A surface treatment method for high-temperature-resistant aluminum alloy plate

Abstract

This invention relates to the field of metal surface treatment technology. The method first involves anodizing an aluminum alloy sheet in a sulfuric acid electrolyte to obtain a porous oxide film. Then, using this film as the cathode, ultrasonic pulse electrochemical sealing is performed in a colloidal sealing solution containing an oxidant, organic fuel, and a boron source. Utilizing the ultrasonic cavitation effect and the relaxation characteristics of the pulsed electric field, directional deposition of colloidal particles deep within the micropores is achieved. Finally, gradient heat treatment completes low-temperature drying, liquid-phase pre-melting, self-propagating reaction initiation, and densification sintering. This method optimizes mass transfer and buffers thermal stress through a boron-source molten liquid-phase medium. It utilizes an in-situ self-propagating exothermic reaction to create localized high temperatures, promoting the transformation of the pore filler into a chemically inert, dense ceramic phase. This solves the problems of high-temperature cracking in traditional hydrated sealing layers and air pockets at the bottom of conventional physical filling pores, improving the high-temperature resistance, thermal shock resistance, and long-term chemical corrosion resistance of high-strength aluminum alloy sheets such as 6061 and 7075.

Description

Technical Field

[0001] This invention relates to the field of metal surface treatment technology, specifically to a method for surface treatment of high-temperature resistant aluminum alloy sheets. Background Technology

[0002] High-strength aluminum alloy sheets are widely used in aerospace, transportation, and precision machinery manufacturing due to their excellent specific strength and processing performance. To improve the wear resistance and corrosion resistance of the aluminum alloy substrate, anodizing is usually performed to form a porous alumina film on the surface. However, the surface of the anodized film has a large number of micron- or nanometer-sized vertical pores. If effective sealing treatment is not performed, corrosive media can easily penetrate the film layer and reach the substrate interface through these pores, leading to premature material failure.

[0003] Currently, commonly used sealing technologies in industry mainly include boiling water sealing, high-temperature steam sealing, and nickel salt sealing. These methods are primarily based on the hydration reaction mechanism, which promotes the absorption of water by porous alumina to form hydrates such as boehmite or bayonetite. The volume expansion of these hydrates then blocks the pores. This type of sealing layer based on hydration reaction has good protective effects at room temperature, but it has inherent defects under high-temperature conditions. When the ambient temperature rises, the hydrate sealing layer undergoes a dehydration reaction, leading to volume shrinkage and subsequent cracking or even powdering of the oxide film surface. This not only destroys the integrity of the film but also provides diffusion channels for corrosive media, severely reducing the corrosion resistance of aluminum alloy components at high temperatures.

[0004] To address the high-temperature resistance issue, existing technologies have attempted physical filling using sol-gel methods or organic resin impregnation. While these methods introduce inorganic or organic materials with good heat resistance, the small pore size and high aspect ratio of anodic oxide films make it difficult for high-viscosity sols or resins to overcome capillary resistance and penetrate deep into the micropores. Often, only a shallow layer is formed at the pore openings, leaving voids at the bottom of the pores. During subsequent high-temperature service or thermal shock cycles, the expansion of residual gas within the pores and the mismatch in thermal expansion coefficients between the filler material and the substrate can easily lead to coating peeling or cracking. Therefore, existing sealing technologies struggle to simultaneously meet the dual requirements of dense micropore filling and long-term high-temperature protection. Summary of the Invention

[0005] To address the shortcomings of existing technologies, this invention provides a surface treatment method for high-temperature resistant aluminum alloy sheets. This method solves the problems that existing aluminum alloy anodized film sealing technology is prone to dehydration and cracking under high-temperature environments, leading to a decrease in corrosion resistance. Furthermore, conventional physical filling methods are difficult to achieve dense filling deep into micropores, and cannot simultaneously meet the requirements of high-temperature impact resistance and long-term corrosion resistance.

[0006] To achieve the above objectives, the present invention provides the following technical solution: a surface treatment method for high-temperature resistant aluminum alloy sheets, comprising the following steps: S1. After surface treatment, the aluminum alloy sheet is placed in sulfuric acid electrolyte for anodic oxidation to prepare a porous oxide film on the surface. After washing with water, it is kept moist. S2. Dissolve hydrated zirconium nitrate and glycine to form solution A. Dissolve and hydrolyze boric acid and 3-glycidyl etheroxypropyltrimethoxysilane to form solution B. Mix solution A and solution B and adjust the pH value. After aging, obtain cationic colloidal sealing solution. S3. Using the aluminum alloy plate processed in step S1 as the cathode, immerse it in the cationic colloidal sealing solution prepared in step S2, and apply pulsed direct current under ultrasonic assistance to drive the colloidal particles to deposit into the micropores of the porous oxide film. S4. The aluminum alloy sheet processed in step S3 is subjected to low-temperature drying, liquid phase pre-melting, self-propagating reaction initiation and densification sintering in sequence, and cooled to room temperature in the furnace to synthesize a ceramic phase sealing layer in situ in the micropores.

