A magnesium alloy surface oxide-modified conductive corrosion-resistant coating and its preparation method

Abstract

The present invention belongs to the technical field of metal protection, and specifically relates to an oxide-modified conductive corrosion-resistant composite coating on the surface of a magnesium alloy and a preparation method thereof. The coating comprises a base layer and a surface layer, wherein the base layer is an oxide-modified polypyrrole-silane layer, and the surface layer is a resin-conductive metal layer. The preparation method of the oxide-modified polypyrrole-silane layer comprises the following steps: depositing the base layer on the surface of the magnesium alloy by an electrochemical method, wherein the electrolyte of the electrochemical method is a mixture of pyrrole, ruthenium dioxide, a dispersant, and a silane coupling agent solution; and curing the resin-conductive metal layer by coating a resin-conductive metal coating on the base layer, wherein the resin-conductive metal coating comprises the following components by weight: 40-60% conductive metal powder, 20-30% epoxy resin, 10-20% organic solvent, and 1-10% curing agent. The present invention simultaneously improves electrical conductivity and corrosion resistance.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal protection, and in particular relates to an oxide-modified conductive corrosion-resistant composite coating on the surface of a magnesium alloy and a preparation method thereof. Background Art

[0002] With the development of cutting-edge fields such as aviation, aerospace, weapons, and 3C electronics, advanced light alloy materials have flourished. Magnesium alloy, as the lightest metal structural material, offers advantages such as low density, high specific strength and stiffness, easy machinability, good electrical and thermal conductivity, excellent damping and vibration reduction, electromagnetic shielding, and ease of recycling. It is now widely used in the aerospace industry for various load-bearing components such as aircraft and missile skins and hulls, aircraft siding, satellites, and spacecraft.

[0003] However, there is still a huge gap between the application potential of magnesium alloys and reality. Magnesium is very active in metallic properties, has a low potential at room temperature and is easily corroded and oxidized. The magnesium oxide film spontaneously formed on its surface is loose and porous and easily dissolves in the atmospheric environment or corrosive media and loses its structural integrity, causing it to fail during service due to a decrease in mechanical support. Therefore, the poor corrosion resistance of magnesium alloys has become a key bottleneck hindering the large-scale industrial application of magnesium alloys. In some specific occasions, magnesium alloy parts are not only required to have excellent corrosion resistance, but also excellent electrical conductivity to achieve electromagnetic shielding or electromagnetic compatibility. Magnesium alloys themselves cannot achieve high conductivity and high corrosion resistance. For this reason, magnesium alloys need to be surface modified to improve their corrosion resistance.

[0004] Common conductive corrosion protection surface treatment technologies for magnesium alloys currently include chemical oxidation and nickel plating. Through chemical or electrochemical corrosion protection, a refractory film composed of oxides, chromides, phosphides, or other compounds is formed on the surface of the magnesium alloy. Currently, the chemical conversion processes used for magnesium alloys primarily include chromate, phosphate / permanganate, and stannate processes. Chemical conversion coatings offer excellent conductivity and superior corrosion resistance compared to the magnesium alloy substrate. However, due to their thinness and softness, magnesium alloy chemical conversion coatings still exhibit poor corrosion resistance, with salt spray resistance typically exceeding 24 hours. Therefore, they are rarely used alone, except as a primer for coatings and as intermediate process protection. Nickel plating on magnesium alloys is primarily an electroless plating method. Nickel coatings (such as Ni-P) on magnesium alloys offer advantages such as high gloss, electrical and thermal conductivity, excellent corrosion resistance, and high hardness, and have been widely used. However, the high density of the nickel coating compromises the lightweight advantages of magnesium alloys and makes coating complex structures such as deep pores and sharp corners difficult. Therefore, new surface coating technologies are needed that combine lightweighting, high conductivity, and high corrosion resistance for magnesium alloys. Summary of the Invention

[0005] The technical problem to be solved by the present invention is to provide an oxide-modified conductive corrosion-resistant coating on the surface of a magnesium alloy and a preparation method thereof, while improving the conductivity and corrosion resistance.

