Corrosion-resistant antibacterial and osteogenesis-promoting medical magnesium alloy and preparation method thereof

Abstract

The present application is directed to the problem of the fast degradation rate and the insufficient biological function of medical magnesium alloy, and proposes a kind of corrosion-resistant antibacterial and osteogenesis-promoting medical magnesium alloy and its preparation method. The magnesium alloy is composed of a substrate and a surface coating. The substrate is a Mg-Zn-Mn-Sr-Ca alloy containing graphitizing carbon (GC) and cerium dioxide (CeO2) reinforcing phase. The surface coating is a double-layer structure, the inner layer is a calcium-phosphorus-strontium (Ca-P-Sr) coating doped with zinc oxide (ZnO) nanoparticles, and the outer layer is a silicon dioxide (SiO2) coating. The preparation method includes melting, hot extrusion, micro-arc oxidation (MAO), electrophoretic deposition (EPD) and post-heat treatment.

Description

Technical Field

[0001] This invention belongs to the field of metal material processing technology, specifically relating to a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy and its preparation method. Background Technology

[0002] In recent years, magnesium alloys, as biodegradable metallic materials, have received widespread attention in the medical field. Compared with traditional medical metals (such as titanium alloys, nickel-titanium alloys, and cobalt-chromium alloys), magnesium alloys have many advantages: First, they have low density, high specific strength, and an elastic modulus closer to that of human bone, effectively reducing stress shielding effects; second, their unique biodegradability avoids the need for secondary removal surgery; and finally, their good biocompatibility can regulate human physiological activities, maintain normal metabolism, and promote bone growth. Based on these advantages, magnesium alloys have broad application prospects in orthopedics. However, the excessively rapid degradation rate of magnesium alloys in bodily fluids can damage the integrity of the implant structure in the early stages of implantation, making it unable to provide sufficient mechanical support. Simultaneously, the excessive hydrogen gas produced during the degradation process can easily trigger inflammation, hindering tissue healing and repair. To address these issues, composite preparation processes are needed to endow magnesium alloys with superior corrosion resistance and biological functions.

[0003] Alloying is a common method to improve the corrosion resistance of magnesium alloys. Adding appropriate alloying elements can alter the microstructure of magnesium alloys, improving their mechanical properties through solid solution strengthening and precipitation strengthening. Furthermore, alloying elements can improve the density of the oxide film, promote the formation of corrosion product layers, and enhance the material's corrosion resistance. Currently, medical-grade magnesium alloys based on Mg-Zn, Mg-Ca, Mg-Sr, and Mg-Li systems are under development. In addition to alloying elements, introducing suitable reinforcing phases to achieve composite formation can further improve the overall performance of magnesium alloys. SiC, Al2O3, TiC, and TiN can be used as reinforcing phases to enhance material properties.

[0004] Surface modification can effectively improve the overall performance of magnesium alloys by optimizing the microstructure, chemical composition, and phase composition of the material surface to regulate the corrosion behavior and biological functions of the substrate without altering its microstructure and properties. Micro-arc oxidation (MAO) is a commonly used surface modification technique for biomedical metals. The resulting film consists of an inner dense layer and an outer porous layer, exhibiting good adhesion to the substrate and excellent corrosion resistance. By controlling the chemical composition of the micro-arc oxidation electrolyte, the coating can also be endowed with certain antibacterial and osteogenic functions. Electrophoretic deposition (EPD), as a commonly used surface modification technique for metallic materials, has advantages such as low cost, high efficiency, and environmental friendliness. The prepared film has high hardness, good adhesion, and strong corrosion resistance. Due to the high discharge intensity at defects in the micro-arc oxidation film, charged colloidal particles preferentially enter and fill the pores and cracks in the micro-arc oxidation film during electrophoretic deposition. Therefore, the composite process of micro-arc oxidation and electrophoretic deposition holds promise for preparing high-performance coatings.

[0005] In summary, to improve the overall performance of medical magnesium alloys, this invention proposes a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy and its preparation method. The magnesium alloy matrix is ​​prepared by alloying and composite processing, and a corrosion-resistant, antibacterial, and osteogenic coating is prepared on the magnesium alloy matrix using a micro-arc oxidation-electrophoretic deposition composite process. Summary of the Invention

[0006] This invention addresses the problems of excessively rapid degradation and insufficient biological function in medical magnesium alloys by proposing a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy and its preparation method. The magnesium alloy comprises a matrix and a surface coating. The matrix is ​​a Mg-Zn-Mn-Sr-Ca alloy containing graphitizing carbon (GC) and cerium dioxide (CeO2) reinforcing phases. The surface coating has a double-layer structure: an inner layer is a calcium-phosphorus-strontium (Ca-P-Sr) coating doped with zinc oxide (ZnO) nanoparticles, and an outer layer is a silicon dioxide (SiO2) coating. The preparation method includes smelting, hot extrusion, MAO (magnesium oxide oxide) process, EPD (epidermal decomposition), and post-heat treatment.

