Corrosion-resistant rare earth magnesium alloy and preparation method thereof

Abstract

The invention discloses a corrosion-resistant rare earth magnesium alloy and a preparation method thereof, and the corrosion-resistant rare earth magnesium alloy comprises the following components in percentage by mass: 1.5-2.5% of rare earth element, 0.5-1.5% of zinc, 0.2-0.8% of zirconium, 0.1-0.5% of calcium, 0.1-0.3% of manganese and the balance of magnesium. Elements such as rare earth, zinc and zirconium are precisely added in stages through a gradient smelting process, oxide inclusions and impurity residues are reduced under the action of argon protection and electromagnetic stirring, and local component segregation and galvanic corrosion tendency of melt are effectively inhibited; calcium and manganese elements are preferentially combined with trace impurities in the smelting process to form harmless compounds, so that the catalytic action of the impurities on the corrosion rate is reduced; the rare earth elements, zirconium and zinc have a synergistic effect to form a uniform and compact corrosion-resistant phase network, permeation erosion of a corrosive medium to a matrix in a physiological environment is delayed, the degradation rate of the material is dynamically matched with the regeneration period of bone tissues, meanwhile, the mechanical supporting strength is maintained through solid solution strengthening and precipitation strengthening, and the long-acting stability of alloy implantation is improved.

Description

Technical Field

[0001] The present invention relates to the technical field of rare earth magnesium alloy preparation, in particular to a corrosion-resistant rare earth magnesium alloy and a preparation method thereof. Background Art

[0002] In the field of orthopedic implant materials, traditional medical metal materials such as stainless steel, titanium alloys, and cobalt-chromium alloys have long dominated. However, their high elastic modulus can easily induce a stress shielding effect, leading to bone resorption and the risk of secondary fractures. Furthermore, a second surgery is required to remove the implant, adding to the burden on patients. Biodegradable medical magnesium alloys are considered a revolutionary alternative due to their elastic modulus close to that of natural bone, excellent biocompatibility, and in vivo degradability. As an essential element for the human body, magnesium's degradation products can participate in metabolism. However, pure magnesium corrodes too rapidly in a physiological environment, often losing its mechanical integrity before bone healing, severely restricting its clinical application.

[0003] To control the degradation rate of magnesium alloys, alloying and surface modification are used to synergistically optimize material properties. Rare earth elements (REs) are key alloying components due to their unique physical and chemical properties. However, existing RE-Mg alloys and their preparation methods still face several technical bottlenecks. The lack of precise control over the ratio of RE addition to degradation rates in existing RE-Mg alloys makes it difficult to effectively inhibit corrosion, leading to premature failure of the material in vivo.

[0004] The composite coating preparation process needs to be optimized. Insufficient bonding strength between coating layers can easily lead to coating peeling. The magnesium hydroxide film layer generated by the existing hydrothermal method is prone to brittle fracture under dynamic load and lacks long-term stability. Summary of the Invention

[0005] Problems existing in the prior art are: the existing rare earth magnesium alloy has insufficient corrosion inhibition ability, the coating is easy to peel off, and lacks long-term stability. In response to the above technical problems, the present invention provides a corrosion-resistant rare earth magnesium alloy and a preparation method thereof.

[0006] The technical solution of the present invention is: a corrosion-resistant rare earth magnesium alloy, which is composed of 1.5-2.5% rare earth elements, 0.5-1.5% zinc, 0.2-0.8% zirconium, 0.1-0.5% calcium, 0.1-0.3% manganese and the balance magnesium in terms of mass percentage.

[0007] Description: By optimizing the synergistic ratio of rare earth elements to zinc, zirconium, calcium, and manganese, while maintaining the lightweight and biocompatibility of the magnesium matrix, rare earth elements are used to refine the grains and form a uniformly distributed corrosion-resistant phase. Combined with the solid solution strengthening effect of zinc and zirconium and the impurity neutralization effect of calcium and manganese, the corrosion resistance of the alloy in a physiological environment is significantly improved, the degradation rate is effectively regulated to match the bone healing cycle, and local galvanic corrosion caused by harmful impurities is reduced, thereby extending the mechanical support time of the material in the body and reducing the risk of biological toxicity.

