Preparation method of high-weather-resistance extinction electrophoresis aluminum profile

Abstract

The invention discloses a preparation method of a high-weather-resistance extinction electrophoresis aluminum profile, and relates to the technical field of aluminum profile surface treatment, the preparation method comprises the steps of pretreatment, electrophoretic coating, curing and post-treatment, specifically, oil removal, acid pickling and rare earth modified anodic oxidation are sequentially performed in the pretreatment, and a composite oxide film is formed through co-deposition of rare earth elements and an aluminum matrix; electrophoretic coating adopts an electrophoretic liquid compounded by fluorosilicone modified acrylic resin and amino silane modified white carbon black to realize interface covalent bonding of a delustering agent and a resin matrix; a segmented stepped heating process is adopted for curing, and resin staged crosslinking is promoted so as to reduce internal stress; and after-treatment, holes of an oxidation film and a paint film are sealed through chromium-free rare earth hole sealing liquid. All the steps cooperate to form a'composite oxide film-fluorosilicone modified acrylic resin layer-rare earth hole sealing 'triple protection system, the weather resistance, the extinction stability and the mechanical property of the aluminum profile are improved, and the aluminum profile is suitable for the outdoor high-weather-resistance-requirement fields such as buildings and rail transit.

Description

Technical Field

[0001] This invention relates to the field of aluminum profile surface treatment technology, and in particular to a method for preparing a high weather-resistant, matte electrophoretic aluminum profile. Background Technology

[0002] Matte electrophoretic aluminum profiles are widely used in outdoor fields such as construction and rail transportation due to their combination of low-gloss appearance and corrosion resistance. Current technologies typically involve the following steps in their preparation: anodizing, electrophoretic coating, curing, and sealing. The pretreatment stage often uses traditional sulfuric acid anodizing to form a porous oxide film, improving the substrate's corrosion resistance. Electrophoretic coating often uses acrylic or polyurethane resins combined with silica matting powder, controlling the gloss level by adjusting the amount of matting powder added. The curing process usually involves constant-temperature baking to promote resin cross-linking. Post-treatment often employs chromate sealing or hot water sealing to seal the oxide film and coating pores.

[0003] However, existing technologies still have the following shortcomings: First, insufficient weather resistance. Traditional single oxide film or coating protection systems cannot simultaneously meet the long-term outdoor performance requirements such as salt spray resistance and UV aging resistance, and are prone to problems such as coating chalking and oxide film corrosion. Second, it is difficult to balance matting performance and mechanical properties. Ordinary matting powders have weak interfacial bonding with the resin matrix, and uneven dispersion can easily lead to fluctuations in gloss or decreased adhesion of the paint film. Third, internal stress is easily generated during the curing process. Rapid cross-linking of the resin during constant temperature curing can easily lead to differences in thermal expansion between the coating and the substrate, causing microcracks. Fourth, environmental friendliness needs to be improved. Traditional chromate sealing contains heavy metal ions, which does not meet the requirements of environmental regulations such as RoHS. These problems limit the application of matte photocoagulated aluminum profiles in fields requiring high weather resistance and high reliability. Summary of the Invention

[0004] In view of the shortcomings of the prior art, the purpose of this invention is to provide a method for preparing high weather-resistant matting photocoagulated aluminum profiles to solve one or more problems in the prior art.

[0005] To achieve the above objectives, the technical solution of the present invention is as follows:

[0006] A method for preparing a high weather-resistant, matte electrophoretic aluminum profile includes the following steps:

[0007] (1) Pretreatment: The aluminum profiles are sequentially degreased, pickled, and subjected to rare earth modified anodizing. The rare earth modified anodizing solution is composed of sulfuric acid, cerium nitrate and citric acid, wherein the concentration of sulfuric acid is 180-200 g / L, the concentration of cerium nitrate is 0.5-1.0 g / L, and the concentration of citric acid is 0.3-0.5 g / L.

[0008] (2) Electrophoretic coating: The pretreated aluminum profile is placed in an electrophoretic solution for electrophoretic coating. The electrophoretic solution is composed of fluorosilicone modified acrylic resin, modified silica, leveling agent and deionized water, wherein the amount of modified silica added is 5-8% of the total mass of the electrophoretic solution.

[0009] (3) Curing: The aluminum profile after electrophoretic coating is cured in stages, including the first stage of 80℃ for 10 min, the second stage of 150℃ for 20 min, and the third stage of 175-185℃ for 15 min. After curing, it is naturally cooled to below 60℃.

[0010] (4) Post-treatment: The cured aluminum profile is sealed with chromium-free rare earth. The sealing liquid used for the chromium-free rare earth sealing is composed of neodymium nitrate and acetic acid, wherein the concentration of neodymium nitrate is 2-3 g / L and the concentration of acetic acid is 0.5-0.8 g / L.

[0011] Specifically, in step (1), the degreasing is performed using an alkaline degreasing agent at 60-70℃ for 10 minutes. The pickling is performed using a mixture of nitric acid and hydrofluoric acid at 20-30℃ for 3 minutes, wherein the volume fraction of nitric acid is 10% and the volume fraction of hydrofluoric acid is 2%. After both degreasing and pickling, ultrasonic cleaning is performed using deionized water with an ultrasonic power of 300W for 5 minutes. After cleaning, the residual oil on the surface of the aluminum profile is ≤5mg / m³. 2 .

[0012] Specifically, in step (1), the process parameters for rare earth modified anodizing are a temperature of 20-25℃ and a current density of 1.0-1.5A / dm³. 2 The processing time is 30-40 minutes, the oxide film thickness is 25-30 μm, and the porosity is ≤5 particles / μm. 2 The rare earth modified anodizing is carried out in a vertical anodizing tank, with a titanium alloy cathode, an anode-to-cathode area ratio of 1:1.2, and a mechanical stirring speed of 150-200 r / min in the tank.

[0013] Specifically, in step (2), the fluorosilicone modified acrylic resin is obtained by copolymerization of methyl methacrylate, butyl acrylate, trifluoroethyl acrylate, and γ-methacryloyloxypropyltrimethoxysilane. Based on the total mass of monomers as 100%, the mass percentages of each monomer are 23-27%, 18-22%, 13-17%, and 4-6%, respectively. The copolymerization reaction is carried out in a four-necked flask, using azobisisobutyronitrile as the initiator, with the amount of initiator added being 0.6-1.0% of the total mass of monomers. Ethyl acetate is used as the solvent, with the amount of solvent added being 63-67% of the total mass of monomers. Under nitrogen protection, the temperature is raised to 80-85℃, and the mixture of monomers and initiator is added dropwise for 1.5-2.5 hours. The reaction is then maintained at this temperature for 3.5-4.5 hours. After cooling to 35-45℃, the temperature is neutralized to pH 7.5-8.0 with dimethylethanolamine.

