A magnesium alloy and a preparation method and application thereof

Abstract

The application relates to the technical field of alloy materials, in particular to a magnesium alloy and a preparation method and application thereof. The magnesium alloy contains, in percentage by mass, Al: 0.05%-0.12%, Zn: 0.005%-0.02%, Mn: 0.005%-0.03%, Fe: <=0.015%, Cu: <=0.005%, Ni: 0.15%-0.25%, Si: <=0.01%, Gd: 2.5%-3.2%, and the balance is magnesium and inevitable impurities. The first manganese source, the second manganese source and the pretreated manganese powder without the controlled release layer are constructed to have different controlled release layer structures, and are added in stages when the base melt is cooled to the semi-solid window, so that the manganese element is released in sequence, the obtained magnesium alloy has high compressive strength, excellent early pitting corrosion resistance and stable late dissolution rate, and is suitable for preparing the center tube or the cone of the soluble segmented fracturing bridge plug, and effectively solves the technical problem that the existing soluble magnesium alloy cannot simultaneously have stable pressure resistance in the early stage and uniform dissolution in the late stage.

Description

Technical Field

[0001] This invention relates to the field of alloy materials technology, specifically to a magnesium alloy and its preparation method and application. Background Technology

[0002] Soluble magnesium alloys, due to their controllable degradation characteristics under specific environments, have shown great application potential in the oil and gas extraction field, particularly in staged fracturing technology. Downhole tools such as bridge plugs, center tubes, and cones made of soluble magnesium alloys can automatically dissolve in the downhole environment after fracturing operations, thus eliminating drilling and grinding processes, significantly shortening the construction cycle, and reducing operating costs and risks. Therefore, developing soluble magnesium alloys with both excellent mechanical properties and ideal degradation behavior has become a research hotspot in this field.

[0003] In the development of soluble magnesium alloys, balancing the core contradiction between early-stage pressure stability and later-stage uniform dissolution is crucial to the successful application of the material. On the one hand, the tool needs sufficient strength and resistance to localized corrosion during the setting and pressure-bearing stages to ensure the successful execution of fracturing operations; on the other hand, after the mission is completed, the material needs to dissolve rapidly and uniformly in the flowback fluid to avoid large residues clogging the wellbore. However, in existing technologies, these two goals are often difficult to achieve simultaneously. The material is prone to premature failure due to localized pitting corrosion in the early stages of service, or the uneven dissolution rate during the later stages affects the overall degradation effect.

[0004] Among numerous alloying elements, manganese is widely used because it can effectively weaken the harmful effects of impurity iron (Fe) on the corrosion resistance of magnesium alloys. Manganese can combine with iron to form high-potential-difference Mn-Fe intermetallic compounds, thereby changing the microscopic distribution of impurity iron and reducing its risk of microgalvanic corrosion as a strong cathode phase. However, conventional manganese addition methods result in the release of manganese being instantaneous and disordered. This process cannot precisely control the location and timing of manganese's action in the melt. Manganese often diffuses indiscriminately throughout the melt, making it difficult to preferentially act on iron-rich micro-regions, especially at critical locations such as grain boundary triple points. When the alloy is in a state containing chloride ions (Cl... - When in the environment of completion fluid or flowback fluid, trace iron impurities that are not effectively shielded can easily induce microgalvanic corrosion, amplify local pitting corrosion, and cause the material to undergo penetrating corrosion in the early stage of pressure bearing, resulting in catastrophic tool failure. In addition, this extensive addition method has poor tolerance to the fluctuation of raw material impurity content between batches, making it difficult to guarantee the corrosion resistance and degradation consistency of the product, which seriously restricts the stable industrial production of high-performance soluble magnesium alloys. Summary of the Invention

[0005] In view of this, the purpose of this invention is to propose a magnesium alloy, its preparation method and application, so as to solve the problem that existing soluble magnesium alloys are difficult to balance in terms of early pressure stability and later uniform solubility in chlorine-containing environments.

[0006] To achieve the above objectives, the present invention provides a method for preparing a magnesium alloy, comprising the following steps:

[0007] S1: Magnesium powder is mechanically embedded onto the surface of manganese powder and then placed in a fluorine-containing treatment solution for fluorine treatment to obtain the first manganese source and the second manganese source respectively.

