Preparation method of Y2O3-SiO2-Al2O3 composite ceramic shell suitable for magnesium alloy investment casting

Abstract

The invention belongs to the technical field of non-ferrous metal casting, and relates to a preparation method of a Y2O3-SiO2-Al2O3 composite ceramic shell suitable for magnesium alloy investment casting. Through design of a composite shell material system and development of a preparation process, a series of engineering application technical problems of surface layer water reverse redissolution, overhigh sintering temperature and the like are efficiently solved at low cost, the casting / casting mold interface reaction phenomenon in the magnesium alloy investment casting process is effectively restrained, and the preheating temperature of the shell can reach 900 DEG C or above.

Description

Technical Field

[0001] The present invention belongs to the technical field of non-ferrous metal casting, and relates to a method for preparing a Y2O3-SiO2-Al2O3 composite ceramic shell for investment casting of magnesium alloys. Background Art

[0002] At present, magnesium alloy castings are used more and more widely in aviation equipment, and the demand is increasing day by day. International industry competition and national strategic needs have made precision casting of magnesium alloys receive unprecedented attention. However, due to the extremely active chemical properties of magnesium and magnesium alloys, different degrees of casting / mold interface reactions can occur with the currently commonly used mold shell materials in investment casting. This seriously damages the surface quality of precision castings of magnesium alloys, limits the engineering application of precision castings of magnesium alloys in the field of aviation equipment, and delays the development process of the country in the direction of precision casting of magnesium alloys.

[0003] At present, the mold shells used in the process of investment precision casting of magnesium alloys mainly include silica sol mold shells, aluminosilicate sol mold shells, etc. These mold shells all have different degrees of reaction phenomena with magnesium alloys. Taking silica sol mold shells and aluminosilicate sol mold shells as examples, when the mold shell is preheated ≤ 500 °C, although there is a certain degree of interface reaction between the two mold shells, it is not intense. However, when the preheating temperature of the mold shell ≥ 550 °C, serious interface reactions appear on the contact surface between the casting and the mold shell, seriously damaging the surface quality of the casting. The interface reaction mechanism between the magnesium alloy melt and the two mold shells is that silicon dioxide (SiO2) in the silica sol mold shell undergoes a series of reactions to generate magnesium silicate (MgSiO4) and magnesium oxide (MgO), forming surface slag; a displacement reaction occurs with aluminum oxide (Al2O3) in the aluminosilicate sol mold shell, and the displaced aluminum (Al) atoms combine with rare earth elements in the magnesium alloy melt in the contact area between the casting / mold to form a reaction phase, and finally form a reaction layer, which adheres to the surface of the casting and cannot be removed. This seriously damages the surface quality of the casting, and even causes the casting to be scrapped, resulting in huge potential safety hazards and economic losses.

[0004] From the perspective of material availability and its standard Gibbs free energy, yttrium oxide (Y2O3) is one of the few relatively inert oxides among common oxides with magnesium alloy melts, that is, it is not prone to casting / mold interface reaction phenomena and can be an actual application of mold shell materials. However, yttrium oxide as a mold shell material is extremely prone to back dissolution, especially surface layer back dissolution, and its relatively high sintering temperature is extremely unfavorable for engineering application promotion. At present, yttrium oxide materials have only been partially applied as refractory powders in the process of investment casting of titanium alloys. However, the chemical activity of magnesium alloys is higher than that of titanium alloys, and the reactivity is stronger. At the same time, relevant research shows that in the process of investment casting of magnesium alloys, compared with powders, the colloid (i.e., binder) in the mold shell material system is the decisive factor for casting / mold reactions. Therefore, the mold shells containing yttrium oxide materials in investment casting of titanium alloys are not applicable to investment casting of magnesium alloys.

