Antioxidant corrosion-resistant high-performance magnesium alloy as well as preparation method and application thereof

Abstract

The invention belongs to the technical field of metal material preparation, and particularly relates to an anti-oxidation corrosion-resistant high-performance magnesium alloy and a preparation method and application thereof.The magnesium alloy comprises, by mass, 10%-13% of Gd, 0.95%-3% of Y, 0.44%-0.61% of Al and the balance Mg, the total percentage is 100%, and the anti-oxidation corrosion-resistant high-performance magnesium alloy is prepared by optimizing alloy components, accurately controlling microelements in the alloy and particularly adding a proper amount of rare earth elements. And the elements can form a layer of compact protective film on the surface of the alloy, so that invasion of a corrosive medium is effectively prevented. Meanwhile, the microstructure of the magnesium alloy is optimized and the corrosion sensitivity of a grain boundary and a precipitated phase is reduced by regulating and controlling the microstructure and controlling the solidification process and subsequent heat treatment of the alloy, so that the overall corrosion resistance is improved.

Description

Technical Field

[0001] The present invention belongs to the technical field of metal material preparation, and in particular relates to an oxidation-resistant and corrosion-resistant high-performance magnesium alloy and a preparation method and application thereof. Background Art

[0002] When astronauts return to Earth, they usually take specially designed spacecraft, which are called "return capsules" or "reentry capsules." In addition to manned missions, lunar probe series missions such as China's Chang'e 5 also require sample return capsules to return lunar samples to Earth. The return process usually includes re-entry, descent, landing and other stages, each of which has strict safety measures and procedures. These return capsules or spacecraft are equipped with special thermal protection systems. During the mission, especially during the re-entry stage, the return capsule faces extremely high temperatures and friction, which places extremely high demands on the materials inside and outside the capsule. Although the existing cabin materials of the return capsule have a certain strength, they still need to be improved in terms of oxidation resistance and corrosion resistance.

[0003] With the continuous development of aerospace technology, the performance requirements for space return capsules are getting higher and higher. Especially in deep space exploration and manned space missions, more stringent requirements are placed on the lightweight, anti-oxidation and corrosion resistance of the return capsule. Traditional commercial magnesium alloys, as the cabin material of the return capsule, are prone to oxidation at high temperatures when re-entering the atmosphere, affecting the mechanical properties and structural integrity of the material. In addition, traditional magnesium alloys are not stable enough in a variety of corrosive environments, especially in harsh environments such as salt water and acid rain. They are prone to corrosion, affecting the long-term reliability of spacecraft. Summary of the invention

[0004] In view of the deficiencies of the above-mentioned prior art, the purpose of the present invention is to provide an oxidation-resistant and corrosion-resistant high-performance magnesium alloy and a preparation method and application thereof. The present invention improves the oxidation resistance of the magnesium alloy material at high temperatures by optimizing the alloy elements, and enhances the corrosion resistance of each alloy in various environments by optimizing the total elements and regulating the surrounding structure.

[0005] In order to solve the above technical problems, the present invention adopts the following technical methods: A high-performance magnesium alloy with oxidation resistance and corrosion resistance, comprising, by mass percentage, 10% to 13% Gd, 0.95% to 3% Y, 0.44% to 0.61% Al, and the remainder being Mg, which totals 100%.

[0006] The second object of the present invention is to provide a method for preparing the above-mentioned oxidation-resistant and corrosion-resistant high-performance magnesium alloy, comprising the following steps: Pure Mg, pure Al, Mg-Gd master alloy, and Mg-Y master alloy are used as raw materials, 10wt.%~13wt.% Gd, 0.95wt.%~3wt.% Y, 0.44wt.%~0.61wt.% Al, and the balance Mg are mixed, and the mixture is melted after preheating. After the melting is completed, the mixture is stirred and kept warm.

[0007] After that, the temperature is reduced and refined, the steel is cooled in the furnace, the slag is skimmed off, and casting is carried out.

[0008] After casting, solution treatment and aging treatment are carried out to obtain an oxidation-resistant and corrosion-resistant high-performance magnesium alloy.

[0009] Pure magnesium uses commercial magnesium ingots with a purity of ≥99.99%. Magnesium ingots purified by vacuum distillation are selected to ensure that the impurity content is extremely low, especially the content of harmful elements such as iron, nickel, and copper is controlled below a few ten-thousandths.

