A soluble magnesium alloy and a method for producing the same

Abstract

This invention relates to the field of alloy materials technology, specifically to a soluble magnesium alloy and its preparation method. The method involves first modifying magnesium-calcium intermediate alloy particles with a fluorine-containing surface layer, then introducing the modified particles into the matrix melt in a segmented, batch-wise, and fixed-depth manner to reduce calcium burn-off and improve the distribution of the Ca-containing second phase, thereby balancing early-stage pressure resistance and later-stage uniform dissolution. The resulting soluble magnesium alloy, by mass percentage, contains: Al: 6.00%–6.20%, Zn: 0.005%–0.02%, Mn: 0.35%–0.45%, Ni: 0.30%–0.40%, Si: 0.01%–0.02%, Ca: 2.60%–3.00%, Fe: ≤0.005%, Cu: ≤0.005%, with the balance being Mg and unavoidable impurities. It is suitable for soluble segmented fracturing bridge plug center tubes or cones.

Description

Technical Field

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

[0002] Soluble magnesium alloys, due to their controllable degradation 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, eliminating the need for drilling and grinding, 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] Among various magnesium alloy systems, Mg-Ca alloys have attracted widespread attention due to their good biocompatibility and controllable degradation rate. The addition of calcium can regulate the corrosion behavior of the alloy by forming the Mg2Ca second phase, while also refining the grain size and improving casting performance. However, Mg-Ca alloys still face a series of severe challenges in practical applications. On the one hand, Mg2Ca, as a brittle phase, when distributed along grain boundaries in a continuous network morphology, severely disrupts the continuity of the matrix, becoming stress concentration points and crack initiation sites, leading to a sharp decline in the alloy's plasticity and toughness. This is undoubtedly a fatal flaw for bridge plug components that need to withstand high pressure and high stress. On the other hand, the composition, morphology, and volume fraction of the second phase are key factors determining the alloy's dissolution rate. If the second phase is unevenly distributed or its morphology is out of control, it will lead to significant differences in the dissolution behavior of the alloy during service, manifesting as large batch-to-batch performance fluctuations, and even premature failure due to localized corrosion or stress cracking in the early stages of pressure bearing.

[0004] To improve the distribution morphology of Mg2Ca, methods such as adding other alloying elements or adjusting heat treatment processes are commonly employed. For example, zinc, manganese, or rare earth elements can be added to alter the precipitation behavior of the second phase, or solution treatment can be used to attempt to re-dissolve Mg2Ca at grain boundaries. However, these methods often have significant limitations. Adding multiple alloying elements significantly increases the complexity and cost of the alloy system, and the interactions between multiple elements are difficult to predict, easily leading to other uncontrollable microstructural problems. While heat treatment can improve microstructure uniformity to some extent, its effectiveness is limited by the initial as-cast microstructure. Furthermore, for coarse Mg2Ca that has already formed a continuous grain boundary network, solution treatment often fails to completely eliminate it and may even cause grain growth due to high-temperature treatment, further weakening mechanical properties.

[0005] In addition, traditional alloying methods usually involve adding the magnesium-calcium master alloy all at once in the early stages of smelting, allowing it to exist and completely dissolve in the high-temperature melt for a long time. This process results in a uniform distribution of calcium in the melt. However, during the subsequent solidification process, due to solute redistribution, calcium is very likely to accumulate in the grain boundary region at the last solidification stage, thus forming a continuous brittle Mg2Ca network. This inherent pattern of uniform distribution followed by grain boundary segregation is the root cause of why Mg-Ca alloys are difficult to balance strength and plasticity.

[0006] Therefore, how to fundamentally change the state of calcium in the melt and the timing of its entry, suppress its continuous segregation to the grain boundaries, and at the same time reduce its oxidation loss during the smelting process has become a technical bottleneck that must be overcome in the development of high-performance, high-stability soluble magnesium alloys. Summary of the Invention

[0007] In view of this, the purpose of this invention is to propose a soluble magnesium alloy and its preparation method to solve the problems of poor batch consistency, early cracking under pressure, or premature failure that often occur in existing Mg-Ca soluble magnesium alloys used in bridge plug materials.