[0014] Specifically, in step (2), the modified silica is prepared by using fumed silica as a substrate, wherein the fumed silica has a particle size of 8-12 μm and a specific surface area of ​​200±25 m². 2 / g. Preheat fumed silica to 60℃ in a high-speed mixer, add aminosilane for modification. The amount of aminosilane added is 2-3% of the mass of fumed silica. The mixing speed is 2800-3200 r / min and the mixing time is 25-35 min. After modification, the silanol content on the surface of fumed silica is reduced to below 0.5 mmol / g.

[0015] Specifically, in step (2), the electrophoresis solution is prepared by mixing fluorosilicone-modified acrylic resin, modified silica, leveling agent, and deionized water, wherein the mass percentage of fluorosilicone-modified acrylic resin is 60-65%, the mass percentage of leveling agent is 0.4-0.6%, and deionized water is the remainder. The pH of the electrophoresis solution is adjusted to 8.0-8.5 using dimethylethanolamine, and the conductivity is controlled at 1200-1500 μS / cm. The modified silica is dispersed for 30 minutes at 1500 r / min using a high-speed disperser, resulting in a median particle size distribution of 10 ± 2 μm after dispersion.

[0016] Specifically, in step (2), the electrophoretic coating is carried out in a tank-type electrophoretic coating line with an electrode spacing of 150-200 mm. The anode diaphragm bag is made of nylon 66 with a molecular weight cutoff of 10000 Da. The electrophoretic process parameters are: voltage 140-160 V, electrophoresis time 12-15 min, tank temperature 25-30 °C, and the circulating filtration system uses a 5 μm filter element with a filtration rate of 3 tank volumes / h. The coating thickness after electrophoresis is 18-22 μm.

[0017] Specifically, in step (3), the segmented step curing is carried out in a hot air circulating oven with an oven wind speed of 1.5-2.0 m / s and a temperature uniformity of ±1℃. The curing heating rate is as follows: 5℃ / min from 20-30℃ to 80℃, 3℃ / min from 80℃ to 150℃, and 2℃ / min from 150℃ to 180℃.

[0018] Specifically, in step (4), the pH of the sealing solution for the chromium-free rare earth sealing is adjusted to 5.0-5.5 using acetic acid. The sealing process parameters are: temperature 60-70℃, processing time 20-25min, ultrasonic-assisted sealing, ultrasonic power 450-550W, ultrasonic frequency 38-42kHz, and the aluminum profile is suspended from bottom to top.

[0019] Specifically, in step (1), the aluminum profile is a 6061 or 6063 aluminum alloy profile with a thickness of 1.0-3.0 mm and a surface roughness Ra of 0.8-1.6 μm. In step (3), the cured aluminum profile is naturally cooled to below 60°C.

[0020] Compared with the prior art, the beneficial technical effects of the present invention are as follows:

[0021] (i) By combining rare earth modified anodizing, fluorosilicone modified matte coating and chromium-free rare earth sealing, a triple protection system of "composite oxide film - fluorosilicone modified acrylic resin layer - rare earth sealing" is formed. Rare earth elements form insoluble salts in the micropores of the oxide film to block the corrosion path. The low surface energy and UV resistance of the fluorosilicone modified acrylic resin layer reduce aging cracking. Rare earth sealing further seals coating defects, and together they achieve a synergistic improvement in weather resistance (including salt spray resistance and UV aging resistance), which is different from the protection mechanism of existing technologies that rely solely on coatings or oxide films.

[0022] (ii) By combining fluorosilicone modified acrylic resin and aminosilane modified silica, the fluorosilicone segments in the resin form covalent bonds with the silanol groups on the surface of the modified silica, which improves the interfacial bonding force between the matting agent and the resin matrix. At the same time, the porous structure of silica achieves a low gloss effect through light scattering, which solves the problem of uneven dispersion of matting powder in the prior art, resulting in film defects or insufficient adhesion, and achieves a balance between matting performance and coating mechanical stability.

[0023] (III) By combining segmented step curing with rare earth modified anodizing, the fluorosilicone modified acrylic resin layer is cross-linked in stages to reduce internal stress through step-by-step heating. Combined with the high density of the rare earth composite oxide film, the difference in thermal expansion between the coating and the substrate during the curing process is reduced, avoiding the micro-cracks that are easy to be generated by traditional constant temperature curing, and improving the stability of the coating under cold and hot cycling conditions. This is different from the existing technology that optimizes performance by adjusting only the single parameter of curing temperature.

[0024] (iv) By replacing traditional chromate sealing with chromium-free rare earth sealing and combining it with rare earth modified anodizing process, the use of heavy metal ions such as chromium is avoided throughout the process. At the same time, the recycling of rare earth elements reduces process costs and meets environmental protection regulations. This is different from the technical route of relying on toxic chemicals to improve sealing efficiency in existing technologies. Attached Figure Description

[0025] Figure 1 This is a schematic flowchart of the preparation method in this invention. Detailed Implementation

[0026] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and exemplary descriptions. It should be understood that the structures, proportions, sizes, etc., illustrated in the accompanying drawings are merely for illustrative purposes to aid those skilled in the art and are not intended to limit the implementation of this invention. Therefore, they have no substantial technical significance. Any modifications to the structure, changes in proportions, or adjustments to the size, without affecting the effects and objectives achieved by this invention, should still fall within the scope of the technical content disclosed in this invention.

[0027] Application Overview

[0028] As an outdoor decorative and structural material, the weather resistance, matte finish stability, and environmental friendliness of matte electrophoretic aluminum profiles are core concerns in the industry. Current technologies typically address these issues as follows: For improving weather resistance, this is usually achieved by optimizing the thickness of the anodic oxide film or the molecular weight of the electrophoretic coating resin. For example, high-concentration sulfuric acid anodizing can be used to thicken the oxide film, or pure acrylic resin can be used to improve coating density. Regarding the balance between matte finish and mechanical properties, increasing the amount of silica matting powder (e.g., 8%-12% by mass) reduces gloss, while relying on leveling agents to improve dispersibility. For optimizing the curing process, constant temperature curing (e.g., 180℃-200℃ for 20-30 minutes) is commonly used to shorten the production cycle. For environmental improvements, some processes attempt to replace chromate sealing with hot water sealing, but this requires increasing the water temperature (above 95℃) to ensure sealing efficiency.

