A regenerative magnesium alloy component and a semi-solid injection molding method and degradable bridge plug thereof

Abstract

The application belongs to the field of recycling of recycled magnesium alloy components, and particularly relates to a recycled magnesium alloy component, a semi-solid injection molding method thereof and a degradable bridge plug. The core of the preparation method is to combine recycled magnesium alloy waste with a semi-solid injection molding process, fully recycle the recycled magnesium alloy waste, add pure Mg powder and respectively add Mg-aCu or Mg-bNi intermediate alloy powder into the recycled magnesium alloy waste through the semi-solid injection molding process, so that the recycled magnesium alloy component is obtained. The method not only accelerates the dissolution rate of the recycled magnesium alloy, but also improves the mechanical properties of the recycled magnesium alloy. At the same time, the high-performance degradable recycled magnesium alloy component is obtained, the imbalance between the degradation rate and the strength of the traditional magnesium alloy is solved, and the low cost and environmental protection benefits are achieved. In addition, the recycled magnesium alloy component lays a key material foundation for manufacturing high-performance controllable degradable bridge plug structural parts.

Description

Technical Field

[0001] This invention belongs to the field of recycled magnesium alloy components, specifically relating to a recycled magnesium alloy component, its semi-solid injection molding method, and a biodegradable bridge plug. Background Technology

[0002] Magnesium alloys are among the lightest metallic structural materials used in engineering applications and have gained increasing attention in recent years, particularly in aerospace, automotive, electronics, and defense industries. Therefore, magnesium alloys are considered one of the most promising weight-reduction structural materials. Meanwhile, my country ranks first in the world in primary magnesium production, accounting for 40% of global output, making it a major producer and exporter of magnesium resources. Magnesium alloys possess high specific strength and specific stiffness, excellent damping capacity, resistance to electromagnetic interference, and good biocompatibility. Magnesium alloys also have good recyclability; recycled magnesium alloys can be recovered and reused through various clean recycling technologies without significantly affecting their performance. With increasing awareness of sustainable development and environmental protection, magnesium alloy recycling technology is of great significance for the rational recycling of waste materials, resource conservation, cost reduction of magnesium alloys, and mitigation of environmental pollution.

[0003] The poor corrosion resistance of magnesium alloys is usually a major factor limiting their widespread application. However, due to their highly corrosive nature, magnesium alloys are considered ideal materials for manufacturing biodegradable fracturing tools. In oil and other extraction industries, fracturing tools are often one of the key technologies for increasing oil and gas production. Because of the rapid corrosion of magnesium alloys, biodegradable bridge plugs made from them can dissolve quickly after fracturing operations, thus avoiding long-term blockage of oil wells. Currently, the performance requirements for biodegradable fracturing tools are mainly strength and corrosion rate. However, for traditional biodegradable magnesium alloys, it is often difficult to achieve a certain balance between degradation rate and strength simultaneously. Semi-solid injection molding is considered one of the most promising net-shape manufacturing processes of the 21st century. Components prepared using this process have a series of advantages, including stable filling, dense structure, fewer internal defects such as porosity and segregation, and good overall mechanical properties. Compared with traditional high-pressure die casting, its plasticity and mechanical properties are improved. Summary of the Invention

[0004] In view of this, and in response to the above problems, the first objective of this invention is to provide a semi-solid injection molding method for recycled magnesium alloy components. This method improves the degradation rate of recycled magnesium alloy waste by adjusting its composition and combining it with a semi-solid injection molding process, thereby obtaining recycled magnesium alloy components with excellent comprehensive mechanical properties, which can be used in the preparation of bridge plugs for fracturing temporary plugging tools.

[0005] The second objective of this invention is to provide a recycled magnesium alloy component prepared based on the above method, which aims to overcome the problem of balancing the degradation rate and strength of recycled magnesium alloy, thereby ensuring high strength while obtaining a controllable degradation rate that matches the working cycle, and also achieving low cost and environmental benefits.

[0006] A third objective of this invention is to provide a biodegradable bridge plug based on the above-mentioned recycled magnesium alloy component.

[0007] To achieve the objectives of the invention described above, the present invention adopts the following technical solution:

[0008] In a first aspect, a semi-solid injection molding method for recycled magnesium alloy components includes the following steps:

[0009] S1. Pre-treat the recycled Mg-Al magnesium alloy waste and process the pre-treated recycled magnesium alloy waste into recycled magnesium alloy particles.

[0010] S2. The recycled magnesium alloy particles are mixed with pure Mg powder, Mg-aCu master alloy powder or Mg-bNi master alloy powder to obtain a mixed raw material, wherein the mass percentage content of Cu a is 20-30wt%, the mass percentage content of Ni b is 20-30wt%, and the balance is Mg and unavoidable impurities.

[0011] S3. The mixed raw materials are remelted under closed conditions using a semi-solid forming process to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid-liquid two phases. The semi-solid slurry is injected into a preheated mold and injection molded to obtain a recycled magnesium alloy component with a non-dendritic solidification structure. The primary solid particles are uniformly distributed and have a shape close to spherical. The solid fraction of the semi-solid slurry is controlled at 1-20%, and the remelting temperature is set at 560-650℃.

[0012] Preferably, the recycled Mg-Al magnesium alloy waste is selected from waste generated from die casting and machining of AZ91D magnesium alloy and scrapped AZ91D magnesium alloy parts.

