A 6-series energy-absorbing aluminum alloy and its manufacturing method

Abstract

This invention discloses a 6-series energy-absorbing aluminum alloy and its manufacturing method. The aluminum alloy, by mass percentage, comprises: Mg: 0.50–1.20%, Si: 0.40–1.00%, Mn: 0.15–0.95%, Cr: 0–0.25%, Fe: 0.15–0.45%, Ti: 0.015–0.30%, and Cu: 0.10–0.70%; wherein the Mg / Si mass ratio is ≥0.85 / 1, and the total content of Mn+Cr+Fe is ≤1.2%; it also includes an AlTi5C0.25 grain refiner and impurities with a content not exceeding 0.15%, with the balance being Al. This invention optimizes and precisely designs the content of the main alloying elements in the alloy, and introduces TiC nanoparticles using the AlTi5C0.25 grain refiner, enabling the aluminum alloy profile to possess both high strength and excellent crushability.

Description

Technical Field

[0001] This invention belongs to the field of alloy technology, specifically relating to a 6-series energy-absorbing aluminum alloy and its manufacturing method. Background Technology

[0002] With the development of new energy vehicles, reducing vehicle weight to increase range and improving the safety performance of the vehicle body structure are among the development directions of modern automotive materials. 6xxx aluminum alloys, due to their good hot working properties, excellent corrosion resistance, weldability, and high strength, have become the preferred series of alloys for extruded aluminum alloy profiles. Therefore, 6xxx aluminum alloys are increasingly widely used in automotive structural components, especially in safety structural components such as front and rear anti-collision beams, energy-absorbing boxes, battery frames, and side beams. Currently, major aluminum profile manufacturers worldwide are actively developing 6xxx aluminum alloy profiles with higher strength and better application performance, while ensuring their crush resistance.

[0003] Since structural components such as energy-absorbing boxes and anti-collision beams are typically used in the front and rear of automobiles, these parts often face high-temperature service environments, sometimes reaching around 100°C. Therefore, long-term heat resistance is also a problem that energy-absorbing aluminum alloys need to solve.

[0004] Currently, several crushable alloys with yield strengths of 200-280 MPa have been developed both domestically and internationally, exhibiting good crushing performance. When the required yield strength exceeds 240 MPa, the alloying design of such crushable alloys typically requires further increasing the Mg and Si content, reducing excess Si, and introducing Cu elements for auxiliary strengthening. Otherwise, brittle Si or MgSi phases and a wide PFZ (precipitation zone without grain boundaries) are prone to precipitate at grain boundaries. Simultaneously, strong water cooling after extrusion is necessary to reduce the precipitation of excess Si and Cu at grain boundaries and decrease the PFZ width, ensuring high strength without sacrificing ductility and toughness while maintaining Mg+Si ≤ 1.5%, thus guaranteeing its crushing performance. However, this alloy design approach and manufacturing process introduce the following three problems.

[0005] (1) The requirement for strong water cooling at the extrusion outlet results in a large temperature difference between the inner and outer surfaces of the profile after cooling, which increases the internal stress of the profile and causes the dimensions and shape tolerances to exceed the limits. This restricts the configuration design and weight per meter of the energy-absorbing alloy.

[0006] (2) In actual vehicle collision tests, it was found that the energy-absorbing box and anti-collision beam and other components have good deformation characteristics, but the failure occurred at the welded joint. The main reason is that under welding conditions, the welded joint and heat-affected zone will form Al2Cu phase. At the same time, the cooling rate of the heat-affected zone decreases, which leads to an increase in the width of the PFZ in the heat-affected zone. In particular, with the increase of Cu content, the metastable Al2Cu phase is sensitive to aging and is easy to coarsen, thus reducing the mechanical properties of the HAZ.

[0007] (3) Due to the increase in Cu content, the IGC (intergranular corrosion) sensitivity of 6 series aluminum alloys increases significantly. The main reason is that a local galvanic cell is formed between the Cu-rich phase at the grain boundary and the PFZ (grain boundary without precipitation zone), which increases the sensitivity to intergranular corrosion.

[0008] The present invention is made to address the aforementioned problems existing in the prior art. Summary of the Invention

[0009] To address the aforementioned shortcomings in existing technologies, this invention provides a high-strength, medium-to-high-strength 6-series energy-absorbing aluminum alloy with excellent comprehensive performance and its manufacturing method. The inventors discovered that cracks in crushed alloys are usually caused by grain boundary segregation of Si atoms during the cooling process after solution treatment. This invention innovatively employs controlled AlTi5C0.25 and Mg / Si ratios, combined with intense cooling after homogenization and extrusion, to ensure the solution of the grain boundary segregation problem.

