CN111321331B - Preparation method of Mg-Zn-Ca biomedical magnesium alloy - Google Patents

Abstract

The invention relates to a preparation method of Mg-Zn-Ca biomedical magnesium alloy, belonging to the technical field of batch preparation of biomedical degradable magnesium alloy. The method comprises the steps of material preparation, smelting and solidification system preparation, alloy smelting and purification, undercurrent type transfer injection and forced filtration, accurate control of solidification and waste heat homogenization, near-solidus homogenization treatment and plastic deformation treatment. The preparation technology has the greatest advantage of meeting the requirement that the cross-sectional area of the Mg-Zn-Ca biomedical magnesium alloy with high heat cracking tendency is larger than 70000mm²The preparation of the ingot blank realizes the homogeneous and clean casting in industrial scale, thereby greatly improving the production efficiency, increasing the deformation degree and improving the performance; meanwhile, the cracking risk of a large cast ingot is greatly reduced, the homogenization of a mushy zone and a liquid phase zone is realized, the nucleation rate is increased, and the specific gravity segregation and the inverse segregation of Zn are effectively avoided while the dendritic crystal is refined.

Description

Preparation method of Mg-Zn-Ca biomedical magnesium alloy

Technical Field

The invention relates to a preparation method of Mg-Zn-Ca biomedical magnesium alloy, in particular to a low-cost preparation method of Mg-Zn-Ca biomedical wrought magnesium alloy, belonging to the technical field of batch preparation of biomedical degradable magnesium alloy.

Background

The biomedical metal materials clinically applied at present mainly comprise three major types of stainless steel, titanium alloy and cobalt-based alloy, which are all non-degradable materials and need to be taken out again after short-term implantation, thus increasing the pain of patients and the medical expense. In addition, the existing metal implant materials such as stainless steel, titanium alloy and the like have the common problems of poor mechanical compatibility with biological bones, 5 times higher tensile strength and 10 times higher elastic modulus than natural bones. After being implanted into a human body, the material can generate a great stress shielding effect on local bone tissues, thereby causing three serious consequences: (1) the original biological bone around the implanted material is weakened; (2) poor growth of new bone around the implant material; (3) the interface between the implant material and the biological bone is subject to stress concentration, which causes inflammation.

The biomedical magnesium alloy is a degradable implant material with great clinical application prospect, and has excellent mechanical property, processability and biocompatibility and mechanical compatibility. The qualified degradable biomedical magnesium alloy can be gradually corroded and degraded by body fluid in a living body, the released corrosion product can not bring toxic hazard to a host, and when the body is assisted to complete the tissue repair mission, 100 percent of the magnesium alloy is dissolved by the body fluid, and no implant is left. Magnesium is the metal material with the mechanical property which is closest to that of human bones in all the metal materials at present. The elastic modulus of the magnesium alloy is about 45GPa, is closer to the elastic modulus (20GPa) of human bones than the elastic modulus (100GPa) of the titanium alloy which is widely used at present, and can effectively reduce the stress shielding effect and promote the healing of the bones. Meanwhile, the magnesium alloy has higher yield strength, can bear larger load and is applied to bone tissue bearing parts. From the biological point of view, magnesium is a necessary metal element for human body, the content of magnesium is only second to calcium, sodium and potassium elements, the magnesium almost participates in all physiological and biochemical reactions in vivo, and has important regulation effect in the synthesis of protein and nucleic acid. Magnesium also serves as a cofactor for various enzymes, stabilizing DNA and RNA structures, and maintaining cell membrane potential. The recommended daily intake of magnesium for adults is 375mg, which stabilizes the magnesium content in the body through the intestines and kidneys, and in normal humans, excess magnesium is rapidly excreted in the body through the urine. A normal adult contains about 24g of magnesium, of which over 50% is present in bone. In orthopedic applications, magnesium is an essential element for bone growth and metabolism, and promotes the adhesion and proliferation of osteoblasts through interaction with integrin on the surface of osteoblasts, thereby achieving the effect of bone growth. The magnesium deficiency of the human body can cause bone resorptionOsteoporosis, which adversely affects the normal growth and development of bone. Developed by Syntellix AG in 2013 of Germany

The degradable magnesium alloy compression screw becomes the first CE-certified orthopedic product (three types of implantation instruments) all over the world and is used for fixing small bones and bone fragments. In 2014, the Korean drug administration approves the Mg-Zn-Ca alloy metacarpal fracture bone nail product to be on the market. In 2014, the green channel of the innovative product of the medical instrument technical review center of the national food and drug administration of supervision and administration of the China has approved the pure magnesium bone nail product to carry out clinical tests. The application fields of the biomedical magnesium alloy are mainly bone fixation and correction materials, bone tissue engineering scaffolds and cardiovascular scaffolds. The related data of the industry show that the market scale of the orthopedic implant in China breaks through 120 billion yuan in 2015, about 300 million people do fracture surgery in the same year, about 25 million joints are replaced, and about 40 million spinal devices are used, so that the opportunity is brought to the development and application of biomedical magnesium alloy. Therefore, the method has important practical significance for research and development and industrialization of biomedical magnesium alloy products, and has a huge market prospect.