[0006] The embodiment of the present invention provides an oxide-modified conductive corrosion-resistant coating on the surface of a magnesium alloy, comprising a bottom layer and a surface layer, wherein the bottom layer is an oxide-modified polypyrrole-silane layer, and the surface layer is a resin-conductive metal layer;

[0007] The method for preparing the oxide-modified polypyrrole-silane layer comprises depositing a base layer on the surface of a magnesium alloy by an electrochemical method, wherein the electrolyte of the electrochemical method is a mixture of pyrrole, ruthenium dioxide, a dispersant, and a silane coupling agent solution. In the electrolyte, the pyrrole concentration is 0.1-0.3 mol / L, the ruthenium dioxide concentration is 0.1-0.5 mol / L, and the dispersant concentration is 0.1-0.3 mol / L. In the silane coupling agent solution, the solvent is a mixture of water and methanol, the volume ratio of water to methanol is 8-9:1-2, and the volume fraction of the silane coupling agent is 5-10%.

[0008] The resin-conductive metal layer is obtained by curing a resin-conductive metal coating on a base layer by coating, wherein the resin-conductive metal coating comprises the following components by weight: 40-60% conductive metal powder, 20-30% epoxy resin, 10-20% organic solvent, and 1-10% curing agent;

[0009] The silane coupling agent is at least one selected from KH550, KH560, and KH570;

[0010] The conductive metal powder is copper powder, and the particle size of the conductive metal powder is 0.1-20 μm, or a mixture of multiple particle sizes within the particle size range of 0.1-20 μm.

[0011] Optionally, the thickness of the bottom layer is 5-20 μm, and the thickness of the surface layer is 20-120 μm.

[0012] Optionally, the electrolyte further includes sodium salicylate.

[0013] Optionally, the particle size of ruthenium dioxide is not greater than 1 μm, the dispersant is sodium dodecylbenzenesulfonate (concentration is 0.1-0.3 mol / L), and the solvent of the silane coupling agent solution is a mixture of water and methanol.

[0014] Optionally, the resin-conductive metal coating comprises the following components in parts by weight: 50-60% conductive metal powder, 20-30% epoxy resin, 10-15% organic solvent, and 2.5-5% curing agent.

[0015] Optionally, the epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and novolac epoxy resin;

[0016] The organic solvent is selected from at least one of propylene glycol methyl ether, propylene glycol methyl ether acetate, propylene glycol ethyl ether, propylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol methyl ether, diethylene glycol ethyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, and diethylene glycol butyl ether.

[0017] The curing agent is selected from at least one of 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole;

[0018] The resin-conductive metal layer further comprises a functional auxiliary agent, which is selected from at least one of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

[0019] The embodiment of the present invention provides a method for preparing an oxide-modified conductive corrosion-resistant coating on the surface of a magnesium alloy, wherein a base layer is first deposited on the surface of the magnesium alloy, and then a surface layer is deposited on the surface of the base layer;

[0020] The bottom layer is an oxide-modified polypyrrole-silane layer, and the oxide-modified polypyrrole-silane layer is prepared by depositing the bottom layer on the surface of the magnesium alloy by an electrochemical method, wherein the electrolyte of the electrochemical method is a mixture of pyrrole, ruthenium dioxide, a dispersant, and a silane coupling agent solution, wherein the concentration of pyrrole in the electrolyte is 0.1 to 0.3 mol / L, and the concentration of ruthenium dioxide is 0.1 to 0.5 mol / L;

[0021] The surface layer is a resin-conductive metal layer, which is obtained by curing a resin-conductive metal coating on a bottom layer by coating. The resin-conductive metal coating includes 40-60% conductive metal powder, 20-30% epoxy resin, 10-20% solvent, and 1-10% curing agent.

[0022] Alternatively, the electrochemical method is electrochemical cyclic voltammetry (using a three-electrode system) with a scanning potential range of -0.5 to 2 V. SCE , the scanning rate is 5~20mV / s, and the scanning cycle is 5~20 times; the curing temperature after coating is 20~120℃, and the curing time is 0.5~24h.

