Composite coating and method for producing same, magnesium alloy article

Abstract

The application discloses a composite coating and a preparation method thereof and a magnesium alloy product. The preparation method comprises the following steps: providing a deposition liquid, wherein the deposition liquid comprises a calcium salt, phosphoric acid and water; placing an electrically conductive substrate into the deposition liquid to deposit calcium hydrogen phosphate dihydrate on the surface of the electrically conductive substrate, so as to obtain a calcium hydrogen phosphate dihydrate layer; providing an organic coating, wherein the organic coating comprises an A component and a B component, the A component comprises a high-solid resin with a hindered secondary amine group, a filler, an additive and a solvent, and the B component comprises a curing agent; and placing the organic coating on the calcium hydrogen phosphate dihydrate layer to form an organic coating layer, so as to obtain the composite coating. The composite coating prepared by the preparation method has strong corrosion resistance.

Description

Technical Field

[0001] This application relates to the field of coating technology, and in particular to a composite coating and its preparation method, and magnesium alloy products. Background Technology

[0002] Magnesium alloys possess properties such as low density, high strength, high elastic modulus, good heat dissipation, good vibration damping, and greater impact load capacity than aluminum alloys, making them widely used in electronics, medical devices, biological scaffolds, aircraft, spacecraft, and rocket / missile manufacturing. However, magnesium alloys suffer from poor corrosion resistance, which hinders their application in various fields.

[0003] Existing technologies improve the corrosion resistance of magnesium alloys by applying coatings to their surfaces. Current methods for preparing coatings on magnesium alloy surfaces include anodic oxidation, chemical conversion, electroless plating, and micro-arc oxidation.

[0004] However, existing methods for preparing coatings on magnesium alloy surfaces produce coatings with low corrosion resistance, which needs further improvement. Summary of the Invention

[0005] In view of this, this application provides a method for preparing a composite coating, which aims to improve the problem of low corrosion resistance of existing composite coatings.

[0006] The embodiments of this application are implemented as follows: a method for preparing a composite coating includes the following steps:

[0007] Calcium nitrate, phosphoric acid, and water are provided and mixed to obtain a sedimentation solution;

[0008] The conductive substrate is placed in the deposition solution, and calcium hydrogen phosphate dihydrate is deposited on the surface of the conductive substrate by electrodeposition to obtain a calcium hydrogen phosphate dihydrate layer.

[0009] An organic coating is provided, comprising component A and component B, wherein component A comprises a high-solids resin with sterically hindered secondary amine groups, fillers, additives, and solvents, and component B comprises a curing agent. The organic coating is applied to the calcium phosphate dihydrate layer to form an organic coating, thereby obtaining a composite coating.

[0010] Optionally, in some embodiments, the current density of the electrodeposition is 0.01–1 mA / cm². 2 The electrodeposition time is 10 min to 2.1 h.

[0011] Optionally, in some embodiments, the temperature of the deposition solution is 60–80°C.

[0012] Optionally, in some embodiments, the mass concentration of calcium salt in the deposition solution is 10–100 g / L; and / or

[0013] The volume concentration of phosphoric acid in the sediment is 5–17 mL / L.

[0014] Optionally, in some embodiments, the mixing process further includes adjusting the pH to 3.0–3.5 using an alkaline solution.

[0015] Optionally, in some embodiments, the alkaline solution includes one or more of ammonia and sodium bicarbonate.

[0016] Optionally, in some embodiments, the calcium salt includes one or more of calcium nitrate and calcium oxalate; and / or

[0017] The sterically hindered secondary amine group high-solids resin includes hyperbranched polyurethane resin; and / or

[0018] The sterically hindered secondary amine-based high-solids resin has a viscosity of 200–1000 cps at 20°C and a density of 0.95–1.05 g / ml at 20°C; and / or

[0019] The end groups of the hyperbranched polyurethane resin include one or more of hydroxyl, amino, and fluoroalkyl groups; and / or

[0020] The filler includes one or more of carbon nanotubes and graphene; and / or

[0021] The adjuvant includes one or more of propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, and propylene glycol phenyl ether; and / or

[0022] The solvent includes one or more of n-butyl ester, propylene glycol methyl ether acetate, and aliphatic isocyanates; and / or

[0023] The curing agent comprises one or more of aliphatic isocyanates and modified polyester prepolymer flexible isocyanates; the aliphatic isocyanate comprises one or more of n-butyl acetate, propylene glycol methyl ether acetate, and aliphatic isocyanates; the modified polyester prepolymer flexible isocyanate comprises one or more of toluene diisocyanate and xylenemethane diisocyanate; and / or

[0024] The conductive substrate comprises an alloy, and the alloy comprises a magnesium alloy.

