Anti-sagging and anti-cracking 6005 aluminum alloy water-based epoxy resin coating and preparation method thereof

Abstract

This invention discloses a water-based epoxy resin coating for 6005 aluminum alloy that prevents sagging and cracking, and its preparation method. The coating is a two-component system. Component A contains water-based epoxy resin emulsion, CTBN-modified toughening resin, composite anti-rust pigments, flake-shaped shielding fillers, and compounded thixotropic rheology agents, etc. Component B is a water-based amine curing agent. This coating can solve the sagging and cracking problems of existing coatings on 6005 aluminum alloy, achieving a coating adhesion grade of 0, a neutral salt spray test of ≥900h, and VOC ≤42g / L. It meets the stringent protection requirements of 6005 aluminum alloy and has excellent prospects for industrial application.

Description

Technical Field

[0001] This invention belongs to the field of coating technology, specifically relating to a water-based epoxy resin coating for 6005 aluminum alloy that prevents sagging and cracking, and its preparation method. This coating is used on 6005 aluminum alloy components that have stringent requirements for surface smoothness, adhesion, toughness and corrosion resistance, and is especially suitable for high-end industrial fields such as photovoltaic brackets, rail transit, and automobile manufacturing. Background Technology

[0002] Aluminum alloys, with their core advantages of being lightweight, high-strength, and easy to process, have become key structural materials in fields such as photovoltaic brackets, rail transportation, automobile manufacturing, electronic equipment, and building curtain walls. Among them, 6005 aluminum alloy, due to its excellent extrusion formability and comprehensive mechanical properties, is particularly widely used in complex structural components. However, compared with ordinary metal materials, the inherent characteristics of 6005 aluminum alloy make its requirements for protective coatings more stringent, which is one of the fundamental reasons why existing coatings are prone to problems such as sagging and cracking.

[0003] From the perspective of material composition, 6005 aluminum alloy typically contains 0.4-0.6% Si and 0.5-0.8% Mg. The effects of these elements on its surface properties include: First, the oxide film is amorphous Al2O3 with a porosity of 5%-8%, which is higher than that of pure aluminum and ordinary carbon steel oxide films, resulting in more complex wetting and spreading behavior of coatings on the surface; Second, the presence of the Mg2Si reinforcing phase in the alloy makes the surface micro-roughness significantly higher than that of ordinary metals, making it easy for coatings to accumulate in micro-depressions and run off at protrusions, thus increasing the risk of sagging; Third, 6005 aluminum alloy is often used in vertical structures or complex cross-section components, and during construction, the coating must overcome both gravity and uneven adsorption on the substrate surface, making sagging control far more difficult than with ordinary metal substrates.

[0004] Waterborne epoxy resin coatings have become the mainstream choice for aluminum alloy protection due to their advantages such as environmental friendliness and strong adhesion. Among them, Type II waterborne epoxy resin emulsions (i.e., nonionic emulsified epoxy resin systems) have advantages such as small emulsion particle size, good storage stability, excellent wetting and dispersibility of pigments and fillers, and broad compatibility with various curing agents. The cured films formed by these emulsions typically have good gloss and fullness. However, the inherent hydrophilic segments and nonionic emulsifiers in Type II waterborne epoxy resin emulsions lead to relatively weak water resistance in the cured film, and also result in higher curing shrinkage stress. Applying Type II waterborne epoxy resin emulsions to 6005 aluminum alloys presents problems such as uncontrolled sag and easy cracking of the coating, leading to a decline in the overall performance of the aluminum alloy. On the one hand, the porous oxide film and micro-roughness caused by the Mg2Si reinforcing phase on the surface of 6005 aluminum alloys result in uneven coating wetting and spreading, and large differences in local adsorption forces. On the other hand, conventional Type II waterborne epoxy resin emulsions lack targeted strong thixotropic structures. When applied to vertical surfaces or complex components, the viscosity of the coating recovers slowly after shearing, making it unable to withstand gravity. This leads to coating accumulation in microscopic depressions and runoff at protrusions, resulting in sagging. Furthermore, the coefficient of thermal expansion of 6005 aluminum alloy is significantly higher than that of epoxy resin coatings. During temperature changes, the difference in expansion and contraction between the two generates substantial interfacial shear stress. The high resin curing shrinkage in Type II waterborne epoxy resin emulsions, combined with the aforementioned thermal stress, results in excessively high internal stress within the coating. The coating exhibits sufficient rigidity but insufficient toughness, making it unable to release and disperse these stresses through plastic deformation. When the coating cracks due to brittleness, the cracks extend to the surface of the aluminum alloy substrate, forming stress concentration points. Under dynamic loads or corrosive environments, this can easily induce fatigue cracks or stress corrosion cracking in the substrate, severely impairing the mechanical properties and durability of the aluminum alloy component. Therefore, developing a high-performance waterborne epoxy coating with synergistic component optimization and balanced performance, tailored to the material characteristics of 6005 aluminum alloy, has become an urgent technical challenge to be solved in this field. Summary of the Invention

[0005] This invention aims to overcome the application bottlenecks of existing waterborne epoxy coatings on 6005 aluminum alloy, addressing core defects such as uncontrolled sag, film cracking, and poor performance. Through component synergistic design and process optimization, it provides a waterborne epoxy resin coating and its preparation method that combine excellent anti-sag properties, high toughness, strong adhesion, and long-term corrosion resistance, to meet the stringent protection requirements of 6005 aluminum alloy and achieve long-term stable use of components in harsh environments.

