A composite crucible for smelting aluminum-lithium alloy and a method of manufacturing the same

Abstract

The application discloses a composite crucible for smelting aluminum-lithium alloy and a preparation method thereof. The composite crucible is composed of an outer heat-resistant cast steel layer, a middle carbon fiber felt layer and an inner silicon carbide ceramic layer. The heat-resistant cast steel is one of ZG40Cr24Si2, ZG50Cr28Ni48W5 and ZG35Cr24Ni7NRE. The middle layer is a carbon fiber felt with a porosity of 30-70% prepared from mesophase pitch-based carbon fibers. The silicon carbide ceramic layer is composed of 85-90% silicon carbide, 5-8% SiO2 and 2-10% mullite. The preparation process of the crucible is simple. The main body of the crucible does not react with lithium, thereby ensuring the quality of the melt. The multi-layer structure makes it easier to replace and repair the damaged crucible, thereby prolonging the service life of the crucible. Meanwhile, the crucible is convenient to transfer and will not crack during the smelting process.

Description

Technical Field

[0001] This invention belongs to the field of melting crucible equipment, specifically relating to a composite crucible for melting aluminum-lithium alloys and its preparation method. Background Technology

[0002] Aluminum alloys, as lightweight alloys, possess the advantages of low density and high strength, and have broad application prospects in aviation, aerospace, and marine fields. Aluminum-lithium alloys are made by adding lithium to aluminum alloys. For every 1% of lithium added to an aluminum alloy, the alloy density decreases by 3% and the modulus increases by 6%. Compared to aluminum alloys, aluminum-lithium alloys have lower density and higher modulus, making them suitable for manufacturing parts such as missile hulls, hypersonic vehicle structural components, and the shells of weapons used in deep-sea diving.

[0003] In recent years, the requirements for lightweighting in aerospace equipment have been continuously increasing, and aluminum-lithium alloy components used in aerospace have gradually shifted from small, simple structures to large, complex devices. Large, complex aluminum-lithium alloy components can typically only be formed using sand casting. The crucible is one of the core pieces of equipment in the sand casting smelting process. Lithium is a highly chemically reactive element that easily reacts during smelting, causing the crucible to crack and reducing the quality of the melt. Therefore, this invention develops a crucible specifically for smelting aluminum-lithium alloys, improving the purity of the smelting process and extending the crucible's service life.