[0005] The chemical properties of magnesium and magnesium alloys are extremely active. In investment casting, they can produce varying degrees of casting / mold interface reactions with currently commonly used shell materials. Especially under continuous high temperature environments, a large amount of black attachments are generated on the surface of the casting, and they cannot be completely and effectively removed even after surface treatments such as sandblasting. At the same time, the reactants will also invade the casting body, forming a certain range of continuous reaction layers in the near-surface area inside the casting. Even in the part with intense local reactions, a small amount of reactants enters deep into the casting body, which has a serious impact on the surface quality and metallurgical quality of the casting, and may even cause the casting to be scrapped, resulting in huge economic losses. Summary of the invention

[0006] The present invention discloses a material system design and preparation method of a Y2O3-SiO2-Al2O3 composite ceramic shell suitable for magnesium alloy investment casting. Through the design of the composite shell material system and the development of the preparation process, a series of engineering application technical problems such as the reverse dissolution of surface water and excessive sintering temperature are solved at low cost and high efficiency, effectively curbing the casting / mold interface reaction phenomenon in the magnesium alloy investment casting process. The shell can be preheated to a temperature of more than 900°C, breaking through the industry common technical barriers of magnesium alloy investment casting.

[0007] Purpose of the Invention

[0008] Yttrium oxide is an ideal choice for high-temperature shell materials for magnesium alloy investment casting. The present invention mainly discloses a method for preparing a Y2O3-SiO2-Al2O3 composite ceramic shell suitable for magnesium alloy investment casting, and through the design of the shell material system, the surface layer dissolution problem of yttrium oxide shell is solved at low cost and high efficiency, breaking through the technical barriers of high-temperature shells for magnesium alloy precision casting (shell preheating temperature ≥ 900°C), thereby solving the industry basic problem of casting / mold reaction in the process of magnesium alloy investment casting.

[0009] Technical Solution

[0010] To achieve the above object, the present invention adopts the following technical solution:

[0011] A method for preparing a Y2O3-SiO2-Al2O3 composite ceramic shell for magnesium alloy investment casting comprises the following steps:

[0012] Step 1: Slurry preparation,

[0013] (1) Preparation of surface coating: Yttrium oxide powder, low sodium corundum powder, yttrium oxide sand, ammonium alginate reagent, wetting agent and defoamer are added to yttrium sol in sequence, and each material is fully mixed before adding the next material; when the viscosity flow rate reaches 24s~26s, the shell surface coating is obtained.

[0014] (2) Preparation of transitional layer coating: Add corundum powder into silica sol, and then successively add wetting agent and defoaming agent. When the flow rate reaches 12 s - 16 s, it is the qualified viscosity flow rate, and thus the coating for the transitional layer of the mold shell is obtained.

[0015] (3) Preparation of backing layer coating: Add coal gangue powder into silica sol, and then add activated carbon fiber filaments. When the flow rate reaches 8 s - 12 s, it is the qualified viscosity flow rate, and thus the coating for the backing transitional layer of the mold shell is obtained.

[0016] Step 2. Coating and sand sprinkling of the module

[0017] (1) Clean the investment casting module, dry it, immerse it in the surface layer coating for uniform coating, take it out after uniform coating, and when the coating stops flowing, uniformly sprinkle yttrium oxide sand. Let it dry naturally in a windless environment, then immerse it in calcium chloride ethanol solution for continuous soaking, take it out and continue to dry naturally in a windless environment to form the surface layer mold shell;

[0018] (2) Immerse the surface layer mold shell in the transitional layer coating for uniform coating, take it out after uniform coating, and when the coating stops flowing, uniformly sprinkle corundum sand. Let it dry naturally in a slightly flowing wind environment to form the transitional layer mold shell;

[0019] (3) Immerse the transitional layer mold shell in the backing layer coating for uniform coating, take it out after uniform coating, and when the coating stops flowing, uniformly sprinkle coal gangue refractory sand. Let it dry naturally in a strong flowing wind environment to form a three - layer mold shell;

[0020] (4) Immerse the three - layer mold shell in the backing layer coating again for uniform coating, take it out after uniform coating, and when the coating stops flowing, uniformly sprinkle coal gangue refractory sand. Let it dry naturally in a strong flowing wind environment to form a four - layer mold shell;

[0021] (5) Repeat step (4) four times to form an eight - layer mold shell;

[0022] (6) Sealing slurry treatment, that is, immerse the eight - layer mold shell in the backing layer slurry for uniform coating, take it out after uniform coating, and when the coating stops flowing, let it dry naturally in a strong flowing wind environment to form a pre - fabricated mold shell.

