~1.0%, Fe: ≤0.10%, Cu: 0.10~0.15%, Mn: 0.40~0.60%, Cr: 0.03~0.05%, Zn: ≤0.02%, Ti: 0.02~0.03%, individual impurities ≤0.05%, total impurities ≤0.15%, balance Al; S2. Homogenization treatment: The ingot is subjected to a three-stage gradient heating homogenization treatment; S3. Extrusion molding: The homogenized ingot is heated and then extruded. S4. Quenching and stretching straightening treatment: Online three-stage gradient cooling quenching and stretching straightening treatment is performed on the extruded aluminum profiles. S5. Aging treatment: Perform three-stage over-aging treatment on the quenched aluminum profiles.

2. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 1, characterized in that, In step S1, the melting temperature is 730-750℃, and the melt is refined, degassed, filtered, and cast to obtain an aluminum alloy ingot.

3. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 1, characterized in that, The three-stage gradient heating homogenization process in step S2 specifically involves: First stage: Increase the temperature to 440-460℃ at a rate of 75-85℃ / h, and hold for 1-3 hours; Second stage: Increase the temperature to 520-540℃ at a rate of 55-65℃ / h, and hold for 3-5 hours; The third stage: raise the temperature to 565-575℃ at a rate of 35-45℃ / h and hold for 5-7 hours; The total heat preservation time is 9-15 hours. After completion, the product is removed from the oven and air-cooled to room temperature.

4. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 1, characterized in that, In step S3, the ingot head is heated to 525-530℃, the middle part to 515-525℃, and the tail to 510-515℃, with the head temperature being higher than the middle and tail temperatures; the extrusion cylinder temperature is 455-465℃; the die preheating temperature is 500-510℃; and the extrusion speed is controlled at 1.2-1.6 m / min.

5. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 1, characterized in that, The three-stage gradient cooling quenching in step S4 specifically involves: The first stage of air cooling: use an air speed of 20m / s-30m / s to cool the profile for 15-25 seconds, so that the profile temperature drops to 390-410℃; The second stage is water mist cooling: water mist at a pressure of 0.3 to 0.5 MPa is used to cool the profile for 20 to 30 seconds, so that the profile temperature drops to 140-160℃; The third stage is spray cooling: water with a pressure of 0.1 to 0.2 MPa is used as the medium to cool the profile for 20-30 seconds, so that the final cooling temperature of the profile is ≤50℃.

6. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 5, characterized in that, In the stretching and straightening step S4, the stretching amount of the profile is controlled between 0.5% and 1.0%.

7. The manufacturing process for 6xxx aluminum profiles for automobiles according to claim 1, characterized in that, The three-level timeout processing in step S5 specifically includes: First stage: Heat to 100-110℃ and keep warm for 3-5 hours; Second stage: Heat to 150-160℃ and keep warm for 5-7 hours; Third stage: Heat to 245-255℃ and keep warm for 5-7 hours; After the third stage is completed, the product is removed from the oven and allowed to cool naturally to room temperature.

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