Method for microstructure re-optimization of magnesium alloy ultrafine wires

Abstract

The present application relates to the technical field of preparation of metal material magnesium alloy, and particularly provides a microstructure re-optimization method of magnesium alloy ultrafine wire. The existing heat treatment system is difficult to uniformly treat the wire material, and increasing the heat treatment temperature will lead to magnesium alloy grain growth and significant reduction of plasticity; prolonging the heat treatment time will reduce the tensile strength and yield strength of the wire material, leading to large performance difference of the wire material in the same batch, and affecting the performance and stability of the final product. In order to solve the above problems, the present application uses high-energy pulse current through the magnesium alloy wire material, adjusts the current density, frequency and space occupation ratio, eliminates the internal stress of the wire material, promotes the occurrence of dynamic and static recrystallization process, refines the alloy grain, and finally the strength of the wire material, especially the elongation, is greatly improved, and good corrosion resistance is obtained, meeting the performance requirements of the magnesium alloy wire material.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of preparation of magnesium alloy, and particularly provides a microstructure re-optimization method of magnesium alloy ultra-fine wire. BACKGROUND

[0002] The magnesium alloy wire material is a material which can be degraded and has good biological safety, can be gradually degraded and metabolized in the body after realizing the implantation function until disappearing, avoids secondary removal operation, has broad application prospects in the biomedical field, and can be used as implantation materials such as sternum connection in cardiac surgery, cartilage connection in plastic surgery, gastrointestinal anastomosis in general surgery, tracheal stent support, esophageal stent support and duodenal food filtration. In addition, the magnesium alloy wire material can also be used as a raw material for enhancing and improving the performance of composite materials. Therefore, the final performance of the magnesium alloy wire material directly determines the quality of the product.

[0003] The magnesium alloy wire material is prepared by melting, casting, extrusion and drawing process, and the crystal grains in the wire material subjected to cold deformation are irregular and have work hardening phenomenon, so that a heat treatment process is usually introduced to improve the microstructure of the alloy and eliminate stress. The heat treatment temperature of the magnesium alloy wire material is usually 300-400℃, and the holding time is 10-60min. When a large amount of wire materials are wound together, the existing heat treatment system is difficult to uniformly treat the wire materials, resulting in large differences in microstructure and mechanical properties of the same batch of wire materials, which affects the quality and performance stability of the final product. Increasing the heat treatment temperature will lead to the growth of magnesium alloy grains and the significant reduction of plasticity, and prolonging the heat treatment time will reduce the tensile strength and yield strength of the wire material, which are not the best methods to solve the above problems. SUMMARY

[0004] The purpose of the present application is to solve the problem of uneven heat treatment of magnesium alloy wire material, which leads to uneven microstructure, strength, plasticity and corrosion resistance of the final wire material, and is difficult to meet the use requirements of the wire material. A microstructure re-optimization method of magnesium alloy ultra-fine wire is provided.

[0005] The technical scheme of the present application is:

[0006] A microstructure re-optimization method of magnesium alloy ultra-fine wire changes the traditional heat treatment process of metal wire material, utilizes high-energy pulse current through the magnesium alloy wire material, adjusts the current density, frequency and space occupation ratio to realize the microstructure re-optimization of the magnesium alloy wire material, and improves the mechanical properties and corrosion resistance of the wire material, which comprises the following operation steps:

[0007] (1) The magnesium alloy is prepared into a wire material with a diameter of 0.20-0.30mm by a process of batching, melting, casting, hot extrusion and cold drawing;

[0008] (2) the magnesium alloy wire in step (1) is polished on a wire drawing machine respectively, then cleaned by ultrasonic alcohol cleaning, and dried by blowing;

[0009] (3) the magnesium alloy wire in step (2) is subjected to high-energy pulse current treatment, the output current is 0-20 A, the frequency is 100 HZ-3000 HZ, and the duty cycle is 5%-80%.

[0010] The main alloying elements in the magnesium alloy include one or more than two of Zn, Nd, Zr, Mn, Si, Ca and Y, and Mg is the remainder.

[0011] The magnesium alloy ultrafine wire is prepared by the method, and the magnesium alloy contains Zn: 0%-2.0%, Nd: 0%-1.5%, Zr: 0%-1.0%, Mn: 0%-0.5%, Si: 0%-0.2%, Ca: 0%-0.3%, and Y: 0%-0.1% by mass percentage.

[0012] In step (1), pulse current is applied in the last cold drawing process, and the pulse current is applied in the dynamic drawing process, the output current is 5-20 A, the frequency is 500 HZ-2000 HZ, and the duty cycle is 30%-60%.