[0025] Optionally, in some embodiments, by weight, component A contains 40-60 parts of the high-solids resin, 1-2 parts of the additives, 8-40 parts of the filler, and 10-30 parts of the solvent; and / or

[0026] The mass ratio of component A to component B is 1:1 to 3:1.

[0027] Accordingly, this application also provides a composite coating prepared by the above preparation method, the composite coating comprising a calcium phosphate dihydrate layer and an organic coating bonded to at least one surface of the calcium phosphate dihydrate layer.

[0028] Optionally, in some embodiments, the thickness of the dicalcium phosphate dihydrate layer is 2–45 μm; and / or

[0029] The thickness of the organic coating is 30–150 μm; and / or

[0030] The impedance value of the dihydrated calcium hydrogen phosphate layer is 100-5000 MΩ.

[0031] Accordingly, this application also provides a magnesium alloy article, including a magnesium alloy substrate and a composite coating prepared by the above preparation method bonded to at least one surface of the magnesium alloy substrate.

[0032] The method for preparing the composite coating described in this application involves first depositing a layer of dicalcium phosphate dihydrate on the surface of a conductive substrate using an electrodeposition method, and then forming the organic coating on the dicalcium phosphate dihydrate layer. By combining specific inorganic and organic coatings, the corrosion resistance of the composite coating is effectively improved, especially the corrosion resistance of the composite coating to magnesium alloys. Attached Figure Description

[0033] To more clearly illustrate the technical solutions in the embodiments of this application, the accompanying drawings used in the description of the embodiments will be briefly introduced below. Obviously, the accompanying drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0034] Figure 1 This is a flowchart illustrating a method for preparing a composite coating according to an embodiment of this application;

[0035] Figure 2 This is a schematic diagram of the structure of a composite coating provided in an embodiment of this application;

[0036] Figure 3 This is a structural schematic diagram of a magnesium alloy product provided in an embodiment of this application.

[0037] Figure label:

[0038] Composite coating 100; dicalcium phosphate dihydrate layer 10; organic coating 20; magnesium alloy product 200; magnesium alloy substrate 201. Detailed Implementation

[0039] The technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of this application, and not all embodiments. Based on the embodiments of this application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of this application. Furthermore, it should be understood that the specific embodiments described herein are only for illustration and explanation of this application and are not intended to limit this application.

[0040] In this application, unless otherwise stated, directional terms such as "upper" and "lower" generally refer to the upper and lower positions of the device in its actual use or operating state, specifically the drawing directions in the accompanying drawings; while "inner" and "outer" refer to the outline of the device. Furthermore, in the description of this application, the term "comprising" means "including but not limited to". The terms first, second, third, etc., are used merely as illustrative purposes and do not impose numerical requirements or establish a numerical order.

[0041] In this application, "and / or" describes the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, A and B existing simultaneously, or B existing alone. A and B can be singular or plural.

[0042] In this application, "at least one" means one or more, and "more than one" means two or more. "At least one," "at least one of the following," or similar expressions refer to any combination of these items, including any combination of single or multiple items. For example, "at least one of a, b, or c," or "at least one of a, b, and c," can both mean: a, b, c, ab (i.e., a and b), ac, bc, or abc, where a, b, and c can be single or multiple.

