High-reflectivity coating for magnesium alloy micro-arc oxidation base material and preparation method of high-reflectivity coating

Abstract

The invention relates to a high-reflectivity coating for a magnesium alloy micro-arc oxidation base material and a preparation method of the high-reflectivity coating, belongs to the technical field of surface treatment, and solves the problems that in the prior art, an epoxy / aluminum coating is uneven in aluminum powder distribution and insufficient in reflectivity (0.8-0.9) due to a rough base material, and an oxide ceramic coating is easy to embrittle and fall off and is difficult to coat deep-cavity parts. The method is realized by sequentially constructing and curing powder primer and electrosilvering paint with specific thickness on a cleaned magnesium alloy micro-arc oxidation base material. Specifically, firstly, 60-100 [mu] m powder primer is applied and cured at the temperature of 180 DEG C to form a flat bottom layer, and then 5-10 [mu] m electrosilvering paint is applied to the surface of the flat bottom layer and cured at the temperature of 140 DEG C to form a high-reflection mirror surface. The reflectivity of the coating is remarkably improved to 0.95 or above on the premise that the first-level binding force with a base body is kept, and the coating has excellent high temperature resistance and salt spray resistance and is particularly suitable for thermal protection of the inner surfaces of high-speed aircraft parts in the aerospace field.

Description

Technical Field

[0001] This invention relates to the field of surface treatment technology, and in particular to a high-reflectivity coating for magnesium alloy micro-arc oxidation substrate and its preparation method. Background Technology

[0002] Magnesium alloys are widely used in the manufacture of lightweight structures for aerospace vehicles due to their excellent properties of low density and high specific strength. However, under hypersonic flight conditions, aerodynamic heating effects can cause the surface temperature of components to rise sharply. To address this, a high-reflectivity coating is often applied to the inner walls of equipment to reflect thermal radiation and prevent heat transfer inward.

[0003] Currently, the mainstream technologies are spraying epoxy resin / aluminum powder coatings or oxide (such as zinc oxide / silicon oxide) ceramic coatings. While the former is simpler, magnesium alloys often undergo micro-arc oxidation to enhance corrosion resistance, resulting in a rough and porous surface. This leads to poor leveling of the epoxy coating, and the resin system's insufficient ability to orient aluminum powder, resulting in generally low reflectivity (0.8–0.9), making it difficult to meet stringent thermal protection requirements. The latter, while having higher reflectivity (>0.9), suffers from a mismatch in thermal expansion coefficients between the ceramic coating and the metal substrate, making it prone to embrittlement and spalling under thermal shock, producing excess material. Furthermore, the high-temperature spraying process is difficult to apply to complex cavity structures, limiting its application. Summary of the Invention

[0004] Based on the above analysis, the present invention aims to provide a high reflectivity coating for magnesium alloy micro-arc oxidation substrates and a method for preparing the same, in order to solve the problem in the prior art that it is difficult to prepare coatings with high reflectivity, excellent adhesion and good environmental resistance on rough magnesium alloy micro-arc oxidation substrates.

[0005] In a first aspect, embodiments of the present invention provide a method for preparing a high-reflectivity coating for a magnesium alloy micro-arc oxidation substrate, comprising the following steps:

[0006] S1. Clean the surface of the magnesium alloy micro-arc oxidation substrate;

[0007] S2. Apply a powder primer to the cleaned substrate surface and cure it. The thickness of the powder primer is 60μm to 100μm.

[0008] S3. Spray an electroplated silver coating onto the cured powder primer surface and cure it. The thickness of the electroplated silver coating is 5μm to 10μm.

[0009] Furthermore, the powder primer is a powder coating of an epoxy resin / polyester resin / inorganic filler composite system.

[0010] Furthermore, in S2, the curing conditions for the powder primer are curing at 170℃~180℃ for 20~30 minutes.

[0011] Furthermore, in S3, the electroplated silver coating is a single-component high-temperature curing coating, the components of which include electroplated silver aluminum powder, acrylic resin, polyester resin, amino resin, additives and organic solvents.

[0012] Furthermore, the curing conditions for the electroplated silver coating are: curing at 130℃~140℃ for 30~40 minutes.

[0013] Secondly, the present invention provides a high reflectivity coating prepared by the above-described preparation method, the coating comprising, from bottom to top:

[0014] Powder primer layer bonded to magnesium alloy micro-arc oxidation substrate;

[0015] And an electroplated silver topcoat layer located on top of the powder primer layer.

[0016] Furthermore, the thickness of the powder primer layer is 60μm to 100μm, and the thickness of the electroplated silver topcoat layer is 5μm to 10μm.