[0013] In step (2), the magnesium alloy wire is subjected to rough polishing and fine polishing on the wire drawing machine, the rough polishing is performed by using a hundred-scrub cloth, the roughness after rough polishing is Ra0.2-Ra0.4, and the fine polishing is performed by using a magic wipe, and the roughness after fine polishing is Ra0.05-Ra0.2.

[0014] The hundred-scrub cloth is a nylon sand-containing hundred-scrub cloth made of nylon fibers and mineral sand abrasive particles, and the magic wipe is a melamine polyurethane foam.

[0015] In step (3), the output current of the high-energy pulse current treatment is 10-20 A, the frequency is 900 HZ-1500 HZ, the duty cycle is 40%-60%, and the pulse current action time is 20 min-60 min.

[0016] In step (3), the prepared magnesium alloy wire is used as a final product or as an intermediate product for preparing a composite material.

[0017] The design idea of the application is:

[0018] Magnesium alloy wire has certain strength, excellent biocompatibility, in-vivo degradability, can be used as anastomosis nail, cosmetic line, cartilage connecting wire, nerve connecting wire and other medical device products, and has great medical application value. In addition, the magnesium alloy wire can also be used as a raw material for reinforcing and improving the performance of composite materials. In practical application, the magnesium alloy wire is required to have good strength and plasticity matching, and the preparation process of the magnesium alloy wire usually includes melting, casting, extrusion, drawing and other processes, and is supplemented by annealing process to achieve the use purpose. However, in the heat treatment process of the magnesium alloy wire, the commonly used heat treatment temperature is 300-400 DEG C, and the holding time is 10-60 min, when a large amount of wire is wound together, the existing heat treatment system is difficult to uniformly treat the wire, and increasing the heat treatment temperature will lead to grain growth of the magnesium alloy, and the plasticity is significantly reduced; prolonging the heat treatment time will reduce the tensile strength and yield strength of the wire, resulting in large difference in performance of the wires in the same batch, affecting the performance and stability of the final product.

[0019] In view of the problem of non-uniform heat treatment of the magnesium alloy ultra-fine wire, leading to non-uniform microstructure, strength, plasticity and corrosion resistance of the final wire, it is difficult to meet the use requirements of the wire. The present application changes the traditional heat treatment process, adopts high-energy pulse current treatment process, first solves the uniformity problem of the wire process, ensures the large-scale treatment of the wire, and then optimizes the process parameters by adjusting the current density, frequency and space ratio, finally improves the microstructure of the alloy and improves the strength and plasticity of the alloy.

[0020] The advantages and beneficial effects of the present application are:

[0021] The present application adopts high-energy pulse current acting on the magnesium alloy wire, optimizes the parameters such as current density, frequency and space ratio, and finally obtains uniform ultra-fine equiaxed crystal, the strength and plasticity of the wire are greatly improved and the performance is stable, which is beneficial to expand the application range of the magnesium alloy wire. BRIEF DESCRIPTION OF DRAWINGS

[0022] Figure 1 The metallographic structure of the cold-drawn magnesium alloy wire.

[0023] Figure 2 The metallographic structure of the magnesium alloy wire after pulse current action.

[0024] Figure 3 The tensile properties of the cold-drawn magnesium alloy wire (No. 1 curve) and the magnesium alloy wire after pulse current action (No. 2 curve). In the figure, the abscissa Engineering strain represents engineering strain (%), and the ordinate Engineering stress represents engineering stress (MPa). DETAILED DESCRIPTION

[0025] The embodiments of the present application are described in detail below with reference to the drawings, which are implemented on the premise of the technical solutions of the present application, and detailed implementation manners and specific operation processes are given, but the protection scope of the present application is not limited to the following embodiments.

[0026] Example 1

[0027] In this embodiment, the Mg-2Zn-0.5Nd alloy has the following components by weight percentage: 2% Zn, 0.5% Nd, and the balance of Mg. The preparation method is as follows: pure magnesium, 2% Zn, and 0.5% Nd are smelted into a liquid metal according to the weight percentage, and then cast into a round ingot. Surface defects and impurities are removed, and homogenization heat treatment is performed at 300°C for 5h. A magnesium alloy rod with a diameter of 5mm is prepared by hot extrusion. The rod is cold drawn, and annealing heat treatment is performed during the drawing process at a temperature of 300°C for 30min. The single pass deformation amount is 10%, and the drawing speed is 10mm / s. Finally, a wire with a diameter of 0.23mm is formed. After polishing treatment (the surface roughness is Ra0.1), the wire is cleaned by ultrasonic cleaning with alcohol and then blown dry.