[0023] Step 3. Dewaxing and roasting of the mold shell:

[0024] (1) Dewaxing of the mold shell: Use a steam dewaxing kettle to dewax the pre - fabricated mold shell,

[0025] (2) Sintering of the mold shell: After dewaxing the mold shell, use a gas furnace to sinter the mold shell to obtain a Y2O3 - SiO2 - Al2O3 composite ceramic mold shell suitable for investment casting of magnesium alloys.

[0026] Furthermore, the specific steps for step 1, slurry preparation are as follows:

[0027] (1) Preparation of the surface layer coating: Yttrium sol is added to yttrium oxide powder under continuous stirring. The ratio of yttrium oxide powder to yttrium sol is 2.8:1. After the complete addition of yttrium oxide powder, low-sodium corundum powder is added, and the addition amount is 4.9% - 5.1% of the weight of yttrium oxide powder. Subsequently, yttrium oxide sand is added, and the addition amount is 4.9% - 5.1% of the sum of the weights of yttrium oxide powder and low-sodium corundum powder. Then, ammonium alginate reagent is added, and the addition amount is 2% of the weight of yttrium sol. Finally, a wetting agent and an antifoaming agent are added in sequence. The addition amounts of the wetting agent and the antifoaming agent are both 0.15% - 0.25% of the weight of yttrium sol. The wetting agent is added first and stirring continues for 2 h, then the antifoaming agent is added, and then stirring continues for more than 10 h. The viscosity of the surface layer slurry is measured using a No. 5 standard flow cup. When the flow rate reaches 24 s - 26 s, it is the qualified viscosity flow rate, and thus the surface layer coating of the mold shell is obtained.

[0028] (2) Preparation of the transition layer coating: Corundum powder is added to silica sol under continuous stirring. The ratio of corundum powder to silica sol is 2.2:1. Subsequently, a wetting agent and an antifoaming agent are added in sequence. The addition amounts of the wetting agent and the antifoaming agent are both 0.3% - 0.5% of the weight of the colloid. The wetting agent is added first and stirring continues for 2 h, then the antifoaming agent is added, and then stirring continues for more than 24 h. The viscosity of the transition layer slurry is measured using a No. 4 standard flow cup. When the flow rate reaches 12 s - 16 s, it is the qualified viscosity flow rate, and thus the transition layer coating of the mold shell is obtained.

[0029] (3) Preparation of the backing layer coating: Coal gangue powder is added to silica sol under continuous stirring. The ratio of coal gangue powder to silica sol is 2:1. Subsequently, activated carbon fiber filaments are added, and the addition amount is 2% of the weight of the powder. Then, stirring continues for more than 24 h. The viscosity of the backing layer slurry is measured using a No. 4 standard flow cup. When the flow rate reaches 8 s - 12 s, it is the qualified viscosity flow rate, and thus the backing layer coating of the mold shell is obtained.

[0030] Further, Step 2, module coating and sand sprinkling are specifically as follows:

[0031] (1) The investment casting module is cleaned with a sodium citrate aqueous solution, dried, and then immersed in the surface layer coating for uniform coating. After uniform coating, it is taken out. After the coating stops flowing, yttrium oxide sand is evenly sprinkled. After sprinkling yttrium oxide sand, it is air-dried for 1 h at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a windless environment. Subsequently, it is immersed in a 5% calcium chloride ethanol solution for continuous soaking for 6 min - 10 min, taken out, and then air-dried for 6 h - 8 h at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a windless environment to form the surface layer mold shell;

[0032] (2) The surface layer mold shell is immersed in the transition layer coating for uniform coating. After uniform coating, it is taken out. After the coating stops flowing, corundum sand is evenly sprinkled, and it is air-dried for more than 12 h at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a slightly flowing wind environment to form the transition layer mold shell;

[0033] (3) Immerse the transition layer shell into the backing layer coating and evenly coat it. After even coating, lift it out. After the coating stops flowing, evenly sprinkle coal gangue refractory sand. Air dry it for more than 6 h under the environment of a temperature of 21°C to 27°C, a humidity of 30% to 55%, and strong flowing wind to form a three-layer shell;

[0034] (4) Immerse the three-layer shell into the backing layer coating again and evenly coat it. After even coating, lift it out. After the coating stops flowing, evenly sprinkle coal gangue refractory sand. Air dry it for more than 6 h under the environment of a temperature of 21°C to 27°C, a humidity of 30% to 55%, and strong flowing wind to form a four-layer shell;

[0035] (5) Repeat step (4) four times to form an eight-layer shell;

[0036] (6) Seal the slurry, that is, immerse the eight-layer shell into the backing layer slurry and evenly coat it. After even coating, lift it out. After the coating stops flowing, air dry it for more than 24 h under the environment of a temperature of 21°C to 27°C, a humidity of 30% to 55%, and strong flowing wind to form a prefabricated shell.