[0007] By adopting the above technical solution, the present invention utilizes the synergistic effect of ultrasonic cavitation and pulsed electric field electrophoresis to overcome the fluid viscosity resistance and capillary reaction force in nanoscale micropores, and to directionally and densely accumulate positively charged colloidal particles from the bottom of the pore to the pore opening. Based on this, in-situ reactions within the confined space are induced through specific gradient heat treatment: In the liquid-phase pre-melting stage, boric acid in the sealing components preferentially dehydrates and transforms into a boron oxide liquid phase. This liquid phase medium wets the pore walls and fills the interparticle gaps using surface tension, providing a mass transfer channel for the solid-phase reaction and alleviating thermal stress; In the self-propagating reaction initiation stage, the oxidant nitrate and the organic fuel glycine inside the micropores undergo a rapid redox exothermic reaction after reaching the reaction threshold temperature. The released chemical energy serves as an endogenous heat source, compensating for the heat transfer attenuation of the external heat source deep within the micropores, constructing a local high-temperature environment, and driving the metastable precursor to transform into thermodynamically stable zirconium oxide and borosilicate composite ceramics; In the densification sintering stage, the reaction products complete grain development and pore healing at high temperatures, ultimately forming a mechanically interlocked and chemically inert ceramic sealing layer with the oxide film skeleton, thereby endowing the aluminum alloy sheet with excellent high-temperature resistance, thermal shock resistance, and long-term corrosion resistance.

[0008] Preferably, in step S2, the cationic colloidal sealing solution comprises the following components in parts by weight: 26.7g to 53.5g of hydrated zirconium oxynitrate; 300mL to 400mL of anhydrous ethanol; 3.8g to 22.5g of glycine, wherein the molar ratio of glycine to zirconium ions is 0.5:1 to 1.5:1, and the zirconium ions are the molar amount of zirconium element in hydrated zirconium oxynitrate; 600mL to 700mL of deionized water; 20.0g to 40.0g of boric acid; and 10.0g to 20.0g of 3-glycidyl etheroxypropyltrimethoxysilane. By adopting the above technical solution, the stoichiometric ratio of oxidant and fuel is precisely controlled to ensure that the reaction system has sufficient chemical potential energy to maintain self-propagating combustion at the microscale, so that the reaction temperature can reach the ceramic transformation point instantly, while avoiding carbon deposits caused by excessive fuel or loose products caused by excessive oxidant; the introduction of silane coupling agent forms an organic network on the surface of colloidal particles, which not only acts as a film-forming aid to prevent drying cracking, but also transforms into silica at high temperature to participate in the construction of ceramic phase, thereby improving the overall density of the sealing layer.

[0009] Preferably, in step S2, the preparation steps of the cationic colloidal sealing solution include: mixing anhydrous ethanol and deionized water evenly to form two matrix solvents; then dissolving 0.10 mol / L to 0.20 mol / L zirconium oxynitrate hydrate in one of the matrix solvents; adding glycine; and magnetically stirring for 20 to 30 minutes until completely dissolved to obtain solution A; heating the other matrix solvent to 40 to 50°C; adding 20 g / L to 40 g / L boric acid; and stirring for 30 minutes until dissolved; then slowly adding 10 g / L to 20 g / L 3-glycidyl etheroxypropyltrimethoxysilane; and stirring for 30 to 60 minutes to obtain solution B; and slowly adding solution B to solution A while stirring at 1000 r / min; mixing evenly; and then adjusting the pH of the mixture dropwise with sodium hydroxide solution to 3.0 to 4.0; finally, sealing and aging at room temperature for 12 to 24 hours to obtain a translucent cationic colloidal sealing solution. By adopting the above technical solution and employing a stepwise dissolution and remixing strategy, uncontrollable precipitation of zirconium ions and borate ions when the local concentration is too high is avoided. By controlling the pH value in the range of 3.0 to 4.0 and aging it, a stable double electric layer structure is formed on the surface of the colloidal particles, carrying a sufficient amount of positive charge to respond to electric field migration. At the same time, the colloidal particle size is controlled within the range that is suitable for the pore size of the anodic oxide film, preventing pore blockage.

[0010] Preferably, in step S3, the frequency of the ultrasonic wave is 28kHz to 40kHz, and the power density is 0.3W / cm² to 0.5W / cm²; the voltage of the pulsed DC current is 20V to 30V, the frequency is 50Hz to 100Hz, the duty cycle is 60% to 80%, and the processing time is 10 to 20 minutes. By adopting the above technical solution, utilizing the intermittent characteristics of the pulsed electric field, the high concentration of ions accumulated at the orifice is allowed to decrease through natural diffusion during the power-off period, eliminating concentration polarization, preventing premature closure of the orifice, and ensuring that the sealing liquid can continuously penetrate to the bottom of the micropore; the high-frequency vibration of the ultrasonic wave not only eliminates the gas trapped in the pore, but also destroys the bridging structure that the colloid may form at the orifice, keeping the material transport channel unobstructed.

[0011] Preferably, in step S4, the low-temperature drying process involves heating to 100°C at a rate of 5°C / min and holding for 10 minutes; the liquid-phase pre-melting process involves heating to 160-180°C at a rate of 2°C / min and holding for 10-20 minutes. By adopting the above technical solution, the slow heating in the low-temperature stage effectively removes physically adsorbed water and solvent, preventing damage to the film structure due to excessively rapid vaporization; the liquid-phase pre-melting stage allows boric acid to be dehydrated in situ to generate a fluid boron oxide melt, which, with its good wettability, penetrates into the microcracks and coats the solid reactant particles, providing a liquid-phase buffer for the subsequent violent exothermic reaction and preventing thermal shock from causing coating cracking.

[0012] Preferably, in step S4, the process of initiating the self-propagating reaction involves rapidly heating to 220-250°C at a rate of 10°C / min and holding at that temperature for 10-15 minutes. By adopting the above technical solution, the higher heating rate reduces the reaction lag time, enabling the system to quickly cross the activation energy barrier and concentrate on inducing the redox reaction between nitrate and glycine; the instantaneous high heat released in this stage promotes the rapid transformation of the precursor from an amorphous structure to a crystalline ceramic phase within the micro-region.