[0010] Pure aluminum uses commercial aluminum ingots with a purity of ≥99.99%.

[0011] In a preferred embodiment of the present invention, the magnesium alloy comprises, by mass percentage, 10% to 12% Gd, 0.95% to 1.25% Y, 0.44% to 0.5% Al, and the remainder is Mg, which totals 100%.

[0012] Mg-Gd master alloy: It is made by melting pure magnesium and gadolinium in a certain proportion, and can be Mg-10wt%Gd master alloy, Mg-20wt%Gd master alloy, or Mg-30wt%Gd master alloy.

[0013] Mg-Y master alloy: It is made by melting pure magnesium and yttrium in a certain proportion, and can be Mg-10wt%Y master alloy, Mg-20 wt%Y master alloy, or Mg-30 wt%Y master alloy.

[0014] Both master alloys are prepared by vacuum melting to ensure uniform distribution of alloy elements and high element recovery rate.

[0015] All raw materials are strictly dried before smelting to remove moisture and oil adsorbed on the surface.

[0016] The raw materials are preheated using a precision temperature control system to ensure uniformity and stability of the preheating temperature.

[0017] The resistance crucible furnace is thoroughly cleaned before melting to avoid contamination of the melt.

[0018] The furnace atmosphere is protected by SF6 / CO2 mixed gas, and the gas ratio is precisely calculated to optimize the protection effect.

[0019] Raw material dosage: The mass ratio is: Mg-10~13 wt%Gd-0.95~3 wt%Y-0.44wt.%~0.61wt.%Al, pure magnesium: determined according to the total amount of the final alloy, usually the main component of the total mass of the alloy. Mg-Gd, Mg-Y master alloy, Al: added in proportions according to the design requirements of the alloy composition.

[0020] The above raw materials are preheated to 180°C-220°C to reduce the temperature gradient during the smelting process and improve the smelting efficiency. By preheating the raw materials to this precise temperature range, the uniform melting of the raw materials is promoted, the smelting time is reduced, and it is also conducive to the uniform distribution of alloy elements in the subsequent melt. In addition, the implementation of preheating also helps to reduce the boiling and splashing of the melt caused by excessive temperature differences, thereby ensuring the safety and stability of the smelting process.

[0021] Melting pure magnesium: The preheated pure magnesium is placed in a pit-type resistance crucible furnace equipped with SF6 / CO2 gas protection to create an oxygen-free or low-oxygen heating environment. During the heating process, the operator needs to closely monitor the temperature changes in the furnace, as well as the flow and pressure of the SF6 / CO2 gas, and start the heating device to gradually melt the magnesium ingot. The melting of pure magnesium adopts a step-by-step heating method, and the heating rate is controlled at 5°C / min~10°C / min. After trial, this heating rate can not only effectively reduce the burning of magnesium during the melting process, but also avoid the violent boiling of the melt and the evaporation loss of magnesium elements caused by too fast heating. The smooth and uniform melting process of magnesium is an important step, so as to maintain the composition of magnesium to the greatest extent. During the heating process, the pure magnesium ingot gradually changes from solid to liquid. There is no visible obvious oxidation phenomenon in the whole process. The surface of the magnesium liquid is smooth and the color is uniform, which indicates the successful completion of the melting stage.

[0022] Adding Mg-Gd master alloy: When the temperature in the furnace is stabilized at 720-740°C, the Mg-Gd master alloy is gradually added to the melt until it is completely melted. Specifically, the operator needs to use a special feeding tool to gradually add the pre-weighed Mg-Gd master alloy to the melted pure magnesium liquid at a slow and uniform rate. Control of the addition speed is crucial to avoid a sudden drop in the melt temperature or local overheating caused by adding too quickly. The master alloy should be added in batches, and each batch needs to be waited for a while after addition to allow it to be fully dispersed and melted in the melt until all the Mg-Gd master alloy is completely integrated into the magnesium liquid to form a uniform alloy melt.

[0023] Adding Mg-Y master alloy: When the melt temperature rises back to 720°C-740°C again, slowly add the Mg-Y master alloy to ensure that it is fully melted. Specifically: after the Mg-Gd master alloy is completely melted and evenly distributed, adjust the melt temperature again and stabilize it within the appropriate range of 720°C-740°C. Then, slowly add the Mg-Y master alloy in the same way as adding the Mg-Gd master alloy. During the addition process, the operator needs to continue to stir the melt to promote uniform dissolution and element distribution of the Mg-Y master alloy. The purpose of this step is to ensure that the yttrium element in the Mg-Y master alloy can be fully combined with other elements in the magnesium liquid.