[0037] Further, step three, dewaxing and roasting of the shell, specifically:

[0038] (1) Shell dewaxing: Use a steam dewaxing kettle to dewax the prefabricated shell. The steam pressure of the dewaxing kettle is 0.4 MPa to 0.6 MPa (4.0 bar to 6.0 bar), and the dewaxing time is 15 min;

[0039] (2) Shell sintering: After shell dewaxing, use a gas furnace to sinter the shell. The sintering temperature is 1150°C, and the sintering time is 2 h. After sintering, a Y2O3 - SiO2 - Al2O3 composite ceramic shell applicable to investment casting of magnesium alloy can be obtained.

[0040] Further, in step one, (1) in the preparation of the surface layer coating, the yttrium oxide specifically selects a 325 - mesh specification.

[0041] Further, in step one, (1) in the preparation of the surface layer coating, the low - sodium corundum powder selects a 1000 - mesh specification.

[0042] Further, in step one, (1) in the preparation of the surface layer coating, the yttrium oxide sand selects an 80 - mesh specification.

[0043] Further, in step one, (1) and (2), the lubricant is specifically the JFC reagent, and the defoaming agent is specifically n - octanol.

[0044] Further, both the wetting agent and the defoaming agent are diluted with distilled water at a ratio of 1:1 before addition.

[0045] Further, in step one (2), corundum powder with a mesh size of 325 is selected.

[0046] Further, in step one (3), coal gangue powder with a mesh size of 320 is selected.

[0047] Further, in step one (3), the diameter of the activated carbon fiber filaments should be less than 10 μm.

[0048] Further, in step two (1), yttrium oxide sand with a mesh size of 80 is specifically selected.

[0049] Further, in step two (2), corundum sand with a mesh size of 60 is specifically selected.

[0050] Further, in step two (3), coal gangue refractory sand with a mesh size of 46 is specifically selected.

[0051] Further, in step two (4), coal gangue refractory sand with a mesh size ranging from 30 to 60 is specifically selected.

[0052] Technical effects

[0053] The present invention discloses a material system design and preparation method for a Y2O3-SiO2-Al2O3 composite ceramic shell applicable to investment casting of magnesium alloys. Through the design of the composite shell material system and the development of the preparation process, a series of engineering application technical problems such as back dissolution of surface layer water, too high sintering temperature of the shell, and powder falling off of the surface layer are solved at low cost and efficiently. The interface reaction phenomenon between the casting and the mold during the investment casting of magnesium alloys is effectively curbed. The preheating temperature of the shell can reach above 900 °C, breaking through the common technical barriers in the field of investment casting of magnesium alloys and strongly supporting the technological development in the field of investment casting of magnesium alloys.

[0054] The achievement stems from the urgent demand for high-quality magnesium alloy castings in the field of aviation equipment. Through the extension of the depth and breadth of the application of this patented technology achievement, on the one hand, the manufacturing technology level of magnesium alloy castings can be significantly improved, the application depth of magnesium alloy lightweight structural materials in the field of aviation equipment can be deepened, and the strategic goal of lightweighting of our country's aviation equipment can be promoted. On the other hand, through the horizontal expansion of this patented technology achievement, it can be popularized and applied to the fields of investment precision casting of titanium alloys, aluminum alloys, and superalloys, significantly promoting the manufacturing technology level of our country's aviation equipment and helping to achieve the national strategic goal of becoming a powerful aviation country. At the same time, this patented technology achievement can be used for both military and civilian purposes, with broad market prospects and remarkable economic and social benefits. Specific implementation manners

[0055] The present invention will be further described below in conjunction with embodiments. The following only describes some embodiments of the present invention, not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts belong to the scope of protection of the present invention.