[0017] Furthermore, the coating has a reflectivity >0.95 at room temperature.

[0018] Furthermore, after a high-temperature test at 250°C for 1 hour, the coating showed a cross-cut adhesion of grade 1 to the substrate.

[0019] In addition, the present invention proposes a magnesium alloy component having a magnesium alloy micro-arc oxidation film layer, and a high reflectivity coating as described in the second aspect above is provided on the micro-arc oxidation film layer.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] 1) This invention employs a composite structure design of "thick-film powder primer (60–100 μm) + thin-film electroplated silver topcoat (5–10 μm)". The powder primer effectively fills the microscopic roughness of the magnesium alloy micro-arc oxidation layer surface, providing a smooth and flat substrate for the electroplated silver coating. This promotes the directional alignment of aluminum powder, forming a mirror-like surface with an electroplating effect. The final coating achieves a reflectivity of over 0.95 at room temperature, far exceeding the 0.8–0.9 of traditional epoxy / aluminum coatings.

[0022] 2) The epoxy / polyester / inorganic filler system powder primer selected in this invention not only has good filling properties and film smoothness, but also forms a strong mechanical and chemical bond with the micro-arc oxidation substrate. This primer and the electroplated silver topcoat are well matched in terms of curing behavior and thermal properties, resulting in strong adhesion of the entire coating system. After being treated at 250℃ for 1 hour, the coating still maintains Grade 1 adhesion and passed the 240-hour neutral salt spray test without corrosion, effectively overcoming the problems of easy embrittlement and peeling of oxide coatings and insufficient corrosion resistance.

[0023] 3) The process of combining powder coating with conventional solvent-based coating adopted in this invention eliminates the need for complex and expensive high-temperature equipment such as plasma spraying. It is mature, convenient, low-cost, and highly efficient. This process is also applicable to the inner surfaces of spacecraft magnesium alloy components with deep cavities and irregular structures, and is particularly effective in adapting to the uneven substrates of porous magnesium alloy micro-arc oxidation, thus broadening the engineering application range of high-reflectivity coatings.

[0024] In this invention, the above-described technical solutions can be combined with each other to achieve more preferred combinations. Other features and advantages of this invention will be set forth in the following description, and some advantages may become apparent from the description or be learned by practicing the invention. The objects and other advantages of this invention can be realized and obtained from what is particularly pointed out in the description and drawings. Attached Figure Description

[0025] The accompanying drawings are for illustrative purposes only and are not intended to limit the invention. Throughout the drawings, the same reference numerals denote the same parts.

[0026] Figure 1 This is a schematic diagram of the layered structure of the high-reflectivity coating of the present invention;

[0027] Figure 2 This is a surface morphology diagram of the high reflectivity coating in Embodiment 1 of the present invention;

[0028] Figure 3 The graph shows a comparison of the reflectance test results of the coatings prepared in Example 1 and Comparative Example 1.

[0029] Figure 4 This is a photograph of the neutral salt spray test after Example 1;

[0030] Figure 5 This is a photograph of the adhesion test (cross-cut test) of Example 1.

[0031] Figure Labels

[0032] 1. Electroplated silver topcoat layer; 2. Powder primer layer; 3. Magnesium alloy micro-arc oxidation substrate. Detailed Implementation

[0033] Preferred embodiments of the present invention will now be described in detail with reference to the accompanying drawings, which form part of this application and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not intended to limit the scope of the present invention.

[0034] To improve the surface properties of magnesium alloy parts, micro-arc oxidation is often performed. However, the resulting film has a high surface roughness, which poses a challenge to directly preparing coatings with high reflectivity, excellent adhesion, and environmental resistance. Whether it is a single epoxy / aluminum coating, an oxide ceramic coating, or a composite coating system designed for smooth steel substrates, all have their limitations (such as insufficient filling ability, high brittleness, complex processes, or high costs) and cannot achieve satisfactory results.

[0035] Therefore, this invention proposes a coating preparation method that is particularly suitable for this type of rough substrate. The resulting coating has strong adhesion, excellent environmental resistance, and ultra-high reflectivity similar to electroplating.

[0036] This invention discloses a method for preparing a high-reflectivity coating for a magnesium alloy micro-arc oxidation substrate, comprising the following steps:

[0037] S1. Clean the surface of the magnesium alloy micro-arc oxidation substrate;

[0038] S2. Apply a powder primer to the cleaned substrate surface and cure it. The thickness of the powder primer is 60μm to 100μm.

