A corrosion-resistant modified coating for the surface of recycled aluminum extruded profiles and its preparation method

Abstract

This invention proposes a corrosion-resistant modified coating for the surface of recycled aluminum extrusion profiles and its preparation method, belonging to the field of aluminum alloy technology. The method includes the following steps: (1) solution treatment and aging treatment of the recycled aluminum extrusion profiles; (2) degreasing, pickling, and water washing of the treated recycled aluminum extrusion profiles, followed by passivation treatment in a passivation solution; (3) immersing the treated profiles in hyperbranched siloxane, removing them, hydrolyzing them in acid, removing them, washing, drying them, uniformly coating the surface with modified organic matter, and drying them to obtain an organic / inorganic hybrid sealing layer. The coating obtained by this invention meets environmental protection requirements, has good corrosion resistance and barrier effects, and maintains its integrity under bending, impact, and other mechanical forces. It can be applied to highly corrosive environments such as coastal high-humidity and high-salt environments and industrial atmospheres.

Description

Technical Field

[0001] This invention relates to the field of aluminum alloy technology, specifically to a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles and its preparation method. Background Technology

[0002] The fundamental difference between recycled aluminum and virgin aluminum lies in the enrichment of impurity elements. Due to the complex sources of recycled aluminum raw materials (scrap building materials, end-of-life automotive parts, industrial scraps, etc.), it is difficult to completely remove impurity elements such as Fe, Cu, and Zn during remelting. These impurity elements form various intermetallic compounds during solidification, such as α-Al(FeMn)Si phase, β-AlFeSi phase, and π-AlFeSiMg phase. Among them, the β-AlFeSi phase has strong cathodic activity, promoting phase-selective dissolution of adjacent α-Al matrix. Studies have confirmed that aluminum alloys added to recycled aluminum have relatively high Si and Fe content, and the second-phase particles containing Al, Si, Fe, and Mn formed in the aluminum matrix have high electrode potentials. These particles form micro-cells with the more negatively potential Mg2Si and Al matrix, accelerating material corrosion. This micro-galvanic corrosion is the core technical bottleneck restricting the widespread application of recycled aluminum.

[0003] Traditionally, chromate chemical conversion technology has been widely used for aluminum alloy surface treatment. This technology can form a self-healing conversion film on the aluminum alloy surface, exhibiting excellent corrosion resistance. However, hexavalent chromium compounds are recognized carcinogens, posing a significant threat to the environment and human health. With increasingly stringent global environmental regulations, chromate passivation technology is facing pressure to be phased out. Although there are researches on chromium-free alternatives, the salt spray resistance of some chromium-free conversion films (such as titanium-based conversion films) is still inferior to that of traditional chromate treatment. Currently, commonly used anti-corrosion methods for recycled aluminum profiles in the industry mostly rely on single coating or passivation treatments, lacking systematic repair and pretreatment of substrate surface defects, and failing to fully consider the interfacial compatibility between the coating and the substrate. The interfacial adhesion between the coating and the substrate is often insufficient due to material differences, leading to problems such as interlayer delamination and cracking after long-term use. Although conventional anodizing can form an aluminum oxide film on the aluminum surface, it cannot effectively shield the dispersed iron-rich phase particles in recycled aluminum. The iron-rich phase may become a preferential site for corrosion initiation during the anodizing process, causing local pitting corrosion to spread from the oxide film defects. Experiments show that aluminum alloys are most severely corroded under peak aging conditions, indicating that a single heat treatment or coating is insufficient to balance mechanical properties and corrosion resistance.

[0004] Chinese invention patent CN102766862B discloses a treatment solution and a method for preparing a self-healing vanadium-zirconium conversion film on an aluminum alloy surface using this treatment solution. First, a treatment solution containing fluorozirconate, metavanadate, sodium fluoride, nitrate, accelerator, and additives is prepared. Then, the pre-treated aluminum alloy is immersed in a working solution prepared by diluting the treatment solution for 2-10 minutes. Finally, it is washed with water, dried, and cooled to obtain the final product. However, this patent only forms a single vanadium-zirconium conversion film on the aluminum alloy surface, without addressing the composite coating structure of the bottom and top layers. Its corrosion resistance mechanism relies entirely on the physical barrier effect of the conversion film itself and the "self-healing" effect of vanadium ions, lacking a secondary barrier of the top sealing layer against corrosive media. Once the film is damaged, it loses its protective capability. In contrast, the composite coating of this invention, through the synergy of the bottom manganese-zirconium conversion film and the top organic / inorganic hybrid coating, forms a gradient protection system, achieving a salt spray resistance time of over 720 hours and a significantly longer protective lifespan.