[0004] Currently, most common aluminum alloy melting crucibles are made of cermet or graphite. Cermet crucibles dissolve rapidly in aluminum-lithium alloys, causing elements such as Fe, Ni, and Cr to easily dissolve into the molten aluminum-lithium alloy. This reduces alloy purity and allows these elements to form compounds within the molten alloy, degrading its performance. Patent CN201010193417.6 (Composite Coating for Iron Crucibles in Aluminum Alloy Melting) discloses a composite coating for iron crucibles in aluminum alloy melting. Its key feature is the application of a composite coating to the crucible surface, using composite aggregates and thermal expansion buffers to address cracking caused by the difference in thermal expansion coefficients between the single coating and the crucible. However, practical experience shows that the composite coating has poor uniformity and flowability, resulting in poor adhesion between the coating and the crucible surface. During melting, the coating inevitably detaches from the crucible surface, contaminating the molten alloy. For graphite crucibles, small-radius lithium ions easily leach out from porous areas. Furthermore, during prolonged melting and holding, lithium and carbon readily react to form lithium carbide. This not only reduces the purity and performance of the aluminum-lithium alloy but also poses a risk of aluminum leakage after the crucible is corroded, thus shortening its service life. Patent CN 113698211 A (A coating for aluminum-lithium alloy melting crucibles and its preparation and coating method) discloses a coating for aluminum-lithium alloy melting crucibles and its preparation and coating method. Its key feature is the use of aluminum dihydrogen phosphate powder coated onto a graphite crucible substrate to solve the problem of poor adhesion between the coating and the crucible surface. In practice, this method can improve the adhesion between the coating and the crucible, but due to differences in thermal expansion coefficients, cracking still occurs after repeated use, affecting the graphite crucible substrate. Besides coating the crucible surface with a paint, a double-layer composite structure is usually used to improve the crucible's service life. Patent CN91104352.7 (Metal-Ceramic Composite Crucible and its Preparation Method) discloses a metal-ceramic composite crucible characterized by a double-layer structure consisting of an outer heat-resistant cast iron layer and an outer metal-ceramic layer, thus improving the crucible's service life. However, in practice, due to the significant difference in the thermal expansion coefficients between the heat-resistant cast iron layer and the metal-ceramic layer, the inner metal-ceramic layer is prone to cracking after long-term use, leading to a shortened lifespan. Furthermore, because the inner ceramic layer is directly composited with the metal layer, the inner ceramic layer is difficult to repair and replace. Patent CN113277867 A (A Preparation Method of a Carbon / Carbon / Silicon Carbide Composite Material Crucible) discloses a method for preparing a carbon / carbon / silicon carbide composite material crucible, characterized by carburizing the crucible surface using vapor deposition and then forming a dense silicon carbide coating on the surface through silicon infiltration to improve the crucible's corrosion resistance. In practice, this method improves the adhesion between the coating and the crucible through vapor deposition, but there is uneven carburization and siliconization, and local cracking occurs after repeated use.Patent CN 113073381.A (A Crucible with a Silicon Carbide / Silicon Composite Ceramic Layer) discloses a ceramic crucible with a silicon carbide and silicon composite layer. Its characteristic is the addition of a silicon carbide / silicon composite ceramic layer to the inner and outer surfaces of the carbon / carbon crucible to improve its corrosion and oxidation resistance. In practice, this improves the corrosion resistance of the carbon / carbon crucible. However, because the same silicon carbide / silicon composite ceramic is used in both the inner and outer layers, the expansion coefficients of the two layers differ from those of the intermediate carbon / carbon crucible. This leads to cracking of the inner and outer silicon carbide / silicon composite ceramic layers and the carbon / carbon crucible after repeated use. Furthermore, the silicon carbide ceramic layer is only 0.5-2 mm thick, which is relatively thin, causing corrosion on the surface of the aluminum-lithium alloy liquid and resulting in performance degradation.

[0005] In summary, this invention argues that, in response to current problems in aluminum-lithium alloy smelting such as aluminum leakage, cracking, and reaction with the molten alloy, it is necessary to develop a new type of crucible for aluminum-lithium alloy smelting. This crucible must not only ensure that the crucible body itself does not react with the molten aluminum-lithium alloy, but also prevent cracking of the crucible body due to thermal expansion during high-temperature smelting, effectively improving the service life of the crucible. The development of such a crucible has significant engineering application value for the further development of large aluminum-lithium alloy castings in key fields such as aerospace. Summary of the Invention

[0006] To address the shortcomings of existing technologies, this invention provides a composite crucible for aluminum-lithium alloy smelting and its preparation method, which can improve the service life of the aluminum-lithium alloy smelting crucible and the quality of the aluminum-lithium alloy melt.

[0007] To achieve the aforementioned effects, this invention develops a novel crucible for melting aluminum-lithium alloys. This differs significantly from existing crucible technologies. Current methods for improving the quality of aluminum-lithium alloy melts and crucible lifespan involve directly coating the surface of graphite or cermet crucibles with a coating. However, this process suffers from poor adhesion and differences in thermal expansion coefficients between the coating and the crucible, leading to cracking and subsequent reaction between the aluminum-lithium alloy melt and the coating, resulting in melt contamination. This invention addresses these issues by proposing a novel three-layer composite melting crucible structure to improve crucible lifespan and chemical stability.