[0008] To achieve the above objectives, the present invention provides a method for preparing a soluble magnesium alloy, comprising the following steps:

[0009] S1: The magnesium-calcium master alloy is mechanically crushed and sieved to obtain magnesium-calcium master alloy particles, which are then vacuum dried for later use.

[0010] S2: Ethylene glycol and ammonium bifluoride are mixed to form a fluorine-containing suspension reaction system. The magnesium-calcium intermediate alloy particles obtained in S1 are added to the fluorine-containing suspension reaction system to carry out the reaction.

[0011] S3: After the system obtained in S2 is cooled, argon gas is bubbled through deionized water and introduced into the space above the liquid surface for gaseous trace water pre-activation. Then, deionized water is added dropwise to the reaction system to continue the reaction.

[0012] S4: After the S3 reaction is completed, the resulting product is filtered, washed and dried to obtain surface-modified intermediate alloy particles.

[0013] S5: Weigh magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloy, magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc according to the proportions and smelt them to obtain the matrix melt;

[0014] S6: After adding the surface-modified intermediate alloy particles obtained in S4 to the matrix melt in batches, gently stir after each addition. After the last batch of particles is added, keep it at 700-705℃ and then pour and cool to obtain a soluble magnesium alloy.

[0015] Preferably, the magnesium-calcium master alloy in step S1 is a MgCa30 grade magnesium-calcium master alloy with a calcium content of 30±2wt%, a total amount of other impurities of less than 0.5wt%, and the balance being magnesium.

[0016] Preferably, the particle size of the magnesium-calcium master alloy particles in step S1 is 0.8-1.2 mm.

[0017] Preferably, the vacuum drying in step S1 is maintained at 80°C and -80 kPa for 120 min.

[0018] Preferably, the weight ratio of ethylene glycol, ammonium bifluoride and magnesium-calcium intermediate alloy particles in step S2 is 5000g:330-390g:900-950g.

[0019] Preferably, the reaction temperature in step S2 is 60°C and the reaction time is 25-30 min.

[0020] Preferably, the argon flow rate in step S3 is 400-500 mL / min.

[0021] Preferably, the cooling temperature in step S3 is 48-52°C.

[0022] Preferably, the reaction temperature in step S3 is 48-52℃ and the reaction time is 10-15 min.

[0023] Preferably, the weight ratio of magnesium-calcium intermediate alloy particles to deionized water in step S3 is 900-950g:140-160g.

[0024] Preferably, the filtration in step S4 needs to be performed while the temperature is high (above 40°C).

[0025] Preferably, the drying in step S4 is carried out at 70°C and -80 kPa.

[0026] Preferably, the magnesium ingot in step S5 has a magnesium content of not less than 99.95%.

[0027] Preferably, the magnesium alloy covering agent in step S5 is DOW230Ca covering agent.

[0028] Preferably, the aluminum-manganese master alloy in step S5 has a Mn mass fraction of 10 wt% and the balance is Al.

[0029] Preferably, the magnesium-nickel master alloy in step S5 has a Ni mass fraction of 20 wt% and the balance is Mg.

[0030] Preferably, the magnesium-silicon master alloy in step S5 has a Si mass fraction of 25 wt% and the balance is Mg.

[0031] Preferably, the specific steps of the smelting in step S5 are as follows: first, the magnesium ingot is completely melted at 720-730°C, while a magnesium alloy covering agent is added; then, industrial pure aluminum ingot and aluminum-manganese master alloy are added and the temperature is raised to 735-740°C; next, magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc are added; after slag removal, the temperature is lowered to 700-710°C and a magnesium alloy covering agent is added.

[0032] The present invention also provides a magnesium alloy, which, by mass percentage, comprises Al: 6.00%-6.20%, Zn: 0.005%-0.02%, Mn: 0.35%-0.45%, Ni: 0.30%-0.40%, Si: 0.01%-0.02%, Ca: 2.60%-3.00%, Fe: ≤0.005%, Cu: ≤0.005%, with the balance being magnesium and unavoidable impurities.