[0005] Chinese invention patent CN100577869C discloses a conversion solution and its application method for preparing a corrosion-resistant composite oxide film on aluminum alloy surfaces. The conversion solution utilizes a composite oxidant containing rare earth salts (nitrates or sulfates of cerium, praseodymium, and neodymium, as well as double salts), permanganate and persulfate, nitrate, and perchlorate, and a film-forming promoter consisting of vanadium and strontium salts. The conversion solution is environmentally friendly as it does not contain hexavalent chromium. Furthermore, the reaction rate is increased by the composite oxidant and film-forming promoter, and the chemical conversion treatment does not require heating, allowing for the rapid preparation of a composite oxide film composed of rare earth oxides, alumina, and manganese oxide with good corrosion resistance on aluminum alloy surfaces at room temperature. However, this patent uses rare earth nitrates / sulfates such as cerium, praseodymium, and neodymium as the main film-forming salts. Rare earth elements are strategic resources, with highly volatile prices and unstable supply chains, and the cost of rare earth salts is much higher than that of manganese / zirconium salts. For bulk industrial products such as recycled aluminum profiles (e.g., building doors and windows, photovoltaic brackets), the economic viability and industrialization feasibility of this patent are clearly insufficient. Summary of the Invention

[0006] The purpose of this invention is to propose a corrosion-resistant modified coating for the surface of recycled aluminum extrusion profiles and its preparation method. The method repairs the corrosion defects of the substrate through solid solution and three-stage aging, constructs an inorganic barrier using a hybrid passivation film, and further synergistically modifies the coating by using hyperbranched siloxane multi-point anchoring interfaces and silane-modified polyurethane organic seals. This solves the problem of early coating failure caused by impurity enrichment in recycled aluminum profiles and achieves good results in terms of corrosion resistance, interfacial bonding, environmental protection, and industrialization feasibility.

[0007] The technical solution of this invention is implemented as follows:

[0008] This invention provides a method for preparing a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles, comprising the following steps:

[0009] (1) The recycled aluminum extruded profiles are subjected to solution treatment and aging treatment. During solution treatment, the iron-rich phases (β-AlFeSi, π-AlFeSiMg, etc.) dispersed in the matrix partially dissolve or spheroidize, and the main alloying elements such as Mg and Si are fully dissolved into the α-Al matrix to form a supersaturated solid solution. This process also eliminates residual extrusion stress, purifies the grain boundaries, and provides a uniform nucleation environment for subsequent aging precipitation. Subsequently, a three-stage aging treatment is adopted. The first stage of pre-aging (80-100℃, 3-5h) forms a large number of fine GP regions and atomic clusters, which serve as uniform nucleation cores for the subsequent β'' phase, increase the density of intragranular precipitates, and reduce the segregation of solute atoms to the grain boundaries. The second stage of main aging (160-180℃, 6-12h) transforms the GP regions into metastable β'' phases, providing the main strengthening effect. The intragranular strengthening phase is dispersed, and precipitates begin to form at the grain boundaries. In the third-stage over-aging process (200-240℃, 5-20min), the continuous precipitates (β' / β-Mg2Si) at the grain boundaries undergo spheroidization and coarsening, becoming discontinuously distributed; the β'' phase within the grains grows moderately, cutting off the grain boundary corrosion current channel, reducing the potential difference between the grain boundary and the grain interior, and inhibiting intergranular corrosion and microgalvanic corrosion.

[0010] (2) The processed recycled aluminum extrusion profiles are degreased, pickled, and washed with water, and then placed in a passivation solution for passivation treatment;

[0011] (3) The treated profile is immersed in hyperbranched siloxane, taken out, placed in acid solution for hydrolysis, taken out, washed, dried, and the modified organic material is uniformly coated on its surface and dried to obtain an organic / inorganic hybrid sealing layer.

[0012] As a further improvement of the present invention, the recycled aluminum in step (1) is 6063 or 6061 aluminum alloy; the conditions for the solution treatment are 520-540℃, 0.5-1h; the conditions for the aging treatment are 80-100℃, 3-5h, 160-180℃, 6-12h, 200-240℃, 5-20min.