[0008] Specifically, this is achieved through the following technical solutions:

[0009] This invention provides a composite crucible for melting aluminum-lithium alloys, comprising a silicon carbide ceramic inner layer, a carbon fiber felt middle layer, and a heat-resistant cast steel outer layer. The composite crucible of this invention adopts a three-layer composite structure, consisting of an inner silicon carbide ceramic layer, a middle carbon fiber felt layer, and an outer heat-resistant cast steel layer.

[0010] In one embodiment of the present invention, the thickness of the silicon carbide ceramic inner layer is 15-20 mm, and the mass fraction of silicon carbide reaches 85%-90%. Silicon carbide ceramic, as the inner layer material of the crucible, has advantages such as good thermal conductivity, non-oxidation, non-aging, and high temperature resistance. Silicon carbide has a high sublimation temperature (approximately 2700℃), and with the increase of silicon carbide content, its oxidation resistance is better and its lifespan is longer. Furthermore, thermodynamic tests have shown that silicon carbide does not react with aluminum-lithium alloy liquid at high temperatures. Therefore, no coating is needed to ensure the melt quality, avoiding the problem of alloy contamination caused by poor adhesion between the coating and the crucible. Adding SiO2 and mucilage to the silicon carbide ceramic layer further improves the heat resistance and stability of the silicon carbide ceramic. During sintering, SiO2 forms a thin film on the silicon carbide surface, binding the silicon carbide particles together. Mucilage is a high-quality refractory material with characteristics such as uniform expansion, excellent thermal shock resistance, high load softening point, low high-temperature creep value, high hardness, and good chemical corrosion resistance. Sintering it with silicon carbide results in silicon carbide ceramics with superior high-temperature performance. A silicon carbide ceramic layer that is too thin will cause the crucible to crack at high temperatures, while a layer that is too thick will cause uneven heating of the inner layer. Therefore, the thickness of the silicon carbide ceramic layer is 15-20 mm.

[0011] In one embodiment of the present invention, the thickness of the carbon fiber felt interlayer is 5-10 mm, and the porosity is 30-70%. The interlayer is made of carbon fiber felt, which has a low coefficient of thermal expansion, good thermal conductivity, good high-temperature resistance, and good resistance to rapid cooling and heating. Using carbon fiber felt as the interlayer provides several advantages: firstly, the carbon fiber in the interlayer has good compatibility with the matrix, effectively isolating heat transfer between the inner silicon carbide ceramic layer and the heat-resistant cast iron layer, thus mitigating thermal mismatch between the silicon carbide ceramic layer and the heat-resistant cast steel layer. Secondly, using carbon fiber as the interlayer effectively avoids cracking caused by the difference in thermal expansion coefficients between the inner and outer layers during use. Furthermore, using carbon fiber as the interlayer material facilitates easy removal and replacement of the silicon carbide layer, allowing the heat-resistant cast iron layer to continue to be used, facilitating the repair of the crucible's inner layer, and reducing costs. Too thin a carbon fiber layer will result in poor insulation, while too thick a layer will reduce adhesion between the carbon fiber layer and the inner silicon carbide ceramic layer; therefore, the thickness of the carbon fiber interlayer is 5-10 mm.

[0012] In one embodiment of the present invention, the thickness of the heat-resistant cast steel outer layer is 15-25 mm. The heat-resistant cast steel is one of ZG40Cr24Si2, ZG50Cr28Ni48W5, or ZG35Cr24Ni7NRE. This type of heat-resistant cast steel possesses excellent properties such as high temperature resistance, corrosion resistance, and wear resistance. Compared with similar heat-resistant steel products, its service life can be increased by 1-3 times, and its material cost is reduced by 5%-15%. It can be used continuously at high temperatures, has good resistance to thermal fatigue and high temperature, and is not prone to thermal cracking after repeated use. This avoids the technical problems of the original crucible base being prone to cracking under the action of thermal expansion force at high temperatures and cracking due to poor thermal shock resistance after repeated use. If the thickness of the heat-resistant cast steel layer is too thin, the strength of the crucible will decrease, leading to cracking during the melting process. If the thickness is too thick, it will increase the weight of the crucible, which is not conducive to movement during the melting process. Therefore, the thickness of the heat-resistant cast steel layer is 15-25 mm.