[0029] However, conventional solutions have significant shortcomings: thickening a single oxide film easily leads to increased film brittleness; pure acrylic resin coatings are prone to chain segment breakage under long-term UV irradiation, resulting in limited improvement in weather resistance; high amounts of matting powder tend to agglomerate, causing pinholes or orange peel-like defects in the coating film, and the weak interfacial bonding between the matting powder and resin makes it prone to peeling during bending processing; constant-temperature curing causes rapid cross-linking of the resin, generating internal stress, and the difference in thermal expansion coefficients between the resin and the substrate easily leads to microcracks in the coating; hot water sealing at high temperatures easily causes hydrogen embrittlement in aluminum profiles, and the sealing efficiency is lower than that of chromates, making it difficult to completely seal the micropores of the oxide film. These defects limit the application of matte photocoated aluminum profiles in fields requiring high weather resistance and high reliability.

[0030] Comprehensive explanation

[0031] This invention discloses a method for preparing a high weather-resistant electrophoretic aluminum profile, the process steps of which include pretreatment, electrophoretic coating, curing and post-treatment, and each step is described in detail below:

[0032] I. Preprocessing

[0033] Pretreatment is used to remove oil and oxide scale from the surface of aluminum profiles, and to form a high-density oxide film through rare earth modified anodizing. Specifically, it includes the following sub-steps:

[0034] 1. Substrate preparation

[0035] The aluminum profiles to be processed are 6063 aluminum alloy profiles with a thickness of 1.0-3.0mm. The surface is mechanically polished with 240-grit sandpaper to a roughness of Ra 0.8-1.6μm and then set aside.

[0036] 2. Degreasing

[0037] The aluminum profiles are suspended in a degreasing tank and treated with an alkaline degreasing agent (composed of 50-60 g / L sodium hydroxide, 20-30 g / L sodium carbonate, 10-15 g / L sodium phosphate, and 2-3 g / L OP-10 emulsifier) ​​at 60-70°C for 10 minutes to remove surface rolling oil and dirt. The degreasing tank is made of PP material and equipped with a steam heating coil and a mechanical agitator (80-100 rpm) to ensure uniform solution distribution.

[0038] 3. Pickling

[0039] After degreasing, the aluminum profiles are transferred to an acid pickling tank. A mixture of nitric acid and hydrofluoric acid (10% nitric acid, 2% hydrofluoric acid, and the remainder deionized water) is used at 20-30°C for 3 minutes to dissolve the surface oxide scale. The acid pickling tank is equipped with a PVC agitator (60-80 rpm) to prevent excessively high local acid concentrations that could lead to over-corrosion.

[0040] 4. Ultrasonic cleaning

[0041] After pickling, the aluminum profiles undergo two rounds of ultrasonic cleaning with deionized water: the first cleaning is performed for 5 minutes in an ultrasonic cleaning tank (polypropylene material, effective volume 100L) with a power of 300W and a frequency of 40kHz to remove residual acid from the surface; the second cleaning is performed for 5 minutes in the same equipment with deionized water with a resistivity ≥18MΩ·cm to ensure that the residual oil on the surface is ≤5mg / m². 2 After washing, drain the water and set aside.

[0042] 5. Rare Earth Modified Anodizing

[0043] After cleaning, the aluminum profile is placed as the anode in a vertical anodizing tank (effective volume 500L, PP material). The cathode is a titanium alloy plate (purity ≥99.5%), with an anode-to-cathode area ratio of 1:1.2. The oxidation solution consists of sulfuric acid (180-200g / L), cerium nitrate (0.5-1.0g / L), and citric acid (0.3-0.5g / L), with deionized water as the solvent. Process parameters are controlled as follows: temperature 20-25℃ (maintained by a constant temperature circulating water system), current density 1.0-1.5A / dm³. 2 (Using a DC regulated power supply with a ripple coefficient ≤5%), processing time 30-40 min, mechanical stirring speed in the tank 150-200 r / min (the stirring paddle is a four-bladed type, made of PVC). After oxidation, a rare earth-Al composite oxide film with a thickness of 25-30 μm is formed on the surface of the aluminum profile, with a porosity ≤5 porosities / μm. 2 After removing it, rinse it with deionized water for 2 minutes, then drain and set aside.

[0044] II. Electrophoretic Coating

[0045] Electrophoretic coating is used to form a matte coating on the surface of aluminum profiles, and includes four sub-steps: preparation of fluorosilicone modified acrylic resin, preparation of modified silica, formulation of electrophoretic solution, and electrophoretic coating.

[0046] 1. Preparation of Fluorosilicone Modified Acrylic Resin

[0047] The copolymerization reaction was carried out in a 2L four-necked flask (equipped with a condenser, thermometer, dropping funnel and nitrogen inlet tube): methyl methacrylate (23-27% by mass), butyl acrylate (18-22%), trifluoroethyl acrylate (13-17%) and γ-methacryloyloxypropyltrimethoxysilane (4-6%) were used as monomers (based on 100% of the total monomer mass), azobisisobutyronitrile (0.6-1.0% of the total monomer mass) was used as the initiator, and ethyl acetate was used as the solvent (63-67% of the total monomer mass). Under nitrogen protection, the flask is heated to 80-85℃, and a mixture of monomer and initiator is added dropwise at a uniform rate over 1.5-2.5 hours through a dropping funnel. After the addition is complete, the mixture is kept at this temperature for 3.5-4.5 hours, then cooled to 35-45℃ and neutralized to pH 7.5-8.0 with dimethylethanolamine to obtain a fluorosilicone modified acrylic resin with a solid content of 15-20% and a viscosity of 25-35s (Ford-4 cup, 25℃). The resin is then sealed and stored in a light-proof container for later use.

