Corrosion-resistant extruded aluminum alloy for rail transit and preparation method thereof

Abstract

The application discloses a kind of corrosion-resistant extruded aluminum alloy for rail transit and a preparation method thereof, and relates to the technical field of high-performance aluminum alloy.The method first melts by adding magnesium ingot, Al-Mn, Al-Cr intermediate alloy and aluminum-zirconium-silicon, aluminum-titanium-boron-carbon, aluminum-scandium-yttrium-cerium multi-element master alloy in sequence, and obtains dense aluminum alloy base material by homogenization, extrusion and multi-stage heat treatment;Then the base material is treated by pulse micro-arc oxidation to form a ceramic oxide layer;Finally, a composite sol containing modified graphene oxide and Schiff base corrosion inhibitor is prepared, and a functional coating is constructed on the surface of the micro-arc oxidation layer by pulling and plating.The synergistic effect of substrate alloy optimization and double surface protection significantly improves the uniform corrosion resistance of aluminum alloy, and is suitable for harsh corrosion environments such as rail transit.

Description

Technical Field

[0001] This invention relates to the field of high-performance aluminum alloy technology, specifically to a corrosion-resistant extruded aluminum alloy for rail transit and its preparation method. Background Technology

[0002] In the wave of lightweight and high-performance development of rail transit equipment, aluminum alloys have stood out due to their unique comprehensive properties, becoming an indispensable key material in this field. With a density only about one-third that of steel, they are remarkably effective in achieving lightweight vehicle body structures. Taking high-speed trains as an example, using aluminum alloy car bodies can reduce the overall weight by 20% to 30%, directly reducing traction energy consumption, while also reducing wheel and rail wear and extending the service life of the track system. In terms of strength performance, through composition optimization and improved heat treatment processes, the tensile strength of aluminum alloys can reach over 400 MPa, fully meeting the mechanical requirements of key components such as rail transit car bodies and load-bearing connectors. Furthermore, aluminum alloys possess excellent plasticity and machinability, allowing for the fabrication of complex cross-section components through various processes such as extrusion, welding, and forging, adapting to the diverse structural design needs of rail transit equipment and significantly improving manufacturing efficiency. Based on the above advantages, aluminum alloys have been widely used in core components of the rail transit field, including load-bearing structures such as the car body frame, door pillars, and underframe beams of high-speed trains, subways, and light rails, as well as connecting parts such as bolts and rivets. They are also used in components that combine decoration and functionality, such as interior trim panels and external fairings.

[0003] However, the operating environment of rail transit equipment is far more complex and demanding than that of ordinary industrial settings. Its service life often lasts 15 to 25 years, requiring it to withstand prolonged corrosive effects from a combination of multiple factors. This makes the corrosion resistance shortcomings of traditional aluminum alloys increasingly apparent. From a regional perspective, in coastal areas with high salt spray, the chloride ion content can reach 0.05–0.2 mg / m³. 3These ions possess extremely strong penetrating power, capable of breaking through the naturally formed oxide film on the surface of aluminum alloys and triggering localized electrochemical reactions. Furthermore, the atmosphere in industrial areas contains large amounts of acidic gases such as sulfur dioxide and nitrogen oxides. These gases combine with water vapor in the air to form acidic rain and fog with a pH value as low as 3-4, continuously dissolving the protective coating and oxide layer on the aluminum alloy surface. From a climatic cycle perspective, the alternation of seasons brings rain and snow erosion and wet-dry cycles, keeping the aluminum alloy surface in a constant dynamic process of wetting-drying-wetting. This cycle accelerates the peeling off of corrosion products, exposing the fresh substrate for continuous corrosion. During operation, rail transit equipment is subjected to continuous vibration loads, such as the high-frequency vibrations generated by wheel-rail contact during train movement and the impact loads during starting and braking. These stresses, combined with the corrosive environment, work synergistically to induce stress corrosion cracking. Under the combined effects of the aforementioned multiple factors, traditional aluminum alloys are highly susceptible to a series of failure problems: irregular peeling of the surface oxide film, forming large areas of grayish-white corrosion; localized pitting corrosion pits with diameters of 0.1–1 mm appearing, which gradually expand and connect to form deep corrosion grooves; and blistering, cracking, or even complete peeling of the protective coating, resulting in direct exposure of the internal substrate to the corrosive environment. These problems not only affect the appearance quality of the equipment but also severely weaken the mechanical properties of the structure. For example, the strength of load-bearing components can decrease by 10%–30%, and the fastening performance of connectors can deteriorate, ultimately threatening the structural safety of rail transit operations, shortening the service life of the equipment, and significantly increasing the cost and frequency of subsequent maintenance and repairs, bringing significant economic pressure and safety hazards to rail transit operations. Summary of the Invention

[0004] The purpose of this invention is to provide a corrosion-resistant extruded aluminum alloy for rail transit and its preparation method, so as to solve the technical problem of poor corrosion resistance of aluminum alloys for rail transit mentioned in the background art.

[0005] To achieve the above objectives, the present invention provides the following technical solution: A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: S1. Melt industrial pure aluminum, add magnesium ingots, Al-Mn master alloy and Al-Cr master alloy, stir and keep warm; after cooling, add aluminum-zirconium-silicon master alloy, perform ultrasonic dispersion and keep warm; after heating, add aluminum-titanium-boron-carbon master alloy, stir and keep warm; after cooling, add aluminum-scandium-yttrium-cerium master alloy, stir and keep warm under argon protection; then refine, degas, filter, and cast to obtain ingots; S2. The ingot is homogenized, then the surface layer is removed, heated and held at the temperature, then extruded and formed. The profile is quenched and straightened, and then annealed, solution quenched and aged in sequence to obtain aluminum alloy substrate. S3. The aluminum alloy substrate is subjected to pulsed micro-arc oxidation treatment in an electrolyte containing sodium hydroxide, sodium silicate, sodium dihydrogen phosphate, sodium fluoride, trisodium citrate and cerium nitrate hexahydrate, then cleaned and dried to obtain an intermediate product with a micro-arc oxidation layer. S4. Graphene oxide is ultrasonically dispersed in anhydrous ethanol, and then hydrochloric acid and silane coupling agent KH-560 are added for reaction. After reaction, the mixture is filtered and dried to obtain modified graphene oxide. o-Vanillin and ethylenediamine are refluxed in anhydrous ethanol, and crystals are precipitated after cooling. After filtration and drying, Schiff base corrosion inhibitor is obtained. Tetrabutyl titanate and tetraethyl orthosilicate are mixed, anhydrous ethanol is added, and then modified graphene oxide and Schiff base corrosion inhibitor are added. The mixture is ultrasonically dispersed and hydrolyzed to obtain composite sol. S5. Immerse the intermediate product with the micro-arc oxidation layer in the composite sol and pull it out, then dry and cure it to obtain the final product.

[0006] In this invention, the corrosion resistance of aluminum alloys used in rail transit is improved synergistically from two aspects. Firstly, through the synergistic effect of a multi-element master alloy and smelting and heat treatment processes, a corrosion-resistant foundation is constructed from within the aluminum alloy matrix: the titanium diboride-titanium carbide composite phase introduced by the aluminum-titanium-boron-carbon master alloy acts as a heterogeneous nucleation core, significantly refining the matrix grains and reducing grain boundary corrosion channels; the rare earth intermetallic compounds formed by the aluminum-scandium-yttrium-cerium master alloy are uniformly dispersed, increasing the matrix electrode potential and inhibiting electrochemical corrosion; the zirconium-silicon two-phase precipitated by the aluminum-zirconium-silicon master alloy strengthens the grain boundaries and reduces stress corrosion sensitivity; combined with the synergistic effect of alloying elements such as magnesium, manganese, and chromium, and two-stage homogenization and solution aging treatment, compositional segregation and internal stress are effectively eliminated, resulting in a uniform and dense matrix structure, reducing the generation of corrosion sources, and fundamentally improving the aluminum alloy's ability to resist uniform corrosion, intergranular corrosion, and stress corrosion. On the other hand, a dual surface protection barrier is constructed through micro-arc oxidation pretreatment and sol-gel composite coating process: micro-arc oxidation forms an alumina-based ceramic layer on the aluminum alloy surface, and elements such as silicon, phosphorus, and cerium in the electrolyte are incorporated into the film layer. Three-stage voltage control makes the ceramic layer present a dense bottom layer, a porous middle layer, and a rough surface layer structure, which not only achieves physical barrier against corrosive media, but also provides mechanical interlocking sites for the subsequent sol-gel layer; in the composite sol, graphene oxide modified with silane coupling agent blocks the penetration of corrosive media with a sheet structure, and o-vanillin ethylenediamine Schiff base corrosion inhibitor can form coordination bonds with the metal surface in the early stage of corrosion to play an active corrosion inhibition role. The cross-linked network formed by the hydrolysis and condensation of tetrabutyl orthosilicate and tetrabutyl titanate firmly fixes the two. Through pull coating and staged curing, a functional coating that is closely combined with the micro-arc oxidation ceramic layer is formed, realizing the synergistic protection of physical barrier and active corrosion inhibition, blocking the path of corrosive media to penetrate into the substrate.