[0013] Preferably, the specific process of pretreating the recycled Mg-Al magnesium alloy waste in step S1 and processing the pretreated recycled magnesium alloy waste into recycled magnesium alloy particles includes:

[0014] S11. The pretreatment steps for recycled Mg-Al magnesium alloy waste include any one or a combination of two or more of the following: manual impurity removal, surface cleaning, degreasing and washing, and drying.

[0015] S12. The pretreated recycled magnesium alloy waste is mechanically stirred and shredded into recycled magnesium alloy particles with a particle size of 1.2 to 1.8 mm.

[0016] Preferably, the specific process of mixing the recycled magnesium alloy particles with pure Mg powder, Mg-aCu master alloy powder, or Mg-bNi master alloy powder in step S2 to obtain the mixed raw material includes:

[0017] S21. The recycled magnesium alloy particles are thoroughly mixed with pure Mg powder with a purity of 99.99 wt% by mechanical stirring for 30 to 60 minutes to obtain an intermediate product.

[0018] S22. Add Mg-aCu or Mg-bNi intermediate alloy powder to the intermediate product and mix thoroughly by mechanical stirring for 30-60 minutes to obtain a mixed raw material.

[0019] Preferably, in step S3, the mixed raw materials are remelted under closed conditions using a semi-solid forming process to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid-liquid two phases. The specific operation steps for injecting the semi-solid slurry into a preheated mold to obtain a recycled magnesium alloy component with a non-dendritic solidification structure are as follows:

[0020] The mixed raw materials are injected into the sealed barrel of a semi-solid injection molding machine and mechanically stirred and conveyed at a screw speed of 40-150 r / min. At the same time, the temperature is gradually increased by an external infrared heating device, which melts the mixed raw materials to form a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles. The semi-solid slurry is injected into a preheated mold under high speed and high pressure in a laminar flow filling mode, and quickly solidifies to form a recycled magnesium alloy component with a non-dendritic solidified structure in one step.

[0021] More preferably, the gradient heating is specifically divided into 11 stages, with the barrel temperature set sequentially according to the conveying direction as follows: stage 1 is 480℃, stage 2 is 580℃, stage 3 is 590℃, stage 4 is 600℃, stage 5 is 635℃, stage 6 is 635℃, stage 7 is 635℃, stage 8 is 635℃, stage 9 is 635℃, stage 10 is 635℃, and stage 11 is 570℃; the temperature of the preheated mold is 150~300℃, the injection speed of the semi-solid slurry is 1~4m / s, and the injection pressure of the semi-solid slurry is 90~102MPa.

[0022] Most preferably, the primary solid particles have an α-Mg phase composition and a particle size of 10–30 μm; the recycled magnesium alloy component has an α-Mg phase and a second phase, the second phase being β-Mg. 17 Al 12Precipitated phases and Ni-containing or Cu-containing phases.

[0023] Secondly, the present invention provides a recycled magnesium alloy component prepared by the above-mentioned semi-solid injection molding method for recycled magnesium alloy components. The chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu or Mg-xAl-yNi, wherein the mass percentage content of Al is 6 to 8 wt%, the mass percentage content of Cu or Ni is 1 to 3 wt%, and the balance is Mg and unavoidable impurities.

[0024] Preferably, in a 3wt% KCl solution, when the mass percentage content of Al (x) is 6-8wt% and the mass percentage content of Cu or Ni (y) is 2wt%, the corrosion rate of the Mg-xAl-2Cu recycled magnesium alloy component is 7.21-8.35 mm / y, and the corrosion rate of the Mg-xAl-2Ni recycled magnesium alloy component is 12.63-14.44 mm / y.

[0025] Thirdly, the present invention also provides a biodegradable bridge plug, including a bridge plug body and a sealing structure, an anchoring structure and a bore structure disposed on the bridge plug body, wherein the bridge plug body is wholly or partially made of the above-mentioned recycled magnesium alloy components.

[0026] The beneficial effects of this invention are:

[0027] 1. For traditional biodegradable magnesium alloys, it is often difficult to coordinate the degradation rate and strength. This invention combines recycled magnesium alloy waste with a semi-solid injection molding process. In the semi-solid injection molding process, the semi-solid slurry is filled in a laminar flow form under high speed and high pressure, and quickly solidifies to form equiaxed, uniform, and fine primary solid particles. This uniform and fine microstructure not only improves the strength of the recycled magnesium alloy, but also increases the phase interface area, providing more active channels for corrosion. This achieves synergistic optimization of degradation rate and mechanical properties, resulting in recycled magnesium alloy components with excellent comprehensive mechanical properties and biodegradable characteristics, which are then used in the preparation of biodegradable bridge plugs.

[0028] 2. This invention not only accelerates the dissolution rate of recycled magnesium alloys, but also improves their mechanical properties. The semi-solid forming process refines the grains and generates a second phase. The increase in the number of grain boundaries and phase boundaries provides more starting points for corrosion and accelerates degradation. At the same time, the grain refinement strengthens the material significantly, thereby obtaining a high-performance biodegradable magnesium alloy, which can be used in the preparation of bridge plugs for fracturing temporary plugging tools.