[0010] The technical solution of this invention is as follows:

[0011] This invention relates to a 6-series energy-absorbing aluminum alloy, comprising, by weight percentage:

[0012] Mg: 0.50-1.20%, Si: 0.40-1.00%, Mn: 0.15-0.95%, Cr: 0-0.25%, Fe: 0.15-0.45%, Ti: 0.015-0.30%, Cu: 0.10-0.70%; wherein, the Mg / Si mass ratio is ≥0.85 / 1, and the total content of Mn+Cr+Fe is ≤1.2%; it also includes AlTi5C0.25 grain refiner and impurities with a content not exceeding 0.15%, with the balance being Al.

[0013] Mg and Si are the main strengthening elements in 6xxx aluminum alloys. To achieve both high strength and good bending performance, the strengthening phases and main strengthening elements must be designed to maximize the strengthening effect of the β” phase and strictly control the excess of Si. Excess Si can precipitate and accumulate at grain boundaries during the cooling process of the supersaturated solid solution, acting as a crack initiation point when the aluminum alloy is under stress, thus reducing its compressibility. The β” phase, as the most coherent and strengthening precipitate in the supersaturated solid solution of AlMgSi alloys, has a composition close to that of Mg. (4+x) Al (3-x) Si4, (x∈[0,1]), therefore theoretically, although the alloy contains Mg / Si freeThe precipitation ratio is between 0.714 and 0.85, but in the Al-Mg-Si system containing Cu, the precipitation order changes significantly. Some Cu atoms will form Mg4Cu5, Mg4Si4Cu, etc., so a slight excess of Mg is required in this alloy, thus requiring an excess of Si. excess <0, forming a strengthening phase with Mg, meaning the Si content in the aging stage and the Si content in the strengthening phase formed by Mg bonding needs to meet the Mg / Si ratio. free >0.85. If calculated according to the ideal state where Mg5Si6 and Mg4Si4Cu are the main reinforcing phases in the matrix, the formula for calculating the excess Si is:

[0014] Si excess =(wt%Si)-[wt%Mg] / 1.4+(wt%Cu) / 1.75+(wt%Fe)*0.25]

[0015] Si free =(wt%Si) excess -0.25 (wt% Fe)

[0016] In the alloy designed above, the total content of Mn+Cr+Fe is ≤1.2%. The addition of Mn and Cr enables the formation of Al(MnCrFe)Si nanoprecipitates during the homogenization process. These nanoprecipitates exhibit high-temperature stability and pinning effect on grain boundaries, ensuring a reduction in the surface grain coarsening layer. Because metal extrusion is a high-temperature, high-pressure deformation process, short-term high-energy deformation promotes grain recrystallization, softening the metal, especially near the metal surface in direct contact with the die, where strain is greatest and recrystallization conditions are most favorable. However, the Mg+Si content of this high-strength alloy is greater than 1.5%, which inhibits recrystallization. After extrusion, the core structure of the profile is mainly fibrous. Without the addition of MnCr, the core structure would be fibrous, while the surface would be coarse-grained equiaxed. This structure would cause microcracks to appear on the surface during longitudinal crushing, leading to reduced crushing capacity. Therefore, adding a certain amount of Mn and Cr has a significant effect on preventing coarse grains on the surface. However, if too much Mn and Cr are added, the precipitation kinetics of MgSi precipitates and Si will be greatly enhanced, significantly increasing the quenching sensitivity and making it difficult to obtain a supersaturated solid solution after quenching. Therefore, this invention requires the addition of a small amount of Mn and Cr to ensure that the total content of Mn+Cr+Fe is ≤1.2%.

[0017] The aforementioned alloy also includes Cu, with a mass percentage of 0.10–0.70%. The addition of Cu compensates for the insufficient increase in strength of the MgSi precipitates. Generally, when the Cu content exceeds 0.5%, it leads to a decrease in resistance to intergranular corrosion. Customers can adjust the Cu content according to their needs. If strength is more important than corrosion resistance, more Cu can be added, with an upper limit of 0.7%. TiC nanoprecipitates act as heterogeneous nucleation cores for α-Al, increasing the nucleation rate and refining grains. Unlike conventional TiB2 particles, TiB2 tends to segregate at grain boundaries, hindering grain boundary movement and leading to grain refinement. However, this can cause TiB2 to act as a core for the segregation of MgSi, free Si, and Cu elements when cooling between 550°C and 300°C. This segregation of these elements and phases at grain boundaries results in decreased plasticity and an increased difference between electrode potential and intragranular potential, thus reducing the corrosion resistance and mechanical properties of the grain boundaries. Similarly, materials in the heat-affected zone of welding also undergo a cooling process from high temperature to low temperature. When the cooling rate is insufficient, grain boundary segregation and PFZ (partially charged zone) intensify, leading to a decrease in the mechanical properties of the welded joint.