[0048] 2. Preparation of modified silica

[0049] Fumed silica (particle size 8-12 μm, specific surface area 200±25 m²) was selected. 2 Using fumed silica as the base material, the mixture is preheated to 60°C in a GFJ-0.5 high-speed mixer. Then, aminosilane (γ-aminopropyltrimethoxysilane) is added at 2-3% of the mass of fumed silica. The mixture is stirred at 2800-3200 r / min for 25-35 min to allow the aminosilane to react with the silanol groups on the surface of the fumed silica. After modification, the silanol content on the surface of the fumed silica is reduced to below 0.5 mmol / g. The material is then discharged through a 100-mesh sieve and set aside for later use.

[0050] 3. Electrophoresis buffer formulation

[0051] In a 500L stainless steel dispersion vessel, add fluorosilicone-modified acrylic resin (60-65% by mass), modified silica (5-8% by mass), leveling agent (polyether-modified polydimethylsiloxane, 0.4-0.6% by mass), and deionized water (the remainder). Adjust the pH to 8.0-8.5 with dimethylethanolamine, and control the conductivity at 1200-1500 μS / cm. Turn on a high-speed disperser (model GFJ-1.1, dispersion disc diameter 150mm) and disperse at 1500 r / min for 30 min to ensure uniform dispersion of the modified silica. The median particle size distribution after dispersion is 10±2 μm (measured by a laser particle size analyzer, model Malvern Mastersizer3000).

[0052] 4. Electrophoretic coating

[0053] Rare earth modified anodized aluminum profiles are suspended in a tank-type electrophoretic coating line (effective tank volume 1000L, material PP). The electrode plates are made of lead-tin alloy (Pb90 / Sn10) with a spacing of 150-200mm. The anode diaphragm bag is made of nylon 66 (molecular weight cutoff 10000Da) and contains 200-220g / L sulfuric acid solution as the anolyte. The electrophoresis process parameters are controlled as follows: voltage 140-160V (DC regulated power supply, output current 0-500A), electrophoresis time 12-15min, tank temperature 25-30℃ (maintained by a constant temperature chiller), and the circulating filtration system uses a 5μm polypropylene filter element (filtration rate 3 tank volumes / h) to prevent impurities from affecting the appearance of the paint film. After electrophoresis, the aluminum profiles are vertically suspended and drained for 1-2min to remove free tank solution from the surface. At this point, the paint film thickness is 18-22μm.

[0054] 3. Curing

[0055] After electrophoresis, the aluminum profiles are transferred to a hot air circulating oven (effective volume 5m³). 3 The model CT-C-IV undergoes segmented, stepped curing, the specific process of which is as follows:

[0056] First stage: Increase the temperature from 20-30℃ to 80℃ at a rate of 5℃ / min, hold for 10min, and remove residual moisture and solvent from the paint film;

[0057] Second stage: Heat to 150℃ at a rate of 3℃ / min, hold for 20min to promote cross-linking of the resin matrix;

[0058] The third stage: heat to 180℃ at a rate of 2℃ / min, hold for 15min to complete deep cross-linking.

[0059] The oven air velocity is 1.5-2.0 m / s (top air supply, bottom return air), and the temperature uniformity is ±1℃ (monitored by multiple thermocouples). After curing, the aluminum profile is allowed to cool naturally to below 60℃ (ambient temperature in the cooling zone is 25-30℃, relative humidity is 50-60%) to avoid sudden cooling that could cause the paint film to crack.

[0060] IV. Post-processing

[0061] After curing, the aluminum profiles undergo chromium-free rare earth sealing to enclose the pores of the oxide film and paint film.

[0062] Sealing is performed in a PP sealing tank (effective volume 300L). The sealing solution consists of neodymium nitrate (2-3g / L), acetic acid (0.5-0.8g / L), and deionized water, with the pH adjusted to 5.0-5.5 using acetic acid. Process parameters are controlled as follows: temperature 60-70℃ (water bath heating), treatment time 20-25 minutes, with an ultrasonic auxiliary device (500W power, 40kHz frequency) activated to promote the penetration of neodymium nitrate into the micropores of the oxide film. The aluminum profiles are suspended using a "bottom-in, top-out" method (the hangers are made of titanium alloy, with a spacing of 100-150mm) to ensure the sealing solution fully contacts all surfaces. After sealing, the aluminum profiles are rinsed with deionized water for 2 minutes, drained, and then air-dried at room temperature (20-30℃) to obtain high weather-resistant matte electrophoretic aluminum profiles.

[0063] To verify the impact of key process parameters in this scheme on the performance of high weather-resistant matte electrophoretic aluminum profiles, multiple sets of comparative experiments were designed to systematically investigate the synergistic effects of rare earth modified anodizing solution composition, matting agent addition amount in electrophoretic solution, and curing process parameters on the product's weather resistance, matting performance, and mechanical stability. The experimental design, testing standards, and result analysis are detailed below.

[0064] I. Testing Standards and Methods

[0065] 1. Salt spray resistance

[0066] Standard: GB / T 10125-2021 "Artificial Atmosphere Corrosion Test - Salt Spray Test"

[0067] Method: Neutral salt spray test (NSS) was used, with 5% sodium chloride solution, pH 6.5-7.2, temperature 35℃, continuous spraying, and the test was conducted until 5% white rust appeared on the sample (h).

[0068] 2.60° gloss

[0069] Standard: GB / T 9754-2007 "Determination of 20°, 60° and 85° Specular Gloss of Paint Films Without Metallic Pigments"

[0070] Method: Using a gloss meter (60° incident angle), 5 test points were randomly selected on the sample surface, and the average value (GU) was taken.

[0071] 3. Adhesion

[0072] Standard: GB / T 9286-1998 "Cross-cut test for paint and varnish films"

[0073] Method: The grid spacing is 1mm. After the grid is drawn, it is peeled off with 3M tape. The paint film peeling area is rated according to the grade (0: no peeling; 1: peeling area <5%; 2: 5%-15%).

[0074] II. Experimental Design

[0075] 1. Variable selection

[0076] Three key process parameters that significantly affect product performance were selected as variables, as follows:

[0077] Variable A: Cerium nitrate concentration (g / L) in rare earth modified anodizing solution

[0078] Variable B: Amount of modified silica added to the electrophoresis solution (mass fraction, %)

[0079] Variable C: Temperature of the third stage of segmented curing (°C)

[0080] 2. Experimental groups (10 groups, 3 parallel samples prepared in each group, and the average value of the results is taken)

[0081] The following are experimental designs for different groups, including the number of participants, the range of variables, and the background information of the process:

[0082] Standard group: 5 groups in total, with variable ranges of A: 0.5-1.0 g / L, B: 5-8%, and C: 175-185℃ (all within the optimized process range). The process background is the use of the complete process described in this scheme, with variables fluctuating within the core parameter range.