[0029] 3. The remelting of mixed raw materials does not require complex refining and impurity removal processes. The semi-solid injection molding process allows almost all materials to be converted into recycled magnesium alloy components, with very little residual material in the gating system. The runner system can be reused, thus achieving an extremely high material recovery rate and simplifying the recycling process. This results in magnesium alloy net-formed components with a recovery rate of nearly 100%.

[0030] 4. Reclaimed magnesium alloy components with biodegradable properties are prepared by remelting Mg-Al alloys using a semi-solid injection molding process. On the one hand, this improves the recovery rate of recycled magnesium alloy waste; on the other hand, the solid particles in the semi-solid slurry are encapsulated in the liquid phase, exhibiting fluid-like behavior under high shear rates, allowing for smooth filling of the mold cavity. Laminar flow filling avoids gas entrapment and melt splashing, while rapid solidification inhibits dendrite growth and compositional segregation, thereby significantly reducing internal defects and improving the density and performance consistency of the recycled magnesium alloy components. Therefore, the semi-solid slurry exhibits good thixotropy and fluidity, enabling laminar flow filling under rapid solidification and high-speed, high-pressure conditions, thus avoiding turbulence and significantly reducing internal defects such as porosity and segregation in the recycled magnesium alloy components.

[0031] 5. Semi-solid injection molding involves injecting a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles into a preheated mold in a laminar flow form through the injection unit of a semi-solid injection molding machine. The slurry then solidifies rapidly, resulting in the one-time molding of recycled magnesium alloy components with high dimensional accuracy, complex shapes, and high performance requirements. Semi-solid injection molding also has advantages such as fewer oxide inclusions, environmental friendliness, low energy consumption, long mold life, and high production efficiency. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a flowchart of a semi-solid injection molding method for recycled magnesium alloy provided in an embodiment of the present invention. Detailed Implementation

[0034] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0035] like Figure 1 As shown in the figure, an embodiment of the present invention discloses a semi-solid injection molding method for recycled magnesium alloy, comprising the following steps:

[0036] S1. Pre-treat the recycled Mg-Al series magnesium alloy waste and process the pre-treated recycled magnesium alloy waste into recycled magnesium alloy particles.

[0037] S2. Mix the recycled magnesium alloy particles with pure Mg powder, Mg-aCu master alloy powder or Mg-bNi master alloy powder to obtain a mixed raw material, wherein the mass percentage content of Cu a is 20-30 wt%, the mass percentage content of Ni b is 20-30 wt%, and the balance is Mg and unavoidable impurities.

[0038] S3. The mixed raw materials are remelted under closed conditions using a semi-solid forming process to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid-liquid two phases. The semi-solid slurry is injected into a preheated mold and injection molded to obtain a recycled magnesium alloy component with a non-dendritic solidified structure. The primary solid particles are uniformly distributed and have a shape close to spherical. The solid fraction of the semi-solid slurry is controlled between 1% and 20%.

[0039] The specific process of pretreating the recycled Mg-Al magnesium alloy waste in step S1 and processing the pretreated magnesium alloy waste into recycled magnesium alloy particles includes:

[0040] S11. The pretreatment steps for recycled Mg-Al magnesium alloy waste include any one or a combination of two or more of the following: manual impurity removal, surface cleaning, degreasing and washing, and drying.

[0041] Manual impurity removal: Waste materials generated from die casting and machining of recycled Mg-Al magnesium alloys, as well as scrapped recycled Mg-Al magnesium alloy parts, are manually sorted to remove foreign metal attachments and strip away non-metallic impurities.

[0042] Surface cleaning: For recycled Mg-Al magnesium alloy waste with coatings or rust products on the surface, mechanical grinding is used to remove the surface coatings and oxide scale.

[0043] Degreasing and cleaning: For machined recycled Mg-Al magnesium alloy waste containing paint, cutting fluid or lubricating oil, clean it with degreasing solvent or alkaline degreasing.

[0044] Drying treatment: The above-treated recycled Mg-Al magnesium alloy waste is repeatedly rinsed with deionized water. The cleaned recycled Mg-Al magnesium alloy waste is placed in a drying oven and dried at 50-80℃ for 4-8 hours to remove moisture, finally obtaining the pretreated recycled magnesium alloy waste.

[0045] Recycled Mg-Al magnesium alloy scrap cannot be directly remelted and refined because it typically contains dissimilar metal parts, non-metallic impurities, coatings, paints, cutting fluids, or lubricants. For example, recycled Mg-Al magnesium alloy scrap is selected from waste generated during die casting and machining of AZ91D magnesium alloy, as well as scrapped AZ91D magnesium alloy parts. Of course, recycled Mg-Al magnesium alloy scrap can also be other recycled magnesium alloy scrap; this invention does not limit this.

[0046] S12. The pretreated recycled magnesium alloy waste is mechanically stirred and shredded into recycled magnesium alloy particles with a particle size of 1.2–1.8 mm. In some embodiments of the present invention, the particle size of the recycled magnesium alloy particles is any value or a range formed by any combination of 1.2 mm, 1.3 mm, 1.4 mm, 1.5 mm, 1.6 mm, 1.7 mm, and 1.8 mm. If the particle size of the recycled magnesium alloy particles is less than 1.2 mm, it will increase the difficulty of controlling the oxidation and semi-solid injection molding processes. If the particle size of the recycled magnesium alloy particles is greater than 1.8 mm, it will lead to uneven heating and melting.

