Preparation method of medical magnesium alloy substrate surface anticorrosion coating

Abstract

The application provides a method for preparing a corrosion-resistant coating on a magnesium alloy surface, which adopts a plasma spraying and electrochemical deposition process. First, a calcium-magnesium coating is formed on the surface of a base material, and then a magnesium-calcium-zinc coating is formed on the outermost layer. The composite coating has good adhesion and binding force, and can generate a dense oxide film in situ between the oxidized and unoxidized regions of the magnesium alloy. Between the Mg-Ca layer and the Mg-Ca-Zn layer, calcium and zinc have a synergistic effect, resulting in the formation of lamellar structures. These lamellar structures can significantly slow down the mechanical strength decay rate of magnesium, while also having other unexpected technical effects. The method can improve the oxidation resistance and structural compactness of the magnesium alloy material, effectively prevent the rapid degradation of the magnesium matrix, and improve the mechanical stability of pure magnesium and magnesium alloys. The addition of zinc to the outermost layer further enhances the mechanical stability of the matrix, slows down the mechanical strength decay rate of magnesium, and enables the magnesium to maintain good mechanical properties during service.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of magnesium alloy corrosion prevention, in particular to a composite coating on the surface of pure magnesium or magnesium alloy and a preparation method thereof. BACKGROUND

[0002] In the field of medical materials, magnesium alloys are considered as a potential human implant material due to their abundant resources, low price, and good biocompatibility and biodegradability. However, the use of magnesium alloys in clinical applications is limited, mainly due to their poor corrosion resistance in the human physiological environment. In the atmosphere or solution, a porous, thin and fragile film layer is often formed on the surface of magnesium alloy, which has a very low density coefficient and almost no protective effect on the substrate, leading to easy corrosion and damage of magnesium alloy. Therefore, it is of great significance to develop a method that can improve the corrosion resistance of magnesium alloy.

[0003] In the prior art, adding calcium is one of the most effective methods to improve the performance of magnesium alloy, and calcium is one of the essential elements for the human body. Studies have shown that magnesium-calcium alloys have good biocompatibility and biodegradability, and the trace release of calcium has no biological toxicity in the human body and has certain benefits. Alloys containing 1.0%-1.5% calcium perform well in terms of mechanical properties. Calcium is more active than magnesium and has stronger binding ability with oxygen. At high temperatures, a composite dense oxide film containing CaO and a small amount of MgO is formed on the surface of magnesium-calcium alloy, and the pores of the MgO film are filled due to the presence of CaO, making it more dense. In addition, the Mg2Ca phase forms a micro-battery with the substrate, promoting the dissolution of the substrate, allowing it to generate an oxide film in situ, thereby preventing further oxidation of magnesium. Adding zinc elements can improve the surface hardness and modulus of magnesium-calcium alloy, and the extruded Mg-Zn-Ca alloy has fine grains and dispersed grain precipitates, thus having high strength and toughness. Since magnesium and calcium are both beneficial elements for the human body and can be degraded by the human body, magnesium-calcium alloy is receiving more and more attention and is expected to become a new type of biodegradable material.

[0004] By using plasma spraying method to form a dense degradable coating on the surface of magnesium alloy, the corrosion resistance of the alloy can be effectively improved. However, there are still some problems in the current coating technology, such as insufficient adhesion of the coating, and the density and uniformity of the coating need to be improved. Therefore, a new type of Mg-Ca-Zn coating and Mg-Ca coating combination is needed to be developed, through a specific preparation process to form a specific new microstructure, to improve the corrosion resistance of magnesium alloy and solve the problems existing in the prior art. SUMMARY

[0005] In order to improve the corrosion resistance of magnesium-based alloy, the application provides a double-coating structure of calcium-containing magnesium alloy and a preparation method thereof. The composite structure of Mg-Ca layer and Mg-Ca-Zn layer has the comprehensive characteristics of corrosion resistance and mechanical properties. The innermost layer is a magnesium alloy substrate, the middle layer is a high-density barrier layer which can block the contact of corrosive medium with the magnesium alloy substrate and can be generated in situ to form a barrier against oxidation and corrosion; the outermost layer is a calcium-magnesium-zinc alloy coating which can effectively prevent the rapid degradation of the substrate, improve the mechanical stability of the material, slow down the mechanical strength decay rate of the substrate, and maintain good mechanical properties during the service period.