[0033] The beneficial effects of this invention are:

[0034] This invention abandons the traditional method of adding the magnesium-calcium master alloy all at once in the early stages of smelting. Instead, it first modifies the surface of the magnesium-calcium master alloy particles with radial gradient fluorination to construct a composite shell structure of an inner dense fluorinated layer and an outer loose fluorinated layer. After the matrix melt is prepared, the calcium is added in batches at a fixed depth in the later stages. This design prevents calcium from completely dissolving and uniformly distributing throughout the melt in the early stages of smelting, but rather releases it gradually in a controlled manner during the solidification stage. The inner dense fluorinated layer provides a reliable physical barrier for calcium at high temperatures, effectively inhibiting its direct oxidation and burn-off; the outer loose fluorinated layer provides a controllable mass transfer channel for calcium release through its unique structure. When the gradient-modified particles enter the melt in the later stages of solidification, calcium release is no longer instantaneous, but rather gradual, occurring through the controlled cracking and mass transfer of the outer loose layer. This gradual release mechanism forces calcium to be preferentially repelled to specific regions such as the triple points of grain boundaries during the growth of primary α-magnesium grains, rather than continuously enriched throughout the entire grain boundary range during the final solidification stage. This effectively avoids the formation of a continuous network of Mg2Ca, promoting the existence of calcium as a discretely distributed short rod-shaped or granular second phase. As a result, while maintaining high strength, the alloy's fracture strain and plasticity are significantly improved, fundamentally solving the problem of early-stage cracking under pressure caused by the brittle network in Mg-Ca alloys.

[0035] The magnesium alloy prepared by this invention exhibits an ideal dissolution rate to meet the desolvation requirements of tools in the later stage, while its structural integrity and resistance to localized corrosion in the early pressure-bearing stage are also effectively guaranteed. This invention successfully achieves the synergistic unity of stable pressure bearing in the early stage and uniform dissolution in the later stage of service life for soluble magnesium alloys. Detailed Implementation

[0036] 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.

[0037] Magnesium ingots: magnesium content not less than 99.95%; Magnesium-calcium master alloy: Mca30 grade magnesium-calcium master alloy, calcium content 30wt%, other impurities less than 0.5wt%, balance magnesium; Magnesium alloy covering agent: DOW230Ca covering agent, aluminum-manganese master alloy Mn mass fraction 10wt%, balance Al; magnesium-nickel master alloy Ni mass fraction 20wt%, balance Mg; magnesium-silicon master alloy Si mass fraction 25wt%, balance Mg; magnesium-calcium master alloy Ca mass fraction 30wt%, balance Mg.

[0038] Example 1: A method for preparing a soluble magnesium alloy, the specific steps of which are as follows:

[0039] S1: Weigh the magnesium-calcium master alloy, mechanically crush and screen it, select particles with a particle size of 0.8-1.2mm, then spread the screened particles evenly on a clean tray, vacuum dry them at 80℃ and -80kPa for 120min, take them out and cool them to room temperature in a desiccator, then seal them for later use.

[0040] S2: Add 5000g of ethylene glycol to a polytetrafluoroethylene-lined atmospheric pressure reactor, heat to 60℃, then add 360g of ammonium bifluoride, stir at 150rpm for 10min to obtain a fluorine-containing suspension reaction system; then add 925g of magnesium-calcium intermediate alloy particles, and continue to react at 60℃ and 150rpm for 28min.

[0041] S3: Cool the S2 reaction system and stabilize the system temperature to 50℃. Then, at a flow rate of 450mL / min, argon gas is bubbled through 25℃ deionized water and introduced into the space above the liquid surface from the top of the reactor for 4min. The end of the gas delivery tube does not contact the liquid. Then, 150g of deionized water is added dropwise to the reaction system at a rate of 10g / min through a metering pump, and the reaction is continued for 13min at 50℃ and 120rpm.