[0013] The present invention also provides a method for preparing the composite crucible, the method comprising the following steps:

[0014] (1) Mix silicon carbide ceramic material with deoxidizer and binder, press into shape, dry and sinter to obtain silicon carbide ceramic inner layer;

[0015] (2) A resin adhesive is coated on the outer surface of the silicon carbide ceramic inner layer, and the carbon fiber felt layer is bonded to the outer surface of the silicon carbide ceramic inner layer. After drying, a composite structure including a carbon fiber felt intermediate layer and a silicon carbide ceramic inner layer is obtained.

[0016] (3) The composite structure is placed in the inner cavity of the heat-resistant cast steel outer layer, heated and kept warm to obtain the composite crucible.

[0017] In one embodiment of the present invention, in step (1), the silicon carbide ceramic material comprises silicon carbide particles with a mass fraction of 85%–90%, 2–10% munetite, and 5%–8% SiO2; the deoxidizer comprises 2–4% of the silicon carbide ceramic material, preferably 3%; and the binder comprises 2–4% of the silicon carbide ceramic material, preferably 3%. The mass fractions of the deoxidizer and binder are relative to the mass fractions of the raw materials.

[0018] As one embodiment of the present invention, in step (1), the oxygen scavenger is C+B4C with a mass ratio of 1-3:1, preferably 2:1; the adhesive is epoxy resin.

[0019] As one embodiment of the present invention, in step (1), the sintering temperature is 1900-2100℃ and the time is 1-2.5h; preferably 2000℃ for 2h.

[0020] In one embodiment of the present invention, in step (2), the resin binder is epoxy resin. Drying is performed at room temperature for 1 to 2 hours.

[0021] In one embodiment of the present invention, in step (3), the heating temperature is 700-800℃, and the holding time is 1-2 hours. Heating is performed in stages: first, the temperature is raised to 450-550℃ and held for 0.5-1 hour, preferably at 500℃ for 0.5 hours; then the temperature is raised to 700-800℃ and held for 1-2 hours to allow the adhesive to fully fuse. Heating carbonizes the resin adhesive, causing the three-layer composite structure to dry and solidify.

[0022] As one embodiment of the present invention, in step (3), the heat-resistant cast steel outer layer is prepared by sand casting; the gap between the inner cavity of the heat-resistant cast steel outer layer and the carbon fiber felt layer is 0.5 to 1 mm.

[0023] The crucible of this invention has a simple manufacturing process, is easy to produce, and has high production efficiency, making it highly practical.

[0024] Compared with the prior art, the present invention has the following advantages:

[0025] 1) This invention adds a heat-resistant carbon fiber felt layer between the inner ceramic layer and the metal layer, which can enhance the thermal insulation performance and also has a certain degree of elasticity, preventing the problem of mismatch between the thermal expansion coefficients of ceramic and metal, resulting in a longer service life and easier replacement and repair of the inner layer.

[0026] 2) By selecting silicon carbide as the inner layer material, this invention inhibits the reaction between the active aluminum-lithium alloy liquid and the crucible, avoids contamination of the alloy melt, and improves the melt quality.

[0027] 3) This invention uses a three-layer composite structure to provide a crucible specifically for aluminum-lithium alloy melting. The preparation process is simple and suitable for industrial production and application. Attached Figure Description

[0028] Other features, objects, and advantages of the present invention will become more apparent from the following detailed description of non-limiting embodiments with reference to the accompanying drawings:

[0029] Figure 1 This is a schematic diagram of the longitudinal section of the crucible prepared in Embodiment 1 of the present invention, wherein 1-heat-resistant cast steel outer layer, 2-carbon fiber felt middle layer, and 3-silicon carbide ceramic inner layer. Detailed Implementation

[0030] The present invention will now be described in detail with reference to the accompanying drawings and specific embodiments. The following examples are implemented under the premise of the technical solution of the present invention, providing detailed implementation methods and specific operating procedures, which will help those skilled in the art to further understand the present invention. It should be noted that the scope of protection of the present invention is not limited to the following embodiments; any adjustments and improvements made under the concept of the present invention are all within the scope of protection of the present invention.