[0013] Preferably, in step S4, the densification sintering process involves heating to 300°C and holding at that temperature for 20 to 30 minutes. By employing the above technical solution, the residual thermal stress generated by the rapid reaction is eliminated during the heat preservation process, promoting the glass transition after the liquid medium solidifies and the development and improvement of ceramic grains, thereby further enhancing the hardness and wear resistance of the sealing layer.

[0014] Preferably, in step S1, the concentration of the sulfuric acid electrolyte is 160 g / L to 200 g / L, the oxidation temperature is 18 to 20°C, and the oxidation voltage is 15 to 18 V or the current density is 1.5 A / dm³. 2The oxidation time is 30 to 45 minutes. By adopting the above technical solution, an anodized film skeleton with uniform pore size, suitable porosity and a certain thickness was obtained, which provides the necessary carrier space for the physical filling and mechanical interlocking of ceramic phase sealing materials.

[0015] Preferably, in step S3, the anode is a high-purity graphite plate or a 316L stainless steel plate, and the electrode spacing is 10cm. By adopting the above technical solution and selecting chemically inert or corrosion-resistant materials as the anode, the contamination of the sealing liquid by metal impurity ions generated by anode dissolution is avoided, thus ensuring the purity and insulation performance of the sealing layer.

[0016] Preferably, the aluminum alloy sheet is 6061-T6 or 7075-T6 aluminum alloy, and the surface treatment includes degreasing, alkaline etching, and brightening processes. By adopting the above technical solution, for high-strength aluminum alloys containing alloying elements such as copper, zinc, and magnesium, the natural oxide film and oil impurities on the surface are removed through standardized pretreatment, exposing a fresh metal substrate and ensuring the growth quality of the anodic oxide film and its adhesion to the substrate.

[0017] This invention provides a surface treatment method for high-temperature resistant aluminum alloy sheets. It has the following beneficial effects: 1. This invention solves the problem of filling high aspect ratio micropores in anodic oxide films through the combined action of ultrasound and pulsed DC electric field. The intermittent relaxation characteristics of the pulsed electric field effectively inhibit the rapid accumulation of colloidal particles at the pore opening, preventing premature closure of the pore opening. Combined with the cavitation dispersion effect of ultrasound, it promotes charged colloidal particles to overcome mass transfer resistance and achieve dense deposition from the bottom of the pore to the pore opening, thereby improving the filling rate and depth of the sealing material inside the micropores.

[0018] 2. This invention utilizes an oxidant, organic fuel, and boron source to construct an in-situ self-propagating reaction sintering system within micropores. During gradient heat treatment, the liquid medium formed by the preferential melting of the boron source wets the pore walls of the oxide film and buffers thermal mismatch stress. The subsequent redox reaction releases chemical heat, creating a localized high-temperature environment in the micro-region. This promotes the transformation of the filler from a metastable precursor to a chemically inert ceramic phase and achieves densification sintering, overcoming the problems of weak bonding and insufficient density in traditional physical filling sealing layers.

[0019] 3. The sealing layer prepared in this invention significantly improves the high-temperature resistance, thermal shock resistance, and corrosion resistance of the aluminum alloy anodic oxide film. The ceramic phase sealing material generated by the reaction has high thermal stability and does not undergo dehydration, shrinkage, or decomposition under high-temperature environments, maintaining the physical integrity of the film layer. At the same time, the dense ceramic structure effectively blocks the diffusion channels of corrosive media to the aluminum alloy substrate, enabling the treated plate to maintain excellent resistance to neutral salt spray corrosion even after undergoing high-temperature thermal shock cycles. Attached Figure Description

[0020] Figure 1 Comparison of Zr strength (1.0 μm) between Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 2 Comparison of Zr strength (8.0 μm) between Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 3 Comparison of Zr strength (14.0 μm) between Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 4 Comparison of B strength (1.0 μm) between Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 5 This is a comparison diagram of the initial Zr strength mass of Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 6 These are comparative images of the B-strength immersion results of Examples 1-4 and Comparative Examples 1-5 of the present invention. Figure 7 This is a comparison diagram of the effective area of ​​B strength in Examples 1-4 and Comparative Examples 1-5 of the present invention; Figure 8 This is a comparison diagram of the B strength mass loss of Examples 1-4 and Comparative Examples 1-5 of the present invention. Detailed Implementation

[0021] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. 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.

[0022] The main raw materials and reagents used in the following examples and comparative examples have the following sources and specifications. Reagents not specifically mentioned are all commercially available analytical grade or higher grade products.

[0023] Both 6061-T6 and 7075-T6 aluminum alloy sheets are commercially available standard industrial-grade metal sheets, which were cut to 100mm×50mm×2mm for use in the experiment.

[0024] CAS No.: 14985-18-3; Boric acid CAS number: 10043-35-3; Glycine CAS No.: 56-40-6; 3-Glycidyl etheroxypropyltrimethoxysilane (CAS No.: 2530-83-8) is a commercially available analytical grade reagent.

[0025] Anhydrous ethanol, 65%-68% nitric acid, 95%-98% sulfuric acid, sodium hydroxide, etc. are all commercially available analytical grade conventional chemical reagents, and the experimental water is laboratory-made deionized water.

[0026] Example 1: This example provides a surface treatment method for high-temperature resistant aluminum alloy sheets, including the following steps: S1. After degreasing, alkaline etching, and pre-brightening treatment, 6061-T6 aluminum alloy sheets are placed in a 180g / L sulfuric acid electrolyte at 18℃ and 1.5A / dm³. 2 Oxidize under DC current density for 40 minutes, then rinse with water and keep moist.