[0056] Implementation case

[0057] This implementation case is for the preparation of the mold shell and pouring of investment castings of aviation magnesium alloy transmission casings. The casting is a medium-sized "gyratory body" structure magnesium alloy casting with a contour size of approximately φ600×200mm. The mold shell preparation process is shown in Table 1, and the detailed process flow is as follows.

[0058] (1) Slurry preparation

[0059] 1) Preparation of the surface layer coating: Yttrium sol is added to 325-mesh yttrium oxide powder under continuous stirring, and the powder-liquid ratio is approximately 2.8:1. After the yttrium oxide powder is completely added, 1000-mesh low-sodium corundum powder is added, and the addition amount is 4.9% - 5.1% of the weight of the yttrium oxide powder. Subsequently, 80-mesh yttrium oxide sand is added, and the addition amount is 4.9% - 5.1% of the weight of (yttrium oxide powder + low-sodium corundum powder). Then, ammonium alginate reagent is added, and the addition amount is 2% of the weight of the yttrium sol. Finally, a wetting agent (JFC reagent) and an antifoaming agent (n-octanol) are added in sequence. The addition amounts of both the wetting agent and the antifoaming agent are 0.15% - 0.25% of the weight of the yttrium sol. Before adding both, they are diluted with about one-fold distilled water. First, the wetting agent is added and stirring continues for 2h, then the antifoaming agent is added, and then stirring continues for more than 10h before it can be used. The viscosity of the surface layer slurry is measured using a No. 5 standard flow cup. When the flow rate reaches 24s - 26s, it is a qualified flow rate (viscosity), that is, the mold shell surface layer coating is obtained.

[0060] The present invention uses yttrium sol, yttrium oxide powder and yttrium oxide sand, which are relatively chemically inert to magnesium alloy, as the main components of the surface layer shell, fundamentally curbing the interfacial reaction phenomenon of the shell in the investment casting process of magnesium alloy. In view of the chemical property of the reverse dissolution of yttrium sol in water, calcium alginate polymer insoluble in water is used as an anti-reverse dissolution agent in the surface layer shell to form a protective film on the inner and outer surfaces of the surface layer, inhibiting the phenomenon of reverse dissolution of the yttrium sol surface layer when encountering water. However, it should be noted that due to the high activity of yttrium sol, almost all anti-reverse dissolution reagents will have a gelation-promoting effect or precipitation effect on the yttrium sol colloid, resulting in its inability to be uniformly mixed and stably present in the yttrium sol surface layer slurry. Therefore, the "separate addition + reaction synthesis" method of ammonium alginate and calcium chloride is adopted to achieve the addition and effect of the anti-reverse dissolution reagent calcium alginate polymer, that is, first add ammonium alginate accounting for 2% of the weight of the yttrium sol colloid to the surface layer slurry. After ammonium alginate is dissolved in the slurry, a large number of hydroxyl groups and carboxyl groups are generated on its molecular chain. When step (2) 1) is carried out subsequently, these hydroxyl groups and carboxyl groups will cross-link with calcium ions in the calcium chloride ethanol solution to form calcium alginate polymer insoluble in water, which will wrap on the surface of yttrium oxide molecules to form a protective layer, preventing the reverse dissolution phenomenon of the yttrium sol surface layer.

[0061] Meanwhile, low-sodium corundum powder (1000 mesh) accounting for 5% of the weight of the powder is used as a mineralizer in the surface layer slurry, reducing the sintering temperature of the composite shell from above 1500 °C to about 1150 °C, greatly reducing the equipment technical requirements and energy consumption, and facilitating large-scale engineering application and promotion. Yttrium oxide sand (325 mesh) accounting for 5% of the weight of the powder is used as a stress release agent in the surface layer slurry. The yttrium oxide sand, which is fine and diffusely distributed throughout the surface layer area, reduces and disperses the stress concentration phenomenon in the surface layer during the drying process, effectively curbing the drying crack phenomenon of the surface layer.

[0062] 2) Preparation of the transition layer coating: Add corundum powder of 325 mesh to the continuously stirred silica sol, and the powder-liquid ratio is about 2.2:1. Subsequently, a wetting agent (JFC reagent) and an antifoaming agent (n-octanol) are added in turn. The addition amounts of the wetting agent and the antifoaming agent are both 0.3% - 0.5% of the weight of the colloid. Before adding them, both are diluted with about one-fold distilled water. First add the wetting agent and continue stirring for 2 h, then add the antifoaming agent, and then continue stirring for more than 24 h before it can be used. The viscosity of the transition layer slurry is measured using a standard flow cup No. 4 cup. When the flow rate reaches 12 s - 16 s, it is the qualified flow rate (viscosity), that is, the transition layer coating of the shell is obtained.