[0024] Add pure Al: After the furnace temperature is raised to 760°C, pure Al is added. After it is melted, the surface scum is skimmed off. Specifically, after the addition and melting of the Mg-Y master alloy, the furnace temperature is gradually raised to 760°C to prepare for the addition of pure Al. After the furnace temperature reaches the predetermined value and remains stable, the precisely weighed pure aluminum is slowly added to the melt in a certain order of addition. The addition speed of pure aluminum needs to be strictly controlled to prevent drastic fluctuations in the melt temperature and ensure that the aluminum element can be evenly distributed in the alloy melt.

[0025] Stirring and keeping warm: The melt is stirred for 15-25 minutes to ensure uniform composition. The furnace temperature is then raised to 780°C and kept warm for 20 minutes. Specifically, after adding all the master alloys to the melt and ensuring that they are completely melted, the next step is the critical stirring and insulation step. The operator will use a special stirring rod to fully stir the melt for 15-25 minutes. The purpose of stirring is to ensure that the various elements in the melt, including magnesium, gadolinium, yttrium and aluminum, can be evenly distributed at the microscopic level, thereby ensuring the composition consistency of the final alloy product. The stirring speed should be controlled within an appropriate range to avoid excessive eddy currents and splashing to reduce oxidation of the melt and burnout of elements. After stirring, the furnace temperature is gradually raised to 780°C and kept warm at this temperature for 20 minutes. This step helps to eliminate tiny bubbles in the melt, promote the homogenization of the melt, and create ideal conditions for subsequent refining processes.

[0026] Cooling and refining: The furnace temperature is lowered to 750°C-755°C for a refining process without power outages for 6-15 minutes. During this process, the furnace temperature may rise to 760°C-785°C. Specifically: After completing the insulation step, the operator begins to gradually lower the furnace temperature to 750°C-755°C in preparation for the refining process. Refining is carried out without power outages, with the aim of removing non-metallic inclusions and gases from the melt and further improving the purity of the alloy. The refining process lasts for 6-15 minutes, during which the operator needs to closely monitor the temperature and state of the melt. Since a certain amount of heat may be released during the refining process, the furnace temperature may rise to 760°C-785°C. At this time, the operator should adjust the heating power in a timely manner to maintain the furnace temperature within the optimal range required for refining.

[0027] Skimming and Cooling: Cool down to 690°C-720°C with the furnace, and skim off the surface scum again to prepare for casting. Specifically: After refining is completed, the operator will stop heating and allow the melt to cool naturally to 690°C-720°C with the furnace. This temperature range is the ideal temperature for casting, which can ensure the fluidity of the melt and reduce the coarsening of the grains. During the cooling process, the scum and oxide layer on the surface of the melt will gradually emerge. The operator needs to use the skimming tool to carefully skim off these impurities again after the temperature drops to the predetermined range. This step is crucial to ensure the surface quality and mechanical properties of the final alloy product. The skimming operation should be carried out carefully to avoid damaging the melt surface and affecting the casting quality. After the skimming is completed, the melt can enter the final casting stage.

[0028] Mold preheating: When using a steel mold for casting, preheat the mold to 200°C-250°C to reduce the cooling rate during the casting process and avoid cracks in the casting.

[0029] Standing time control: The standing time of the refined melt is controlled between 25-40 minutes to ensure uniform composition and reduce pores and inclusions.

[0030] Casting: Under the above process parameters, the melt is slowly poured into the preheated mold to complete the casting process.

[0031] Solution treatment Purpose: To fully dissolve the strengthening phase in the alloy and obtain a uniform solid solution.

[0032] Parameters: Heating temperature: 490°C-510°C, insulation time: 2 hours-5 hours.

[0033] Cooling method after holding: water quenching, cooling rate not less than 200°C / min.