[0018] The aluminum alloy also includes Ti, preferably 0.15%-0.3% by mass percentage. The higher Ti content promotes AlTi peritectic reaction during the early stages of aluminum solidification. Combined with relatively low casting speeds, this results in a sufficient AlTi pre-precipitation structure. This peritectic pre-precipitation structure can form a multilayered structure along the extrusion direction during subsequent extrusion, helping to prevent crack propagation along grain boundaries. Without this layered structure, rapid cooling is necessary to suppress the precipitation of Si, MgSi, etc., at grain boundaries. Therefore, the cooling rate at the extrusion exit of the profile in this invention does not need to be too high.

[0019] The aluminum alloy also includes Fe, at a mass percentage of 0.15-0.45%. During casting, Fe forms the AlFeSi phase at grain boundaries, which is quite brittle, fractures the matrix, and reduces the material's hot workability and plasticity. Therefore, its content should be minimized; however, too low a content can lead to hot cracking in the cast ingot. Furthermore, lower Fe content requires higher purity aluminum, directly increasing alloy costs. Too low an Fe content is also detrimental to the formation of the homogenized Al(FeMnCr)Si nano-precipitates. Therefore, a Fe content of 0.15-0.45% is recommended.

[0020] Other unavoidable impurity elements in the aluminum alloy are individually ≤0.05% and total ≤0.15%.

[0021] The aluminum alloy comprises TiC particles, with over 95% of the particles having a size between 10-900 nm, and an optimal volume fraction of over 0.020%. The TiC particles are added to the melt using an AlTi5C0.25 grain refiner, subsequently dispersing uniformly as heterogeneous nucleation sites, resulting in fine grains. These TiC particles exhibit high-temperature stability and do not undergo solid-state phase transformations during subsequent homogenization, extrusion, and heat treatment. They also have a large wetting angle only with the aluminum matrix. Besides providing increased strength, they do not coarsen the particles or cause grain boundary segregation. On the contrary, during welding, the TiC particles ensure that the molten aluminum solidifies into refined grains, thus preventing deterioration of the weld joint performance.

[0022] In the aforementioned high-strength Al-Mg-Si alloy with excellent comprehensive performance, the thickness of the coarse-grained layer on one side of the Al-Mg-Si alloy surface is controlled to be 1 / 30 of the wall thickness. The core fibrous structure ensures high longitudinal strength and crush resistance of the product, while the uniform grain size of the surface metal and the absence of obvious elemental and phase segregation within the grain boundaries guarantee IGC performance.

[0023] Preferably, the amount of AlTi5C0.25 grain refiner added per ton of aluminum alloy is 1.5-2 kg. AlTi5B1 is generally used as a grain refiner for 6-series aluminum alloys, while AlTi5C0.25 is rarely used as a grain refiner in 6-series alloys because the principles for inhibiting grain growth are different. Therefore, the size of TiC particles in the AlTi5C0.25 grain refiner is subject to strict control. Using AlTi5C0.25 grain refiner makes it easier to control the PFZ region, thereby reducing the susceptibility of Cu to intergranular corrosion.

[0024] Preferably, when the thickness of the aluminum alloy does not exceed 6 mm, the extrusion process can form a fibrous structure with a non-recrystallized cross-section, and the thickness of the surface coarse-grained layer is less than 100 μm. The aluminum alloy product obtained by this invention has a wall thickness ≤ 6 mm. If the wall thickness is too thick, it will increase the difference in properties and structure between the surface metal and the core metal.

[0025] This invention also relates to a method for manufacturing a 6-series energy-absorbing aluminum alloy, comprising the following steps:

[0026] (1) Smelting: Weigh the raw materials aluminum ingots, magnesium ingots, copper granules, aluminum-silicon alloy, manganese agent, iron agent, chromium agent, and aluminum-titanium alloy ingots according to the mass percentage of the elements in the aluminum alloy material, and then add them to the smelting furnace for smelting;

[0027] (2) Refining: Inert gas refining or refining agent refining are used to remove impurities and hydrogen;

[0028] (3) Casting: The air-slip mold semi-continuous casting method is used for casting. When the temperature of the aluminum liquid is between 680-700℃, the casting begins and the casting speed is 40-80mm / min.