[0008] S2: Manganese powder is ultrasonically cleaned with anhydrous ethanol and dried to obtain pretreated manganese powder;

[0009] S3: Weigh magnesium ingots, magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder and silicon powder and smelt them to obtain the matrix melt. Weigh the first manganese source, the second manganese source and the pretreated manganese powder for later use.

[0010] S4: Cool the matrix melt under inert gas protection. When the temperature drops to 640-645℃, first add the first manganese source and second manganese source to the matrix melt. After standing, add pretreated manganese powder. After heat preservation, pour to obtain cast magnesium alloy billet.

[0011] S5: After homogenization treatment, the cast magnesium alloy billet is hot extruded to obtain a magnesium alloy.

[0012] Preferably, in step S1, the ratio of magnesium powder, manganese powder, and fluorine-containing treatment liquid in the first manganese source is 0.6g:14g:10g.

[0013] Preferably, the fluorine-containing treatment solution in step S1 is an aqueous solution of ammonium bifluoride with a mass concentration of 7.5%-8.5%.

[0014] Preferably, in step S1, the ratio of magnesium powder, manganese powder, and fluorine-containing treatment liquid in the second manganese source is 0.15g:6g:5g.

[0015] Preferably, the fluorine-containing treatment solution in step S1 is an aqueous solution of ammonium bifluoride with a mass concentration of 4%-6%;

[0016] Preferably, the magnesium powder in step S1 has a particle size of 1-5 μm.

[0017] Preferably, the manganese powder in step S1 has a purity of not less than 99% and a particle size of 5-20 μm.

[0018] Preferably, the drying temperature in step S2 is 60°C and the drying time is 30 minutes.

[0019] Preferably, the manganese powder in step S2 has a particle size of 15-25 μm.

[0020] Preferably, the smelting in step S3 specifically involves first heating the temperature to 740-750℃ to melt the magnesium ingot, then adding the magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder, and silicon powder, and after all the additions are completed, heating the temperature to 760-770℃ and holding it for 15-20 minutes.

[0021] Preferably, the magnesium ingot in step S3 has a purity of not less than 99.95%.

[0022] Preferably, the gadolinium mass fraction of the magnesium-gadolinium master alloy in step S3 is 30%.

[0023] Preferably, the purity of the aluminum particles in step S3 is not less than 99.9%.

[0024] Preferably, the purity of the zinc granules in step S3 is not less than 99.9%.

[0025] Preferably, the iron powder in step S3 has a purity of not less than 99.5% and a particle size of not more than 75 μm.

[0026] Preferably, the copper powder in step S3 has a purity of not less than 99.9% and a particle size of not more than 75 μm.

[0027] Preferably, the nickel powder in step S3 has a purity of not less than 99.5% and a particle size of not more than 75 μm.

[0028] Preferably, the silicon powder in step S3 has a purity of not less than 99.5% and a particle size of not more than 75 μm.

[0029] Preferably, the metal mold needs to be preheated to 220°C during the casting process described in step S4.

[0030] Preferably, in step S4, the weight ratio of the first manganese source, the second manganese source, and the pretreated manganese powder is 6-8g:2-4g:6g.

[0031] Preferably, the homogenization treatment in step S5 is carried out at a temperature of 480-530℃ for 7.5-8.5 hours.

[0032] Preferably, the hot extrusion temperature in step S5 is 370-400℃.

[0033] The present invention also provides a magnesium alloy comprising, by mass percentage: Al: 0.05%-0.12%, Zn: 0.005%-0.02%, Mn: 0.005%-0.03%, Fe: ≤0.015%, Cu: ≤0.005%, Ni: 0.15%-0.25%, Si: ≤0.01%, Gd: 2.5%-3.2%, with the balance being magnesium and unavoidable impurities.

[0034] Furthermore, the present invention also provides an application of magnesium alloys in the preparation of the central tube or cone of a soluble segmented fracturing bridge plug.