Mg-Zn-Ca magnesium alloy is an important biomedical material. Zn is a trace element necessary for human bodies, participates in more than 300 enzyme reactions, has important influence on immune systems and growth and development, and plays a vital role in maintaining the structure and functional stability of a plurality of biomacromolecules. Adults need to take about 15mg of Zn a day to meet the metabolic needs, excess Zn can be excreted out of the body through gastrointestinal and renal metabolism, and Zn deficiency can reduce osteoblast activity and alkaline phosphatase activity. Zn can greatly improve the mechanical property of magnesium through solid solution and aging strengthening, meanwhile, the addition of Zn can improve the corrosion potential of magnesium, Zn has the same effect of stabilizing a magnesium corrosion product film as Ca and rare earth elements, and can improve the degradation property of magnesium. In order to avoid the galvanic corrosion effect of the second phase, the desirable structure morphology of the Mg-Zn series alloy is to form an α -Mg single-phase solid solution alloy by appropriate deformation processing and heat treatment. According to the literature reports: the hydrogen release and pH of Mg-6 wt.% Zn alloy in simulated body fluids rises rapidly at the beginning of immersion, after which the rate gradually slows, mainly because the surface of the sample is covered by degradation products, mitigating further corrosion of the alloy; meanwhile, comparing the degradation rates of Mg-6 wt.% Zn alloy and pure magnesium immersed in simulated body fluids for 3 days and 30 days, respectively, found: on day 3, the degradation rate of the Mg-6 wt.% Zn alloy was 0.20mm/a, pure magnesium was 0.43 mm/a; on day 30, the degradation rates of Mg-6 wt.% Zn alloy and pure magnesium were 0.07mm/a and 0.10mm/a, respectively; it can be seen that Mg-6 wt.% Zn alloys all degraded more slowly than pure magnesium, and the addition of Zn improved the corrosion resistance of magnesium in simulated body fluids. The biomedical Mg-Zn alloy has good mechanical, degradation and biocompatibility properties, mainly comprises binary, ternary or multicomponent alloys such as Mg-xZn, Mg-Zn-Ca, Mg-Zn-Mn, Mg-Zn-Sr, Mg-Zn-Ca-Sr and the like, can obtain ideal comprehensive mechanical and degradation properties through a tissue regulation and control means, and meets the requirements of different types of clinical application. Ca is an important constituent element of human bone, has no cytotoxicity, is generally added in an amount of 1 wt.% or less as a biomedical material, and excessive Ca causes a decrease in corrosion resistance. According to the literature reports: the binary Mg-1 wt.% Ca bone nail is completely degraded after being implanted in vivo for three months, the mechanical property of the bone nail is lost too early, adverse reactions such as secondary fracture and the like can be caused even in a load bearing occasion, and the clinical requirement of bone tissue repair can not be met to a certain extent. In 2016, Lee et al reported the use of Mg-5Ca-1Zn screws for internal fixation of palm fractures, and in their follow-up studies of up to 1 year, they found that fractures started to heal after the magnesium alloy screws were implanted for 4-6 weeks, that magnesium alloy screws had significantly reduced diameters due to continuous degradation after 6 months of implantation, that magnesium alloy screws had completely degraded after 1 year of implantation, while fractures at the distal radius had completely healed, and that their clinical studies found that magnesium alloy screws did not cause pain or discomfort to the patient during the entire period of implantation, and that normal movement of the palm after healing of fractures at affected sites was not affected. In addition, Sr has good biocompatibility and grain refinement effect, and is an important alloying element of the biomedical magnesium alloy. Sr is an essential metal element of a human body, about 140mg of Sr is contained in a normal human body, 99% of Sr is stored in human bones, the daily recommended intake of the human body is about 2mg, and the Sr can promote the growth of osteoblasts and the synthesis of osteogenic collagen. Sr is added into magnesium alloy as an alloy element, has a strong grain refining effect, and can improve the corrosion resistance of the alloy by improving the surface property of the alloy, and the addition amount of Sr is generally less than or equal to 0.5 wt.% in order to obtain the lowest corrosion rate as a biomedical magnesium alloy. According to the literature reports: after Zn is added into the Mg-Sr binary alloy, the corrosion resistance of the alloy is improved to a certain degree, and in the Mg-0.5Sr- (2,4,6) Zn series alloy, the hydrogen evolution rate of the alloy in Hank's solution is continuously improved along with the increase of the Zn content. Alloys containing 2% Zn and 4% Zn have hydrogen evolution rates significantly lower than binary Mg-0.5Sr alloys, while 6% Zn alloys have hydrogen evolution rates 30 times higher than 4% Zn alloys.

The 2006 patent 'Mg-Zn-Ca ternary magnesium alloy material absorbable in vivo' discloses chemical components (mass fraction) of a Mg-Zn-Ca ternary magnesium alloy, namely: 1-8% Zn, 0.1-2% Ca, which describes the preparation of the alloy as follows: the high-purity raw material and the high-cleanliness smelting technology are adopted for manufacturing; the purity of Mg as a raw material is not less than 99.99 percent, the purity of Zn is not less than 99.999 percent, and the purity of Ca is not less than 99.75 percent; the high-cleanness smelting needs to adopt inert gas argon protection, adopt a special graphite or titanium crucible for smelting, the smelting temperature is about 750 ℃, and then cast ingots in a special iron mould; the ingot is then heat treated and deformed to produce the required section, and various medical instruments implanted into the body are produced from the section for use.

2014 discloses chemical components (mass fraction) of Mg-Zn-Sr-Ca series magnesium alloy: zn: 0.01 to 8 percent; sr: 0.01-2%; ca: 0.01-2%; the balance of Mg; further discloses a preparation method of the alloy, which comprises the following steps: (1) preparing raw materials: selecting pure magnesium, pure zinc, pure strontium and magnesium-calcium intermediate alloy; (2) smelting: heating the selected raw materials to 720-760 ℃ and carrying out heat preservation melting to obtain a magnesium alloy melt; (3) casting: casting the magnesium alloy melt into a die preheated at the temperature of 250-350 ℃, and cooling to obtain a magnesium alloy ingot; (4) homogenizing: heating the magnesium alloy ingot to the temperature of between 300 and 420 ℃, and carrying out water cooling quenching after heat preservation for 10 to 24 hours; (5) and (3) extrusion processing: and (3) preheating the magnesium alloy ingot in the step (4) at the temperature of 380 ℃ at 300 ℃, and then extruding at the preheating temperature, wherein the extrusion speed is 0.5-3.0m/min and the extrusion ratio is 10-80: 1.

The 2017 patent 'an Mg-Zn-Sr-Ca-Zr medical bone nail and a preparation method thereof' discloses an Mg-Zn-Sr-Ca-Zr medical bone nail, which comprises the following chemical components in percentage by mass: zn: 2-4%, Sr: 1-2%, Ca: 0.5-0.7%, Zr: 0.3-0.5%, and the balance of magnesium and other impurities which cannot be removed; and further discloses a preparation method of the bone nail, which is the preparation and forming by powder metallurgy and thread rolling technology.

2017, the patent "a biomedical magnesium alloy and a preparation method thereof" discloses a biomedical magnesium alloy, which comprises the following components in percentage by mass: 1-4%, Mn: 0.05-0.2%, Ca: 0.05-1%, the Zn/Ca molar ratio is more than 1.5, and the rest is Mg and inevitable impurity elements; further discloses a preparation method thereof: (1) preparing raw materials: the raw materials were pure magnesium (99.9 wt.%), pure zinc (99.99 wt.%), Mg-Ca master alloy and Mg-Mn master alloy, respectively; the surface of the raw material is polished and cleaned by a grinding wheel, and surface oxides are removed, so that the generation of smelting impurities is reduced; (2) smelting: preheating a graphite crucible in a resistance furnace, and introducing N into the furnace after the furnace temperature is raised to 300-₂+SF₆Mixing the gas; introducing protective gas for 5min, placing a pure magnesium ingot into a crucible, heating the furnace to 680-DEG C and 760 ℃, adding one alloy after the magnesium ingot is completely melted according to the sequence of pure Zn, Mg-Ca intermediate alloy and Mg-Mn intermediate alloy, stirring at constant speed and anticlockwise for 5-8min after the alloys are completely melted, keeping the temperature at 740 ℃ and standing for 15min, and finally cooling the melt to 720 ℃, and standing for 30 min; continuously introducing N in the whole smelting process₂+SF₆Mixed protective gas (N) of₂And SF₆The volume flow ratio of (1) to (2) is 100:1), preventing oxidation or combustion of the magnesium alloy melt; (3) casting: slagging off, then pouring the molten liquid into a preheated metal mold at a constant speed, and demolding after solidification to obtain an alloy ingot; preheating the mould at 200 deg.C, introducing protective gas into the mould to prevent oxidation or combustion during castingAnd continuously conveying protective gas to the liquid flow for protection.

The 2017 patent 'a magnesium alloy biological implantation material and a preparation method thereof' discloses a magnesium alloy biological implantation material, which comprises the following elements in percentage by mass: 2.0-6.0% of Zn, 0.3-0.9% of Ca, 0.3-0.6% of Zr, and the balance of Mg and inevitable impurity elements; and further discloses a preparation method thereof.

