Anti-cracking new energy automobile threshold aluminum profile material and preparation method thereof

Abstract

This invention discloses a crack-resistant aluminum profile material for the door sill of new energy vehicles and its preparation method, belonging to the technical field of aluminum alloy profiles for new energy vehicles. Step 1: Weigh aluminum source, magnesium source, silicon source, manganese source, chromium source, zirconium source, titanium source and boron source according to mass percentage, and melt them to obtain an aluminum alloy melt. The mass percentage of each element in the aluminum alloy melt is: silicon 0.65-0.90%, magnesium 0.55-0.80%, manganese 0.12-0.25%, chromium 0.05-0. 12%, zirconium 0.05-0.15%, titanium 0.015-0.050%, boron 0.003-0.015%, iron ≤0.18%, copper ≤0.10%, zinc ≤0.05%, single unavoidable impurities ≤0.03%, total unavoidable impurities ≤0.15%, balance is aluminum; by controlling the content range of silicon, magnesium, manganese, chromium, zirconium, titanium and boron, aluminum alloy materials can have the ability to age strengthen, refine grains and inhibit recrystallization.

Description

Technical Field

[0001] This invention belongs to the technical field of aluminum alloy profiles for new energy vehicles, specifically relating to a crack-resistant aluminum profile material for the door sill of new energy vehicles and its preparation method. Background Technology

[0002] With the increasing demands for lightweighting and vehicle safety performance in new energy vehicles, aluminum alloy profiles are widely used in door sill beams, battery pack frames, longitudinal beams, and collision energy absorption structures due to their low density, high specific strength, good extrusion formability, and recyclability. Among these, the door sill beam, located below the side of the vehicle body, is a crucial load-bearing component for side impact protection and battery pack lateral protection. It not only needs high tensile and yield strength but also requires good plasticity and crack resistance during bending, crushing, and collision deformation.

[0003] Most existing aluminum door sill profiles for new energy vehicles use six-series aluminum alloy systems, such as aluminum-magnesium-silicon alloys. While these alloys can achieve good strength through solution treatment and aging, the following problems still exist during actual extrusion and heat treatment: First, improper control of the magnesium-silicon ratio can easily lead to insufficient precipitation of strengthening phases or an increase in coarse precipitates, making it difficult to balance material strength and plasticity. Especially when the magnesium-silicon ratio deviates from a reasonable range, the aging strengthening response is unstable, and the profile is prone to intergranular cracking or localized brittle fracture during bending or impact deformation. Second, door sill beams for new energy vehicles are typically complex cross-sectional structures with multiple cavities, thin walls, or uneven thicknesses. The cooling rates of different wall thickness areas after extrusion vary significantly. Thin-walled areas cool quickly, while thick-walled areas cool slowly, easily causing uneven distribution of microstructure and residual stress, leading to localized cracking of the door sill profile during subsequent straightening, assembly, bending tests, or impact conditions.

[0004] Therefore, it is necessary to develop a new energy vehicle door sill aluminum profile material and its preparation method that achieves synergistic control among alloy composition, ingot homogenization, hot extrusion, online quenching and aging regime, so that it has high strength, good elongation after fracture and excellent resistance to bending cracking. Summary of the Invention

[0005] The purpose of this invention is to provide a crack-resistant aluminum profile material for door sills of new energy vehicles and its preparation method. By controlling the proportions of silicon, magnesium, manganese, chromium, zirconium, titanium and boron, and combining two-stage homogenization, hot extrusion molding, online strong wind-water mist composite quenching, tensile straightening, pre-aging and two-stage artificial aging treatment, the uniformity of the profile structure and the cooling consistency of thick and thin wall areas are improved, thereby improving the strength, plasticity and bending crack resistance of the aluminum profile for door sills of new energy vehicles.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a method for preparing crack-resistant aluminum profile material for door sills of new energy vehicles, comprising the following steps: Step 1: Weigh out aluminum source, magnesium source, silicon source, manganese source, chromium source, zirconium source, titanium source, and boron source by mass percentage, and melt them to obtain an aluminum alloy melt. The mass percentage of each element in the aluminum alloy melt is as follows: silicon 0.65-0.90%, magnesium 0.55-0.80%, manganese 0.12-0.25%, chromium 0.05-0.12%, zirconium 0.05-0.15%, titanium 0.015-0.050%, boron 0.003-0.015%, iron ≤0.18%, copper ≤0.10%, zinc ≤0.05%, single unavoidable impurities ≤0.03%, total unavoidable impurities ≤0.15%, and the balance is aluminum.