[0042] S4: After step S3, stop stirring immediately and filter the slurry quickly using a polytetrafluoroethylene filter while the slurry temperature is 45℃. Then wash twice with anhydrous ethanol to replace and remove the residual mother liquor on the particle surface. After washing, place the particles in a vacuum drying oven and dry them for 120 minutes at 70℃ and -80kPa. After cooling, seal and store them under dry argon protection to obtain surface-modified intermediate alloy particles.

[0043] S5: By mass percentage, it consists of Al: 6.0810%, Zn: 0.0102%, Mn: 0.4065%, Ni: 0.3489%, Si: 0.0149wt%, Ca: 2.8000%, Fe: 0.005%, Cu: 0.005%, with the balance being magnesium and unavoidable impurities. Accurately weigh magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloys, magnesium-nickel master alloys, magnesium-silicon master alloys, pure zinc, and surface-modified master alloy particles. First, place the magnesium ingots on the inner wall pre-... In a steel crucible coated with boron nitride isolation layer, 120g of magnesium alloy covering agent is evenly sprinkled on the surface of magnesium ingot, heated to 725℃ and completely melted, then industrial pure aluminum ingot and aluminum-manganese master alloy are added, and the mixture is gently stirred at 735℃ for 120s and held for 8min to form a uniform matrix melt. Then magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc are added, and the mixture is held for another 5min. After removing the slag, the melt is cooled to 705℃, and then 80g of magnesium alloy covering agent is added to the surface to form a continuous covering layer, thus obtaining the matrix melt.

[0044] S6: Divide the surface-modified intermediate alloy particles into 3 portions and add them to the matrix melt in three batches at 90-second intervals. Before each addition, make a 25-mm wide local window on the capping layer, and then use a graphite bell jar preheated to 300°C to press the batch of particles into the liquid 20mm below the liquid surface along the inner wall of the crucible. After each addition, immediately stir gently with a preheated graphite stirring rod for 15 seconds, then stop stirring and wait for the next addition to close the capping layer again. After the last batch of particles is added, keep it at 703°C for 4 minutes, remove the thin slag on the liquid surface, and then pour the melt into a steel mold preheated to 200°C at 695°C. Let it cool naturally to room temperature to obtain a soluble magnesium alloy.

[0045] Example 2: The difference from Example 1 is that in step S2, the amount of ammonium bifluoride added is 330g, and the reaction continues at 60℃ and 150rpm for 25min; in step S3, the time for introducing argon gas into the space above the liquid surface after bubbling through 25℃ deionized water is set to 3min, and then 140g of deionized water is added dropwise to the reaction system at a rate of 10g / min using a metering pump, and the reaction continues at 48℃ and 120rpm for 10min; in step S5, the mass percentage is Al: 6.00%. The composition is as follows: Zn: 0.005%, Mn: 0.35%, Ni: 0.30%, Si: 0.01%, Ca: 2.60%, Fe: 0.005%, Cu: 0.005%, with the balance being magnesium and unavoidable impurities. Magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloy, magnesium-nickel master alloy, magnesium-silicon master alloy, pure zinc, and surface-modified master alloy particles are accurately weighed. After slag removal, the melt is cooled to 710°C. In step S6, the surface-modified master alloy particles are divided into 4 portions, and the remaining conditions are the same as in Example 1.

[0046] Example 3: The difference from Example 1 is that in step S2, the amount of ammonium bifluoride added is 390g, and the reaction continues at 60℃ and 150rpm for 30min; in step S3, the time for introducing argon gas into the space above the liquid surface after bubbling through 25℃ deionized water is set to 5min, and then 160g of deionized water is added dropwise to the reaction system at a rate of 10g / min using a metering pump, and the reaction continues at 52℃ and 120rpm for 15min; in step S5, the mass percentage is Al: 6.20%. The composition is as follows: Zn: 0.02%, Mn: 0.45%, Ni: 0.40%, Si: 0.02%, Ca: 3.00%, Fe: 0.005%, Cu: 0.005%, with the balance being magnesium and unavoidable impurities. Magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloy, magnesium-nickel master alloy, magnesium-silicon master alloy, pure zinc, and surface-modified master alloy particles are accurately weighed. After slag removal, the melt is cooled to 700°C. In step S6, the surface-modified master alloy particles are divided into two portions, and the remaining conditions are the same as in Example 1.