[0035] The beneficial effects of this invention are:

[0036] This invention abandons the traditional method of adding manganese source all at once in the entire liquid stage. By surface treating manganese powder, an inorganic controlled-release layer mainly composed of magnesium fluoride is constructed on its surface. The manganese source is divided into two types with different controlled-release layer thicknesses and structures. This sequential release mechanism can ensure that manganese forms a fine manganese-iron symbiotic phase in situ while a residual liquid film still exists in the melt. This effectively shields the harmful effects of impurity iron as a strong cathode phase and fundamentally inhibits the initiation of microgalvanic corrosion.

[0037] This invention further introduces pretreated manganese powder without a controlled-release layer and adopts a two-stage spatial feeding strategy. This design enables the pretreated manganese powder to disperse rapidly in the remaining liquid phase, forming an overall manganese concentration compensation, which provides a continuous driving force for subsequent uniform degradation.

[0038] This invention constructs a three-level manganese release structure within the material, characterized by localized preferential inhibition and overall uniform compensation. This structure not only solves the problem of failure caused by localized corrosion in the early stages but also ensures that the material can dissolve continuously and uniformly in the later stages of service, achieving a high level of overall dissolution rate within 7 days.

[0039] This invention precisely controls the addition of manganese within a semi-solid window, and, in conjunction with stirring and settling processes, ensures that the release, diffusion, and reaction of manganese are highly coordinated with the nucleation and growth of α-magnesium grains. This micro-control mechanism effectively suppresses the formation of coarse second phases, promotes the uniform distribution of alloying elements, and thus refines the grain structure.

[0040] This invention, by constructing a manganese source with a controlled-release layer and introducing precise feeding timing, uses a process design-based solidification mechanism to greatly improve the consistency of corrosion resistance and degradation behavior between different batches of products, laying a solid foundation for the large-scale, stable industrial production and application of high-performance soluble magnesium alloys. Detailed Implementation

[0041] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to specific embodiments.

[0042] Properties of raw materials used in this invention:

[0043] Magnesium ingots: purity not less than 99.95%; Magnesium-gadolinium master alloy: gadolinium mass fraction 30%; Aluminum granules: purity not less than 99.9%; Zinc granules: purity not less than 99.9%; Iron powder: purity not less than 99.5%, particle size not greater than 75μm; Copper powder: purity not less than 99.9%, particle size not greater than 75μm; Nickel powder: purity not less than 99.5%, particle size not greater than 75μm; Silicon powder: purity not less than 99.5%, particle size not greater than 75μm; Magnesium powder: particle size 1-5μm.

[0044] Example 1: A method for preparing a magnesium alloy, the specific steps of which are as follows:

[0045] S1: Add 14g of manganese powder (6-10μm) and 0.6g of magnesium powder to an argon-filled sealed mixing tank, and mix at 80rpm for 20min to mechanically embed the magnesium powder onto the surface of the manganese powder. Transfer the resulting mixed powder to a polytetrafluoroethylene beaker, add 80g of anhydrous ethanol, and stir at 300rpm for 5min at 20℃. Separately, dissolve 0.80g of ammonium bifluoride in 9.20g of deionized water to prepare a fluoride-containing treatment solution, add it dropwise to the stirring system within 15min, continue stirring for 12min, let stand for 5min, filter, and rinse once with deionized water and twice with anhydrous ethanol, and then vacuum dry at 70℃ for 2h to obtain the first manganese source.

[0046] S2: Add 6g of manganese powder (10-18μm) and 0.15g of magnesium powder to another argon-filled sealed mixing tank, and tumble mix at 80rpm for 15min to allow the magnesium powder to mechanically adhere to the surface of the manganese powder. Transfer the mixed powder to a polytetrafluoroethylene beaker, add 50g of anhydrous ethanol, and stir at 300rpm for 5min at 20℃. Separately, dissolve 0.25g of ammonium bifluoride in 4.75g of deionized water to prepare a fluorine-containing treatment solution, add it dropwise to the stirring system within 5min, continue stirring for 5min, and then immediately filter. Rinse once with deionized water and twice with anhydrous ethanol, and then vacuum dry at 60℃ for 1.5h to obtain the second manganese source.