[0043] Various embodiments of this application may exist in the form of a range; it should be understood that the description in the form of a range is merely for convenience and brevity and should not be construed as a hard limitation on the scope of this application; therefore, it should be considered that the range description has specifically disclosed all possible sub-ranges and single numerical values ​​within that range. For example, it should be considered that the range description from 1 to 6 has specifically disclosed sub-ranges such as from 1 to 3, from 1 to 4, from 1 to 5, from 2 to 4, from 2 to 6, from 3 to 6, etc., and single numbers within the range, such as 1, 2, 3, 4, 5, and 6, regardless of the range. Furthermore, whenever a numerical range is referred to herein, it means including any referenced number (fraction or integer) within the referred range.

[0044] The technical solution of this application is as follows:

[0045] Firstly, please refer to Figures 1-2 This application provides a method for preparing a composite coating, comprising the following steps:

[0046] Step S11: Provide a sedimentation solution, wherein the sedimentation solution comprises calcium salt, phosphoric acid and water;

[0047] Step S12: Place the conductive substrate in the deposition solution, use the conductive substrate as the working electrode, and use the electrodeposition method to deposit calcium phosphate dihydrate on the surface of the conductive substrate to obtain calcium phosphate dihydrate layer 10.

[0048] Step S13: Provide an organic coating, the organic coating comprising component A and component B, wherein component A comprises a high solids content resin with sterically hindered secondary amine groups, fillers, additives and solvents, and component B comprises a curing agent. The organic coating is applied to the calcium hydrogen phosphate dihydrate layer 10 and cured to form an organic coating 20, thereby obtaining a composite coating 100.

[0049] In step S11:

[0050] The calcium salts include, but are not limited to, one or more of calcium nitrate and calcium oxalate.

[0051] The calcium salt concentration in the sediment is 10–100 g / L, for example, 10 g / L, 20 g / L, 30 g / L, 40 g / L, 50 g / L, 60 g / L, 70 g / L, 80 g / L, 90 g / L, 100 g / L, etc.

[0052] The volume concentration of phosphoric acid in the sediment is 5–17 mL / L, for example, 5 mL / L, 6 mL / L, 7 mL / L, 8 mL / L, 10 mL / L, 12 mL / L, 13 mL / L, 15 mL / L, 16 mL / L, 17 mL / L, etc.

[0053] Within the concentration range of the calcium salt and phosphoric acid, it is advantageous to prepare a calcium hydrogen phosphate dihydrate layer 10 with good corrosion resistance.

[0054] In some embodiments, after mixing, the pH is further adjusted to 3.0–3.5 using an alkaline solution, for example, 3.0, 3.1, 3.2, 3.3, 3.4, 3.5, etc. This is beneficial for preparing a calcium hydrogen phosphate dihydrate layer 10 with good corrosion resistance.

[0055] In some embodiments, the alkaline solution includes, but is not limited to, one or more of ammonia and sodium bicarbonate.

[0056] In some embodiments, the preparation method of the deposition solution includes: providing water, adding phosphoric acid to the water, adjusting the pH to 1.5-2.5, then adding calcium salt, stirring until completely dissolved, adding phosphoric acid in proportion, adjusting the pH to 3.0-3.5 with alkaline solution, and making up the volume to obtain the deposition solution. This method of preparing the deposition solution allows for a longer working life, facilitates subsequent electrodeposition operations, and is beneficial for preparing a highly corrosion-resistant calcium hydrogen phosphate dihydrate layer 10.

[0057] In step S12:

[0058] The conductive substrate can be an alloy, and the alloy can be a magnesium alloy. The magnesium alloy can be a magnesium-aluminum alloy, and further, the magnesium-aluminum alloy can be one or more of the AZ series magnesium-aluminum alloys and the AM series magnesium-aluminum alloys. In at least some embodiments, the alloy is AZ91D magnesium-aluminum alloy or AZ31B magnesium-aluminum alloy.

[0059] The current density for electrodeposition is 0.01–1 mA / cm². 2 For example, 0.01 mA / cm 2 0.1mA / cm 2 0.2mA / cm 2 0.3mA / cm 2 0.4mA / cm 2 0.5mA / cm 2 0.6mA / cm 2 0.7mA / cm 2 0.8mA / cm 2 0.9mA / cm 2 1mA / cm 2 The electrodeposition time is 10 min to 2.1 h, for example, 10 min, 30 min, 50 min, 1 h, 1.5 h, 2 h, 2.1 h, etc. Within the specified current density and time range, it is beneficial to prepare a calcium phosphate dihydrate layer 10 with strong corrosion resistance and good film-forming properties, and it can also ensure a strong adhesion between the organic coating 20 subsequently prepared on the calcium phosphate dihydrate layer 10 and the calcium phosphate dihydrate layer 10.