[0028] The two ends of the wire are respectively connected to the positive and negative electrodes of a pulse power supply. The current value is set to 10A, the frequency is 1000HZ, the duty cycle is 50%, and the action time is 30min. The microstructure of the cold-drawn wire without the action of the pulse current is shown in Figure 1 As shown in the figure, the grains of the alloy gradually elongate along the drawing direction, and the grains change from polygonal to flat or long strip. The microstructure of the wire after the action of the pulse current is shown in Figure 2 As shown in the figure, the microstructure of the alloy is equiaxed grains, and the grains are fine with an average size of 1μm-3μm. The mechanical properties of the cold-drawn wire and the wire after the action of the pulse current are shown in Figure 3 The tensile strength of the cold-drawn wire is 330MPa, and the plasticity is poor with a fracture elongation of 4%. The tensile strength of the wire after the action of the pulse current is 250MPa, and the plasticity is greatly improved with an elongation of 9.6%. The overall has good strength and plasticity matching.

[0029] Example 2

[0030] In this embodiment, the Mg-1Zn-0.8Ca alloy, the composition is in percentage by weight: 1% Zn, 0.8% Ca, the balance is Mg. Preparation method: according to the percentage by weight, the pure magnesium and 1% Zn, 0.8% Ca are smelted into liquid metal, cast into round ingot, remove surface defects and impurities, homogenization heat treatment at 320℃ for 4h, prepare the magnesium alloy rod with a diameter of 5mm by hot extrusion; the rod is cold drawn, and the annealing heat treatment is matched in the drawing process, the temperature is 320℃, the time is 30min, the single pass deformation is 8%, the drawing speed is 10mm / s, and finally the wire with a diameter of 0.23mm is formed. The wire is polished (the surface roughness is Ra0.1) and cleaned with alcohol ultrasonic cleaning, and then dried.

[0031] The two ends of the wire are connected to the positive and negative poles of the pulse power source respectively, the current value is set to 12A, the frequency is 900HZ, the duty cycle is 40%, and the action time is 30min. The grain of the cold-drawn wire without pulse current effect is flat or long strip-shaped. The microstructure of the wire after pulse current effect is equiaxed crystal, the grain is fine, the average size is 1μm-3μm, the tensile strength of the cold-drawn wire is 340MPa, the plasticity is poor, the elongation is 2%, the tensile strength of the wire after pulse current effect is 283MPa, the plasticity is greatly improved, the elongation is 11.5%, and the whole has good strength and plasticity matching.

[0032] Example 3

[0033] In this embodiment, the Mg-1.5Zn-0.2Mn-0.2Nd alloy, the composition is in percentage by weight: 1.5% Zn, 0.2% Mn, 0.2% Nd, the balance is Mg. Preparation method: according to the percentage by weight, the pure magnesium and Zn, Mn, Nd are smelted into liquid metal, cast into round ingot, remove surface defects and impurities, homogenization heat treatment at 330℃ for 6h, prepare the magnesium alloy rod with a diameter of 5mm by hot extrusion; the rod is cold drawn, and the annealing heat treatment is matched in the drawing process, the temperature is 300℃, the time is 60min, the single pass deformation is 9%, the drawing speed is 10mm / s, and finally the wire with a diameter of 0.23mm is formed. The wire is polished (the surface roughness is Ra0.1) and cleaned with alcohol ultrasonic cleaning, and then dried.

[0034] The two ends of the wire are connected to the positive and negative poles of the pulse power source, the current value is set to 20 A, the frequency is 1500 HZ, the duty cycle is 60%, and the action time is 30 min. The grains of the cold-drawing wire without pulse current action are flat or long strip-shaped. The microstructure of the wire after pulse current action is equiaxed crystal, the grains are fine, and the average size is 1-3 μm. The tensile strength of the cold-drawing wire is 360 MPa, the plasticity is poor, and the elongation is 3%. The tensile strength of the wire after pulse current action is 300 MPa, the plasticity is greatly improved, the elongation is 10.2%, and the overall has good strength-plasticity matching.