[0013] As a further improvement of the present invention, the degreasing in step (2) uses a 2-5 wt% alkaline solution, and the pickling uses a 0.5-1 mol / L hydrochloric acid or sulfuric acid solution; the passivation solution is an aqueous solution containing 20-25 g / L K2ZrF6, 3-6 g / L manganese sulfate, 5-10 g / L phytic acid, and 3-8 g / L tannic acid, with a pH of 4-4.5; the passivation treatment time is 10-20 min, and the temperature is room temperature. The Mn in the solution... 2+It exhibits strong reducing properties and is easily oxidized by O2 in solution to form MnO(OH). The resulting MnO(OH) then undergoes a series of chemical reactions with K2ZrF6 and other substances in the solution to generate KMn4O8·3H2O, ultimately forming a composite zirconium-based conversion film. This reaction is chromium-free, making it safer and more environmentally friendly. Each phytic acid molecule can simultaneously react with multiple Al molecules. 3+ Zr 4+ Mn 2+ Ion coordination forms a three-dimensional network of metal-organic chelates; phytic acid forms a dense monomolecular protective film on the metal surface, and its phosphate groups condense or hydrogen bond with the hydroxyl groups on the oxide surface, effectively sealing the micropores of the inorganic conversion membrane; phytic acid adsorbs at active sites, preventing Cl... - It can penetrate corrosive media. Tannic acid molecules contain a large number of phenolic hydroxyl groups and aromatic rings; the phenolic hydroxyl groups react with Al... 3 + Zr 4+ The formation of stable metal-phenol complexes enhances the bonding force between the film and the substrate. The small size of tannic acid molecules can fill the nanoscale pores that phytic acid macromolecules cannot enter, forming a synergistic sealing effect with phytic acid.

[0014] As a further improvement of the present invention, the coating in step (3) is carried out by air spraying, electrostatic spraying, dip coating or roller coating; the immersion time is 0.5-1.5h, the acid solution is a weakly acidic alcohol aqueous solution with a pH value of 4-5 and an alcohol content of 50-70wt%, and the hydrolysis time is 20-50min.

[0015] As a further improvement of the present invention, the preparation method of the hyperbranched siloxane in step (3) is as follows: Diethylene glycol and silane coupling agent KH560 are mixed evenly, water is added, and the mixture is heated under an inert gas atmosphere. During the process, methanol is continuously distilled to remove methanol until no more methanol is produced. Heating is then stopped to obtain the hyperbranched siloxane. The two terminal hydroxyl groups of diethylene glycol undergo a ring-opening reaction with the epoxy groups of KH560 to form a hyperbranched polysiloxane. After the hyperbranched siloxane is impregnated on the surface of the passivation film, it is placed in a weakly acidic alcohol aqueous solution for hydrolysis. The Si-OH on the periphery of the hyperbranched siloxane dehydrates and condenses with the Al-OH, Zr-OH, and Mn-OH on the surface of the passivation film to form Si-O-Al, Si-O-Zr, and Si-O-Mn covalent bonds, forming multi-point covalent anchoring. The bonding force is far greater than that of a single silane coupling agent with single-point or double-point bonding.

[0016] As a further improvement of the present invention, the mass ratio of diethylene glycol, silane coupling agent KH560 and water is 8-10:10-12:2-3; the heating reaction temperature is 120-140℃ and the time is 1-2h.

[0017] As a further improvement of the present invention, the preparation method of the modified organic compound in step (3) is as follows: 2,4-toluene diisocyanate and aminosilane coupling agent are mixed and added to a solvent, heated and stirred to react, then polyethylene glycol is added, the reaction is carried out under heat and stirred, and the -NCO is detected until it is completely consumed. The solvent is removed under reduced pressure to obtain the modified organic compound. First, the isocyanate reacts with the aminosilane in a urea reaction. After the addition of PEG, its terminal hydroxyl group reacts with the residual -NCO to generate a urethane bond. After the silane terminal group is hydrolyzed to Si-OH, it condenses with the Si-OH of the intermediate layer of the substrate to form a Si-O-Si bond. At the same time, the urea bond and urethane bond in the modified organic compound form a hydrogen bond network with the hydroxyl / ether oxygen of the hyperbranched siloxane.

[0018] As a further improvement of the present invention, the molar ratio of 2,4-toluene diisocyanate, aminosilane coupling agent and polyethylene glycol is 0.9-1.1:1:1; the aminosilane coupling agent is selected from at least one of KH550, KH602 and KH792, and the polyethylene glycol is selected from at least one of polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 2000 and polyethylene glycol 4000.

[0019] As a further improvement of the present invention, the temperature of the heating and stirring reaction is 60-70°C and the time is 1-3 hours, and the time of the heat preservation and stirring reaction is 1-3 hours.

[0020] The present invention further protects a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles prepared by the above-described preparation method.

[0021] The present invention has the following beneficial effects:

[0022] 1. This invention employs a specific process sequence combining solution treatment and three-stage aging: First-stage pre-aging promotes uniform nucleation of GP zones and atomic clusters, providing high-density nucleation sites for subsequent β'' phase precipitation; second-stage main aging allows for the full dispersion of metastable β'' phase, ensuring the alloy's strength; third-stage short-time high-temperature regression treatment causes the continuously distributed precipitates at grain boundaries to spheroidize and coarsen, transforming from a continuous film to a discontinuous granular distribution, thereby effectively cutting off the grain boundary corrosion current loop and reducing the potential difference between the grain boundary and the grain interior. Compared with conventional aging, this invention improves corrosion resistance while maintaining tensile strength, fundamentally repairing corrosion defects in recycled aluminum substrates.