[0060] In some embodiments, during electrodeposition, the temperature of the deposition solution is 60–80°C, for example, 60°C, 61°C, 62°C, 63°C, 64°C, 65°C, 66°C, 67°C, 68°C, 69°C, 70°C, 80°C, etc. This facilitates the formation of a well-film-forming calcium hydrogen phosphate dihydrate layer 10 on the conductive substrate.

[0061] In some embodiments, after obtaining the dicalcium phosphate dihydrate layer 10 and before applying the organic coating to the dicalcium phosphate dihydrate layer 10, the method further includes: removing the conductive substrate and then drying the conductive substrate.

[0062] It is understood that the drying can be any known drying method, such as natural drying, cold air drying, oven drying, or vacuum drying.

[0063] It is understood that known counter electrodes for electrodeposition can be used during electrodeposition. In at least some embodiments, a platinum electrode is used as the counter electrode during electrodeposition.

[0064] In at least some embodiments, a constant current mode is used during electrodeposition.

[0065] In some embodiments, the process of placing the conductive substrate into the deposition solution further includes pretreatment of the conductive substrate. In at least some embodiments, the pretreatment includes: encapsulating the conductive substrate with a cold-mounting material, then polishing it, followed by ultrasonic cleaning in a cleaning agent, rinsing, and drying. This pretreatment can remove surface impurities and improve surface smoothness, thereby resulting in a stronger bond between the prepared dicalcium phosphate dihydrate layer 10 and the conductive substrate.

[0066] It is understood that the polishing can be a known method for polishing the substrate. In at least one embodiment, the polishing includes: polishing with SiC sandpaper of 200#, 600#, 1200#, 1500# and 2000# in sequence.

[0067] In some embodiments, the cleaning agent includes an alcohol solvent, which includes, but is not limited to, one or more of methanol, ethanol, isopropanol, and butanol.

[0068] In step S13:

[0069] The sterically hindered secondary amine group high-solids resin includes, but is not limited to, hyperbranched polyurethane resin and other high-solids resins.

[0070] In some embodiments, the sterically hindered secondary amine high solids content resin has a viscosity of 200–1000 cps (20°C) and a density of 0.95–1.05 g / ml (20°C).

[0071] In some embodiments, the end groups of the hyperbranched polyurethane resin include one or more of hydroxyl, amino, and fluoroalkyl groups.

[0072] The filler can be a reinforcing filler, including but not limited to one or more of carbon nanotubes and graphene. The filler can give the prepared organic coating high mechanical strength.

[0073] The additives include, but are not limited to, one or more of propylene glycol methyl ether (PM), propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether (DPM), dipropylene glycol monopropyl ether (DPNP), dipropylene glycol monobutyl ether (DPNB), tripropylene glycol n-butyl ether (TPNB), and propylene glycol phenyl ether (PPH). These additives can give the prepared organic coating 20 better film-forming properties.

[0074] The solvents include, but are not limited to, one or more of n-butyl ester, propylene glycol methyl ether acetate, and aliphatic isocyanates.

[0075] By weight, component A comprises 40-60 parts of the high-solids resin, 1-2 parts of the additives, 8-40 parts of the filler, and 10-30 parts of the solvent. Within this range, on the one hand, the prepared organic coating 20 and the dicalcium phosphate dihydrate layer 10 have strong adhesion, thereby giving the prepared composite coating 100 high corrosion resistance and mechanical strength. On the other hand, the prepared organic coating 20 has good salt spray resistance, weather resistance, wear resistance, and temperature change resistance.

[0076] The curing agent includes, but is not limited to, one or more of aliphatic isocyanates and modified polyester prepolymer flexible isocyanates.

[0077] In some embodiments, the aliphatic isocyanate includes, but is not limited to, one or more of n-butyl ester, propylene glycol methyl ether acetate, and aliphatic isocyanates.