[0047] In step S2, the recycled magnesium alloy particles are mixed with pure Mg powder, Mg-aCu master alloy powder or Mg-bNi master alloy powder to obtain a mixed raw material. The amount of pure Mg powder, Mg-aCu master alloy powder or Mg-bNi master alloy powder added is calculated based on the initial composition of the recycled magnesium alloy particles and the composition of the target alloy.

[0048] Furthermore, the specific process of step S2 is as follows:

[0049] S21. The recycled magnesium alloy particles are thoroughly mixed with pure Mg powder with a purity of 99.99 wt% by mechanical stirring for 30 to 60 minutes. The Al content is controlled by diluting the corresponding Mg to obtain the Mg-xAl intermediate product, wherein the mass percentage content of Al is 6 to 8 wt%, and the balance is Mg and unavoidable impurities.

[0050] In some embodiments of the present invention, the mechanical stirring time is any value or a range formed by any two of 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min. For example, the mechanical stirring time is preferably 45 min.

[0051] It should be noted that, according to the Mg-Al binary phase diagram, as the Al content increases, the solidification range of recycled magnesium alloys gradually increases, and the liquidus temperature decreases. Too low a liquidus temperature is unfavorable for semi-solid injection molding. Semi-solid injection molding, due to its unique solidification characteristics, can significantly improve the mechanical properties of recycled magnesium alloy components. However, it is currently only applicable to recycled magnesium alloy systems with a certain solidification range and requires consideration of the non-equilibrium solidification mechanism and the fluidity of the semi-solid slurry during the semi-solid injection molding process. If the solidification range is too narrow, the semi-solid slurry becomes highly sensitive to temperature, making it impossible to accurately control the solid fraction of the semi-solid slurry, thus affecting the molding process. On the other hand, magnesium alloy injection molding requires maintaining a low liquidus temperature to avoid excessively high heating temperatures. Therefore, an Al mass percentage content (x) of 6–8 wt% is selected.

[0052] S22. Mg-aCu or Mg-bNi master alloy powder is added to the Mg-xAl intermediate product and thoroughly mixed by mechanical stirring for 30-60 minutes to obtain a mixed raw material. For example, the Mg-aCu or Mg-bNi master alloy powder is Mg-20Cu, Mg-20Ni, Mg-25Cu, Mg-25Ni, Mg-30Cu, or Mg-30Ni. Of course, the values ​​of a and b can also be other than those specified in this invention.

[0053] In some embodiments of the present invention, the mechanical stirring time is any value or a range formed by any two of 30 min, 35 min, 40 min, 45 min, 50 min, 55 min, and 60 min. For example, the mechanical stirring time is preferably 45 min.

[0054] It should be noted that, unlike traditional research on enhancing the corrosion resistance of magnesium alloys, biodegradable magnesium alloys are typically produced by adding impurity elements to form intermetallic compounds that promote the dissolution of the magnesium matrix. Furthermore, the element content and forming process also affect the dissolution rate of the biodegradable magnesium alloy. Cu and Ni, both with positive corrosion potentials, can increase the dissolution rate of magnesium alloys. Cu has a very positive corrosion potential, and the precipitates formed by Cu, such as MgZnCu and Mg2Cu, can accelerate the corrosion rate of the magnesium matrix and also affect the mechanical properties of the recycled magnesium alloy. Among the impurity elements in recycled magnesium alloys, Ni can significantly promote the dissolution rate of the matrix. Ni has extremely low solid solubility in the magnesium matrix and readily forms various intermetallic compounds at grain boundaries, such as the Mg2Ni phase. As the Ni content increases, the Mg2Ni phase increases, significantly increasing the corrosion rate of the recycled magnesium alloy, while also improving its strength.

[0055] In step S3, a semi-solid forming process is used to remelt the mixed raw materials under closed conditions to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid and liquid phases. The semi-solid slurry is then injected into a preheated mold to obtain a recycled magnesium alloy component with a non-dendritic solidification structure. The specific operation steps are as follows:

[0056] The mixed raw materials are injected into the sealed barrel of a semi-solid injection molding machine and mechanically stirred and conveyed at a screw speed of 40–150 r / min. Simultaneously, a gradient heating system is implemented using an external infrared heating device, causing the mixed raw materials to melt at 560–650℃ to form a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles, exhibiting a coexistence of solid and liquid phases. This semi-solid slurry is then injected into a mold preheated to 150–300℃ under high-speed, high-pressure laminar flow filling, resulting in rapid solidification and molding. This process yields a recycled magnesium alloy component with a non-dendritic solidification structure in a single step. The primary solid particles consist of an α-Mg phase with a particle size of 10–30 μm. The recycled magnesium alloy component comprises an α-Mg phase and a second phase, the second phase being β-Mg. 17 Al 12 The precipitated phase includes Ni-containing or Cu-containing phases; the injection speed of the semi-solid slurry is 1–4 m / s, and the injection pressure of the semi-solid slurry is 90–102 MPa.