[0063] 3) Preparation of the back layer coating: Add coal gangue powder with a mesh size of 320 to the continuously stirred silica sol, with the powder-liquid ratio being approximately 2:1. Subsequently, add activated carbon fiber filaments (≤10μm) as a strengthening factor. Through the bridging and pulling-out effects of the fiber filaments, the wet strength, high-temperature strength, and residual strength of the mold shell are improved, and the addition amount is 2% of the weight of the powder. Then continue stirring for more than 24 hours before it can be used. The viscosity of the back layer slurry is measured using a No. 4 standard flow cup. When the flow rate reaches 8s - 12s, it is a qualified flow rate (viscosity), and thus the coating for the back layer of the mold shell is obtained.

[0064] (2) Coating and sand sprinkling of the mold

[0065] 1) Clean the investment casting mold thoroughly with an aqueous solution of sodium citrate, dry it, and then immerse it in the surface layer coating for uniform coating. After uniform coating, take it out. After the coating stops flowing, evenly sprinkle yttrium oxide sand with a mesh size of 80. After sand sprinkling, air-dry it for 1 hour in an environment with a temperature of 21°C - 23°C, a humidity of 45% - 65%, and no wind. Subsequently, immerse it in a 2.5% calcium chloride ethanol solution for continuous soaking for 6 min - 10 min. After taking it out, continue to air-dry it for 6 h - 8 h in an environment with a temperature of 21°C - 23°C, a humidity of 45% - 65%, and no wind to form the surface layer mold shell.

[0066] Using an aqueous solution of sodium citrate as the cleaning agent for the investment casting mold can, on the one hand, effectively remove the dust and stains on the surface of the mold, and on the other hand, through the micro-corrosion effect of sodium citrate on the surface of the investment casting, produce an excellent roughness etching effect, which is more conducive to the coating of the surface layer slurry.

[0067] 2) Immerse the surface layer mold shell in the transition layer coating for uniform coating. After uniform coating, take it out. After the coating stops flowing, evenly sprinkle corundum sand with a mesh size of 60. Air-dry it for more than 12 hours in an environment with a temperature of 21°C - 23°C, a humidity of 45% - 65%, and a slightly flowing wind to form the transition layer mold shell;

[0068] 3) Immerse the transition layer mold shell in the back layer coating for uniform coating. After uniform coating, take it out. After the coating stops flowing, evenly sprinkle coal gangue refractory sand with a mesh size of 46. Air-dry it for more than 6 hours in an environment with a temperature of 21°C - 27°C and a humidity of (30% - 55%) under a strong flowing wind environment to form a three-layer mold shell;

[0069] 4) Immerse the three-layer mold shell in the back layer coating again for uniform coating. After uniform coating, take it out. After the coating stops flowing, evenly sprinkle coal gangue refractory sand with a mesh size of 30 - 60. Air-dry it for more than 6 hours in an environment with a temperature of 21°C - 27°C and a humidity of 30% - 55% under a strong flowing wind environment to form a four-layer mold shell;

[0070] 5) Repeat step 4) 4 times to form an eight-layer mold shell;

[0071] 6) Sealing slurry treatment: Immerse the eight-layer shell mold into the back-layer slurry and evenly coat it. After uniform coating, take it out. After the coating stops flowing, let it air-dry for more than 24 hours in an environment with a temperature of 21°C to 27°C, a humidity of 30% to 55%, and strong flowing wind to form a prefabricated shell mold.

[0072] (3) Dewaxing and roasting of the shell mold:

[0073] 1) Dewaxing of the shell mold: Use a steam dewaxing kettle to dewax the prefabricated shell mold. The steam pressure in the dewaxing kettle is 0.4 MPa to 0.6 MPa (4.0 bar to 6.0 bar), and the dewaxing time is 15 minutes. The high-temperature and pressurized steam dewaxing method is used to melt and remove the shell of the investment material, which greatly curbs the phenomenon of shell mold cracks caused by the expansion of the investment material during the dewaxing process.