[0034] Note: In Mg-Al-Gd alloys, common second phases include AlGd phase, Mg5Gd phase and possible Al2Gd phase. These phases play a strengthening role in the alloy, but they need to be fully dissolved in the solution treatment process. Al2Gd cannot be dissolved. Dissolve the phases other than Al2Gd so that they can be re-precipitated evenly in the subsequent aging treatment to form fine and evenly distributed strengthening particles. In the solution treatment stage, the heating temperature, holding time and heating rate must be accurately controlled to promote the dissolution of these second phases. The heating temperature is set within the range that can effectively dissolve the second phase but does not cause overheating of the alloy and excessive grain growth, usually between 490°C-510°C. The length of the holding time needs to be adjusted according to the composition of the alloy and the heating temperature to ensure that all second phases can be fully dissolved. The holding time is generally set to 2 hours to 3 hours, and the heating rate is controlled to not exceed 100°C / hour during this period to avoid melt inhomogeneity and internal stress concentration caused by overheating. Through such fine control, the second phase in the Mg-Al-Gd alloy can be fully dissolved and the uniformity of the solid solution is guaranteed, creating good prerequisites for subsequent aging treatment, thereby ultimately obtaining excellent mechanical properties and corrosion resistance.

[0035] The purpose of aging treatment is to precipitate fine strengthening phases through aging to improve the strength and hardness of the alloy.

[0036] Parameters: Aging temperature: 120°C-220°C, insulation time: 6 hours-24 hours, heating rate: no more than 50°C / hour.

[0037] Cooling method: air cooling to room temperature.

[0038] Through the above-mentioned carefully designed aging treatment process, the strengthening phase in the Mg-Al-Gd-Y alloy can be precipitated uniformly and finely, thereby significantly improving the yield strength, tensile strength and hardness of the alloy, while maintaining good plasticity and toughness, providing reliable material guarantee for high-demand application scenarios such as space return capsules. In addition, aging treatment can also improve the corrosion resistance of the alloy, extend its service life, reduce maintenance costs, and provide important support for the long-term stable operation of spacecraft.

[0039] Oxidation resistance: When the space capsule re-enters the Earth's atmosphere, it will experience extremely high temperatures. This is because the heat generated by friction with the atmosphere can cause the surface temperature of the capsule to rise to thousands of degrees Celsius. Therefore, the outer surface of the return capsule often needs to be coated with high-temperature resistant and oxidation-resistant materials. Although the structural materials on the inner wall of the cabin do not need to serve as harshly as the outer wall of the cabin, their high-temperature oxidation resistance often needs to be considered. This is because during the re-entry process, the inner wall material of the cabin will also face the challenge of rising temperatures. Although it is not as directly exposed to high-temperature gases as the outer wall, the increase in internal temperature may still affect the electronic equipment, scientific samples, and the comfort and safety of the occupants in the cabin. Therefore, the inner wall material must have good high-temperature stability and oxidation resistance to ensure the stability of the cabin environment and the normal operation of the equipment in extreme thermal environments.

[0040] Corrosion resistance: Corrosion resistance is an important design requirement throughout the service life of a spacecraft. Spacecraft may be exposed to a variety of corrosive environments, including the vacuum of space, ultraviolet radiation, extreme temperature changes, and humidity and chemical corrosion in the Earth's atmosphere. Therefore, the materials of the return capsule need to have a certain degree of corrosion resistance to ensure long-term reliability and life. Especially when the landing location of the return capsule is uncertain, the complexity of the environment needs to be taken into account: 1. Terrain diversity: The return capsule may land on a variety of terrains, including plains, mountains, waters, deserts, forests, etc., and each terrain has its own specific challenges.

[0041] 2. Climate variability: The climate conditions at the landing site may be extremely variable, including extreme temperatures such as high or low temperatures, strong winds, precipitation, rain, snow, hail, etc.

[0042] 3. Wide geographical distribution: The potential landing area of ​​the return capsule may cover multiple latitudes and longitudes around the world, which requires the return capsule to be able to adapt to different geographical environments.

[0043] The above content requires that the lightweight, oxidation-resistant, and corrosion-resistant magnesium alloy designed in the present invention for use in the "space return capsule" must meet corrosion resistance standards to ensure stability and reliability in complex and changing environments.

[0044] The beneficial effects of the present invention are: 1. The addition of specific elements, such as Gd, Y, and Al, in the oxidation-resistant and corrosion-resistant high-performance magnesium alloy of the present invention not only improves the oxidation resistance of the material, but also enhances its structural stability at high temperatures, so that the return capsule as a whole can still maintain its mechanical properties and structural integrity in a high-temperature environment caused by drastic temperature changes and high-speed friction. The oxidation resistance of the magnesium alloy of the present invention is manifested in that it can form an extremely stable oxide film Gd2O3 in a high-temperature environment, and its oxidation performance is significantly better than that of traditional magnesium alloys. This oxide film effectively prevents oxygen from further diffusing into the interior of the alloy material, protecting the base material from oxidation damage when it re-enters the Earth's atmosphere.