[0029] (4) Homogenization: After casting, the casting rod is cooled to room temperature and then taken out. The casting rod is placed in a homogenization furnace for heat preservation at a temperature of 550-570℃ for 1-4 hours. Then, water mist cooling is carried out to ensure that the cooling rate of the casting rod is ≥350℃ / h.

[0030] (5) Extrusion molding: Before extrusion molding, the aluminum rod is preheated to a temperature of 450-510℃; the extrusion ratio is between 30-150; different extrusion speeds are set according to different cross-sections to ensure that the outlet temperature is between 550-575℃; strong water cooling is used at the outlet to ensure a cooling rate of 50-100℃ / s.

[0031] (6) Straightening and aging: After the profile cools to room temperature, it is straightened by a straightening machine, and the elongation is controlled between 1% and 5%. Then it is put into an aging furnace for aging treatment. The aging treatment is T7 treatment, the aging temperature is set to 205℃, and the aging time is between 2.5h and 8h.

[0032] Preferably, in the casting process of step (2), the inclusions are removed by refining agent or gas refining to ensure that the hydrogen content is less than 0.15 mL / 100 g aluminum liquid.

[0033] Preferably, in the casting process of step (2), if the segregation layer on the surface of the ingot is >200μm, the surface segregation layer needs to be removed by peeling.

[0034] Preferably, the wire feeding position is located after the refining equipment. For alloys using AlTi5C0.25 grain refiner, placing the wire feeding position after the refining equipment helps prevent the refining equipment from removing large TiC particles, which are beneficial to the grain refiner.

[0035] Preferably, in order to ensure the stability of the strength after aging, the time from extrusion quenching to room temperature to aging in the aging furnace is controlled between 4 and 16 hours.

[0036] Preferably, the aging treatment in step (5) is T7 treatment, with an aging temperature of 205℃ and a time of 4h.

[0037] The beneficial effects of this invention are:

[0038] (1) This invention optimizes and precisely designs the content of the main alloying elements Mg, Si, Cu, Mn, Cr, and Ti in Al-Mg-Si alloys, and introduces a certain volume fraction of TiC nanoparticles using AlTi5C0.25 grain refiner. This enables the 6-series aluminum alloy profiles to possess both high strength and excellent crushability. More importantly, through precise component ratios and the regulation of nano-TiC particles and matrix structure, its weldability, corrosion resistance, and long-term heat resistance are all superior to similar products. Since the required crushability can be achieved without particularly strong water cooling, more complex structures can be designed, making it particularly suitable for the manufacture of energy-absorbing boxes and anti-collision beams for vehicles.

[0039] (2) AlTi5B1 is generally used as a grain refiner for 6-series aluminum alloys because it has a high grain refinement efficiency. This invention breaks through the conventional principle of grain refiners for 6-series aluminum alloys and uses AlTi5C0.25 as a grain refiner for 6-series aluminum alloys. By controlling the amount and location of AlTi5C0.25, nano-sized TiC acts as a heterogeneous nucleation core for αAl before it agglomerates in the melt. This is different from the TiB2 particles in the conventional AlTi5B1 grain refiner, which mainly refine grains by preventing grain growth and movement through agglomeration at grain boundaries. TiC mainly acts as a nucleation core, refining grains by increasing the nucleation rate. This different grain refinement method fundamentally alters the grain boundary structure, minimizing the segregation of free Si and MgSi at grain boundaries during the cooling process from high to low temperatures at the extrusion exit, weld joint, and weld affected zone. This reduces the PFZ width, improves the grain boundary's resistance to crack propagation, enhances grain boundary mechanical properties, and reduces the tendency for IGC due to compositional differences between grain boundaries and within grains. However, using TiC may reduce the ability to inhibit recrystallization. Therefore, this alloy incorporates MnCr to ensure sufficient Fe, Mn, and Cr content, supplemented by precise homogenization control. This optimizes the volume fraction and size of the dispersed phases in the homogenized matrix, inhibiting recrystallization after extrusion and ultimately forming a uniform fibrous structure.

