AU2020101402A4

AU2020101402A4 - Medical magnesium alloy material for 3d printing and preparation method thereof

Info

Publication number: AU2020101402A4
Application number: AU2020101402A
Authority: AU
Inventors: Ziqiong SHI; Jun Tian
Original assignee: Dongguan University of Technology
Current assignee: Dongguan University of Technology
Priority date: 2019-07-23
Filing date: 2020-07-17
Publication date: 2020-08-20
Anticipated expiration: 2028-07-17
Also published as: CN110669971A

Abstract

The present invention discloses a medical magnesium alloy material for 3D printing, which is composed of the following chemical components by weight: 4wt% of Zn, lwt%-3wt% of Nd, 0.5wt% of Ca, with the balance being Mg. The invention also discloses a preparation method of the medical magnesium alloy material for 3D printing, which includes steps of surface cleaning, die preheating, smelting and mixing, cooling, casting and smelting, and atomizing. The invention effectively improves the corrosion resistance of the alloy, enhances the structural uniformity of the metal material and meets the requirements of biomedical metal implant materials. 1/2 DRAWINGS 1-Mg 2 -ZnO MA g-4% Zn-0. 5%a-3 % Nd IMg-4%Zai-O.6%Ca-2%tid A C r j 2030 40 50 60 70 80 9010 Mm FIG.1I