[0035] Example 4

[0036] In this example, the Mg-1.5Zn-0.2Mn-0.2Nd alloy has the following components by weight percentage: 1.5% Zn, 0.2% Mn, 0.2% Nd, and the balance of Mg. The preparation method is as follows: pure magnesium and Zn, Mn, and Nd are melted into liquid metal according to the weight percentage, cast into round ingots, remove surface defects and impurities, homogenize heat treatment at 330℃ for 6 h, and prepare a magnesium alloy rod with a diameter of 5 mm by hot extrusion; the rod is cold-drawn, and annealing heat treatment is performed during the drawing process, the temperature is 300℃, the time is 60 min, the single pass deformation is 9%, the drawing speed is 10 mm / s, the pulse current is applied for the first time in the last 1 pass of cold drawing process, the pulse current action during dynamic drawing, the output current is 10 A, the frequency is 1000 HZ, the duty cycle is 40%, and finally the wire with a diameter of 0.23 mm is formed. The tensile strength of the cold-drawing wire is 360 MPa, the plasticity is poor, and the elongation is 3%. The tensile strength of the wire after the first pulse current action is 320 MPa, the plasticity is greatly improved, the elongation is 8%, and the overall has good strength-plasticity matching. The grains of the cold-drawing wire without pulse current action are flat or long strip-shaped. The microstructure of the wire after the first pulse current action is equiaxed crystal, the grains are fine, and the average size is 5-10 μm.

[0037] The wire is polished (the surface roughness is Ra 0.1) and cleaned with alcohol ultrasonic cleaning, and then blown dry.

[0038] The two ends of the wire are connected to the positive and negative poles of the pulse power source, the second pulse current is applied, the current value is set to 20 A, the frequency is 1500 HZ, the duty cycle is 60%, and the action time is 30 min. The microstructure of the wire after pulse current action is equiaxed crystal, the grains are fine, and the average size is 1-3 μm. The tensile strength of the wire after pulse current action is 290 MPa, the plasticity is greatly improved, the elongation is 13%, and the overall has good strength-plasticity matching.

[0039] The embodiment results show that the magnesium alloy is prepared into 0.23 mm wire through processes such as smelting, casting, extrusion and drawing, the high-energy pulse current is used to pass through the magnesium alloy wire, the internal stress of the wire is eliminated, the dynamic and static recrystallization processes are promoted to occur, the alloy grains are refined, the strength of the wire, especially the elongation, is greatly improved, and good corrosion resistance is obtained, so that the performance requirements of the magnesium alloy wire are met.

Claims

1. A method of microstructure re-optimization of a magnesium alloy ultrafine wire, characterized in that, Change the traditional metal wire heat treatment process, using high-energy pulse current through the magnesium alloy wire, by regulating the current density, frequency and duty cycle, realize the magnesium alloy wire organization re-optimization, improve the mechanical properties and corrosion resistance of the wire, including the following steps: (1) magnesium alloy is prepared into 0.20mm-0.30mm wire by the process of batching, smelting, casting, hot extrusion and cold drawing; In step (1), pulse current is applied in the last cold drawing process, and pulse current is applied in the dynamic drawing process, the output current is 5-20A, the frequency is 500HZ-2000HZ, and the duty cycle is 30%-60%; (2) the magnesium alloy wire in step (1) is polished on the wire drawing machine, cleaned with alcohol ultrasonic cleaning and dried; In step (2), the magnesium alloy wire is polished on the wire drawing machine, and the roughness after rough polishing is Ra0.2-Ra0.4; the roughness after fine polishing is Ra0.05-Ra0.2; (3) the magnesium alloy wire in step (2) is treated by high-energy pulse current, the output current is 10-20A, the frequency is 900HZ-1500HZ, the duty cycle is 40%-60%, and the pulse current action time is 20min-60min; The main alloying elements in the magnesium alloy include one or more than two of Zn, Nd, Zr, Mn, Si, Ca and Y, and the balance is Mg; According to the mass percentage, Zn: 0%-2.0%, Nd: 0%-1.5%, Zr: 0%-1.0%, Mn: 0%-0.5%, Si: 0%-0.2%, Ca: 0%-0.3%, Y: 0%-0.1%; The microstructure of the wire treated by pulse current is equiaxed crystal, the grain is fine, and the average size is 1-3um.

2. The method for microstructure re-optimization of magnesium alloy ultrafine wires according to claim 1, characterized in that, The hundred scrubbing cloth is nylon fiber and mineral sand grinding particles made of nylon sand cloth, and the magic wipe is melamine polyurethane foam.

3. The method of microstructure re-optimization of magnesium alloy ultrafine wires according to claim 1, characterized in that, In step (3), the prepared magnesium alloy wire is used as the final product or as an intermediate product for composite material preparation.

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