[0040] (3) This invention can prepare a medium-to-high strength energy-absorbing Al-Mg-Si alloy with excellent comprehensive performance in terms of yield strength, yield strength 200-320MPa, tensile strength 220-380MPa, elongation ≥11%. After a 300mm profile undergoes a 200mm static compression along the extrusion direction, no visible cracks appear on the profile surface. The corrosion resistance meets the requirements of 10 cycles of 4h neutral salt spray test + 16h humid heat climate storage test + 4h natural conditions, with a maximum corrosion defect depth ≤150um. The mechanical properties decrease by no more than 10% after 1000h × 150℃ treatment. Attached Figure Description

[0041] The present invention will be further described below with reference to the accompanying drawings and embodiments:

[0042] Figure 1 These are photographs of Example 1 and Comparative Example 1 after being crushed;

[0043] Figure 2 These are photographs of Example 4 and Comparative Example 4 after being crushed;

[0044] Figure 3 These are photographs of Example 5 and Comparative Example 5 after being crushed;

[0045] Figure 4 These are photographs of Example 7 and Comparative Example 7 after being crushed;

[0046] Figure 5 The grain structure after anodic coating in Example 1;

[0047] Figure 6 The grain structure after anodic coating in Comparative Example 1;

[0048] Figure 7 The grain structure after anodic coating in Example 4;

[0049] Figure 8 The grain structure after anodic coating in Comparative Example 4;

[0050] Figure 9 The grain structure after anodic coating in Example 5;

[0051] Figure 10 The grain structure of Comparative Example 5 after anodic coating;

[0052] Figure 11 The grain structure after anodic coating in Example 7;

[0053] Figure 12 The grain structure of Comparative Example 7 after anode coating;

[0054] Figure 13 A schematic diagram showing the locations where AlTi5B1 grain refiner and AlTi5C0.25 grain refiner are added. Detailed Implementation

[0055] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments and the accompanying drawings. It should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and techniques are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0056] This invention provides two alloy compositions for each representative strength level, serving as examples and comparative examples respectively. Specific compositions are shown in Table 1. The corresponding grain refiner addition amount per ton of aluminum alloy is 1 kg / t ± 0.3 kg / t for AlTi5B1 and 1.7 ± 0.3 kg / t for AlTi5C0.25. AlTi5B1 is abbreviated as AlTiB, and AlTi5C0.25 as AlTiC. Both are manufactured by AMG. AlTi5C0.25 (5% Ti and 0.25% C by weight), AlTi5B1 (5% Ti and 1% B by weight), AlTi5C0.25 production batch number 20221543-3, and AlTi5B1 production batch number 20221332-1. The basic properties are: grain refiner diameter of 9.8-10.5 mm. Samples of every 200 kg of grain refiner were taken, and metallographic observation was performed at a depth of 2 cm. 2 Under the specified field of view, there should be no inclusions larger than 5 μm, and no more than two inclusions smaller than 1 μm. At least 95% of AlTi3 particles should be smaller than 1 μm, at least 95% of TiB2 aggregates should be smaller than 3 μm, and at least 95% of TiC aggregates should be smaller than 2 μm.

[0057] Table 1. Melting composition of examples and comparative examples

[0058]

[0059]

[0060] Using the above proportions, aluminum alloy profiles were prepared in Examples 1-4 and Comparative Examples 1-4 according to the following method:

[0061] 1) Smelting: Weigh the raw materials aluminum ingots, magnesium ingots, copper granules, aluminum-silicon alloy, manganese agent, iron agent, chromium agent, and aluminum-titanium alloy ingots according to the mass percentage of the elements in the aluminum alloy material, and then add them to the smelting furnace for smelting.

[0062] (2) Refining: Use inert gas refining or refining agent refining to remove inclusions and hydrogen, ensuring that the hydrogen content in the aluminum liquid is less than 0.15ml / 100g.

[0063] Furthermore, for alloys using AlTi5C0.25 grain refiner, the wire feeding position should be placed after the refining equipment, closer to the casting platform. This is to prevent the refining equipment from removing large TiC particles, which are beneficial to the refiner, and to prevent TiC particles from remaining in the molten aluminum for too long, thus reducing the number of effective TiC particles. When TiC particles are used as the nucleation core for heterogeneous formation, the density of the heterogeneous core is more than twice that of TiB2. TiC mainly acts as a nucleation core to increase the nucleation rate and reduce the grain size, thus exhibiting a low tendency for grain boundary segregation.