[0031] Example 1

[0032] This embodiment describes a composite crucible for melting aluminum-lithium alloys, such as... Figure 1 As shown, it is composed of a silicon carbide ceramic inner layer 3, a carbon fiber felt middle layer 2, and a heat-resistant cast steel outer layer 1.

[0033] (1) Silicon carbide ceramic layer:

[0034] 90% silicon carbide particles, 5% mune, 5% SiO2 raw materials, 3% oxygen scavenger C+B4C (mass ratio 2:1), and 3% epoxy resin binder were thoroughly mixed and placed in a mold. The mixture was then held under 90 MPa pressure for 60 s, dried in a drying oven at 60 °C for 2 h, and then sintered at 2050 °C for 1 h. After demolding, a silicon carbide ceramic layer was obtained, with a measured thickness of 15 mm.

[0035] (2) Carbon fiber felt interlayer

[0036] A layer of resin adhesive (epoxy resin) is applied to the outer surface of the silicon carbide ceramic layer. A carbon fiber felt intermediate layer with a porosity of 50% prepared from pitch-based carbon fiber is then bonded to the outer surface of the silicon carbide ceramic layer. After drying at room temperature for 2 hours, a composite structure of carbon fiber felt layer and silicon carbide ceramic layer is obtained. The thickness of the carbon fiber felt layer is 5 mm.

[0037] (3) Heat-resistant cast steel outer layer

[0038] The outer heat-resistant cast steel is ZG40Cr24Si2 heat-resistant cast steel with a thickness of 15mm. The composite structure of carbon fiber felt layer and silicon carbide ceramic layer is placed in the inner cavity of heat-resistant cast steel layer prepared by sand casting. The gap between the inner cavity of heat-resistant cast steel layer and carbon fiber felt layer is 1mm.

[0039] The composite structure consisting of a heat-resistant cast steel layer, a middle carbon fiber felt layer, and an inner silicon carbide ceramic layer is heated to 500°C in an electric resistance furnace and held for 0.5 hours. Then, the temperature is raised to 780°C and held for 1.5 hours to carbonize the resin binder and dry and solidify the three-layer composite structure, resulting in a composite crucible for aluminum-lithium alloy smelting.

[0040] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.15wt%Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.09%, Si: 0.09%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.09%, Si: 0.09%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0041] Example 2

[0042] The preparation method in this embodiment is the same as in Example 1, except that:

[0043] The thickness of the silicon carbide ceramic layer is 20 mm.

[0044] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0045] Example 3

[0046] The preparation method in this embodiment is the same as in Example 1, except that:

[0047] The thickness of the silicon carbide ceramic layer is 25 mm.

[0048] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.09%, Ni: 0.004%, Cr: 0.004%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.09%, Si: 0.08%, Ni: 0.004%, Cr: 0.004%, and the impurity content did not increase.

[0049] Example 4

[0050] The preparation method in this embodiment is the same as in Example 1, except that:

[0051] The thickness of the heat-resistant cast iron layer is 20mm.

[0052] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.1%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.1%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0053] Example 5

[0054] The preparation method in this embodiment is the same as in Example 1, except that:

[0055] The thickness of the heat-resistant cast iron layer is 25mm.

[0056] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.07%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.07%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0057] Example 6

[0058] The preparation method in this embodiment is the same as in Example 1, except that:

[0059] The thickness of the middle carbon fiber felt layer is 10mm.

[0060] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0061] Example 7

[0062] The preparation method in this embodiment is the same as in Example 1, except that:

[0063] The heat-resistant cast steel for the heat-resistant cast iron layer is ZG50Cr28Ni48W5.