At present, for Mg-Zn-Ca (Sr) magnesium alloy, most of Mg-Zn-Ca biomedical magnesium alloy is a wrought magnesium alloy product, except that a few Mg-Zn-Ca biomedical magnesium alloy products are prepared by a powder metallurgy method, most of cast ingots are subjected to homogenization treatment and then are subjected to extrusion deformation. The preparation process of the cast ingot is die casting, namely: after alloying smelting, pouring the high-temperature melt into a mould, and solidifying into an ingot. The preparation method aims at the small ingot with the diameter smaller than phi 300mm in laboratory scale, and the yield is high; and for large and medium-sized cast ingots with the diameter of more than phi 300mm, the existing method can not avoid solidification shrinkage cracking and macrosegregation. Although the section size of the conventional biomedical magnesium alloy product is not large, the large ingot with the diameter larger than 300mm is adopted to prepare the wrought magnesium alloy product, firstly, the production efficiency of the large ingot is high, the yield is larger under the condition of inputting the same person, machine and material, and the preparation cost can be greatly reduced, and secondly, the wrought magnesium alloy product with the same section size is prepared, the deformation degree of the large-diameter ingot is larger, the grain refining effect is better, the crushing effect of the eutectic compound is better, and therefore, the mechanical property is higher, and the uniform corrosion effect is better. However, the Mg-Zn-Ca alloy has a wide solidification temperature range, a large solidification shrinkage amount and a high cumulative shrinkage stress, and thus the alloy has a large tendency to be hot cracked; meanwhile, Zn has the tendency of specific gravity segregation and inverse segregation, which causes the uneven distribution of the second phase in the deformed product and influences the effect of uniform corrosion. For Mg-Zn-Ca series magnesium alloy ingots with the diameter of more than or equal to 300mm, the core solidification speed is slow, the structure is coarse, and in order to refine the core structure, the cooling speed is generally accelerated by adopting a spraying or water spraying mode, but the ingot is easy to crack. Therefore, the biggest technical problem of low-cost manufacture of the Mg-Zn-Ca biomedical magnesium alloy is to provideThe contradiction between the rising of solidification speed and the inhibition of solidification cracking, and the contradiction between the macrosegregation of an ingot and the realization of uniform corrosion. In addition, in the homogenization process in the prior art, the cold ingot is heated to a temperature below the melting point, and in the case of a large ingot, a large amount of energy is consumed in order to raise the core temperature to the homogenization temperature. If the waste heat after solidification can be utilized for homogenization, energy can be greatly saved. Thirdly, Ca with high melting point exists in the cast structure of the Mg-Zn-Ca alloy₂Mg₆Zn₃Ternary eutectic compounds, the melting point of which is above 410 ℃, are mostly distributed among dendrites in a continuous or semi-continuous net shape, a large amount of compounds are remained after the conventional homogenization process treatment in order to avoid oxidation and overburning, coarse compound streamlines exist in the tissues after deformation, uniform corrosion is very unfavorable, if homogenization at higher temperature can be carried out in a protective gas environment, the net-shaped compounds are changed into discrete spherical shapes, the deformation degree of alloy blanks can be increased, and the spherical compounds can prevent recrystallized grains from growing. In a word, the existing Mg-Zn-Ca series biomedical magnesium alloy preparation technology is not suitable for industrial production with strict requirements on cost.

Disclosure of Invention

Aiming at the problems, the invention realizes the low-cost industrial production of the Mg-Zn-Ca biomedical magnesium alloy by the following technical means: (1) smelting a large cast ingot with the diameter larger than 300mm, and reducing oxidation slag inclusion and flux inclusion and reducing crack sources through gas protection, rotary blowing, forced filtration and subsurface flow type transfer injection; (2) the shrinkage resistance is reduced through the coating on the inner wall of the mold, and the cracking of the cast ingot is inhibited; (3) homogenizing is realized through external field assisted solidification, and specific gravity segregation and inverse segregation of Zn are weakened; the solidification is assisted by spray cooling, the core solidification speed is accelerated, and the sequential solidification from bottom to top is realized; carrying out waste heat homogenization on a solid phase region below the valley bottom position, and carrying out spray cooling and outfield treatment on a liquid phase region and a pasty region above the valley bottom position by tracking the valley bottom position of the U-shaped solid-liquid interface in real time; (4) selection of Ca under gas protection₂Mg₆Zn₃The dissolution temperature of the ternary compound is used for carrying out waste heat homogenization and promoting Ca₂Mg₆Zn₃Spheroidizing and discretizing the ternary compound to improve the deformation capacity of the cast ingot and the plasticity of a final product; (5) the discretized spheroidized second phase promotes recrystallization and inhibits grain growth, and meanwhile, uniformity of mechanical properties and degradation rate is realized.

A preparation method of Mg-Zn-Ca biomedical magnesium alloy, in particular to a low-cost industrial preparation method of Mg-Zn-Ca-Sr biomedical wrought magnesium alloy, which comprises the following steps:

(1) batching, smelting and solidification system preparation

Taking magnesium ingot, zinc ingot and Mg-Ca intermediate alloy as raw materials, or taking magnesium ingot, zinc ingot, Mg-Ca intermediate alloy and Mg-Sr intermediate alloy as raw materials, and batching according to the chemical components of the alloy; preheating and drying the raw materials, a smelting furnace and a smelting tool;

(2) alloy smelting and purification

Under the protection of protective gas, firstly melting a magnesium ingot, pressing a Zn ingot into the liquid when the temperature of a melt reaches 700-; after all alloy elements are added, mechanical stirring is carried out, and then rotary blowing treatment is carried out, so that the gas content of the melt is reduced; then, the temperature of the melt is reduced to 700-710 ℃, and standing is carried out to prepare for transferring;

(3) underflow type transfer and forced filtration

Preheating the mould before transferring; and the inner cavity of the mould is firstly subjected to gas washing treatment, and after the gas washing is finished, the inner cavity is vacuumized to ensure that the vacuum degree of the furnace cavity reaches 6 multiplied by 10^-2Introducing argon below Pa to keep a dry argon environment in the furnace chamber and keep the furnace chamber in a micro-positive pressure state; opening a valve of the transfer system, and enabling the melt to stably pass through an MgO granular layer at the bottom of the mold from bottom to top in a submerged flow mode by utilizing the high fall between the smelting furnace and the mold;

(4) precise control of solidification and waste heat homogenization

After the transfer, 1) lifting the mold filled with the melt, wherein the height (horizontal height) of the bottom of the mold is more than or equal to the height (horizontal height) of the upper opening of the well-type heating furnace; a heat insulation layer is arranged at the top end of the mold, and a heat insulation layer is arranged outside the crucible in the riser area; 2) placing a thermocouple and an ultrasonic or current system in the melt, wherein the thermocouple is positioned on the axis of the center part of the inner cavity of the mold, ultrasonic rods or electrode rods of the ultrasonic or current system are arranged according to the optimal effect of analog simulation, and the lower ends of a thermocouple temperature measuring head, the ultrasonic rods or the electrode rods are positioned above a solid-liquid interface; 3) starting the automatic control module, carrying out spray cooling on a liquid phase region and a pasty region above a solid-liquid interface valley by using a spray system, closing spray heads in a riser region and above, weakening the spray strength from bottom to top, ensuring that the upper temperature of the liquid phase region is always higher than the lower temperature, and realizing sequential solidification from bottom to top; the U-shaped solid-liquid interface valley bottom tracking system determines the position of a solid-liquid interface in real time, the thermocouple measures the bottom temperature T of a central shaft of a liquid phase area and transmits the temperature value to the automatic control module in real time, the automatic control module compares T and T ' in real time, and when T is less than T ', the lifting system is started to enable the mold to move downwards slowly until T is equal to T '; all solid phase areas below the valley bottom of the U-shaped solid-liquid interface enter a well type heating furnace, and waste heat homogenization is carried out at the temperature of 380-; the electromagnetic stirring system and the ultrasonic or current system form a coupling field, and the melt is subjected to forced convection to break dendritic crystals, so that the structure is refined, and the macro segregation of solute elements is weakened; 4) when the lower end of the riser area reaches the upper opening of the well-type heating furnace, moving the thermocouple and the ultrasonic rod or the electrode rod of the ultrasonic or current system out of the mold, closing the U-shaped solid-liquid interface valley bottom tracking system, the spraying system, the electromagnetic stirring system and the ultrasonic or current system, and continuously carrying out homogenization treatment on the ingot in the well-type heating furnace;

(5) near solidus homogenization

After the ingot is completely solidified, keeping a protective gas environment, and carrying out constant-temperature homogenization or multi-stage homogenization treatment on the ingot;

(6) plastic deformation treatment

And (4) demoulding after homogenization treatment, and carrying out hot extrusion on the cast ingot.