[0027] S2. Mix 300 mL of anhydrous ethanol and 700 mL of deionized water to prepare two matrix solvents. Dissolve 40.1 g of 0.15 mol / L hydrated zirconium nitrate in one of the matrix solvents, add 11.3 g of glycine (molar ratio of zirconium ions to zirconium ions 1:1), and stir magnetically for 30 minutes until completely dissolved to form solution A; zirconium ions are the molar amount of zirconium element in hydrated zirconium nitrate. Heat the other matrix solvent to 45°C, add 30.0 g of 30 g / L boric acid, and stir for 30 minutes until dissolved. Then slowly add 15.0 g of 15 g / L 3-glycidyl etheroxypropyltrimethoxysilane, pH 3.5, and stir for 45 minutes to hydrolyze to form solution B. Solution B was slowly added dropwise to solution A while stirring at 1000 r / min. After mixing evenly, the pH of the mixture was adjusted dropwise to 3.5 using 1.0 mol / L sodium hydroxide solution. Finally, the mixture was sealed and aged at room temperature for 18 hours to obtain a light milky white, semi-transparent cationic colloidal sealing solution.

[0028] S3. Using the aforementioned aluminum alloy as the cathode and a high-purity graphite plate as the anode, with an electrode spacing of 10 cm, immerse the plate in a pale milky white, semi-transparent cationic colloidal sealing solution. The switching frequency is 40 kHz, and the power density is 0.5 W / cm³. 2 The ultrasonic waves are applied simultaneously with a pulsed DC current, set to 25V, 50Hz, 60% duty cycle, for 15 minutes. Remove and drain for 1 minute.

[0029] S4. Place the workpiece in a forced-air drying oven and heat it to 100°C at a rate of 5°C / min and hold it for 10 minutes to dry it. Continue to heat it to 165°C at a rate of 2°C / min and hold it for 15 minutes to pre-melt the liquid phase. Then, rapidly heat it to 235°C at a rate of 10°C / min and hold it for 10 minutes to initiate a self-propagating reaction. Finally, heat it to 300°C and hold it for 25 minutes to achieve densification and sintering. Cool it to room temperature with the furnace.

[0030] Example 2: This example provides a surface treatment method for high-temperature resistant aluminum alloy sheets, including the following steps: S1. After standard pretreatment, 6061-T6 aluminum alloy sheet is placed in 160g / L sulfuric acid electrolyte and oxidized at 20℃ and 15V constant voltage for 45 minutes. After washing with water, it is kept moist.

[0031] S2. Mix 300 mL of anhydrous ethanol and 700 mL of deionized water to prepare two matrix solvents. Dissolve 26.7 g of 0.10 mol / L hydrated zirconium nitrate in one of the matrix solvents. Add 3.8 g of glycine (molar ratio of zirconium ions to glycine is 0.5:1) and stir magnetically for 20 minutes until completely dissolved to form solution A. Heat the other matrix solvent to 40°C, add 20.0 g of 20 g / L boric acid, and stir for 30 minutes until dissolved. Then slowly add 10.0 g of 10 g / L 3-glycidyl etheroxypropyltrimethoxysilane, maintaining the pH at 3.0, and stir for 30 minutes to hydrolyze and form solution B. Solution B was slowly added dropwise to solution A while stirring at 1000 r / min. After mixing evenly, the pH of the mixture was adjusted dropwise to 3.0 using 1.0 mol / L sodium hydroxide solution. Finally, the mixture was sealed and aged at room temperature for 12 hours to obtain a semi-transparent cationic colloidal sealing solution.

[0032] S3. Using the aforementioned aluminum alloy as the cathode and a 316L stainless steel plate as the anode, immerse the sample in a semi-transparent cationic colloidal sealing solution. The switching frequency is 28kHz, and the power density is 0.3W / cm³. 2 The ultrasonic waves were applied with pulsed DC current at a voltage of 20V, a frequency of 100Hz, a duty cycle of 80%, and a processing time of 20 minutes. The mixture was then removed and drained.

[0033] S4. Place the workpiece in a high-temperature furnace and dry it at 100°C for 10 minutes; then raise the temperature to 160°C and hold for 20 minutes; then rapidly raise the temperature to 220°C and hold for 15 minutes; finally raise the temperature to 300°C and hold for 20 minutes, and then cool it with the furnace.

[0034] Example 3: This example provides a surface treatment method for high-temperature resistant aluminum alloy sheets, including the following steps: S1. After degreasing, alkaline etching and pre-brightening treatment, the 7075-T6 aluminum alloy sheet is placed in 200g / L sulfuric acid electrolyte and oxidized at 18℃ and 18V constant voltage for 30 minutes. After washing with water, it is kept moist.

[0035] S2. Mix 400 mL of anhydrous ethanol and 600 mL of deionized water thoroughly to form two matrix solvents. Dissolve 53.5 g of 0.20 mol / L hydrated zirconium nitrate in one of the matrix solvents. Add 22.5 g of glycine (molar ratio of zirconium ions to glycine is 1.5:1) and stir magnetically for 30 minutes until completely dissolved to form solution A. Heat the other matrix solvent to 50°C, add 40.0 g of 40 g / L boric acid, and stir for 30 minutes until dissolved. Then slowly add 20.0 g of 20 g / L 3-glycidyl etheroxypropyltrimethoxysilane, maintaining the pH at 4.0, and stir for 60 minutes to hydrolyze and form solution B. Solution B was slowly added dropwise to solution A while stirring at 1000 r / min. After mixing evenly, the pH of the mixture was adjusted dropwise to 4.0 using 1.0 mol / L sodium hydroxide solution. Finally, the mixture was sealed and aged at room temperature for 24 hours to obtain a milky white cationic colloidal sealing solution.