[0064] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.07%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.08%, Si: 0.07%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0065] Example 8

[0066] The preparation method in this embodiment is the same as in Example 1, except that:

[0067] The heat-resistant cast steel for the heat-resistant cast iron layer is ZG35Cr24Ni7NRE.

[0068] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity element content by mass percentage was: Fe: 0.08%, Si: 0.07%, Ni: 0.004%, Cr: 0.003%. The alloy impurities in the raw materials of the smelting alloy by mass percentage were: Fe: 0.08%, Si: 0.07%, Ni: 0.004%, Cr: 0.003%, and the impurity content did not increase.

[0069] Example 9

[0070] The preparation method of this embodiment is the same as that of embodiment 1, except that the silicon carbide ceramic contains 85% silicon carbide particles, 7% muneite, and 8% SiO2 raw materials.

[0071] The prepared composite crucible material was put into actual smelting use to smelt Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr aluminum-lithium alloy. The service life was more than 10 times longer than that of traditional graphite crucibles. Elemental mass spectrometry analysis of the ingot obtained from the alloy smelting showed that the impurity content, by mass percentage, was Fe:0.08%, Si:0.08%, Cr:0.04%, and Ni:0.03%. The impurities in the raw materials for the alloy smelting were Fe:0.08%, Si:0.08%, Cr:0.04%, and Ni:0.03%, and the impurity content did not increase.

[0072] Comparative Example 1

[0073] This comparative example is essentially the same as Example 1, except that it uses a traditional graphite alloy, consisting of a single-layer graphite crucible and a surface coating. The Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy was smelted. Compared to the example, the crucible's service life decreased by 90%. Elemental mass spectrometry analysis of the alloy impurities revealed the following impurity contents: Fe: 0.08%, Si: 0.12%, Ni: 0.004%, Cr: 0.003%, C: 0.04%. The alloy impurities in the smelted alloy raw material, by mass percentage, were: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, Cr: 0.003%, indicating an increase in impurity content.

[0074] Comparative Example 2

[0075] This comparative example is essentially the same as Example 1, except that a cermet crucible is used, consisting of a single-layer ceramic crucible made of cermet and a surface coating. The Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy was smelted. Compared to Example 1, the crucible's service life decreased by 85%. Elemental mass spectrometry analysis of the alloy impurities revealed impurity contents of Fe: 0.13%, Si: 0.12%, Ni: 0.004%, and Cr: 0.003%. The mass percentages of alloy impurities in the smelted alloy raw material were: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, and Cr: 0.003%, indicating an increase in impurity content.

[0076] Comparative Example 3

[0077] This comparative example is basically the same as Example 1, except that the intermediate carbon fiber felt layer is not added. It consists of a silicon carbide ceramic inner layer and an outer heat-resistant cast steel layer. The Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy is also smelted. Compared with Example 1, the service life of the crucible is reduced by 40%. Elemental mass spectrometry analysis of the alloy impurities showed that the impurity content was Fe: 0.08%, Si: 0.08%, Ni: 0.0084%, and Cr: 0.005%. The alloy impurities in the smelting alloy raw material, by mass percentage, were Fe: 0.08%, Si: 0.08%, Ni: 0.004%, and Cr: 0.003%, indicating an increase in impurity content.

[0078] Comparative Example 4

[0079] This comparative example is basically the same as Example 1, except that the thickness of the silicon carbide ceramic layer is 5 mm.

[0080] Similarly, when smelting the Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy, the crucible lifespan decreased by 30% compared to Example 1. Furthermore, elemental mass spectrometry analysis of the alloy impurities revealed impurity contents of Fe: 0.08%, Si: 0.09%, Ni: 0.004%, and Cr: 0.005%. The mass percentages of alloy impurities in the smelting alloy raw material were: Fe: 0.08%, Si: 0.08%, Ni: 0.004%, and Cr: 0.005%, indicating an increase in impurity content.