[0008] Furthermore, the rare earth element is yttrium or neodymium.

[0009] Description: Yttrium preferentially passivates grain boundaries by forming stable yttrium oxide (Y2O3), significantly inhibiting intergranular corrosion. Neodymium forms a dispersed Nd-Mg intermetallic compound with the magnesium matrix, achieving the dual effects of grain refinement and reducing localized galvanic corrosion. Both elements effectively complement the synergistic strengthening mechanism of zinc, zirconium, and other elements, avoiding phase structural instability caused by multiple rare earth elements, ensuring controllable degradation rates and biosafety.

[0010] Furthermore, a method for preparing a corrosion-resistant rare earth magnesium alloy comprises the following steps:

[0011] S1. Melting and purification

[0012] S1-1, raw material pretreatment: mechanically polishing the magnesium raw material, zinc raw material, and rare earth element raw material to remove the oxide layer, then ultrasonically cleaning with ethanol for 10-15 minutes, and then drying at a temperature of 75-85° C. to obtain pretreated magnesium raw material, pretreated zinc raw material, and pretreated rare earth element raw material;

[0013] S1-2, gradient melting: introducing argon into a vacuum induction furnace to control the oxygen content to be reduced to 0-50 ppm, melting the pretreated magnesium raw material at a temperature of 710-730°C, adding the pretreated rare earth raw material, then heating to 740-760°C, and holding for 12-18 minutes while performing electromagnetic stirring at a stirring rate of 200-300 rpm; then cooling to 670-730°C, sequentially adding the zirconium raw material and the pretreated zinc raw material, and holding for 10-15 minutes; then sequentially adding the calcium raw material and the manganese raw material, and electromagnetically stirring at 660-700°C for 4-6 minutes, and then standing for 4-6 minutes to remove slag to obtain a melt;

[0014] S1-3, casting and cooling: pouring the melt into a steel mold preheated to 280-320°C, and then cooling and shaping at a cooling rate of 35-45°C / min to obtain an ingot;

[0015] S2. Heat treatment strengthening

[0016] S2-1, solution treatment: placing the ingot in a vacuum furnace, keeping it at 410-430° C. for 8-12 hours, and then water quenching to obtain a solid solution;

[0017] S2-2, aging treatment: keeping the solid solution at 200-220° C. for 11-13 hours, and air-cooling to room temperature to obtain a uniform precipitated phase, thereby obtaining a corrosion-resistant rare earth magnesium alloy.

[0018] Description: By polishing the oxide layer Y2O3 on the surface of the magnesium-yttrium master alloy and the Nd2O3 on the surface of the magnesium-neodymium master alloy, the melting effect is improved, and the oxides are prevented from entering the melt to form inclusions, which affects the mechanical properties of the final alloy. By strengthening the mechanical support time through the solid solution of zirconium and zinc, the corrosion resistance, degradation controllability and biocompatibility of the alloy are optimized, providing a solution for degradable orthopedic implants that combines structural functionality and clinical safety.

[0019] Furthermore, the magnesium raw material is a magnesium ingot, the zinc raw material is a zinc ingot, the zirconium raw material is a magnesium-zirconium master alloy, the calcium raw material is a magnesium-calcium master alloy, and the manganese raw material is a magnesium-manganese master alloy.

[0020] Explanation: Using magnesium ingots as the primary raw material ensures the initial purity of the magnesium matrix, while direct melting of zinc ingots reduces oxidation losses. The addition of zirconium, calcium, and manganese in the form of a magnesium-based master alloy avoids component segregation and burnout during direct smelting of high-melting-point or active metals, ensuring a precise alloying ratio. The pre-dispersed microstructure of the master alloy facilitates rapid homogenization of the melt, reducing the risk of incorporation of impurities such as Fe and Ni during the smelting process, suppressing galvanic corrosion at the source and improving alloy batch stability.

[0021] Furthermore, the surface of the corrosion-resistant rare earth magnesium alloy is also covered with a composite coating, and the coating method of the composite coating is: taking 8-12 g / L of sodium silicate, 2-4 g / L of potassium fluoride and 1-2 g / L of sodium hydroxide to prepare an electrolyte with a pH of 10-12; placing the corrosion-resistant rare earth magnesium alloy in the electrolyte and micro-arc oxidation treatment for 16-20 minutes to generate a MgO-SiO2 oxide layer with a thickness of 10-14 μm; then preparing a sol for immersion and pulling coating to obtain a composite coating magnesium alloy.