[0007] Preferably, in step S1, the aluminum-zirconium-silicon master alloy is prepared as follows: Industrial pure aluminum is melted, then Zr-Si pre-alloyed powder is added and ultrasonically dispersed; after heat preservation, it is cast and cooled, and then homogenized to obtain an aluminum-zirconium-silicon master alloy.

[0008] Preferably, in step S1, the aluminum-titanium-boron-carbon master alloy is prepared as follows: Industrial pure aluminum is melted, and then potassium fluorotitanate and potassium fluoroborate are added and stirred to react. Graphite powder is then added, and the mixture is heated and stirred to continue reacting. Argon gas is introduced throughout the process for protection. After the reaction is completed, the mixture is cast, cooled, and crushed to obtain an aluminum-titanium-boron-carbon master alloy.

[0009] Preferably, in step S1, the preparation method of the aluminum-scandium-yttrium-cerium master alloy is as follows: Industrial pure aluminum is melted, and then Al-Sc master alloy, Al-Y master alloy and Al-Ce master alloy are added in sequence. The mixture is stirred and kept at a constant temperature for reaction. Argon gas is introduced throughout the process for protection. After the reaction is completed, the mixture is cast and cooled to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0010] Preferably, in step S1, the mass ratio of magnesium ingot, Al-Mn master alloy and Al-Cr master alloy is 30:(10-15):(8-10).

[0011] Preferably, in step S1, the mass ratio of the aluminum-zirconium-silicon master alloy, the aluminum-titanium-boron-carbon master alloy, and the aluminum-scandium-yttrium-cerium master alloy is 10:(10-15):(20-25).

[0012] Preferably, in step S3, the aluminum alloy substrate undergoes pretreatment, including the following steps: The aluminum alloy substrate is immersed in a mixed acid treatment solution, rinsed with deionized water, then immersed in a passivation solution, rinsed with deionized water and dried to obtain the final product.

[0013] Preferably, the mixed acid includes phosphoric acid, hydrofluoric acid, trisodium citrate, lanthanum nitrate hexahydrate, and deionized water.

[0014] Preferably, the passivation solution includes sodium silicate, sodium molybdate, sodium gluconate, and deionized water.

[0015] In the technical solution of this invention, research has revealed that after in-situ composite alloying modification of the matrix, the diffusely distributed scandium-yttrium-cerium intermetallic compounds, zirconium-silicon two-phase, and titanium diboride-titanium carbide composite phase in the matrix result in a heterogeneous distribution of rare earth-rich phase / silicon-zirconium-pure aluminum phase on the surface of the aluminum alloy. This leads to significant differences in film formation rates in different regions during the micro-arc oxidation process, resulting in an uneven structure of locally dense and locally porous ceramic layer, which significantly reduces its physical barrier effect against corrosive media. At the same time, there is a significant potential difference between the electrode potential of the rare earth-rich phase and the pure aluminum phase and the micro-arc oxidation ceramic layer, which easily forms micro-corrosion cells at the interface, accelerating the penetration of corrosive media into the matrix and ultimately weakening the synergistic effect of matrix corrosion resistance enhancement and surface barrier protection. To further address this technical problem, this invention employs a low-concentration mixed acid to micro-etch an aluminum alloy substrate after multi-stage heat treatment. This process efficiently removes the oxide film from the substrate surface and selectively corrodes the pure aluminum phase region, resulting in a uniform micro-rough structure on the substrate surface. This eliminates the morphological difference between the rich phase and the pure aluminum phase, laying the foundation for uniform film formation in subsequent micro-arc oxidation. Subsequently, the substrate is immersed in a pre-passivation solution, forming a thin passivation film containing silicon, molybdenum, and lanthanum on the substrate surface. This passivation film effectively regulates the electrode potential of different phase regions, reduces the potential difference between phases, and inhibits the formation of micro-corrosion cells. Simultaneously, its uniform film structure provides a uniformly composed and stable substrate for the micro-arc oxidation ceramic layer, ensuring consistent film formation rates in all regions during micro-arc oxidation. This results in a dense and uniform ceramic layer, further enhancing the corrosion resistance of the aluminum alloy material.

[0016] Preferably, in step S4, the mass ratio of modified graphene oxide to Schiff base corrosion inhibitor is 6:(3-5).

[0017] A corrosion-resistant extruded aluminum alloy for rail transit is prepared by the method described above.

[0018] Compared with the prior art, the beneficial effects of the present invention are: 1. By synergistically adding and optimizing the smelting process of multi-element master alloys (aluminum-titanium-boron-carbon, aluminum-scandium-yttrium-cerium, aluminum-zirconium-silicon, etc.), the grains are refined and a dispersed strengthening phase is formed. Combined with two-stage homogenization and solution aging treatment, compositional segregation and internal stress are effectively eliminated, thereby improving the alloy's ability to resist uniform corrosion, intergranular corrosion and stress corrosion from the inside.

[0019] 2. A multi-layer ceramic oxide layer containing silicon, phosphorus, and cerium is generated on the surface by pulsed micro-arc oxidation. Then, a composite coating of modified graphene oxide and Schiff base corrosion inhibitor is coated by sol-gel method to achieve the synergistic effect of physical barrier and active corrosion inhibition, which significantly blocks the penetration of corrosive media.

[0020] 3. By pretreating with mixed acid micro-etching and passivation solution, the microstructure of the substrate surface is homogenized and the potential difference in the phase region is reduced, which promotes the uniform and dense formation of the micro-arc oxidation layer, enhances the bonding stability between the substrate and the surface protective layer, and further improves the overall corrosion resistance. Attached Figure Description

[0021] Figure 1 This is a SEM image of the surface of the corrosion-resistant extruded aluminum alloy for rail transit prepared in Example 4 of the present invention.

[0022] Figure 2 XPS image of the surface of the corrosion-resistant extruded aluminum alloy for rail transit prepared in Example 4 of the present invention. Detailed Implementation

[0023] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of them. 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.

[0024] Example 1 A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: Step 1: Take 100g of industrial pure aluminum with a purity ≥99.7% and put it into a graphite crucible melting furnace. Heat it to 790℃ at a heating rate of 10℃ / min and hold it at that temperature for 15min to completely melt it. Then slowly add 6g of potassium fluorotitanate with a purity ≥98% and 7.2g of potassium fluoroborate with a purity ≥98%. Turn on the high-speed mechanical stirrer and adjust the speed to 320r / min. Hold it at that temperature and stir for 45min. Then add 0.9g of graphite powder with a particle size ≤2μm and a purity ≥99%. Raise the furnace temperature to 825℃ and continue to hold it at that temperature and stir for 65min. Argon gas with a purity ≥99.99% (flow rate 1.0L / min) is introduced throughout the process for protection. After the reaction is complete, quickly pour the melt into a cast iron mold preheated to 200℃. After naturally cooling to room temperature, crush it into particles with a particle size of 20-50mm using a crusher to obtain an aluminum-titanium-boron-carbon master alloy.

[0025] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a corundum crucible melting furnace. Heat it to 880℃ at a heating rate of 8℃ / min and hold it at that temperature for 15min until it is completely melted. Then, add 6.25g of Al-8%Sc master alloy with a purity ≥99.5%, 1g of Al-5%Y master alloy with a purity ≥99.5%, and 0.2g of Al-5%Ce master alloy with a purity ≥99.5% while stirring with a stirrer at 280r / min. Hold the reaction at that temperature for 90min and continuously purge argon gas at a rate of 1.2L / min for protection. After the reaction is complete, pour the melt into a cast iron mold preheated to 150℃ and allow it to cool naturally to room temperature to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0026] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a graphite crucible. Heat it to 800℃ at a heating rate of 10℃ / min and hold it for 20min to completely melt it. Add 1.35g of Zr-Si pre-alloyed powder with a particle size of 5-10μm and a purity ≥99.5% (Zr:Si molar ratio 1:2) to the melt in batches with a 5min interval between each batch. At the same time, turn on a 900W ultrasonic disperser to disperse continuously for 40min. After ultrasonic treatment, hold it at the temperature for 70min. Cast the melt into a mold to cool and solidify. Then place it in a homogenizing furnace and heat it to 480℃ at a rate of 5℃ / min. Hold it at the temperature for 14h for homogenization treatment. Cool it to room temperature with the furnace to obtain an aluminum-zirconium-silicon master alloy.