[0057] In some embodiments of the present invention, the screw rotation speed is any value or a range formed by any two of the following: 40 r / min, 50 r / min, 60 r / min, 70 r / min, 80 r / min, 90 r / min, 100 r / min, 110 r / min, 120 r / min, 130 r / min, 140 r / min, and 150 r / min. For example, the screw rotation speed is preferably 40 r / min. The injection speed of the semi-solid slurry is any value or a range formed by any two of the following: 1 m / s, 2 m / s, 3 m / s, and 4 m / s. For example, the injection speed of the semi-solid slurry is preferably 3 m / s. The injection pressure of the semi-solid slurry is any value or a range formed by any two of the following: 90 MPa, 91 MPa, 92 MPa, 93 MPa, 94 MPa, 95 MPa, 96 MPa, 97 MPa, 98 MPa, 99 MPa, 100 MPa, 101 MPa, and 102 MPa. For example, the injection pressure of the semi-solid slurry is preferably 100 MPa.

[0058] It should be noted that semi-solid injection molding involves the preparation and molding of thixotropic slurry under closed conditions. This avoids the transfer of molten magnesium and eliminates the use of smelting protective gases such as SF6, resulting in virtually no wastewater, waste gas, or solid waste. The closed environment prevents the molten magnesium from directly contacting the outside air, thus minimizing the probability of oxide inclusions generated during the semi-solid injection molding process. During the forward transport of the mixed raw materials, heating and shearing by a high-strength, corrosion-resistant screw ultimately form a precisely controlled semi-solid phase. In the initial stage, the solid components in the semi-solid slurry have irregular geometric shapes. In the middle of the barrel, the mixed raw materials undergo thermoplastic deformation through the screw compression section. Under the mechanical shearing force generated by the screw rotation, the semi-solid slurry undergoes dendritic fragmentation, transforming into a spherical, non-dendritic structure. In the storage section at the front of the screw, the mixed raw materials transform into a semi-solid slurry of molten liquid metal containing the initial solid particles, which are uniformly distributed and nearly spherical. The microstructure, solid fraction, and rheological properties of semi-solid slurry have a decisive influence on the quality of the final molded recycled magnesium alloy components.

[0059] For example, the gradient heating is divided into 11 stages, with the barrel temperature set sequentially according to the conveying direction: stage 1 is 480℃, stage 2 is 580℃, stage 3 is 590℃, stage 4 is 600℃, stage 5 is 635℃, stage 6 is 635℃, stage 7 is 635℃, stage 8 is 635℃, stage 9 is 635℃, stage 10 is 635℃, and stage 11 is 570℃. The above temperature range setting is only a preferred example; in actual production, it can be adjusted according to the equipment model and barrel segmentation, as long as the barrel temperature can be maintained within the range of 560–650℃.

[0060] For example, the semi-solid injection molding machine is model MTX4000D, which mainly consists of two modules: an injection unit and a mold-closing unit. The injection unit comprises an accumulator device, an injection unit, a hopper, and a controller control box; the mold-closing unit comprises a safety door, a mold-closing device, and alarm lights. The process parameters of the semi-solid injection molding machine include: a screw diameter of 170mm and a theoretical injection capacity of 13619cm³. 3 The injection weight is 17432g, the injection pressure is 102MPa, the injection stroke is 600mm, the screw speed is 0-150r / min, the barrel heating power is 428KW, the clamping force is 40000KN, the horizontal spacing inside the tie rod is 2000mm, the vertical spacing inside the tie rod is 1850mm, the maximum allowable mold thickness / T-slot is 1920mm, the minimum allowable mold thickness / T-slot is 770mm, the mold transfer stroke is 1900mm, the maximum mold plate opening distance / T-slot is 3820mm, the ejection stroke is 400mm, the ejection force is 1000KN, the number of ejector pins is 31PC, the oil pump motor power is 183KW, the length of the minimum mold is 1482mm, and the width of the minimum mold is 1240mm.

[0061] This invention provides a recycled magnesium alloy component prepared by the semi-solid injection molding method of the recycled magnesium alloy component mentioned above. The chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu or Mg-xAl-yNi, wherein the mass percentage content of Al is 6 to 8 wt%, the mass percentage content of Cu or Ni is 1 to 3 wt%, and the balance is Mg and unavoidable impurities.

[0062] Preferably, in a 3wt% KCl solution, when the mass percentage content of Al (x) is 6-8wt% and the mass percentage content of Cu or Ni (y) is 2wt%, the corrosion rate of the Mg-xAl-2Cu recycled magnesium alloy component is 7.21-8.35 mm / y, and the corrosion rate of the Mg-xAl-2Ni recycled magnesium alloy component is 12.63-14.44 mm / y.

[0063] This invention also provides a biodegradable bridge plug, comprising a bridge plug body and a sealing structure, an anchoring structure, and a bore structure disposed on the bridge plug body, wherein the bridge plug body is wholly or partially made of the recycled magnesium alloy component prepared above. The biodegradable bridge plug mainly consists of a plunger, a central tube, a release pin, a soluble ball, a shear pin, a sliding sleeve, a rubber sleeve, a back ring, a locking ring back ring, an O-ring, a locking ring, and a cone.

[0064] Next, the present invention provides several specific embodiments and comparative examples to illustrate that the content of Al, Cu or Ni has a significant impact on the mechanical properties of magnesium alloys.

[0065] Example 1

[0066] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu, where the mass percentage content of Al is 6wt%, the mass percentage content of Cu is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-6Al-2Cu, it is calculated that 40g of pure Mg powder and 10g of Mg-30Cu master alloy powder need to be added.