[0007] The roles of alloying elements are as follows: Zn is a biodegradable and biocompatible element that can effectively improve the mechanical properties of magnesium alloys. Appropriate amounts of Zn can also improve the corrosion behavior of magnesium alloys. Mn can effectively reduce Fe impurities in magnesium alloy melts and refine magnesium alloy grains, thereby improving its corrosion resistance. Sr, as a magnesium alloy grain refiner, has good biocompatibility and can promote the growth and development of osteoblasts. Ca can refine magnesium alloy grains and improve its corrosion resistance, inhibiting pitting corrosion formation. It is also an essential nutrient element for bone tissue growth and development. The roles of reinforcing phases are as follows: Adding GC can purify the magnesium alloy melt and improve its microstructure. Its uniform dispersion in the matrix can simultaneously improve the strength and plasticity of magnesium alloys. Adding CeO2 can refine magnesium alloy grains, improve its strength and toughness, and enhance the stability of the surface passivation film, thus improving corrosion resistance. Utilizing the size difference between GC and CeO2, a size effect can be achieved, synergistically improving the mechanical and corrosion resistance of magnesium alloys. In addition, neither GC nor CeO2 is biotoxic and will not compromise the biocompatibility of magnesium alloys.

[0008] The functions of the MAO coating are as follows: Its electrolyte, composed of Ca(OH)₂, Na₃PO₄·12H₂O, Sr(CH₃COO)₂, KF, and ZnO, possesses excellent conductivity, ensuring the nucleation probability and growth efficiency of the film. By optimizing process parameters, the thickness, porosity, and pore size of the MAO coating can be controlled. Its chemical composition, consisting of Ca, P, Sr, and ZnO, exhibits good osteogenic and antibacterial properties. The MAO coating consists of an inner dense layer and an outer porous layer. The inner dense layer ensures good corrosion resistance, while the outer porous layer can support ZnO particles. ZnO, while exerting antibacterial and osteogenic functions, also has a certain pore-sealing effect, further improving the corrosion resistance of the MAO coating. Furthermore, the MAO coating as a whole can serve as a transition layer between the substrate and the EPD coating, improving the bonding strength between the substrate and the surface coating, which is beneficial for improving the coating's lifespan and functionality. The EPD coating serves two purposes: firstly, it seals the pores of the MAO coating, preventing the intrusion of corrosive media and thus improving its corrosion resistance; secondly, SiO2 has excellent corrosion resistance and biocompatibility, which can further improve the overall performance of magnesium alloys.

[0009] The roles of each process in the preparation method are as follows: smelting is used to prepare Mg-Zn-Mn-Sr-Ca alloy ingots with different chemical compositions containing GC and CeO2 reinforcing phases; hot extrusion is used to prepare alloy ingots into alloy rods of different specifications; MAO is used to prepare Ca-P-Sr coatings doped with ZnO nanoparticles with high bonding strength and possessing corrosion resistance, antibacterial properties and osteogenic properties; EPD is used to prepare SiO2 coatings that are well bonded to the MAO coating, uniform, flat, and without obvious defects; post-heat treatment is used to reduce residual stress at adjacent interfaces of the substrate / MAO coating / EPD coating, improve microstructure, balance chemical composition, and improve the overall performance of the material system.

[0010] The technical solution of this invention is as follows:

[0011] A corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy, comprising a matrix and a surface coating, wherein the matrix is ​​a Mg-Zn-Mn-Sr-Ca alloy containing GC and CeO2 reinforcing phases, and the surface coating is a double-layer structure, wherein the inner layer is a Ca-P-Sr coating doped with ZnO nanoparticles, and the outer layer is a SiO2 coating.

[0012] A method for preparing a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy includes the following steps:

[0013] Step 1: Melting and preparing alloy ingots

[0014] Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy was adjusted. The mass fraction of Zn was 1–5 wt.%, the mass fraction of Mn was 0.5–1.5 wt.%, the mass fraction of Sr was 0.5–2.5 wt.%, and the mass fraction of Ca was 0.5–3.5 wt.%. GC and CeO2 nanoparticles were used as raw materials. To enhance the phase, the mass fraction of the reinforcing phase was adjusted, with GC at 3–6 wt.% and CeO2 at 1–4 wt.%. Melting was carried out in a resistance heating furnace using a mixture of SF6 and CO2 as a protective atmosphere. The temperature was first maintained at 750–790℃ for 10–15 min, then at 710–730℃ for 8–15 min, ensuring thorough mixing of the melt. The melt was then poured into a mold preheated to 700℃ and cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm.

[0015] Preferably, the mass fraction of Zn is 2-4 wt.%, the mass fraction of Mn is 0.8-1.2 wt.%, the mass fraction of Sr is 1-2 wt.%, the mass fraction of Ca is 1-3 wt.%, the mass fraction of GC is 4-5 wt.%, and the mass fraction of CeO2 is 2-3 wt.%. The temperature is first maintained at 760-780℃ for 12-15 min, and then maintained at 715-725℃ for 10-15 min.

[0016] Step 2: Hot extrusion preparation of alloy rods

[0017] The alloy ingot obtained in the first step is homogenized by holding it at 400-450℃ for 2-4 hours. After rapid cooling, the ingot is peeled off to obtain an alloy ingot with a diameter of 100mm×80mm. Then, it is preheated at 350-450℃ for 1-2 hours and hot extruded using a horizontal extrusion press with an extrusion ratio of 10-48, an extrusion temperature of 300-400℃, and an extrusion speed of 1-20m / min to obtain alloy bars.

[0018] Preferably, the alloy ingot is homogenized at 420–440°C for 2.5–3.5 hours, then preheated at 380–420°C for 1.0–1.5 hours, with an extrusion ratio of 18–36, an extrusion temperature of 340–380°C, and an extrusion speed of 5–10 m / min.