[0047] Example 4: The difference from Example 1 is that in step S2, the amount of ammonium bifluoride added is 350g, and the reaction continues at 60℃ and 150rpm for 28min; in step S3, the time for introducing argon gas into the space above the liquid surface after bubbling through 25℃ deionized water is set to 4min, and then 145g of deionized water is added dropwise to the reaction system at 10g / min using a metering pump, and the reaction continues at 50℃ and 120rpm for 13min; in step S5, the mass percentage is Al: 6.10%, Zn: 0.01%, Mn: 0.38%, Ni: 0.34%, Si: 0.01%, Ca: 2.70%, Fe: 0.005%, Cu: 0.005%, with the balance being magnesium and unavoidable impurities. Accurately weigh magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloy, magnesium-nickel master alloy, magnesium-silicon master alloy, pure zinc, and surface-modified master alloy particles. After slag removal, cool the melt to 705°C. In step S6, the surface-modified master alloy particles are divided into 5 portions, and the remaining conditions are the same as in Example 1.

[0048] Comparative Example 1: The difference from Example 1 is that after step S1, steps S2, S3 and S4 are not performed. Instead, the magnesium-calcium intermediate alloy particles pretreated in step S1 are directly added to the matrix melt obtained in step S5 in the manner of step S6. The other conditions are the same as in Example 1.

[0049] Comparative Example 2: The difference from Example 1 is that after step S2, step S3 is not performed. After step S2, the filtration, washing and drying are carried out directly according to step S4, and then added according to step S6. The other conditions are the same as those in Example 1.

[0050] Comparative Example 3: The difference from Example 1 is that before step S2, the deionized water from step S3 is added all at once to the reaction system formed by ethylene glycol and ammonium bifluoride, and the treatment of argon gas being bubbled through deionized water at 25°C and introduced into the space above the liquid surface for 4 minutes is not performed. Then, magnesium-calcium intermediate alloy particles pretreated in step S1 are added. After the reaction is completed, the mixture is filtered, washed and dried according to step S4, and then added according to step S6. The other conditions are the same as in Example 1.

[0051] Comparative Example 4: The difference from Example 1 is that in step S2, the reaction was continued at 150 rpm for 10 min at 60 °C; in step S3, argon gas was bubbled through 25 °C deionized water and then introduced into the space above the liquid surface for 2 min, and the amount of deionized water used was 80 g. The other conditions were the same as in Example 1.

[0052] Comparative Example 5: The difference from Example 1 is that in step S6, the surface-modified intermediate alloy particles are not divided into 3 parts, but all the particles are added at once. The other conditions are the same as in Example 1.

[0053] Comparative Example 6: The difference from Example 1 is that after adding magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc in step S5, the melt is not cooled after slag removal, and the surface-modified master alloy particles are added in three portions in sequence; the other conditions are the same as in Example 1.

[0054] Performance testing

[0055] Brinell hardness: The Brinell hardness test was conducted in accordance with GB / T 231.1-2018. For each sample, a polished specimen of 15mm×15mm×5mm was selected. Five indentations were evenly arranged on the specimen surface, avoiding the edge within 2mm. A cemented carbide ball indenter with a diameter of 2.5mm was used. The test force was 612.9N and the holding time was 15s. The average Brinell hardness was measured and calculated.

[0056] Room temperature compression performance: The room temperature compression test was carried out in accordance with GB / T 7314-2017. Each group of samples had no less than 5 parallel specimens. The cylindrical specimens were Φ8mm×12mm in size, and the parallelism of the two end faces was controlled within 0.02mm. An electronic universal testing machine was used to load the specimens at a beam speed of 1.0mm / min at 23℃. The stress-strain curves were continuously recorded, and the 0.2% compressive yield strength, compressive strength and fracture strain were determined.