[0023] 2. The passivation solution of this invention adopts a quaternary synergistic system of K2ZrF6-manganese sulfate-phytic acid-tannic acid: K2ZrF6 and manganese sulfate react synergistically to generate a zirconium-based conversion film. This reaction does not involve chromium, making it safer and more environmentally friendly, and significantly improving corrosion resistance; phytic acid, with its multiple active phosphate oxygen atoms in its molecule, reacts with Al³⁺ and Zr 4⁺ and Mn²⁺ undergo multidentate chelation to form a three-dimensional network of metal-organic chelates, while tannic acid complexes with metal ions through its phenolic hydroxyl groups. Its aromatic ring provides hydrophobic regions and forms a synergistic sealing effect with phytic acid. The synergistic effect of these four components significantly improves the corrosion resistance of the aluminum alloy.

[0024] 3. This invention innovatively introduces a hyperbranched siloxane intermediate layer. This hyperbranched structure has an extremely high end group density. After hydrolysis in a weakly acidic alcohol aqueous solution, a large number of Si-OH groups on its periphery dehydrate and condense with Al-OH, Zr-OH, and Mn-OH groups on the passivation film surface to form multi-point covalent bonds of Si-O-Al, Si-O-Zr, and Si-O-Mn. Compared with the single-point or double-point bonding of traditional silane coupling agents, this multi-legged anchoring structure improves the bonding strength of the organic / inorganic interface and effectively avoids interface cracking and interlayer delamination caused by temperature cycling (difference in thermal expansion coefficients between the aluminum substrate and the coating).

[0025] 4. This invention uses 2,4-toluene diisocyanate, an aminosilane coupling agent, and polyethylene glycol to react and prepare a silane-terminated polyurethane prepolymer as a modified organic material. In this molecular chain, urea bonds provide high cohesive strength and hardness, urethane bonds impart flexibility and wear resistance, polyethylene glycol segments provide chain mobility and a hydrogen bond network, and silane end groups ensure chemical bonding with the underlying hyperbranched siloxane. After coating and curing, the modified organic material and the hyperbranched siloxane form an integrated organic / inorganic hybrid sealing layer through the dual effects of covalent bonds and hydrogen bond networks. This retains the organic coating's ability to block water molecules, oxygen, and chloride ions, while the inorganic siloxane skeleton provides thermal stability and mechanical strength, allowing the coating to maintain its integrity under bending, impact, and other mechanical forces.

[0026] 5. This invention constructs a gradient synergistic protection system. The substrate layer eliminates microgalvanic corrosion sources by controlling the morphology of grain boundary precipitates through three-stage aging; the inorganic layer provides a basic chemical barrier and physical isolation through a quaternary hybrid passivation film; the interface layer achieves efficient bonding of the organic / inorganic interface through multi-point covalent bonding of hyperbranched siloxanes; and the organic layer provides long-lasting hydrophobic sealing and mechanical protection through silane-modified polyurethane. The multiple layers form an integrated gradient structure through chemical bonding (Si-OM, Si-O-Si, hydrogen bonding), significantly improving the service life of the aluminum alloy.

[0027] 6. This invention contains no hexavalent chromium compounds throughout the entire process from substrate treatment to surface coating, thus avoiding strategic resource dependence and price fluctuation risks associated with rare earth salts, meeting environmental protection requirements, and is suitable for large-scale industrial production of recycled aluminum profiles.

[0028] 7. The recycled aluminum extrusion profiles obtained by the process of this invention can replace virgin aluminum in highly corrosive environments such as coastal high humidity and high salinity and industrial atmosphere, significantly reducing the raw material costs and carbon footprint of bulk products such as building profiles and photovoltaic brackets. Attached Figure Description

[0029] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0030] Figure 1 This is a surface SEM image of the product in Example 1.

[0031] Figure 2 This is a cross-sectional SEM image of the product in Example 1. Detailed Implementation

[0032] The technical solutions in the embodiments of the present invention will be clearly and completely described below. 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 skilled in the art without creative effort are within the scope of protection of the present invention.

[0033] Preparation Example 1: Hyperbranched siloxanes

[0034] The preparation method is as follows: 8g of diethylene glycol and 10g of silane coupling agent KH560 are mixed evenly, 2g of water is added, and the mixture is heated to 120℃ under a nitrogen atmosphere and stirred for 2h. During the process, methanol is continuously distilled off until no more methanol is produced. Heating is then stopped to obtain hyperbranched siloxane.

[0035] Preparation Example 2: Hyperbranched siloxanes

[0036] The preparation method is as follows: 10g of diethylene glycol and 12g of silane coupling agent KH560 are mixed evenly, 3g of water is added, and the mixture is heated to 140℃ under a nitrogen atmosphere and stirred for 1h. During the process, methanol is continuously distilled off until no more methanol is produced. Heating is then stopped to obtain hyperbranched siloxane.