[0019] Step 3: MAO preparation of surface coating

[0020] For ease of experimentation, alloy rods were cut into Φ10mm×3mm discs using a wire EDM machine. Before coating preparation, mechanical grinding was performed to remove surface oxide scale and impurities. The discs were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, dried with cold air, and subjected to MAO treatment using a high-power, multi-functional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was then prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)₂, Na₃PO₄·12H₂O, Sr(CH₃COO)₂, KF, and ZnO. The concentrations of (OH)2 were 1.5–5.0 g / L, Na3PO4·12H2O were 5–12 g / L, Sr(CH3COO)2 were 3–8 g / L, KF was 10–15 g / L, and ZnO was 2–8 g / L. The pH of the electrolyte was adjusted to 9–12 using NaOH. The MAO was applied in constant voltage mode with a voltage of 350–500 V, a processing time of 5–10 min, a pulse count of 30–80, a duty cycle of 30%–60%, and a frequency of 400–1200 Hz.

[0021] Preferably, the concentration of Ca(OH)2 is 2-4 g / L, the concentration of Na3PO4·12H2O is 6-10 g / L, the concentration of Sr(CH3COO)2 is 5-7 g / L, the concentration of KF is 12-14 g / L, the concentration of ZnO is 4-6 g / L, the pH of the electrolyte is adjusted to 10-11 using NaOH, the voltage is 400-500V, the treatment time is 6-8 min, the number of pulses is 40-60, the duty cycle is 40%-50%, and the frequency is 600-1000 Hz.

[0022] Step 4: EPD preparation of surface coating

[0023] An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.0. The SiO2 content of the neutral SiO2 dispersion was 20%–40%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25℃. The sample was used as the anode, the platinum sheet was used as the cathode, the electrode distance was 8–12 cm, the deposition voltage was 250–350 V, and the deposition time was 1–3 min.

[0024] Preferably, the neutral SiO2 dispersion has a SiO2 content of 25% to 35%, an electrode distance of 9 to 11 cm, a deposition voltage of 275 to 325 V, and a deposition time of 1.5 to 2.5 min.

[0025] Step 5: Post-heat treatment

[0026] The magnesium alloy with surface coating obtained in step four is subjected to post-heat treatment at a temperature of 100–300℃ for a holding time of 0.5–2 hours.

[0027] Preferably, the temperature is 150–250℃ and the holding time is 0.5–1h.

[0028] The corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy prepared by the above method consists of a matrix and a surface coating. The material system is novel in design and ingenious in composition: For the matrix, the alloying elements are not only commonly used alloying elements in magnesium alloys, but also biocompatible elements. By controlling their content, a synergistic effect can be achieved, which can simultaneously improve the mechanical properties, corrosion resistance, and biofunctionality of magnesium alloys. The selection of the reinforcing phase can further improve the comprehensive performance of magnesium alloys. For the surface coating, the inner layer is a MAO coating and the outer layer is an EPD coating. The coating is composed of biocompatible elements, and the inner and outer layers are well bonded. It can provide certain antibacterial and osteogenic effects on the basis of improving the corrosion resistance of magnesium alloys. The preparation method described is rationally designed and feasible, with each process closely integrated: smelting can prepare alloy ingots with different chemical compositions; hot extrusion can prepare alloy bars with different specifications; MAO can prepare coatings that bond well with the matrix and have corrosion resistance, antibacterial properties, and osteogenic properties; EPD can prepare coatings that bond well with the MAO coating, are uniform and smooth, and have no obvious defects; post-heat treatment can improve the comprehensive performance of the material system by reducing residual stress, improving microstructure, and balancing chemical composition.

[0029] The beneficial effects of this invention are as follows:

[0030] (1) The inventors comprehensively utilized processes such as smelting, hot extrusion, MAO, EPD, and post-heat treatment, and through numerous experiments, prepared a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy, and summarized the optimal range of process parameters: For smelting to prepare alloy ingots, the mass fraction of Zn is 2-4 wt.%, the mass fraction of Mn is 0.8-1.2 wt.%, the mass fraction of Sr is 1-2 wt.%, the mass fraction of Ca is 1-3 wt.%, the mass fraction of GC is 4-5 wt.%, and the mass fraction of CeO2 is 2-3 wt.%. First, it is held at 760-780℃ for 12-15 min, and then held at 715-725℃ for 10-15 min; For hot extrusion to prepare alloy bars, the alloy ingot is homogenized at 420-440℃ for 2.5-3.5 h, and then preheated at 380-420℃ for 1-1.5 h, with an extrusion ratio of 18-36 and an extrusion temperature of 340-380℃. The extrusion speed is 5–10 m / min; for the preparation of surface coatings with MAO, the concentrations are: Ca(OH)₂ 2–4 g / L, Na₃PO₄·12H₂O 6–10 g / L, Sr(CH₃COO)₂ 5–7 g / L, KF 12–14 g / L, ZnO 4–6 g / L. The pH of the electrolyte is adjusted to 10–11 using NaOH, and the voltage is 400–500 V. The deposition time is 6–8 min, the number of pulses is 40–60, the duty cycle is 40%–50%, and the frequency is 600–1000 Hz. For EPD preparation of surface coatings, the SiO2 content of the neutral SiO2 dispersion is 25%–35%, the electrode distance is 9–11 cm, the deposition voltage is 275–325 V, and the deposition time is 1.5–2.5 min. For post-heat treatment, the temperature is 150–250 °C, and the holding time is 0.5–1 h. Using the above combination of process parameters, corrosion-resistant, antibacterial, and osteogenic medical magnesium alloys can be prepared.