[0036] S3. Using the aforementioned aluminum alloy as the cathode and a high-purity graphite plate as the anode, immerse the sample in a milky white cationic colloidal sealing solution. The switching frequency is 40kHz, and the power density is 0.4W / cm³. 2 Apply ultrasonic waves and pulsed DC current at a voltage of 30V, a frequency of 50Hz, a duty cycle of 70%, and a processing time of 10 minutes. Remove and drain.

[0037] S4. Place the workpiece in a high-temperature furnace and dry it at 100℃ for 10 minutes; then raise the temperature to 170℃ and hold it for 15 minutes; then rapidly raise the temperature to 250℃ at a rate of 10℃ / min and hold it for 10 minutes; finally raise the temperature to 300℃ and hold it for 30 minutes, and then cool it with the furnace.

[0038] Example 4: This example provides a surface treatment method for high-temperature resistant aluminum alloy sheets, including the following steps: S1. After degreasing, alkaline etching and pre-brightening treatment, the 7075-T6 aluminum alloy sheet is placed in 200g / L sulfuric acid electrolyte and oxidized at 18℃ and 18V constant voltage for 30 minutes. After washing with water, it is kept moist.

[0039] S2 is the same as in Example 1.

[0040] S3. Using the aforementioned aluminum alloy as the cathode, immerse it in a pale milky white, semi-transparent cationic colloidal sealing solution. Turn on the ultrasonic wave, apply a pulsed DC current, set the voltage to 22V, the frequency to 80Hz, the duty cycle to 75%, and the treatment time to 18 minutes. Remove and drain.

[0041] S4. Place the workpiece in a forced-air drying oven. The drying stage is the same as in Example 1. The pre-melting stage is adjusted to 180°C and held for 10 minutes. The reaction initiation stage is adjusted to 240°C and held for 12 minutes. The densification sintering stage is the same as in Example 1. Cool with the furnace.

[0042] Comparative Example 1: Compared with Example 1, the difference is that after step S1, anodizing and water washing, the aluminum alloy workpiece is directly immersed in boiling deionized water at 98-100℃ for 40 minutes, and then taken out and air-dried. The electrophoretic injection in step S2 and the gradient heat treatment in step S3 are not performed.

[0043] Comparative Example 2: Compared with Example 1, the difference is that in step S2, no pulsed DC electric field is applied, and the workpiece is simply immersed in the sealing liquid with the ultrasonic waves turned on for 15 minutes. The remaining steps are the same as in Example 1.

[0044] Comparative Example 3: Compared with Example 1, the difference is that boric acid is not added in the preparation process of the sealing liquid, while the other components and preparation process remain unchanged; and in step S3, gradient heat treatment, due to the lack of the low melting point characteristics of boric acid, the 165°C pre-melting and heat preservation stage is cancelled, and the temperature is directly raised from 100°C to 235°C, while the other steps are the same as in Example 1.

[0045] Comparative Example 4: Compared with Example 1, the difference is that glycine is not added during the preparation of the sealing solution, while the other components and preparation process remain unchanged; the heat treatment process in step S3 is exactly the same. At this time, only the thermal decomposition of zirconium oxynitrate occurs in the pores, without a violent exothermic reaction.

[0046] Comparative Example 5: Compared with Example 1, the difference is that in step S2, during the electrophoretic injection process, the aluminum alloy workpiece is connected to the positive terminal of the power supply, and the graphite plate is connected to the negative terminal of the power supply, that is, the traditional anodic electrophoresis mode is adopted. The remaining electrical parameters and operations are the same as in Example 1.

[0047] Test Example 1: Experimental steps: Take 50 mL of the colloidal sealing solution corresponding to the preparation process of Example 1, Example 2, Example 3, Example 4, Comparative Example 3 and Comparative Example 4 as the test samples.

[0048] The above liquid samples were placed in a vacuum drying oven and dried at 60°C for 24 hours to remove the solvent. The resulting solid was then ground to obtain a dry gel powder.

[0049] The powder samples were tested using a simultaneous thermal analyzer. The test conditions were set as follows: flowing air atmosphere, gas flow rate of 50 mL / min, alumina crucible as support, and an empty crucible as reference.

[0050] The heating program is set to linearly increase from 30℃ to 600℃, with the heating rate controlled at 10℃ / min.

[0051] Differential scanning calorimetry signals are acquired, and the starting temperature, peak temperature, and enthalpy change of characteristic endothermic or exothermic peaks in the curve are recorded.

[0052] The test results are shown in Table 1: Table 1 Differential scanning calorimetry data of each group of sealing precursor powders From Table 1, we can obtain: Based on the data in Table 1 and the characteristics of the thermal analysis curves: The samples from Examples 1 to 4 all exhibited single, square, or sharp exothermic peaks in the temperature range of 230°C to 240°C, with absolute exothermic enthalpies ranging from 800 J / g to 1600 J / g. This exothermic characteristic corresponds to the redox reaction between the nitrate oxidant and the glycine fuel. The formulation in Example 3, with a higher proportion of glycine, measured the highest exothermic enthalpy at -1582.7 J / g; the formulation in Example 2, with the lowest concentration and fuel ratio, showed a correspondingly lower exothermic enthalpy, but still exhibited a clear exothermic characteristic.

[0053] No exothermic peak was detected in sample 4 across the entire test temperature range; it exhibited an endothermic characteristic of +215.8 J / g, corresponding to the thermal decomposition process of nitrates. This result indicates that the system without added organic fuels cannot generate an endogenous heat source during heating and relies solely on an external heat source for energy.

[0054] In Examples 1 to 4, an endothermic step or peak was detected near 168°C, corresponding to the phase transition process of boric acid dehydration into boron oxide melt. This endothermic characteristic temperature is lower than the initiation temperature of the aforementioned redox reaction. The data indicate that a liquid phase component has already formed in the system before the exothermic reaction is initiated.