[0006] The specific technical solution is as follows: A water-based epoxy resin coating for 6005 aluminum alloy that prevents sagging and cracking, the coating being a two-component system consisting of component A and component B; by weight, component A comprises: 40-60 parts water-based epoxy resin emulsion, 5-15 parts toughening modified resin, 10-20 parts composite anti-rust pigment, 5-12 parts flake-shaped shielding filler, 0.5-2.5 parts thixotropic rheology modifier, 0.3-1.2 parts dispersant, 0.1-0.8 parts defoamer, and 10-25 parts deionized water; component B is a water-based amine curing agent; the toughening modified resin is a carboxyl-terminated nitrile rubber modified epoxy resin, and the thixotropic rheology modifier is composed of fumed silica and organobentonite.

[0007] Furthermore, component A comprises the following components: 40-60 parts of waterborne epoxy resin emulsion, 8-12 parts of toughening modified resin, 10-20 parts of composite anti-rust pigment, 10-12 parts of sheet-like shielding filler, 1-2.5 parts of thixotropic rheology modifier, 0.3-1.2 parts of dispersant, 0.1-0.8 parts of defoamer, and 10-25 parts of deionized water. The sheet-like shielding filler is mica iron oxide or sericite with a particle size of 10-15 micrometers.

[0008] Furthermore, in component A, the mass ratio of the aqueous epoxy resin emulsion to the toughening modified resin is 4-6:1, and the mass ratio of the aqueous epoxy resin emulsion to deionized water is 2-6:1.

[0009] Furthermore, in component A, the thixotropic rheology modifier is compounded from fumed silica and organobentonite in a mass ratio of (1-2):(1-2); the viscosity of the coating is adjusted to 800-2000 mPa·s, measured at 25°C using a rotational viscometer.

[0010] Furthermore, the composite anti-rust pigment is composed of zinc phosphate and aluminum tripolyphosphate in a mass ratio of 2:(1-2); before use, the A component and the B component are independent of each other, and before coating, they are mixed according to the mass ratio of A component to B component of 4:(1-2).

[0011] This invention also protects a method for preparing the coating, comprising the following steps: A1: Add the water-based epoxy resin emulsion, toughening modified resin, composite anti-rust pigment, flake shielding filler, thixotropic rheology modifier, dispersant, and defoamer to the high-speed dispersion kettle in sequence according to the formula. A2: Adjust the speed to 1000-1500 rpm and disperse at high speed for 25-35 minutes until the fineness of the slurry is ≤40μm; A3: Reduce the stirring speed to 250-350 rpm, slowly add deionized water, adjust the viscosity of the system, and filter to obtain component A; A4: Mix component A and component B at a mass ratio of 4:(1-2), stir mechanically for 3-8 minutes, and let it mature at room temperature for 10-20 minutes before use.

[0012] This invention also includes a method for processing 6005 aluminum alloy, comprising the following steps: S1: Substrate pretreatment: Control the mass content of each element in 6005 aluminum alloy as follows: Si 0.62-0.65%, Mg 0.55-0.58%, Fe≤0.15%, Mn 0.1-0.2%, Cr≤0.1%, with the balance being aluminum, and the Mg / Si mass ratio is 0.7-0.8; Load the raw materials into the furnace and melt them at 700-750℃, then refine them at 730-750℃ for 10-30 minutes, cast them into φ150-155mm ingots at 690-720℃, then homogenize them at 560-580℃ for 8-12 hours, extrude them at 530-550℃, and after T6 solution treatment + artificial aging, after oxidation treatment and finishing, obtain a substrate with a clean and defect-free surface; S2: Coating spraying: Applying the coating described in any one of claims 1-5 to the surface of the substrate by air spraying, controlling the wet film thickness to be 140-160 μm; S3: Curing treatment: Use room temperature curing or accelerated curing methods to ensure complete film formation of the coating.