[0045] 2. The present invention mainly optimizes the alloy composition and precisely controls the trace elements in the alloy, especially by adding an appropriate amount of rare earth elements, to enhance the corrosion resistance of the magnesium alloy. These elements can form a dense protective film on the surface of the alloy, effectively preventing the invasion of corrosive media. At the same time, the present invention optimizes the microstructure of the magnesium alloy through microstructure regulation, controls the solidification process of the alloy and subsequent heat treatment, reduces the corrosion sensitivity of the grain boundary and the precipitated phase, and thus improves the overall corrosion resistance. A corrosion coupon test was conducted in a simulated marine environment with a 3.5% NaCl solution, and the corrosion rate was 0.016 mg / cm 2 / d, and has excellent corrosion resistance, ensuring that the alloy components of the present invention can maintain good corrosion resistance even in a marine environment. BRIEF DESCRIPTION OF THE DRAWINGS

[0046] Figure 1 This is a scanning electron microscope image of the cast state of the Mg-10.14Gd-1.25Y-0.53Al alloy prepared in Example 1 of the present invention.

[0047] Figure 2 This is a scanning electron microscope image of the cast state of the Mg-11.48Gd-0.95Y-0.44Al alloy prepared in Example 2 of the present invention.

[0048] Figure 3 This is a scanning electron microscope image of the cast state of the Mg-12.67Gd-1.45Y-0.61Al alloy prepared in Example 3 of the present invention.

[0049] Figure 4 This is a magnified electron microscope image of the second phase of the cast Mg-10.14Gd-1.25Y-0.53Al alloy prepared in Example 1 of the present invention under a scanning electron microscope.

[0050] Figure 5 These are morphology diagrams of the Mg-10.14Gd-1.25Y-0.53Al alloy of Example 1 of the present invention after oxidation for different times.

[0051] Figure 6This is a graph showing the anti-oxidation results of the Mg-10.14Gd-1.25Y-0.53Al alloy prepared in Example 1 of the present invention. DETAILED DESCRIPTION

[0052] The following is a detailed description of the technical solutions in the embodiments of the present invention in combination with the preferred embodiments and the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of them. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0053] It should be noted that all professional terms used in the present invention are only for the purpose of describing specific embodiments and are not intended to limit the scope of protection of the present invention. Unless otherwise specifically stated, various raw materials, reagents, instruments and equipment used in the following embodiments of the present invention can be purchased from the market or prepared by existing methods.

[0054] Example 1 A method for preparing a Mg-10.14Gd-1.25Y-0.53Al alloy comprises the following steps: (1) Pure magnesium, pure aluminum, Mg-Gd master alloy, and Mg-Y master alloy were mixed in a mass percentage of 10.14% Gd, 1.25% Y, 0.5% Al, and the balance Mg, and preheated at 200°C.

[0055] (2) The preheated raw materials are added into a melting furnace in the order of pure magnesium, Mg-Gd master alloy, Mg-Y master alloy and pure Al for melting to obtain a mixed melt.

[0056] (3) The mixed melt is stirred for 20 minutes, and then the temperature in the furnace is raised to 780°C and kept at this temperature for 20 minutes; then the furnace temperature is lowered to 753°C and a refining process is carried out without power outage for 8 minutes, and then the furnace is cooled to 700°C, and the surface scum is skimmed off to prepare for casting.

[0057] (4) Use a steel mold for casting. Preheat the mold to 230°C. The standing time of the refined melt is controlled within 30 minutes. Then, under the above-mentioned process parameters, slowly pour the melt into the preheated mold to complete the casting process.

[0058] (5) The cast alloy was heated to 500°C for solution treatment with a holding time of 3 hours, and then aging treatment was performed at 180°C with a holding time of 12 hours, finally obtaining an oxidation-resistant and corrosion-resistant high-performance Mg-10.14Gd-1.25Y-0.53Al alloy.

[0059] Example 2 A method for preparing a Mg-11.48Gd-0.95Y-0.44Al alloy comprises the following steps: (1) Pure magnesium, pure aluminum, Mg-Gd master alloy, and Mg-Y master alloy were mixed in a mass percentage of 11.48% Gd, 0.95% Y, 0.44% Al, and the balance Mg, and preheated at 200°C.