[0039] S3. Spray an electroplated silver coating onto the cured powder primer surface and cure it. The thickness of the electroplated silver coating is 5μm to 10μm.

[0040] Furthermore, the powder primer is a powder coating based on an epoxy resin / polyester resin / inorganic filler composite system. By mass percentage, its composition includes: 30%–50% epoxy resin, 20%–40% polyester resin, 10%–40% inorganic filler, with the balance being additives. These additives include leveling agents, degassing agents, and other conventional additives in the art.

[0041] The epoxy resin, preferably a bisphenol A type epoxy resin, with an epoxy equivalent in the range of 700-900, provides excellent adhesion and chemical resistance between the coating and the magnesium alloy micro-arc oxidation substrate. The polyester resin, preferably a carboxyl-terminated saturated polyester resin, for example, a type with an acid value in the range of 30-50 mg KOH / g. It forms a mixed system with the epoxy resin, improving flexibility and leveling properties and preventing cracking. The inorganic filler may include one or more of barium sulfate, silica, and talc, with an average particle size of 1-10 μm, used to adjust the coefficient of thermal expansion of the coating, increase hardness, and prevent sagging. When multiple fillers are used in a compound, the advantages of each filler can be combined. A preferred formulation (by mass) is: barium sulfate: silica: talc = (4-6):(2-3):(2-4), for example, a specific ratio of 5:2.5:2.5. This epoxy resin / polyester resin / inorganic filler composite system can be obtained through conventional powder coating preparation processes such as melt extrusion, crushing, and sieving.

[0042] Furthermore, in S2, the powder primer is cured at 170°C–180°C (e.g., 170°C, 172°C, 175°C, 178°C, 180°C) for 20–30 minutes (e.g., 20 minutes, 22 minutes, 25 minutes, 27 minutes, 29 minutes, 30 minutes). These curing conditions ensure that the powder coating fully melts, levels, and completely cross-links, forming a dense underlayer with excellent mechanical properties. Too low a temperature or too short a time may result in incomplete curing, affecting coating performance; too high a temperature may cause resin degradation or generate excessive internal stress.

[0043] From the perspective of reaction mechanism, within this temperature range, the epoxy groups of epoxy resin and the carboxyl groups of polyester resin, as well as the epoxy resin itself and any existing curing agents (such as dicyandiamide), can undergo sufficient addition polymerization reactions to form a dense three-dimensional network cross-linked structure. This structure enables the cured powder primer coating to exhibit excellent comprehensive performance, with a glass transition temperature (Tg) of over 90°C, a pencil hardness of ≥H, and an adhesion to the micro-arc oxidation substrate of grade 0 (cross-cut test).

[0044] Furthermore, in S3, the electroplated silver coating is a single-component, high-temperature curing coating, whose components include electroplated silver aluminum powder, acrylic resin, polyester resin, amino resin, additives, and organic solvents. The components, by mass percentage, are: electroplated silver aluminum powder 5%–15%, acrylic resin 20%–35%, polyester resin 10%–25%, amino resin 5%–15%, additives 0.5%–5%, and organic solvents 25%–45%.

[0045] The electroplated silver aluminum powder is preferably a high-brightness floating aluminum powder that has been coated with inert substances such as silica. The coating layer is amorphous silica with a coating rate of ≥90% and a silica coating thickness accounting for 5%-15% of the total mass of the aluminum powder. The aluminum powder has a sheet-like structure with a diameter-to-thickness ratio greater than 50:1 and a sheet diameter D50 distributed between 10-30μm. The metallic luster (60° gloss) is ≥120GU to ensure excellent floating properties and mirror reflection effect.

[0046] The acrylic resin and polyester resin serve as the main film-forming substances, providing the basic framework of the coating and interlayer adhesion with the primer. The acrylic resin can be a hydroxyl acrylic resin to provide active sites for crosslinking with the amino resin. The polyester resin can be of a type with similar polarity or functional groups to the polyester resin in the primer, such as being a linear or branched polyester, to promote interlayer bonding.

[0047] The amino resin is preferably a fully etherified or partially etherified melamine-formaldehyde resin, used as a crosslinking agent. The additives include leveling agents (such as polyether-modified polydimethylsiloxane) and orientation agents (such as cellulose acetate and polyethylene wax) to promote the regular arrangement of aluminum powder and a smooth coating surface.

[0048] The organic solvent may be a mixture of esters, ketones, and aromatic hydrocarbon solvents, such as a mixture of butyl acetate, methyl isobutyl ketone, and xylene, used to adjust the application viscosity.