[0057] Potentiodynamic polarization test: Following GB / T 24196-2009, the potentiodynamic polarization test was performed in a 3.0 wt% KCl solution at 90.0℃ using a three-electrode system: the working electrode was the packaged sample with an exposed area of ​​1.000 cm². 2The reference electrode is a saturated calomel electrode; the auxiliary electrode is a platinum sheet. After the sample is immersed in the liquid, the open circuit potential is stabilized for 1800s, and then the relative open circuit potential is scanned from -250mV to +500mV at a scan rate of 0.5mV / s. The self-corrosion potential is obtained by Tafel extrapolation. Each sample is tested in parallel 3 times.

[0058] Static dissolution test in simulated downhole environment: Static immersion corrosion test was conducted according to GB / T 19291-2003, and weight loss was calculated after removing corrosion products according to GB / T 16545-2025. The immersion medium was a 3.0wt% KCl solution at 90.0℃, and the liquid-to-solid ratio was 40mL / cm³. 2 Each sample measures 20mm × 15mm × 5mm, with three parallel samples per group. Samples were taken at 2h, 6h, 24h, and 48h. Corrosion products were removed using standard methods, and the samples were dried to constant weight and weighed. The hydrogen evolution volume was recorded using the water displacement gas collection method, and the weight loss rate and hydrogen evolution rate per unit area were calculated. When the residual mass of the sample was less than 1.0% of the initial mass, it was considered completely dissolved. All test results are shown in Table 1.

[0059] Table 1 Performance Test Results

[0060] Data Analysis: As can be seen from the data in Table 1, the soluble magnesium alloy prepared by this invention achieves a good balance between chemical composition stability, microstructure uniformity, early-stage pressure resistance, and later-stage stable dissolution. With the matching of the radial gradient shell of the surface-modified intermediate alloy particles and the subsequent fixed-depth batch addition method, its Brinell hardness, compressive yield strength, and compressive strength remain at high levels, while the self-corrosion current density, weight loss rate, and hydrogen evolution rate remain within a range suitable for bridge plug service. It is speculated that this is because the dense inner fluorinated layer first restricts the instantaneous exposure of calcium in the high-temperature melt, and the loose outer fluorinated layer then provides a controlled release channel. Combined with batch addition, the calcium entry process changes from a concentrated burst release to a gradual release, thus taking into account smelting yield, microstructure control, and stable failure during the application stage.

[0061] As can be seen from the data in Table 1 for Example 1 and Comparative Example 1, when steps S2 to S4 are omitted, the calcium source particles directly contact the matrix melt, resulting in increased calcium burn-off, a significant increase in the continuous grain boundary network second phase, and a simultaneous decrease in mechanical properties and fracture strain, while electrochemical activity and static dissolution rate are significantly accelerated. The main reason for this is that without the inner dense fluorinated layer and the outer loose fluorinated layer, the particles are instantaneously exposed under high-temperature conditions, which is neither conducive to the effective entry of calcium into the melt nor to subsequent discrete distribution.

[0062] As can be seen from the data in Table 1 for Example 1 and Comparative Example 2, although the initial weight loss rate and hydrogen evolution rate decreased, the complete dissolution time was significantly prolonged, and the compressive yield strength and compressive strength did not reach a satisfactory level. It is speculated that this is because an overly dense or thick surface layer weakens the controlled cracking and mass transfer function of the outer, loose fluorinated layer, causing particles to release too slowly after entering the melt, making it difficult for calcium to participate uniformly in microstructure regulation during the most favorable solidification stage.

[0063] As can be seen from the data in Table 1 for Examples 1, 3, and 4, introducing deionized water all at once before the start of main fluorination causes surface layer instability, resulting in decreased mechanical properties and poorer dissolution uniformity. The main reason is that the former disrupts the order of first forming a dense inner fluorinated layer and then building a loose outer fluorinated layer, making the surface layer more prone to overall coarsening or localized cracking; the latter makes it difficult to provide sufficient diffusion resistance when particles enter the melt, causing calcium to be released again in a concentrated manner.