Description

1/2

DRAWINGS

1-Mg 2-ZnO

MA g-4% Zn-0. 5%a-3 %Nd

IMg-4%Zai-O.6%Ca-2%tid

A C

r j 2030 40 50 60 70 80 9010 Mm

FIG.1I

MEDICAL MAGNESIUM ALLOY MATERIAL FOR 3D PRINTING AND PREPARATION METHOD THEREOF TECHNICAL FIELD The invention relates to the technical field of biomedical metal materials and manufacturing technique thereof, in particular to a medical magnesium alloy material for 3D printing and a preparation method thereof. BACKGROUND Three-dimensional (3D) printing, also called additive manufacturing, is a process that uses special new materials for rapid prototyping and offers a unique combination of computer modeling, reproduction and traditional manufacturing technique. 3D printing is significantly different from traditional processing technique and no longer requires traditional tools such as knives or molds that have been created by mankind for a long time. In addition, 3D printing designs three dimensional solid model using a computer, and forms 3D objects with various special materials through 3D printing equipment. 3D printing technology breaks through the limitations of traditional manufacturing technique conditions in the manufacture of complex shapes. Due to the rapid development of materials science, the development of modem 3D printing technology has broken through the limitation of a single raw material, and can simultaneously print multiple complex objects and products. Biomaterials play an essential role in the development of 3D printing, development level of which also determines the breadth and depth of 3D printing technology in the medical field. Medical 3D printing materials should meet the requirements of bionics, and must have corrosion resistance, wear resistance and good compatibility. The medical metal materials currently used in clinical practice are mainly stainless steel, titanium alloys, and cobalt-chromium alloys, which have excellent mechanical properties and corrosion resistance; however, the elastic modulus of such materials differs greatly from that of natural bone, which may cause a stress shielding effect during use and is not conducive to bone healing. More importantly, these metal materials that are mostly permanent implant materials need to be removed by a second operation after the fracture is healed, which increases pain and economic burden for patients. In view of the limitations of existing medical implant materials, it is a research hotspot to develop new medical metal materials that have good biocompatibility, excellent mechanical properties, and can be absorbed by the human body after autodegradation in the field of biomedical metal implant materials. Magnesium and magnesium alloys have the following advantages as medical metal materials: (1) an elastic modulus of magnesium alloy is about 45 GPa that is closer to that of human bone, which can effectively reduce the stress shielding effect; (2) it has good biocompatibility, is non-toxic and can be degraded in the body to avoid secondary surgery; (3) it has high specific strength and specific rigidity and can meet the requirements of medical implant materials. However, due to the excessive degradation rate of bio-magnesium alloys in the human environment, the mechanical properties are reduced, which cannot meet the mechanical properties of medical metal implants. Meanwhile, the gas and elevation of pH generated by the degradation may cause inflammation. Therefore, there is an urgent need to improve the corrosion resistance of bio-magnesium alloys in the field of biomedical magnesium alloy materials. SUMMARY In order to overcome the deficiencies of the prior art, the present invention aims to provide a medical magnesium alloy material for 3D printing, which improves the corrosion resistance of the alloy, enhances the uniformity of the metal material structure, and meets the requirements of biomedical metal implant materials. The present invention also aims to provide a method for preparing a medical magnesium alloy material for 3D printing, by which a corrosion-resistant medical magnesium alloy is obtained. To achieve the above objectives, the technical solution of the present invention is as follows: a medical magnesium alloy material for 3D printing is composed of the following chemical components by weight: 4wt% of Zn, lwt%-3wt% of Nd, 0.5wt% of Ca, with the balance being Mg. As a further preferred scheme, the medical magnesium alloy material for 3D printing is composed of the following chemical components by weight: 4wt% of Zn, 2wt% of Nd, 0.5wt% of Ca, with the balance being Mg. A method for preparing a medical magnesium alloy material for 3D printing includes the following steps of: surface cleaning: cleaning surfaces of raw materials of high-purity magnesium, magnesium zinc and magnesium-calcium master alloy; die preheating: polishing a steel die by using sand paper to remove surface impurities such as rust, and then placing the steel die into a preheating furnace for preheating; smelting and mixing: cleaning impurities in an iron crucible, putting a cut magnesium ingot into the crucible, putting the crucible into a protective atmosphere resistance furnace, heating to 350-450°C, introducing a protective gas, adding a weighed master alloy when temperature rises until the magnesium ingot is completely melted, and simultaneously fully stirring and refining the alloy to be uniformly mixed; cooling: after the alloy is uniformly mixed, reducing the temperature of the protective atmosphere resistance furnace to 650-700°C, standing, deslagging the alloy, and removing surface oxides inclusion; casting and smelting: pouring the molten alloy subjected to refining and deslagging into the preheated die under a protective atmosphere, and smelting to obtain a medical magnesium alloy melt; and atomizing: overheating the medical magnesium alloy melt, and then placing the medical molten magnesium alloy in an atomization device for atomizing to obtain medical magnesium alloy powder. As a further preferred scheme, in the step of die preheating of the present invention, a preheating temperature is 180-220°C. As a further preferred scheme, the magnesium-calcium master alloy of the present invention includes lwt%-3wt% neodymium. As a further preferred scheme, in the smelting step of the present invention, the protective gas is a mixed protective gas composed of CO 2 and SF 6 at a volume ratio of 99:1. As a further preferred scheme, in the step of casting and smelting of the present invention, the smelting is carried out at 550-700°C for 30-70 min under vacuum of 5-25 kPa. Compared with the prior art, the present invention has the following beneficial effects: 1. The magnesium alloy material disclosed by the present invention has good biocompatibility, the added elements of neodymium, zinc and calcium are essential elements for functions of human body, and the alloy is designed and obtained by adopting a micronization concept. Density and elastic modulus of the magnesium alloy material having good absorbability and biocompatibility are close to that of bone in orthopedic implantation, and degradation products of the magnesium alloy material have no toxic effect on a human body and can be absorbed by the human body. 2. Density and elastic modulus of the magnesium alloy material disclosed by the present invention are close to that of human bone tissues, which may effectively reduce the stress shielding effect. The above description is merely an overview of the technical solutions of the present invention and, in order that the technical means of the present invention may be more clearly understood, may be implemented in accordance with the contents of the description, and in order that the above and other objects, features and advantages of the present invention may be more clearly understood, reference being made to the following detailed description of the preferred examples, taken in conjunction with the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is an XRD pattern of a magnesium casting alloy in the present invention; FIG. 2 is an SEM image of magnesium alloy substrates with different contents of Nd in