In the invention, the Mg-Zn-Ca series biomedical magnesium alloy comprises Mg-Zn-Ca and Mg-Zn-Ca-Sr magnesium alloy. The Mg-Zn-Ca magnesium alloy comprises, by mass, 0.01% -8% of Zn, 0.01% -2% of Ca and the balance of Mg. The Mg-Zn-Ca-Sr magnesium alloy comprises, by mass, 0.01% -8% of Zn, 0.01% -2% of Ca, 0.01% -2% of Sr and the balance of Mg.

In the step (1), the purity of the magnesium ingot is more than or equal to 99.9 percent (weight percent), and the purity of the zinc ingot is more than or equal to 99.9 percent (weight percent); cleaning and polishing the raw materials before smelting, and removing an oxide layer.

The submerged flow type die casting equipment is adopted for smelting and transferring, and the inner wall of the die is coated with a coating which can reduce metallurgical bonding between the ingot and the crucible wall, so that the shrinkage resistance is reduced. A MgO ceramic particle layer is paved at the bottom of the mould, the grain diameter of the MgO ceramic particle is 5-30mm, and about 13-20Kg of ceramic particles are generally needed for filtering one ton of magnesium alloy melt. And a vacuum-pumping system and a protective gas device are arranged at the top of the mold.

The temperature for preheating and drying the raw materials, the smelting furnace and the smelting tool is 100-300 ℃.

In the step (2), the protective gas is tetrafluoroethane (R134 a).

The mechanical stirring time is 5-10 minutes, and the rotary blowing treatment time is 5-20 minutes; the standing time is 15-30 minutes.

In the step (3), before melt transfer, the temperature of the mold and the MgO particle layer at the bottom of the mold is heated to 600-800 ℃ in a well-type heating furnace.

The gas washing treatment comprises the following steps: sealing the top cover of the mold, opening the mechanical pump, vacuumizing the furnace chamber, closing the mechanical pump when the vacuum degree in the furnace chamber is reduced to 30-45Pa, opening the argon valve, filling argon to 150-220Pa, closing the argon valve, and opening the mechanical pump again for 2-3 times so as to exhaust the air in the furnace chamber as much as possible and keep the inside of the furnace chamber in a dry environment.

After the gas washing is finished, starting a mechanical pump to pump vacuum, starting a molecular pump to pump high vacuum when the vacuum degree in the furnace chamber is reduced to be below 25Pa, and reducing the vacuum degree in the furnace chamber to be 6 multiplied by 10^-2Closing the molecular pump and the mechanical pump when Pa is below, and filling argon to 0.06 × 10⁶Pa。

The fused mass passes through the MgO ceramic particle layer from bottom to top stably in a subsurface flow mode, so that not only can the oxidation in the fused mass transfer process be effectively avoided, but also a stable static liquid level can be formed, the conditions of turbulence and air entrainment existing in the common pouring can be effectively avoided, and meanwhile, small oxidized inclusions can be effectively filtered.

And (4) performing solidification and waste heat homogenization by adopting an accurate control solidification and waste heat homogenization integrated device. The equipment consists of a U-shaped solid-liquid interface valley bottom tracking system, a spraying system, an auxiliary external field system and a waste heat homogenizing system. The main body of the device consists of a lifting rod, a well-type heating furnace, an electromagnetic stirring system, a spraying system, a thermocouple and an ultrasonic or current system. The spraying system and the electromagnetic stirring system are positioned above the well-type heating furnace and arranged around the die; a thermocouple, ultrasonic or galvanic system is located inside the mold.

In the step (5), the constant temperature is homogenized at 380-₂Mg₆Zn₃The ternary eutectic compound is dissolved, and multi-stage homogenization treatment can be adopted to prevent over-burning. The multi-stage homogenization treatment system comprises the following steps: a first stage: 330-; and a second stage: 380 ℃ and 420 ℃, and keeping the temperature for 12-24 hours. The ideal effect is: most of the eutectic compounds in the interdendritic network are dissolved, and a small amount of the eutectic compounds are distributed in a spherical discrete manner.

(6) Plastic deformation treatment

The temperature of the hot extrusion is 280-380 ℃. The extrusion can be carried out once to obtain a proper section size, or the extrusion cogging can be carried out firstly, and then the second plastic deformation is carried out.

The invention has the beneficial effects that:

the preparation technology has the greatest advantage of meeting the requirement that the cross-sectional area of the Mg-Zn-Ca biomedical magnesium alloy with high heat cracking tendency is larger than 70000mm²The preparation of the ingot blank realizes the homogeneous and clean casting in industrial scale, thereby greatly improving the production efficiency, increasing the deformation degree and improving the performance; in addition, by capturing the valley bottom of the U-shaped solid-liquid interface in real time, the solid phase region at the lower part of the valley bottom of the solid-liquid interface is ensured to start constant temperature homogenization when the core temperature is close to the solidus temperature, so that the condensation is reducedThe shrinkage is fixed, the cracking risk of large cast ingots is greatly reduced, and the large cast ingots not only can improve the production efficiency, but also can improve the deformation degree, so that the material performance is improved; secondly, energy waste caused by secondary heating can be avoided by on-line waste heat homogenization; thirdly, capturing the valley bottom of the U-shaped solid-liquid interface in real time, simultaneously performing linkage control on the spraying system and the external field auxiliary stirring, distributing different spraying strengths to different positions of the liquid phase region, realizing sequential solidification, realizing homogenization of the pasty region and the liquid phase region by coupling an electromagnetic field, an ultrasonic field and an electric field, increasing the nucleation rate, refining dendritic crystals and effectively avoiding specific gravity segregation and inverse segregation of Zn; in addition, the combination of subsurface flow type transfer injection and forced filtration can greatly improve the purity of the material, reduce impurities and reduce crack sources; finally, the near-solidus homogenization treatment is adopted in a protective gas environment, so that the dissolution, spheroidization and discretization of the eutectic compound are promoted, and the uniformity of the degradation rate can be greatly improved.

Drawings

FIG. 1 is a structural view of an apparatus for producing a Mg-Zn-Ca-based biomedical magnesium alloy at a low cost, showing a state at the end of transfer.

FIG. 2 is a view showing the construction of an apparatus for the low-cost preparation of a biomedical magnesium alloy of Mg-Zn-Ca system, in which the solidification process is precisely controlled to be about half the time when the solid phase region of the lower part of the mold has been introduced into a shaft furnace for the homogenization of the residual heat.