[0023] The magnesium alloy is polished, degreased, deoiled and cleaned before the base layer is deposited.

[0024] The present invention has the beneficial effect of using polypyrrole, a conductive and corrosion-resistant polymer, to form a coating with other materials, providing additional performance advantages. Polypyrrole exhibits excellent conductivity, corrosion resistance, and wear resistance, as well as high chemical stability and high-temperature resistance. However, polypyrrole coatings lack the corrosion resistance required for long-term corrosion protection of magnesium alloys.

[0025] The oxide-modified conductive corrosion-resistant coating of the present invention has a composite structure consisting of a base layer and a top layer. A conductive polymer is used as the base layer, and the base layer is optimized and modified with silane and the precious metal oxide RuO2. RuO2 has excellent high conductivity and corrosion resistance. Silane modification further enhances the corrosion resistance of the base layer, thereby improving both its conductivity and corrosion resistance.

[0026] In terms of the surface layer, highly conductive metal copper is used as the main conductor to achieve excellent conductive properties of the surface layer; at the same time, functional additives such as alkane coupling agent, titanate coupling agent and aluminate coupling agent are added to the surface layer slurry, which not only promotes the group reaction on the surface of the magnesium alloy, but also forms an interface layer between the magnesium alloy and the resin through chemical reaction. The interface layer enhances the bonding between the magnesium alloy and the resin by transferring stress, and can also improve the interface state, preventing other media from penetrating into the interface, which is beneficial to the corrosion resistance and weather resistance of the product.

[0027] The oxide-modified conductive, corrosion-resistant composite coating of this invention combines lightweight, high conductivity, and high corrosion resistance. Compared to magnesium alloy conductive oxidation (chemical oxidation) coatings, this coating offers significant corrosion resistance advantages. While magnesium alloy conductive oxidation coatings typically withstand salt spray for less than 24 hours, this coating offers a salt spray resistance of 48 hours or longer. Compared to nickel plating on magnesium alloys, this coating boasts a density only one-third that of nickel plating, offering significant advantages in weight reduction.

[0028] The oxide-modified conductive corrosion-resistant coating of the present invention has a simple process and is easy to operate, and is very suitable for being used as a conductive corrosion-resistant coating on the surface of magnesium alloys. BRIEF DESCRIPTION OF THE DRAWINGS

[0029] Figure 1 This is a SEM photograph of the polypyrrole-silane base layer modified with RuO2 according to Example 1 of the present invention.

[0030] Figure 2 This is a SEM photograph of the surface layer (organic resin-copper) of Example 1 of the present invention.

[0031] Figure 3 This is a SEM photograph of the polypyrrole-silane bottom layer without RuO2 modification in Comparative Example 1 of the present invention. DETAILED DESCRIPTION

[0032] The present invention will be further described below with reference to specific embodiments in conjunction with the accompanying drawings, but the present invention is not limited thereto.

[0033] Example 1

[0034] Step 1: Take a magnesium alloy sheet with a size of 100mm*100mm*5mm, polish it with sandpaper, and then degrease it. Then, ultrasonically clean the magnesium alloy sheet with deionized water and anhydrous ethanol in sequence, blow dry it, and set it aside.

[0035] Step 2: Take water and methanol in proportion and mix them evenly, add silane coupling agent KH550 to the mixed solution, and mix again to obtain a silane coupling agent solution, wherein the volume ratio of water to methanol is 9:1, and the volume fraction of the silane coupling agent KH550 is 5%;

[0036] Sodium salicylate is added to the above silane coupling agent solution and mixed uniformly, and then pyrrole, RuO2 oxide and sodium dodecylbenzenesulfonate are added to obtain an electrolyte containing pyrrole and oxide, wherein the electrolyte has a pyrrole concentration of 0.1 mol / L, a sodium dodecyl sulfate concentration of 0.1 mol / L, an oxide RuO2 concentration of 0.1 mol / L, and a sodium salicylate concentration of 0.1 mol / L;