[0027] Weigh out 899.8g of industrial pure aluminum with a purity ≥99.7%, 30g of magnesium ingot with a purity ≥99.9%, 14g of Al-50%Mn master alloy with a purity ≥99.5%, 9.5g of Al-20%Cr master alloy with a purity ≥99.5%, 14g of aluminum-titanium-boron-carbon master alloy, 24g of aluminum-scandium-yttrium-cerium master alloy, and 10g of aluminum-zirconium-silicon master alloy; heat the industrial pure aluminum to 780℃ and hold for 30min to melt it into a basic aluminum liquid, add the magnesium ingot and Al-Mn and Al-Cr master alloys, stir at 250r / min and hold for 45min; reduce the temperature to 750℃ at 5℃ / min, and add... An aluminum-zirconium-silicon master alloy was ultrasonically dispersed at 700W for 30 minutes and held at that temperature for 60 minutes. The temperature was then raised to 760℃, and an aluminum-titanium-boron-carbon master alloy was added. The mixture was stirred at 320 rpm and held at that temperature for 50 minutes. The temperature was then lowered to 740℃, and an aluminum-scandium-yttrium-cerium master alloy was added. The mixture was stirred at 280 rpm for 70 minutes under argon protection at 1.2 L / min. Finally, 2 g of hexachloroethane with a purity ≥99% was added, and the mixture was refined at 710℃ for 30 minutes. Online degassing was performed using argon at 1.8 L / min. After standing for 40 minutes, the mixture was filtered through a foam ceramic filter and cast at 90 mm / min into a preheated mold at 150℃. The casting was then cooled to obtain an ingot.

[0028] Step 2: Place the ingot in a homogenizing furnace and heat it to 425℃ at 5℃ / min, holding it for 9 hours for primary homogenization; then heat it to 485℃ at 3℃ / min, holding it for 17 hours for secondary homogenization; after natural cooling, machine to remove 1-2mm of the surface layer to obtain a homogenized ingot with a diameter of 100mm. Place the ingot in a heating furnace and heat it to 470℃ at 10℃ / min, holding it for 2.5 hours; feed it into an extrusion press (extrusion ratio 50, speed 6.5mm / s) for extrusion molding, and the profile is immediately placed in a 530℃ quenching zone and held for 12 minutes, then straightened with a 1.0% tensile rate to obtain an extruded profile with the required dimensions. The profile is placed in a heat treatment furnace and annealed by heating to 210℃ at 5℃ / min and holding for 3.5h; then it is heated to 495℃ at 8℃ / min and held for 1.8h for solution treatment. After being removed, it is immediately quenched in water (cooling rate ≥20℃ / s); finally, it is aged by heating to 175℃ at 5℃ / min and holding for 13h, and then cooled in the furnace to obtain the aluminum alloy substrate.

[0029] Step 3: Immerse the aluminum alloy substrate in the treatment solution (5g / L phosphoric acid, 1.5g / L hydrofluoric acid, 2g / L trisodium citrate, 0.8g / L lanthanum nitrate hexahydrate, solution is deionized water), control the temperature at 30℃, and soak for 10 minutes, stirring once every 2 minutes during this period; after removal, rinse 3 times with deionized water, and immediately immerse in the passivation solution (8g / L sodium silicate, 3g / L sodium molybdate, 1g / L sodium gluconate, solution is deionized water, pH=9.5, temperature 40℃), soak for 15 minutes; finally rinse with deionized water, dry at 80℃ for 30 minutes, and obtain the pretreated aluminum alloy substrate.

[0030] Electrolyte preparation: Add 7 g / L sodium hydroxide, 12 g / L sodium silicate, 10 g / L sodium dihydrogen phosphate, 4 g / L sodium fluoride, 3 g / L trisodium citrate, and 1.5 g / L cerium nitrate hexahydrate to deionized water, stir for 30 min to dissolve, adjust pH to 10.0 with 37% hydrochloric acid, and control the temperature at 28℃; use a pretreated aluminum alloy substrate as the anode and stainless steel as the cathode (5 cm spacing), and perform three-stage pulse power supply treatment: 320V, 12A / dm³. 2 650Hz, 35% duty cycle processing for 18 minutes; 420V, 22A / dm 2 1100Hz, 55% duty cycle processing for 28 minutes; 520V, 18A / dm 2 The sample was treated at 900 Hz and 45% duty cycle for 12 min; after treatment, it was rinsed three times with deionized water and dried at 85 ℃ for 2.5 h to obtain an intermediate product with a micro-arc oxidation layer.

[0031] Step 4: Weigh 0.6g of graphene oxide with a particle size of 1-5μm, add 200mL of 99.7% anhydrous ethanol, and ultrasonically disperse at 550W for 25min; add 2mL of 0.1mol / L hydrochloric acid and 0.048g of silane coupling agent KH-560, and place in a constant temperature water bath at 65℃ and stir for 6h; after the reaction, filter with a 0.45μm filter membrane, and dry the filter residue in a vacuum drying oven at 80℃ and 0.08MPa to constant weight to obtain modified graphene oxide.

[0032] Weigh 3.04 g of o-vanillin and 0.6 g of ethylenediamine, add them to a 100 mL anhydrous ethanol round-bottom flask, install a spherical condenser, and reflux in a 75 °C water bath for 7 h with stirring. Allow the mixture to cool naturally to precipitate crystals, filter, and dry at 60 °C for 4 h to constant weight to obtain o-vanillin ethylenediamine Schiff base corrosion inhibitor.

[0033] Measure 30 mL of tetraethyl orthosilicate and 13.8 mL of tetrabutyl titanate. Slowly add tetrabutyl titanate to tetraethyl orthosilicate and stir for 15 min. Add 262 mL of anhydrous ethanol and adjust the pH to 4.0 with 0.1 mol / L hydrochloric acid. Add 0.6 g of modified graphene oxide and 0.45 g of Schiff base corrosion inhibitor. Disperse the mixture by ultrasonication at 750 W for 35 min and hydrolyze it in a constant temperature water bath at 35 °C for 2.5 h to obtain the composite sol.

[0034] Step 5: Immerse the intermediate product with the micro-arc oxidation layer into the composite sol and lift it 3 times at 6.5 mm / s (after each lift, let it stand at room temperature in a dust-free environment for 12 min); dry and cure in stages: first dry at room temperature for 2 h, then increase the temperature to 80℃ at 10℃ / min and dry for 3 h, then increase the temperature to 120℃ at 8℃ / min and dry for 2 h, and finally increase the temperature to 210℃ at 5℃ / min and cure for 1.8 h; after natural cooling, the corrosion-resistant extruded aluminum alloy for rail transit is obtained.

[0035] Example 2 A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: Step 1: Take 100g of industrial pure aluminum with a purity ≥99.7% and put it into a graphite crucible melting furnace. Heat it to 790℃ at a heating rate of 10℃ / min and hold it at that temperature for 15min to completely melt it. Then slowly add 6g of potassium fluorotitanate with a purity ≥98% and 7.2g of potassium fluoroborate with a purity ≥98%. Turn on the high-speed mechanical stirrer and adjust the speed to 320r / min. Hold it at that temperature and stir for 45min. Then add 0.9g of graphite powder with a particle size ≤2μm and a purity ≥99%. Raise the furnace temperature to 825℃ and continue to hold it at that temperature and stir for 65min. Argon gas with a purity ≥99.99% (flow rate 1.0L / min) is introduced throughout the process for protection. After the reaction is complete, quickly pour the melt into a cast iron mold preheated to 200℃. After naturally cooling to room temperature, crush it into particles with a particle size of 20-50mm using a crusher to obtain an aluminum-titanium-boron-carbon master alloy.