[0013] Furthermore, the oxidation process in step S1 specifically includes: alkaline washing, neutralization, oxidation, electrolytic coloring, and sealing. The alkaline washing uses NaOH with a concentration of 80-90 g / L, a temperature of 40-45°C, and a time of 80-90 seconds. The electrolytic coloring uses a colorant concentration of 16-17 g / L and a voltage of 16-17 V. The finishing process includes sawing, punching, and ultrasonic cleaning. The sawing results in a sample length tolerance of ±1.2 mm and a burr height ≤0.2 mm. The punching results in a hole diameter tolerance of ±0.3 mm.

[0014] Furthermore, the curing method for step S3 is as follows: for room temperature curing, cure for 6-8 days at a temperature of 20-25℃ and a relative humidity of 45-55%; for accelerated curing, bake in an oven at 75-85℃ for 1.5-2.5 hours.

[0015] This invention also protects an aluminum alloy product prepared using the aforementioned processing method. The coating performance of the product meets the following requirements: anti-sagging ≥180μm, adhesion grade 0, pencil hardness H-2H, axial rod bending of 1-3mm in flexibility test, and impact resistance ≥45kg. cm, neutral salt spray test ≥900h, VOC content ≤42g / L.

[0016] Beneficial effects First, this invention selects carboxyl-terminated nitrile butadiene rubber (CTBN) modified epoxy resin as the toughening core, a technical feature that endows the coating with excellent crack resistance. The carboxyl groups in the CTBN molecular chain can undergo a ring-opening reaction with the epoxy groups of the epoxy resin, forming an "island" structure after curing—the rubber phase (islands) is uniformly dispersed in the continuous epoxy phase, which can effectively induce crazes and shear bands, absorbing and dispersing curing shrinkage stress and external impact energy. The flexible segments of CTBN can buffer the stress concentration of the rigid epoxy network, improving the fracture toughness of the coating and solving the cracking problem caused by the thermal expansion mismatch between 6005 aluminum alloy and the coating.

[0017] Secondly, the thixotropic rheology modifier composed of fumed silica and organobentonite in this invention constructs a dual network structure. To address the existing problem of coating sagging, fumed silica forms a three-dimensional physical network through hydrogen bonding, while organobentonite enhances structural stability through layer stacking. The synergy of the two enables the coating to spread evenly and quickly set on the micro-rough surface and vertical structure of 6005 aluminum alloy, with an anti-sagging wet film thickness of ≥180μm, meeting the requirements for thick coating construction.

[0018] Furthermore, the synergistic effect of the sheet-like shielding filler and the composite anti-corrosion pigment in this invention achieves long-term corrosion protection. The sheet-like structures of mica iron oxide or sericite are arranged in parallel within the coating, forming a dense physical barrier that prolongs the diffusion path of corrosive media (water, oxygen, chloride ions); the zinc phosphate and aluminum tripolyphosphate in the composite anti-corrosion pigment can react with the Al³⁺ on the substrate surface. + The reaction generates a stable phosphate passivation film. The synergistic effect of both physical shielding and chemical passivation blocks the penetration channels of corrosive media, while the chemical passivation inhibits anodic dissolution of the substrate, resulting in a neutral salt spray test lifespan exceeding 1000 hours, more than double that of conventional coatings.

[0019] Furthermore, this invention achieves a balance between hardness and toughness through precise proportioning of each component. The toughening effect of CTBN in the coating, the stress-dispersing effect of the lamellar filler, and the rigid support effect of the epoxy network work synergistically, avoiding the contradiction of "hardness and toughness being mutually exclusive" in conventional coatings, and adapting to the mechanical performance requirements of 6005 aluminum alloy under complex working conditions.

[0020] Finally, the VOC content of the coating of this invention is ≤42g / L, which is far lower than the national standard (≤80g / L), showing significant environmental advantages; and the adhesion to 6005 aluminum alloy substrate reaches level 0 (GB / T9286-2021), the construction process is simple, and industrial production can be achieved by conventional air spraying.

[0021] In summary, this invention specifically addresses the protection challenges of 6005 aluminum alloy, and its overall performance is superior to existing products, demonstrating high practical value and promising prospects for widespread application. Detailed Implementation

[0022] Preferred embodiments of the present invention will now be described in more detail. While preferred embodiments of the present invention are described below, it should be understood that the invention can be implemented in various forms and should not be limited to the embodiments set forth herein. Where specific techniques or conditions are not specified in the embodiments, they are performed in accordance with techniques or conditions described in the literature in the art or according to the product instructions. Reagents or instruments used, unless otherwise specified, are all commercially available conventional products. In the following embodiments, unless otherwise explicitly stated, "%" refers to weight percentage.

[0023] The aqueous epoxy resin emulsions used in the examples and comparative examples were Type II. In this text, Type II refers to bisphenol A type solid epoxy resin emulsions emulsified with nonionic surfactants, purchased from Hexion, brand name EPI-REZ™ Resin 3522-W-60. The modified polyamide amine curing agent was an aqueous curing agent based on hydrophilic modification of polyamide and epoxy adduct, purchased from Westlake, brand name EPIKURE™ 6870-W-53. The CTBN toughened modified epoxy resin was purchased from Cardolite, brand name NC-547X. The dispersant was a polycarboxylate, purchased from BYK Chemicals, brand name DISPERBYK®-190.