[0006] The application provides a composite structure of Mg-Ca layer and Mg-Ca-Zn layer, which adopts the following technical scheme:

[0007] (1) The magnesium alloy substrate is polished and pretreated to ensure a clean and smooth surface. The polished and pretreated magnesium alloy substrate is immersed in anhydrous ethanol for ultrasonic treatment for 40-50 min to remove surface contaminants. The surface to be sprayed is sandblasted to improve the adhesion and uniformity of the coating;

[0008] (2) Magnesium and calcium with a mass percentage purity of 99% are mixed in a mass ratio of 2:1, mechanically alloyed by a ball mill to obtain a particle size of 42-54 μm, and then sealed and stored;

[0009] (3) The magnesium alloy substrate pretreated in step (1) is heated to 60-100℃, and then the temperature of the magnesium alloy substrate is maintained at 60-100℃. Plasma spraying is performed on the surface of the magnesium alloy substrate. Argon is used as the main protective gas, and hydrogen is used as the antioxidant gas. After the substrate to be sprayed is fixed, argon is sent to remove impurities in the spray gun, and then hydrogen is introduced for spraying;

[0010] (4) Atmospheric cooling. A first corrosion-resistant coating is obtained on the surface of the magnesium alloy substrate;

[0011] (5) The substrate with the first corrosion-resistant coating formed in step (4) is immersed in a deposition solution, and a magnesium-calcium-zinc alloy is formed on the outermost layer by electrochemical deposition to obtain a second strong and tough protective coating;

[0012] (6) The thickness of the first corrosion-resistant coating is 2 μm-10 μm, and the thickness of the second strong and tough protective coating is 2 μm-10 μm;

[0013] (7) The prepared biological magnesium alloy is surface cleaned and dried to remove any possible residual contaminants and moisture, ensuring the adhesion and stability of the coating.

[0014] The application has the following beneficial effects:

[0015] 1. In the coating of the present invention, the first corrosion-resistant coating acts as an oxide film, blocking contact between the substrate and the body fluid. At the same time, it can be generated in situ during the corrosion process of the substrate, thereby keeping the surrounding area of ​​the material normal and stable, resulting in a longer service life and better therapeutic effect of the alloy material.

[0016] 2. The double-layer coating structure and the second tough protective coating improve the mechanical properties of the implant, giving it excellent biocompatibility.

[0017] 3. The alloy coating of the present invention comprises, by mass percentage: 0.1-1.0% calcium (Ca), 0.1-5.0% zinc (Zn), with the balance being magnesium (Mg) and unavoidable impurities, the content of which does not exceed 0.01%; it can be absorbed and metabolized by the human body after it has completed its function, has high biocompatibility, and has the advantages of simple material composition and low preparation cost. Attached Figure Description

[0018] Appendix Figure 1 This is a microstructure diagram of the multilayer structure of the present invention. Detailed Implementation

[0019] To more clearly illustrate the present invention, specific embodiments are described in detail below. These embodiments will help those skilled in the art to further understand the present invention. The specific descriptions below are illustrative rather than restrictive and should not be construed as limiting the scope of protection of the present invention.

[0020] Example 1

[0021] like Figure 1 As shown, this is an anti-corrosion coating for magnesium alloy surfaces according to the present invention.

[0022] Includes: a magnesium alloy substrate 1, a corrosion-resistant coating 2, and a tough protective coating 3;

[0023] The matrix material is selected from high-purity magnesium (magnesium content greater than 99.99%), and the preparation method is as follows:

[0024] The high-purity magnesium material was polished sequentially with sandpaper of different grits, and finally polished repeatedly with 2500-grit fine sandpaper. It was then rinsed with deionized water, ultrasonically cleaned with anhydrous ethanol, and air-dried for later use.

[0025] The thickness of the coating can be controlled by adjusting the spraying time.

[0026] Magnesium and calcium, both with a purity of 99% by mass, were mixed in a mass ratio of 2:1 and mechanically alloyed using a ball mill to achieve a particle size of 42-54 μm. The mixture was then sealed and stored.