[0055] An exothermic peak was detected in Comparative Example 3 sample at 228.6℃, but no endothermic melting characteristics were detected in the 160℃ to 170℃ range. This indicates that in the absence of boric acid, the reaction system did not form a liquid-phase buffer environment during the exothermic phase, and the reaction proceeded in a solid or quasi-solid state. Based on the exothermic peak data, the reaction temperature of Comparative Example 3 was slightly lower than that of Example 1. It is speculated that due to the lack of endothermic buffering and dilution effects from the boric acid melting process, the reaction system reached the ignition temperature more easily, leading to an earlier exothermic peak temperature.

[0056] Test Example 2: Experimental steps: Aluminum alloy sealing samples prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were selected as the samples to be tested.

[0057] Elemental analysis was performed using a glow discharge emission spectrometer. The instrument operating parameters were set as follows: discharge voltage 700V, discharge current 20mA, argon pressure 600Pa, and rinsing time 60s.

[0058] The analytical elements and their corresponding characteristic spectral lines were set as follows: zirconium (Zr), 343.82 nm; boron (B), 249.77 nm; and aluminum (Al), 396.15 nm. The aluminum signal was set as the matrix reference signal to define the interface between the film and the matrix.

[0059] The sample surface was sputtered and stripped, with the sputtering rate calibrated to 0.05 μm / s. The changes in emission spectral intensity of each element with sputtering time and depth were continuously recorded, and the termination criterion was set at 90% of the steady-state intensity of the aluminum matrix signal.

[0060] The relative spectral intensity data of zirconium and boron were extracted from three characteristic depth points: 1.0 μm from the surface near the surface, 8.0 μm from the surface in the middle of the film, and 14.0 μm from the surface at the bottom of the film, close to the barrier layer.

[0061] The test results are shown in Table 2: Table 2. Relative intensity distribution of characteristic elements along the depth direction of the sealing film layer (unit: cps) From Table 2, we can obtain: Based on the data in Table 2 and the element depth distribution characteristics: In Examples 1 to 4, zirconium (Zr) and boron (B) signals were detected at three characteristic depth points: near the surface, middle, and bottom of the membrane. The signal intensity ratio between the bottom and near the surface was calculated, and the values ​​ranged from 0.85 to 0.92. The data indicate that the sealing material is continuously distributed along the pore depth direction. In Example 2, a low-concentration sealing solution was used, resulting in a lower overall signal intensity compared to Example 1, but the depth distribution trend remained stable, indicating that under low-voltage, long-term electrophoresis conditions, the particles migrated to the bottom of the pores.

[0062] Comparative Example 2, after natural immersion in the near-surface layer (1.0 μm), detected a zirconium / boron signal of similar intensity to that of Example 1. However, the signal intensity significantly decreased in the middle layer (8.0 μm) and the bottom layer (14.0 μm), with the bottom signal approaching background noise levels. This data indicates that, without an external electric field, colloidal particles cannot penetrate deep into the pores and are mainly enriched in the pore opening region.

[0063] In Comparative Example 5, the zirconium and boron signals detected by the reverse electric field across the entire depth range were low, with only trace signals detected at the surface. The applied electric field made the aluminum substrate the anode, repelling the positively charged micelles and preventing them from entering the pores.

[0064] In Comparative Example 3, no boric acid was detected, and the zirconium signal distribution was uniform, while no boron signal was detected, confirming the source of boron in the system. The zirconium and boron distribution data in Comparative Example 4 (without fuel) were similar to those in Example 1, indicating that the addition or absence of glycine fuel does not change the physical migration behavior during electrophoretic injection; the difference lies in the reaction characteristics of the subsequent heat treatment stage.

[0065] Based on the combined data from various groups, the electric field transports the sealing material to the bottom of the pores, and combined with the cationic colloid design, material filling is achieved across the entire film thickness range.

[0066] Test Example 3: Experimental steps: Aluminum alloy sealing samples prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were selected as test samples.

[0067] Place the sample in the isothermal zone of a muffle furnace preheated to 300°C and hold for 60 minutes. Remove the sample and immediately immerse it vertically in 20°C deionized water for quenching and cooling. After holding for 30 seconds, remove the sample and dry it with cold air. Repeat this heating-water cooling process three times.

[0068] Select a test area on the surface of the sample after thermal shock treatment, and add 50 mg / mL acidic potassium dichromate solution to completely cover the test area.

[0069] Let stand for 2 minutes. First, use a damp cotton ball to wipe away any excess dye from the surface, then use a dry cotton ball to vigorously wipe the test area until there is no residual dye on the surface.

[0070] The color residue in the test area was observed under 1000 lx illumination and rated according to ISO2143 standard: level 0 represents no color residue; level 5 represents dark spots with surface chalking or cracking.

[0071] The test results are shown in Table 3: Table 3. Staining spot test rating results after 300℃ thermal shock cycling. From Table 3, we can obtain: Based on the data in Table 3 and the staining test results: After undergoing three cycles of rapid cooling and thermal shock from 300°C to 20°C, the staining ratings of samples 1 to 4 remained between 0 and 1. This data indicates that the sealing layer maintained the integrity of its physically closed structure under abrupt high-temperature conditions. The ratings of Examples 1, 3, and 4 (0) demonstrate the resistance of the ceramicized sealing layer to thermal stress damage.

[0072] Comparative Example 1 shows that the boiling water sealing product is rated as level 5. Traditional hydrated alumina sealing products undergo dehydration reaction in a high-temperature environment, and the volume shrinkage leads to through-cracks in the film layer, allowing the dye solution to seep into the pores along the cracks.