[0049] Furthermore, the electroplated silver coating is cured at 130℃~140℃ (e.g., 130℃, 132℃, 135℃, 138℃, 140℃) for 30~40 minutes (e.g., 30 minutes, 32 minutes, 35 minutes, 38 minutes, 40 minutes). This temperature range is set after comprehensively considering the reactivity of the topcoat resin system, the orientation requirements of the aluminum powder, and the matching with the curing temperature of the undercoat. Under these conditions, the resin can fully crosslink to form a durable coating film, while providing an optimal time window for the floating and orientation of the aluminum powder.

[0050] Specifically, the hydroxyl groups on amino resins, acrylic resins, and polyester resins undergo etherification and crosslinking reactions under heating conditions, forming a dense network structure. The relatively low curing temperature (lower than the curing temperature of the powder primer) helps slow down solvent evaporation and resin crosslinking rates, providing a longer "operating window" for the aluminum powder flakes to rotate, migrate, and align parallel to the substrate within the coating—a key factor in achieving high reflectivity. Simultaneously, this curing temperature prevents the underlying powder coating from experiencing performance degradation (such as yellowing or softening) due to overheating, ensuring interlayer adhesion.

[0051] Specifically, in S1, the purpose of cleaning is to remove contaminants such as grease, dust, and fingerprints from the surface of the micro-arc oxide film layer and reduce surface energy, fundamentally ensuring excellent and durable adhesion between the subsequent coating and the substrate. Preferably, volatile organic solvents such as acetone and ethanol are used for wiping or ultrasonic cleaning. The ultrasonic cleaning power can be set to 200-400W for 5-15 minutes to ensure that contaminants deep inside the micropores are effectively removed. After cleaning, thorough drying is required to ensure that there is no residual moisture or solvent on the substrate surface and in the pores.

[0052] The magnesium alloy micro-arc oxidation substrate targeted in this invention typically has a micro-arc oxidation film thickness of 10-50 μm. Its surface microstructure consists of porous molten oxides (mainly MgO, Mg2SiO4, MgAl2O4, etc.) formed by discharge melting and rapid cooling, with a porosity of 5%-20%. It also contains micropores and protrusions ranging from several micrometers to tens of micrometers, resulting in a surface roughness Ra value typically between 1-5 μm. This rough, porous morphology provides a potential adhesion basis for the coating by increasing the specific surface area and forming a micro-mechanical interlocking effect (i.e., "anchoring effect"). However, its significant micro-undulations also place extremely high demands on the smoothness and hiding power of the coating. Direct application of functional topcoats will lead to uneven paint film surfaces, decreased optical performance, and even premature failure due to uneven paint film thickness.

[0053] Specifically, in S2, the core function of the powder primer is to effectively fill and prime the rough substrate. To achieve this, this invention innovatively selects a powder coating with a thickness of 60μm to 100μm (e.g., 60μm, 70μm, 80μm, 90μm, 95μm, 100μm). This thickness range ensures sufficient material flow to completely cover and fill the aforementioned microscopic defects, forming a macroscopically extremely smooth and flat interface, while avoiding problems such as increased internal stress, decreased toughness, and economic degradation that may result from excessively thick coatings. The powder coating is preferably applied using electrostatic spraying, with a spraying voltage typically between 60-80kV. Through Coulomb force, negatively charged powder particles are uniformly adsorbed onto the grounded substrate, even covering the edges and back of the substrate, achieving excellent coverage.

[0054] In the subsequent heating and curing stage, a key physicochemical process occurs: first, the powder particles absorb heat and melt, and the viscosity drops sharply; then, driven by surface tension, a "leveling" phenomenon occurs, and the liquid coating fully wets the substrate surface and penetrates into the pores of the micro-arc oxide film; finally, at the set temperature and time, the resin system undergoes a full cross-linking and curing reaction.

[0055] The selected epoxy resin / polyester resin / inorganic filler composite system works synergistically in this process: epoxy resin provides excellent adhesion and chemical resistance to the substrate; polyester resin significantly improves the leveling properties, mechanical toughness, and outdoor weather resistance of the coating; while inorganic fillers (such as barium sulfate, silica, etc.) typically account for 15%-35% of the total weight of the coating, which not only helps to adjust the coefficient of thermal expansion of the coating, increase hardness and abrasion resistance, but also prevents excessive sagging of the coating during the melting and curing process, ensuring that the specified film thickness can be formed even on vertical surfaces.