Examples 1-3 and Comparative Example 1; FIG. 3 is a graph showing polarization curves of magnesium alloy materials with different contents of Nd in Examples 1-3 and Comparative Example 1. DETAILED DESCRIPTION To further describe the adopted technical means and the effects of the present invention to achieve an intended purpose of the invention, the following describes examples, structural features and effects of the present invention in detail with reference to the accompanying drawings and examples. A medical magnesium alloy material for 3D printing is composed of the following chemical components by weight: 4wt% of Zn, lwt%-3wt% of Nd, 0.5wt% of Ca, with the balance being Mg. As a further preferred scheme, the medical magnesium alloy material for 3D printing is composed of the following chemical components by weight: 4wt% of Zn, 2wt% of Nd, 0.5wt% of Ca, with the balance being Mg. In the research of the present invention, it is found that a proper amount of Nd element may effectively refine alloy structures and lead to thinning of a phase separation of the magnesium alloy material, which may effectively improve tensile strength, yield strength and elongation of the alloy. Excess rare earth Nd may consume more Zn element in the alloy and lead to coarsening of Mg-Zn phase, which may decrease mechanical properties of the magnesium alloy. Therefore, the content of Nd in the magnesium alloy material does not exceed 3%. A method for preparing a medical magnesium alloy material for 3D printing includes the following steps of: surface cleaning: cleaning surfaces of raw materials of high-purity magnesium, magnesium zinc and magnesium-calcium master alloy; die preheating: polishing a steel die by using sand paper to remove surface impurities such as rust, and then placing the steel die into a preheating furnace for preheating; smelting and mixing: cleaning impurities in an iron crucible, putting a cut magnesium ingot into the crucible, putting the crucible into a protective atmosphere resistance furnace, heating to 350-450°C, introducing a protective gas, adding a weighed master alloy when temperature rises until the magnesium ingot is completely melted, and simultaneously fully stirring and refining the alloy to be uniformly mixed; cooling: after the alloy is uniformly mixed, reducing the temperature of the protective atmosphere resistance furnace to 650-700°C, standing, deslagging the alloy, and removing surface oxides inclusion; casting and smelting: pouring the molten alloy subjected to refining and deslagging into the preheated die under a protective atmosphere, and smelting to obtain a medical magnesium alloy melt; and atomizing: overheating the medical magnesium alloy melt, and then placing the medical molten magnesium alloy in an atomization device for atomizing to obtain medical magnesium alloy powder. In the research of the present invention, it is found that the preheating temperature influences the as-cast performance of the magnesium alloy material, and the mechanical property is continuously increased along with the increase of the preheating temperature of the casting die, because when the preheating temperature is higher, the fluidity is increased, the molten alloy feeding capacity is increased, the micro shrinkage porosity is reduced, and the as-cast performance of the magnesium alloy is improved. However, if the preheating temperature is too high, the grains become coarser, the dispersed precipitated phase grows in the grains, and the eutectic structure layer at the grain boundary grows, resulting in an increase in inclusions and pores, and a decrease in strength. Therefore, in order to obtain a magnesium alloy material having excellent properties, as a further preferred scheme, in the step of die preheating of the present invention, a preheating temperature is 180-220°C. The optimum preheating temperature is 200°C. As a further preferred scheme, the magnesium-calcium master alloy of the present invention includes lwt%-3wt% neodymium. In the present invention, a mixed gas composed of CO 2 and SF 6 is used as a protective gas. SF has effects of anti-conductive protection and isolating air simultaneously. Due to the high cost of SF, mixed CO2 can not only achieve the purpose of preventing air from being oxidized, but also reduce costs. As a further preferred scheme, in the smelting step of the present invention, the protective gas is a mixed protective gas composed of C02 and SF6 at a volume ratio of 99:1. As a further preferred scheme, in the step of casting and smelting of the present invention, the smelting is carried out at 550-700°C for 30-70 min under vacuum of 5-25 kPa. Example 1 A method for preparing a medical magnesium alloy material for 3D printing includes the following steps: 1) a required master alloy was weighed according to a mass percentage of the elements in the alloy: 1% of neodymium, 4% of zinc, 0.5% of calcium and the balance of magnesium, and raw materials were polished by a grinding wheel to remove surface oxides; 2) a cast steel die was polished by using sand paper to remove surface impurities such as rust, and then the steel die was placed into a 200°C preheating furnace for preheating; meanwhile, an iron crucible was cleaned, and various impurities in the iron crucible were removed;