[0047] S3: Weigh 12g of manganese powder (15-25μm), add 20g of anhydrous ethanol and ultrasonically clean for 3min, filter and dry at 60℃ for 30min to obtain pretreated manganese powder;

[0048] S4: By mass percentage, Al: 0.0853%, Zn: 0.0104%, Mn: 0.0134%, Fe: 0.0121%, Cu: 0.0026%, Ni: 0.1923%, Si: 0.0064%, Gd: 2.8190%, with the balance being magnesium and unavoidable impurities. Assuming a total magnesium alloy weight of 10 kg, accurately weigh 90.2808 kg of magnesium ingots, 9.3967 kg of magnesium-gadolinium master alloy, 0.0853 kg of aluminum granules, 0.0104 kg of zinc granules, 0.0121 kg of iron powder, 0.0026 kg of copper powder, 0.1923 kg of nickel powder, 0.0064 kg of silicon powder, the first manganese source, and the second manganese source. The first manganese source, the second manganese source, and the pretreated manganese powder were added in a weight ratio of 7:3:6. Magnesium ingots were then added to a graphite crucible, protected with 99.99% argon gas, and heated to 745°C. After the magnesium ingots were completely melted, a magnesium-gadolinium master alloy was added, and the mixture was stirred at 180 rpm for 8 minutes using a graphite stirring paddle. Aluminum and zinc granules were then added, and stirring continued for 3 minutes. Iron, copper, nickel, and silicon powders were pre-coated with magnesium foil and pressed into small blocks, then added to the melt in three batches, stirring at 180 rpm for 2 minutes after each addition. After all the powders were added, the melt was heated to 765°C and held for 18 minutes to allow gadolinium and other elements to be fully dispersed in the melt, resulting in the matrix melt.

[0049] S5: The matrix melt obtained in S4 is slowly cooled to 643℃ under argon protection (this temperature range is the temperature range for determining entry into the semi-solid window). After entering the semi-solid window, the first manganese source and the second manganese source are premixed for 1 minute to form a mixture. The mixture is sent to a position 60mm below the liquid surface and 15mm below the stirring paddle through a preheated feeding pipe. It is then stirred at 80rpm for 25s. After stopping the stirring, it is allowed to stand for 60s. Then, pretreated manganese powder is added through another preheated feeding pipe to a position 40mm below the liquid surface and near the side wall of the crucible. It is stirred at 80rpm for 20s. It is held at 643℃ for 4 minutes and then poured into a metal mold preheated to 220℃ to obtain a cast magnesium alloy billet.

[0050] S6: The obtained as-cast magnesium alloy billet was homogenized at 500℃ for 8 hours, air-cooled to room temperature, heated to 375℃ and hot-extruded to obtain a magnesium alloy.

[0051] Example 2: The difference from Example 1 is that in S1, the amount of ammonium bifluoride added is adjusted to 0.85g, and the amount of deionized water is adjusted to 9.15g, added dropwise over 15min and then stirred for 13min; in S2, the amount of ammonium bifluoride added is adjusted to 0.30g, and the amount of deionized water is adjusted to 4.70g, added dropwise over 4min and then stirred for 4min; in S4, the mass percentages are Al: 0.12%, Zn: 0.02%, Mn: 0.03%, Fe: 0.015%, Cu:0.005%, Ni:0.25%, Si:0.01%, Gd:3.2%, with the balance being magnesium and unavoidable impurities. Accurately weigh magnesium ingots, magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder, silicon powder, first manganese source, second manganese source, and pretreated manganese powder (the weight ratio of the first manganese source, second manganese source, and pretreated manganese powder is 6:2:6). In S5, the matrix melt is slowly cooled to 645°C under argon protection. The other conditions are the same as in Example 1.

[0052] Example 3: The difference from Example 1 is that in S1, the amount of ammonium bifluoride added is adjusted to 0.75g, and the amount of deionized water is adjusted to 9.25g, added dropwise over 15min and then stirred for 13min; in S2, the amount of ammonium bifluoride added is adjusted to 0.20g, and the amount of deionized water is adjusted to 4.80g, added dropwise over 4min and then stirred for 4min; in S4, the mass percentages are Al: 0.05%, Zn: 0.005%, Mn: 0.005%, Fe: 0.005%, and Fe: 0.005%. The following components were used: 0.015% Cu, 0.005% Ni, 0.15% Si, 0.01% Gd, and the balance being magnesium and unavoidable impurities. Magnesium ingots, magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder, silicon powder, first manganese source, second manganese source, and pretreated manganese powder (the weight ratio of the first manganese source, second manganese source, and pretreated manganese powder was 8:4:6). In S5, the matrix melt was slowly cooled to 640°C under argon protection. The other conditions were the same as in Example 1.