[0037] Preparation Example 3: Hyperbranched siloxanes

[0038] The preparation method is as follows: 9g of diethylene glycol and 11g of silane coupling agent KH560 are mixed evenly, 2.5g of water is added, and the mixture is heated to 130℃ under a nitrogen atmosphere and stirred for 1.5h. During the process, methanol is continuously distilled off until no more methanol is produced. Heating is then stopped to obtain hyperbranched siloxane.

[0039] Preparation Example 4: Modified Organic Compound

[0040] The preparation method is as follows: 0.5 mol of 2,4-toluene diisocyanate and 0.5 mol of silane coupling agent KH550 are mixed and added to 300 mL of acetonitrile. The mixture is heated to 60 °C and stirred for 3 h. Then, 0.5 mol of polyethylene glycol 400 is added, and the mixture is stirred for 3 h while maintaining the temperature. The -NCO content is monitored until it is completely consumed. The solvent is removed under reduced pressure to obtain the modified organic compound.

[0041] Preparation Example 5: Modified Organic Compound

[0042] The preparation method is as follows: 0.5 mol of 2,4-toluene diisocyanate and 0.5 mol of silane coupling agent KH550 are mixed and added to 300 mL of acetonitrile. The mixture is heated to 70 °C and stirred for 1 h. Then, 0.5 mol of polyethylene glycol 4000 is added and the mixture is stirred for 1 h. The -NCO content is monitored until it is completely consumed. The solvent is removed under reduced pressure to obtain the modified organic compound.

[0043] Preparation Example 6: Modified Organic Compound

[0044] The preparation method is as follows: 0.5 mol of 2,4-toluene diisocyanate and 0.5 mol of silane coupling agent KH550 are mixed and added to 300 mL of acetonitrile. The mixture is heated to 65 °C and stirred for 2 h. Then, 0.5 mol of polyethylene glycol 1000 is added and the mixture is stirred for 2 h. The -NCO content is monitored until it is completely consumed. The solvent is removed under reduced pressure to obtain the modified organic compound.

[0045] Preparation Example 7

[0046] The only difference from Preparation Example 6 is that polyethylene glycol 1000 is replaced with polyethylene glycol 600.

[0047] Preparation Example 8

[0048] The only difference from Preparation Example 6 is that polyethylene glycol 1000 is replaced with polyethylene glycol 2000.

[0049] Example 1

[0050] This embodiment provides a method for preparing a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles, including the following steps:

[0051] (1) The 6061 recycled aluminum extrusion profiles are subjected to solution treatment and aging treatment;

[0052] Solution treatment conditions: 520℃, 1h;

[0053] The aging treatment conditions were 80℃ for 5 hours, 160℃ for 12 hours, and 200℃ for 20 minutes.

[0054] (2) The treated recycled aluminum extrusion profiles were degreased with 5wt% NaOH solution, pickled with 0.5mol / L hydrochloric acid, washed with water, dried at 105℃ for 1h, and then placed in passivation solution for 10min at room temperature to obtain profiles covered with conversion film.

[0055] The passivation solution is an aqueous solution containing 20 g / L K2ZrF6, 3 g / L manganese sulfate, 5 g / L phytic acid, and 3 g / L tannic acid, with a pH value of 4-4.5.

[0056] (3) The profile coated with the conversion film was immersed in the hyperbranched siloxane prepared in Preparation Example 1, removed, and placed in an HCl-ethanol aqueous solution (50wt% ethanol content) with a pH of 4-5 for hydrolysis for 20 min. It was then removed, washed, and dried at 105°C for 2 h. The modified organic material prepared in Preparation Example 4 was electrostatically sprayed onto the surface of the profile, and dried and cured at 105°C for 6 h to obtain an organic / inorganic hybrid sealing layer. Its surface SEM image is shown below. Figure 1 The surface coating is uniform and dense, with no obvious cracks or pores. Its cross-sectional SEM image is shown below. Figure 2 The coating is uniform and dense, the conversion film layer is well bonded to the substrate, the interface is clear, and there are no obvious defects.

[0057] Example 2

[0058] This embodiment provides a method for preparing a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles, including the following steps:

[0059] (1) The 6061 recycled aluminum extrusion profiles are subjected to solution treatment and aging treatment;

[0060] Solution treatment conditions: 540℃, 0.5h;

[0061] The aging treatment conditions were 100℃ for 3 hours, 180℃ for 6 hours, and 240℃ for 5 minutes.

[0062] (2) The treated recycled aluminum extrusion profiles were degreased with 5wt% NaOH solution, pickled with 1mol / L hydrochloric acid, washed with water, dried at 105℃ for 1h, and then placed in passivation solution for 20min at room temperature to obtain profiles covered with conversion film.