Fig. 3 is a configuration diagram of the integrated device for precisely controlling solidification and waste heat homogenization in fig. 2.

Description of reference numerals:

i smelting system II undercurrent type transfer injection transfusion tube

III undercurrent type transfer injection mold and integrated device for accurately controlling solidification and waste heat homogenization

1 undercurrent type transfer injection mould 2 plug

3 MgO ceramic filter layer 4 solid phase region

5 solid-liquid interface 6 liquid phase region

7 mould top cover 8 pressure sensor

9 spraying system 10 vacuum pumping system

11 ultrasound or current system 12 thermocouple

13 protective gas system 14 electromagnetic stirring system

15 lifting system

Detailed Description

The invention provides a low-cost preparation method of Mg-Zn-Ca biomedical magnesium alloy, which is further described by combining the accompanying drawings and an embodiment.

The preparation method of the Mg-Zn-Ca biomedical magnesium alloy comprises the following steps:

(1) batching, smelting and solidification system preparation

Determining the chemical components of the alloy according to the required mechanical and degradation properties, adopting magnesium ingots with the purity of more than or equal to 99.9 percent, zinc ingots with the purity of more than or equal to 99.9 percent and Mg-Ca and Mg-Sr intermediate alloys, cleaning and polishing the raw materials before smelting, and removing an oxide layer.

The invention adopts undercurrent type die casting equipment for smelting and transferring, and adopts integrated equipment for accurately controlling solidification and waste heat homogenization to carry out solidification and homogenization. As shown in figures 1-2, the adopted equipment comprises a smelting system I, a subsurface flow type transfer injection infusion tube II, a subsurface flow type transfer injection mould and an integrated equipment III for accurately controlling solidification and waste heat homogenization.

The raw materials, the smelting furnace and the smelting tool are fully preheated and dried, and before the melt is transferred, the temperature of the mould and the MgO granular layer at the bottom of the mould is heated to 600 ℃ in a well-type heating furnace.

(2) Alloy smelting and purification

Under the protection of protective gas, firstly, melting the magnesium ingot, rapidly pressing the Zn ingot into the liquid when the melt temperature reaches 700-710 ℃, and rapidly pressing the Mg-Ca and Mg-Sr intermediate alloys into the liquid when the melt temperature reaches 750-760 ℃. After all the alloy elements are added, mechanical stirring is carried out for 5-10 minutes, and then rotary blowing treatment is carried out for 5-20 minutes, so that the gas content of the melt is reduced. Then the temperature of the melt is reduced to 700 ℃ and 710 ℃, and the melt is kept stand for 15 to 30 minutes to prepare for transferring.

(3) Underflow type transfer and forced filtration

Before transfer, firstly, performing gas washing treatment on the inner cavity of the mold, sealing the top cover of the mold, opening the mechanical pump, vacuumizing the furnace cavity, closing the mechanical pump when the vacuum degree in the furnace cavity is reduced to about 45Pa, opening the argon valve, filling argon to 220Pa, closing the argon valve, and opening the mechanical pump again, repeating the steps for 2-3 times so as to discharge the air in the furnace cavity as much as possible and keep the inside of the furnace cavity in a dry environment. After the gas washing is finished, when the vacuum degree in the furnace chamber is reduced to below 25Pa, the molecular pump is started to pump high vacuum, and when the vacuum degree in the furnace chamber is reduced to 6 multiplied by 10^-2Closing the molecular pump and the mechanical pump when Pa is below, and filling argon to 0.06 × 10⁶Pa. At this time, a dry argon atmosphere is maintained in the furnace chamber and a slight positive pressure state is maintained. The valve of the transfer system is opened, and the high fall between the smelting furnace and the mould is utilized to realize that the melt stably passes through the MgO ceramic particle layer from bottom to top in a subsurface flow mode, thereby not only effectively avoiding the oxidation in the melt transfer process, but also being beneficial to forming a stable static liquid level, further effectively avoiding the turbulence and air entrainment conditions existing in the common pouring, and simultaneously effectively filtering small oxidation inclusions. And after the transfer, adjusting the temperature of the well-type heating furnace to 380-420 ℃. As shown in fig. 1, the state of the apparatus at the end of the transfer.

(4) Precise control of solidification and waste heat homogenization

And after the transfer is finished, solidification and waste heat homogenization are carried out by adopting an integrated device for accurately controlling solidification and waste heat homogenization. As shown in figure 3, the equipment consists of a U-shaped solid-liquid interface valley bottom tracking system, a spraying system, an auxiliary external field system and a waste heat homogenizing system. The main body of the device consists of a lifting system 15, a well-type heating furnace, an electromagnetic stirring system 14, a spraying system 9, a thermocouple 12 and an ultrasonic or current system 11. The spraying system 9 and the electromagnetic stirring system 14 are positioned above the well-type heating furnace and arranged around the subsurface flow type transfer mold 1; a thermocouple 12, an ultrasonic or electrical current system 11 is located inside the down-the-flow transfer mold 1.

The U-shaped solid-liquid interface valley bottom tracking system consists of a thermocouple 12, a lifting system 15 and an automatic control module which are positioned on the central shaft of the subsurface flow type transfer mold 1, wherein the thermocouple 12 and the lifting system 15 are respectively connected with the automatic control module; the lifting system 15 is arranged at the top of the subsurface flow type transfer molding die 1; the thermocouple 12 is arranged above the solid-liquid interface 5 of the melt in the subsurface flow type transfer mold 1 and is close to the bottom of the liquid phase region 6 of the melt, and the lifting system 15 is controlled to lift through the automatic control module, so that the temperature T measured by the thermocouple 12 is kept at a certain temperature T' above the solidus. Preferably, the temperature T 'is 5 ℃ to 15 ℃ above the solidus temperature, e.g., T' is the solid-liquid interface mushy zone temperature of the alloy system. The functions of the system are: in the process of sequentially solidifying the melt from bottom to top, the temperature of the upper part of the liquid phase region 6 is always higher than the temperature of the lower part, the thermocouple 12 measures the temperature T of the bottom of the central shaft of the liquid phase region 6 and transmits the temperature value to the automatic control module in real time, the automatic control module compares T and T ' in real time, and when T is less than T ', the lifting system 15 is enabled to move downwards slowly until T is equal to T '.

The spraying system 9 is composed of spray heads arranged in an array mode around the undercurrent type transfer mold 1, control valves and automatic control modules, the control valves are used for adjusting the water flow intensity of the spray heads, and the automatic control modules achieve automatic control of the spraying intensity through adjusting the control valves. The spraying intensity of the spray heads with different heights is controlled by an automatic control module, the spraying intensity is gradually reduced from bottom to top, and the spray heads do not spray within a certain range (overflow area) below the liquid level, so that sequential solidification from bottom to top is realized, and a liquid phase area 6, a solid-liquid interface 5 and a solid phase area 4 are respectively arranged from top to bottom in the die shown in figure 3.

The auxiliary external field system consists of an electromagnetic stirring system 14 positioned outside the die and an ultrasonic or current system 11 positioned in the die, and in the solidification process, an electromagnetic field, an ultrasonic vibration field and an electric field are applied to a liquid phase region and a pasty region to realize dendritic crystal crushing and uniform dispersion of alloy elements, so that tissue refinement and solute homogenization are realized.