[0007] The magnesium to silicon mass ratio is controlled at 0.80-1.10, with an excess silicon content of 0.05-0.18%. This ratio control ensures that the strengthening β-bipyridine phase mainly precipitates during aging, while the appropriate excess silicon enhances the aging response speed and precipitation strengthening effect. The sum of the mass percentages of manganese, chromium, and zirconium is controlled at 0.22-0.45%, which is beneficial for the formation of a stable dispersed phase, inhibiting recrystallization coarsening, and reducing the tendency for flexural cracking.

[0008] Step 2: The aluminum alloy melt obtained in Step 1 is refined, degassed, slag removed, and filtered, and then semi-continuously cast to obtain aluminum alloy ingots.

[0009] Step 3: Perform a two-stage homogenization treatment on the aluminum alloy ingot to promote the diffusion and homogenization of magnesium and silicon elements in the ingot, and to promote the formation of zirconium, manganese and chromium-containing dispersed phases, thus obtaining a homogenized ingot.

[0010] Step 4: After heating the homogenized ingot, hot extrusion molding is carried out to obtain a new energy vehicle door sill aluminum profile billet with a multi-cavity structure.

[0011] Step 5: Online strong wind-water mist composite quenching is carried out on the aluminum profile blank for the door sill of new energy vehicles. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled area and the thin-walled area of ​​the profile is controlled within 60℃ / s.

[0012] The cooling rate difference between the thick-walled and thin-walled regions can be obtained through offline calibration. Specifically, fast-response thermocouples are placed in both the thick-walled and thin-walled regions after the profile extrusion outlet. Temperature drop curves are recorded under different water mist pressures, air volumes, and nozzle zone openings. The average cooling rate difference between the thick-walled and thin-walled regions within a set temperature range is calculated, establishing a correspondence between water mist pressure, air volume, nozzle zone opening, and the cooling rate difference. During continuous industrial production, the flow rate, air volume, and zone opening of the water mist nozzles are adjusted according to the offline calibration relationship to achieve online control of the cooling rate difference between the thick-walled and thin-walled regions.

[0013] Step 6: After quenching, the profile is stretched and straightened and pre-aged, and then subjected to two-stage artificial aging treatment to obtain crack-resistant aluminum profile material for new energy vehicle door sills.

[0014] Further, in step one, the melting temperature is 720-760℃. After the aluminum source is completely melted, the silicon source, manganese source, chromium source and zirconium source are added. After holding at this temperature for 20-40 minutes, the magnesium source is added, and then the aluminum-titanium-boron master alloy is added to refine the grains, thus obtaining the aluminum alloy melt.

[0015] Furthermore, in step two, the refining and degassing are carried out using argon rotary jetting, with a degassing time of 12-25 min and the hydrogen content of the melt controlled below 0.15 mL / 100g aluminum; the filtration process uses 30-50 ppi ceramic foam filter plates, the semi-continuous casting speed is 60-100 mm / min, and the casting cooling water flow rate is 80-140 L / min.

[0016] Furthermore, in step three, the two-stage homogenization process specifically involves: first, holding the aluminum alloy ingot at 330-390℃ for 2-6 hours, then raising the temperature to 530-560℃ and holding it for 8-16 hours, followed by cooling it to room temperature at a cooling rate of 30-80℃ / h.

[0017] Furthermore, in step four, the extrusion heating temperature of the homogenized ingot is 460-500℃, the extrusion cylinder temperature is 430-470℃, the die temperature is 440-480℃, the extrusion ratio is 25-55, and the extrusion exit speed is 3-10m / min.

[0018] Furthermore, in step four, the multi-cavity aluminum profile blank for the new energy vehicle door sill includes an outer energy-absorbing wall, an inner load-bearing wall, and connecting ribs. The thickness of the outer energy-absorbing wall is 1.8-3.0 mm, the thickness of the inner load-bearing wall is 2.5-4.0 mm, and the thickness of the connecting ribs is 1.5-2.8 mm. The radius of curvature at the junction of adjacent wall panels is not less than 1.2 mm. By controlling the wall thickness range and the radius of curvature, stress concentration at the junction of wall panels can be reduced, improving the profile's resistance to cracking during bending and impact deformation.

[0019] Furthermore, in step five, during online strong wind-water mist composite quenching, the profile outlet temperature is controlled at 500-540℃, the water mist pressure is 0.20-0.45MPa, and the strong wind speed is 15-35m / s. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled and thin-walled areas is controlled within 60℃ / s, and the profile temperature drops below 80℃ after quenching.