[0031] (2) The inventors prepared a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy. Microstructural and performance analysis showed that the coating thickness was 16.5–25.2 μm, and the self-corrosion potential of the surface-modified magnesium alloy was -1.12–-0.64 V / SCE, with a self-corrosion current density of (0.5–4.8) × 10⁻⁶. -6 A / cm 2Compared with unmodified magnesium alloys, the self-corrosion potential increased by 30.9%–60.5%, and the self-corrosion current density decreased by 171–1640 times, indicating that the coating effectively improved the corrosion resistance of the magnesium alloy. The inhibition rates of the magnesium alloy against Staphylococcus aureus and Escherichia coli increased from 60%–80% and 50%–70% before surface modification to 90%–100% and 95%–100% after surface modification, respectively, demonstrating a significant improvement in the material's antibacterial properties. The magnesium alloy also increased the alkaline phosphatase (ALP) activity of mouse embryonic osteoblasts (MC3T3-E1) from 70%–80% before surface modification to 95%–100% after surface modification, indicating a significant improvement in the material's osteogenic properties. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the cross-sectional structure of the magnesium alloy surface coating in Example 1.

[0033] Figure 2 The change in corrosion resistance of magnesium alloy before and after surface modification in Example 1 is shown.

[0034] Figure 3 This refers to the changes in the antibacterial properties of the magnesium alloy before and after surface modification in Example 1.

[0035] Figure 4 The changes in the osteogenic properties of magnesium alloy before and after surface modification in Example 1 are shown. Detailed Implementation

[0036] The present invention will now be described in further detail with reference to the accompanying drawings and embodiments.

[0037] The present invention discloses a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy, which is composed of a matrix and a surface coating. The matrix is ​​a Mg-Zn-Mn-Sr-Ca alloy containing GC and CeO2 reinforcing phases. The surface coating has a double-layer structure, with the inner layer being a Ca-P-Sr coating doped with ZnO nanoparticles and the outer layer being a SiO2 coating.

[0038] The present invention discloses a method for preparing a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy, comprising the following steps:

[0039] Step 1: Melting and preparing alloy ingots

[0040] Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy is adjusted. The mass fraction of Zn is 1-5 wt.%, preferably 2-4 wt.%, the mass fraction of Mn is 0.5-1.5 wt.%, preferably 0.8-1.2 wt.%, the mass fraction of Sr is 0.5-2.5 wt.%, preferably 1-2 wt.%, and the mass fraction of Ca is 0.5-3.5 wt.%, preferably 1-3 wt.%. GC and CeO2 nanoparticles are used as reinforcing phases, and the reinforcing phases are adjusted accordingly. The mass fraction of GC is 3-6 wt.%, preferably 4-5 wt.%, and the mass fraction of CeO2 is 1-4 wt.%, preferably 2-3 wt.%. The melting is carried out in a resistance heating furnace, using a mixture of SF6 and CO2 as a protective atmosphere. First, the temperature is maintained at 750-790°C for 10-15 min, preferably at 760-780°C for 12-15 min, and then at 710-730°C for 8-15 min, preferably at 715-725°C for 10-15 min. The melt is thoroughly mixed during melting and poured into a mold preheated to 700°C. The melt is then cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm.

[0041] Step 2: Hot extrusion preparation of alloy rods

[0042] The alloy ingot obtained in the first step is homogenized at 400–450°C for 2–4 hours, preferably at 420–440°C for 2.5–3.5 hours. After rapid cooling, the ingot is peeled to obtain an alloy ingot with a diameter of 100 mm × 80 mm. The ingot is then preheated at 350–450°C for 1–2 hours, preferably at 380–420°C for 1.0–1.5 hours. Hot extrusion is performed using a horizontal extrusion press with an extrusion ratio of 10–48, preferably 18–36, an extrusion temperature of 300–400°C, preferably 340–380°C, and an extrusion speed of 1–20 m / min, preferably 5–10 m / min, to obtain an alloy bar.

[0043] Step 3: MAO preparation of surface coating

[0044] For ease of experimentation, the alloy rods were cut into Φ10mm×3mm discs using a wire EDM machine. Before coating preparation, mechanical grinding was performed to remove surface oxide scale and impurities. The discs were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, dried with cold air, and subjected to MAO treatment using a high-power, multi-functional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was then prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)₂, Na₃PO₄·12H₂O, Sr(CH₃COO)₂, KF, and ZnO. The concentration of Ca(OH)₂ was 1.5–5.0 g / L, preferably 2–4 g / L, and the concentration of Na₃PO₄·12H₂O was 5–12 g / L. The preferred concentrations are 6–10 g / L, Sr(CH3COO)2 concentration is 3–8 g / L, preferably 5–7 g / L, KF concentration is 10–15 g / L, preferably 12–14 g / L, ZnO concentration is 2–8 g / L, preferably 4–6 g / L, the pH of the electrolyte is adjusted to 9–12 using NaOH, preferably 10–11, MAO is used in constant voltage mode with a voltage of 350–500 V, preferably 400–500 V, the treatment time is 5–10 min, preferably 6–8 min, the number of pulses is 30–80, preferably 40–60, the duty cycle is 30%–60%, preferably 40%–50%, and the frequency is 400–1200 Hz, preferably 600–1000 Hz.