[0073] Comparative Example 3, without boric acid, was rated as level 4, and network cracks were observed on its surface. This system lacked a liquid phase medium for boric acid formation, and the rigid ceramic phase could not release thermal mismatch stress through viscous flow during the exothermic reaction and external thermal shock, leading to brittle cracking.

[0074] Comparative Example 4, without fuel, was rated as level 5, and showed signs of powdering on the surface. The system lacked an internal combustion heat source, and the precursor within the pores only underwent physical drying and decomposition, failing to reach the energy threshold required for ceramic sintering and densification. The product was loose and porous, unable to prevent dye penetration.

[0075] Comparative Example 2 (immersion method) and Comparative Example 5 (reverse electric field rating) were rated as level 4 to 5. Combined with the elemental depth distribution test results, due to the ineffective filling of deep pores and the thin surface sealing layer, the substrate was damaged under thermal shock, resulting in exposure and adsorption of the dye solution.

[0076] Test Example 4: Experimental steps: Aluminum alloy sealing samples prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were selected. The back and edges of the samples were coated with a mixture of paraffin and rosin, retaining an effective test area of ​​approximately 100 cm² on each side. 2 .

[0077] Prepare the salt solution according to GB / T10125-2012 standard, controlling the sodium chloride concentration to 50±5g / L and adjusting the solution pH to 6.5-7.2.

[0078] The sample was placed in a salt spray test chamber with the test surface at a 20-degree angle to the vertical. The test chamber temperature was set to 35±2℃, and continuous spray mode was used.

[0079] Visually inspect the sample surface every 24 hours and record the cumulative spraying time when the first visible corrosion point with a diameter ≥0.5mm appears on the surface of each sample.

[0080] The termination criterion is set as the corrosion area on the sample surface exceeding 5% or the appearance of dense pitting corrosion. For samples that have not shown corrosion pits after a cumulative testing time of more than 1200 hours, it is recorded as >1200h and the test is stopped.

[0081] The test results are shown in Table 4: Table 4. Time of first corrosion point appearance in neutral salt spray tests for each group of samples (unit: hours) From Table 4, we can obtain: Based on the data and corrosion morphology analysis in Table 4: The resistance times to neutral salt spray corrosion in Examples 1 to 4 ranged from 984 hours to 1200 hours. No corrosion points were observed in Examples 1 and 3 after 1200 hours of testing. The results indicate that the zirconium-boron-silicon ceramic phase formed within the pores is chemically inert, and the dense structure formed by sintering blocks the diffusion channels of chloride ions to the aluminum alloy matrix.

[0082] Comparative Example 1 showed a boiling water sealing corrosion resistance time of 336 hours. The hydrated alumina film lacked stability under continuous high chloride ion conditions, and dissolved or was penetrated over time.

[0083] The corrosion resistance times of the immersion method in Comparative Example 2 and the reverse electric field method in Comparative Example 5 were 42 hours and 36 hours, respectively. Due to the lack of electric field driving, the sealing material did not fill the pores to a deep depth, and there was no effective protection above the barrier layer. Chloride ions penetrated the residual oxide film and reached the substrate interface, causing pitting corrosion.

[0084] Comparative Example 3 showed a boric acid-free corrosion resistance time of 168 hours, exhibiting linear corrosion along the grain. Microcracks generated during heat treatment became diffusion channels for the corrosive medium, reducing the overall protective effectiveness of the film.

[0085] Comparative Example 4 showed a fuel-free corrosion resistance time of 120 hours. The filling material inside the pores did not undergo a high-temperature ceramic transformation and remained in a loose powder accumulation state, unable to form a dense physical shielding layer.

[0086] Comprehensive data show that electrophoretic injection to achieve full pore filling and self-propagating reaction to achieve ceramicized dense sintering improve the corrosion resistance of aluminum alloy anodic oxide films.

[0087] Test Example 5: Experimental steps: Aluminum alloy sealing samples prepared in Examples 1 to 4 and Comparative Examples 1 to 5 were selected. The effective surface area SS, dm² of each sample was measured and calculated. 2 The values ​​are accurate to 0.01 dm. 2 .

[0088] Place the sample in a desiccator to equilibrate for 24 hours, and weigh the initial mass m1 before testing using an analytical balance, accurate to 0.1 mg.

[0089] Prepare an acidic corrosion solution according to ISO 3210 standard: Dissolve 35 mL of phosphoric acid with a specific gravity of 1.70 and 20 g of chromium trioxide in distilled water, and dilute to a final volume of 1000 mL.

[0090] Heat the solution to 38±1℃ and maintain a constant temperature. Vertically immerse the sample completely in the solution for 15 minutes.

[0091] Remove the sample, rinse it immediately with running tap water, then wash it with distilled water, and dry it in a 100℃ oven for 30 minutes.

[0092] The sample was placed in a desiccator and cooled to room temperature. The final mass m after the test was then measured. 2 .

[0093] According to the formula Calculate the mass loss per unit area (mg / dm²) using W=(m1-m2) / S. 2 .

[0094] The test results are shown in Table 5: Table 5. Data on mass loss per unit area after 15 minutes of phosphochromic acid immersion. From Table 5, we can obtain: Based on the data in Table 5 and the analysis of the weight loss characteristics of acid etching: The mass loss values ​​of Examples 1 to 4 ranged from 4.71 mg / dm³. 2 Up to 8.27 mg / dm 2 Between, and below the 30 mg / dm³ specified in ISO 3210 standard. 2 Limits. The zirconium-boron-silicon-based ceramic phase generated by the self-propagating reaction exhibits chemical stability in a phosphoric acid-chromic acid environment. Compared with hydrated alumina, this ceramic phase is poorly soluble in acid, thus protecting the oxide film framework.