[0053] Example 4: The difference from Example 1 is that in S1, the amount of ammonium bifluoride added is adjusted to 0.78g, and the amount of deionized water is adjusted to 9.22g, added dropwise over 15min and then stirred for 13min; in S2, the amount of ammonium bifluoride added is adjusted to 0.23g, and the amount of deionized water is adjusted to 4.77g, added dropwise over 4min and then stirred for 4min; in S4, the mass percentages are Al: 0.10%, Zn: 0.01%, Mn: 0.02%, Fe: 0.015%, Cu:0.005%, Ni:0.20%, Si:0.01%, Gd:2.8%, with the balance being magnesium and unavoidable impurities. Accurately weigh magnesium ingots, magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder, silicon powder, first manganese source, second manganese source, and pretreated manganese powder (the weight ratio of the first manganese source, second manganese source, and pretreated manganese powder is 7:4:6). In S5, the matrix melt is slowly cooled to 642°C under argon protection. The remaining conditions are the same as in Example 1.

[0054] Comparative Example 1: The difference from Example 1 is that neither ammonium bifluoride is added in S1 nor fluorine treatment is performed; the powder obtained in S1 is used as the first manganese source and the powder obtained in S2 is used as the second manganese source, and the other conditions are the same as in Example 1.

[0055] Comparative Example 2: The difference from Example 1 is that the first manganese source in S1 is treated with fluorine in the manner of S2, while the other conditions are the same as in Example 1.

[0056] Comparative Example 3: The difference from Example 1 is that the second manganese source in S2 is treated with fluorine in the manner of S1, while the other conditions are the same as in Example 1.

[0057] Comparative Example 4: The difference from Example 1 is that after holding at 760°C for 15 minutes in S5, the first manganese source, the second manganese source, and the pretreated manganese powder were immediately added to the matrix melt, and the feeding was completed in the full liquid stage. The other conditions were the same as in Example 1.

[0058] Comparative Example 5: The difference from Example 1 is that in S5, the first manganese source, the second manganese source and the pretreated manganese powder are premixed and then fed into the liquid at a position 60 mm below the liquid surface and 20 mm below the stirring paddle through the same preheated feeding pipe. The mixture is stirred for only 25 seconds and is not allowed to stand for a second time. The other conditions are the same as in Example 1.

[0059] Comparative Example 6: The difference from Example 1 is that in S5, the first manganese source and the second manganese source are replaced with equal amounts of pretreated manganese powder, and the order of addition and process remain unchanged. The other conditions are the same as in Example 1.

[0060] Comparative Example 7: The difference from Example 1 is that in S5, pretreated manganese powder is not added, but an equal amount of a second manganese source is added to keep the total amount of powder added consistent with that in Example 1. The other conditions are the same as those in Example 1.

[0061] Performance testing

[0062] Average grain size determination: Take the magnesium alloys obtained in the examples and comparative examples, take samples along the longitudinal section of the extrusion direction, grind and polish them according to GB / T 13298-2015, and determine the average grain size according to GB / T 6394-2017. At least 5 different fields of view are selected for each sample.

[0063] Room temperature tensile properties test: Magnesium alloy samples obtained from the examples and comparative examples were tested at room temperature according to GB / T 228.1-2021. The test temperature was 23℃. An electronic universal testing machine was used. After clamping, a 25mm gauge length extensometer was installed. The load was applied at a beam speed of 1.0mm / min until fracture. The tensile strength, specified plastic extension strength and elongation after fracture were recorded. Five parallel samples were tested in each group, and the average value was taken.

[0064] Room temperature compression performance test: Magnesium alloy samples (cylindrical compression specimens) obtained from the examples and comparative examples were tested at room temperature according to GB / T 7314-2017. The test temperature was 23℃. An electronic universal testing machine was used to load the specimen at a beam speed of 1.0 mm / min until obvious cracking occurred or the total compressive strain reached 30%. The maximum compressive stress was recorded as the compressive strength. Five parallel samples were tested in each group, and the average value was taken.