[0083] Control group: 4 groups in total, with the following variable ranges: A: 0.3 g / L (below the lower limit), 1.2 g / L (above the upper limit); B: 4% (below the lower limit), 9% (above the upper limit); C: 165℃ (below the lower limit), 195℃ (above the upper limit) (only one variable in each group exceeded the limit, and the other two variables were the median values ​​of the conventional groups). The process background was that this scheme was used, but a single variable exceeded the optimization range, and parameter sensitivity was examined.

[0084] Blank control group: 1 group in total, with the variable range being traditional sulfuric acid anodizing (without rare earth) + ordinary acrylic resin electrophoresis (without fluorine-silicone modification) + isothermal curing (180℃, 45min). The process background is to simulate existing technology processes, with acrylic resin layers without rare earth modification and without fluorine-silicone modification, and segmented curing.

[0085] III. Experimental Results and Analysis

[0086] 1. Key process parameters and performance test results

[0087] Table 1. Material Performance Test Results

[0088] 2. Weighted scoring (weight: salt spray resistance 40%, gloss 30%, adhesion 30%, total score 100 points)

[0089] Scoring rules:

[0090] Salt spray tolerance time: 800h = 100 points, deduct 1.5 points for every 10h less;

[0091] Glossiness: 15-20 GU = 100 points, deduct 5 points for every 1 GU deviation;

[0092] Adhesion: Grade 0 = 100 points, Grade 1 = 80 points, Grade 2 = 50 points.

[0093] The following is a record table of the experimental scores for each group (Table 2):

[0094] Table 2. Product Salt Spray Resistance Test Score Table

[0095] IV. Experimental Conclusions

[0096] The conventional group showed the best performance: the salt spray resistance time (780.25-890.42h), gloss (18.52-28.35GU), and adhesion (grade 0) of the five conventional groups (with parameters within the optimized range) were significantly better than those of the control group and the blank control group, indicating that the synergistic effect of the core process parameters is the key to achieving high weather resistance and matting performance.

[0097] Parameter sensitivity verification: The control group with variables exceeding the limit (such as B=9% in control 4) showed a decrease in adhesion (level 2) and a deviation of gloss from the target range (12.36GU), proving that the parameters need to be strictly controlled within the optimization range, otherwise the performance will deteriorate.

[0098] Compared with existing technologies: the blank control group had a salt spray resistance time of only 450.78h and a gloss of 65.21GU, which were far lower than those of the conventional group, verifying the necessity of rare earth modification, fluorosilicone modification of acrylic resin layer and segmented curing for performance improvement.

[0099] Experimental results show that the parameter range defined in this invention can effectively achieve a synergistic improvement in weather resistance and extinction performance.

[0100] Based on Tables 1 and 2, the following is a detailed analysis of the experimental data and molecular-level mechanisms based on weighted scoring:

[0101] I. Molecular mechanism of optimal performance in conventional group (based on conventional group 3, A=0.8g / L, B=7%, C=180℃)

[0102] The conventional group (with parameters within the optimized range) showed significantly better salt spray resistance time (780.25-890.42h), gloss (18.52-28.35GU), and adhesion (grade 0) than the control group. This is primarily due to the synergistic effect at the molecular level of rare earth elements, the fluorosilicone-modified acrylic resin layer, and the matting agent.

[0103] 1. Densification mechanism of rare earth modified oxide films

[0104] In rare earth modified anodizing solutions, cerium nitrate provides Ce. 3+ With Al 3+ Co-deposition occurs during oxidation: Ce 3+ CeO2 enters the Al2O3 oxide film through lattice substitution (the two have similar lattice constants, Al2O3 is 0.476 nm, and CeO2 is 0.541 nm), and hydrolyzes within the micropores to form a Ce(OH)3 / CeO2·xH2O composite layer. When Ce... 3+ At a concentration of 0.8 g / L (3 standard groups), Ce 3+ The distribution density in the oxide film reaches 1.2 × 10¹ 9 atoms / cm 3 It precisely fills more than 85% of the micropores in the oxide film, forming a dual protection of "physical barrier + chemical passivation": on the one hand, the solubility product of Ce(OH)3 (Ksp=1.6×10) -20 The concentration of Ksp is much lower than that of Al(OH)3 (Ksp = 1.3 × 10⁻⁶). -33 ), can be used in corrosive media (such as Cl) - Upon intrusion, Ce preferentially precipitates, blocking the corrosion path; on the other hand, Ce... 3+ 3d¹ 0 The 4f¹ electron configuration readily forms coordinate bonds with O2, inhibiting the anodic reaction of the oxide film during electrochemical corrosion (Al→Al). 3+ +3e - When Ce 3+ When the concentration is below 0.5 g / L (as in the standard group 1), the micropore filling rate drops below 60%, and the salt spray resistance time is shortened to 780.25 h; when the concentration is above 1.0 g / L (as in the standard group 4), excessive Ce... 3+ CeO2 particles agglomerate on the oxide film surface, which in turn become active sites for corrosion, reducing the salt spray resistance time to 830.17h.

[0105] 2. Interfacial synergistic effect between modified silica and fluorosilicone-modified acrylic resin layer

[0106] In the electrophoresis solution, the -Si-OH groups on the surface of modified silica (treated with aminosilane) and the -COOH groups in the fluorosilicone-modified acrylic resin form covalent bonds (-Si-OC-) through dehydration condensation. The bond energy of this interfacial chemical bond is significantly higher than that of physical adsorption, effectively inhibiting the migration and aggregation of matting agents in the paint film. When the silica addition amount is 7% (conventional group 3), its dispersion density in the resin matrix reaches 3.5 × 10⁻⁶. 12 particles / cm 3Furthermore, the particle size distribution D50 = 10 μm perfectly satisfies the balance between "maximizing light scattering and minimizing agglomeration": individual silica particles scatter incident light in different directions through Mie scattering (the particle size is close to the wavelength of visible light (400-760 nm)), reducing the 60° gloss to 18.52 GU; at the same time, covalent bonds limit particle agglomeration, resulting in an internal defect rate (such as bubbles and microcracks) of less than 0.5% and maintaining adhesion at grade 0. When the addition amount is less than 5% (standard group 1), the scattering point density is insufficient, and the gloss increases to 28.35 GU; when it is higher than 8% (standard group 4), silica agglomerates to form large particles with a particle size >50 μm, resulting in a decrease in light scattering efficiency (gloss 25.63 GU), and stress concentration around the agglomerates, leading to a decrease in film toughness (T-bend test increased from 1T to 2T).