[0022] Description: The collaborative design of the micro-arc oxidation layer and the sol-gel sealing layer provides both physical barrier and chemical inertness. The MgO-SiO2 base layer provides high hardness and wear resistance, while the amorphous SiO2 sealing layer isolates the pores from body fluids through its dense structure. This dual protection mechanism increases the corrosion resistance of the composite coating by more than three times compared to a single micro-arc oxidation layer. The bio-inertness of SiO2 further reduces the risk of inflammatory reactions in the material and tissue. The coating system remains stable in a dynamic physiological environment, ensuring the mechanical integrity of magnesium alloy implants during the bone healing period while precisely matching degradation rate with new bone growth.

[0023] Furthermore, the forward voltage of the micro-arc oxidation treatment of the corrosion-resistant rare earth magnesium alloy is 300-340V, the frequency is 580-620Hz, and the duty cycle is 22-28%.

[0024] Description: During micro-arc oxidation, a 10-14μm thick MgO-SiO2 oxide layer is formed on the surface of the magnesium alloy by controlling the coordinated parameters of 300-340V high-voltage pulses, 580-620Hz high-frequency pulses, and a low duty cycle of 22-28%. The high-frequency pulses reduce the energy of a single discharge, preventing film ablation. The low duty cycle extends the cooling gap and alleviates thermal stress concentration, significantly reducing the density of micropores and cracks in the oxide layer. This forms a continuous, dense base protective layer, providing a stable interface for subsequent sol-gel sealing.

[0025] Furthermore, the sol is prepared by mixing ethyl orthosilicate, ethanol, and water in a mass ratio of 1-2:4-5:0.5, adjusting the pH to 3-4 with nitric acid, and then magnetically stirring for 24-26 hours to obtain the sol.

[0026] Description: A specific ratio of ethyl orthosilicate, ethanol, and water is mixed, combined with a nitric acid-catalyzed hydrolysis environment at a pH of 3-4, to ensure that the ethyl orthosilicate is fully hydrolyzed into a silicic acid sol. Magnetic stirring is then applied for 24-26 hours to promote the polycondensation reaction and form a uniform and stable sol system, preventing premature gel solidification or particle agglomeration. This ensures sol fluidity during dip coating and a uniform SiO2 network structure during the subsequent drying process, laying the foundation for a highly dense sealing layer.

[0027] Furthermore, the pulling rate of the immersion pulling coating is 2-4 mm / s, the coating is repeated 2-4 times, the thickness of each wet film before drying is 100-300 nm, and the drying time of each layer is 20-40 min; after all are dried, the film is kept at 470-490 ° C for 1.5-2.5 hours to form a dense amorphous SiO2 sealing layer with a thickness of 1-2 μm.

[0028] Description: Through a pull-up rate of 2-4 mm / s and 2-4 repeated coatings, the wet film thickness is accumulated layer by layer to 100-300 nm. Combined with low-temperature drying for 20-40 minutes per layer, the solvent is gradually evaporated and the sol is pre-cured to avoid shrinkage and cracking caused by rapid drying. Finally, the high temperature of 470-490°C is maintained for 1.5-2.5 hours to densify the SiO2 network and eliminate residual organic matter, forming an amorphous SiO2 sealing layer with a thickness of 1-2 μm. This layer completely fills the pores and cracks of the micro-arc oxidation layer, blocking the penetration path of the corrosive medium, and simultaneously forms a chemical bond with the underlying MgO-SiO2 layer, significantly improving the coating's bonding strength and long-term corrosion resistance.