[0064] For alloys using AlTi5B1 grain refiner, the wire feeding position can be placed before online refining. A certain amount of TiB2 can be removed by the refining equipment, as TiB2 primarily refines grains by inhibiting grain boundary growth, and it is unnecessary to introduce too many TiB2 particles. See [link to details regarding wire feeding position] for more information. Figure 13 .

[0065] (3) Casting: The air-slip mold semi-continuous casting method was adopted. In Examples 1-4 and Comparative Examples 1-4, the casting temperature was between 695±5℃ when casting began. The casting speed in Examples 1-4 and Comparative Examples 1-4 was 60-80m / min.

[0066] (4) Homogenization: After casting, the cast rod is cooled to room temperature and then taken out. The cast rod is placed in a homogenizing furnace for heat preservation. For Examples 1-4 and Comparative Examples 1-4, the heat preservation temperature is set at 570±5℃ and the heat preservation time is 1-2h. Then, water mist cooling is carried out to ensure that the cooling rate of the cast rod is ≥350℃ / h.

[0067] (5) Extrusion molding: The homogenized aluminum rod is heated in an aluminum rod heating furnace. For Examples 1-4 and Comparative Examples 1-4, the heating temperature of the aluminum rod is set between 450-480℃; the extrusion ratio can be controlled between 30-150. For Examples 1-4 and Comparative Examples 1-4, the profile extrusion outlet temperature is controlled between 535-570℃; strong water cooling is used for the outlet to ensure a cooling rate of 50-100℃ / s.

[0068] (6) Straightening and aging: After the profiles have cooled to room temperature, they are straightened using a straightening machine. The elongation is controlled between 1% and 5%. The aging temperature is set to 205℃. For Examples 1-4 and Comparative Examples 1-4, the aging time is 4-6 hours.

[0069] Using the above proportions, aluminum alloy profiles were prepared in Examples 5-8 and Comparative Examples 5-8 according to the following method:

[0070] 1) Smelting: Weigh the raw materials aluminum ingots, magnesium ingots, copper granules, aluminum-silicon alloy, manganese agent, iron agent, chromium agent, and aluminum-titanium alloy ingots according to the mass percentage of the elements in the aluminum alloy material, and then add them to the smelting furnace for smelting.

[0071] (2) Refining: Use inert gas refining or refining agent refining to remove inclusions and hydrogen, ensuring that the hydrogen content in the aluminum liquid is less than 0.15ml / 100g.

[0072] Furthermore, for alloys using AlTi5C0.25 grain refiner, the wire feeder must be positioned after the refining equipment to prevent the refining equipment from removing large TiC particles, which are beneficial to the grain refiner. For alloys using AlTi5B1 grain refiner, the wire feeder can be positioned before online refining; see [link to details regarding wire feeder positioning] for more information. Figure 13 .

[0073] (3) Casting: The air-slip mold semi-continuous casting method was adopted. In Examples 5-8 and Comparative Examples 5-8, the casting temperature was 685±5℃. Casting was started. The casting speed of Examples 1-4 and Comparative Examples 1-4 was 60-80m / min.

[0074] (4) Homogenization: After casting, the cast rod is cooled to room temperature and then taken out. The cast rod is placed in a homogenizing furnace for heat preservation. For Examples 1-4 and Comparative Examples 1-4, the heat preservation temperature is set at 570±5℃ and the heat preservation time is 1-2h. Then, water mist cooling is carried out to ensure that the cooling rate of the cast rod is ≥350℃ / h.

[0075] (5) Extrusion molding: The homogenized aluminum rod is heated in an aluminum rod heating furnace. For Examples 5-8 and Comparative Examples 5-8, the heating temperature of the aluminum rod is set between 490-510℃. The extrusion ratio can be controlled between 30-150. Different extrusion speeds are set according to different profiles. For Examples 1-4 and Comparative Examples 1-4, the profile extrusion outlet temperature is controlled between 535-570℃. Strong water cooling is used for the outlet to ensure a cooling rate of 50-100℃ / s.

[0076] (6) Straightening and aging: After the profiles have cooled to room temperature, they are straightened using a straightening machine. The elongation is controlled between 1% and 5%. The aging temperature is set to 205℃. For Examples 5-8 and Comparative Examples 5-8, the aging time is 2.5-4h.

[0077] To ensure crush resistance, the interaction between dislocations and second-phase particles is typically required to be an Orovan bypass mechanism, not a cut-through mechanism. Because these components operate at high temperatures and usually undergo long-term cryogenic testing, over-aging is a common aging process for them.