[0027] The treated high-purity magnesium material is heated to 60-100 DEG C, and then the temperature of the magnesium alloy substrate is maintained at 60-100 DEG C, and plasma spraying is performed on the surface of the magnesium alloy substrate to obtain a corrosion-resistant coating 2 with a thickness of 2 microns.

[0028] A deposition solution is prepared, calcium nitrate tetrahydrate 0.01 mol / L, zinc nitrate 0.02 mol / L, and sodium nitrate 0.1 mol / L are all dissolved in deionized water, the temperature of the deposition solution is 60 DEG C, and the pH value is adjusted to 4.0 by using ammonia water and 1 mol / L nitric acid;

[0029] Electrochemical deposition is performed, the polished high-purity magnesium substrate material is immersed in the deposition solution, high-purity magnesium is used as the cathode, and stainless steel is used as the anode, and the current density is adjusted to 0.5 mA / cm 2 The electrochemical deposition is performed for 2 hours.

[0030] In the fourth step, the electrochemically deposited high-purity magnesium material is taken out, washed with deionized water, placed in an oven for constant temperature drying at 60 DEG C for 1 hour, and a strong and tough protective coating 3 with a thickness of 10 microns is obtained.

[0031] Example 2

[0032] As shown in the figure, it is a magnesium alloy surface corrosion-resistant coating according to the present application. Figure 1

[0033] It comprises a magnesium alloy substrate 1, a corrosion-resistant coating 2, and a strong and tough protective coating 3.

[0034] The substrate material is selected from alloy Mg-4%Y-3.3%RE(Nd, Gd)-0.5Zr%(referred to as WE43), and the preparation method is as follows:

[0035] The WE43 magnesium alloy material is polished with sandpaper of different mesh sizes in sequence, and finally polished repeatedly with 2500-mesh fine sandpaper, washed with deionized water, ultrasonically cleaned with anhydrous ethanol, and naturally air-dried; then placed in a 40wt% hydrofluoric acid aqueous solution for activation treatment for 5 min, washed with deionized water, and naturally air-dried for standby use.

[0036] The thickness of the coating is controlled by controlling the spraying time.

[0037] Magnesium and calcium with a mass percentage purity of 99% are mixed in a mass ratio of 2:1, mechanically alloyed by a ball mill to have a particle size of 42-54 microns, and then sealed and stored.

[0038] The treated high-purity magnesium material is heated to 60-100 DEG C, and then the temperature of the magnesium alloy substrate is maintained at 60-100 DEG C, and plasma spraying is performed on the surface of the magnesium alloy substrate to obtain a corrosion-resistant coating 2 with a thickness of 2 microns. ​

[0039] Prepare the sedimentation solution by dissolving 0.05 mol / L calcium nitrate tetrahydrate, 0.1 mol / L zinc nitrate, and 0.1 mol / L sodium nitrate in deionized water. Set the sedimentation solution temperature to 65°C and adjust the pH to 6.0 using ammonia and 1 mol / L nitric acid.

[0040] Electrochemical deposition involves immersing a polished high-purity magnesium substrate in a deposition solution, using high-purity magnesium as the cathode and stainless steel as the anode, and adjusting the current density to 0.5 mA / cm² for 2 hours.

[0041] The fourth step is to remove the high-purity magnesium material that has been electrochemically deposited, clean it with deionized water, and dry it in an oven at 60°C for 1 hour to obtain a tough protective coating 3 with a thickness of 10μm.

[0042] Example 3

[0043] Same as Example 1, except that:

[0044] The thickness of the first corrosion-resistant coating is 10 μm;

[0045] The second toughness protective coating has a thickness of 2μm.

[0046] Example 4

[0047] Same as Example 1, except that:

[0048] The thickness of the first corrosion-resistant coating is 6 μm;

[0049] The second toughness protective coating has a thickness of 6μm.

[0050] Example 5

[0051] Same as Example 2, except that:

[0052] The thickness of the first corrosion-resistant coating is 10 μm;

[0053] The second toughness protective coating has a thickness of 2μm.

[0054] Example 6

[0055] Same as Example 2, except that:

[0056] The thickness of the first corrosion-resistant coating is 6 μm;

[0057] The second toughness protective coating has a thickness of 6μm.