[0060] (2) The preheated raw materials are added into a melting furnace in the order of pure magnesium, Mg-Gd master alloy, Mg-Y master alloy and pure Al for melting to obtain a mixed melt.

[0061] (3) The mixed melt is stirred for 20 minutes, and then the temperature in the furnace is raised to 780°C and kept at this temperature for 20 minutes; then the furnace temperature is lowered to 753°C and a refining process is carried out without power outage for 8 minutes, and then the furnace is cooled to 700°C, and the surface scum is skimmed off to prepare for casting.

[0062] (4) Use a steel mold for casting. Preheat the mold to 230°C. The standing time of the refined melt is controlled within 30 minutes. Then, under the above-mentioned process parameters, slowly pour the melt into the preheated mold to complete the casting process.

[0063] (5) The cast alloy was heated to 500°C for solution treatment with a holding time of 3 hours, and then aging treatment was performed at 180°C with a holding time of 12 hours, finally obtaining an oxidation-resistant and corrosion-resistant high-performance Mg-11.48Gd-0.95Y-0.44Al alloy.

[0064] Example 3 A method for preparing a Mg-12.67Gd-1.45Y-0.61Al alloy comprises the following steps: (1) Pure magnesium, pure aluminum, Mg-Gd master alloy, and Mg-Y master alloy were mixed in a mass percentage of 12.67% Gd, 1.45% Y, 0.61% Al, and the balance Mg, and preheated at 200°C.

[0065] (2) The preheated raw materials are added into a melting furnace in the order of pure magnesium, Mg-Gd master alloy, Mg-Y master alloy and pure Al for melting to obtain a mixed melt.

[0066] (3) The mixed melt is stirred for 20 minutes, and then the temperature in the furnace is raised to 780°C and kept at this temperature for 20 minutes; then the furnace temperature is lowered to 753°C and a refining process is carried out without power outage for 8 minutes, and then the furnace is cooled to 700°C, and the surface scum is skimmed off to prepare for casting.

[0067] (4) Use a steel mold for casting. Preheat the mold to 230°C. The standing time of the refined melt is controlled within 30 minutes. Then, under the above-mentioned process parameters, slowly pour the melt into the preheated mold to complete the casting process.

[0068] (5) The cast alloy was heated to 500°C for solution treatment with a holding time of 3 hours, and then aging treatment was performed at 180°C with a holding time of 12 hours, finally obtaining an oxidation-resistant and corrosion-resistant high-performance Mg-12.67Gd-1.45Y-0.61Al alloy.

[0069] Example 4 A method for preparing a Mg-10.14Gd-1.25Y-0.53Al alloy comprises the following steps: (1) Pure magnesium, pure aluminum, Mg-Gd master alloy, and Mg-Y master alloy were mixed in a mass percentage of 10.14% Gd, 1.25% Y, 0.5% Al, and the balance Mg, and preheated at 200°C.

[0070] (2) The preheated raw materials are added into a melting furnace in the order of pure magnesium, Mg-Gd master alloy, Mg-Y master alloy and pure Al for melting to obtain a mixed melt.

[0071] (3) The mixed melt is stirred for 15 minutes, and then the temperature in the furnace is raised to 780°C and kept at this temperature for 20 minutes. The furnace temperature is then lowered to 750°C and a refining process is carried out without power outage for 6 minutes. The mixture is then cooled to 690°C in the furnace, and the scum on the surface is skimmed off in preparation for casting.

[0072] (4) Use a steel mold for casting. Preheat the mold to 230°C. The standing time of the refined melt is controlled within 30 minutes. Then, under the above-mentioned process parameters, slowly pour the melt into the preheated mold to complete the casting process.

[0073] (5) The cast alloy was heated to 490°C for solution treatment with a holding time of 2 hours, and then aging treatment was performed at 120°C with a holding time of 6 hours, thereby finally obtaining an oxidation-resistant and corrosion-resistant high-performance Mg-10.14Gd-1.25Y-0.53Al alloy.

[0074] Example 5 A method for preparing a Mg-10.14Gd-1.25Y-0.53Al alloy comprises the following steps: (1) Pure magnesium, pure aluminum, Mg-Gd master alloy, and Mg-Y master alloy were mixed in a mass percentage of 10.14% Gd, 1.25% Y, 0.5% Al, and the balance Mg, and preheated at 200°C.