3) a cut magnesium ingot was put into the crucible, then the crucible was put into a pit-type protective atmosphere resistance furnace and heated to 400°C, then a mixed protective gas (99%CO 2+1%SF) was introduced, the weighed master alloy was added when the temperature rose to about 720°C and the magnesium ingot was completely melted, followed by fully stirring and refining for 10 min to uniformly mix the alloy; 4) after the alloy was uniformly mixed, the temperature of the pit-type protective atmosphere resistance furnace was reduced to 680°C, followed by standing for 20 min, and the alloy was deslagged for removing surface oxides inclusion; 5) the molten alloy subjected to refining and deslagging was poured into the preheated die under a protective atmosphere, where the die had a certain inclination angle in the process, and during casting, the pouring was conducted slow firstly, then fast and then slow, without stop, and a medical magnesium alloy base material was obtained; 6) the medical magnesium alloy base material obtained in the step 5) was put into a preheated container, melted at 550°C for 70 min under vacuum of 5 kPa, a medical molten magnesium alloy was obtained and overheated to 80-300°C, then placed in an atomization device for atomizing, medical magnesium alloy powder was obtained, collected, sieved and packaged, and a medical magnesium alloy material for 3D printing was obtained. Example 2 A method for preparing a medical magnesium alloy material for 3D printing includes the following steps: 1) a required master alloy was weighed according to a mass percentage of the elements in the alloy: 2% of neodymium, 4% of zinc, 0.5% of calcium and the balance of magnesium, and raw materials were polished by a grinding wheel to remove surface oxides; 2) a cast steel die was polished by using sand paper to remove surface impurities such as rust, and then the steel die was placed into a 200°C preheating furnace for preheating; meanwhile, an iron crucible was cleaned, and various impurities in the iron crucible were removed; 3) a cut magnesium ingot was put into the crucible, then the crucible was put into a pit-type protective atmosphere resistance furnace and heated to 400°C, then a mixed protective gas (99%CO 2+1%SF) was introduced, the weighed master alloy was added when the temperature rose to about 720°C and the magnesium ingot was completely melted, followed by fully stirring and refining for 10 min to uniformly mix the alloy; 4) after the alloy was uniformly mixed, the temperature of the pit-type protective atmosphere resistance furnace was reduced to 680°C, followed by standing for 20 min, and the alloy was deslagged for removing surface oxides inclusion;

5) the molten alloy subjected to refining and deslagging was poured into the preheated die under a protective atmosphere, where the die had a certain inclination angle in the process, and during casting, the pouring was conducted slow firstly, then fast and then slow, without stop, and a medical magnesium alloy base material was obtained; 6) the medical magnesium alloy base material obtained in the step 5) was put into a preheated container, melted at 630°C for 70 min under vacuum of 15 kPa, a medical molten magnesium alloy was obtained and overheated to 80-300°C, then placed in an atomization device for atomizing, medical magnesium alloy powder was obtained, collected, sieved and packaged, and a medical magnesium alloy material for 3D printing was obtained. Example 3 A method for preparing a medical magnesium alloy material for 3D printing includes the following steps: 1) a required master alloy was weighed according to a mass percentage of the elements in the alloy: 3% of neodymium, 4% of zinc, 0.5% of calcium and the balance of magnesium, and raw materials were polished by a grinding wheel to remove surface oxides; 2) a cast steel die was polished by using sand paper to remove surface impurities such as rust, and then the steel die was placed into a 200°C preheating furnace for preheating; meanwhile, an iron crucible was cleaned, and various impurities in the iron crucible were removed; 3) a cut magnesium ingot was put into the crucible, then the crucible was put into a pit-type protective atmosphere resistance furnace and heated to 400°C, then a mixed protective gas (99%CO 2+1%SF) was introduced, the weighed master alloy was added when temperature rose to about 720°C and the magnesium ingot was completely melted, followed by fully stirring and refining for 10 min to uniformly mix the alloy; 4) after the alloy was uniformly mixed, the temperature of the pit-type protective atmosphere resistance furnace was reduced to 680°C, followed by standing for 20 min, and the alloy was deslagged for removing surface oxides inclusion; 5) the molten alloy subjected to refining and deslagging was poured into the preheated die under a protective atmosphere, where the die had a certain inclination angle in the process, and during casting, the pouring was conducted slow firstly, then fast and then slow, without stop, and a medical magnesium alloy base material was obtained; 6) the medical magnesium alloy base material obtained in the step 5) was put into a preheated container, melted at 700°C for 30 min under vacuum of 25 kPa, a medical molten magnesium alloy was obtained and overheated to 80-300°C, then placed in an atomization device for atomizing, medical magnesium alloy powder was obtained, collected, sieved and packaged, and a medical magnesium alloy material for 3D printing was obtained. Comparative Example 1: The steps follow that of Example 1 above, with a Nd content of 0. Results 1) The magnesium alloy materials of the above Examples 1 to 3 and Comparative Example 1 were subjected to X-ray diffraction and their diffraction patterns were analyzed, and the results were shown in FIG. 1 and Table 1. Table 1: Phase Energy Spectrum In Alloys Element (wt%) Mg K Zn L CaK OK NdL