[0065] Vickers hardness test: Take the hot-extruded magnesium alloy samples obtained from the examples and comparative examples, and conduct Vickers hardness test according to GB / T4340.1-2024. The test force is 1.961N and the holding time is 15s. Ten test points are evenly selected for each sample. After removing the maximum and minimum values, the average value is taken. The result is expressed as HV0.2.

[0066] Immersion Dissolution Test: Hot-extruded magnesium alloy samples (sheet form) obtained from the examples and comparative examples were used as the immersion medium with a KCl solution of 3.0% by mass and a liquid-to-solid ratio of 50 mL / cm². The samples were immersed in a constant-temperature glass reactor with a reflux condenser at 93.0 °C. Samples were taken at 24 h, 72 h, and 168 h. The 24 h samples were used to observe whether penetrating pitting occurred and the maximum pitting depth was measured. The 168 h samples were used to calculate the overall dissolution rate. After the samples were removed, they were rinsed with deionized water and then corrosion products were removed according to GB / T 16545-2025. After drying to constant weight, they were weighed. The overall dissolution rate at 7 days was calculated based on the initial mass and the remaining mass after 168 h. The maximum pitting depth at 24 h was measured by metallographic section method. Five maximum corrosion pits were selected for each sample and the average value was calculated. When the corrosion pit penetrated 3 mm of the sample thickness, it was determined that penetrating pitting had occurred.

[0067] The test results are shown in Table 1.

[0068] Table 1 Performance Test Results

[0069] Data Analysis: Data from the examples in the table show that the magnesium alloy prepared by this invention exhibits a good balance between average grain size, tensile strength, specified ductile elongation strength, compressive strength, Vickers hardness, and immersion dissolution behavior. With the first and second manganese sources operating within their respective ranges and fed in a two-stage space after entering the semi-solid window, the material maintains high compressive stability in the early stages of use and a high overall dissolution level in the later immersion stage, while also exhibiting more uniform local corrosion morphology.

[0070] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 1 and 6, in the absence of a fluorine-containing inorganic controlled-release layer mainly composed of magnesium fluoride, although the material still retains a certain strength and the overall dissolution in the later stages is not low, the maximum pitting depth in the first 24 hours is significantly increased, and penetrating pitting occurs. The main reason for this is that manganese is more easily released locally and rapidly after its addition, leading to premature and strong local reactions near the grain boundary triple points and iron-rich micro-regions.

[0071] As can be seen from the data in Table 1 for Example 1 and Comparative Examples 2 and 3, when the first manganese source and the second manganese source are processed into the same controlled-release layer morphology, the early-stage stability and later-stage overall dissolution of the material cannot be maintained simultaneously. This is because the former weakens the delayed-release effect of the first manganese source, while the latter weakens the early-release effect of the second manganese source. This indicates that different controlled-release layer thicknesses and local opening regions are not simply process fine-tuning, but rather necessary conditions for establishing two manganese supply pathways.

[0072] As can be seen from the data in Example 1 and Comparative Example 4 in Table 1, simply moving the feeding timing forward to the fully liquid stage increases the average grain size of the material, while simultaneously decreasing its strength and hardness, and significantly deepening the pitting corrosion after 24 hours. The main reason for this is that although the same total amount of manganese was added, its release and action sites were disconnected, failing to form a locally preferential action zone based on sequential addition. Therefore, it is difficult to simultaneously ensure pressure resistance in the early stage and uniform dissolution in the later stage.

[0073] As can be seen from the data in Table 1 for Example 1 and Comparative Example 5, under the premise of maintaining the semi-solid window addition, if the first manganese source, the second manganese source, and the pretreated manganese powder are all added to the same location at once, the material properties are improved compared to the fully liquid addition, but it is still difficult to reach the equilibrium state of Example 1. It is speculated that the reason is that the single addition weakens the continuous relationship between establishing a local preferential action zone in the previous stage and forming an overall manganese concentration compensation in the later stage, causing the two to overlap in time and space, making it difficult to further reduce local corrosion in the early stage, and lacking continuous impetus for overall dissolution in the later stage.