[0045] Step 4: EPD preparation of surface coating

[0046] An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.0. The SiO2 content of the neutral SiO2 dispersion was 20%–40%, preferably 25%–35%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25°C. The sample was used as the anode, and the platinum sheet was used as the cathode. The electrode distance was 8–12 cm, preferably 9–11 cm. The deposition voltage was 250–350 V, preferably 275–325 V, and the deposition time was 1–3 min, preferably 1.5–2.5 min.

[0047] Step 5: Post-heat treatment

[0048] The magnesium alloy with surface coating obtained in the fourth step is subjected to post-heat treatment at a temperature of 100-300℃, preferably 150-250℃, for a holding time of 0.5-2.0h, preferably 0.5-1.0h.

[0049] The corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy prepared by the method described in this invention was analyzed. It consists of a Mg-Zn-Mn-Sr-Ca alloy matrix containing GC and CeO2 reinforcing phases, a Ca-P-Sr micro-arc oxidation coating doped with ZnO nanoparticles, and a SiO2 electrophoretic deposition coating. The coating has no obvious defects and effectively improves the corrosion resistance, antibacterial properties, and osteogenic properties of the magnesium alloy.

[0050] The following detailed description is provided through specific embodiments.

[0051] Example 1:

[0052] Step 1: Melting and preparing alloy ingots

[0053] Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy was adjusted to have a Zn mass fraction of 2 wt.%, a Mn mass fraction of 0.8 wt.%, a Sr mass fraction of 1 wt.%, and a Ca mass fraction of 1 wt.%. GC and CeO2 nanoparticles were used as reinforcing phases, with the mass fractions of the reinforcing phases adjusted to 4 wt.% for GC and 2 wt.% for CeO2. The melting was carried out in a resistance heating furnace with a mixed gas of SF6 and CO2 as a protective atmosphere. The temperature was first maintained at 760℃ for 12 min, and then at 715℃ for 10 min to ensure thorough mixing of the melt. The melt was then poured into a mold preheated to 700℃ and cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm.

[0054] Step 2: Hot extrusion preparation of alloy rods

[0055] The alloy ingot obtained in the first step was homogenized by holding it at 420℃ for 2.5h, and then rapidly cooled to remove the skin, resulting in an alloy ingot with a diameter of 100mm and a diameter of 80mm. Subsequently, it was preheated at 380℃ for 1h and hot extruded using a horizontal extrusion press with an extrusion ratio of 18, an extrusion temperature of 340℃, and an extrusion speed of 5m / min to obtain alloy bars.

[0056] Step 3: MAO preparation of surface coating

[0057] For ease of testing, the alloy rods were cut into Φ10mm×3 pieces using a wire EDM machine. The wafers were mechanically ground to remove surface oxide scale and impurities before coating preparation. They were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 min each, dried with cold air, and subjected to MAO treatment using a high-power multifunctional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)2, Na3PO4·12H2O, Sr(CH3COO)2, KF, and ZnO. The concentrations of Ca(OH)2, Na3PO4·12H2O, Sr(CH3COO)2, KF, and ZnO were 2 g / L, 6 g / L, 5 g / L, 12 g / L, and 4 g / L, respectively. The pH of the electrolyte was adjusted to 10 using NaOH. The MAO treatment was performed in constant voltage mode at 400V for 6 min, with 40 pulses, a duty cycle of 40%, and a frequency of 600Hz.

[0058] Step 4: EPD preparation of surface coating

[0059] An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.0. The SiO2 content of the neutral SiO2 dispersion was 25%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25℃. The sample was used as the anode, the platinum sheet was used as the cathode, the electrode distance was 9 cm, the deposition voltage was 275 V, and the deposition time was 1.5 min.

[0060] Step 5: Post-heat treatment

[0061] The magnesium alloy with surface coating obtained in step four was subjected to post-heat treatment at 150°C for 0.5 hours.

[0062] The tissue structure and properties of the samples prepared in Example 1 were characterized and analyzed.

[0063] (A) Microstructure of the coating

[0064] The surface and cross-sectional microstructure of the coating were observed using scanning electron microscopy (SEM). The coating thickness was found to be approximately 16.5 μm, with good interfacial bonding and no defects such as cracks. A schematic diagram of the coating's cross-section is attached. Figure 1 As shown, the inner layer is a MAO coating and the outer layer is an EPD coating.

[0065] (B) Corrosion properties of magnesium alloys before and after surface modification

[0066] The electrodynamic polarization curves of the samples in simulated body fluid were measured using an electrochemical workstation. The changes in self-corrosion potential and self-corrosion current density before and after surface modification were analyzed, as shown in the attached figure. Figure 2 As shown. For the magnesium alloy in Example 1, after surface modification, its self-corrosion potential and self-corrosion current density are -1.12V / SCE and 4.8×10⁻⁶, respectively. -6 A / cm 2 Before surface modification, its self-corrosion potential and self-corrosion current density were -1.62V / SCE and 8.20×10⁻⁶, respectively. -4 A / cm 2 In contrast, the coating increased its self-corrosion potential by 30.9% and decreased its self-corrosion current density by 171 times.