[0020] Furthermore, in step six, the tensile deformation during tension straightening is 0.5-1.8%; the pre-aging treatment temperature is 80-110℃, and the holding time is 1-4h; the two-stage artificial aging treatment is as follows: first, hold at 120-150℃ for 2-5h, and then raise the temperature to 165-185℃ and hold for 4-8h.

[0021] The present invention also provides a crack-resistant aluminum profile material for the door sill of new energy vehicles, which is prepared by the above preparation method; the grains of the aluminum profile material are distributed in a fibrous manner along the extrusion direction, the average recrystallized grain size is not greater than 35μm, and the matrix contains dispersed phases containing zirconium, manganese and chromium.

[0022] Compared with existing technologies, this invention provides a crack-resistant aluminum profile material for the door sills of new energy vehicles and its preparation method, which has the following beneficial effects: By controlling the content range of silicon, magnesium, manganese, chromium, zirconium, titanium, and boron, the aluminum alloy material possesses aging strengthening ability, grain refinement effect, and recrystallization inhibition ability. Magnesium and silicon form the main strengthening phases in a reasonable ratio, and an appropriate excess of silicon promotes the aging response; manganese, chromium, and zirconium form stable dispersed phases, which can inhibit grain coarsening during hot extrusion and heat treatment, thereby improving the profile strength and resistance to bending cracking.

[0023] This invention controls the magnesium-to-silicon mass ratio to be 0.80-1.10 and the excess silicon content to be 0.05-0.18%, avoiding insufficient magnesium content leading to insufficient precipitation of the strengthening phase, and also avoiding excessive silicon content leading to an increase in coarse silicon phases or brittle phases. This control method enables the material to achieve high tensile strength and yield strength while maintaining high elongation after fracture.

[0024] This invention employs a two-stage homogenization process to fully dissolve the low-melting-point non-equilibrium phases in the ingot and promote the uniform precipitation of zirconium, manganese, and chromium-containing dispersed phases. These dispersed phases can pin grain boundaries during subsequent extrusion and aging processes, reducing the recrystallization ratio and resulting in a finer, more uniform fibrous structure in the profile, thus improving its crack resistance during bending deformation.

[0025] This invention employs online high-pressure airflow-water mist composite quenching, with zoned control of water mist nozzle flow rate and airflow, to maintain the cooling rate difference between thick-walled and thin-walled regions within 60℃ / s. This cooling rate difference can be established offline through calibration, establishing a correlation between water mist pressure, airflow, nozzle zone opening, and the cooling rate difference, and then adjusted online during continuous production based on this calibration. This process reduces microstructural and residual stress differences between different regions of multi-cavity sill profiles, preventing performance inconsistencies caused by overcooling in thin-walled areas and underquenching in thick-walled areas, thereby improving the dimensional stability and crack resistance of complex cross-section profiles.

[0026] This invention employs pre-aging and two-stage artificial aging treatments to gradually form a stable precipitation sequence of solute atoms after solution treatment, avoiding coarsening of the precipitated phase caused by single-stage high-temperature aging. This aging process balances strength, plasticity, and bending performance, enabling the profile to meet the comprehensive requirements of new energy vehicle door sill beams for load-bearing capacity, protection, and deformation energy absorption.

[0027] This invention controls the wall thickness of the multi-cavity section of the aluminum sill profile, the thickness of the connecting ribs, and the radius of the fillet at the connection of the wall panels to match the material microstructure with the structural crack resistance design, thereby reducing stress concentration and improving the reliability of the sill beam during bending, assembly, and collision deformation. Attached Figure Description

[0028] Figure 1 This is an EBSD grain orientation diagram of the cross-section of the threshold aluminum profile obtained in Example 2 of the present invention; Figure 2 This is an EBSD grain orientation diagram of the cross-section of the threshold aluminum profile obtained in Comparative Example 3 of the present invention; Figure 3 This is a TEM image of the dispersed phase in the aluminum profile matrix obtained in Example 2 of the present invention; Figure 4 The images show the SEM images of the outer curved surface of the aluminum sill profiles obtained in Embodiment 2 and Comparative Example 5 of the present invention after bending 180°. Detailed Implementation

[0029] The technical solutions of the present invention will be clearly and completely described below with reference to the embodiments of the present invention. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

[0030] Please see Figures 1-4 This invention provides a technical solution for a crack-resistant aluminum profile material for the door sill of new energy vehicles and its preparation method: In the following examples and comparative examples, the aluminum source is industrial pure aluminum ingot, the silicon source is aluminum-silicon master alloy, the manganese source is aluminum-manganese master alloy, the chromium source is aluminum-chromium master alloy, the zirconium source is aluminum-zirconium master alloy, the magnesium source is pure magnesium ingot, and the titanium and boron sources are aluminum-titanium-boron master alloys. Unless otherwise specified, in all examples and comparative examples, the melt was refined, degassed, slag removed, and filtered through a ceramic foam filter before being semi-continuously cast.