The waste heat homogenizing system consists of a well-type heating furnace and a temperature control module, the temperature control module is connected with the well-type heating furnace, the furnace temperature is ensured to be constant at a reasonable homogenizing temperature, and the energy consumption can be greatly reduced due to the solidification waste heat fully utilized.

The inner wall of the undercurrent type transfer injection mould 1 is coated with a coating which can reduce metallurgical bonding between the cast ingot and the crucible wall, and the shrinkage resistance is reduced. The bottom of the undercurrent type transfer injection mould 1 is paved with an MgO ceramic filter layer 3, and the top of the mould is provided with a vacuum pumping system 10 and a protective gas system 13. Debugging the integrated equipment for accurately controlling solidification and homogenizing waste heat, completing the matching of the thermocouple and the ultrasonic rod or the electrode rod with the mould, and debugging the spraying system, the mould lifting system and the electromagnetic stirring system.

A mould top cover 7 (a heat insulation layer) is arranged at the top end of the undercurrent type transfer mould 1, a pressure sensor 8 is arranged on the mould top cover 7, a riser area is arranged in a range of 300mm below the liquid level, and the heat insulation layer is arranged on the outer side of a crucible in the riser area; the bottom of the undercurrent type transfer injection mould 1 is provided with a plug 2; the thermocouples 12 are located at the axis of the core of the mould cavity and the ultrasound or electrode rods of the ultrasound or current system 11 are arranged according to the best effect of the simulation. The lower ends of the thermocouple 12 temperature measuring head, the ultrasonic rod or the electrode rod are positioned above the solid-liquid interface 5.

The specific process comprises the following steps:

1) lifting the mold filled with the melt, wherein the bottom of the mold is higher than or equal to the upper opening of the well-type heating furnace; the top end of the mould is provided with a heat insulation layer, the range 300mm below the liquid level is a riser area, and the outer side of a crucible in the riser area is provided with the heat insulation layer;

2) and placing a thermocouple and an ultrasonic or current system, wherein the thermocouple is positioned on the axis of the center part of the inner cavity of the die, and ultrasonic rods or electrode rods of the ultrasonic or current system are arranged according to the optimal effect of simulation. The lower ends of the thermocouple temperature measuring head, the ultrasonic rod or the electrode rod are positioned above the solid-liquid interface;

3) and starting the automatic control module, and starting the operation of each system. The spraying system carries out spray cooling on a liquid phase region and a pasty region above a solid-liquid interface valley bottom, the spray heads in the overflow region and above are closed, the spray strength from bottom to top is weakened, the upper temperature of the liquid phase region is guaranteed to be always higher than the lower temperature, and sequential solidification from bottom to top is realized. The U-shaped solid-liquid interface valley bottom tracking system determines the position of a solid-liquid interface in real time, the thermocouple measures the bottom temperature T of a central shaft of a liquid phase area and transmits the temperature value to the automatic control module in real time, T 'is the temperature of a mushy area of the alloy system, the automatic control module compares T and T' in real time, and when T is less than T ', the lifting system is started to enable the mold to move downwards slowly until T is equal to T'. All solid phase regions below the valley bottom of the U-shaped solid-liquid interface enter a well type heating furnace, and waste heat homogenization is carried out at the temperature of 380-420 ℃. The electromagnetic stirring system and the ultrasonic or current system form a coupling field, and the melt is subjected to forced convection to break dendritic crystals, so that the structure is refined, and the macro segregation of solute elements is weakened; as shown in FIG. 2, in order to precisely control the solidification process to about half of the time, the solid phase region at the lower part of the mold enters a well-type heating furnace for waste heat homogenization.

4) When the lower end of the dead head area reaches the upper opening of the well-type heating furnace, the thermocouple and the ultrasonic rod or the electrode rod of the ultrasonic or current system are moved out of the mold, and the U-shaped solid-liquid interface valley bottom tracking system, the spraying system, the electromagnetic stirring system and the ultrasonic or current system are closed. And (4) continuously carrying out homogenization treatment on the ingot in a well-type heating furnace until the proper heat preservation time is reached.

(5) Near solidus homogenization

After complete solidification, the protective gas environment is kept, the whole ingot is continuously homogenized at the constant temperature of 380-420 ℃, the heat preservation time is more than 12-24 hours, and Ca is promoted₂Mg₆Zn₃The ternary eutectic compound is dissolved, and multi-stage homogenization treatment can be adopted to prevent over-burning. The ideal effect is: most of the eutectic compounds in the interdendritic network are dissolved, and a small amount of the eutectic compounds are distributed in a spherical discrete manner.

(6) Plastic deformation treatment

After homogenization treatment, the film is rapidly stripped and hot extrusion is carried out at the temperature of 280-380 ℃. The extrusion can be carried out once to obtain a proper section size, or the extrusion cogging can be carried out firstly, and then the second plastic deformation is carried out.

The method of the present invention will be described in detail below by taking as an example the method for producing Mg-3% Zn-1% Ca-0.5% Sr.

The target products are absorbable fracture internal fixation screws and bone plates with chemical compositions of Mg-3% Zn-1% Ca-0.5% Sr (mass fraction), and the temperature of a paste forming area (solid-liquid interface) of the alloy is about 430 ℃ in the conventional solidification process. In order to realize low-cost production on an industrial scale and to increase the degree of deformation (extrusion ratio) of an ingot blank, an ingot having a diameter of phi 310mm is first produced. In the pilot scale process in the earlier stage, adopt conventional die casting technique to carry out diameter phi 310mm ingot production, promptly: transferring the purified melt into a mold through an infusion pump, and simply spraying and cooling the outer wall of the mold in the solidification process; and turning the cast ingot, turning off the black skin on the surface, performing two-stage homogenization treatment, and finally performing hot extrusion. The pilot test results show that: firstly, cracks which are expanded from the surface layer to the central part often appear in the cast ingot, so that the yield is reduced; secondly, the two-stage homogenization treatment time is long, and the energy consumption is large; in addition, the compound flow lines in the extruded material are thick, so that the uniformity of the degradation rate is influenced; in conclusion, the conventional process has low yield and high cost. Aiming at the problems, the low-cost preparation process provided by the invention is developed as follows: melting, subsurface flow transfer, forced filtration, solidification structure control and waste heat homogenization are carried out by adopting the equipment shown in figures 1-3; the ingot was then extruded into rods (bone nails) and plates (bone plates) using a conventional extruder.

The preparation process comprises the following steps:

(1) batching, smelting and solidification system preparation

The preparation method comprises the following steps of proportioning according to chemical components, and adopting a magnesium ingot with the purity of 99.9%, a zinc ingot with the purity of 99.9%, a Ca intermediate alloy with the purity of 30-wt% and a Sr intermediate alloy with the purity of 25-wt%, wherein the burning loss of Zn is 0, and the burning loss of Ca and Sr is 10%. Before smelting, the raw materials are polished and cleaned, and an oxide layer is removed.