[0063] The passivation solution is an aqueous solution containing 25 g / L K2ZrF6, 6 g / L manganese sulfate, 10 g / L phytic acid, and 8 g / L tannic acid, with a pH value of 4-4.5.

[0064] (3) The profile coated with the conversion film was immersed in the hyperbranched siloxane prepared in Preparation Example 1, taken out, placed in an HCl-ethanol aqueous solution (ethanol content 70wt%) with a pH value of 4-5, hydrolyzed for 50 min, taken out, washed, dried at 105°C for 2 h, and the modified organic material prepared in Preparation Example 4 was electrostatically sprayed onto the surface of the profile and dried and cured at 105°C for 6 h to obtain an organic / inorganic hybrid sealing layer.

[0065] Example 3

[0066] This embodiment provides a method for preparing a corrosion-resistant modified coating on the surface of recycled aluminum extruded profiles, including the following steps:

[0067] (1) The 6061 recycled aluminum extrusion profiles are subjected to solution treatment and aging treatment;

[0068] Solution treatment conditions: 530℃, 45 min;

[0069] The aging treatment conditions were 90℃ for 4 hours, 170℃ for 9 hours, and 220℃ for 10 minutes.

[0070] (2) The treated recycled aluminum extrusion profiles were degreased with 3wt% NaOH solution, acid-washed with 0.5mol / L sulfuric acid solution, then washed with water, dried at 105℃ for 1h, and then placed in passivation solution for 15min at room temperature to obtain profiles covered with conversion film.

[0071] The passivation solution is an aqueous solution containing 22 g / L K2ZrF6, 4.5 g / L manganese sulfate, 7 g / L phytic acid, and 5 g / L tannic acid, with a pH value of 4-4.5.

[0072] (3) The profile coated with the conversion film was immersed in the hyperbranched siloxane prepared in Preparation Example 1, taken out, placed in an HCl-ethanol aqueous solution (ethanol content 60wt%) with a pH value of 4-5, hydrolyzed for 35 min, taken out, washed, dried at 105°C for 2 h, and the modified organic material prepared in Preparation Example 4 was electrostatically sprayed onto the surface of the profile and dried and cured at 105°C for 6 h to obtain an organic / inorganic hybrid sealing layer.

[0073] Example 4

[0074] The only difference from Example 3 is that the modified organic compound was prepared in Preparation Example 7.

[0075] Example 5

[0076] The only difference from Example 3 is that the modified organic compound was prepared by Example 8.

[0077] Comparative Example 1

[0078] The only difference from Example 3 is that the aging treatment conditions are 170°C for 13 hours.

[0079] Comparative Example 2

[0080] The only difference from Example 3 is that phytic acid was not added to the passivation solution.

[0081] Specifically, the passivation solution is an aqueous solution containing 22 g / L K2ZrF6, 4.5 g / L manganese sulfate, and 12 g / L tannic acid, with a pH value of 4-4.5.

[0082] Comparative Example 3

[0083] The only difference from Example 3 is that tannic acid was not added to the passivation solution.

[0084] Specifically, the passivation solution is an aqueous solution containing 22 g / L K2ZrF6, 4.5 g / L manganese sulfate, and 12 g / L phytic acid, with a pH value of 4-4.5.

[0085] Comparative Example 4

[0086] The only difference from Example 3 is that phytic acid and tannic acid were not added to the passivation solution.

[0087] Specifically, the passivation solution is an aqueous solution containing 22 g / L K2ZrF6 and 4.5 g / L manganese sulfate, with a pH value of 4-4.5.

[0088] Comparative Example 5

[0089] Compared with Example 3, the only difference is that hyperbranched siloxane was not impregnated in step (3), as follows:

[0090] The modified organic material obtained in Preparation Example 4 was electrostatically sprayed onto the surface of a profile covered with a conversion film and dried and cured at 105°C for 6 hours to obtain an organic / inorganic hybrid sealing layer.

[0091] Comparative Example 6

[0092] Compared with Example 3, the only difference is that no modified organic material was sprayed in step (3), as follows:

[0093] The profile coated with the conversion film was immersed in the hyperbranched siloxane prepared in Preparation Example 1, taken out, placed in an HCl-ethanol aqueous solution (ethanol content 60wt%) with a pH of 4-5, hydrolyzed for 35 min, taken out, washed, and dried at 105℃ for 2 h to obtain an organic / inorganic hybrid sealing layer.

[0094] Comparative Example 7

[0095] Compared with Example 3, the only difference is that the method in step (3) is different, as follows:

[0096] Polyethylene oxide was electrostatically sprayed onto the surface of the treated profile and dried and cured at 105°C for 6 hours to obtain an organic / inorganic hybrid sealing layer.