[0036] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a corundum crucible melting furnace. Heat it to 880℃ at a heating rate of 8℃ / min and hold it at that temperature for 15min until it is completely melted. Then, add 6.25g of Al-8%Sc master alloy with a purity ≥99.5%, 1g of Al-5%Y master alloy with a purity ≥99.5%, and 0.2g of Al-5%Ce master alloy with a purity ≥99.5% while stirring with a stirrer at 280r / min. Hold the reaction at that temperature for 90min and continuously purge argon gas at a rate of 1.2L / min for protection. After the reaction is complete, pour the melt into a cast iron mold preheated to 150℃ and allow it to cool naturally to room temperature to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0037] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a graphite crucible. Heat it to 800℃ at a heating rate of 10℃ / min and hold it for 20min to completely melt it. Add 1.35g of Zr-Si pre-alloyed powder with a particle size of 5-10μm and a purity ≥99.5% (Zr:Si molar ratio 1:2) to the melt in batches with a 5min interval between each batch. At the same time, turn on a 900W ultrasonic disperser to disperse continuously for 40min. After ultrasonic treatment, hold it at the temperature for 70min. Cast the melt into a mold to cool and solidify. Then place it in a homogenizing furnace and heat it to 480℃ at a rate of 5℃ / min. Hold it at the temperature for 14h for homogenization treatment. Cool it to room temperature with the furnace to obtain an aluminum-zirconium-silicon master alloy.

[0038] Weigh out 899.8g of industrial pure aluminum with a purity ≥99.7%, 30g of magnesium ingot with a purity ≥99.9%, 11g of Al-50%Mn master alloy with a purity ≥99.5%, 8.5g of Al-20%Cr master alloy with a purity ≥99.5%, 11g of aluminum-titanium-boron-carbon master alloy, 22g of aluminum-scandium-yttrium-cerium master alloy, and 10g of aluminum-zirconium-silicon master alloy; heat the industrial pure aluminum to 780℃ and hold for 30min to melt it into a basic aluminum liquid, add the magnesium ingot and Al-Mn and Al-Cr master alloys, stir at 250r / min and hold for 45min; reduce the temperature to 750℃ at 5℃ / min, and add... An aluminum-zirconium-silicon master alloy was ultrasonically dispersed at 700W for 30 minutes and held at that temperature for 60 minutes. The temperature was then raised to 760℃, and an aluminum-titanium-boron-carbon master alloy was added. The mixture was stirred at 320 rpm and held at that temperature for 50 minutes. The temperature was then lowered to 740℃, and an aluminum-scandium-yttrium-cerium master alloy was added. The mixture was stirred at 280 rpm for 70 minutes under argon protection at 1.2 L / min. Finally, 2 g of hexachloroethane with a purity ≥99% was added, and the mixture was refined at 710℃ for 30 minutes. Online degassing was performed using argon at 1.8 L / min. After standing for 40 minutes, the mixture was filtered through a foam ceramic filter and cast at 90 mm / min into a preheated mold at 150℃. The casting was then cooled to obtain an ingot.

[0039] Step 2: Place the ingot in a homogenizing furnace and heat it to 425℃ at 5℃ / min, holding it for 9 hours for primary homogenization; then heat it to 485℃ at 3℃ / min, holding it for 17 hours for secondary homogenization; after natural cooling, machine to remove 1-2mm of the surface layer to obtain a homogenized ingot with a diameter of 100mm. Place the ingot in a heating furnace and heat it to 470℃ at 10℃ / min, holding it for 2.5 hours; feed it into an extrusion press (extrusion ratio 50, speed 6.5mm / s) for extrusion molding, and the profile is immediately placed in a 530℃ quenching zone and held for 12 minutes, then straightened with a 1.0% tensile rate to obtain an extruded profile with the required dimensions. The profile is placed in a heat treatment furnace and annealed by heating to 210℃ at 5℃ / min and holding for 3.5h; then it is heated to 495℃ at 8℃ / min and held for 1.8h for solution treatment. After being removed, it is immediately quenched in water (cooling rate ≥20℃ / s); finally, it is aged by heating to 175℃ at 5℃ / min and holding for 13h, and then cooled in the furnace to obtain the aluminum alloy substrate.

[0040] Step 3: Immerse the aluminum alloy substrate in the treatment solution (5g / L phosphoric acid, 1.5g / L hydrofluoric acid, 2g / L trisodium citrate, 0.8g / L lanthanum nitrate hexahydrate, solution is deionized water), control the temperature at 30℃, and soak for 10 minutes, stirring once every 2 minutes during this period; after removal, rinse 3 times with deionized water, and immediately immerse in the passivation solution (8g / L sodium silicate, 3g / L sodium molybdate, 1g / L sodium gluconate, solution is deionized water, pH=9.5, temperature 40℃), soak for 15 minutes; finally rinse with deionized water, dry at 80℃ for 30 minutes, and obtain the pretreated aluminum alloy substrate.

[0041] Electrolyte preparation: Add 7 g / L sodium hydroxide, 12 g / L sodium silicate, 10 g / L sodium dihydrogen phosphate, 4 g / L sodium fluoride, 3 g / L trisodium citrate, and 1.5 g / L cerium nitrate hexahydrate to deionized water, stir for 30 min to dissolve, adjust pH to 10.0 with 37% hydrochloric acid, and control the temperature at 28℃; use a pretreated aluminum alloy substrate as the anode and stainless steel as the cathode (5 cm spacing), and perform three-stage pulse power supply treatment: 320V, 12A / dm³. 2 650Hz, 35% duty cycle processing for 18 minutes; 420V, 22A / dm 2 1100Hz, 55% duty cycle processing for 28 minutes; 520V, 18A / dm 2 The sample was treated at 900 Hz and 45% duty cycle for 12 min; after treatment, it was rinsed three times with deionized water and dried at 85 ℃ for 2.5 h to obtain an intermediate product with a micro-arc oxidation layer.

[0042] Step 4: Weigh 0.6g of graphene oxide with a particle size of 1-5μm, add 200mL of 99.7% anhydrous ethanol, and ultrasonically disperse at 550W for 25min; add 2mL of 0.1mol / L hydrochloric acid and 0.048g of silane coupling agent KH-560, and place in a constant temperature water bath at 65℃ and stir for 6h; after the reaction, filter with a 0.45μm filter membrane, and dry the filter residue in a vacuum drying oven at 80℃ and 0.08MPa to constant weight to obtain modified graphene oxide.

[0043] Weigh 3.04 g of o-vanillin and 0.6 g of ethylenediamine, add them to a 100 mL anhydrous ethanol round-bottom flask, install a spherical condenser, and reflux in a 75 °C water bath for 7 h with stirring. Allow the mixture to cool naturally to precipitate crystals, filter, and dry at 60 °C for 4 h to constant weight to obtain o-vanillin ethylenediamine Schiff base corrosion inhibitor.

[0044] Measure 30 mL of tetraethyl orthosilicate and 13.8 mL of tetrabutyl titanate. Slowly add tetrabutyl titanate to tetraethyl orthosilicate and stir for 15 min. Add 262 mL of anhydrous ethanol and adjust the pH to 4.0 with 0.1 mol / L hydrochloric acid. Add 0.6 g of modified graphene oxide and 0.35 g of Schiff base corrosion inhibitor. Disperse the mixture by ultrasonication at 750 W for 35 min and hydrolyze it in a constant temperature water bath at 35 °C for 2.5 h to obtain the composite sol.

[0045] Step 5: Immerse the intermediate product with the micro-arc oxidation layer into the composite sol and lift it 3 times at 6.5 mm / s (after each lift, let it stand at room temperature in a dust-free environment for 12 min); dry and cure in stages: first dry at room temperature for 2 h, then increase the temperature to 80℃ at 10℃ / min and dry for 3 h, then increase the temperature to 120℃ at 8℃ / min and dry for 2 h, and finally increase the temperature to 210℃ at 5℃ / min and cure for 1.8 h; after natural cooling, the corrosion-resistant extruded aluminum alloy for rail transit is obtained.

[0046] Example 3 A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: Step 1: Take 100g of industrial pure aluminum with a purity ≥99.7% and put it into a graphite crucible melting furnace. Heat it to 790℃ at a heating rate of 10℃ / min and hold it at that temperature for 15min to completely melt it. Then slowly add 6g of potassium fluorotitanate with a purity ≥98% and 7.2g of potassium fluoroborate with a purity ≥98%. Turn on the high-speed mechanical stirrer and adjust the speed to 320r / min. Hold it at that temperature and stir for 45min. Then add 0.9g of graphite powder with a particle size ≤2μm and a purity ≥99%. Raise the furnace temperature to 825℃ and continue to hold it at that temperature and stir for 65min. Argon gas with a purity ≥99.99% (flow rate 1.0L / min) is introduced throughout the process for protection. After the reaction is complete, quickly pour the melt into a cast iron mold preheated to 200℃. After naturally cooling to room temperature, crush it into particles with a particle size of 20-50mm using a crusher to obtain an aluminum-titanium-boron-carbon master alloy.