[0037] Step 3: Based on the above electrolyte, a three-electrode system is used to deposit an oxide-modified polypyrrole-silane bottom layer on the surface of the magnesium alloy sheet by electrochemical cyclic voltammetry, wherein the scanning potential range is -0.5 to 2 VSCE, the scanning rate is 5 mV / s, and the scanning cycle is 15 times;

[0038] Step 4: After completion, the magnesium alloy sheet is repeatedly rinsed with deionized water, placed in a drying oven, and dried at 50° C. for 5 hours to obtain a RuO2-modified polypyrrole-silane bottom layer of about 10 μm on the magnesium alloy sheet.

[0039] In step five, a conductive coating containing conductive copper powder was prepared by mixing and dissolving bisphenol A epoxy resin, copper powder, curing agent (2-ethyl-4-methylimidazole), and organic solvent (propylene glycol methyl ether) in a mass ratio of 20%: 60%: 5%: 15%. This mixture was then sprayed onto the treated magnesium alloy substrate to a thickness of 50 μm. The magnesium alloy was then cured in a 130°C drying oven for 0.3 hours. Upon completion of the curing process, an oxide-modified conductive, corrosion-resistant composite coating was formed on the magnesium alloy surface.

[0040] The magnesium alloy conductive corrosion-resistant composite coating obtained in this example has a square resistance of 2Ω / sq and is salt spray resistant for 72 hours.

[0041] Example 2

[0042] A magnesium alloy sheet with a size of 100 mm*100 mm*5 mm was taken, and the magnesium alloy sheet was polished with sandpaper and then degreased. The magnesium alloy sheet was ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, and then dried for use.

[0043] Water and methanol are taken in proportion and mixed evenly, silane coupling agent KH550 is added to the mixed solution, and mixed evenly again to obtain a silane coupling agent solution, wherein the volume ratio of water to methanol is 8:2, and the volume fraction of the silane coupling agent is 10%;

[0044] Sodium salicylate is added to the above silane coupling agent solution and mixed uniformly, followed by adding pyrrole, RuO2 oxide and sodium dodecylbenzenesulfonate to obtain an electrolyte containing pyrrole and oxide, wherein the electrolyte has a pyrrole concentration of 0.2 mol / L, a sodium dodecyl sulfate concentration of 0.15 mol / L, a RuO2 oxide concentration of 0.2 mol / L, and a sodium salicylate concentration of 0.15 mol / L;

[0045] Based on the above electrolyte, an oxide-modified polypyrrole-silane underlayer was deposited on the surface of a magnesium alloy sheet using a three-electrode system via cyclic voltammetry. The scanning potential range was -0.5 to 2 VSCE, the scan rate was 10 mV / s, and the scan cycle was 20 times.

[0046] After completion, the magnesium alloy sheet was repeatedly rinsed with deionized water, placed in a drying oven, and dried at 50°C for 5 hours to obtain a RuO2-modified polypyrrole-silane bottom layer of about 12 μm on the magnesium sheet.

[0047] A conductive coating containing conductive copper powder was prepared by mixing and dissolving bisphenol F epoxy resin, copper powder, curing agent (2-phenyl-4-methylimidazole), organic solvent (propylene glycol butyl ether acetate), and silane coupling agent (KH550) in a mass ratio of 30%:55%:2.5%:10%:2.5%. A 60-μm-thick coating was sprayed onto the treated magnesium alloy substrate. The magnesium alloy was then cured in a 120°C drying oven for 0.5 h. Upon completion of the curing process, an oxide-modified conductive, corrosion-resistant coating formed on the magnesium alloy surface.

[0048] The magnesium alloy conductive corrosion-resistant coating obtained in this example has a square resistance of 1.5Ω / sq and is salt spray resistant for 96 hours.

[0049] Example 3

[0050] A magnesium alloy sheet with a size of 100 mm*100 mm*5 mm was taken, and the magnesium alloy sheet was polished with sandpaper and then degreased. The magnesium alloy sheet was ultrasonically cleaned with deionized water and anhydrous ethanol in sequence, and then dried for use.