[0097] Test Example 1

[0098] The adhesion between the conversion film and the substrate, and the adhesion between the conversion film and subsequent coatings, were tested in the profiles coated with the conversion film in Examples 1-3 and Comparative Examples 1-7. The results are shown in Table 1.

[0099] Adhesion test between conversion film and substrate: The adhesion between the conversion film and substrate was tested according to GB / T 9286-2021 "Cross-cut test of paint and varnish film".

[0100] Adhesion test between conversion film and subsequent coating: The coating adhesion is tested according to the method specified in GB / T 9286-2021 "Paints and Varnishes Cross-cut Test", and the impact resistance is tested according to the method specified in GB / T 1732-2020 "Paint Film Impact Resistance Test".

[0101] Table 1

[0102]

[0103] As can be seen from the table above, the conversion film of the present invention has strong adhesion between itself and the coating, as well as between itself and the substrate, and the coating has high impact resistance.

[0104] Test Example 2

[0105] The heat resistance of the corrosion-resistant modified coatings on the surfaces of recycled aluminum extruded profiles prepared in Examples 1-3 and Comparative Examples 1-7 was tested. The coatings underwent high-temperature flame erosion testing using an oxy-acetylene torch, achieving a flame core temperature of approximately 2200°C and erosion at a 45° angle. The torch was controlled to reciprocate between the sample and the sample at a speed of 1.25 cm / s, and the surface temperature was measured. After the temperature dropped below 450°C, the quality change of the coating was tested, and the results are shown in Table 2.

[0106] Table 2. Test results of average mass loss of coating (%)

[0107]

[0108] As shown in the table above, some elements on the coating surface underwent oxidation at the beginning of the flame scouring process, resulting in an increase in mass. Subsequent scouring resulted in the loss of some material. The coatings obtained in Examples 1-3 showed little change in mass and exhibited good heat resistance stability.

[0109] Test Example 3

[0110] The corrosion resistance of the corrosion-resistant modified coatings on the surfaces of recycled aluminum extruded profiles prepared in Examples 1-3 and Comparative Examples 1-7 was tested. The results are shown in Table 3. The neutral salt spray test was conducted using a LYW-025 multi-purpose corrosion test chamber. The test conditions were: (5±1)% sodium chloride aqueous solution, salt spray deposition rate of 1-2 ml / (80cm²). 2 The pH was 6.5-7.2, the density was 1.036 g / L, the spraying was continuous, the treatment time was 168 h, and the corrosion area was calculated.

[0111] Table 3

[0112]

[0113] As can be seen from the table above, the corrosion-resistant modified coatings on the surface of recycled aluminum extruded profiles prepared in Examples 1-3 of the present invention have good corrosion resistance.

[0114] Test Example 4

[0115] The mechanical properties of the alloys prepared in Examples 1-3 and Comparative Example 1 were tested on a CMT5305 universal testing machine. The results are shown in Table 4.

[0116] Table 4

[0117]

[0118] As can be seen from the table above, the mechanical properties of the samples obtained in Examples 1-3 of the present invention are not much different from those of the sample in Comparative Example 1. It can be seen that the multi-stage aging process has little effect on the mechanical properties of aluminum alloys.

[0119] Compared with Example 3, Comparative Example 1 showed a decrease in corrosion resistance, indicating that multi-stage aging treatment can significantly improve the corrosion resistance of aluminum alloy substrates compared to single aging treatment.

[0120] Compared with Example 3, Comparative Examples 2, 3, and 4 showed decreased adhesion and corrosion resistance when using only tannic acid, phytic acid, or neither in the passivation solution. Comparative Example 4 also showed decreased impact resistance. This demonstrates that phytic acid, with its multiple active phosphate oxygen atoms in its molecule, interacts with Al³⁺ and Zr... 4 ⁺ and Mn²⁺ undergo multidentate chelation to form a three-dimensional network of metal-organic chelates. Tannic acid complexes with metal ions through phenolic hydroxyl groups, and its aromatic ring provides hydrophobic regions and forms a synergistic sealing effect with phytic acid, which significantly improves adhesion and corrosion resistance.