A 95.18 1.60 - 3.22

B 33.36 61.15 1.45 4.05

C 94.10 1.49 0.11 4.30

D 33.26 35.58 2.03 4.92 24.22

The results of X-Ray Diffraction (XRD) analysis show that the phase composed of magnesium and other alloying elements was not detected. According to the phase diagram of magnesium and zinc, it can be seen that zinc has a solid solubility of 6.2% at 325°C in magnesium, and the cooling rate during casting is faster than that measured by the phase diagram, suggesting that more zinc is dissolved in magnesium, and some zinc may be dissolved out to form a zinc compound which is difficult to detect due to the low content; the presence of zinc oxide may be due to the oxidation of zinc in the alloy by oxygen in the air. 2) To investigate the effect of Nd content on the morphology of the magnesium alloy materials, the magnesium alloy materials of the above Examples 1-3 and Comparative Example 1 are subjected to electron microscope scanning, and the results are shown in FIG. 2. As can be seen from the SEM morphology results of FIG. 2, the alloy matrix is mainly composed of gray phases, with irregularly-shaped white particles distributed on the matrix; the shape and distribution of the particles are related to the type of alloy elements; compared with Mg 4% Zn-0.5% Ca, when 1% Nd is added, white particles are coarsened into worms and distributed more uniformly; combined with energy spectrum, it can be seen that the matrix is mainly magnesium-rich phase, the Nd content at the particles is 24 times the average composition, and Zn is 9 times the average composition, so the white particles are Nd-rich and Zn-rich phase; when 2% Nd and 3% Nd were added, the second phase coarsens, the morphology of worms is more complete, and the distribution uniformity is improved with the increase of Nd content. The results show that a proper amount of Nd may refine the alloy structure effectively and make the phase separation of the magnesium alloy thinner. Excess rare earth Nd may consume more Zn element in the alloy and lead to coarsening of Mg-Zn phase, which may decrease mechanical properties of the magnesium alloy. 3) To investigate effects of Nd content on the corrosion resistance of magnesium alloy materials, electrochemical detection is performed on a CHI660D (Shanghai Huake) electrochemical workstation using SBF solution at room temperature for Examples 1-3 and Comparative Example 1. A traditional three-electrode system is adopted, with platinum sheet as an auxiliary electrode, a saturated calomel electrode as a reference electrode, and a detection sample as a working electrode. The detection method includes the steps of measuring open circuit potential-time curve and Tafel polarization curve, where the detection area is 1 cm2 , the detection range is 0.5 V, and the scanning speed is 1 mV/s. The results show that the corrosion potential increases and the corrosion resistance increases significantly with the increase of Nd content, and the corrosion resistance is the best when the Nd content is 3%. While the above-described embodiments are merely preferred embodiments of the present invention, it is not intended to limit the scope of the present invention, and any insubstantial changes and replacements made by those skilled in the art on the basis of the present invention fall within the scope of the present invention.

Claims

What is claimed is: 1. A medical magnesium alloy material for 3D printing, comprising the following chemical components by weight: 4wt% of Zn, lwt%-3wt% of Nd, 0.5wt% of Ca, with the balance being Mg.
2. The medical magnesium alloy material for 3D printing according to claim 1, comprising the following chemical components by weight: 4wt% of Zn, 2wt% of Nd, 0.5wt% of Ca, with the balance being Mg.
3. A preparation method of the medical magnesium alloy material for 3D printing according to claim 1, comprising the following steps of: surface cleaning: cleaning surfaces of raw materials of high-purity magnesium, magnesium zinc and magnesium-calcium master alloy; die preheating: polishing a steel die by using sand paper to remove surface impurities such as rust, and then placing the steel die into a preheating furnace for preheating; smelting and mixing: cleaning impurities in an iron crucible, putting a cut magnesium ingot into the crucible, putting the crucible into a protective atmosphere resistance furnace, heating to 350-450°C, introducing a protective gas, adding a weighed master alloy when temperature rises until the magnesium ingot is completely melted, and simultaneously fully stirring and refining the alloy to be uniformly mixed; cooling: after the alloy is uniformly mixed, reducing the temperature of the protective atmosphere resistance furnace to 650-700°C, standing, deslagging the alloy, and removing surface oxides inclusion; casting and smelting: pouring the molten alloy subjected to refining and deslagging into the preheated die under a protective atmosphere, and smelting to obtain a medical magnesium alloy melt; and atomizing: overheating the medical magnesium alloy melt, and then placing the medical molten magnesium alloy in an atomization device for atomizing to obtain medical magnesium alloy powder.
4. The preparation method according to claim 3, wherein in the step of die preheating, a preheating temperature is 180-220°C.
5. The preparation method according to claim 3, wherein the magnesium-calcium master alloy comprises lwt%-3wt% of neodymium.