[0029] The beneficial effects of the present invention are:

[0030] The present invention uses a gradient smelting process to precisely add rare earth, zinc, zirconium and other elements in stages. Under the protection of argon and electromagnetic stirring, it reduces oxide inclusions and impurity residues, effectively suppressing the local component segregation and galvanic corrosion tendency of the melt; a casting process with a specific cooling rate is used to refine the ingot grain structure to avoid the negative impact of coarse grain boundaries on corrosion resistance. Through solid solution treatment, the alloying elements are fully dissolved and evenly diffused, and aging treatment is used to further control the size and distribution of the precipitated phase, strengthen the grain boundary bonding force and improve the matrix stability. During the smelting process, calcium and manganese elements preferentially combine with trace impurities to form harmless compounds, reducing the catalytic effect of impurities on the corrosion rate. Rare earth elements synergistically form a uniform and dense corrosion-resistant phase network with zirconium and zinc, delaying the penetration and erosion of corrosive media on the matrix in a physiological environment, making the material degradation rate dynamically adaptable to the bone tissue regeneration cycle, while maintaining the mechanical support strength through solid solution strengthening and precipitation strengthening, thereby improving the long-term stability of the alloy implant. DETAILED DESCRIPTION

[0031] In order to further illustrate the approach and effects achieved by the present invention, the technical solution of the present invention will be clearly and completely described below in conjunction with experiments.

[0032] Example 1:

[0033] A corrosion-resistant rare earth magnesium alloy, comprising, by mass percentage, 2% rare earth elements, 1% zinc, 0.5% zirconium, 0.3% calcium, 0.2% manganese, and the balance magnesium;

[0034] A method for preparing a corrosion-resistant rare earth magnesium alloy comprises the following steps:

[0035] S1. Melting and purification

[0036] S1-1. Raw material pretreatment: Mechanically polish the magnesium raw material, the zinc raw material, and the rare earth element raw material to remove the oxide layer, then ultrasonically clean them with ethanol for 12.5 minutes, and then dry them at 80° C. to obtain pretreated magnesium raw material, pretreated zinc raw material, and pretreated rare earth element raw material;

[0037] S1-2, gradient melting: argon gas was introduced into a vacuum induction furnace to control the oxygen content to be reduced to 25 ppm, and the pretreated magnesium raw material was melted at a temperature of 720°C. The pretreated rare earth raw material was added, and the temperature was raised to 750°C and kept warm for 15 minutes while electromagnetically stirring at a stirring rate of 250 rpm; then the temperature was lowered to 700°C, and the zirconium raw material and the pretreated zinc raw material were added in sequence and kept warm for 12.5 minutes; then the calcium raw material and the manganese raw material were added in sequence, and the mixture was electromagnetically stirred at 680°C for 5 minutes. The mixture was allowed to stand for 5 minutes to remove slag to obtain a melt;

[0038] S1-3, casting and cooling: pouring the melt into a steel mold preheated to 300° C., and then cooling and shaping the melt at a cooling rate of 40° C. / min to obtain an ingot;

[0039] S2. Heat treatment strengthening

[0040] S2-1, solution treatment: placing the ingot in a vacuum furnace, keeping it at 420° C. for 10 hours, and then quenching with water to obtain a solid solution;

[0041] S2-2, aging treatment: keeping the solid solution at 210° C. for 12 hours, and air-cooling to room temperature to obtain a uniform precipitate phase, thereby obtaining a corrosion-resistant rare earth magnesium alloy;

[0042] The rare earth element is yttrium; the raw material of the rare earth element is a magnesium-yttrium master alloy; the raw material of the magnesium element is a magnesium ingot, the raw material of the zinc element is a zinc ingot, the raw material of the zirconium element is a magnesium-zirconium master alloy, the raw material of the calcium element is a magnesium-calcium master alloy, and the raw material of the manganese element is a magnesium-manganese master alloy.

[0043] Example 2: This example is basically the same as Example 1, except that the surface of the corrosion-resistant rare earth magnesium alloy is further covered with a composite coating. The composite coating is coated by preparing an electrolyte with a pH of 10 by taking 8 g / L of sodium silicate, 2 g / L of potassium fluoride, and 1 g / L of sodium hydroxide; placing the corrosion-resistant rare earth magnesium alloy in the electrolyte and performing micro-arc oxidation treatment for 16 minutes to form a MgO-SiO2 oxide layer with a thickness of 10 μm; then preparing a sol for immersion coating to obtain a composite-coated magnesium alloy;

[0044] The forward voltage of the micro-arc oxidation treatment of the corrosion-resistant rare earth magnesium alloy is 300V, the frequency is 580Hz, and the duty cycle is 22%;