[0031] The aluminum sill profile has a multi-cavity structure, including an outer energy-absorbing wall, an inner load-bearing wall, and connecting ribs. In each embodiment, the outer energy-absorbing wall, the inner load-bearing wall, the connecting ribs, and the fillet radii are all controlled within the range defined by this invention. During performance testing, samples are taken from the stable extrusion section of the profile, and tensile properties, bending properties, and microstructure tests are performed respectively.

[0032] The online high-pressure airflow-water mist composite quenching process undergoes offline calibration before mass production. During offline calibration, fast-response thermocouples are placed in the thick-walled and thin-walled zones after the profile extrusion outlet to record temperature drop curves under different water mist pressures, high-pressure airflow velocities, nozzle zone openings, and nozzle flow rates. The average cooling rate difference between the thick-walled and thin-walled zones within the 500℃ to 250℃ range is calculated. Based on the test results, a correlation between process parameters and the cooling rate difference is established. During industrial production, the flow rate and airflow of the water mist nozzles in each zone are adjusted according to this correlation to stably control the cooling rate difference between the thick-walled and thin-walled zones within 60℃ / s.

[0033] Example 1 A method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle includes the following steps: S1: Weigh the raw materials according to the following mass percentages to ensure the following elemental content in the aluminum alloy melt: silicon 0.65%, magnesium 0.55%, manganese 0.12%, chromium 0.05%, zirconium 0.05%, titanium 0.015%, boron 0.003%, iron 0.12%, copper 0.04%, zinc 0.03%, with a single unavoidable impurity ≤0.03% and a total unavoidable impurity content ≤0.15%, the balance being aluminum. The mass ratio of magnesium to silicon is 0.85, the excess silicon content is 0.08%, and the sum of the mass percentages of manganese, chromium, and zirconium is 0.22%.

[0034] S2: Add the aluminum source to the melting furnace and melt it at 720℃. After the aluminum source is completely melted, add the silicon source, manganese source, chromium source and zirconium source. After holding for 20 minutes, add the magnesium source, and then add the aluminum-titanium-boron master alloy to refine the grains and obtain the aluminum alloy melt.

[0035] S3: The aluminum alloy melt is refined and degassed using an argon rotary jet method for 12 minutes, and the hydrogen content of the melt is controlled below 0.15 mL / 100g aluminum. Then, slag is removed and the mixture is filtered using a 30ppi ceramic foam filter plate. Semi-continuous casting is then carried out at a casting speed of 60 mm / min and a cooling water flow rate of 80 L / min to obtain aluminum alloy ingots.

[0036] S4: Hold the aluminum alloy ingot at 330℃ for 2 hours, then raise the temperature to 530℃ and hold for 8 hours, and then cool it to room temperature at a cooling rate of 30℃ / h to obtain a homogenized ingot.

[0037] S5: The homogenized ingot is heated to 460℃, the extrusion cylinder temperature is controlled at 430℃, the die temperature at 440℃, the extrusion ratio at 25, and the extrusion exit speed at 3m / min. Hot extrusion yields aluminum profile blanks for new energy vehicle door sills. The outer energy-absorbing wall thickness of the profile is 1.8mm, the inner load-bearing wall thickness is 2.5mm, the connecting rib thickness is 1.5mm, and the fillet radius at the connection between adjacent wall panels is 1.2mm.

[0038] S6: Online strong wind-water mist composite quenching is performed on the profile at the extrusion outlet. The profile outlet temperature is controlled at 500℃, the water mist pressure is 0.20MPa, and the strong wind speed is 15m / s. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled and thin-walled areas is controlled within 60℃ / s. After quenching, the profile temperature drops to below 80℃.

[0039] S7: The quenched profile is stretched and straightened with a stretching deformation of 0.5%; then it is pre-aged at 80℃ for 1 hour; then it undergoes a two-stage artificial aging treatment, first held at 120℃ for 2 hours, and then heated to 165℃ for 4 hours to obtain crack-resistant aluminum profile material for new energy vehicle door sills.