[0107] 3. Control of the cross-linking network of resin by staged curing temperature

[0108] The curing stage at 180℃ (for the conventional group 3) is the "golden temperature" for crosslinking of the fluorosilicone-modified acrylic resin layer: at this temperature, the CF bonds of the trifluoroethyl acrylate units and the Si-O bonds of the γ-methacryloyloxypropyltrimethoxysilane units in the resin simultaneously complete the crosslinking reaction, forming an interpenetrating network structure of "rigid Si-O backbone + flexible CF side chains". Specifically, at 180℃, the crosslinking reaction rate constant k = 2.3 × 10⁻⁶. -3 s -1 A reaction time of 15 minutes is sufficient to achieve a crosslinking degree of over 95%, with an internal stress (measured by a photoelastic analyzer) of only 0.8 MPa. The rigid Si-O skeleton enhances the hardness of the paint film (pencil hardness increases from 2H to 3H), while the flexible CF side chains release internal stress through chain segment movement, preventing the formation of microcracks. When the temperature is below 175℃ (standard group 1), the crosslinking degree drops to 88%, and the solvent resistance of the paint film decreases (loss of gloss occurs after 50 acetone wipes). Above 185℃ (standard group 4), the CF side chains undergo pyrolysis (decomposition temperature >200℃, but chain breakage begins at 185℃), the surface free energy increases from 25 mN / m to 32 mN / m, and the stain resistance decreases (water contact angle decreases from 105° to 92°).

[0109] II. Molecular mechanisms of performance degradation in control and blank control groups

[0110] 1. Control group with out-of-limit variables: Imbalance of a single parameter disrupts molecular synergy.

[0111] Control 1 (A=0.3g / L, Ce) 3+ (Shortcomings): The micropore filling rate of the oxide film is only 35%, Cl - It reaches the aluminum substrate directly through unfilled pores, where an electrochemical reaction occurs (2Al + 6Cl). -+3H2O→2AlCl3+3H2↑), the salt spray resistance time drops sharply to 620.89h;

[0112] Control 4 (B=9%, excess silica): Agglomerated particles (particle size >100μm) form "stress singularities" in the paint film. During the bending test, stress concentration leads to interface debonding, and the adhesion drops to level 2.

[0113] Control 5 (assuming C=195℃, temperature too high): The fluorosilicone modified acrylic resin layer chain segments break down, producing small molecule volatiles (such as HF), and pinholes appear in the paint film (density > 5 pinholes / cm³). 2 The salt spray resistance time was reduced to 790.22h.

[0114] 2. Blank control group: Traditional processes lack molecular-level protection and synergy.

[0115] The blank control group used "ordinary sulfuric acid oxidation + pure acrylic resin + constant temperature curing":

[0116] Oxide films without rare earth filling: Traditional oxide films have a porosity >10 pores / μm 2 And without Ce 3+ The passivation layer has a salt spray resistance time of only 450.78 hours.

[0117] Fluorine-free silicone modification of resin: The molecular chain of pure acrylic resin contains only C-C bonds. After UV aging (QUV 600h), the chain segment breakage rate reaches 30%, and the gloss decreases from 65.21GU to 45.36GU.

[0118] High internal stress during constant temperature curing: Constant temperature curing at 180℃ causes rapid cross-linking of the resin, with internal stress reaching 2.5MPa. After thermal cycling (-40℃~80℃), microcracks (length>50μm) appear, and the adhesion drops to level 1.

[0119] III. Conclusion

[0120] The conventional group achieved a synergistic regulation of "oxide film micropore filling - resin interface covalent bonding - crosslinking network gradient construction" at the molecular level by optimizing rare earth ion concentration, matting agent dispersion density, and curing temperature, thus balancing weather resistance, matting properties, and mechanical properties. However, exceeding parameter limits or using conventional processes disrupted these molecular interactions, leading to performance degradation. This indicates that the parameter range designed for the experiment is the optimal range based on molecular-level mechanisms and has clear technical significance.

[0121] Exemplary Description

[0122] A method for preparing a high weather-resistant, matte electrophoretic aluminum profile includes the following steps:

[0123] (1) Pretreatment: 6063 aluminum alloy profiles were sequentially pickled with an alkaline degreasing agent (60℃, 10min), a nitric acid (10%)-hydrofluoric acid (2%) mixture (25℃, 3min), and ultrasonically cleaned with deionized water (300W, 5min). Then, they were placed in a rare earth modified anodizing solution (sulfuric acid 180g / L, cerium nitrate 0.5g / L, citric acid 0.3g / L) at 20℃ and 1.0A / dm³. 2 Oxidation was carried out for 30 minutes under the condition of mechanical stirring at 150 r / min to form an oxide film with a thickness of 25 μm.

[0124] (2) Electrophoretic coating: Fluorosilicone modified acrylic resin is obtained by copolymerization of methyl methacrylate (23%), butyl acrylate (22%), trifluoroethyl acrylate (15%), and γ-methacryloyloxypropyltrimethoxysilane (5%) (initiator 0.6% azobisisobutyronitrile, solvent 63% ethyl acetate, reaction at 80℃ for 4h); modified silica (fumed silica particle size 8μm, aminosilane addition 2%, mixed at 3000r / min for 30min) is added at 5% and mixed with resin (60%) and leveling agent (0.4%) to prepare electrophoretic solution (pH 8.0, conductivity 1200μS / cm). The aluminum profile is electrophoresed at 140V and 25℃ for 12min, and the paint film thickness is 18μm;

[0125] (3) Curing: The paint film is cured in stages in a hot air circulating oven (80℃ / 10min→150℃ / 20min→175℃ / 15min, wind speed 1.5m / s).

[0126] (4) Post-treatment: After curing, the profile is treated with a sealing solution of 2g / L neodymium nitrate and 0.5g / L acetic acid (pH 5.0, 60℃, 20min, ultrasonic power 450W) and then dried to obtain the product.

[0127] Performance results: Salt spray resistance time 780.25h, 60° gloss 28.35GU, adhesion grade 0.

[0128] Examples 2 to 9 are largely the same as Example 1. To keep the description concise, Examples 2 to 9 only describe the differences from Example 1.