[0075] (2) The preheated raw materials are added into a melting furnace in the order of pure magnesium, Mg-Gd master alloy, Mg-Y master alloy and pure Al for melting to obtain a mixed melt.

[0076] (3) The mixed melt is stirred for 25 minutes, and then the temperature in the furnace is raised to 780°C and kept at this temperature for 20 minutes; then the furnace temperature is lowered to 755°C and a refining process is carried out without power outage for 15 minutes, and then the mixture is cooled to 720°C with the furnace, and the scum on the surface is skimmed off to prepare for casting.

[0077] (4) Use a steel mold for casting. Preheat the mold to 230°C. The standing time of the refined melt is controlled within 30 minutes. Then, under the above-mentioned process parameters, slowly pour the melt into the preheated mold to complete the casting process.

[0078] (5) The cast alloy was heated to 510°C for solution treatment with a holding time of 5 hours, and then aging treatment was performed at 220°C with a holding time of 24 hours, thereby finally obtaining an oxidation-resistant and corrosion-resistant high-performance Mg-10.14Gd-1.25Y-0.53Al alloy.

[0079] Results Analysis Figure 1 This is a scanning electron microscope image of the Mg-10.14Gd-1.25Y-0.53Al alloy prepared in Example 1 of the present invention. It can be seen from the figure that the microstructure of the alloy is uniform, with fine grains and obvious second phase precipitation characteristics, showing good composition distribution and compatibility. The results show that the alloy has excellent fine grain strengthening effect in microstructure, which helps to improve its mechanical properties and corrosion resistance, proving its potential in high-performance applications.

[0080] Figure 2 This is a scanning electron microscope image of the Mg-11.48Gd-0.95Y-0.44Al alloy prepared in Example 2 of the present invention. It can be seen from the figure that the microstructure of the alloy also shows a uniform grain distribution, and the precipitation of the second phase is more obvious. The results show that after optimizing the element ratio, the alloy further enhances its strength and toughness, and shows good oxidation resistance and corrosion resistance.

[0081] Figure 3This is a scanning electron microscope image of the Mg-12.67Gd-1.45Y-0.61Al alloy prepared in Example 3 of the present invention. It can be seen from the figure that the microstructure of the alloy presents a more detailed grain distribution, and the precipitation of the second phase is more uniform, which enhances the overall strength of the material. The results show that after increasing the alloy element content, the alloy further optimizes its microstructural characteristics, improves its oxidation resistance and corrosion resistance, and shows excellent application potential in extreme environments.

[0082] Figure 4 This is a magnified electron microscope image of the second phase of the Mg-10.14Gd-1.25Y-0.53Al alloy cast under a scanning electron microscope prepared by the present invention. Figure 4 As can be seen in Figure (a), the metallographic components in the cast state include angular Al2Gd phase, rod-shaped Mg5Gd phase distributed in the white area, and short bone fishtail to petal-shaped (Mg, Al)3Gd phase. Among them, the precipitation of Al2Gd phase can effectively hinder the movement of dislocations, thereby significantly improving the yield strength and hardness of the alloy. This strengthening mechanism is crucial to improving the mechanical properties of the material. In addition, the Al2Gd phase has high thermal stability and can maintain its strengthening effect even in high temperature environments, which makes the alloy suitable for high temperature applications. Figure 4 As can be seen from Figures (b) and (c), the metallographic components contain a large amount of Mg5Gd phase in the cast state, and a large amount of Mg5Gd phase exists at the Gd segregation of the grain boundaries before the solid solution of this phase. This phase, as a cathode phase, increases the dissolution of the Mg anode, which is not conducive to improving the corrosion resistance of the magnesium alloy. This key problem is solved in the present invention by solid solution treatment at 420 degrees Celsius.

[0083] Figure 5 The morphology of the Mg-10.14Gd-1.25Y-0.53Al alloy of Example 1 of the present invention after oxidation for different times is shown. Through characterization, it is found that after the oxidation time reaches 150 h, dense oxidized particles have appeared on the surface, but the oxidized particles only exist in the Mg-rich area. In the Gd-rich area, that is, the Gd2O3 oxide layer is still intact without cracks. SEM intuitively shows that Gd enrichment will have a significant protective effect on the oxidation of Mg alloy. The antioxidant properties of the magnesium alloy of the present invention are manifested in that it can form a very stable oxide film Gd2O3 in a high temperature environment, and its oxidation performance is significantly better than that of traditional magnesium alloys. This oxide film effectively prevents oxygen from further diffusing into the interior of the alloy material, protecting the matrix material from oxidation when it re-enters the Earth's atmosphere.