[0040] Example 2 A method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle includes the following steps: S1: Weigh the raw materials according to the following mass percentages to ensure the following elemental contents in the aluminum alloy melt: silicon 0.78%, magnesium 0.68%, manganese 0.18%, chromium 0.08%, zirconium 0.10%, titanium 0.030%, boron 0.008%, iron 0.10%, copper 0.05%, zinc 0.03%, with individual unavoidable impurities ≤0.03% and total unavoidable impurities ≤0.15%, the balance being aluminum. The mass ratio of magnesium to silicon is 0.87, the excess silicon content is 0.12%, and the sum of the mass percentages of manganese, chromium, and zirconium is 0.36%.

[0041] S2: Add the aluminum source to the melting furnace and melt it at 740℃. After the aluminum source is completely melted, add the silicon source, manganese source, chromium source and zirconium source. After holding for 30 minutes, add the magnesium source, and then add the aluminum-titanium-boron master alloy to refine the grains and obtain the aluminum alloy melt.

[0042] S3: Argon rotary blowing is used for refining and degassing, with a degassing time of 18 minutes. The hydrogen content of the melt is controlled below 0.15 mL / 100g aluminum. Then, slag is removed and filtered with a 40ppi ceramic foam filter plate. Semi-continuous casting is then carried out at a casting speed of 80 mm / min and a cooling water flow rate of 110 L / min to obtain aluminum alloy ingots.

[0043] S4: The aluminum alloy ingot is held at 360℃ for 4 hours, then heated to 545℃ and held for 12 hours, and then cooled to room temperature at a cooling rate of 55℃ / h to obtain a homogenized ingot.

[0044] S5: The homogenized ingot is heated to 480℃, the extrusion cylinder temperature is controlled at 450℃, the die temperature at 460℃, the extrusion ratio at 40, and the extrusion exit speed at 6m / min. Hot extrusion yields an aluminum profile billet for the door sill of a new energy vehicle. The outer energy-absorbing wall thickness of the profile is 2.4mm, the inner load-bearing wall thickness is 3.2mm, the connecting rib thickness is 2.1mm, and the fillet radius at the connection between adjacent wall panels is 1.5mm.

[0045] S6: Online strong wind-water mist composite quenching is performed on the profile at the extrusion outlet. The profile outlet temperature is controlled at 520℃, the water mist pressure is 0.32MPa, and the strong wind speed is 25m / s. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled and thin-walled areas is controlled within 60℃ / s. After quenching, the profile temperature drops to below 80℃.

[0046] S7: The quenched profile is stretched and straightened with a stretching deformation of 1.1%; then it is pre-aged at 95℃ for 2.5h; then it undergoes a two-stage artificial aging treatment, first held at 135℃ for 3.5h, and then heated to 175℃ for 6h to obtain crack-resistant aluminum profile material for new energy vehicle door sills.

[0047] Example 3 A method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle includes the following steps: S1: Weigh the raw materials according to the following mass percentages to ensure the following elemental contents in the aluminum alloy melt: silicon 0.90%, magnesium 0.80%, manganese 0.25%, chromium 0.12%, zirconium 0.08%, titanium 0.050%, boron 0.015%, iron 0.14%, copper 0.05%, zinc 0.04%, with a single unavoidable impurity ≤0.03% and a total unavoidable impurity content ≤0.15%, the balance being aluminum. The mass ratio of magnesium to silicon is 0.89, the excess silicon content is 0.15%, and the sum of the mass percentages of manganese, chromium, and zirconium is 0.45%.

[0048] S2: Add the aluminum source to the melting furnace and melt it at 760℃. After the aluminum source is completely melted, add the silicon source, manganese source, chromium source and zirconium source. After holding for 40 minutes, add the magnesium source, and then add the aluminum-titanium-boron master alloy to refine the grains and obtain the aluminum alloy melt.

[0049] S3: Refining and degassing are carried out using argon rotary blowing for 25 minutes, and the hydrogen content of the melt is controlled below 0.15 mL / 100g aluminum. Then, slag is removed and filtered using a 50ppi ceramic foam filter plate. Semi-continuous casting is then carried out at a casting speed of 100 mm / min and a cooling water flow rate of 140 L / min to obtain aluminum alloy ingots.