[0024] Table 1. Raw Material Usage Table for Coatings (parts by weight)

[0025] Example 1 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as Si 0.63%, Mg 0.56%, Fe 0.12%, Mn 0.15%, Cr 0.08%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75; aluminum ingots → scrap casting rods → profile scrap are loaded into the furnace in the order of aluminum ingots → scrap casting rods, smelted at 730℃, and refined for 20 minutes at 740℃ with 1.2 kg / ton of refining agent; φ152mm casting rods are cast at 700℃ at a speed of 110 mm / min; homogenization treatment is performed at 570℃ for 10 hours, and the furnace exit temperature is 490℃; the aluminum alloy is processed by a 1500T extruder according to the following steps: after holding at 540℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod, then... The molding time is 18 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are carried out; the sawing length is controlled to a tolerance of +1.0mm (actual length 150mm), the burr height is 0.15mm, the mounting hole is machined by a 16T punch press (hole diameter 4mm, tolerance +0.2mm), and after ultrasonic cleaning, it is inspected according to GB / T1804-2000 C grade tolerance to obtain qualified substrate.

[0026] S2: Coating preparation: According to the raw material dosage in Example 1 in Table 1, 50 parts of waterborne epoxy resin emulsion, 12 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 10 parts of mica iron oxide, 1.8 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 35 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 20 parts of deionized water were slowly added to adjust the viscosity to 1000 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0027] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the above-mentioned substrate using air spraying, and the wet film thickness is controlled at 150μm; it is cured at room temperature for 7 days in a standard environment of 24℃ and 52% relative humidity.

[0028] Example 2 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as follows: Si 0.62%, Mg 0.55%, Fe 0.10%, Mn 0.12%, Cr 0.05%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75. The aluminum ingots are charged into the furnace in the order of aluminum ingots → scrap casting rods → profile scrap. Melting is performed at 720℃, followed by refining at 735℃ with 1.2 kg / ton of refining agent for 20 minutes. A φ152mm casting rod is cast at 695℃ at a speed of 110 mm / min. Homogenization is performed by holding at 570℃ for 10 hours, and the furnace exit temperature is 485℃. The aluminum alloy is processed using a 1500T extruder according to the following steps: after holding at 535℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod. The molding time is 19 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are carried out; the sawing length tolerance is controlled to +0.9mm (actual length 200mm), the burr height is 0.1mm, the mounting hole is machined by 16T punch press (hole diameter 5mm, tolerance +0.2mm), and after ultrasonic cleaning, it is inspected according to GB / T1804-2000 grade C tolerance to obtain qualified substrate.

[0029] S2: Coating preparation: According to the raw material dosage in Example 2 in Table 1, 50 parts of waterborne epoxy resin emulsion, 8 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 12 parts of mica iron oxide, 2.2 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 38 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 20 parts of deionized water were slowly added to adjust the viscosity to 1000 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0030] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the above-mentioned substrate using air spraying method, and the wet film thickness is controlled at 150μm; it is cured at room temperature for 7 days in a standard environment of 22℃ and 48% relative humidity.

[0031] Example 3 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as Si 0.65%, Mg 0.58%, Fe 0.14%, Mn 0.18%, Cr 0.09%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75; aluminum ingots → scrap casting rods → profile scrap are loaded into the furnace in the order of aluminum ingots → scrap casting rods, smelted at 740℃, and refined for 20 minutes at 745℃ with 1.2 kg / ton of refining agent; φ152mm casting rods are cast at 710℃ at a speed of 110 mm / min; homogenization treatment is performed at 570℃ for 10 hours, and the furnace exit temperature is 495℃; the aluminum alloy is processed by a 1500T extruder according to the following steps: after holding at 545℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod, then... The molding time is 17 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are carried out; the sawing length is controlled to a tolerance of +1.1mm (actual length 180mm), the burr height is 0.18mm, and the mounting hole is machined by a 16T punch press (hole diameter 6mm, tolerance +0.3mm). After ultrasonic cleaning, it is inspected according to GB / T1804-2000 C grade tolerance to obtain qualified substrate.

[0032] S2: Coating preparation: According to the raw material dosage in Example 3 in Table 1, 50 parts of waterborne epoxy resin emulsion, 15 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 10 parts of sericite, 1.5 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 32 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 20 parts of deionized water were slowly added to adjust the viscosity to 1000 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0033] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the above-mentioned substrate using air spraying, and the wet film thickness is controlled at 150μm; it is cured at room temperature for 7 days in a standard environment of 23℃ and 50% relative humidity.