[0078] In some embodiments, the modified polyester prepolymer flexible isocyanate includes, but is not limited to, one or more of toluene diisocyanate (TDI) and xylene methane diisocyanate (MDI).

[0079] It is understood that the curing described in this application can be natural curing.

[0080] In some embodiments, the mass ratio of component A to component B is 1:1 to 3:1. Within this mass ratio range, it is beneficial for the curing of the organic coating and for the prepared organic coating 20 to have strong adhesion to the dicalcium phosphate dihydrate layer 10, thereby giving the prepared composite coating 100 high corrosion resistance and mechanical strength. It also gives the prepared organic coating 20 good salt spray resistance, weather resistance, abrasion resistance, and temperature change resistance.

[0081] In some embodiments, the method for preparing the organic coating includes: mixing a sterically hindered secondary amine high-solids resin, filler, additives and solvent to obtain component A; providing component B, wherein component B includes a curing agent; and mixing component A and component B to obtain the organic coating.

[0082] The method for preparing the composite coating 100 described in this application involves first depositing an inorganic dicalcium phosphate dihydrate layer 10 on the surface of a conductive substrate using electrodeposition, and then forming the organic coating 20 on the dicalcium phosphate dihydrate layer 10. Through the specific combination of the inorganic and organic coatings, the corrosion resistance of the composite coating 100 is effectively improved, especially its corrosion resistance to magnesium alloys. Furthermore, this application, by employing specific electrodeposition parameters and a specific composition of organic coating material, achieves a composite coating 100 with high corrosion resistance through the synergistic effect of deposition condition parameters, composition, and content.

[0083] Secondly, please refer to Figure 2 This application embodiment also provides a composite coating 100 prepared by the above preparation method, including the calcium phosphate dihydrate layer 10 and an organic coating 20 bonded to at least one surface of the calcium phosphate dihydrate layer 10.

[0084] In some embodiments, the thickness of the dicalcium phosphate dihydrate layer 10 is 2–45 μm. Within this thickness range, the impedance value of the dicalcium phosphate dihydrate layer 10 is approximately 100–5000 MΩ, which is beneficial for the prepared composite coating 100 to have high corrosion resistance.

[0085] In some embodiments, the thickness of the organic coating 20 is 30–150 μm. Within this thickness range, it is advantageous for the prepared composite coating 100 to simultaneously possess high corrosion resistance.

[0086] Thirdly, please refer to Figure 3 This application also provides a magnesium alloy article 200, including a magnesium alloy substrate 201 and a composite coating 100 as described above bonded to at least one surface of the magnesium alloy substrate 201.

[0087] The dicalcium phosphate dihydrate layer 10 of the composite coating 100 is bonded to the surface of the magnesium alloy substrate 201, and the organic coating 20 of the composite coating 100 is bonded to the surface of the dicalcium phosphate dihydrate layer 10 away from the magnesium alloy substrate 201.

[0088] The magnesium alloy product 200 described in this application includes a composite coating 100 prepared by the preparation method of this application, which has strong corrosion resistance.

[0089] The magnesium alloy product 200 can be used in fields such as electronic products, medical devices, biological scaffolds, aircraft, spacecraft, and rocket and missile manufacturing.

[0090] The present application will be specifically described below through specific embodiments. The following embodiments are only some embodiments of the present application and are not intended to limit the present application.

[0091] Example 1

[0092] AZ91D magnesium-aluminum alloy is used as the conductive substrate. After being encapsulated with cold-mounted material, it is polished in sequence with SiC sandpaper of 200#, 600#, 1200#, 1500# and 2000#, and then ultrasonically cleaned in ethanol. After rinsing, it is dried with cold air and then set aside for use.

[0093] Add phosphoric acid to 100 mL of deionized water to adjust the pH to 2.0, then add calcium nitrate and stir until completely dissolved. Next, slowly add the remaining phosphoric acid while simultaneously adjusting the pH to 3.0 with ammonia. Finally, bring the volume to a final volume to obtain the sediment. In the sediment, the mass concentration of calcium nitrate is 50 g / L and the volume concentration of phosphoric acid is 12.17 mL / L.