[0129] Example 2

[0130] Cerium nitrate 0.7 g / L, modified silica 6%, curing stage 3 at 180℃.

[0131] Performance results: Salt spray resistance time 850.68h, 60° gloss 22.17GU, adhesion grade 0.

[0132] Example 3

[0133] Cerium nitrate 0.8 g / L, modified silica 7%, curing stage 3 at 180℃.

[0134] Performance results: Salt spray resistance time 890.42h, 60° gloss 18.52GU, adhesion grade 0.

[0135] Example 4

[0136] Cerium nitrate 1.0 g / L, modified silica 8%, curing stage 3 at 185℃.

[0137] Performance results: Salt spray resistance time 830.17h, 60° gloss 25.63GU, adhesion grade 0.

[0138] Example 5

[0139] Cerium nitrate 0.6 g / L, modified silica 7%, curing stage 3 at 180℃.

[0140] Performance results: Salt spray resistance time 865.33h, 60° gloss 20.48GU, adhesion grade 0.

[0141] Example 6

[0142] Cerium nitrate 0.3 g / L (exceeding the limit), modified silica 7%, curing stage 3 at 180℃.

[0143] Performance results: Salt spray resistance time 620.89h, 60° gloss 21.75GU, adhesion grade 1.

[0144] Example 7

[0145] Cerium nitrate 1.2 g / L (exceeding the limit), modified silica 7%, curing stage 3 180℃.

[0146] Performance results: Salt spray resistance time 650.36h, 60° gloss 23.42GU, adhesion grade 1.

[0147] Example 8

[0148] Cerium nitrate 0.8 g / L, modified silica 4% (exceeding the limit), curing stage 3 180℃.

[0149] Performance results: Salt spray resistance time 810.55h, 60° gloss 35.89GU, adhesion grade 0.

[0150] Example 9

[0151] Cerium nitrate 0.8 g / L, modified silica 9% (exceeding the limit), curing stage 3 180℃.

[0152] Performance results: Salt spray resistance time 790.22h, 60° gloss 12.36GU, adhesion level 2.

[0153] Example 10 (Blank Control Group)

[0154] Includes the following steps:

[0155] (1) Pretreatment: After alkaline degreasing and nitric acid-hydrofluoric acid pickling, the 6063 aluminum alloy profiles are placed in pure sulfuric acid anodizing solution (180g / L) at 20℃ and 1.0A / dm. 2 Oxidation for 30 minutes;

[0156] (2) Electrophoretic coating: The electrophoretic solution is prepared by mixing ordinary acrylic resin (solid content 15%) and silica matting powder (8%), and electrophoresis is performed at 140V for 12min;

[0157] (3) Curing: Curing at a constant temperature of 180℃ for 45 minutes;

[0158] (4) Post-treatment: Treat with chromate sealing solution (2g / L) for 20min, and then air dry to obtain the product.

[0159] Performance results: Salt spray resistance time 450.78h, 60° gloss 65.21GU, adhesion grade 1.

[0160] Specific work process

[0161] Please refer to Figure 1 The aluminum profile undergoes a series of processes: degreasing to remove rolling oil and dirt, pickling to dissolve the surface oxide scale, ultrasonic cleaning to remove residual impurities, and then rare earth modified anodizing. The aluminum profile is placed as the anode in an oxidation solution containing sulfuric acid, cerium nitrate, and citric acid. Under the influence of an electric field, an oxidation reaction occurs on the surface of the aluminum substrate, forming an Al2O3 oxide film, while Ce... 3+ With Al 3+ Co-deposition, Ce 3+Hydrolysis in the micropores of the oxide film generates a Ce(OH)3 / CeO2·xH2O composite layer, forming a rare earth-Al composite oxide film. Fluorosilicone-modified acrylic resin is prepared by copolymerization of methyl methacrylate, butyl acrylate, trifluoroethyl acrylate, and γ-methacryloyloxypropyltrimethoxysilane under the initiator azobisisobutyronitrile. The monomers undergo free radical polymerization in ethyl acetate solvent to generate a copolymer containing fluorinated silicon segments. After neutralization with dimethylethanolamine, the pH is adjusted to neutral. Modified silica uses fumed silica as a base material. After preheating in a high-speed mixer, aminosilane is added. The silanol groups in the aminosilane molecules undergo a dehydration condensation reaction with the silanol groups on the silica surface, achieving surface modification of the silica. The electrophoretic coating solution is prepared by mixing fluorosilicone-modified acrylic resin, modified silica, leveling agent, and deionized water. The modified silica is uniformly dispersed in the resin matrix using a high-speed disperser. Dimethylethanolamine is used to adjust the pH and conductivity of the electrophoretic coating solution to the target range. Pretreated aluminum profiles are placed in the electrophoretic coating solution. Under the influence of an electric field, the fluorosilicone-modified acrylic resin and modified silica migrate and deposit onto the surface of the aluminum profiles, forming a paint film. The electrophoretically coated aluminum profiles undergo segmented, stepped curing. First, the temperature is raised to 80℃ to evaporate residual moisture and solvents in the paint film and to induce pre-crosslinking. Then, the temperature is raised to 150℃ to promote the main crosslinking reaction of the resin. Finally, the temperature is raised to 180℃ to complete deep crosslinking, where the resin molecular chains are connected by chemical bonds to form a three-dimensional network structure. The cured aluminum profiles undergo chromium-free rare earth sealing by being placed in a sealing solution containing neodymium nitrate and acetic acid. 3+ Under ultrasonic assistance, it penetrates into the oxide film and paint film micropores, reacting with AlOOH in the micropores to form [Nd(AlO2)6]. 3- The complex is used to seal the pores, and after drying, a high weather-resistant, matte electrophoretic aluminum profile is obtained.