[0050] S4: The aluminum alloy ingot is held at 390℃ for 6 hours, then heated to 560℃ and held for 16 hours, and then cooled to room temperature at a cooling rate of 80℃ / h to obtain a homogenized ingot.

[0051] S5: The homogenized ingot is heated to 500℃, the extrusion cylinder temperature is controlled at 470℃, the die temperature at 480℃, the extrusion ratio at 55, and the extrusion exit speed at 10m / min. Hot extrusion yields aluminum profile blanks for new energy vehicle door sills. The outer energy-absorbing wall thickness of the profile is 3.0mm, the inner load-bearing wall thickness is 4.0mm, the connecting rib thickness is 2.8mm, and the fillet radius at the connection between adjacent wall panels is 1.8mm.

[0052] S6: Online strong wind-water mist composite quenching is performed on the profile at the extrusion outlet. The profile outlet temperature is controlled at 540℃, the water mist pressure is 0.45MPa, and the strong wind speed is 35m / s. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled and thin-walled areas is controlled within 60℃ / s. After quenching, the profile temperature drops to below 80℃.

[0053] S7: The quenched profile is stretched and straightened with a tensile deformation of 1.8%; then it is pre-aged at 110℃ for 4 hours; then it undergoes a two-stage artificial aging treatment, first held at 150℃ for 5 hours, and then heated to 185℃ for 8 hours to obtain crack-resistant aluminum profile material for new energy vehicle door sills.

[0054] Comparative Example 1 differs in that: the silicon content is 0.78%, the magnesium content is 0.50%, and the mass ratio of magnesium to silicon is 0.64, which is lower than the range of 0.80-1.10 defined in this invention; the content of other elements and the preparation process are the same as in Example 2.

[0055] Comparative Example 2 differs in that: the silicon content is 0.95%, the magnesium content is 0.68%, and the excess silicon content is 0.25%, which is higher than the 0.05-0.18% range specified in this invention; the content of other elements and the preparation process are the same as in Example 2.

[0056] Comparative Example 3 differs in that: no zirconium source is added, the zirconium content is less than 0.01%, and the sum of the mass percentages of manganese, chromium and zirconium is 0.26%, but zirconium is absent from the formation of the thermally stable dispersed phase; the content of other elements and the preparation process are the same as in Example 2.

[0057] Comparative Example 4 differs in that the homogenization process uses a single-stage homogenization regime, i.e., after holding at 545℃ for 12 hours, it is directly cooled to room temperature, instead of using a two-stage homogenization process of first low temperature and then high temperature; the content of other elements and the preparation process are the same as in Example 2.

[0058] Comparative Example 5 differs in that: the online quenching adopts a general water mist spraying method, without controlling the flow rate and air volume of the water mist nozzles in different zones, thus failing to stably control the cooling rate difference between the thick-walled and thin-walled regions within 60℃ / s; the content of other elements and the preparation process are the same as in Example 2.

[0059] Comparative Example 6 differs in that: the aging treatment adopts a single-stage artificial aging system, that is, it is kept at 175°C for 8 hours, without pre-aging and double-stage artificial aging treatment; the content of other elements and the pretreatment process are the same as those in Example 2.

[0060] Performance testing The performance of the aluminum profile materials for the door sills of new energy vehicles obtained in Examples 1-3 and Comparative Examples 1-6 was tested.

[0061] 1. Tensile property test: The tensile strength, yield strength and elongation after fracture were tested in accordance with GB / T 228.1-2021 "Metallic materials - Tensile testing - Part 1: Test method at room temperature".

[0062] 2. Bending performance test: The test was conducted in accordance with GB / T 232-2024 "Metallic Materials Bending Test Method". The sample was taken from the aluminum profile wall panel area of ​​the door sill of new energy vehicles. The bending radius was twice the wall thickness of the profile and the bending angle was 180°. After bending, the surface of the sample was observed to see if any visible cracks appeared.

[0063] 3. Microstructure testing: Tests were conducted according to GB / T 3246.1-2024 "Test Methods for Microstructure of Wrought Aluminum and Aluminum Alloy Products - Part 1: Microstructure Testing Methods". Samples were taken from the thick-walled area, thin-walled area, and thick-thin-walled transition area of ​​the profile cross-section. After mechanical polishing and etching, metallographic observation was performed. The average recrystallized grain size was statistically analyzed using the intercept method or image analysis software. Measurements were taken at no fewer than 10 fields of view at different locations on the profile cross-section. After removing areas with obvious sample preparation defects, the average value was calculated as the average recrystallized grain size.