[0067] (C) Antibacterial properties of magnesium alloys before and after surface modification

[0068] Using Staphylococcus aureus and Escherichia coli as evaluation targets, the changes in the antibacterial properties of magnesium alloys before and after surface modification were analyzed by bacterial culture method on the material surface. The results are shown in the attached figure. Figure 3 As shown. For the magnesium alloy in Example 1, after surface modification, its inhibition rates against Staphylococcus aureus and Escherichia coli were 90% and 95%, respectively, while before surface modification, its inhibition rates against Staphylococcus aureus and Escherichia coli were 80% and 70%, respectively. The coating effectively improved the antibacterial properties of the magnesium alloy.

[0069] (D) Osteogenic properties of magnesium alloys before and after surface modification

[0070] Mouse embryonic osteoblasts (MC3T3-E1) were used as the evaluation subject. The cells were co-cultured on the material surface for one day, and the cell viability was analyzed by alkaline phosphatase (ALP) assay. The results are shown in the attached figure. Figure 4 As shown. For the magnesium alloy in Example 1, after surface modification, its ALP activity against MC3T3-E1 cells was 95%, while before surface modification, its ALP activity against MC3T3-E1 cells was 80%. The coating effectively improved the osteogenic properties of the magnesium alloy.

[0071] Example 2:

[0072] Step 1: Melting and preparing alloy ingots

[0073] Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy was adjusted to have a Zn mass fraction of 3 wt.%, a Mn mass fraction of 1 wt.%, a Sr mass fraction of 1.5 wt.%, and a Ca mass fraction of 2 wt.%. GC and CeO2 nanoparticles were used as reinforcing phases, and the mass fractions of the reinforcing phases were adjusted to have a GC mass fraction of 4.5 wt.% and a CeO2 mass fraction of 2.5 wt.%. Melting was carried out in a resistance heating furnace using a mixed gas of SF6 and CO2 as a protective atmosphere. The temperature was first maintained at 770℃ for 13.5 min, and then at 720℃ for 12.5 min, ensuring thorough mixing of the melt. The melt was then poured into a mold preheated to 700℃ and cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm.

[0074] Step 2: Hot extrusion preparation of alloy rods

[0075] The alloy ingot obtained in the first step was homogenized by holding it at 430℃ for 3 hours. After rapid cooling, the ingot was peeled off to obtain an alloy ingot with a diameter of 100mm×80mm. Then, it was preheated at 400℃ for 1.25 hours and hot extruded using a horizontal extrusion press with an extrusion ratio of 27, an extrusion temperature of 360℃, and an extrusion speed of 7.5m / min to obtain alloy bars.

[0076] Step 3: MAO preparation of surface coating

[0077] For ease of experimentation, alloy rods were cut into Φ10mm×3mm discs using a wire EDM machine. Before coating preparation, mechanical grinding was performed to remove surface oxide scale and impurities. The discs were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, dried with cold air, and subjected to MAO treatment using a high-power, multi-functional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was then prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)2, Na3PO4·12H2O, and Sr(CH4)2O. The electrolyte is composed of Sr(CH3COO)2, KF, and ZnO. The concentration of Ca(OH)2 is 3 g / L, the concentration of Na3PO4·12H2O is 8 g / L, the concentration of Sr(CH3COO)2 is 6 g / L, the concentration of KF is 13 g / L, and the concentration of ZnO is 5 g / L. The pH of the electrolyte is adjusted to 10.5 using NaOH. The MAO is in constant voltage mode with a voltage of 450V, a processing time of 7 min, a pulse count of 50, a duty cycle of 45%, and a frequency of 800Hz.

[0078] Step 4: EPD preparation of surface coating

[0079] An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.0. The SiO2 content of the neutral SiO2 dispersion was 30%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25℃. The sample was used as the anode, the platinum sheet was used as the cathode, the electrode distance was 10 cm, the deposition voltage was 300 V, and the deposition time was 2.0 min.

[0080] Step 5: Post-heat treatment

[0081] The magnesium alloy with surface coating obtained in step four was subjected to post-heat treatment at a temperature of 200℃ for a holding time of 0.75h.

[0082] Organizational and performance analysis revealed that the thickness of the magnesium alloy surface coating in Example 2 was 20.4 μm, and the self-corrosion potential and self-corrosion current density of the surface-modified sample were -0.85 V / SCE and 2.7 × 10⁻⁶, respectively. -6 A / cm 2 The self-corrosion potential and self-corrosion current density of the magnesium alloy before surface modification were -1.62V / SCE and 8.20×10⁻⁶, respectively. -4 A / cm 2 In contrast, the coating increased the self-corrosion potential of the magnesium alloy by 47.5% and decreased the self-corrosion current density by 304 times. After surface modification, the inhibition rates against Staphylococcus aureus and Escherichia coli were 95% and 98%, respectively, compared to 70% and 60% before surface modification. After surface modification, the ALP activity against MC3T3-E1 cells was 99%, compared to 75% before surface modification. The coating significantly improved the corrosion resistance, antibacterial properties, and osteogenic properties of the magnesium alloy.