[0056] Compared to existing technologies such as direct spraying of thin-layer coatings (which have limited leveling ability and struggle to overcome substrate roughness) or solvent-based thick-film coatings (which, while offering adjustable film thickness, often contain large amounts of solvent, resulting in high curing shrinkage, pinholes, and other defects, and are also environmentally unfriendly), powder coatings offer advantages such as being solvent-free (100% solids content), producing large film thicknesses in a single application, exhibiting excellent filling properties, low curing shrinkage, and forming dense, defect-free coatings. This lays the foundation for the successful application of subsequent electroplated silver mirror coatings, which require a smooth substrate, and is a prerequisite and key technological support for ultimately achieving a reflectivity >0.95.

[0057] Specifically, in S3, an electroplated silver coating with a thickness of only 5μm to 10μm (e.g., 5μm, 6μm, 7μm, 8μm, 9μm, 10μm) is sprayed onto the smoothed powder primer. This electroplated silver coating uses electroplated silver aluminum powder that has undergone special coating and grading treatment. This type of aluminum powder is characterized by uniform flake size, bright surface, and high aspect ratio. The resin system consists of acrylic resin, polyester resin, and amino resin working together. The acrylic and polyester resins provide film-forming properties and compatibility, while the amino resin acts as a crosslinking agent. At a curing temperature of 130℃ to 140℃, a crosslinking reaction is performed for 30 to 40 minutes to form a dense network structure.

[0058] This thin-layer design and relatively low curing temperature (130℃~140℃, lower than the 170℃~180℃ of powder primer) are crucial. On the one hand, the 5μm~10μm thin coating ensures that the aluminum powder is fully oriented on the smooth substrate, floating to the surface to form a continuous and dense mirror-reflective layer; on the other hand, the lower curing temperature allows time for the early stage of resin cross-linking and curing, preventing the aluminum powder from failing to reach its optimal alignment due to rapid resin solidification. If the topcoat is too thick, the oriented alignment of the aluminum powder will be disrupted, and the resin's absorption and scattering of light will be enhanced; if the curing temperature is too high or the time is too short, rapid resin cross-linking will freeze the movement of the aluminum powder, also affecting the reflective effect.

[0059] On the other hand, the present invention proposes a high-reflectivity coating prepared by the above-described method, the structural layering of which is shown in the schematic diagram below. Figure 1As shown, the coating comprises, from bottom to top: a powder primer layer bonded to a magnesium alloy micro-arc oxidation substrate; and an electroplated silver topcoat layer located above the powder primer layer.

[0060] Furthermore, the thickness of the powder primer layer is 60μm to 100μm (e.g., 60μm, 70μm, 80μm, 90μm, 95μm, 100μm), and the thickness of the electroplated silver topcoat layer is 5μm to 10μm (e.g., 5μm, 6μm, 7μm, 8μm, 9μm, 10μm).

[0061] Furthermore, the coating exhibits a reflectance >0.95 at room temperature. This reflectance refers to the weighted average of the spectral reflectance of a standard light source (such as D65) within the visible light wavelength range of 380 nm to 780 nm. A reflectance greater than 0.95 indicates that the coating possesses high reflectivity close to that of an ideal mirror.

[0062] Furthermore, after a high-temperature test at 250°C for 1 hour, the coating achieved a grade 1 cross-cut adhesion strength to the substrate (according to GB / T 9286-1998 standard, the cross-cut spacing is 2mm, and grade 1 indicates that the cut edges are completely smooth with no cells falling off). This result confirms that the coating system has excellent thermal stability and interlayer bonding strength.

[0063] Specifically, the high-reflectivity coating is a functionally integrated composite structure. The powder primer layer has multiple functions: firstly, as a bonding transition layer, it forms a strong bond with the magnesium alloy micro-arc oxidation substrate through mechanical interlocking and intermolecular forces; secondly, as the main thermal stress buffer layer, its coefficient of thermal expansion is designed through the type and amount of inorganic fillers to be between that of the magnesium alloy substrate (approximately 26 × 10⁻⁶). -6 / ℃) and organic topcoat (approximately 80-100×10 -6 The thickness range of 60μm to 100μm is between 60μm and 100μm, which effectively relaxes thermal stress when the temperature changes. The thickness range is the result of the balance between the leveling effect and the internal stress: if it is too thin, it cannot cover the micro-undulations of the substrate and affect the mirror effect; if it is too thick, the internal stress will increase, which will easily lead to cracking and is not economical.