The equipment as shown in the figures 1-3 is adopted for smelting, subsurface flow type transfer injection, forced filtration, solidification structure control and waste heat homogenization. The die is prepared by adopting a low-carbon steel seamless tube with the inner diameter phi of 310mm, and the high-temperature heat-resistant coating boron nitride is sprayed on the inner wall of the die, so that the service life of the die is prolonged, the surface smoothness of a casting is improved, the metallurgical bonding between an ingot and the crucible wall is prevented, and the shrinkage resistance is reduced. The bottom of the mould is paved with an MgO ceramic layer, and the top of the mould is provided with a vacuum and gas protection device. Adjusting the equipment shown in the figure 3, completing the matching of the thermocouple and the ultrasonic rod or the electrode rod with the mould, and adjusting the spraying system, the mould lifting system and the electromagnetic stirring system.

The raw materials, a smelting furnace and a smelting tool are fully preheated and dried at the temperature of 200 ℃, before the melt is transferred, a mold is filled with high-purity tetrafluoroethane (R134a) protective gas, and the temperature of the mold and an MgO particle layer at the bottom of the mold is heated to 600 ℃ in a well-type heating furnace.

(2) Alloy smelting and purification

Under the protection of high-purity tetrafluoroethane (R134a) protective gas, in a smelting system of the equipment shown in the figure 1, firstly, magnesium ingots are melted, Zn ingots are quickly pressed into the liquid when the temperature of the melt reaches 700-. After all the alloy elements are added, mechanical stirring is carried out for 5-10 minutes to ensure that the alloy elements are uniformly distributed, and then rotary blowing treatment is carried out for 5-20 minutes to reduce the gas content of the melt. Then the temperature of the melt is reduced to 700 ℃ and 710 ℃, and the melt is kept stand for 20 minutes to prepare for transfer injection.

(3) Underflow type transfer and forced filtration

Before transfer, firstly, performing gas washing treatment on the inner cavity of the mold, sealing the top cover of the mold, opening the mechanical pump, vacuumizing the furnace cavity, closing the mechanical pump when the vacuum degree in the furnace cavity is reduced to about 45Pa, opening the argon valve, filling argon to 220Pa, closing the argon valve, and opening the mechanical pump again, repeating the steps for 2-3 times so as to discharge the air in the furnace cavity as much as possible and keep the inside of the furnace cavity in a dry environment. After the gas washing is finished, when the vacuum degree in the furnace chamber is reduced to below 25Pa, the molecular pump is started to pump high vacuum, and when the vacuum degree in the furnace chamber is reduced to 6 multiplied by 10^-2Closing the molecular pump and the mechanical pump when Pa is below, and filling argon to 0.06 × 10⁶Pa. At this time, a dry argon atmosphere is maintained in the furnace chamber and a slight positive pressure state is maintained. A valve of a subsurface flow type transfer injection infusion tube in the device shown in figure 1 is opened, and the melt stably passes through the MgO ceramic particle layer from bottom to top in a subsurface flow mode by utilizing the high fall between a smelting furnace and a mould, wherein the temperature of the ceramic particle layer is 600 ℃, and the fluidity of the melt can be maintained. The process not only can effectively avoid oxidation in the melt transfer process, but also is beneficial to forming a stable static liquid level, thereby effectively avoiding oxidationAvoids the turbulence and air entrainment existing in the common casting, and can effectively filter out the fine oxide inclusions. After the transfer, the temperature of the shaft furnace was adjusted to 390 ℃.

(4) Precise control of solidification and waste heat homogenization

After the transfer, the equipment shown in fig. 2 and 3 carries out accurate control solidification and waste heat homogenization, and the part consists of a U-shaped solid-liquid interface valley bottom tracking system, a spraying system, an auxiliary external field system and a waste heat homogenization system. The main body of the device consists of a lifting rod, a well-type heating furnace, an electromagnetic stirring system, a spraying system, a thermocouple and an ultrasonic or current system. The spraying system and the electromagnetic stirring system are positioned above the well-type heating furnace and arranged around the die; a thermocouple, ultrasonic or galvanic system is located inside the mold. The specific process comprises the following steps: (1) lifting the mold filled with the melt, wherein the bottom of the mold is higher than or equal to the upper opening of the well-type heating furnace; the top end of the mould is provided with a heat insulation layer, the range 300mm below the liquid level is a riser area, and the outer side of a crucible in the riser area is provided with the heat insulation layer; (2) and placing a thermocouple and an ultrasonic or current system, wherein the thermocouple is positioned on the axis of the center part of the inner cavity of the die, and ultrasonic rods or electrode rods of the ultrasonic or current system are arranged according to the optimal effect of simulation. The lower ends of the thermocouple temperature measuring head, the ultrasonic rod or the electrode rod are positioned above the solid-liquid interface; (3) and starting the automatic control module, and starting the operation of each system. The spraying system carries out spray cooling on a liquid phase region and a pasty region above a solid-liquid interface valley bottom, the spray heads in the overflow region and above are closed, the spray strength from bottom to top is weakened, the upper temperature of the liquid phase region is guaranteed to be always higher than the lower temperature, and sequential solidification from bottom to top is realized. The U-shaped solid-liquid interface valley bottom tracking system determines the position of a solid-liquid interface in real time, the thermocouple measures the bottom temperature T of a central shaft in a liquid phase area and transmits the temperature value to the automatic control module in real time, T 'is the temperature of a mushy area and is set as 430 ℃, the automatic control module compares T and T' in real time, and when T is less than T ', the lifting system is started to enable the mold to move downwards slowly until T is equal to T'. And (3) all solid phase regions below the valley bottom of the U-shaped solid-liquid interface enter a well type heating furnace, and waste heat homogenization is carried out at 390 ℃. The electromagnetic stirring system and the ultrasonic or current system form a coupling field, and the melt is subjected to forced convection to break dendritic crystals, so that the structure is refined, and the macro segregation of solute elements is weakened; (4) when the lower end of the dead head area reaches the upper opening of the well-type heating furnace, the thermocouple and the ultrasonic rod or the electrode rod of the ultrasonic or current system are moved out of the mold, and the U-shaped solid-liquid interface valley bottom tracking system, the spraying system, the electromagnetic stirring system and the ultrasonic or current system are closed. And (4) continuously carrying out homogenization treatment on the ingot in a well-type heating furnace until the proper heat preservation time is reached.

(5) Near solidus homogenization

After complete solidification, keeping a high-purity tetrafluoroethane (R134a) protective gas environment, continuously carrying out constant-temperature homogenization on the whole cast ingot at 390 ℃, keeping the temperature for 12 hours, and then carrying out secondary constant-temperature homogenization at 410 ℃, and keeping the temperature for 24 hours. Promoting Ca₂Mg₆Zn₃The ternary eutectic compound is mostly dissolved, and a small amount of the ternary eutectic compound is in spherical discrete distribution.

(6) Plastic deformation treatment

After homogenization treatment, the film is rapidly removed, the residual heat of an ingot blank is about 350 ℃, the temperature of an extrusion die and an extrusion cylinder is set to be 350 ℃, the ingot blank is extruded into a round bar with the cross section phi of 30mm or a bar with the thickness of 10mm at one time, because an ingot with the diameter phi of 310mm is adopted, the deformation degree is greatly increased, the extrusion ratio is close to 100:1, the grain refining effect and the compound crushing and refining effect are very obvious, and the mechanical property and the degradation property are greatly improved.

The Mg-3% Zn-1% Ca-0.5% Sr bone nail and bone plate prepared by the invention has a grain size less than 10 μm. The room temperature mechanical properties are as follows: the tensile strength is 350MPa, the yield strength is 300MPa, and the elongation is 20%. The degradation performance is as follows: alloy sample surface area (cm)²) And volume of Hank's solution ((ml) ratio 1/150), immersion corrosion in Hank's solution at 37.4 ℃ with an alloy corrosion rate of 0.85 mm/y.