[0094] A two-electrode constant current mode was employed, using a platinum electrode as the counter electrode and an AZ91D magnesium alloy electrode placed in a deposition solution at 60°C as the working electrode. Calcium phosphate dihydrate was deposited on the surface of the conductive substrate, with a current density of 0.5 mA / cm². 2 The deposition time was 1 hour, and a 20 μm thick layer of dicalcium phosphate dihydrate was obtained. After that, the surface was cleaned with deionized water and then dried with cold air.

[0095] Component A and component B are provided, wherein component A includes hyperbranched polyurethane resin, carbon nanotubes, dipropylene glycol monobutyl ether and aliphatic isocyanate, and component B includes isocyanate dimer. Component A and component B are mixed in a mass ratio of 1:1 to obtain an organic coating. The organic coating is applied to the calcium hydrogen phosphate dihydrate layer 10 to form an organic coating with a thickness of 100 μm, thereby obtaining a composite coating 100 and a magnesium alloy product 200.

[0096] Example 2

[0097] This embodiment is basically the same as Embodiment 1, except that the current density is 0.1 mA / cm². 2 The thickness of the dicalcium phosphate dihydrate layer 10 is 15 μm.

[0098] Example 3

[0099] This embodiment is basically the same as Embodiment 1, except that the current density is 1 mA / cm² in this embodiment. 2 The thickness of the dicalcium phosphate dihydrate layer 10 is 30 μm.

[0100] Example 4

[0101] This embodiment is basically the same as Embodiment 1, except that the current density in this embodiment is 0.01 mA / cm². 2 The thickness of the dicalcium phosphate dihydrate layer 10 is 10 μm.

[0102] Example 5

[0103] This embodiment is basically the same as Embodiment 1, except that the current density is 1.5 mA / cm². 2 The thickness of the dicalcium phosphate dihydrate layer 10 is 40 μm.

[0104] Example 6

[0105] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the electrodeposition time is 10 min and the thickness of the calcium hydrogen phosphate dihydrate layer 10 is 10 μm.

[0106] Example 7

[0107] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the electrodeposition time is 2 hours and the thickness of the calcium hydrogen phosphate dihydrate layer 10 is 40 μm.

[0108] Example 8

[0109] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the electrodeposition time is 5 min and the thickness of the calcium hydrogen phosphate dihydrate layer 10 is 5 μm.

[0110] Example 9

[0111] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the electrodeposition time is 2.1 h and the thickness of the calcium hydrogen phosphate dihydrate layer 10 is 45 μm.

[0112] Example 10

[0113] This embodiment is basically the same as Embodiment 1, except that the temperature of the sedimentation liquid is 50°C in this embodiment.

[0114] Example 11

[0115] This embodiment is basically the same as Embodiment 1, except that the temperature of the sedimentation liquid is 40°C in this embodiment.

[0116] Example 12

[0117] This embodiment is basically the same as Embodiment 1, except that the temperature of the sedimentation liquid is 70°C in this embodiment.

[0118] Example 13

[0119] This embodiment is basically the same as Embodiment 1, except that the temperature of the sedimentation liquid is 80°C in this embodiment.

[0120] Example 14

[0121] This embodiment is basically the same as Embodiment 1, except that in this embodiment, AZ31B magnesium-aluminum alloy is used instead of AZ91D magnesium-aluminum alloy in Embodiment 1.

[0122] Example 15

[0123] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the mass ratio of component A to component B is 3:1.

[0124] Example 16

[0125] This embodiment is basically the same as Embodiment 1, except that in this embodiment, the mass ratio of component A to component B is 2:1.

[0126] Example 17

[0127] This embodiment is basically the same as Embodiment 1, except that the thickness of the organic coating is 30 μm in this embodiment.

[0128] Example 18

[0129] This embodiment is basically the same as Embodiment 1, except that the thickness of the organic coating is 150 μm in this embodiment.

[0130] Comparative Example 1

[0131] This comparative example is basically the same as Example 1, except that in this comparative example, only the dicalcium phosphate dihydrate layer 10 is formed on the surface of the AZ91D magnesium alloy as in Example 1, and no organic coating 20 is formed.