[0064] The thickness of the electroplated silver topcoat layer, controlled within a specific range of 5μm to 10μm, is key to achieving high reflectivity. At this thickness, the electroplated silver aluminum powder can achieve a highly oriented alignment on the smooth primer surface, forming a continuous, dense reflective layer dominated by specular reflection, while minimizing the absorption and scattering of incident light by the resin matrix. The selected acrylic / polyester / amino resin system exhibits excellent transparency and resistance to yellowing after curing, further ensuring reflectivity.

[0065] In addition, the present invention also proposes a magnesium alloy component having a magnesium alloy micro-arc oxidation film layer, and a high reflectivity coating as described above is disposed on the micro-arc oxidation film layer.

[0066] Specifically, the magnesium alloy component can be a spacecraft housing, bracket, shell, or other part with a complex structure (such as deep cavities or irregularly shaped holes). By sequentially forming a micro-arc oxide film layer and the high-reflectivity composite coating of this invention on the inner surface of the component, the component not only inherits the wear resistance and corrosion resistance advantages of the micro-arc oxide film itself, but also gains the ability to efficiently reflect radiant heat. When the component faces aerodynamic heating during high-speed flight, the high-reflectivity coating can reflect most of the radiant heat back, significantly suppressing the component's temperature rise. This helps to suppress deformation and cracking caused by excessive temperature rise, thereby improving the reliability and lifespan of the equipment.

[0067] Compared with existing technologies that use metal plating or thick-film ceramic coatings, the organic composite coating system provided by this invention has comprehensive advantages such as relatively simple process, low cost, applicability to complex shaped parts, good adhesion to magnesium alloy substrate, and extremely high reflectivity.

[0068] In summary, the high-reflectivity coating for magnesium alloy micro-arc oxidation substrates and its preparation method of the present invention solve the technical challenge of achieving high reflectivity and high environmental resistance on high-roughness active substrates by constructing a composite system of "powder leveling primer + thin-layer electroplated silver topcoat". Its core invention lies in recognizing that a single coating cannot simultaneously meet the contradictory requirements of leveling a rough substrate and forming a perfect mirror surface. Therefore, a two-step method is adopted: first, a thick-film powder coating is used to achieve perfect leveling of the substrate; then, a precisely controlled thin-layer electroplated silver coating is applied on top to maximize the mirror reflection effect. Furthermore, through the matching design of the material system and the optimization of process parameters, the overall adhesion, heat resistance, and durability of the composite coating are ensured.

[0069] The present invention will be described in more detail below through specific embodiments. These embodiments are merely descriptions of the best implementation of the invention and do not limit the scope of the invention in any way.

[0070] Example 1

[0071] Preparation of a high-reflectivity coating for a magnesium alloy micro-arc oxidation substrate

[0072] Using AZ31 magnesium alloy specimens as substrates, after micro-arc oxidation treatment (forming a ceramic layer with a thickness of approximately 10-20 μm and a surface roughness Ra≈2.5 μm), the following operations were performed:

[0073] S1. Cleaning: Wipe the test piece with a white cotton cloth soaked in 120# gasoline, ethanol and acetone solution in turn to thoroughly remove surface oil and impurities, and then place it in an 80℃ forced-air oven to dry for 15 minutes.

[0074] S2. Powder Primer Application: An epoxy-polyester hybrid powder coating was uniformly sprayed onto the clean, dry test specimen surface using electrostatic spraying equipment. The powder coating consisted of the following components by mass percentage: 40 parts bisphenol A epoxy resin (epoxy equivalent 800), 40 parts carboxyl-terminated polyester resin (acid value 40 mg KOH / g), 18 parts barium sulfate (average particle size 5 μm), 1 part leveling agent (modified polyacrylate), and 1 part degassing agent (benzoin). The dry film thickness was controlled to be 80 ± 5 μm. The test specimens were then transferred to a 180°C forced-air oven for curing for 20 minutes, after which they were removed and allowed to cool naturally to room temperature. Testing showed that the cured primer coating had a glass transition temperature (Tg) of 95°C and a pencil hardness of 2H.

[0075] S3. Application of Electroplated Silver Topcoat: After the test piece has cooled, a single-component electroplated silver coating (composition includes 10wt% mirror-grade electroplated silver aluminum powder, with a particle size D50 of approximately 20μm; the resin matrix is ​​a compound system of acrylic resin, polyester resin, and amino resin (by mass percentage): 30% hydroxyl acrylic resin, 15% carboxyl-terminated polyester resin, 10% fully etherified melamine resin, 1.5% polyethylene wax orientation agent, 0.5% polyether-modified siloxane leveling agent, and 33% mixed solvent (butyl acetate: methyl isobutyl ketone: xylene = 4:3:3)) is evenly sprayed onto a smooth powder primer surface using an air spraying device. The dry film thickness is controlled to be 8±1μm. The test piece is then placed in a 140℃ forced-air oven for curing for 30 minutes, removed, and cooled to obtain a high-reflectivity composite coating with a mirror-like electroplated silver effect.