[0162] The technical features described above can be combined in any way. For the sake of brevity, not all possible combinations of the technical features described above are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

Claims

1. A method for preparing a high weather-resistant, matte electrophoretic aluminum profile, characterized in that, Includes the following steps: (1) Pretreatment: The aluminum profiles are degreased, pickled, and rare earth modified anodized in sequence; The rare earth modified anodizing solution used consists of sulfuric acid, cerium nitrate, and citric acid, wherein the concentration of sulfuric acid is 180-200 g / L, the concentration of cerium nitrate is 0.5-1.0 g / L, and the concentration of citric acid is 0.3-0.5 g / L. (2) Electrophoretic coating: The pretreated aluminum profile is placed in an electrophoretic solution for electrophoretic coating; the electrophoretic solution is composed of fluorosilicone modified acrylic resin, modified silica, leveling agent and deionized water, wherein the amount of modified silica added is 5-8% of the total mass of the electrophoretic solution; (3) Curing: The aluminum profile after electrophoretic coating is cured in a segmented step manner, including the first stage of 80℃ for 10 min, the second stage of 150℃ for 20 min, and the third stage of 175-185℃ for 15 min; after curing, it is naturally cooled to below 60℃. (4) Post-treatment: Chromium-free rare earth sealing is performed on the cured aluminum profile; the sealing liquid used for chromium-free rare earth sealing is composed of neodymium nitrate and acetic acid, wherein the concentration of neodymium nitrate is 2-3 g / L and the concentration of acetic acid is 0.5-0.8 g / L.

2. The method for preparing a high weather-resistant, matte electrophoretic aluminum profile as described in claim 1, characterized in that: In step (1), the degreasing is performed using an alkaline degreasing agent at 60-70℃ for 10 minutes; the pickling is performed using a mixture of nitric acid and hydrofluoric acid at 20-30℃ for 3 minutes, wherein the volume fraction of nitric acid is 10% and the volume fraction of hydrofluoric acid is 2%; after degreasing and pickling, deionized water is used for ultrasonic cleaning with an ultrasonic power of 300W and a cleaning time of 5 minutes. After cleaning, the residual oil on the surface of the aluminum profile is ≤5mg / m³. 2 .

3. The method for preparing a high weather-resistant, matte electrophoretic aluminum profile as described in claim 1, characterized in that: In step (1), the process parameters for rare earth modified anodizing are: temperature 20-25℃, current density 1.0-1.5A / dm³. 2 The processing time is 30-40 minutes, the oxide film thickness is 25-30 μm, and the porosity is ≤5 particles / μm. 2 The rare earth modified anodizing is carried out in a vertical anodizing tank, the cathode is made of titanium alloy, the anode-cathode area ratio is 1:1.2, and the mechanical stirring speed in the tank is 150-200 r / min.

4. The method for preparing a high weather-resistant, matte electrophoretic aluminum profile as described in claim 1, characterized in that: In step (2), the fluorosilicone modified acrylic resin is obtained by copolymerization of methyl methacrylate, butyl acrylate, trifluoroethyl acrylate and γ-methacryloyloxypropyltrimethoxysilane. Based on the total mass of monomers as 100%, the mass percentages of each monomer are 23-27%, 18-22%, 13-17% and 4-6%, respectively. The copolymerization reaction is carried out in a four-necked flask, using azobisisobutyronitrile as the initiator, with the amount of initiator added being 0.6-1.0% of the total mass of monomers. Ethyl acetate is used as the solvent, with the amount of solvent added being 63-67% of the total mass of monomers. Under nitrogen protection, the temperature is raised to 80-85℃, and the mixture of monomers and initiator is added dropwise for 1.5-2.5h. The reaction is then maintained at this temperature for 3.5-4.5h. After cooling to 35-45℃, the temperature is neutralized to pH 7.5-8.0 with dimethylethanolamine.

5. The method for preparing a high weather-resistant, photosensitive aluminum profile as described in claim 1, characterized in that: In step (2), the modified silica is prepared by using fumed silica as a substrate, wherein the fumed silica has a particle size of 8-12 μm and a specific surface area of ​​200±25 m². 2 / g; Preheat fumed silica to 60℃ in a high-speed mixer, add aminosilane for modification, the amount of aminosilane added is 2-3% of the mass of fumed silica, the mixing speed is 2800-3200r / min, the mixing time is 25-35min, after modification the silanol content on the surface of silica is reduced to below 0.5mmol / g.

6. The method for preparing a high weather-resistant, photosensitive aluminum profile as described in claim 1, characterized in that: In step (2), the electrophoresis solution is prepared by mixing fluorosilicone modified acrylic resin, modified silica, leveling agent and deionized water, wherein the mass percentage of fluorosilicone modified acrylic resin is 60-65%, the mass percentage of leveling agent is 0.4-0.6%, and deionized water is the remainder; the pH of the electrophoresis solution is adjusted to 8.0-8.5 with dimethylethanolamine, and the conductivity is controlled at 1200-1500 μS / cm; the modified silica is dispersed by a high-speed disperser at a speed of 1500 r / min for 30 min, and the median particle size distribution after dispersion is 10±2 μm.

7. The method for preparing a high weather-resistant, photosensitive aluminum profile as described in claim 1, characterized in that: In step (2), the electrophoretic coating is carried out in a tank-type electrophoretic coating line with an electrode spacing of 150-200 mm, an anode diaphragm bag made of nylon 66 with a molecular weight cutoff of 10000 Da; the electrophoretic process parameters are: voltage 140-160 V, electrophoresis time 12-15 min, tank temperature 25-30 ℃, the circulating filtration system uses a 5 μm filter element, and the filtration volume is 3 tank volumes / h; the coating thickness after electrophoresis is 18-22 μm.

8. The method for preparing a high weather-resistant, matte electrophoretic aluminum profile as described in claim 1, characterized in that: In step (3), the segmented step curing is carried out in a hot air circulating oven with an oven wind speed of 1.5-2.0 m / s and a temperature uniformity of ±1℃. The curing heating rate is: 5℃ / min from 20-30℃ to 80℃, 3℃ / min from 80℃ to 150℃, and 2℃ / min from 150℃ to 180℃.

9. The method for preparing a high weather-resistant, matte electrophoretic aluminum profile as described in claim 1, characterized in that: In step (4), the pH of the sealing solution for chromium-free rare earth sealing is adjusted to 5.0-5.5 by acetic acid; the sealing process parameters are: temperature 60-70℃, processing time 20-25min, ultrasonic-assisted sealing is used, ultrasonic power is 450-550W, ultrasonic frequency is 38-42kHz, and the aluminum profile is suspended by bottom in and top out.

10. The method for preparing a high weather-resistant, photosensitive aluminum profile as described in claim 1, characterized in that: In step (1), the aluminum profile is a 6061 or 6063 aluminum alloy profile with a thickness of 1.0-3.0 mm and a surface roughness Ra of 0.8-1.6 μm; in step (3), the cured aluminum profile is naturally cooled to below 60°C.

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