The above embodiments are only used for illustrating but not limiting the technical solutions of the present invention, and although the above embodiments describe the present invention in detail, those skilled in the art should understand that: modifications and equivalents may be made thereto without departing from the spirit and scope of the invention and any modifications and equivalents may fall within the scope of the claims.

Claims (10)

1. A preparation method of Mg-Zn-Ca biomedical magnesium alloy comprises the following steps:

(1) preparing a material mixing, smelting and solidifying system: the Mg-Zn-Ca series biomedical magnesium alloy comprises Mg-Zn-Ca and Mg-Zn-Ca-Sr magnesium alloy; the Mg-Zn-Ca magnesium alloy comprises 0.01-8% of Zn, 0.01-2% of Ca and the balance of Mg by mass percent; the Mg-Zn-Ca-Sr magnesium alloy comprises, by mass, 0.01% -8% of Zn, 0.01% -2% of Ca, 0.01% -2% of Sr and the balance of Mg; taking magnesium ingot, zinc ingot and Mg-Ca intermediate alloy as raw materials, or taking magnesium ingot, zinc ingot, Mg-Ca intermediate alloy and Mg-Sr intermediate alloy as raw materials, and batching according to the chemical components of the alloy; preheating and drying the raw materials, a smelting furnace and a smelting tool;

(2) alloy smelting and purifying: under the protection of protective gas, firstly melting a magnesium ingot, pressing a Zn ingot into the liquid when the temperature of a melt reaches 700-; after all alloy elements are added, mechanical stirring is carried out, and then rotary blowing treatment is carried out, so that the gas content of the melt is reduced; then, the temperature of the melt is reduced to 700-710 ℃, and standing is carried out to prepare for transferring;

(3) undercurrent type transfer and forced filtration: preheating the mould before transferring; and the inner cavity of the mould is firstly subjected to gas washing treatment, and after the gas washing is finished, the inner cavity is vacuumized to ensure that the vacuum degree of the furnace cavity reaches 6 multiplied by 10^-2Introducing argon below Pa to keep a dry argon environment in the furnace chamber and keep the furnace chamber in a micro-positive pressure state; opening a valve of the transfer system, and enabling the melt to stably pass through an MgO granular layer at the bottom of the mold from bottom to top in a submerged flow mode by utilizing the high fall between the smelting furnace and the mold;

(4) accurately controlling solidification and waste heat homogenization: after the transfer, firstly, lifting the mold filled with the melt, wherein the horizontal height of the bottom of the mold is more than or equal to the horizontal height of the upper opening of the well-type heating furnace; a heat insulation layer is arranged at the top end of the mold, and a heat insulation layer is arranged outside the crucible in the riser area; secondly, placing a thermocouple and an ultrasonic or current system in the melt, wherein the thermocouple is positioned on the axis of the center part of the inner cavity of the mold, ultrasonic rods or electrode rods of the ultrasonic or current system are arranged according to the optimal effect of analog simulation, and the lower ends of a thermocouple temperature measuring head, the ultrasonic rods or the electrode rods are positioned above a solid-liquid interface; thirdly, starting the automatic control module, carrying out spray cooling on a liquid phase region and a pasty region above the valley of a solid-liquid interface by a spray system, closing a spray head at a riser region and above, weakening the spray strength from bottom to top, ensuring that the upper temperature of the liquid phase region is always higher than the lower temperature, and realizing sequential solidification from bottom to top; the U-shaped solid-liquid interface valley bottom tracking system determines the position of a solid-liquid interface in real time, the thermocouple measures the bottom temperature T of a central shaft in a liquid phase area and transmits the temperature value to the automatic control module in real time, T 'is the temperature of a mushy area of the alloy system, the automatic control module compares T and T' in real time, and when T is less than T ', the lifting system is started to enable the mold to move downwards slowly until T = T'; all solid phase areas below the valley bottom of the U-shaped solid-liquid interface enter a well type heating furnace, and waste heat homogenization is carried out at the temperature of 380-; the electromagnetic stirring system and the ultrasonic or current system form a coupling field, and the melt is subjected to forced convection to break dendritic crystals, so that the structure is refined, and the macro segregation of solute elements is weakened; finally, when the lower end of the riser area reaches the upper opening of the well-type heating furnace, moving the thermocouple and the ultrasonic rod or the electrode rod of the ultrasonic or current system out of the mold, closing the U-shaped solid-liquid interface valley bottom tracking system, the spraying system, the electromagnetic stirring system and the ultrasonic or current system, and continuously carrying out homogenization treatment on the ingot in the well-type heating furnace;

(5) near solidus homogenization treatment: after the ingot is completely solidified, keeping a protective gas environment, and carrying out constant-temperature homogenization or multi-stage homogenization treatment on the ingot;

(6) plastic deformation treatment: and (4) demoulding after homogenization treatment, and carrying out hot extrusion on the cast ingot.

2. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: the purity of the magnesium ingot is more than or equal to 99.9 weight percent, and the purity of the zinc ingot is more than or equal to 99.9 weight percent; cleaning and polishing the raw materials before smelting to remove an oxide layer; the preheating and drying temperatures of the raw materials, the smelting furnace and the smelting tool are 100-300 ℃.

3. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: smelting and transferring are carried out by adopting undercurrent type die casting equipment, a coating capable of reducing metallurgical bonding between an ingot and a crucible wall is coated on the inner wall of the die, a MgO ceramic particle layer is laid at the bottom of the die, and a vacuum and gas protection device is installed at the top of the die.

4. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: the protective gas is tetrafluoroethane.

5. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: the mechanical stirring time is 5-10 minutes, and the rotary blowing treatment time is 5-20 minutes; the standing time is 15-30 minutes.

6. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: before melt transfer, the temperature of the mold and the MgO granular layer at the bottom of the mold is heated to 600-800 ℃ in a well-type heating furnace.

7. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: the gas washing treatment comprises the following steps: sealing the top cover of the mold, opening the mechanical pump, vacuumizing the furnace chamber, closing the mechanical pump when the vacuum degree in the furnace chamber is reduced to 30-45Pa, opening the argon gas valve, filling argon gas to 150-220Pa, closing the argon gas valve, and opening the mechanical pump again, and repeating the steps for 2-3 times.

8. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: after the gas washing is finished, starting a mechanical pump to pump vacuum, starting a molecular pump to pump high vacuum when the vacuum degree in the furnace chamber is reduced to below 25Pa, and starting the molecular pump to pump high vacuum when the furnace chamber is heatedThe vacuum degree is reduced to 6 x 10^-2Closing the molecular pump and the mechanical pump when Pa is below, and filling argon to 0.06 × 10⁶ Pa。

9. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein: the constant-temperature homogenization temperature is 380-420 ℃, and the heat preservation time is more than 12-24 hours; the multi-stage homogenization treatment comprises the following steps: a first stage: 330-; and a second stage: 380 ℃ and 420 ℃, and keeping the temperature for 12-24 hours.

10. The method for preparing Mg-Zn-Ca biomedical magnesium alloy according to claim 1, wherein:

the temperature of the hot extrusion is 280-380 ℃; the first extrusion is carried out to obtain the proper section size, or the first extrusion cogging is carried out and then the second plastic deformation is carried out.

Images