[0074] 2) Sintering of the shell mold: After dewaxing the shell mold, use a gas furnace to sinter the shell mold. The sintering temperature is 1150°C, and the sintering time is 2 hours. After sintering, a Y2O3-SiO2-Al2O3 composite ceramic shell mold suitable for investment casting of magnesium alloys can be obtained. The mineralizer (low-sodium corundum powder) added in step 1) can generate lattice defects inside the yttrium oxide crystal through valence change, activate the lattice, and promote sintering, thereby significantly reducing the sintering temperature of the composite ceramic shell mold from higher than 1500°C to 1800°C to 1150°C.

[0075] In addition, unless otherwise defined, the technical terms or scientific terms used in the description of this application should have the ordinary meaning understood by those of ordinary skill in the art to which this application belongs. The words indicating directions such as "upper", "lower", "left", "right", "center", "vertical", "horizontal", "inner", "outer", etc. used in the description of this application are only used to indicate relative directions or position relationships, rather than implying that the device or component must have a specific orientation, be constructed and operated in a specific orientation. When the absolute position of the described object changes, its relative position relationship may also change accordingly. Therefore, it should not be understood as a limitation to this application. The terms "first", "second", "third", and similar terms used in the description of this application are only for descriptive purposes to distinguish different components, and cannot be understood as indicating or implying relative importance. The words "a", "one", or "the" and similar words used in the description of this application should not be understood as an absolute limitation on the quantity, but should be understood as having at least one. The words "including" or "comprising" and similar words used in the description of this application are intended to mean that the elements or objects appearing before this word cover the elements or objects listed after this word and their equivalents, without excluding other elements or objects.

[0076] In addition, it should be noted that, unless otherwise clearly specified and defined, the similar terms such as "installed", "connected", and "joined" used in the description of this application should be understood in a broad sense. For example, the connection can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium, and it can also be the communication inside two components. Those skilled in the art can understand its specific meaning in this application according to the specific situation.

[0077] The above are only specific embodiments of the present invention and are not used to limit the present invention. Any person skilled in the art may, within the spirit and principle of the present invention, use the disclosed technical content to make changes or modifications into equivalent embodiments with equivalent changes and apply them to other fields. However, any simple modification, equivalent change, and modification made to the above embodiments based on the technical essence of the present invention without departing from the technical solution content of the present invention, any modification, equivalent replacement, improvement, etc., shall be included in the protection scope of the present invention.

Claims

1. A preparation method of Y2O3-SiO2-Al2O3 composite ceramic mold shell for investment casting of magnesium alloy, characterized in that, The following steps: Step 1: Slurry preparation; (1) Add yttrium oxide powder, low-sodium corundum powder, yttrium oxide sand, ammonium alginate reagent, wetting agent and defoamer to the yttrium sol in sequence, and enter the next material after each material is fully mixed; when the viscosity flow rate reaches 24 s - 26 s, the coating for the shell surface layer is obtained; (2) Add corundum powder to the silica sol, and then add the wetting agent and defoamer in sequence. When the flow rate reaches 12 s - 16 s, it is the qualified viscosity flow rate, and the coating for the shell transition layer is obtained; (3) Add coal gangue powder to the silica sol, and then add activated carbon fiber filaments. When the flow rate reaches 8 s - 12 s, it is the qualified viscosity flow rate, and the coating for the shell back layer is obtained; Step 2: Coating and sanding of the module; (1) Clean the investment casting module, dry it, immerse it in the surface layer coating for uniform coating, lift it out after uniform coating, wait for the coating to stop flowing, and then evenly sprinkle yttrium oxide sand; dry it naturally in a windless environment, then immerse it in the calcium chloride ethanol solution for continuous soaking, lift it out and dry it naturally in a windless environment to form the surface layer shell; (2) Immerse the surface layer shell in the transition layer coating for uniform coating, lift it out after uniform coating, wait for the coating to stop flowing, and then evenly sprinkle corundum sand, and dry it naturally in a slightly flowing wind environment to form the transition layer shell; (3) Immerse the transition layer shell in the back layer coating for uniform coating, lift it out after uniform coating, wait for the coating to stop flowing, and then evenly sprinkle coal gangue refractory sand, and dry it naturally in a strong flowing wind environment to form a three-layer shell; (4) Immerse the three-layer shell in the back layer coating again for uniform coating, lift it out after uniform coating, wait for the coating to stop flowing, and then evenly sprinkle coal gangue refractory sand, and dry it naturally in a strong flowing wind environment to form a four-layer shell; (5) Repeat step (4) 4 times to form an eight-layer shell; (6) Sealing slurry treatment, that is, immerse the eight-layer shell in the back layer slurry for uniform coating, lift it out after uniform coating, wait for the coating to stop flowing, and dry it naturally in a strong flowing wind environment to form a prefabricated shell; Step 3: Dewaxing and roasting of the shell; (1) Shell dewaxing: Use a steam dewaxing kettle to dewax the prefabricated shell, (2) Shell sintering: After shell dewaxing, use a gas furnace to sinter the shell.