[0081] Comparative Example 5

[0082] This comparative example is basically the same as Example 1, except that the total amount of additives in the silicon carbide ceramic layer remains unchanged, consisting entirely of munelix, with no SiO2 added.

[0083] Similarly, when smelting the Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy, the crucible lifespan decreased by 25% compared to Example 1. Furthermore, elemental mass spectrometry analysis of the alloy impurities revealed the following impurity contents: Fe: 0.08%, Si: 0.11%, Ni: 0.003%, Cr: 0.005%. The mass percentages of alloy impurities in the smelting alloy raw material were: Fe: 0.08%, Si: 0.08%, Ni: 0.003%, Cr: 0.005%, indicating an increase in impurity content.

[0084] Comparative Example 6

[0085] This comparative example is basically the same as Example 1, except that the total amount of additives in the silicon carbide ceramic layer remains unchanged, consisting entirely of SiO2, with no addition of munexite.

[0086] Similarly, when smelting the Al-3.5wt%Li-1wt%Cu-1.5wt%Mg-0.1wt%5Zr alloy, the crucible lifespan decreased by 25% compared to Example 1. Furthermore, elemental mass spectrometry analysis of the alloy impurities revealed the following impurity contents: Fe: 0.08%, Si: 0.10%, Ni: 0.003%, Cr: 0.004%. The mass percentages of alloy impurities in the smelting alloy raw material were: Fe: 0.08%, Si: 0.07%, Ni: 0.003%, Cr: 0.004%, indicating an increase in impurity content.

[0087] The specific embodiments of the present invention have been described above. It should be understood that the present invention is not limited to the specific embodiments described above, and those skilled in the art can make various modifications or variations within the scope of the claims, which do not affect the essence of the present invention.

Claims

1. A method for preparing a composite crucible, characterized in that, The preparation method includes the following steps: (1) Mix silicon carbide ceramic material with deoxidizer and binder, press into shape, dry and sinter to obtain silicon carbide ceramic inner layer; (2) A resin adhesive is coated on the outer surface of the silicon carbide ceramic inner layer, and the carbon fiber felt layer is bonded to the outer surface of the silicon carbide ceramic inner layer. After drying, a composite structure including a carbon fiber felt intermediate layer and a silicon carbide ceramic inner layer is obtained. (3) The composite structure is placed in the inner cavity of the heat-resistant cast steel outer layer, heated and kept at a constant temperature to obtain the composite crucible; The composite crucible comprises a silicon carbide ceramic inner layer, a carbon fiber felt middle layer, and a heat-resistant cast steel outer layer. The thickness of the silicon carbide ceramic inner layer is 15~20 mm; The thickness of the carbon fiber felt interlayer is 5-10 mm, and the porosity is 30%-70%. In step (1), the raw materials in the silicon carbide ceramic material include silicon carbide particles with a mass fraction of 85%~90%, 2%~10% muneite, and 5%~8% SiO2.

2. The method for preparing the composite crucible according to claim 1, characterized in that, The thickness of the heat-resistant cast steel outer layer is 15~25 mm; the heat-resistant cast steel is one of ZG40Cr24Si2, ZG50Cr28Ni48W5, and ZG35Cr24Ni7NRE.

3. The method for preparing the composite crucible according to claim 1, characterized in that, In step (1), the mass of the deoxidizer is 2-4% of the silicon carbide ceramic material; the mass of the adhesive is 2%-4% of the silicon carbide ceramic material; the deoxidizer is C+B4C; and the adhesive is epoxy resin.

4. The method for preparing the composite crucible according to claim 1, characterized in that, In step (1), the sintering temperature is 1900-2100 ℃ and the time is 1-2.5 h.

5. The method for preparing the composite crucible according to claim 1, characterized in that, In step (2), the resin adhesive is epoxy resin.

6. The method for preparing the composite crucible according to claim 1, characterized in that, In step (3), the heating is done in stages. Specifically, the temperature is first raised to 450-550℃ and held for 0.5-1h; then the temperature is raised to 700-800℃ and held for 1-2h.

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