[0067] The first step: the pretreatment of recycled Mg-Al magnesium alloy waste includes any one or a combination of two or more of the following steps: manual impurity removal, surface cleaning, degreasing and washing, and drying.

[0068] Manual impurity removal: Waste materials generated from die casting and machining of recycled Mg-Al magnesium alloys, as well as scrapped recycled Mg-Al magnesium alloy parts, are manually sorted to remove foreign metal attachments and strip away non-metallic impurities.

[0069] Surface cleaning: For recycled Mg-Al magnesium alloy waste with coatings or rust products on the surface, mechanical grinding is used to remove the surface coatings and oxide scale.

[0070] Degreasing and cleaning: For machined recycled Mg-Al magnesium alloy waste containing paint, cutting fluid or lubricating oil, clean it with degreasing solvent or alkaline degreasing.

[0071] Drying treatment: The above-treated recycled Mg-Al magnesium alloy waste is repeatedly rinsed with deionized water. The cleaned components are placed in a drying oven and dried at 50-80℃ for 4-8 hours to remove moisture, finally obtaining the pretreated recycled magnesium alloy waste.

[0072] S12. The pretreated recycled magnesium alloy waste is mechanically stirred and shredded into recycled magnesium alloy particles with a particle size of 1.2 to 1.8 mm.

[0073] The second step: 100g of AZ91D recycled magnesium alloy particles and 40g of pure Mg powder with a purity of 99.99wt% are thoroughly mixed by mechanical stirring for 45min to obtain an intermediate product; 10g of Mg-30Cu intermediate alloy powder is added to the intermediate product and thoroughly mixed by mechanical stirring for 45min to obtain a mixed raw material.

[0074] The third step involves injecting the mixed raw materials into the sealed barrel of a semi-solid injection molding machine. Mechanical stirring and conveying are performed at a screw speed of 40 r / min, while a gradient heating system is applied externally to the barrel. This melts the mixed raw materials at 635℃, forming a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles, representing a coexistence of solid and liquid phases. This semi-solid slurry is then injected into a mold preheated to 200℃ under high speed and high pressure using a laminar flow filling mode, allowing for rapid solidification and molding. This process yields a non-dendritic solidified Mg-6Al-2Cu recycled magnesium alloy component in a single step. The injection speed of the semi-solid slurry is 3 m / s, and the injection pressure is 100 MPa.

[0075] Example 2

[0076] The preparation method in this embodiment is the same as that in Example 1, except that:

[0077] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu, where the mass percentage content of Al is 7wt%, the mass percentage content of Cu is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-7Al-2Cu, it is calculated that 15.71g of pure Mg powder and 12.86g of Mg-30Cu intermediate alloy powder need to be added in the second step. The third step is to obtain a semi-solid injection molded Mg-7Al-2Cu recycled magnesium alloy component.

[0078] Example 3

[0079] The preparation method in this embodiment is the same as that in Example 1, except that:

[0080] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu, where the mass percentage content of Al is 8wt%, the mass percentage content of Cu is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-8Al-2Cu, it is calculated that only 16.67g of Mg-30Cu intermediate alloy powder needs to be added in the second step; the third step produces a semi-solid injection molded Mg-8Al-2Cu recycled magnesium alloy component.

[0081] Comparative Example 1

[0082] The preparation method of this comparative example is the same as that of Example 1, except that:

[0083] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yNi, where the mass percentage content of Al is 6wt%, the mass percentage content of Ni is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-6Al-2Ni, it is calculated that 35g of pure Mg powder and 15g of Mg-20Ni intermediate alloy powder need to be added in the second step; the third step is to obtain a semi-solid injection molded Mg-6Al-2Ni recycled magnesium alloy component.

[0084] Comparative Example 2

[0085] The preparation method of this comparative example is the same as that of Example 1, except that:

[0086] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yNi, where the mass percentage content of Al is 7wt%, the mass percentage content of Ni is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-7Al-2Ni, it is calculated that 15.71g of pure Mg powder and 12.86g of Mg-20Ni intermediate alloy powder need to be added in the second step; the third step is to obtain a semi-solid injection molded Mg-7Al-2Ni recycled magnesium alloy component.

[0087] Comparative Example 3

[0088] The preparation method of this comparative example is the same as that of Example 1, except that:

[0089] Taking 100g of recycled magnesium alloy particles as an example, the chemical composition of the recycled magnesium alloy component is Mg-xAl-yNi, where the mass percentage content of Al is 8wt%, the mass percentage content of Ni is 2wt%, and the balance is Mg and unavoidable impurities. Based on the target composition Mg-8Al-2Ni, it is calculated that only 11.11g of Mg-20Ni intermediate alloy powder needs to be added in the second step; the third step produces a semi-solid injection molded Mg-8Al-2Ni recycled magnesium alloy component.

[0090] The recycled magnesium alloy components synthesized in Examples 1-3 and Comparative Examples 1-3 were cut into 10×10×10mm pieces. 3 Block samples were prepared and sealed with epoxy resin, leaving one side as the test surface. Electrochemical tests were performed in a 3wt% KCl solution, using a saturated silver chloride electrode (Ag / AgCl) as the reference electrode, a platinum electrode as the counter electrode, and an alloy as the working electrode, at a constant temperature of 25±1℃. The corrosion potential (E) was obtained by fitting using the Tafel extrapolation method. corr ) and corrosion current density (i corrThe corrosion rate (Pc) of the recycled magnesium alloy component was calculated using corrosion current density. i The calculation formula is as follows: The calculation results are shown in Table 1.