[0064] 4. Cooling Rate Difference Test: During the offline calibration stage, fast-response thermocouples are placed in the thick-walled and thin-walled zones after the profile extrusion exit. The temperature drop curves during the quenching process are recorded, and the average cooling rate difference between the thick-walled and thin-walled zones within the range of 500℃ to 250℃ is calculated. Multiple calibration tests are conducted to establish the correlation between water mist pressure, strong wind speed, nozzle zone opening, nozzle flow rate, and the cooling rate difference between the thick and thin-walled zones. In industrial production, the flow rate and air volume of the zoned water mist nozzles are adjusted according to this correlation to control the cooling rate difference between the thick-walled and thin-walled zones within 60℃ / s.

[0065] The test results are shown in the table below. Table 1

[0066] As shown in the table, Examples 1-3 all meet the requirements of tensile strength not less than 285MPa, yield strength not less than 245MPa, elongation after fracture not less than 12%, and average recrystallized grain size not greater than 35μm. Furthermore, after undergoing a bending radius of 2 times the wall thickness and a 180° bending test according to GB / T232-2024, no visible cracks were found on the surface of the samples.

[0067] In Comparative Example 1, the mass ratio of magnesium to silicon was lower than the range specified in this invention. Although the elongation after fracture was still acceptable, the tensile strength and yield strength decreased significantly, indicating that insufficient magnesium-silicon ratio would weaken the aging strengthening effect.

[0068] In Comparative Example 2, the excessive silicon content was higher than the limit specified in this invention. Although the strength was high, the elongation after fracture was significantly reduced, and fine cracks appeared on the outer bending surface after bending. This indicates that excessive silicon content increases the risk of brittle cracking.

[0069] Comparative Example 3, without the addition of effective zirconium, showed an increase in average recrystallized grain size to 47.6 μm, and continuous cracks appeared after bending. This indicates that the dispersed structure formed by zirconium, manganese, and chromium plays an important role in inhibiting recrystallization coarsening and improving crack resistance.

[0070] Comparative Example 4, which uses single-stage homogenization treatment, has a strength close to that of the example, but the grain size increases and cracks appear near the fillet after bending. This indicates that two-stage homogenization is beneficial to improving the ingot structure and the distribution of dispersed phases.

[0071] Comparative Example 5, without zoned control of strong wind-water mist composite quenching, showed a cooling rate difference of 92℃ / s between thick and thin walls. Cracks appeared in the transition zone between thick and thin walls after bending. This indicates that by offline calibration and adjusting the flow rate and air volume of the water mist nozzles according to the calibration relationship during production, the cooling difference between thick and thin wall areas of complex multi-cavity sill profiles can be effectively reduced, thereby improving crack resistance.

[0072] Comparative Example 6, which underwent single-stage artificial aging treatment, showed higher strength but decreased elongation after fracture and fine cracks after bending. This indicates that pre-aging and two-stage artificial aging can improve the distribution of precipitated phases, thereby enhancing the plasticity and resistance to bending cracks of the material while maintaining its strength.

[0073] In summary, this invention, through the synergistic control of alloy composition, magnesium-silicon ratio, excess silicon, manganese-chromium-zirconium dispersed phases, two-stage homogenization, zoned composite quenching, and two-stage aging, enables the aluminum door sill profile material for new energy vehicles to possess both high strength, good plasticity, and excellent crack resistance. This technical solution cannot be achieved through a single component adjustment or a single heat treatment process, but rather is the result of the combined effect of multiple key technical features, demonstrating that this invention represents a significant advancement over conventional new energy vehicle door sill profile preparation methods.