[0058] The substrate is high-purity magnesium or magnesium alloy. The magnesium alloy surface corrosion-resistant coating of the present application has a yield strength of 150-200 MPa and an elongation of not less than 15%, meeting certain mechanical property requirements. By strictly controlling the impurities in the magnesium alloy composite to not more than 0.01%, the uniformity of the structure and properties of the magnesium alloy composite is effectively ensured, and the biological safety of the magnesium alloy composite is effectively ensured. The pore diameter and the coating thickness can be measured under a scanning electron microscope. It has been proved through repeated experiments that when the thickness of the corrosion-resistant coating is less than 2 μm, the degradation rate is too fast, and if the thickness is greater than 10 μm, a large internal stress is easily generated in the corrosion-resistant coating, and there is a risk of cracking and peeling during the plastic process before implantation and during implantation. Therefore, the thickness of the corrosion-resistant coating is controlled to be between 2-10 μm, and the overall coating thickness is 12 μm.

[0059] The specific embodiments of the present application are described above. It should be understood that the present application is not limited to the specific embodiments described above, and various modifications or changes can be made by those skilled in the art within the scope of the claims, which do not affect the essential content of the present application.

Claims

1. A corrosion protective coating for a magnesium alloy surface, characterized by, The first corrosion-resistant coating and the second toughness protective coating; the first corrosion-resistant coating is arranged on the outer surface of the magnesium alloy substrate; the second toughness protective coating is arranged on the outer surface of the first corrosion-resistant coating; The first corrosion-resistant coating is a calcium-magnesium alloy layer with a dense oxide film, and the thickness is 2-10 microns; the second toughness protective coating is a calcium-magnesium-zinc alloy layer with mechanical stability, and the thickness is 2-10 microns; The first corrosion-resistant coating has Mg2Ca phase, which can generate a dense oxide film on the surface of the magnesium alloy substrate, and slow down the degradation rate of the magnesium alloy; In the second toughness protective coating, zinc element is injected into the surface of the magnesium-calcium alloy, which improves the surface hardness and modulus of the substrate, and maintains good mechanical properties during the service period.

2. A corrosion resistant coating for a magnesium alloy surface according to claim 1, characterised in that, The ion spraying equipment is used for spraying, argon is used as the main protective gas during the spraying process, and hydrogen is used as the anti-oxidation gas; after the workpiece to be sprayed is fixed, argon is sent first to spray off impurities in the spray gun, and then hydrogen is introduced for spraying; the process parameters during spraying are as follows: spraying distance 100-150 mm, working current 360-440 A, working voltage 145-147 V, Ar gas speed 100-150 L / min, hydrogen speed 10-20 L / min, powder feeding amount 30-40 g / min, and the moving speed of the spraying gun body relative to the crankshaft spraying surface is 10-100 mm / s.

3. The corrosion resistant coating for magnesium alloy surfaces according to claim 1, characterized in that, A coating is formed on the surface using electrochemical deposition. In the deposition solution, Ca... 2+ The concentration is 0.005-0.05 mol / L, Zn 2+ The concentration is 0.01-0.1 mol / L, Ca 2 + and Zn 2+ The molar concentration ratio is 1:2, the supporting electrolyte concentration is 0.05-0.1 mol / L, and the pH value is 4.0-6.0; using a substrate material as the cathode and graphite or stainless steel as the anode, it is immersed in the deposition solution at a temperature of 50-70℃ and a current density of 0.5-5 mA / cm². 2 Electrodeposition is performed under specific conditions.

4. The method of claim 1-3, wherein the magnesium alloy surface corrosion protective coating is prepared by the steps of: The method comprises the following steps: (1) pretreating the magnesium alloy substrate; (2) heating the magnesium alloy substrate after the pretreatment in step (1) to 60-100 DEG C, then maintaining the temperature of the magnesium alloy substrate at 60-100 DEG C, using calcium-magnesium alloy particles as the material to be sprayed, and using ion spraying to obtain a calcium-magnesium alloy corrosion-resistant coating on the surface of the magnesium alloy substrate; (3) immersing the substrate material after the spraying of step (2) into a deposition solution to deposit a calcium-magnesium-zinc coating on the surface of the substrate material by electrochemical deposition; the deposition solution is an aqueous solution containing Ca 2+ , Zn 2+ and a supporting electrolyte; (4) obtaining a magnesium alloy surface corrosion-resistant coating.

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