[0045] The sol is prepared by mixing tetraethyl orthosilicate, ethanol, and water in a mass ratio of 1:4:0.5, adjusting the pH to 3 with nitric acid, and then magnetically stirring for 24 hours to obtain the sol;

[0046] The pulling rate of the immersion pull coating is 2 mm / s, and the coating is repeated twice. The thickness of each wet film before drying is 100 nm, and the drying time of each layer is 20 minutes. After all are dried, the film is kept at 470° C. for 1.5 hours to form a dense amorphous SiO2 sealing layer with a thickness of 1 μm.

[0047] Example 3: This example is basically the same as Example 1, except that the surface of the corrosion-resistant rare earth magnesium alloy is further covered with a composite coating. The composite coating is coated by preparing an electrolyte with a pH of 12 by using 12 g / L of sodium silicate, 4 g / L of potassium fluoride, and 2 g / L of sodium hydroxide; placing the corrosion-resistant rare earth magnesium alloy in the electrolyte and performing micro-arc oxidation treatment for 20 minutes to form a MgO-SiO2 oxide layer with a thickness of 14 μm; and then preparing a sol for immersion coating to obtain a composite-coated magnesium alloy.

[0048] The forward voltage of the micro-arc oxidation treatment of the corrosion-resistant rare earth magnesium alloy is 340V, the frequency is 620Hz, and the duty cycle is 28%;

[0049] The sol is prepared by mixing tetraethyl orthosilicate, ethanol, and water in a mass ratio of 1:4:0.5, adjusting the pH to 3 with nitric acid, and then magnetically stirring for 24 hours to obtain the sol;

[0050] The pulling rate of the immersion pull coating is 2 mm / s, and the coating is repeated twice. The thickness of each wet film before drying is 100 nm, and the drying time of each layer is 20 minutes. After all are dried, the film is kept at 470° C. for 1.5 hours to form a dense amorphous SiO2 sealing layer with a thickness of 1 μm.

[0051] Example 4: This example is basically the same as Example 1, except that the surface of the corrosion-resistant rare earth magnesium alloy is further covered with a composite coating. The composite coating is coated by preparing an electrolyte with a pH of 11 by taking 10 g / L of sodium silicate, 3 g / L of potassium fluoride, and 1.5 g / L of sodium hydroxide; placing the corrosion-resistant rare earth magnesium alloy in the electrolyte and performing micro-arc oxidation treatment for 18 minutes to form a MgO-SiO2 oxide layer with a thickness of 12 μm; then preparing a sol for immersion coating to obtain a composite-coated magnesium alloy;

[0052] The forward voltage of the micro-arc oxidation treatment of the corrosion-resistant rare earth magnesium alloy is 320V, the frequency is 600Hz, and the duty cycle is 24%;

[0053] The sol is prepared by mixing tetraethyl orthosilicate, ethanol, and water in a mass ratio of 3:9:1, adjusting the pH to 3.5 with nitric acid, and then magnetically stirring for 25 hours to obtain the sol;

[0054] The pulling rate of the immersion pull coating is 3 mm / s, and the coating is repeated 3 times. The thickness of each wet film before drying is 200 nm, and the drying time of each layer is 30 minutes. After all are dried, the film is kept at 480°C for 2 hours to form a dense amorphous SiO2 sealing layer with a thickness of 1.5 μm.

[0055] Example 5: This example is basically the same as Example 1, except that, by mass percentage, it consists of 1.5% rare earth elements, 0.5% zinc, 0.2% zirconium, 0.1% calcium, 0.1% manganese, and the balance magnesium.

[0056] Example 6: This example is basically the same as Example 1, except that, by mass percentage, it consists of 2.5% rare earth elements, 1.5% zinc, 0.8% zirconium, 0.5% calcium, 0.3% manganese, and the balance magnesium.

[0057] Example 7: This example is basically the same as Example 1, except that the rare earth element is neodymium; and the raw material of the rare earth element is a magnesium-neodymium intermediate alloy.