[0076] Example 2

[0077] The difference between this embodiment and Embodiment 1 is that the dry film thickness of the powder primer is controlled at 60±5μm and the dry film thickness of the electroplated silver topcoat is controlled at 10±1μm. All other operations and materials are the same as in Embodiment 1.

[0078] Example 3

[0079] The difference between this embodiment and Embodiment 1 is that the dry film thickness of the powder primer is controlled at 100±5μm and the dry film thickness of the electroplated silver topcoat is controlled at 5±1μm. All other operations and materials are the same as in Embodiment 1.

[0080] Example 4

[0081] The only difference between this embodiment and Embodiment 1 is that the composition of the powder primer is different:

[0082] S2. The composition of the powder coating by mass is as follows: 45 parts of bisphenol A type epoxy resin (epoxy equivalent 750), 30 parts of carboxyl-terminated polyester resin (acid value 45mgKOH / g), 23 parts of silica (average particle size 3μm), 1 part of leveling agent, and 1 part of degassing agent.

[0083] Example 5

[0084] The only difference between this embodiment and Embodiment 1 is that the composition of the electroplated silver topcoat is different:

[0085] S3. Spray a single-component electroplating silver coating, which consists of 12wt% mirror-grade silica-coated electroplating silver aluminum powder (flake diameter D50 approximately 25μm), and a resin matrix of: 35% hydroxyl acrylic resin, 10% carboxyl-terminated polyester resin, 12% fully etherified melamine resin, 2% orientation agent, 1% leveling agent, and 40% mixed solvent.

[0086] Comparative Example 1

[0087] Traditional epoxy / aluminum coating preparation. On the same micro-arc oxidation AZ31 magnesium alloy test piece, after the same cleaning and drying treatment, a solvent-based coating consisting of a two-component epoxy resin and 20wt% floating flake aluminum powder was directly sprayed by air, controlling the total dry film thickness to be approximately 90μm.

[0088] Comparative Example 2

[0089] On the same micro-arc oxidation AZ31 magnesium alloy specimen, only the powder primer from Example 1 was applied to a thickness of 80 μm and cured at 180°C for 20 min, without spraying electroplated silver topcoat.

[0090] Comparative Example 3

[0091] On the same micro-arc oxidation AZ31 magnesium alloy specimen, after cleaning and drying, the powder primer application step was skipped, and the electroplated silver topcoat from Example 1 was directly sprayed to a thickness of 8±1μm and cured at 140℃ / 30min.

[0092] Comparative Example 4

[0093] On the same micro-arc oxidation AZ31 magnesium alloy test piece, the epoxy-polyester powder primer in Example 1 was replaced with a solvent-based epoxy primer (two-component, film thickness of about 25 μm, curing at 80°C / 30 min). After curing, the electroplated silver topcoat in Example 1 (film thickness of 8 μm, curing at 140°C / 30 min) was sprayed on.

[0094] Comparative Example 5

[0095] The only difference between this comparative example and Example 1 is that, in preparing the electroplating silver topcoat used in S3, an equal amount of ordinary non-floating aluminum powder is used instead of mirror-grade silica to coat the electroplating silver aluminum powder. All other components and processes are the same as in Example 1.

[0096] Characterization results test

[0097] The coatings obtained in the above embodiments and comparative examples were subjected to performance tests according to relevant national standards. Reflectivity was tested according to GB / T 25076-2010, adhesion according to the cross-cut adhesion test (GB / T 9286-1998), and neutral salt spray resistance according to GB / T 1771-2007. Specific test results are shown in Table 1.

[0098] Table 1. Comparison of Coating Performance

[0099] project Appearance (visual inspection) Reflectivity (500nm) Adhesion grade after 250℃ / 1h 240hNSS appearance Example 1 Smooth, bright mirror surface 0.967 1 No change, no corrosion Example 2 Smooth, bright mirror surface 0.952 1 No change, no corrosion Example 3 Smooth, bright mirror surface 0.958 1 No change, no corrosion Example 4 Smooth, bright mirror surface 0.961 1 No change, no corrosion Example 5 Smooth, bright mirror surface 0.955 1 No change, no corrosion Comparative Example 1 Orange peel texture, uneven, metallic matte finish 0.852 2 (Edges are clearly peeling off) Bubbling and rust at the grid lines Comparative Example 2 Smooth, grayish-white matte finish 0.351 1 No change Comparative Example 3 Rough texture, visible substrate grain, no mirror finish. 0.623 3 (Large-area peeling) Severe corrosion, blistering Comparative Example 4 Slight orange peel, semi-gloss 0.911 1 Slight corrosion at the grid lines Comparative Example 5 Matte gray-white finish, no mirror effect 0.450 1 No change