[0121] Compared to Example 3, Comparative Example 5, without impregnation with hyperbranched siloxane, exhibited decreased corrosion resistance, heat resistance, adhesion, and impact resistance. This demonstrates that the present invention, by introducing a hyperbranched siloxane intermediate layer with extremely high end-group density, hydrolyzes in a weakly acidic alcoholic aqueous solution. The abundant Si-OH groups on its periphery dehydrate and condense with the Al-OH, Zr-OH, and Mn-OH groups on the passivation film surface, forming multi-point covalent bonds of Si-O-Al, Si-O-Zr, and Si-O-Mn. Compared to the single-point or double-point bonding of traditional silane coupling agents, this multi-legged anchoring structure enhances the bonding strength of the organic / inorganic interface, effectively preventing interfacial cracking and interlayer delamination caused by temperature cycling (due to the difference in thermal expansion coefficients between the aluminum substrate and the coating). Compared to Example 3, Comparative Example 6, without the application of modified organic material, exhibited decreased corrosion resistance, heat resistance, adhesion, and impact resistance. As can be seen, in the modified organic material, urea bonds provide high cohesive strength and hardness, urethane bonds impart flexibility and wear resistance, polyethylene glycol segments provide segmental mobility and a hydrogen bond network, and silane end groups ensure chemical bonding with the underlying hyperbranched siloxane. After coating and curing, the barrier effect is improved, and the inorganic siloxane skeleton provides thermal stability and mechanical strength, allowing the coating to maintain its integrity under bending, impact, and other mechanical forces. In Comparative Example 7, compared to Example 3, ordinary polyethylene oxide was used instead of the hyperbranched siloxane and modified organic material. The effect was significantly reduced. Therefore, the coating formed by the hyperbranched siloxane and modified organic material of this invention is significantly better than that of ordinary polymer layers.

[0122] The above description is only a preferred embodiment of the present invention and is not intended to limit the present invention. 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 modified coating on the surface of recycled aluminum extruded profiles, characterized in that, Includes the following steps: (1) The recycled aluminum extrusion profiles are subjected to solution treatment and aging treatment; (2) The processed recycled aluminum extrusion profiles are degreased, pickled, and washed with water, and then placed in a passivation solution for passivation treatment; (3) The treated profile is immersed in hyperbranched siloxane, taken out, placed in acid solution for hydrolysis, taken out, washed, dried, and the modified organic material is uniformly coated on its surface and dried to obtain an organic / inorganic hybrid sealing layer.

2. The preparation method according to claim 1, characterized in that, The recycled aluminum in step (1) is 6063 or 6061 aluminum alloy; the conditions for the solution treatment are 520-540℃ for 0.5-1h; the conditions for the aging treatment are 80-100℃ for 3-5h, 160-180℃ for 6-12h, and 200-240℃ for 5-20min.

3. The preparation method according to claim 1, characterized in that, In step (2), the degreasing is performed using a 2-5 wt% alkaline solution, and the pickling is performed using a 0.5-1 mol / L hydrochloric acid or sulfuric acid solution. The passivation solution is an aqueous solution containing 20-25 g / L K2ZrF6, 3-6 g / L manganese sulfate, 5-10 g / L phytic acid, and 3-8 g / L tannic acid, with a pH of 4-4.

5. The passivation treatment takes 10-20 minutes at room temperature.

4. The preparation method according to claim 1, characterized in that, The coating in step (3) is applied by air spraying, electrostatic spraying, dip coating or roller coating; the immersion time is 0.5-1.5h, the acid solution is a weakly acidic alcohol aqueous solution with a pH of 4-5 and an alcohol content of 50-70wt%, and the hydrolysis time is 20-50min.

5. The preparation method according to claim 1, characterized in that, The preparation method of the hyperbranched siloxane in step (3) is as follows: Diethylene glycol and silane coupling agent KH560 are mixed evenly, water is added, and the reaction is carried out under an inert gas atmosphere. During the process, methanol is continuously distilled to remove methanol until no more methanol is produced. Heating is then stopped to obtain the hyperbranched siloxane.

6. The preparation method according to claim 5, characterized in that, The mass ratio of diethylene glycol, silane coupling agent KH560, and water is 8-10:10-12:2-3; the heating reaction temperature is 120-140℃, and the time is 1-2 hours.

7. The preparation method according to claim 1, characterized in that, The modified organic compound in step (3) is prepared as follows: 2,4-toluene diisocyanate and aminosilane coupling agent are mixed and added to a solvent, heated and stirred to react, then polyethylene glycol is added, the reaction is carried out under heat and stirred, -NCO is detected until it is completely consumed, the solvent is removed under reduced pressure to obtain the modified organic compound.

8. The preparation method according to claim 7, characterized in that, The molar ratio of 2,4-toluene diisocyanate, aminosilane coupling agent, and polyethylene glycol is 0.9-1.1:1:1; the aminosilane coupling agent is selected from at least one of KH550, KH602, and KH792; and the polyethylene glycol is selected from at least one of polyethylene glycol 400, polyethylene glycol 600, polyethylene glycol 1000, polyethylene glycol 2000, and polyethylene glycol 4000.

9. The preparation method according to claim 7, characterized in that, The heating and stirring reaction is carried out at a temperature of 60-70℃ for 1-3 hours, and the heat preservation and stirring reaction is carried out for 1-3 hours.

10. A corrosion-resistant modified coating on the surface of a recycled aluminum extrusion profile prepared by the preparation method according to any one of claims 1-9.

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