[0095] The mass loss of the boiling water seal in Comparative Example 1 was 20.77 mg / dm³. 2 This value meets the standard but is higher than the example value. Boehmite formed by boiling water sealing partially dissolves under hot acid immersion.

[0096] Comparative Example 4 showed a fuel-free mass loss value of 66.92 mg / dm³. 2 This comparative example lacks a combustion synthesis reaction; the material within the pores only undergoes physical drying and dehydration, existing as amorphous salts or dry gels. Such materials dissolve in hot acid solutions, leading to the dissolution of the sealing material and corrosion of the oxide film framework. This result indicates a difference in corrosion resistance between chemical ceramicization and physical filling.

[0097] Comparative Example 3 showed a boric acid-free mass loss of 41.35 mg / dm³. 2 The result exceeded the acceptable limit. Combined with the results of test example 3, the microcracks in the film increased the acid contact area, leading to increased weight loss.

[0098] The mass loss values ​​of the immersion method in Comparative Example 2 and the reverse electric field in Comparative Example 5 were 63.53 mg / dm³. 2 and 70.77 mg / dm 2Because the pores were not effectively filled, the phosphoric acid-chromic acid solution came into contact with and dissolved the inner surface of the anodic oxide film, resulting in the loss of the substrate alumina.

[0099] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A surface treatment method for high-temperature resistant aluminum alloy sheets, characterized in that, Includes the following steps: S1. After surface treatment, the aluminum alloy sheet is placed in sulfuric acid electrolyte for anodic oxidation, and a porous oxide film is prepared on the surface. After washing with water, it is kept moist. S2. Dissolve hydrated zirconium nitrate and glycine to form solution A. Dissolve and hydrolyze boric acid and 3-glycidyl etheroxypropyltrimethoxysilane to form solution B. Mix solution A and solution B and adjust the pH value. After aging, obtain cationic colloidal sealing solution. S3. Using the aluminum alloy plate processed in step S1 as the cathode, immerse it in the cationic colloidal sealing solution prepared in step S2, and apply pulsed direct current under ultrasonic assistance to drive the colloidal particles to deposit into the micropores of the porous oxide film. S4. The aluminum alloy sheet processed in step S3 is subjected to low-temperature drying, liquid phase pre-melting, self-propagating reaction initiation and densification sintering in sequence, and cooled to room temperature in the furnace to synthesize a ceramic phase sealing layer in situ in the micropores.

2. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S2, the cationic colloidal sealing solution comprises the following components in parts by weight: Zirconium oxyhydrate: 26.7g-53.5g; Anhydrous ethanol: 300mL-400mL; Glycine: 3.8g-22.5g, the molar ratio of glycine to zirconium ions is 0.5:1-1.5:1, and the zirconium ion is the molar amount of zirconium in hydrated zirconium nitrate; Deionized water: 600mL-700mL; Boric acid: 20.0g-40.0g; 3-Glycidyl etheroxypropyltrimethoxysilane: 10.0g-20.0g.

3. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S2, the preparation steps of the cationic colloidal sealing solution include: Anhydrous ethanol and deionized water were mixed evenly to form two matrix solvents. Then, 0.10 mol / L-0.20 mol / L hydrated zirconium nitrate was dissolved in one of the matrix solvents. Glycine was added, and the mixture was magnetically stirred for 20-30 minutes until completely dissolved to obtain solution A. Heat another portion of the matrix solvent to 40-50℃, add boric acid with a concentration of 20g / L-40g / L, keep warm and stir for 30 minutes until dissolved, then slowly add 3-glycidyl etheroxypropyltrimethoxysilane with a concentration of 10g / L-20g / L, stir and hydrolyze for 30-60 minutes to obtain solution B; Solution B was slowly added dropwise to solution A while stirring at 1000 r / min. After mixing evenly, the pH of the mixture was adjusted dropwise with sodium hydroxide solution to 3.0-4.

0. Finally, the mixture was sealed and aged at room temperature for 12-24 hours to obtain a semi-transparent cationic colloidal sealing solution.

4. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S3, the frequency of the ultrasonic wave is 28kHz-40kHz, and the power density is 0.3W / cm². 2 -0.5W / cm 2 The voltage of the pulsed DC current is 20V-30V, the frequency is 50Hz-100Hz, the duty cycle is 60%-80%, and the processing time is 10-20 minutes.

5. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S4, the low-temperature drying process is as follows: the temperature is increased to 100°C at a rate of 5°C / min and held for 10 minutes; the liquid phase pre-melting process is as follows: the temperature is increased to 160-180°C at a rate of 2°C / min and held for 10-20 minutes, and the boron oxide liquid phase generated by the dehydration of boric acid wets the pore walls and fills the voids.

6. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S4, the process initiated by the self-propagating reaction is as follows: rapidly heating to 220-250°C at a rate of 10°C / min and holding at that temperature for 10-15 minutes, using the redox reaction of nitrate and glycine to release heat and drive the precursor to transform into the ceramic phase.

7. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S4, the densification sintering process is as follows: heat to 300°C and hold for 20-30 minutes to promote densification of the reaction products and grain development.

8. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S1, the concentration of the sulfuric acid electrolyte is 160 g / L-200 g / L, the oxidation temperature is 18-20℃, and the oxidation voltage is 15-18 V or the current density is 1.5 A / dm³. 2 The oxidation time is 30-45 minutes.

9. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, In step S3, the anode is a high-purity graphite plate or a 316L stainless steel plate, and the electrode spacing is 10cm.

10. The surface treatment method for high-temperature resistant aluminum alloy sheet according to claim 1, characterized in that, The aluminum alloy sheet is 6061-T6 or 7075-T6 aluminum alloy, and the surface treatment includes degreasing, alkaline etching and brightening processes.

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