[0074] As can be seen from the data in Table 1 for Example 1 and Comparative Example 7, when the pretreated manganese powder is not added but an equal amount of the second manganese source is used instead, the pitting corrosion of the material in the first 24 hours can still be suppressed to some extent, but the overall dissolution is significantly limited after 7 days. The main reason is that the first and second manganese sources focus more on establishing a local preferential action zone within the semi-solid window, while the pretreated manganese powder undertakes the subsequent overall manganese concentration compensation role; when the latter is missing, the connection between the initial stability and the later overall dissolution is weakened.

[0075] Those skilled in the art should understand that the discussion of any of the above embodiments is merely exemplary and is not intended to imply that the scope of the invention is limited to these examples; within the framework of the invention, the technical features of the above embodiments or different embodiments can also be combined, the steps can be implemented in any order, and there are many other variations of the different aspects of the invention as described above, which are not provided in detail for the sake of brevity.

Claims

1. A method for preparing a magnesium alloy, characterized in that, Includes the following steps: S1: Magnesium powder is mechanically embedded onto the surface of manganese powder and then placed in a fluorine-containing treatment solution for fluorine treatment to obtain the first manganese source and the second manganese source, respectively; S2: The manganese powder is cleaned and dried to obtain pretreated manganese powder; S3: Magnesium ingots, magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder and silicon powder are weighed and smelted to obtain a matrix melt; S4: The matrix melt is cooled under inert gas protection. When the temperature drops to 640-645℃, the first manganese source and the second manganese source are added to the matrix melt first, then the pretreated manganese powder is added. After heat preservation, it is poured to obtain a cast magnesium alloy billet; S5: The cast magnesium alloy billet is homogenized and then hot extruded to obtain a magnesium alloy; In step S1, the ratio of magnesium powder, manganese powder, and fluorine-containing treatment solution in the first manganese source is 0.6g:14g:10g; the ratio of magnesium powder, manganese powder, and fluorine-containing treatment solution in the second manganese source is 0.15g:6g:5g; the fluorine-containing treatment solution in the first manganese source is an aqueous solution of ammonium bifluoride with a mass concentration of 7.5%-8.5%; the fluorine-containing treatment solution in the second manganese source is an aqueous solution of ammonium bifluoride with a mass concentration of 4%-6%.

2. The method for preparing magnesium alloy according to claim 1, characterized in that, The magnesium powder in step S1 has a particle size of 1-5 μm; the manganese powder has a purity of not less than 99% and a particle size of 5-20 μm.

3. The method for preparing magnesium alloy according to claim 1, characterized in that, The manganese powder in step S2 has a particle size of 15-25 μm.

4. The method for preparing magnesium alloy according to claim 1, characterized in that, The smelting process in step S3 specifically involves first heating the magnesium ingot to 740-750℃ to melt it completely, then adding magnesium-gadolinium master alloy, aluminum granules, zinc granules, iron powder, copper powder, nickel powder, and silicon powder, and then heating the mixture to 760-770℃ and holding it there for 15-20 minutes after adding all the ingredients.

5. The method for preparing magnesium alloy according to claim 1, characterized in that, In step S4, the weight ratio of the first manganese source, the second manganese source, and the pretreated manganese powder is 6-8g:2-4g:6g.

6. The method for preparing magnesium alloy according to claim 1, characterized in that, The homogenization process in step S5 is carried out at a temperature of 480-530℃ for 7.5-8.5 hours.

7. The method for preparing magnesium alloy according to claim 1, characterized in that, The hot extrusion temperature in step S5 is 370-400℃.

8. A magnesium alloy, characterized in that, It is prepared by the method of any one of claims 1-7.

9. The magnesium alloy according to claim 8, characterized in that, It contains, by mass percentage: Al: 0.05%-0.12%, Zn: 0.005%-0.02%, Mn: 0.005%-0.03%, Fe: ≤0.015%, Cu: ≤0.005%, Ni: 0.15%-0.25%, Si: ≤0.01%, Gd: 2.5%-3.2%, with the balance being magnesium and unavoidable impurities.

10. An application of the magnesium alloy according to claim 8, characterized in that, Application in the preparation of the central tube or cone of soluble segmented fracturing bridge plug.

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