[0058] Example 8: This example is basically the same as Example 1, except that, S1-1, raw material pretreatment: the magnesium raw material, the zinc raw material, and the rare earth element raw material are respectively subjected to mechanical polishing to remove the oxide layer, and then ultrasonically cleaned with ethanol for 10 minutes, and then dried at 75°C to obtain pretreated magnesium raw material, pretreated zinc raw material, and pretreated rare earth element raw material;

[0059] S1-2, gradient melting: argon gas was introduced into a vacuum induction furnace to control the oxygen content to be reduced to 1.8 ppm, and the pretreated magnesium raw material was melted at 710°C. The pretreated rare earth raw material was added, and the temperature was raised to 740°C and kept warm for 12 minutes while electromagnetically stirring at a stirring rate of 200 rpm; the temperature was then lowered to 670°C, and the zirconium raw material and the pretreated zinc raw material were added in sequence and kept warm for 10 minutes; then the calcium raw material and the manganese raw material were added in sequence, and the mixture was electromagnetically stirred at 660°C for 4 minutes. The mixture was allowed to stand for 4 minutes to remove slag to obtain a melt;

[0060] S1-3, casting and cooling: pouring the melt into a steel mold preheated to 280° C., and then cooling and shaping the melt at a cooling rate of 35° C. / min to obtain an ingot.

[0061] Example 9: This example is basically the same as Example 1, except that, S1-1, raw material pretreatment: the magnesium raw material, the zinc raw material, and the rare earth element raw material are respectively mechanically polished to remove the oxide layer, then ultrasonically cleaned with ethanol for 15 minutes, and then dried at 85°C to obtain pretreated magnesium raw material, pretreated zinc raw material, and pretreated rare earth element raw material;

[0062] S1-2, gradient melting: argon gas was introduced into a vacuum induction furnace to control the oxygen content to be reduced to 50 ppm, and the pretreated magnesium raw material was melted at a temperature of 730°C. The pretreated rare earth raw material was added, and the temperature was raised to 760°C and kept warm for 18 minutes while electromagnetic stirring was performed at a stirring rate of 300 rpm; then the temperature was lowered to 730°C, and the zirconium raw material and the pretreated zinc raw material were added in sequence and kept warm for 15 minutes; then the calcium raw material and the manganese raw material were added in sequence, and electromagnetic stirring was performed at 700°C for 6 minutes. The mixture was allowed to stand for 6 minutes to remove slag to obtain a melt;

[0063] S1-3, casting and cooling: pouring the melt into a steel mold preheated to 320° C., and then cooling and shaping the melt at a cooling rate of 45° C. / min to obtain an ingot.

[0064] Example 10: This example is basically the same as Example 1, except that S2, heat treatment strengthening

[0065] S2-1, solution treatment: placing the ingot in a vacuum furnace, keeping the temperature at 410° C. for 8 hours, and then water quenching to obtain a solid solution;

[0066] S2-2. Aging treatment: keeping the solid solution at 200° C. for 11 hours, and air-cooling it to room temperature to obtain a uniform precipitated phase, thereby obtaining a corrosion-resistant rare earth magnesium alloy.

[0067] Example 11: This example is basically the same as Example 1, except that S2, heat treatment strengthening

[0068] S2-1, solution treatment: placing the ingot in a vacuum furnace, keeping it at 430° C. for 12 hours, and then water quenching to obtain a solid solution;

[0069] S2-2. Aging treatment: keeping the solid solution at 220° C. for 13 hours, and air-cooling it to room temperature to obtain a uniform precipitated phase, thereby obtaining a corrosion-resistant rare earth magnesium alloy.

[0070] Comparative Example 1: Using Example 1 as a reference, the difference is that, by mass percentage, it consists of 0.5% rare earth elements, 0.2% zinc, 0.1% zirconium, 0.05% calcium, 0.02% manganese, and the balance magnesium.

[0071] Comparative Example 2: Using Example 1 as a reference, the difference is that, by mass percentage, it consists of 3% rare earth elements, 3% zinc, 2% zirconium, 1% calcium, 0.5% manganese, and the balance magnesium.

[0072] Comparative Example 3: Example 1 is used as a reference, except that the rare earth element is lanthanum, and the lanthanum element raw material is a magnesium-lanthanum intermediate alloy.