[0034] Example 4 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as follows: Si 0.64%, Mg 0.57%, Fe 0.13%, Mn 0.16%, Cr 0.07%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75. The aluminum ingots are charged into the furnace in the order of aluminum ingot → scrap casting rod → profile scrap. Melting is performed at 725℃, followed by refining at 738℃ with 1.2 kg / ton of refining agent for 20 minutes. A φ152mm casting rod is cast at 705℃ at a speed of 110 mm / min. Homogenization is performed by holding at 570℃ for 10 hours, and the furnace exit temperature is 488℃. The aluminum alloy is processed using a 1500T extruder according to the following steps: after holding at 538℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod. The molding time is 20 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are performed; the sawing length is controlled to a tolerance of +0.8mm (actual length 160mm), the burr height is 0.12mm, and the mounting holes are machined on a 16T punch press (hole diameter 3mm, tolerance +0.2mm). After ultrasonic cleaning, the substrate is inspected according to GB / T1804-2000 grade C tolerance to obtain qualified substrate.

[0035] S2: Coating preparation: According to the raw material dosage in Example 4 of Table 1, 40 parts of waterborne epoxy resin emulsion, 10 parts of CTBN modified epoxy resin, 10 parts of composite anti-rust pigment, 8 parts of mica iron oxide, 1.0 part of thixotropic rheology modifier, 0.3 parts of dispersant, and 0.1 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 36 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 10 parts of deionized water were slowly added to adjust the viscosity to 1500 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 30 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0036] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the above-mentioned substrate using an air spraying method, and the wet film thickness is controlled at 150μm; it is cured at room temperature for 7 days in a standard environment of 25℃ and 53% relative humidity.

[0037] Example 5 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as follows: Si 0.63%, Mg 0.56%, Fe 0.11%, Mn 0.14%, Cr 0.06%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75. The aluminum ingots are charged into the furnace in the order of aluminum ingot → scrap casting rod → profile scrap. Melting is performed at 735℃, followed by refining at 742℃ with 1.2 kg / ton of refining agent for 20 minutes. A φ152mm casting rod is cast at 715℃ at a speed of 110 mm / min. Homogenization is performed by holding at 570℃ for 10 hours, and the furnace exit temperature is 492℃. The aluminum alloy is processed using a 1500T extruder according to the following steps: after holding at 542℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod. The molding time is 18 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are carried out; the sawing length is controlled to a tolerance of +1.2mm (actual length 170mm), the burr height is 0.16mm, and the mounting hole is machined by a 16T punch press (hole diameter 5mm, tolerance +0.2mm). After ultrasonic cleaning, it is inspected according to GB / T1804-2000 C grade tolerance to obtain qualified substrate.

[0038] S2: Coating preparation: According to the raw material dosage in Example 5 of Table 1, 60 parts of waterborne epoxy resin emulsion, 10 parts of CTBN modified epoxy resin, 20 parts of composite anti-rust pigment, 10 parts of mica iron oxide, 2.5 parts of thixotropic rheology modifier, 1.2 parts of dispersant, and 0.8 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 34 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 25 parts of deionized water were slowly added to adjust the viscosity to 1500 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 40 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0039] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the substrate using an air spraying method, with the wet film thickness controlled at 150μm; then it is placed in an 80℃ oven for 2 hours to accelerate baking and complete curing.

[0040] Example 6 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as follows: Si 0.62%, Mg 0.57%, Fe 0.12%, Mn 0.13%, Cr 0.08%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75. The aluminum ingots are charged into the furnace in the order of aluminum ingot → scrap casting rod → profile scrap. Melting is performed at 728℃, followed by refining at 736℃ with 1.2 kg / ton of refining agent for 20 minutes. A φ152mm casting rod is cast at 702℃ at a speed of 110 mm / min. Homogenization is performed by holding at 570℃ for 10 hours, and the furnace exit temperature is 486℃. The aluminum alloy is processed using a 1500T extruder according to the following steps: after holding at 536℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod. The molding time is 19 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are performed; the sawing length tolerance is controlled to +0.9mm (actual length 190mm), the burr height is 0.14mm, and the mounting hole is processed by a 16T punch press (hole diameter 4mm, tolerance +0.2mm). After ultrasonic cleaning, it is inspected according to GB / T1804-2000 C grade tolerance to obtain qualified substrate.

[0041] S2: Coating preparation: According to the raw material dosage in Example 6 of Table 1, 50 parts of waterborne epoxy resin emulsion, 10 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 10 parts of sericite, 2.0 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 33 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 20 parts of deionized water were slowly added to adjust the viscosity to 800 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0042] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the substrate using an air spraying method, with the wet film thickness controlled at 150μm; then it is placed in an 80℃ oven for 2 hours to accelerate baking and complete curing.