[0083] Example 3:

[0084] Step 1: Melting and preparing alloy ingots

[0085] Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy was adjusted to have a Zn mass fraction of 4 wt.%, a Mn mass fraction of 1.2 wt.%, a Sr mass fraction of 2 wt.%, and a Ca mass fraction of 3 wt.%. GC and CeO2 nanoparticles were used as reinforcing phases, with the mass fractions of the reinforcing phases adjusted to 5 wt.% for GC and 3 wt.% for CeO2. The melting was carried out in a resistance heating furnace with a mixed gas of SF6 and CO2 as a protective atmosphere. The temperature was first maintained at 780℃ for 15 min, and then at 725℃ for 15 min to ensure thorough mixing of the melt. The melt was then poured into a mold preheated to 700℃ and cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm.

[0086] Step 2: Hot extrusion preparation of alloy rods

[0087] The alloy ingot obtained in the first step was homogenized by holding it at 440℃ for 3.5h, and then rapidly cooled to remove the skin, resulting in an alloy ingot with a diameter of 100mm×80mm. Subsequently, it was preheated at 420℃ for 1.5h and then hot-extruded using a horizontal extrusion press with an extrusion ratio of 36, an extrusion temperature of 380℃, and an extrusion speed of 10m / min to obtain alloy bars.

[0088] Step 3: MAO preparation of surface coating

[0089] For ease of experimentation, alloy rods were cut into Φ10mm×3mm discs using a wire EDM machine. Before coating preparation, mechanical grinding was performed to remove surface oxide scale and impurities. The discs were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, dried with cold air, and subjected to MAO treatment using a high-power, multi-functional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was then prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)2, Na3PO4·12H2O, and Sr(CH4)2O. The electrolyte is composed of Sr(CH3COO)2, KF, and ZnO. The concentration of Ca(OH)2 is 4 g / L, the concentration of Na3PO4·12H2O is 10 g / L, the concentration of Sr(CH3COO)2 is 7 g / L, the concentration of KF is 14 g / L, and the concentration of ZnO is 6 g / L. The pH of the electrolyte is adjusted to 11 using NaOH. The MAO is in constant voltage mode with a voltage of 500V, a processing time of 8 min, a pulse count of 60, a duty cycle of 50%, and a frequency of 1000Hz.

[0090] Step 4: EPD preparation of surface coating

[0091] An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.0. The SiO2 content of the neutral SiO2 dispersion was 35%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25℃. The sample was used as the anode, the platinum sheet was used as the cathode, the electrode distance was 11 cm, the deposition voltage was 325 V, and the deposition time was 2.5 min.

[0092] Step 5: Post-heat treatment

[0093] The magnesium alloy with surface coating obtained in step four was subjected to post-heat treatment at a temperature of 250℃ for 1 hour.

[0094] Organizational and performance analysis revealed that the thickness of the magnesium alloy surface coating in Example 3 was 25.2 μm, and the self-corrosion potential and self-corrosion current density of the surface-modified sample were -0.64 V / SCE and 0.5 × 10⁻⁶ V / SCE, respectively. -6 A / cm 2 The self-corrosion potential and self-corrosion current density of the magnesium alloy before surface modification were -1.62V / SCE and 8.2×10⁻⁶, respectively. -4 A / cm 2 In contrast, the coating increased the self-corrosion potential of the magnesium alloy by 60.5% and decreased the self-corrosion current density by 1640 times. After surface modification, the inhibition rates against Staphylococcus aureus and Escherichia coli were 100% and 100%, respectively, compared to 60% and 50% before surface modification. After surface modification, the ALP activity against MC3T3-E1 cells was 100%, compared to 70% before surface modification. The coating significantly improved the corrosion resistance, antibacterial properties, and osteogenic properties of the magnesium alloy.

[0095] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made based on the description and drawings of the present invention, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

[0096] Matters not covered in this invention are common knowledge.

Claims

1. A corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy, characterized in that, The magnesium alloy comprises a matrix and a surface coating. The matrix is ​​a Mg-Zn-Mn-Sr-Ca alloy containing graphitizing carbon (GC) and cerium dioxide (CeO2) reinforcing phases. The surface coating has a double-layer structure: an inner layer is a calcium-phosphorus-strontium (Ca-P-Sr) coating doped with zinc oxide (ZnO) nanoparticles, and an outer layer is a silicon dioxide (SiO2) coating. The coating thickness is 16.5–25.2 μm. After surface modification, the magnesium alloy exhibits a self-corrosion potential of -1.12–-0.64 V / SCE and a self-corrosion current density of (0.5–4.8) × 10⁻⁶ V / SCE. -6 A / cm 2 Compared with unmodified magnesium alloys, the self-corrosion potential increased by 30.9%–60.5%, and the self-corrosion current density decreased by 171–1640 times. The inhibition rates of magnesium alloys against Staphylococcus aureus and Escherichia coli increased from 60%–80% and 50%–70% before surface modification to 90%–100% and 95%–100% after surface modification, respectively. The activity of alkaline phosphatase (ALP) in mouse embryonic osteoblasts (MC3T3-E1) increased from 70%–80% before surface modification to 95%–100% after surface modification.