[0051] Water and methanol were taken in proportion and mixed evenly, silane coupling agent KH550 was added to the mixed solution, and mixed evenly again to obtain a silane coupling agent solution, wherein the volume ratio of water to methanol was 8.5:1.5, and the volume fraction of the silane coupling agent was 8%;

[0052] Sodium salicylate is added to the above silane coupling agent solution and mixed uniformly, followed by adding pyrrole, RuO2 oxide and sodium dodecylbenzenesulfonate to obtain an electrolyte containing pyrrole and oxide, wherein the electrolyte has a pyrrole concentration of 0.25 mol / L, a sodium dodecyl sulfate concentration of 0.2 mol / L, an oxide RuO2 concentration of 0.3 mol / L, and a sodium salicylate concentration of 0.25 mol / L;

[0053] Based on the above electrolyte, an oxide-modified polypyrrole-silane underlayer was deposited on the surface of a magnesium alloy sheet using a three-electrode system via cyclic voltammetry. The scanning potential range was -0.5 to 2 VSCE, the scan rate was 15 mV / s, and the scan cycle was 20 times.

[0054] After completion, the magnesium alloy sheet was repeatedly rinsed with deionized water, placed in a drying oven, and dried at 50°C for 5 hours to obtain a RuO2-modified polypyrrole-silane bottom layer of about 15 μm on the magnesium sheet.

[0055] A conductive coating containing conductive copper powder was prepared by mixing and dissolving a phenolic epoxy resin, copper powder, curing agent (2-ethyl-4-methylimidazole), solvent (ethylene glycol ethyl ether acetate), and silane coupling agent (KH550) in a ratio of 25% by mass: 50% by mass: 5% by mass: 15% by mass: 5% by mass. An 80-μm-thick coating was then sprayed onto the treated magnesium alloy substrate. The magnesium alloy was then cured in a drying oven at 120°C for 0.5 h. Upon completion of the curing process, an oxide-modified conductive, corrosion-resistant coating formed on the magnesium alloy surface.

[0056] The magnesium alloy conductive corrosion-resistant coating obtained in this example has a square resistance of 1.8Ω / sq and is salt spray resistant for 96 hours.

[0057] Comparative Example 1

[0058] The remaining components and process steps are the same as those in Example 1, except that the electrolyte in step 2 does not contain RuO2 oxide.

[0059] The magnesium alloy conductive corrosion-resistant coating obtained in this comparative example has a square resistance of 3.5Ω / sq and is salt spray resistant for 60 hours.

[0060] Comparative Example 2

[0061] The remaining components and process steps are the same as those in Example 1, except that RuO2 in the electrolyte of step 2 is replaced by ZrO2.

[0062] The magnesium alloy conductive corrosion-resistant coating obtained in this comparative example has a square resistance of 2.2Ω / sq and is salt spray resistant for 84 hours.

[0063] Comparative Example 3

[0064] The remaining ingredients and process steps are the same as those in Example 1, except that the electrolyte in step 2 does not contain the silane coupling agent KH550.

[0065] The magnesium alloy conductive corrosion-resistant coating obtained in this comparative example has a square resistance of 1.8Ω / sq and is salt spray resistant for 48 hours.

[0066] Those skilled in the art should understand that the discussion of any of the above embodiments is merely illustrative and is not intended to imply that the scope of protection of the present application is limited to these examples. In line with the present application, the technical features in the above embodiments or different embodiments may be combined, the steps may be implemented in any order, and there are many other variations of different aspects of one or more embodiments of the present application as described above, which are not provided in detail for the sake of simplicity.

[0067] The one or more embodiments of this application are intended to encompass all such substitutions, modifications, and variations that fall within the broad scope of this application. Therefore, any omissions, modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of one or more embodiments of this application should be included in the scope of protection of this application.