[0132] Comparative Example 2

[0133] This comparative example is basically the same as Example 1, except that in this comparative example, only the organic coating 20 of Example 1 is formed on the surface of the AZ91D magnesium alloy, and the dicalcium phosphate dihydrate layer 10 is not formed.

[0134] Comparative Example 3

[0135] This comparative example is basically the same as Example 14, except that in this comparative example, only the calcium hydrogen phosphate dihydrate layer 10 is formed on the surface of the AZ31B magnesium alloy as in Example 1, and no organic coating 20 is formed.

[0136] Comparative Example 4

[0137] This comparative example is basically the same as Example 14, except that in this comparative example, only the organic coating 20 of Example 1 is formed on the surface of the AZ31B magnesium alloy, and the dicalcium phosphate dihydrate layer 10 is not formed.

[0138] Comparative Example 5

[0139] This embodiment is basically the same as Embodiment 1, except that in this embodiment, hyperbranched epoxy resin is used to replace the sterically hindered secondary amine group high solids content hyperbranched polyurethane resin in Embodiment 1.

[0140] Comparative Example 6

[0141] This embodiment is basically the same as Embodiment 1, except that in this embodiment, diaminodiphenyl sulfone (DDS) is used to replace the curing agent xylenemethane diisocyanate (MDI) in Embodiment 1.

[0142] Electrochemical tests, salt spray resistance tests, and adhesion tests were conducted on the magnesium alloy products of Examples 1-18 and Comparative Examples 1-6, respectively.

[0143] The electrochemical testing method was as follows: electrochemical impedance spectroscopy (EIS) was used to test the coatings of Example 1 and Comparative Example 1 at 0.5 mA / cm². 2 E at current density for 1 hour coor (corrosion resistant voltage), I coor (self-corrosion current) and R ct (Charge transfer resistance) is used to characterize the corrosion resistance of a coating;

[0144] The method for salt spray resistance testing is a neutral salt spray test.

[0145] The electrochemical test results of Example 1 and Comparative Example 1 are shown in Table 1 below.

[0146] Table 1:

[0147] <![CDATA[E corr (V)]]> <![CDATA[I corr (A·cm -2 )]]> <![CDATA[R ct (Oh)]]> Example 1 -1.51 <![CDATA[9.50×10 -7 ]]> 2270 Comparative Example 1 -1.38 <![CDATA[3.92×10 -5 ]]> 394.8

[0148] As shown in Table 1:

[0149] Compared to the composite coating of Comparative Example 1, the R of the composite coating 100 in Example 1 is higher. ct The value increased nearly fivefold. Specifically, the composite coating 100 of Example 1 showed an increase of 0.5 mA / cm². 2 When deposited at a current density for 1 hour, R ct The value can be increased to 2270Ω, and the self-corrosion current can be reduced to 9.50×10. -7 A·cm -2As can be seen, compared with the composite coating of Comparative Example 1, the composite coating 100 of Example 1 has a significantly improved corrosion protection capability for magnesium alloy.

[0150] The results of the salt spray resistance test and adhesion test are shown in Table 2 below:

[0151] Table 2:

[0152]

[0153]

[0154] As shown in Table 2:

[0155] Compared with the coatings of Comparative Examples 1 to 6, the composite coatings of Examples 1 to 18 have a longer salt spray resistance time and higher adhesion. It can be seen that the composite coating of this application has a better corrosion protection capability for magnesium alloys, and the composite coating of this application has higher mechanical strength.

[0156] In composite coating 100, under the same current conditions, the corrosion resistance is related to the preparation time and conditions of the inorganic film calcium hydrogen phosphate dihydrate layer 10: deposition solution at 60℃, deposition current density of 0.5 mA / cm². 2 The composite coating 100 prepared with a deposition time of 1 hour exhibited the best corrosion resistance. Among all composite coatings, the composite coating 100 showed the best corrosion resistance when the organic coating 20 had a thickness of 100 μm.