[0078] Each embodiment and comparative example is in accordance with Figure 1-4 The images show the cross-sections of the displayed profiles after extrusion. Examples 1, 4, 5, and 7, and Comparative Examples 1, 4, 5, and 7, are photographs of the crushed profiles after extrusion. Figure 1-4 As shown.

[0079] Comparative Example 1 had a high Mn content, resulting in a fibrous structure in the core of the matrix and thus failing the crushing performance test. Comparative Example 2 had a low Mg / Si ratio, and the use of AlTi5B1 grain refiner made it difficult to avoid Si segregation at grain boundaries, leading to failure in crushing performance. Comparative Example 3 had a low Mg / Si ratio, resulting in failures in bending angle and crushing performance. Comparative Example 4 did not add Mn, resulting in insufficient strength after aging. Comparative Example 5 had a low Mg / Si ratio, resulting in failure in crushing performance. Comparative Example 6, using AlTi5B1 grain refiner, achieved acceptable performance at T7, but its high copper content resulted in failure in IGC performance. Comparative Example 7, due to reduced Cr addition, had fewer dispersed phases in the cast rod after homogenization, and the dispersed phases were unevenly distributed, failing to form sufficient fibrous structure and resulting in a coarse-grained layer. Comparative Example 8 had acceptable conventional mechanical properties, but due to the use of only AlTi5B1 grain refiner, the mechanical properties and IGC performance of the heat-affected zone of the welded joint were unacceptable.

[0080] According to VDA238, the bending angle along the extrusion direction of the profile is used to test its tensile properties and crushing properties in the extrusion direction. The crushing test involves compressing a 300mm profile axially downwards by 200mm to 100mm, ensuring that no cracks exceeding 10mm appear except at the reinforcing ribs, and the total number of cracks does not exceed four. The energy absorbed (area under the compression curve) exceeds J. The morphology of the crushed part and the metallographic structure of the cross-section after anodizing are shown in the attached figure. Figures 1 to 12 As shown in the table below. Specific performance details are also shown:

[0081] Table 2. Longitudinal mechanical properties of all examples under T7 condition.

[0082]

[0083]

[0084] Intergranular corrosion testing standards typically vary between OEMs. This example and comparative example were tested according to BS ISO 11846:1995, as detailed below:

[0085] (1) Degrease with acetone before testing.

[0086] (2) The sample was immersed in sodium hydroxide at 60°C and 5% mass concentration for 2 minutes, then washed with water, then immersed in concentrated nitric acid for 2 minutes to remove dirt, then rinsed with running water, rinsed with distilled water, and dried.

[0087] (3) Immerse the sample in a mixed solution of 30 g / L sodium chloride and 10 ml / L hydrochloric acid at room temperature for 24 h.

[0088] (4) Then wash the sample with clean water, then wash with deionized water, then dry it and perform metallographic analysis.

[0089] (5) The maximum corrosion depth of the profile cross section was detected by metallographic method.

[0090] After the above five steps, the IGC depth in Example 6 was approximately 56 μm, while the IGC depth in Comparative Example 6 was 203 μm. This demonstrates the effect of the AlTi5C0.25 grain refiner on improving IGC resistance.

[0091] Different OEMs use inconsistent welding methods, making it difficult to measure the heat-affected zone (HAZ) performance of welded joints using a unified standard. This invention uses long-term heat resistance tests to demonstrate the degradation of HAZ performance in welded joints. Simultaneously, energy-absorbing box anti-collision beams installed on the engine or front of automobiles must also undergo long-term heat resistance tests, typically requiring a mechanical property degradation of no more than 10% after 1000 hours at 150°C. The results are shown in Table 2.

[0092] Figure 5-12 The grain structure of the profiles after anodic coating in Examples 1, 4, 5, 7 and Comparative Examples 1, 4, 5, 7.

[0093] This invention, through research on this series of crushable aluminum alloys, found that: (1) with the increase of Cu content and Mg / Si ratio, the low-temperature long-term thermal stability of the material increases. (2) with the increase of Mg / Si ratio, the bending angle and crushability of the material improve. (3) TiC nano-reinforcing particles introduced by AlTi5C0.25 grain refiner can significantly reduce the corrosion reduction caused by the addition of Cu. (4) TiC nano-reinforcing particles introduced by AlTi5C0.25 grain refiner can significantly reduce the mechanical property degradation in the weld heat-affected zone. (5) with the increase of cooling rate after extrusion, the crushability and bending angle increase.