[0043] Example 7 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as Si 0.64%, Mg 0.56%, Fe 0.13%, Mn 0.17%, Cr 0.09%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75; aluminum ingots → scrap casting rods → profile scrap are loaded into the furnace in the order of aluminum ingots → scrap casting rods, smelted at 732℃, and refined for 20 minutes at 740℃ with 1.2 kg / ton of refining agent; φ152mm casting rods are cast at 708℃ at a speed of 110 mm / min; homogenization treatment is performed at 570℃ for 10 hours, and the furnace exit temperature is 490℃; the aluminum alloy is processed by a 1500T extruder according to the following steps: after holding at 540℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod, then... The molding time is 18 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are performed; the sawing length is controlled to a tolerance of +1.1mm (actual length 140mm), the burr height is 0.17mm, and the mounting hole is machined by a 16T punch press (hole diameter 6mm, tolerance +0.3mm). After ultrasonic cleaning, it is inspected according to GB / T1804-2000 C grade tolerance to obtain qualified substrate.

[0044] S2: Coating preparation: According to the raw material dosage in Example 7 of Table 1, 50 parts of waterborne epoxy resin emulsion, 12 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 10 parts of mica iron oxide, 2.0 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 37 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 18 parts of deionized water were slowly added to adjust the viscosity to 2000 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0045] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the above-mentioned substrate using an air spraying method, and the wet film thickness is controlled at 150μm; it is cured at room temperature for 7 days in a standard environment of 23℃ and 51% relative humidity.

[0046] Example 8 Follow these steps to process aluminum alloy: S1: Substrate Pretreatment: The alloy composition is controlled as Si 0.63%, Mg 0.58%, Fe 0.14%, Mn 0.19%, Cr 0.07%, with the balance being aluminum, and the Mg / Si mass ratio is 0.75; aluminum ingots → scrap casting rods → profile scrap are loaded into the furnace in the order of aluminum ingots → scrap casting rods, smelted at 738℃, and refined for 20 minutes at 743℃ with 1.2 kg / ton of refining agent; φ152mm casting rods are cast at 712℃ at a speed of 110 mm / min; homogenization treatment is performed at 570℃ for 10 hours, and the furnace exit temperature is 493℃; the aluminum alloy is processed by a 1500T extruder according to the following steps: after holding at 543℃ for 2.5 hours, extrusion is performed at a speed of 4 minutes / rod, then... The molding time is 17 minutes; then T6 solution treatment (530 degrees Celsius, 30-60 minutes) + artificial aging (180±5 degrees Celsius, 7-8 hours) is performed; after that, alkaline washing (NaOH concentration 85g / L, 43℃, 88 seconds), neutralization, oxidation, electrolytic coloring (colorant concentration 16.5g / L, voltage 16.5V), and sealing oxidation process are carried out; the sawing length is controlled to a tolerance of +1.0mm (actual length 210mm), the burr height is 0.13mm, the mounting hole is machined by a 16T punch press (hole diameter 5mm, tolerance +0.2mm), and after ultrasonic cleaning, it is inspected according to GB / T1804-2000 grade C tolerance to obtain qualified substrate.

[0047] S2: Coating preparation: According to the raw material dosage in Example 8 of Table 1, 50 parts of waterborne epoxy resin emulsion, 13 parts of CTBN modified epoxy resin, 15 parts of composite anti-rust pigment, 10 parts of sericite, 1.8 parts of thixotropic rheology modifier, 1.0 part of dispersant, and 0.4 parts of defoamer were added to a high-speed dispersion kettle in sequence; the mixture was dispersed at 1200 rpm for 30 minutes, and the fineness of the slurry was measured to be 31 μm; the speed was reduced to 300 rpm and the stirring was slowed down, and 22 parts of deionized water were slowly added to adjust the viscosity to 1000 mPa·s (measured at 25°C using a rotational viscometer), and the mixture was filtered to obtain component A; component A was mixed with 35 parts of component B at a mass ratio of 4:1, mechanically stirred for 5 minutes, and allowed to mature at room temperature for 15 minutes for later use.

[0048] S3: Coating spraying and curing: The mixed coating is uniformly applied to the surface of the substrate using an air spraying method, with the wet film thickness controlled at 150μm; then it is placed in an 80℃ oven for 2 hours to accelerate baking and complete curing.

[0049] Comparative Example 1 (without toughening modified resin, cured at room temperature) Processing method for 6005 aluminum alloy substrate: completely consistent with Example 1.

[0050] Coating preparation and application: Component A does not contain CTBN modified epoxy resin. 12 parts of it are replaced with an equal amount of waterborne epoxy resin emulsion (i.e., the total amount of waterborne epoxy resin emulsion is increased to 62 parts). The remaining components, proportions and preparation process are the same as in Example 1. The spraying method is the same as in Example 1. The coating is cured at room temperature for 7 days at a temperature of 24°C and a relative humidity of 52%.