2. The preparation method of a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 1, characterized in that, Includes the following steps: Step 1: Melting and preparing alloy ingots Using 99.99% pure Mg, 99.99% pure Zn, Mg-5Mn master alloy, Mg-10Sr master alloy, and Mg-20Ca master alloy as raw materials, the chemical composition of the Mg-Zn-Mn-Sr-Ca alloy was adjusted. The mass fraction of Zn was 1–5 wt.%, the mass fraction of Mn was 0.5–1.5 wt.%, the mass fraction of Sr was 0.5–2.5 wt.%, and the mass fraction of Ca was 0.5–3.5 wt.%. GC and CeO2 nanoparticles were used as raw materials. To enhance the phase, the mass fraction of the enhancing phase was adjusted, with GC at 3–6 wt.% and CeO2 at 1–4 wt.%. The melting was carried out in a resistance heating furnace, using a mixture of SF6 and CO2 as a protective atmosphere. The temperature was first maintained at 750–790℃ for 10–15 min, and then at 710–730℃ for 8–15 min. The melt was thoroughly mixed during melting and then poured into a mold preheated to 700℃. The melt was then cooled at room temperature to obtain an alloy ingot with a diameter of 120 mm × 80 mm. Step 2: Hot extrusion preparation of alloy rods The alloy ingot obtained in the first step is homogenized by holding it at 400-450℃ for 2-4 hours, and then rapidly cooled to remove the scale, resulting in an alloy ingot with a diameter of 100mm×80mm. Subsequently, it is preheated at 350-450℃ for 1-2 hours and hot extruded using a horizontal extrusion press with an extrusion ratio of 10-48, an extrusion temperature of 300-400℃, and an extrusion speed of 1-20m / min to obtain alloy bars. Step 3: Micro-arc oxidation (MAO) to prepare surface coating For ease of experimentation, alloy rods were cut into Φ10mm×3mm discs using a wire EDM machine. Before coating preparation, mechanical grinding was performed to remove surface oxide scale and impurities. The discs were then ultrasonically cleaned in acetone and anhydrous ethanol for 10 minutes each, dried with cold air, and subjected to MAO treatment using a high-power, multi-functional micro-arc oxidation device. A Ca-P-Sr coating doped with ZnO nanoparticles was then prepared on the surface of the alloy rods obtained in the second step. The electrolyte consisted of Ca(OH)₂, Na₃PO₄·12H₂O, Sr(CH₃COO)₂, KF, and ZnO. The concentrations of (OH)2 are 1.5–5.0 g / L, Na3PO4·12H2O is 5–12 g / L, Sr(CH3COO)2 is 3–8 g / L, KF is 10–15 g / L, and ZnO is 2–8 g / L. The pH of the electrolyte is adjusted to 9–12 using NaOH. MAO is used in constant voltage mode with a voltage of 350–500 V, a processing time of 5–10 min, a pulse count of 30–80, a duty cycle of 30%–60%, and a frequency of 400–1200 Hz. Step 4: Electrophoretic deposition (EPD) to prepare surface coating An EPD treatment was performed using an electrophoretic deposition apparatus to prepare a SiO2 coating on the surface of the Ca-P-Sr coating doped with ZnO nanoparticles obtained in the third step. The electrophoretic solution consisted of acrylic anodic electrophoretic paint, neutral SiO2 dispersion, and deionized water, with a volume ratio of 0.5:1.5:3.

0. The SiO2 content of the neutral SiO2 dispersion was 20%–40%. The prepared electrophoretic solution was stirred in the electrophoresis tank for 15 min, and the temperature of the electrophoretic solution was maintained at 25℃. The sample was used as the anode, the platinum sheet was used as the cathode, the electrode distance was 8–12 cm, the deposition voltage was 250–350 V, and the deposition time was 1–3 min. Step 5: Post-heat treatment The magnesium alloy with surface coating obtained in step four is subjected to post-heat treatment at a temperature of 100–300℃ for a holding time of 0.5–2.0h.

3. The preparation method of a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 2, characterized in that, In the first step, the mass fraction of Zn is 2-4 wt.%, the mass fraction of Mn is 0.8-1.2 wt.%, the mass fraction of Sr is 1-2 wt.%, the mass fraction of Ca is 1-3 wt.%, the mass fraction of GC is 4-5 wt.%, and the mass fraction of CeO2 is 2-3 wt.%. The temperature is first maintained at 760-780℃ for 12-15 min, and then maintained at 715-725℃ for 10-15 min.

4. The preparation method of a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 2, characterized in that, In the second step, the alloy ingot is homogenized at 420-440℃ for 2.5-3.5 hours, and then preheated at 380-420℃ for 1.0-1.5 hours. The extrusion ratio is 18-36, the extrusion temperature is 340-380℃, and the extrusion speed is 5-10 m / min.

5. The method for preparing a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 2, characterized in that, In the third step, the concentration of Ca(OH)2 is 2-4 g / L, the concentration of Na3PO4·12H2O is 6-10 g / L, the concentration of Sr(CH3COO)2 is 5-7 g / L, the concentration of KF is 12-14 g / L, the concentration of ZnO is 4-6 g / L, the pH of the electrolyte is adjusted to 10-11 using NaOH, the voltage is 400-500V, the processing time is 6-8 min, the number of pulses is 40-60, the duty cycle is 40%-50%, and the frequency is 600-1000Hz.

6. The method for preparing a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 2, characterized in that, In the fourth step, the SiO2 content of the neutral SiO2 dispersion is 25% to 35%, the electrode distance is 9 to 11 cm, the deposition voltage is 275 to 325 V, and the deposition time is 1.5 to 2.5 min.

7. The preparation method of a corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 2, characterized in that, In the fifth step, the temperature is 150–250℃ and the holding time is 0.5–1.0h.

8. The corrosion-resistant, antibacterial, and osteogenic medical magnesium alloy as described in claim 1, characterized in that, It can be applied in the biomedical field.

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