[0064] As can be seen from the data in Table 1 for Example 1 and Comparative Example 5, even if the surface-modified intermediate alloy particles themselves have formed a gradient shell, if the addition is done in a single step, the phenomenon of increased continuous grain boundary network second phase, decreased fracture strain, and accelerated dissolution rate will still occur. The main reason is that a single addition causes the particles to be released in a concentrated manner at the same time, resulting in a short-term increase in local calcium concentration, which weakens the redistribution effect of subsequent fixed-depth batch addition on the solidification process.

[0065] As can be seen from the data in Table 1 for Example 1 and Comparative Example 6, adding the intermediate alloy particles at a higher melt temperature will prevent the advantages of the surface-modified intermediate alloy particles from being fully utilized.

[0066] 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 soluble magnesium alloy, characterized in that, Includes the following steps: S1: The magnesium-calcium master alloy is mechanically crushed and sieved to obtain magnesium-calcium master alloy particles, which are then dried for later use. S2: Ethylene glycol and ammonium bifluoride are mixed to form a fluorine-containing suspension reaction system. The magnesium-calcium intermediate alloy particles obtained in S1 are added to the fluorine-containing suspension reaction system to carry out the reaction. S3: After the system obtained in S2 is cooled, argon gas is bubbled through deionized water and introduced into the space above the liquid surface for gaseous trace water pre-activation. Then, deionized water is added dropwise to the reaction system to continue the reaction. S4: After the S3 reaction is completed, the resulting product is filtered, washed and dried to obtain surface-modified intermediate alloy particles. S5: Weigh magnesium ingots, industrial pure aluminum ingots, aluminum-manganese master alloy, magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc according to the proportions and smelt them to obtain the matrix melt; S6: After adding the surface-modified intermediate alloy particles to the matrix melt in batches, gently stir after each addition. After the last batch of particles is added, keep it at a certain temperature and then pour and cool to obtain a soluble magnesium alloy. The weight ratio of ethylene glycol, ammonium bifluoride and magnesium-calcium intermediate alloy particles in step S2 is 5000g:330-390g:900-950g; The weight ratio of magnesium-calcium intermediate alloy particles to deionized water in step S3 is 900-950g:140-160g.

2. The preparation method according to claim 1, characterized in that, The magnesium-calcium intermediate alloy particles mentioned in step S1 have a particle size of 0.8-1.2 mm.

3. The preparation method according to claim 1, characterized in that, The reaction temperature in step S2 is 60℃, and the reaction time is 25-30 min.

4. The preparation method according to claim 1, characterized in that, In step S3, the argon flow rate is 400-500 mL / min; the reaction temperature is 48-52℃; and the reaction time is 10-15 min.

5. The preparation method according to claim 1, characterized in that, The specific steps of the smelting in step S5 are as follows: first, the magnesium ingot is completely melted at 720-730℃, and a magnesium alloy covering agent is added at the same time. Then, industrial pure aluminum ingot and aluminum-manganese master alloy are added and the temperature is raised to 735-740℃. Next, magnesium-nickel master alloy, magnesium-silicon master alloy and pure zinc are added. After slag removal, the temperature is lowered to 700-710℃ and magnesium alloy covering agent is added again.

6. The preparation method according to claim 1, characterized in that, The insulation temperature in step S6 is 700-705℃.

7. A soluble magnesium alloy, characterized in that, It is prepared by the method of any one of claims 1-6.

8. The soluble magnesium alloy according to claim 7, characterized in that, By mass percentage, it contains Al: 6.00%-6.20%, Zn: 0.005%-0.02%, Mn: 0.35%-0.45%, Ni: 0.30%-0.40%, Si: 0.01%-0.02%, Ca: 2.60%-3.00%, Fe: ≤0.005%, Cu: ≤0.005%, with the balance being magnesium and unavoidable impurities.

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