[0051] Comparative Example 2 (without thixotropic rheology modifier, cured at room temperature) Processing method for 6005 aluminum alloy substrate: completely consistent with Example 1.

[0052] Coating preparation and application: Component A does not contain thixotropic rheology modifiers compounded with fumed silica and organobentonite. The remaining components and preparation process are the same as in Example 1. The spraying method is the same as in Example 1. The coating is cured at room temperature for 7 days at 24°C and 52% relative humidity.

[0053] Comparative Example 3 (using spherical fillers instead of sheet-like shielding fillers, cured at room temperature) Processing method for 6005 aluminum alloy substrate: completely consistent with Example 1.

[0054] Coating preparation and application: 10 parts of mica iron oxide in component A were replaced with heavy calcium carbonate (spherical filler) with D50=5μm. The remaining components and preparation process were the same as in Example 1. The spraying method was the same as in Example 1. The coating was cured at room temperature for 7 days at 24℃ and 52% relative humidity.

[0055] The samples prepared in the examples and comparative examples were subjected to performance tests, and the results are shown in the table below: Table 2 Performance test results of the examples and comparative examples

[0056] The test results are analyzed as follows: (1) Anti-sagging performance analysis: Thixotropic rheology modifier is the core of solving the sagging problem in this invention. Comparative Example 2, due to the absence of thixotropic rheology modifier, exhibited extremely poor anti-sagging properties, with significant sagging occurring when the wet film thickness exceeded 100 μm, failing to meet the requirements for thick coating application on vertical surfaces. In contrast, all examples and Comparative Examples 1 and 3 demonstrated excellent anti-sagging properties, which is attributed to the three-dimensional network structure formed by the compounding of fumed silica and organobentonite, endowing the coating with strong thixotropic properties—high viscosity during standing to prevent sedimentation, viscosity decreases during construction shearing to facilitate leveling, and high viscosity is rapidly restored after shearing to resist sagging.

[0057] (2) Flexibility and Crack Resistance Analysis: CTBN-toughened modified resin is key to improving coating toughness and preventing cracking. The mechanical property data of Comparative Example 1 (without toughening agent) clearly show the defects of the rigid system: its flexibility and impact resistance are significantly inferior to all examples. This indicates that the untoughened coating is brittle and easily cracks under internal stress and external impact. In contrast, Examples 1-3, by introducing CTBN, formed an "island" structure or interpenetrating network, which can effectively induce crazing, absorb and disperse stress, thereby improving the elongation at break and impact resistance of the coating to an excellent level, fundamentally solving the problem of easy cracking of the coating.

[0058] (3) Corrosion Resistance Analysis: The synergistic effect of the sheet-like shielding filler and the toughening coating is the guarantee for achieving long-term corrosion resistance. Comparative Example 3 uses ordinary spherical calcium carbonate filler, and its salt spray resistance is significantly lower than that of the examples using mica iron oxide or sericite. This shows that the sheet-like filler can be arranged in parallel in the coating to form a dense physical barrier, greatly extending the diffusion path of water, oxygen, and ions. At the same time, Comparative Example 1 has the worst salt spray resistance due to the brittleness and easy cracking of the coating, proving that the integrity of the coating (no cracks) is a prerequisite for any corrosion protection mechanism. Therefore, the coating provided by this invention achieves synergistic effect by ensuring that the coating does not crack through toughening and by supplementing it with the shielding effect of the sheet-like filler.

[0059] Conclusion: Test data show that by introducing CTBN toughening agent, compounding thixotropic rheology agent and selecting sheet-like shielding filler, this invention successfully overcomes the technical problem of "sagging" and "cracking" coexisting when waterborne epoxy coatings are applied to 6005 aluminum alloy, and simultaneously achieves high strength, high toughness and excellent corrosion resistance.

[0060] The preferred embodiments of the present invention have been described in detail above. However, the present invention is not limited to the specific details in the above embodiments. Within the scope of the technical concept of the present invention, various simple modifications can be made to the technical solution of the present invention, and these simple modifications all fall within the protection scope of the present invention.

[0061] It should also be noted that the various specific technical features described in the above embodiments can be combined in any suitable manner without contradiction. To avoid unnecessary repetition, the present invention will not describe the various possible combinations separately.

[0062] Furthermore, various different embodiments of the present invention can be combined in any way, as long as they do not violate the spirit of the present invention, they should also be regarded as the content disclosed by the present invention.

Claims

1. A sag-resistant, crack-resistant 6005 aluminum alloy waterborne epoxy resin paint, characterized by, The coating is a two-component system, consisting of component A and component B. By weight, component A comprises: 40-60 parts of waterborne epoxy resin emulsion, 5-15 parts of toughening modified resin, 10-20 parts of composite anti-rust pigment, 5-12 parts of flake-shaped shielding filler, 0.5-2.5 parts of thixotropic rheology modifier, 0.3-1.2 parts of dispersant, 0.1-0.8 parts of defoamer, and 10-25 parts of deionized water. Component B is a waterborne amine curing agent. The toughening modified resin is a carboxyl-terminated butadiene-acrylonitrile rubber modified epoxy resin, and the thixotropic rheology modifier is composed of fumed silica and organobentonite.