Claims

1. A preparation method of an anti-cracking new energy vehicle threshold aluminum profile material, characterized in that, Includes the following steps: Step 1: Weigh out aluminum source, magnesium source, silicon source, manganese source, chromium source, zirconium source, titanium source, and boron source by mass percentage, and melt them to obtain an aluminum alloy melt. The mass percentage of each element in the aluminum alloy melt is as follows: silicon 0.65-0.90%, magnesium 0.55-0.80%, manganese 0.12-0.25%, chromium 0.05-0.12%, zirconium 0.05-0.15%, titanium 0.015-0.050%, boron 0.003-0.015%, iron ≤0.18%, copper ≤0.10%, zinc ≤0.05%, single unavoidable impurities ≤0.03%, total unavoidable impurities ≤0.15%, and the balance is aluminum. Step 2: The aluminum alloy melt obtained in Step 1 is refined, degassed, slag removed, and filtered, and then semi-continuously cast to obtain aluminum alloy ingots. Step 3: Perform a two-stage homogenization treatment on the aluminum alloy ingot to promote the diffusion and homogenization of magnesium and silicon elements in the ingot, and promote the formation of dispersed phases containing zirconium, manganese and chromium, and obtain a homogenized ingot. Step 4: After heating the homogenized ingot, hot extrusion molding is performed to obtain a new energy vehicle door sill aluminum profile billet with a multi-cavity structure; Step 5: Online strong wind-water mist composite quenching is carried out on the aluminum profile blank for the door sill of new energy vehicles. By controlling the flow rate and air volume of the water mist nozzles in different zones, the average cooling rate difference between the thick-walled area and the thin-walled area of ​​the profile in the range of 500℃ to 250℃ is controlled within 60℃ / s. Step 6: After quenching, the profile is stretched and straightened and pre-aged, and then subjected to two-stage artificial aging treatment to obtain crack-resistant aluminum profile material for the door sill of new energy vehicles.

2. The preparation method according to claim 1, characterized in that, The mass ratio of magnesium to silicon is controlled at 0.80-1.10, the excess silicon content is 0.05-0.18%, and the sum of the mass percentages of manganese, chromium and zirconium is 0.22-0.45%.

3. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step one, the melting temperature is 720-760℃. After the aluminum source is completely melted, silicon source, manganese source, chromium source and zirconium source are added. After holding at this temperature for 20-40 minutes, magnesium source is added, and then aluminum-titanium-boron master alloy is added to refine the grains and obtain aluminum alloy melt.

4. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step two, refining and degassing are carried out using argon rotary jetting, with a degassing time of 12-25 minutes and the hydrogen content of the melt controlled below 0.15 mL / 100g aluminum. Filtration is performed using 30-50 ppi ceramic foam filter plates, with a semi-continuous casting speed of 60-100 mm / min and a casting cooling water flow rate of 80-140 L / min.

5. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step three, the two-stage homogenization process specifically involves: first, holding the aluminum alloy ingot at 330-390℃ for 2-6 hours, then raising the temperature to 530-560℃ and holding it for 8-16 hours, and finally cooling it to room temperature at a cooling rate of 30-80℃ / h.

6. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step four, the extrusion heating temperature of the homogenized ingot is 460-500℃, the extrusion cylinder temperature is 430-470℃, the die temperature is 440-480℃, the extrusion ratio is 25-55, and the extrusion exit speed is 3-10m / min.

7. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step four, the aluminum profile blank for the new energy vehicle door sill with multi-cavity structure includes an outer energy-absorbing wall, an inner load-bearing wall, and connecting ribs. The thickness of the outer energy-absorbing wall is 1.8-3.0 mm, the thickness of the inner load-bearing wall is 2.5-4.0 mm, the thickness of the connecting ribs is 1.5-2.8 mm, and the radius of the rounded corner at the connection between adjacent wall panels is not less than 1.2 mm.

8. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step five, during online strong wind-water mist composite quenching, the profile outlet temperature is controlled at 500-540℃, the water mist pressure is 0.20-0.45MPa, and the strong wind speed is 15-35m / s. By controlling the flow rate and air volume of the water mist nozzles in different zones, the cooling rate difference between the thick-walled and thin-walled areas is controlled within 60℃ / s, and the profile temperature drops below 80℃ after quenching.

9. The method for preparing a crack-resistant aluminum profile material for the door sill of a new energy vehicle according to claim 1, characterized in that, In step six, the tensile deformation during tension straightening is 0.5-1.8%; the pre-aging treatment temperature is 80-110℃, and the holding time is 1-4h; the two-stage artificial aging treatment is as follows: first, hold at 120-150℃ for 2-5h, and then raise the temperature to 165-185℃ and hold for 4-8h.

10. A crack-resistant aluminum profile material for the door sill of new energy vehicles, characterized in that, The aluminum profile is prepared by the preparation method according to any one of claims 1-9; in the cross-sectional microstructure of the aluminum profile, the average grain size of the recrystallization zone is not greater than 35 μm, and the matrix contains dispersed phases containing zirconium, manganese, and chromium; the tensile strength of the aluminum profile is not less than 285 MPa, the yield strength is not less than 245 MPa, and the elongation after fracture is not less than 12%; according to GB / T 232-2024, under the condition that the bending radius is twice the profile wall thickness and the bending angle is 180°, there are no visible cracks on the outer bending surface.

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