[0157] The technical solutions provided by the embodiments of this application have been described in detail above. Specific examples have been used to illustrate the principles and implementation methods of this application. The description of the above embodiments is only for the purpose of helping to understand the method and core ideas of this application. At the same time, for those skilled in the art, there will be changes in the specific implementation methods and application scope based on the ideas of this application. Therefore, the content of this specification should not be construed as a limitation of this application.

Claims

1. A method for preparing a composite coating, characterized in that, Includes the following steps: Calcium salt, phosphoric acid, and water are provided and mixed to obtain a sedimentation solution; The conductive substrate is placed in the deposition solution, and calcium hydrogen phosphate dihydrate is deposited on the surface of the conductive substrate by electrodeposition to obtain a calcium hydrogen phosphate dihydrate layer. An organic coating is provided, comprising component A and component B, wherein component A comprises a high-solids resin with sterically hindered secondary amine groups, fillers, additives, and solvents, and component B comprises a curing agent. The organic coating is applied to the calcium phosphate dihydrate layer to form an organic coating, thereby obtaining a composite coating.

2. The preparation method according to claim 1, characterized in that, The current density for electrodeposition is 0.01–1 mA / cm². 2 The electrodeposition time is 10 min to 2.1 h; and / or The temperature of the sediment is 60–80°C.

3. The preparation method according to claim 1, characterized in that, The calcium salt concentration in the sediment is 10–100 g / L; and / or The volume concentration of phosphoric acid in the sediment is 5–17 mL / L.

4. The preparation method according to claim 1, characterized in that, The mixture also includes adjusting the pH to 3.0–3.5 using an alkaline solution.

5. The preparation method according to claim 4, characterized in that, The alkaline solution includes one or more of ammonia and sodium bicarbonate.

6. The preparation method according to claim 1, characterized in that, The calcium salt includes one or more of calcium nitrate and calcium oxalate; and / or The sterically hindered secondary amine group high-solids resin includes hyperbranched polyurethane resin; and / or The sterically hindered secondary amine-based high-solids resin has a viscosity of 200–1000 cps at 20°C and a density of 0.95–1.05 g / ml at 20°C; and / or The end groups of the hyperbranched polyurethane resin include one or more of hydroxyl, amino, and fluoroalkyl groups; and / or The filler includes one or more of carbon nanotubes and graphene; and / or The adjuvant includes one or more of propylene glycol methyl ether, propylene glycol ethyl ether, propylene glycol butyl ether, dipropylene glycol monomethyl ether, dipropylene glycol monopropyl ether, dipropylene glycol monobutyl ether, tripropylene glycol n-butyl ether, and propylene glycol phenyl ether; and / or The solvent includes one or more of n-butyl ester, propylene glycol methyl ether acetate, and aliphatic isocyanates; and / or The curing agent comprises one or more of aliphatic isocyanates and modified polyester prepolymer flexible isocyanates; the aliphatic isocyanate comprises one or more of n-butyl acetate, propylene glycol methyl ether acetate, and aliphatic isocyanates; the modified polyester prepolymer flexible isocyanate comprises one or more of toluene diisocyanate and xylenemethane diisocyanate; and / or The conductive substrate comprises an alloy, and the alloy comprises a magnesium alloy.

7. The preparation method according to claim 1, characterized in that, By weight, component A comprises 40-60 parts of the high-solids resin, 1-2 parts of the additives, 8-40 parts of the filler, and 10-30 parts of the solvent; and / or The mass ratio of component A to component B is 1:1 to 3:

1.

8. A composite coating prepared by the preparation method according to any one of claims 1 to 7, characterized in that, The composite coating includes a dicalcium phosphate dihydrate layer and an organic coating bonded to at least one surface of the dicalcium phosphate dihydrate layer.

9. The composite coating as described in claim 8, characterized in that, The thickness of the calcium hydrogen phosphate dihydrate layer is 2–45 μm; and / or The thickness of the organic coating is 30–150 μm; and / or The impedance value of the dihydrated calcium hydrogen phosphate layer is 100-5000 MΩ.

10. A magnesium alloy product, characterized in that, It includes a magnesium alloy substrate and a composite coating prepared by the preparation method according to any one of claims 1 to 7 bonded to at least one surface of the magnesium alloy substrate.

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