[0073] Comparative Example 4: Example 1 was used as a reference, except that the electromagnetic stirring step was not performed during the gradient melting in S1-2.

[0074] Comparative Example 5: Example 1 is used as a reference, except that the S2 solid solution and aging heat treatment steps are not performed, and the ingot is directly machined into shape.

[0075] In order to explore the performance of the rare earth magnesium alloys of the above examples and control examples, the main materials were determined according to the experimental formula and samples were obtained for testing. The results are shown in Table 1 below. The specific exploration is as follows:

[0076] Table 1 Performance test table of oil displacement agent samples of Examples 1-11 and Comparative Examples 1-5

[0077]

[0078] 1. Explore the influence of the type and content of rare earth elements in the ingredients on the properties of rare earth magnesium alloys:

[0079] As shown in Table 1, by comparing Examples 1, 5, 6, and 7 with Control Examples 1, 2, and 3, it can be seen that when Example 1 uses 2% yttrium as the ingredient, the corrosion rate is the lowest, reaching 0.85 mm / year, the bone healing period is the longest, and the performance is the best; after Example 7 uses neodymium instead of yttrium, the corrosion rate slightly increases to 0.89 mm / year, but is still better than Control Example 3; when Example 5 reduces the rare earth content to 1.5%, the corrosion rate rises to 1.12 mm / year, and the bone healing period is shortened to 12-14 weeks. The performance is weaker than Example 1 but better than Control Example 1; the rare earth in Control Example 2 exceeds the specified range of this method, and the corrosion rate abnormally increases to 2.10 mm / year, verifying that the rare earth ratio needs to strictly match the degradation requirements; when other rare earth lanthanums are used in Control Example 3, the performance is significantly inferior to yttrium or neodymium, which shows that the selection of rare earth species also plays an important role in corrosion resistance.

[0080] 2. Investigate the influence of smelting process on the properties of rare earth magnesium alloy:

[0081] As shown in Table 1, Example 1 achieves low corrosion rate and high strength through gradient melting and electromagnetic stirring, while Control Example 4 omits the electromagnetic stirring step, resulting in component segregation, the corrosion rate increases to 1.80 mm / year, the tensile strength decreases to 240 MPa, and the bone healing period is shortened to 10-12 weeks, directly proving the necessity of component homogenization in this method.

[0082] 3. Investigate the influence of composite coating process on the performance of rare earth magnesium alloy:

[0083] As shown in Table 1, by comparing Examples 1-4, it can be seen that Example 3 generates a 14 μm oxide layer through the highest micro-arc oxidation voltage and the longest processing time, has the lowest corrosion rate, the longest bone healing cycle, and the best performance; Example 4 adopts intermediate process parameters, and its corrosion rate is 0.21 mm / year, slightly higher than Example 3; Example 2 uses the lowest coating process parameters, and its corrosion rate rises to 0.26 mm / year, but is still significantly better than Example 1 without coating. It can be seen that the protective effect of the composite coating gradually improves with the thickening of the oxide layer and the densification of the pores.

[0084] 4. Investigate the influence of heat treatment process on the properties of rare earth magnesium alloy:

[0085] As shown in Table 1, by comparing Examples 1, 10, 11 and Control Example 5, it can be seen that after standard solution treatment and aging treatment, Example 1 has a tensile strength of 285 MPa and a corrosion rate of 0.85 mm / year, and has the best comprehensive performance; after extending the aging time in Example 11, the tensile strength of the sample increased to 290 MPa, but the corrosion rate slightly increased to 0.82 mm / year, indicating a marginal gain in mechanical properties due to aging strengthening; shortening the solution treatment time in Example 10 resulted in the tensile strength of the sample decreasing to 255 MPa and the corrosion rate increasing to 1.20 mm / year, and the performance was weaker than that of Example 1; after completely omitting the heat treatment in Control Example 5, the sample had the worst tensile strength, only 230 MPa, and the corrosion rate was 1.55 mm / year, which shows that the control of the heat treatment process is indispensable for the regulation of the precipitated phase.

Claims

1. A corrosion-resistant rare earth magnesium alloy, characterized in that: Calculated by mass percentage, it consists of 1.5-2.5% of rare earth elements, 0.5-1.5% of zinc, 0.2-0.8% of zirconium, 0.1-0.5% of calcium, 0.1-0.3% of manganese, and the balance of magnesium.