[0084] Figure 6The antioxidant effect diagram of the Mg-10.14Gd-1.25Y-0.53Al alloy prepared in Example 1 of the present invention and the commercial Mg-Gd-Zr alloy shows that the alloy of the present invention exhibits lower oxidation weight gain and more stable oxide film during oxidation, indicating that its antioxidant performance is significantly better than that of the commercial alloy. The results show that the high-performance magnesium alloy can effectively resist oxidation in a high temperature environment, improving its application potential under harsh conditions.

[0085] In summary, the addition of specific elements, such as Gd, Y, and Al elements, in the oxidation-resistant and corrosion-resistant high-performance magnesium alloy of the present invention not only improves the oxidation resistance of the material, but also enhances its structural stability at high temperatures. This allows the return capsule as a whole to maintain its mechanical properties and structural integrity in a high-temperature environment caused by drastic temperature changes and high-speed friction. The oxidation resistance of the magnesium alloy of the present invention is manifested in its ability to form a very stable oxide film Gd2O3 in a high-temperature environment, and its oxidation performance is significantly better than that of traditional magnesium alloys. This oxide film effectively prevents oxygen from further diffusing into the interior of the alloy material, protecting the base material from oxidation damage when it re-enters the Earth's atmosphere.

[0086] In the description of this specification, the description with reference to the terms "one embodiment", "some embodiments", "example", "specific example", or "some examples" etc. means that the specific features, structures, materials or characteristics described in conjunction with the embodiment or example are included in at least one embodiment or example of the present invention. In this specification, the schematic representations of the above terms are not necessarily for the same embodiment or example. Moreover, the specific features, structures, materials or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, those skilled in the art may combine and combine the different embodiments or examples described in this specification and the features of the different embodiments or examples, without contradiction.

[0087] Although the embodiments of the present invention have been shown and described above, it is to be understood that the above embodiments are exemplary and are not to be construed as limitations of the present invention. A person skilled in the art may change, modify, replace and vary the above embodiments within the scope of the present invention.

Claims

1. An oxidation-resistant and corrosion-resistant high-performance magnesium alloy, characterized in that: The magnesium alloy comprises, by mass percentage, 10% to 13% Gd, 0.95% to 3% Y, 0.44% to 0.61% Al, and the remainder is Mg, which is 100% in total.

2. An oxidation-resistant and corrosion-resistant high-performance magnesium alloy, characterized in that: The magnesium alloy comprises, by mass percentage, 10% to 12% Gd, 0.95% to 1.25% Y, 0.44% to 0.5% Al, and the remainder is Mg, which is 100% in total.

3. A method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 1, characterized in that: The following steps are involved: Pure Mg, pure Al, Mg-Gd master alloy, and Mg-Y master alloy are used as raw materials, 10wt.%~13wt.% Gd, 0.95wt.%~3wt.% Y, 0.44wt.%~0.61wt.% Al, and the balance Mg are mixed, and the mixture is melted after preheating, and stirred and kept warm after the melting is completed; Then the temperature is reduced and refined, cooled with the furnace, the scum is skimmed off, and casting is carried out; After casting, solution treatment and aging treatment are carried out to obtain an oxidation-resistant and corrosion-resistant high-performance magnesium alloy.

4. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The smelting process is to firstly melt pure Mg, then add Mg-Gd master alloy for melting, then add Mg-Y master alloy, and finally add pure Al for melting to obtain a mixed melt.

5. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The stirring time is 15 minutes to 25 minutes, the insulation temperature is 780°C, and the insulation time is 20 minutes.

6. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The temperature is lowered to 750°C~755°C for refining, and the refining time is 6 minutes~15 minutes.

7. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The cooling temperature is 690°C~720°C.

8. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The solution treatment temperature is 490°C~510°C, and the solution treatment time is 2 hours~5 hours.

9. The method for preparing an oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 3, characterized in that: The aging treatment temperature is 120°C~220°C, and the aging treatment time is 6 hours~24 hours.

10. Use of the oxidation-resistant and corrosion-resistant high-performance magnesium alloy according to claim 1 in a thermal protection system inside a space return capsule.

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