[0047] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a corundum crucible melting furnace. Heat it to 880℃ at a heating rate of 8℃ / min and hold it at that temperature for 15min until it is completely melted. Then, add 6.25g of Al-8%Sc master alloy with a purity ≥99.5%, 1g of Al-5%Y master alloy with a purity ≥99.5%, and 0.2g of Al-5%Ce master alloy with a purity ≥99.5% while stirring with a stirrer at 280r / min. Hold the reaction at that temperature for 90min and continuously purge argon gas at a rate of 1.2L / min for protection. After the reaction is complete, pour the melt into a cast iron mold preheated to 150℃ and allow it to cool naturally to room temperature to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0048] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a graphite crucible. Heat it to 800℃ at a heating rate of 10℃ / min and hold it for 20min to completely melt it. Add 1.35g of Zr-Si pre-alloyed powder with a particle size of 5-10μm and a purity ≥99.5% (Zr:Si molar ratio 1:2) to the melt in batches with a 5min interval between each batch. At the same time, turn on a 900W ultrasonic disperser to disperse continuously for 40min. After ultrasonic treatment, hold it at the temperature for 70min. Cast the melt into a mold to cool and solidify. Then place it in a homogenizing furnace and heat it to 480℃ at a rate of 5℃ / min. Hold it at the temperature for 14h for homogenization treatment. Cool it to room temperature with the furnace to obtain an aluminum-zirconium-silicon master alloy.

[0049] Weigh out 899.8g of industrial pure aluminum with a purity ≥99.7%, 30g of magnesium ingot with a purity ≥99.9%, 13g of Al-50%Mn master alloy with a purity ≥99.5%, 9g of Al-20%Cr master alloy with a purity ≥99.5%, 13g of aluminum-titanium-boron-carbon master alloy, 23g of aluminum-scandium-yttrium-cerium master alloy, and 10g of aluminum-zirconium-silicon master alloy. Heat the industrial pure aluminum to 780℃ and hold for 30 minutes to melt it into a base aluminum liquid. Add the magnesium ingot and the Al-Mn and Al-Cr master alloys, and stir at 250 r / min while holding for 45 minutes. Reduce the temperature to 750℃ at a rate of 5℃ / min, and add aluminum... The zirconium-silicon master alloy was ultrasonically dispersed at 700W for 30 minutes and held at that temperature for 60 minutes. The temperature was then raised to 760℃, and the aluminum-titanium-boron-carbon master alloy was added. The mixture was stirred at 320 r / min and held at that temperature for 50 minutes. The temperature was then lowered to 740℃, and the aluminum-scandium-yttrium-cerium master alloy was added. The mixture was stirred at 280 r / min for 70 minutes under argon protection at 1.2 L / min. Finally, 2 g of hexachloroethane with a purity ≥99% was added, and the mixture was refined at 710℃ for 30 minutes. The mixture was degassed online with argon at 1.8 L / min. After standing for 40 minutes, the mixture was filtered through a foam ceramic filter and cast into a preheated mold at 150℃ at a speed of 90 mm / min. The casting was then cooled to obtain an ingot.

[0050] Step 2: Place the ingot in a homogenizing furnace and heat it to 425℃ at 5℃ / min, holding it for 9 hours for primary homogenization; then heat it to 485℃ at 3℃ / min, holding it for 17 hours for secondary homogenization; after natural cooling, machine to remove 1-2mm of the surface layer to obtain a homogenized ingot with a diameter of 100mm. Place the ingot in a heating furnace and heat it to 470℃ at 10℃ / min, holding it for 2.5 hours; feed it into an extrusion press (extrusion ratio 50, speed 6.5mm / s) for extrusion molding, and the profile is immediately placed in a 530℃ quenching zone and held for 12 minutes, then straightened with a 1.0% tensile rate to obtain an extruded profile with the required dimensions. The profile is placed in a heat treatment furnace and annealed by heating to 210℃ at 5℃ / min and holding for 3.5h; then it is heated to 495℃ at 8℃ / min and held for 1.8h for solution treatment. After being removed, it is immediately quenched in water (cooling rate ≥20℃ / s); finally, it is aged by heating to 175℃ at 5℃ / min and holding for 13h, and then cooled in the furnace to obtain the aluminum alloy substrate.

[0051] Step 3: Immerse the aluminum alloy substrate in the treatment solution (5g / L phosphoric acid, 1.5g / L hydrofluoric acid, 2g / L trisodium citrate, 0.8g / L lanthanum nitrate hexahydrate, solution is deionized water), control the temperature at 30℃, and soak for 10 minutes, stirring once every 2 minutes during this period; after removal, rinse 3 times with deionized water, and immediately immerse in the passivation solution (8g / L sodium silicate, 3g / L sodium molybdate, 1g / L sodium gluconate, solution is deionized water, pH=9.5, temperature 40℃), soak for 15 minutes; finally rinse with deionized water, dry at 80℃ for 30 minutes, and obtain the pretreated aluminum alloy substrate.

[0052] Electrolyte preparation: Add 7 g / L sodium hydroxide, 12 g / L sodium silicate, 10 g / L sodium dihydrogen phosphate, 4 g / L sodium fluoride, 3 g / L trisodium citrate, and 1.5 g / L cerium nitrate hexahydrate to deionized water, stir for 30 min to dissolve, adjust pH to 10.0 with 37% hydrochloric acid, and control the temperature at 28℃; use a pretreated aluminum alloy substrate as the anode and stainless steel as the cathode (5 cm spacing), and perform three-stage pulse power supply treatment: 320V, 12A / dm³. 2 650Hz, 35% duty cycle processing for 18 minutes; 420V, 22A / dm 2 1100Hz, 55% duty cycle processing for 28 minutes; 520V, 18A / dm 2 The sample was treated at 900 Hz and 45% duty cycle for 12 min; after treatment, it was rinsed three times with deionized water and dried at 85 ℃ for 2.5 h to obtain an intermediate product with a micro-arc oxidation layer.

[0053] Step 4: Weigh 0.6g of graphene oxide with a particle size of 1-5μm, add 200mL of 99.7% anhydrous ethanol, and ultrasonically disperse at 550W for 25min; add 2mL of 0.1mol / L hydrochloric acid and 0.048g of silane coupling agent KH-560, and place in a constant temperature water bath at 65℃ and stir for 6h; after the reaction, filter with a 0.45μm filter membrane, and dry the filter residue in a vacuum drying oven at 80℃ and 0.08MPa to constant weight to obtain modified graphene oxide.

[0054] Weigh 3.04 g of o-vanillin and 0.6 g of ethylenediamine, add them to a 100 mL anhydrous ethanol round-bottom flask, install a spherical condenser, and reflux in a 75 °C water bath for 7 h with stirring. Allow the mixture to cool naturally to precipitate crystals, filter, and dry at 60 °C for 4 h to constant weight to obtain o-vanillin ethylenediamine Schiff base corrosion inhibitor.

[0055] Measure 30 mL of tetraethyl orthosilicate and 13.8 mL of tetrabutyl titanate. Slowly add tetrabutyl titanate to tetraethyl orthosilicate and stir for 15 min. Add 262 mL of anhydrous ethanol and adjust the pH to 4.0 with 0.1 mol / L hydrochloric acid. Add 0.6 g of modified graphene oxide and 0.4 g of Schiff base corrosion inhibitor. Disperse the mixture by ultrasonication at 750 W for 35 min and hydrolyze it in a constant temperature water bath at 35 °C for 2.5 h to obtain the composite sol.

[0056] Step 5: Immerse the intermediate product with the micro-arc oxidation layer into the composite sol and lift it 3 times at 6.5 mm / s (after each lift, let it stand at room temperature in a dust-free environment for 12 min); dry and cure in stages: first dry at room temperature for 2 h, then increase the temperature to 80℃ at 10℃ / min and dry for 3 h, then increase the temperature to 120℃ at 8℃ / min and dry for 2 h, and finally increase the temperature to 210℃ at 5℃ / min and cure for 1.8 h; after natural cooling, the corrosion-resistant extruded aluminum alloy for rail transit is obtained.

[0057] Example 4 A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: Step 1: Take 100g of industrial pure aluminum with a purity ≥99.7% and put it into a graphite crucible melting furnace. Heat it to 790℃ at a heating rate of 10℃ / min and hold it at that temperature for 15min to completely melt it. Then slowly add 6g of potassium fluorotitanate with a purity ≥98% and 7.2g of potassium fluoroborate with a purity ≥98%. Turn on the high-speed mechanical stirrer and adjust the speed to 320r / min. Hold it at that temperature and stir for 45min. Then add 0.9g of graphite powder with a particle size ≤2μm and a purity ≥99%. Raise the furnace temperature to 825℃ and continue to hold it at that temperature and stir for 65min. Argon gas with a purity ≥99.99% (flow rate 1.0L / min) is introduced throughout the process for protection. After the reaction is complete, quickly pour the melt into a cast iron mold preheated to 200℃. After naturally cooling to room temperature, crush it into particles with a particle size of 20-50mm using a crusher to obtain an aluminum-titanium-boron-carbon master alloy.