[0094] It should be understood that the specific embodiments described above are merely illustrative or explanatory of the principles of the invention and do not constitute a limitation thereof. Therefore, any modifications, equivalent substitutions, improvements, etc., made without departing from the spirit and scope of the invention should be included within the protection scope of the invention. Furthermore, the appended claims are intended to cover all variations and modifications falling within the scope and boundaries of the appended claims, or equivalent forms of such scope and boundaries.

Claims

1. A 6-series energy-absorbing aluminum alloy, characterized in that, By weight percentage, including: Mg: 0.50-1.20%, Si: 0.40-1.00%, Mn: 0.15-0.95%, Cr: 0.0015-0.25%, Fe: 0.15-0.45%, Ti: 0.015-0.30%, Cu: 0.10-0.70%; wherein, the Mg / Si mass ratio is ≥0.85 / 1, and the total content of Mn+Cr+Fe is ≤1.2%; it also includes AlTi5C0.25 grain refiner and impurities with a content not exceeding 0.15%, with the balance being Al; The amount of AlTi5C0.25 grain refiner added per ton of aluminum alloy is 1.5-2 kg; For alloys using AlTi5C0.25 grain refiner, the wire feeding position should be after the refining equipment. The 6-series energy-absorbing aluminum alloy has a yield strength of 200-320MPa, a tensile strength of 220-380MPa, and an elongation of ≥11%. After a 300mm profile undergoes a 200mm static compression along the extrusion direction, no visible cracks appear on the profile surface. Its corrosion resistance meets the requirements of 10 cycles of 4h neutral salt spray test + 16h humid heat climate storage test + 4h natural conditions, with a maximum corrosion defect depth ≤150μm. The yield strength decreases by no more than 10% in mechanical properties after treatment at 1000h×150℃.

2. The 6-series energy-absorbing aluminum alloy according to claim 1, characterized in that, The content of any single impurity element does not exceed 0.05%.

3. The 6-series energy-absorbing aluminum alloy according to claim 1, characterized in that, Aluminum alloys contain TiC particles, with over 95% of the particles having a size between 10-900 nm.

4. A method for manufacturing a 6-series energy-absorbing aluminum alloy according to any one of claims 1-3, characterized in that, Includes the following steps: (1) Smelting: Weigh the raw materials aluminum ingots, magnesium ingots, copper granules, aluminum-silicon alloy, manganese agent, iron agent, chromium agent, and aluminum-titanium alloy ingots according to the mass percentage of the elements in the aluminum alloy material, and then add them to the smelting furnace for smelting; (2) Refining: Inert gas refining or refining agent refining is used to remove impurities and hydrogen; (3) Casting: Casting is carried out using the air slip mold semi-continuous casting method; (4) Homogenization: After casting, the cast rod is cooled to room temperature and then removed. The cast rod is placed in a homogenizing furnace for heat preservation, followed by water mist cooling; (5) Extrusion molding: The homogenized aluminum rods are heated to between 450℃ and 510℃ in an aluminum rod heating furnace, the extrusion ratio is between 30 and 150, the extrusion outlet temperature is between 550 and 575℃, and the outlet is cooled by strong water with a cooling rate of 50-100℃ / s; (6) Straightening and aging: After the profile cools to room temperature, it is straightened using a straightening machine, and the elongation is controlled between 1% and 5%. Then it is put into an aging furnace for aging treatment.

5. The method for manufacturing the 6-series energy-absorbing aluminum alloy according to claim 4, characterized in that, After refining, ensure that the hydrogen content in the molten aluminum is below 0.15 ml / 100g.

6. The method for manufacturing the 6-series energy-absorbing aluminum alloy according to claim 4, characterized in that, In step (3), when the temperature of the molten aluminum is between 680-700℃, casting begins, and the casting speed is 40-80mm / min.

7. The method for manufacturing the 6-series energy-absorbing aluminum alloy according to claim 4, characterized in that, The wire feeding position is located after the refining equipment.

8. The method for manufacturing the 6-series energy-absorbing aluminum alloy according to claim 4, characterized in that, In step (4), the heat preservation temperature is 550-570℃, the heat preservation time is 1-4h, and the water mist cooling ensures that the cooling rate of the casting rod is ≥350℃ / h.

9. The method for manufacturing the 6-series energy-absorbing aluminum alloy according to claim 4, characterized in that, In step (5), the aging treatment is T7 treatment, the aging temperature is set to 205℃, and the aging time is between 2.5h and 8h.

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