[0091] Table 1. Corrosion performance test results of recycled magnesium alloy components prepared in Examples 1-3 and Comparative Examples 1-3

[0092]

[0093] As can be seen from Table 1, the recycled magnesium alloy component obtained in Example 1 has the worst corrosion resistance compared to Examples 2 and 3. This may be due to the discontinuous β-Mg 17 Al 12 The first example, consisting of the Mg2Cu phase and the cathode Mg2Cu phase, constitutes the micro-galvanic corrosion, resulting in the worst corrosion resistance. Compared to Example 1, Example 2 shows improved corrosion resistance, likely due to the increased Al content, which promotes the transformation of the cathode Mg2Cu phase to the MgAlCu phase. Furthermore, the relatively continuous second phase begins to play a role, thus improving corrosion resistance. Example 3 exhibits the best corrosion resistance, likely because the high Al content forms a continuous, dense network of second phase, acting as a barrier and significantly delaying corrosion propagation. The high Al content also inhibits the precipitation of the Cu-containing phase or disperses it within the second phase, effectively "diluting" and isolating the Cu-containing cathode phase, thus minimizing the micro-galvanic effect of the Cu-containing phase.

[0094] Comparative Example 1 exhibited the worst corrosion resistance compared to the Examples and Comparative Examples, which may be due to the second phase β-Mg. 17 Al 12 The Ni phase has the lowest volume fraction, forming a discontinuous phase. Ni readily combines with Al and Mg to form discrete, discontinuous high-potential Ni-containing phases, such as Mg2Ni and AlMnNi phases, significantly exacerbating microgalvanic corrosion and resulting in the worst corrosion resistance. Comparative Example 2 shows a slight improvement in corrosion resistance compared to Comparative Example 1, possibly because the increased Al content promotes the formation of more stable Al- and Ni-containing phases, such as Al3Ni2, but localized corrosion remains dominant, and overall corrosion resistance is still very poor. Comparative Example 3 exhibits the best corrosion resistance compared to Comparative Examples 1 and 2, possibly due to the increased Al content leading to the formation of the second phase β-Mg. 17 Al 12It is easier to form a continuous network structure distributed along the grain boundaries, thus playing a certain barrier role, but it cannot completely eliminate the microcouple effect of the strong cathode Ni-containing phase. Ni is one of the "most harmful" alloying elements in recycled magnesium alloys. The equilibrium potential of its Ni-containing phase is much higher than that of the magnesium matrix, and even greater than that of the Cu-containing phase. Ni and its compounds will drastically accelerate the dissolution rate of the magnesium matrix. Therefore, compared with all the embodiments, the corrosion resistance of the recycled magnesium alloy components prepared in the comparative example is significantly lower than that of the recycled magnesium alloy components in the embodiments.

[0095] The embodiments and comparative examples of this invention provide relatively typical corrosion performance test results for Mg-xAl-2Cu or Mg-xAl-2Ni recycled magnesium alloy components, wherein the Al content percentage x is 6-8%. If the mass percentage content of Cu or Ni is only 1wt%, the amount of reinforcing phase formed is insufficient, resulting in limited strength improvement of the recycled magnesium alloy component. For tools such as biodegradable bridge plugs that need to withstand downhole high pressure, insufficient strength may lead to premature tool failure and inability to complete fracturing operations. If the mass percentage content of Cu or Ni is increased to 3wt%, for Ni, the amount of Ni-containing second phases such as Mg2Ni and AlNi will further increase, forming a more severe microcouple effect, which may cause the corrosion rate to increase exponentially, far exceeding 14.44 mm / y. This will cause the bridge plug to degrade too quickly, and it may not be able to maintain structural integrity within the designed operating window, resulting in "premature degradation" and operation failure. For Cu, although the couple effect of Cu-containing phases is weaker than that of Ni, a 3wt% content will still increase its corrosion current density. Meanwhile, a high Cu content may form coarse, hard, and brittle phases distributed in a continuous or semi-continuous network along grain boundaries, which could impair the plasticity and toughness of recycled magnesium alloy components. Therefore, choosing a Cu or Ni addition of 2 wt% is to achieve the optimal balance between insufficient strength caused by 1 wt% and excessively rapid corrosion caused by 3 wt%, thereby synergistically optimizing the mechanical properties and controllable degradation rate of recycled magnesium alloy components.