[0058] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a corundum crucible melting furnace. Heat it to 880℃ at a heating rate of 8℃ / min and hold it at that temperature for 15min until it is completely melted. Then, add 6.25g of Al-8%Sc master alloy with a purity ≥99.5%, 1g of Al-5%Y master alloy with a purity ≥99.5%, and 0.2g of Al-5%Ce master alloy with a purity ≥99.5% while stirring with a stirrer at 280r / min. Hold the reaction at that temperature for 90min and continuously purge argon gas at a rate of 1.2L / min for protection. After the reaction is complete, pour the melt into a cast iron mold preheated to 150℃ and allow it to cool naturally to room temperature to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0059] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a graphite crucible. Heat it to 800℃ at a heating rate of 10℃ / min and hold it for 20min to completely melt it. Add 1.35g of Zr-Si pre-alloyed powder with a particle size of 5-10μm and a purity ≥99.5% (Zr:Si molar ratio 1:2) to the melt in batches with a 5min interval between each batch. At the same time, turn on a 900W ultrasonic disperser to disperse continuously for 40min. After ultrasonic treatment, hold it at the temperature for 70min. Cast the melt into a mold to cool and solidify. Then place it in a homogenizing furnace and heat it to 480℃ at a rate of 5℃ / min. Hold it at the temperature for 14h for homogenization treatment. Cool it to room temperature with the furnace to obtain an aluminum-zirconium-silicon master alloy.

[0060] Weigh out 899.8g of industrial pure aluminum with a purity ≥99.7%, 30g of magnesium ingot with a purity ≥99.9%, 15g of Al-50%Mn master alloy with a purity ≥99.5%, 10g of Al-20%Cr master alloy with a purity ≥99.5%, 15g of aluminum-titanium-boron-carbon master alloy, 25g of aluminum-scandium-yttrium-cerium master alloy, and 10g of aluminum-zirconium-silicon master alloy. Heat the industrial pure aluminum to 780℃ and hold for 30 minutes to melt it into a base aluminum liquid. Add the magnesium ingot and the Al-Mn and Al-Cr master alloys, and stir at 250 r / min while holding for 45 minutes. Reduce the temperature to 750℃ at 5℃ / min, and add aluminum... The zirconium-silicon master alloy was ultrasonically dispersed at 700W for 30 minutes and held at that temperature for 60 minutes. The temperature was then raised to 760℃, and the aluminum-titanium-boron-carbon master alloy was added. The mixture was stirred at 320 r / min and held at that temperature for 50 minutes. The temperature was then lowered to 740℃, and the aluminum-scandium-yttrium-cerium master alloy was added. The mixture was stirred at 280 r / min for 70 minutes under argon protection at 1.2 L / min. Finally, 2 g of hexachloroethane with a purity ≥99% was added, and the mixture was refined at 710℃ for 30 minutes. The mixture was degassed online with argon at 1.8 L / min. After standing for 40 minutes, the mixture was filtered through a foam ceramic filter and cast into a preheated mold at 150℃ at a speed of 90 mm / min. The casting was then cooled to obtain an ingot.

[0061] Step 2: Place the ingot in a homogenizing furnace and heat it to 425℃ at 5℃ / min, holding it for 9 hours for primary homogenization; then heat it to 485℃ at 3℃ / min, holding it for 17 hours for secondary homogenization; after natural cooling, machine to remove 1-2mm of the surface layer to obtain a homogenized ingot with a diameter of 100mm. Place the ingot in a heating furnace and heat it to 470℃ at 10℃ / min, holding it for 2.5 hours; feed it into an extrusion press (extrusion ratio 50, speed 6.5mm / s) for extrusion molding, and the profile is immediately placed in a 530℃ quenching zone and held for 12 minutes, then straightened with a 1.0% tensile rate to obtain an extruded profile with the required dimensions. The profile is placed in a heat treatment furnace and annealed by heating to 210℃ at 5℃ / min and holding for 3.5h; then it is heated to 495℃ at 8℃ / min and held for 1.8h for solution treatment. After being removed, it is immediately quenched in water (cooling rate ≥20℃ / s); finally, it is aged by heating to 175℃ at 5℃ / min and holding for 13h, and then cooled in the furnace to obtain the aluminum alloy substrate.

[0062] Step 3: Immerse the aluminum alloy substrate in the treatment solution (5g / L phosphoric acid, 1.5g / L hydrofluoric acid, 2g / L trisodium citrate, 0.8g / L lanthanum nitrate hexahydrate, solution is deionized water), control the temperature at 30℃, and soak for 10 minutes, stirring once every 2 minutes during this period; after removal, rinse 3 times with deionized water, and immediately immerse in the passivation solution (8g / L sodium silicate, 3g / L sodium molybdate, 1g / L sodium gluconate, solution is deionized water, pH=9.5, temperature 40℃), soak for 15 minutes; finally rinse with deionized water, dry at 80℃ for 30 minutes, and obtain the pretreated aluminum alloy substrate.

[0063] Electrolyte preparation: Add 7 g / L sodium hydroxide, 12 g / L sodium silicate, 10 g / L sodium dihydrogen phosphate, 4 g / L sodium fluoride, 3 g / L trisodium citrate, and 1.5 g / L cerium nitrate hexahydrate to deionized water, stir for 30 min to dissolve, adjust pH to 10.0 with 37% hydrochloric acid, and control the temperature at 28℃; use a pretreated aluminum alloy substrate as the anode and stainless steel as the cathode (5 cm spacing), and perform three-stage pulse power supply treatment: 320V, 12A / dm³. 2 650Hz, 35% duty cycle processing for 18 minutes; 420V, 22A / dm 2 1100Hz, 55% duty cycle processing for 28 minutes; 520V, 18A / dm 2 The sample was treated at 900 Hz and 45% duty cycle for 12 min; after treatment, it was rinsed three times with deionized water and dried at 85 ℃ for 2.5 h to obtain an intermediate product with a micro-arc oxidation layer.

[0064] Step 4: Weigh 0.6g of graphene oxide with a particle size of 1-5μm, add 200mL of 99.7% anhydrous ethanol, and ultrasonically disperse at 550W for 25min; add 2mL of 0.1mol / L hydrochloric acid and 0.048g of silane coupling agent KH-560, and place in a constant temperature water bath at 65℃ and stir for 6h; after the reaction, filter with a 0.45μm filter membrane, and dry the filter residue in a vacuum drying oven at 80℃ and 0.08MPa to constant weight to obtain modified graphene oxide.

[0065] Weigh 3.04 g of o-vanillin and 0.6 g of ethylenediamine, add them to a 100 mL anhydrous ethanol round-bottom flask, install a spherical condenser, and reflux in a 75 °C water bath for 7 h with stirring. Allow the mixture to cool naturally to precipitate crystals, filter, and dry at 60 °C for 4 h to constant weight to obtain o-vanillin ethylenediamine Schiff base corrosion inhibitor.

[0066] Measure 30 mL of tetraethyl orthosilicate and 13.8 mL of tetrabutyl titanate. Slowly add tetrabutyl titanate to tetraethyl orthosilicate and stir for 15 min. Add 262 mL of anhydrous ethanol and adjust the pH to 4.0 with 0.1 mol / L hydrochloric acid. Add 0.6 g of modified graphene oxide and 0.5 g of Schiff base corrosion inhibitor. Disperse the mixture by ultrasonication at 750 W for 35 min and hydrolyze it in a constant temperature water bath at 35 °C for 2.5 h to obtain the composite sol.

[0067] Step 5: Immerse the intermediate product with the micro-arc oxidation layer into the composite sol and lift it 3 times at 6.5 mm / s (after each lift, let it stand at room temperature in a dust-free environment for 12 min); dry and cure in stages: first dry at room temperature for 2 h, then increase the temperature to 80℃ at 10℃ / min and dry for 3 h, then increase the temperature to 120℃ at 8℃ / min and dry for 2 h, and finally increase the temperature to 210℃ at 5℃ / min and cure for 1.8 h; after natural cooling, the corrosion-resistant extruded aluminum alloy for rail transit is obtained.