2. The coating of claim 1, wherein, Component A consists of the following components: 40-60 parts of waterborne epoxy resin emulsion, 8-12 parts of toughening modified resin, 10-20 parts of composite anti-rust pigment, 10-12 parts of sheet-like shielding filler, 1-2.5 parts of thixotropic rheology modifier, 0.3-1.2 parts of dispersant, 0.1-0.8 parts of defoamer, and 10-25 parts of deionized water. The sheet-like shielding filler is mica iron oxide or sericite with a particle size of 10-15 micrometers.

3. The coating of claim 2, wherein, In component A, the mass ratio of the aqueous epoxy resin emulsion to the toughening modified resin is 4-6:1, and the mass ratio of the aqueous epoxy resin emulsion to deionized water is 2-6:

1.

4. The coating of claim 2, wherein, In component A, the thixotropic rheology modifier is compounded from fumed silica and organobentonite in a mass ratio of (1-2):(1-2); the viscosity of the coating is adjusted to 800-2000 mPa·s, measured at 25°C using a rotational viscometer.

5. The coating according to any one of claims 1 to 4, characterized in that The composite anti-rust pigment is made by compounding zinc phosphate and aluminum tripolyphosphate in a mass ratio of 2:(1-2); before the coating is used, the A component and the B component are independent of each other, and they are mixed in a mass ratio of 4:(1-2) before coating.

6. A process for the preparation of the coating according to any one of claims 1 to 5, characterized in that, Includes the following steps: A1: Add the water-based epoxy resin emulsion, toughening modified resin, composite anti-rust pigment, flake shielding filler, thixotropic rheology modifier, dispersant, and defoamer to the high-speed dispersion kettle in sequence according to the formula. A2: Adjust the speed to 1000-1500 rpm and disperse at high speed for 25-35 minutes until the fineness of the slurry is ≤40μm; A3: Reduce the stirring speed to 250-350 rpm, slowly add deionized water, adjust the viscosity of the system, and filter to obtain component A; A4: Before use, mix component A and component B at a mass ratio of 4:(1-2), stir mechanically for 3-8 minutes, and let it mature at room temperature for 10-20 minutes before use.

7. A method of working a 6005 aluminium alloy characterised in that, Includes the following steps: S1: Substrate pretreatment: Control the mass content of each element in 6005 aluminum alloy as follows: Si 0.62-0.65%, Mg 0.55-0.58%, Fe≤0.15%, Mn 0.1-0.2%, Cr≤0.1%, with the balance being aluminum, and the Mg / Si mass ratio is 0.7-0.8; Load the raw materials into the furnace and melt them at 700-750℃, then refine them at 730-750℃ for 10-30 minutes, cast them into φ150-155mm ingots at 690-720℃, then homogenize them at 560-580℃ for 8-12 hours, extrude them at 530-550℃, and after T6 solution treatment + artificial aging, after oxidation treatment and finishing, obtain a substrate with a clean and defect-free surface; S2: Coating spraying: Applying the coating described in any one of claims 1-5 to the surface of the substrate by air spraying, controlling the wet film thickness to be 140-160 μm; S3: Curing treatment: Use room temperature curing or accelerated curing methods to ensure complete film formation of the coating.

8. The method of claim 7, wherein, The oxidation process in step S1 specifically includes: alkaline washing, neutralization, oxidation, electrolytic coloring, and sealing. The alkaline washing uses NaOH with a concentration of 80-90 g / L, a temperature of 40-45℃, and a time of 80-90 seconds. The electrolytic coloring uses a colorant concentration of 16-17 g / L and a voltage of 16-17 V. The finishing process includes sawing, punching, and ultrasonic cleaning. The sample length tolerance obtained by sawing is ±1.2 mm, the burr height is ≤0.2 mm, and the hole diameter tolerance of punching is ±0.3 mm.

9. The method of claim 7, wherein, The curing method for step S3 is as follows: for room temperature curing, cure for 6-8 days in an environment with a temperature of 20-25℃ and a relative humidity of 45-55%; for accelerated curing, bake in an oven at 75-85℃ for 1.5-2.5 hours.

10. An aluminum alloy product, characterized in that, The product is prepared by the processing method according to any one of claims 7-9, and the coating performance of the product meets the following requirements: anti-sagging ≥180μm, adhesion grade 0, pencil hardness H-2H, axial rod bending of 1-3mm in flexibility test, and impact resistance ≥45kg. cm, neutral salt spray test ≥900h, VOC content ≤42g / L.

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