Claims

1. A conductive corrosion-resistant coating modified with oxide on the surface of a magnesium alloy, characterized in that: It comprises a bottom layer and a surface layer, wherein the bottom layer is an oxide-modified polypyrrole-silane layer, and the surface layer is a resin-conductive metal layer; The oxide-modified polypyrrole-silane layer is prepared by depositing a base layer on the surface of a magnesium alloy by an electrochemical method, wherein the electrolyte of the electrochemical method is a mixture of pyrrole, ruthenium dioxide, a dispersant, and a silane coupling agent solution, wherein the concentration of pyrrole in the electrolyte is 0.1 to 0.3 mol / L and the concentration of ruthenium dioxide is 0.1 to 0.5 mol / L; The resin-conductive metal layer is obtained by curing a resin-conductive metal coating on a base layer by coating, wherein the resin-conductive metal coating comprises the following components by weight: 40-60% conductive metal powder, 20-30% epoxy resin, 10-20% organic solvent, and 1-10% curing agent; The silane coupling agent is at least one selected from KH550, KH560, and KH570; The conductive metal powder is copper powder, and the particle size of the conductive metal powder is 0.1 to 20 μm.

2. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to claim 1, characterized in that: The thickness of the bottom layer is 5-20 μm, and the thickness of the surface layer is 20-120 μm.

3. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to claim 1, characterized in that: The electrolyte also includes sodium salicylate.

4. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to claim 1, characterized in that: The particle size of ruthenium dioxide is no more than 1 μm, the dispersant is sodium dodecylbenzenesulfonate, and the solvent of the silane coupling agent solution is a mixture of water and methanol.

5. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to any one of claims 1 to 4, characterized in that: The resin-conductive metal coating comprises the following components by weight: 50-60% conductive metal powder, 20-30% epoxy resin, 10-15% organic solvent, and 2.5-5% curing agent.

6. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to any one of claims 1 to 4, characterized in that: The epoxy resin is selected from at least one of bisphenol A epoxy resin, bisphenol F epoxy resin, and novolac epoxy resin; The organic solvent is selected from at least one of propylene glycol methyl ether, propylene glycol methyl ether acetate, propylene glycol ethyl ether, propylene glycol butyl ether acetate, ethylene glycol ethyl ether acetate, diethylene glycol methyl ether, diethylene glycol ethyl ether, dipropylene glycol methyl ether, dipropylene glycol ethyl ether, and diethylene glycol butyl ether.

7. The conductive corrosion-resistant coating modified with oxide on the surface of magnesium alloy according to claim 5, characterized in that: The curing agent is selected from at least one of 2-ethyl-4-methylimidazole, 2-phenyl-4-methylimidazole, and 1-cyanoethyl-2-ethyl-4-methylimidazole; The resin-conductive metal layer further comprises a functional auxiliary agent, which is selected from at least one of a silane coupling agent, a titanate coupling agent and an aluminate coupling agent.

8. A method for preparing an oxide-modified conductive corrosion-resistant coating on the surface of a magnesium alloy according to any one of claims 1 to 7, characterized in that: A base layer is first deposited on the surface of the magnesium alloy, and then a surface layer is deposited on the surface of the base layer; The bottom layer is an oxide-modified polypyrrole-silane layer, and the oxide-modified polypyrrole-silane layer is prepared by depositing the bottom layer on the surface of the magnesium alloy by an electrochemical method, wherein the electrolyte of the electrochemical method is a mixture of pyrrole, ruthenium dioxide, a dispersant, and a silane coupling agent solution, wherein the concentration of pyrrole in the electrolyte is 0.1 to 0.3 mol / L, and the concentration of ruthenium dioxide is 0.1 to 0.5 mol / L; The surface layer is a resin-conductive metal layer, which is obtained by curing a resin-conductive metal coating on a bottom layer by coating. The resin-conductive metal coating includes 40-60% conductive metal powder, 20-30% epoxy resin, 10-20% solvent, and 1-10% curing agent.

9. The preparation method according to claim 8, wherein The electrochemical method was electrochemical cyclic voltammetry with a scanning potential range of -0.5 to 2 V. SCE , the scanning rate is 5~20mV / s, and the scanning cycle is 5~20 times; the curing temperature after coating is 20~120℃, and the curing time is 0.5~24h.

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