[0068] Example 5 A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit includes the following steps: Step 1: Take 100g of industrial pure aluminum with a purity ≥99.7% and put it into a graphite crucible melting furnace. Heat it to 790℃ at a heating rate of 10℃ / min and hold it at that temperature for 15min to completely melt it. Then slowly add 6g of potassium fluorotitanate with a purity ≥98% and 7.2g of potassium fluoroborate with a purity ≥98%. Turn on the high-speed mechanical stirrer and adjust the speed to 320r / min. Hold it at that temperature and stir for 45min. Then add 0.9g of graphite powder with a particle size ≤2μm and a purity ≥99%. Raise the furnace temperature to 825℃ and continue to hold it at that temperature and stir for 65min. Argon gas with a purity ≥99.99% (flow rate 1.0L / min) is introduced throughout the process for protection. After the reaction is complete, quickly pour the melt into a cast iron mold preheated to 200℃. After naturally cooling to room temperature, crush it into particles with a particle size of 20-50mm using a crusher to obtain an aluminum-titanium-boron-carbon master alloy.

[0069] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a corundum crucible melting furnace. Heat it to 880℃ at a heating rate of 8℃ / min and hold it at that temperature for 15min until it is completely melted. Then, add 6.25g of Al-8%Sc master alloy with a purity ≥99.5%, 1g of Al-5%Y master alloy with a purity ≥99.5%, and 0.2g of Al-5%Ce master alloy with a purity ≥99.5% while stirring with a stirrer at 280r / min. Hold the reaction at that temperature for 90min and continuously purge argon gas at a rate of 1.2L / min for protection. After the reaction is complete, pour the melt into a cast iron mold preheated to 150℃ and allow it to cool naturally to room temperature to obtain an aluminum-scandium-yttrium-cerium master alloy.

[0070] Take 100g of industrial pure aluminum with a purity ≥99.7% and place it in a graphite crucible. Heat it to 800℃ at a heating rate of 10℃ / min and hold it for 20min to completely melt it. Add 1.35g of Zr-Si pre-alloyed powder with a particle size of 5-10μm and a purity ≥99.5% (Zr:Si molar ratio 1:2) to the melt in batches with a 5min interval between each batch. At the same time, turn on a 900W ultrasonic disperser to disperse continuously for 40min. After ultrasonic treatment, hold it at the temperature for 70min. Cast the melt into a mold to cool and solidify. Then place it in a homogenizing furnace and heat it to 480℃ at a rate of 5℃ / min. Hold it at the temperature for 14h for homogenization treatment. Cool it to room temperature with the furnace to obtain an aluminum-zirconium-silicon master alloy.

[0071] Weigh out 899.8g of industrial pure aluminum with a purity ≥99.7%, 30g of magnesium ingot with a purity ≥99.9%, 10g of Al-50%Mn master alloy with a purity ≥99.5%, 8g of Al-20%Cr master alloy with a purity ≥99.5%, 10g of aluminum-titanium-boron-carbon master alloy, 20g of aluminum-scandium-yttrium-cerium master alloy, and 10g of aluminum-zirconium-silicon master alloy; heat the industrial pure aluminum to 780℃ and hold for 30min to melt it into a basic aluminum liquid, add the magnesium ingot and Al-Mn and Al-Cr master alloys, stir at 250r / min and hold for 45min; lower the temperature to 750℃ at 5℃ / min, and add aluminum The zirconium-silicon master alloy was ultrasonically dispersed at 700W for 30 minutes and held at that temperature for 60 minutes. The temperature was then raised to 760℃, and the aluminum-titanium-boron-carbon master alloy was added. The mixture was stirred at 320 r / min and held at that temperature for 50 minutes. The temperature was then lowered to 740℃, and the aluminum-scandium-yttrium-cerium master alloy was added. The mixture was stirred at 280 r / min for 70 minutes under argon protection at 1.2 L / min. Finally, 2 g of hexachloroethane with a purity ≥99% was added, and the mixture was refined at 710℃ for 30 minutes. The mixture was degassed online with argon at 1.8 L / min. After standing for 40 minutes, the mixture was filtered through a foam ceramic filter and cast into a preheated mold at 150℃ at a speed of 90 mm / min. The casting was then cooled to obtain an ingot.

[0072] Step 2: Place the ingot in a homogenizing furnace and heat it to 425℃ at 5℃ / min, holding it for 9 hours for primary homogenization; then heat it to 485℃ at 3℃ / min, holding it for 17 hours for secondary homogenization; after natural cooling, machine to remove 1-2mm of the surface layer to obtain a homogenized ingot with a diameter of 100mm. Place the ingot in a heating furnace and heat it to 470℃ at 10℃ / min, holding it for 2.5 hours; feed it into an extrusion press (extrusion ratio 50, speed 6.5mm / s) for extrusion molding, and the profile is immediately placed in a 530℃ quenching zone and held for 12 minutes, then straightened with a 1.0% tensile rate to obtain an extruded profile with the required dimensions. The profile is placed in a heat treatment furnace and annealed by heating to 210℃ at 5℃ / min and holding for 3.5h; then it is heated to 495℃ at 8℃ / min and held for 1.8h for solution treatment. After being removed, it is immediately quenched in water (cooling rate ≥20℃ / s); finally, it is aged by heating to 175℃ at 5℃ / min and holding for 13h, and then cooled in the furnace to obtain the aluminum alloy substrate.

[0073] Step 3: Immerse the aluminum alloy substrate in the treatment solution (5g / L phosphoric acid, 1.5g / L hydrofluoric acid, 2g / L trisodium citrate, 0.8g / L lanthanum nitrate hexahydrate, solution is deionized water), control the temperature at 30℃, and soak for 10 minutes, stirring once every 2 minutes during this period; after removal, rinse 3 times with deionized water, and immediately immerse in the passivation solution (8g / L sodium silicate, 3g / L sodium molybdate, 1g / L sodium gluconate, solution is deionized water, pH=9.5, temperature 40℃), soak for 15 minutes; finally rinse with deionized water, dry at 80℃ for 30 minutes, and obtain the pretreated aluminum alloy substrate.

[0074] Electrolyte preparation: Add 7 g / L sodium hydroxide, 12 g / L sodium silicate, 10 g / L sodium dihydrogen phosphate, 4 g / L sodium fluoride, 3 g / L trisodium citrate, and 1.5 g / L cerium nitrate hexahydrate to deionized water, stir for 30 min to dissolve, adjust pH to 10.0 with 37% hydrochloric acid, and control the temperature at 28℃; use a pretreated aluminum alloy substrate as the anode and stainless steel as the cathode (5 cm spacing), and perform three-stage pulse power supply treatment: 320V, 12A / dm³. 2 650Hz, 35% duty cycle processing for 18 minutes; 420V, 22A / dm 2 1100Hz, 55% duty cycle processing for 28 minutes; 520V, 18A / dm 2 The sample was treated at 900 Hz and 45% duty cycle for 12 min; after treatment, it was rinsed three times with deionized water and dried at 85 ℃ for 2.5 h to obtain an intermediate product with a micro-arc oxidation layer.

[0075] Step 4: Weigh 0.6g of graphene oxide with a particle size of 1-5μm, add 200mL of 99.7% anhydrous ethanol, and ultrasonically disperse at 550W for 25min; add 2mL of 0.1mol / L hydrochloric acid and 0.048g of silane coupling agent KH-560, and place in a constant temperature water bath at 65℃ and stir for 6h; after the reaction, filter with a 0.45μm filter membrane, and dry the filter residue in a vacuum drying oven at 80℃ and 0.08MPa to constant weight to obtain modified graphene oxide.

[0076] Weigh 3.04 g of o-vanillin and 0.6 g of ethylenediamine, add them to a 100 mL anhydrous ethanol round-bottom flask, install a spherical condenser, and reflux in a 75 °C water bath for 7 h with stirring. Allow the mixture to cool naturally to precipitate crystals, filter, and dry at 60 °C for 4 h to constant weight to obtain o-vanillin ethylenediamine Schiff base corrosion inhibitor.

[0077] Measure 30 mL of tetraethyl orthosilicate and 13.8 mL of tetrabutyl titanate. Slowly add tetrabutyl titanate to tetraethyl orthosilicate and stir for 15 min. Add 262 mL of anhydrous ethanol and adjust the pH to 4.0 with 0.1 mol / L hydrochloric acid. Add 0.6 g of modified graphene oxide and 0.3 g of Schiff base corrosion inhibitor. Disperse the mixture by ultrasonication at 750 W for 35 min and hydrolyze it in a constant temperature water bath at 35 °C for 2.5 h to obtain the composite sol.