2. The corrosion-resistant rare earth magnesium alloy according to claim 1, characterized in that: The rare earth element is yttrium or neodymium.

3. The method for preparing a corrosion-resistant rare earth magnesium alloy according to claim 1, wherein: The following steps are involved: S1. Melting and purification S1-1, raw material pretreatment: mechanically polishing the magnesium raw material, zinc raw material, and rare earth element raw material to remove the oxide layer, then ultrasonically cleaning with ethanol for 10-15 minutes, and then drying at a temperature of 75-85° C. to obtain pretreated magnesium raw material, pretreated zinc raw material, and pretreated rare earth element raw material; S1-2, gradient melting: introducing argon into a vacuum induction furnace to control the oxygen content to be reduced to 0-50 ppm, melting the pretreated magnesium raw material at a temperature of 710-730°C, adding the pretreated rare earth raw material, then heating to 740-760°C, and holding for 12-18 minutes while performing electromagnetic stirring at a stirring rate of 200-300 rpm; then cooling to 670-730°C, sequentially adding the zirconium raw material and the pretreated zinc raw material, and holding for 10-15 minutes; then sequentially adding the calcium raw material and the manganese raw material, and electromagnetically stirring at 660-700°C for 4-6 minutes, and then standing for 4-6 minutes to remove slag to obtain a melt; S1-3, casting and cooling: pouring the melt into a steel mold preheated to 280-320°C, and then cooling and shaping at a cooling rate of 35-45°C / min to obtain an ingot; S2. Heat treatment strengthening S2-1, solution treatment: placing the ingot in a vacuum furnace, keeping it at 410-430° C. for 8-12 hours, and then water quenching to obtain a solid solution; S2-2, aging treatment: keeping the solid solution at 200-220° C. for 11-13 hours, and air-cooling to room temperature to obtain a uniform precipitated phase, thereby obtaining a corrosion-resistant rare earth magnesium alloy.

4. The method for preparing a corrosion-resistant rare earth magnesium alloy according to claim 3, wherein: The magnesium raw material is magnesium ingot, the zinc raw material is zinc ingot, the zirconium raw material is magnesium-zirconium master alloy, the calcium raw material is magnesium-calcium master alloy, and the manganese raw material is magnesium-manganese master alloy.

5. The method for preparing the corrosion-resistant rare earth magnesium alloy according to claim 3, characterized in that: The surface of the corrosion-resistant rare earth magnesium alloy is also covered with a composite coating. The coating method of the composite coating is as follows: 8-12 g / L of sodium silicate, 2-4 g / L of potassium fluoride and 1-2 g / L of sodium hydroxide are prepared into an electrolyte with a pH of 10-12; the corrosion-resistant rare earth magnesium alloy is placed in the electrolyte and subjected to micro-arc oxidation treatment for 16-20 minutes to generate an MgO-SiO2 oxide layer with a thickness of 10-14 μm; and then a sol is prepared for immersion and pulling coating to obtain a composite-coated magnesium alloy.

6. The method for preparing the corrosion-resistant rare earth magnesium alloy according to claim 5, characterized in that: The forward voltage of the corrosion-resistant rare earth magnesium alloy micro-arc oxidation treatment is 300-340V, the frequency is 580-620Hz, and the duty cycle is 22-28%.

7. The method for preparing the corrosion-resistant rare earth magnesium alloy according to claim 5, characterized in that: The sol is prepared by mixing ethyl orthosilicate, ethanol, and water in a mass ratio of 1-2:4-5:0.5, adjusting the pH to 3-4 with nitric acid, and then magnetically stirring for 24-26 hours to obtain the sol.

8. The method for preparing the corrosion-resistant rare earth magnesium alloy according to claim 7, characterized in that: The pulling rate of the dip-pull coating is 2-4 mm / s, and the coating is repeated 2-4 times. The thickness of each wet film before drying is 100-300 nm, and the drying time of each layer is 20-40 min. After all are dried, the film is kept at 470-490° C. for 1.5-2.5 h to form a dense amorphous SiO2 sealing layer with a thickness of 1-2 μm.

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