[0096] The above description is merely a preferred embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A semi-solid injection molding method for recycled magnesium alloy components, characterized in that, Includes the following steps: S1. Pre-treat the Mg-Al series magnesium alloy waste and process the pre-treated magnesium alloy waste into recycled magnesium alloy particles. S2. The recycled magnesium alloy particles are mixed with pure Mg powder, Mg-aCu master alloy powder or Mg-bNi master alloy powder to obtain a mixed raw material, wherein the mass percentage content of Cu a is 20-30wt%, the mass percentage content of Ni b is 20-30wt%, and the balance is Mg and unavoidable impurities. S3. The mixed raw materials are remelted under closed conditions using a semi-solid forming process to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid-liquid two phases. The semi-solid slurry is injected into a preheated mold and injection molded to obtain a recycled magnesium alloy component with a non-dendritic solidification structure. The primary solid particles are uniformly distributed and have a shape close to spherical. The solid fraction of the semi-solid slurry is controlled at 1-20%, and the remelting temperature is set at 560-650℃. The chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu or Mg-xAl-yNi, wherein the mass percentage content of Al is 6-8wt%, the mass percentage content of Cu or Ni is 1-3wt%, and the balance is Mg and unavoidable impurities.

2. The semi-solid injection molding method for recycled magnesium alloy components according to claim 1, characterized in that, The Mg-Al series magnesium alloy scrap is selected from the waste generated from die casting and machining of AZ91D magnesium alloy, as well as scrapped AZ91D magnesium alloy parts.

3. The semi-solid injection molding method for recycled magnesium alloy components according to claim 1, characterized in that, The specific process of pretreating the Mg-Al magnesium alloy waste in step S1 and processing the pretreated magnesium alloy waste into recycled magnesium alloy particles includes: S11. The pretreatment steps for Mg-Al magnesium alloy waste include any one or a combination of two or more of the following: manual impurity removal, surface cleaning, degreasing and washing, and drying. S12. The pretreated magnesium alloy waste is mechanically stirred and shredded into recycled magnesium alloy particles with a particle size of 1.2 to 1.8 mm.

4. The semi-solid injection molding method for recycled magnesium alloy components according to claim 1, characterized in that, The specific process of mixing the recycled magnesium alloy particles with pure Mg powder, Mg-aCu master alloy powder, or Mg-bNi master alloy powder in step S2 to obtain the mixed raw material includes: S21. The recycled magnesium alloy particles are thoroughly mixed with pure Mg powder with a purity of 99.99 wt% by mechanical stirring for 30 to 60 minutes to obtain an intermediate product. S22. Add Mg-aCu or Mg-bNi intermediate alloy powder to the intermediate product and mix thoroughly by mechanical stirring for 30-60 minutes to obtain a mixed raw material.

5. The semi-solid injection molding method for recycled magnesium alloy components according to claim 1, characterized in that, In step S3, the mixed raw materials are remelted under closed conditions using a semi-solid forming process to obtain a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles with coexisting solid-liquid two phases. The specific operation steps for injecting the semi-solid slurry into a preheated mold to obtain a recycled magnesium alloy component with a non-dendritic solidification structure are as follows: The mixed raw materials are injected into the sealed barrel of a semi-solid injection molding machine and mechanically stirred and conveyed at a screw speed of 40-150 r / min. At the same time, the temperature is gradually increased by an external infrared heating device, which melts the mixed raw materials to form a semi-solid slurry containing equiaxed, uniform, and fine primary solid particles. The semi-solid slurry is injected into a preheated mold under high speed and high pressure in a laminar flow filling mode, and quickly solidifies to form a recycled magnesium alloy component with a non-dendritic solidified structure in one step.

6. The semi-solid injection molding method for recycled magnesium alloy components according to claim 5, characterized in that, The gradient heating is specifically divided into 11 stages, with the barrel temperature set sequentially according to the conveying direction: stage 1 is 480℃, stage 2 is 580℃, stage 3 is 590℃, stage 4 is 600℃, stage 5 is 635℃, stage 6 is 635℃, stage 7 is 635℃, stage 8 is 635℃, stage 9 is 635℃, stage 10 is 635℃, and stage 11 is 570℃; the temperature of the preheated mold is 150~300℃, the injection speed of the semi-solid slurry is 1~4m / s, and the injection pressure of the semi-solid slurry is 90~102MPa.

7. The semi-solid injection molding method for recycled magnesium alloy components according to claim 5, characterized in that, The primary solid particles are composed of an α-Mg phase, with a particle size of 10–30 μm; the recycled magnesium alloy component is composed of an α-Mg phase and a second phase, the second phase being β-Mg. 17 Al 12 Precipitated phases and Ni-containing or Cu-containing phases.

8. A recycled magnesium alloy component, characterized in that, The recycled magnesium alloy component is obtained by a semi-solid injection molding method according to any one of claims 1-7, wherein the chemical composition of the recycled magnesium alloy component is Mg-xAl-yCu or Mg-xAl-yNi, wherein the mass percentage content of Al is 6-8 wt%, the mass percentage content of Cu or Ni is 1-3 wt%, and the balance is Mg and unavoidable impurities.

9. A recycled magnesium alloy component according to claim 8, characterized in that, In a 3 wt% KCl solution, when the mass percentage content of Al (x) is 6–8 wt% and the mass percentage content of Cu or Ni (y) is 2 wt%, the corrosion rate of Mg-xAl-2Cu recycled magnesium alloy components is 7.21–8.35 mm / y, and the corrosion rate of Mg-xAl-2Ni recycled magnesium alloy components is 12.63–14.44 mm / y.

10. A biodegradable bridge plug, characterized in that, It includes a bridge plug body and a sealing structure, an anchoring structure and a bore structure disposed on the bridge plug body, wherein the entire or part of the bridge plug body is made of a recycled magnesium alloy component as described in any one of claims 8-9.

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