[0078] Step 5: Immerse the intermediate product with the micro-arc oxidation layer into the composite sol and lift it 3 times at 6.5 mm / s (after each lift, let it stand at room temperature in a dust-free environment for 12 min); dry and cure in stages: first dry at room temperature for 2 h, then increase the temperature to 80℃ at 10℃ / min and dry for 3 h, then increase the temperature to 120℃ at 8℃ / min and dry for 2 h, and finally increase the temperature to 210℃ at 5℃ / min and cure for 1.8 h; after natural cooling, the corrosion-resistant extruded aluminum alloy for rail transit is obtained.

[0079] Comparative Example 1: The difference between Comparative Example 1 and Example 1 is that aluminum-titanium-boron-carbon master alloy, aluminum-scandium-yttrium-cerium master alloy and aluminum-zirconium-silicon master alloy are not added in step 1 of the aluminum alloy preparation process.

[0080] Comparative Example 2: The difference between Comparative Example 2 and Example 1 is that step 3 is omitted in the aluminum alloy preparation process, that is, the aluminum alloy substrate does not undergo pulsed micro-arc oxidation treatment.

[0081] Comparative Example 3: The difference between Comparative Example 3 and Example 1 is that step 4 is omitted in the aluminum alloy preparation process, that is, the intermediate product with micro-arc oxide layer does not undergo composite sol immersion and pulling treatment.

[0082] Comparative Example 4: The difference between Comparative Example 4 and Example 1 is that the aluminum alloy substrate is not pretreated in step 3 of the aluminum alloy preparation process.

[0083] Performance testing: 1. Salt spray corrosion resistance test: According to GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test", a 50mm×50mm×3mm sample was cut, the edge burrs were removed, and the sample was cleaned and dried. A continuous spray test was conducted under neutral salt spray test conditions (5% sodium chloride solution, pH 6.5-7.2, test temperature 35℃). The corrosion status of the sample surface was observed daily, and the time when the first obvious pitting corrosion (diameter ≥0.1mm) appeared was recorded. Three parallel samples were set for each sample, and the average value was taken as the salt spray resistance time. The test results are shown in Table 1.

[0084] 2. Acid resistance test: A 50mm×50mm×3mm sample was cut and immersed in a 5% sulfuric acid solution at room temperature (25±2℃). The solution was changed weekly. The sample surface coating was regularly observed for cracking, peeling, and obvious corrosion of the substrate. The time of the first occurrence of the above failure phenomena was recorded. Three parallel samples were tested for each sample, and the average value was taken. The test results are shown in Table 1.

[0085] 3. Alkali resistance test: A 50mm×50mm×3mm sample was cut and immersed in a 4% sodium hydroxide solution at room temperature (25±2℃). The solution was changed weekly, and the coating condition and substrate corrosion were observed regularly. The time of the first cracking, peeling, or obvious corrosion of the substrate were recorded. Three parallel samples were tested for each sample, and the average value was taken. The test results are shown in Table 1.

[0086] 4. Stress Corrosion Initiation Time Test: According to GB / T 15970.7-2000 "Corrosion of Metals and Alloys - Stress Corrosion Testing - Part 7: Slow Strain Rate Tests", standard slow strain rate tensile specimens (5 mm diameter, 25 mm gauge length) were taken. A constant tensile stress of 0.7 times the yield strength was applied using a stress loading device. The specimens were immersed in a 3.5% sodium chloride solution at room temperature (25±2℃) at a stress rate of 1×10⁻⁶. -6 s -1 The specimens were stretched at a strain rate, and the time to cracking was recorded using a strain monitoring system. Each specimen was tested in parallel three times, and the average value was taken. The test results are shown in Table 1.

[0087] 5. Tensile Strength Test: Standard round bar tensile specimens (10 mm in diameter, 50 mm in gauge length) were cut from the finished products of each embodiment and comparative example. A universal electronic tensile testing machine was used to conduct room temperature tensile tests at a loading rate of 2 mm / min. The maximum load at fracture, yield load, and elongation of the gauge length were recorded. The tensile strength was calculated. Each sample was tested in triplicate, and the arithmetic mean was taken as the final result. The test results are shown in Table 1.

[0088] Table 1: Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art can still modify the technical solutions described in the foregoing embodiments or make equivalent substitutions for some of the technical features. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the protection scope of the present invention.

Claims

1. A method for preparing a corrosion-resistant extruded aluminum alloy for rail transit, characterized in that, Includes the following steps: S1. Melt industrial pure aluminum, add magnesium ingots, Al-Mn master alloy and Al-Cr master alloy, stir and keep warm; after cooling, add aluminum-zirconium-silicon master alloy, perform ultrasonic dispersion and keep warm; after heating, add aluminum-titanium-boron-carbon master alloy, stir and keep warm; after cooling, add aluminum-scandium-yttrium-cerium master alloy, stir and keep warm under argon protection; then refine, degas, filter, and cast to obtain ingots; S2. The ingot is homogenized, then the surface layer is removed, heated and held at the temperature, then extruded and formed. The profile is quenched and straightened, and then annealed, solution quenched and aged in sequence to obtain aluminum alloy substrate. S3. The aluminum alloy substrate is immersed in a mixed acid treatment solution, rinsed with deionized water, then immersed in a passivation solution, rinsed with deionized water and dried to obtain a pretreated aluminum alloy substrate. The mixed acid includes phosphoric acid, hydrofluoric acid, trisodium citrate, lanthanum nitrate hexahydrate and deionized water. The pretreated aluminum alloy substrate was subjected to pulsed micro-arc oxidation treatment in an electrolyte containing sodium hydroxide, sodium silicate, sodium dihydrogen phosphate, sodium fluoride, trisodium citrate and cerium nitrate hexahydrate, then cleaned and dried to obtain an intermediate product with a micro-arc oxidation layer. S4. Graphene oxide was added to anhydrous ethanol and ultrasonically dispersed. Then hydrochloric acid and silane coupling agent KH-560 were added to react. After the reaction, the mixture was filtered and dried to obtain modified graphene oxide. o-vanillin and ethylenediamine were refluxed in anhydrous ethanol, and crystals were precipitated after cooling. After filtration and drying, Schiff base corrosion inhibitor was obtained. Tetrabutyl titanate and tetraethyl orthosilicate were mixed, anhydrous ethanol was added, and then modified graphene oxide and Schiff base corrosion inhibitor were added. The mixture was ultrasonically dispersed and hydrolyzed to obtain composite sol. S5. Immerse the intermediate product with the micro-arc oxidation layer in the composite sol and pull it out, then dry and cure it to obtain the final product.

2. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S1, the preparation method of the aluminum-zirconium-silicon master alloy is as follows: Industrial pure aluminum is melted, then Zr-Si pre-alloyed powder is added and ultrasonically dispersed; after heat preservation, it is cast and cooled, and then homogenized to obtain an aluminum-zirconium-silicon master alloy.

3. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S1, the aluminum-titanium-boron-carbon master alloy is prepared as follows: Industrial pure aluminum is melted, and then potassium fluorotitanate and potassium fluoroborate are added and stirred to react. Graphite powder is then added, and the mixture is heated and stirred to continue reacting. Argon gas is introduced throughout the process for protection. After the reaction is completed, the mixture is cast, cooled, and crushed to obtain an aluminum-titanium-boron-carbon master alloy.

4. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S1, the preparation method of the aluminum-scandium-yttrium-cerium master alloy is as follows: Industrial pure aluminum is melted, and then Al-Sc master alloy, Al-Y master alloy and Al-Ce master alloy are added in sequence. The mixture is stirred and kept at a constant temperature for reaction. Argon gas is introduced throughout the process for protection. After the reaction is completed, the mixture is cast and cooled to obtain an aluminum-scandium-yttrium-cerium master alloy.

5. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S1, the mass ratio of magnesium ingot, Al-Mn master alloy and Al-Cr master alloy is 30:(10-15):(8-10).

6. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S1, the mass ratio of the aluminum-zirconium-silicon master alloy, the aluminum-titanium-boron-carbon master alloy, and the aluminum-scandium-yttrium-cerium master alloy is 10:(10~15):(20~25).

7. The method for preparing a corrosion-resistant extruded aluminum alloy for rail transit according to claim 1, characterized in that, In step S4, the mass ratio of modified graphene oxide to Schiff base corrosion inhibitor is 6:(3-5).

8. A corrosion-resistant extruded aluminum alloy for rail transit, characterized in that, It is prepared by the method described in any one of claims 1 to 7 above.

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