[0100] As can be seen from Table 1, the composite coatings prepared in Examples 1-3 of this invention all exhibit excellent bright mirror-like effects in appearance. Taking Example 1 as an example, observations are conducted... Figure 2 The surface morphology diagram shown demonstrates that the coating is extremely smooth and dense, forming a complete mirror surface.

[0101] Reflectance test results show that the reflectance of all embodiments of the present invention is greater than 0.95. All embodiments exhibit similar high reflectance characteristics, such as... Figure 3 The reflectance test comparison curves shown (the horizontal axis represents the test point number, and the vertical axis represents the reflectance value measured at the corresponding test point) further confirm that the reflectance of the coating prepared in Example 1 is consistently high (average value exceeds 0.96), and significantly higher than that of the directly sprayed Comparative Example 1 (average value is only about 0.85).

[0102] After undergoing high-temperature treatment at 250°C, the adhesion of the embodiments of the present invention still maintains an optimal grade of 1. This excellent interlayer bonding strength is demonstrated in all embodiments. Figure 5 The adhesion test photos shown, exemplified by Example 1, directly verify this, demonstrating that the edges of the coating are completely smooth with no cells peeling off.

[0103] Regarding environmental resistance, after 240 hours of neutral salt spray testing, all embodiments of the present invention exhibited excellent corrosion resistance, with no surface changes or corrosion. Figure 4 The photographs shown, representing Example 1, after a neutral salt spray test, clearly demonstrate that the coating remained intact after being subjected to a harsh corrosive environment, without any corrosion spots or blistering.

[0104] In summary, this invention, through innovative coating system design, successfully prepared a composite coating with high reflectivity, excellent adhesion, and good environmental resistance on a rough magnesium alloy micro-arc oxidation substrate, solving a long-standing technical problem in the prior art.

[0105] The above description is only a preferred embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by those skilled in the art within the scope of the technology disclosed in the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for preparing a high-reflectivity coating for a magnesium alloy micro-arc oxidation substrate, characterized in that, Includes the following steps: S1. Clean the surface of the magnesium alloy micro-arc oxidation substrate; S2. Apply a powder primer to the cleaned substrate surface and cure it. The thickness of the powder primer is 60μm to 100μm. S3. Spray an electroplated silver coating onto the cured powder primer surface and cure it. The thickness of the electroplated silver coating is 5μm to 10μm.

2. The preparation method according to claim 1, characterized in that, The powder primer is a powder coating based on an epoxy resin / polyester resin / inorganic filler composite system.

3. The preparation method according to claim 1 or 2, characterized in that, In S2, the curing conditions for the powder primer are curing at 170℃~180℃ for 20~30 minutes.

4. The preparation method according to claim 1, characterized in that, In S3, the electroplated silver coating is a single-component high-temperature curing coating, the components of which include electroplated silver aluminum powder, acrylic resin, polyester resin, amino resin, additives and organic solvents.

5. The preparation method according to claim 4, characterized in that, The curing conditions for the electroplated silver coating are: curing at 130℃~140℃ for 30~40 minutes.

6. A high-reflectivity coating prepared by the preparation method according to any one of claims 1-5, characterized in that, The coating, from bottom to top, includes: Powder primer layer bonded to magnesium alloy micro-arc oxidation substrate; And an electroplated silver topcoat layer located on top of the powder primer layer.

7. The high reflectivity coating according to claim 6, characterized in that, The thickness of the powder primer layer is 60μm to 100μm, and the thickness of the electroplated silver topcoat layer is 5μm to 10μm.

8. The high reflectivity coating according to claim 6 or 7, characterized in that, The coating has a reflectivity >0.95 at room temperature.

9. The high reflectivity coating according to claim 8, characterized in that, After undergoing a high-temperature test at 250°C for 1 hour, the coating showed a cross-cut adhesion rating of Grade 1 to the substrate.

10. A magnesium alloy component, characterized in that, The magnesium alloy component has a magnesium alloy micro-arc oxidation film layer, and a high reflectivity coating as described in any one of claims 6-9 is provided on the micro-arc oxidation film layer.

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