2. The method according to claim 1, wherein Step 1: The specific slurry preparation is as follows: (1) Preparation of the surface layer coating: The ratio of yttrium oxide powder to yttrium sol is 2.8:1; the addition amount of low-sodium corundum powder is 4.9% - 5.1% of the weight of the yttrium oxide powder, the addition amount of yttrium oxide sand is 4.9% - 5.1% of the sum of the weights of the yttrium oxide powder and the low-sodium corundum powder, the addition amount of ammonium alginate reagent is 2% of the weight of the yttrium sol; the addition amounts of the wetting agent and the defoamer are both 0.15% - 0.25% of the weight of the yttrium sol. First add the wetting agent and continue stirring for 2 h, then add the defoamer, and then continue stirring for more than 10 h. The viscosity of the surface layer slurry is measured using a No. 5 standard flow cup. When the flow rate is qualified, the coating for the shell surface layer is obtained; (2) Preparation of the transition layer coating: The ratio of corundum powder to silica sol is 2.2:1; the addition amounts of the wetting agent and the defoaming agent are both 0.3% - 0.5% of the weight of the colloid. First, add the wetting agent and continue stirring for 2 hours, then add the defoaming agent, and then continue stirring for more than 24 hours. The viscosity of the transition layer slurry is measured using a No. 4 standard flow cup. When the flow rate is qualified, the mold shell transition layer coating is obtained; (3) Preparation of the back layer coating: The ratio of coal gangue powder to silica sol is 2:

1. Then, add activated carbon fiber filaments, and the addition amount is 2% of the weight of the powder. Then, continue stirring for more than 24 hours. The viscosity of the back layer slurry is measured using a No. 4 standard flow cup. When the flow rate is qualified, the mold shell back transition layer coating is obtained.

3. The method according to claim 1, wherein Step 2. The specific process of coating and sanding the module is as follows: (1) After sprinkling yttrium oxide sand, air-dry it for 1 hour at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a windless environment. Then, immerse it in a 5% calcium chloride ethanol solution and soak for 6 - 10 minutes. After taking it out, continue to air-dry it for 6 - 8 hours at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a windless environment to form the surface layer mold shell; (2) Air-dry it for more than 12 hours at a temperature of 21°C - 23°C, a humidity of 45% - 65%, and in a slightly flowing wind environment to form the transition layer mold shell; (3) Air-dry it for more than 6 hours at a temperature of 21°C - 27°C, a humidity of 30% - 55%, and in a strong flowing wind environment to form a three-layer mold shell; (4) Air-dry it for more than 6 hours at a temperature of 21°C - 27°C, a humidity of 30% - 55%, and in a strong flowing wind environment to form a four-layer mold shell; (5) Repeat step (4) 4 times to form an eight-layer mold shell; (6) Air-dry it for more than 24 hours at a temperature of 21°C - 27°C, a humidity of 30% - 55%, and in a strong flowing wind environment to form a precast mold shell.

4. The method according to claim 1, characterized in that, Step 3. Dewaxing and roasting of the mold shell, specifically as follows: (1) Dewaxing of the mold shell: Use a steam dewaxing kettle to dewax the precast mold shell. The steam pressure of the dewaxing kettle is 0.4 MPa - 0.6 MPa, and the dewaxing time is 15 minutes; (2) Sintering of the mold shell: After the mold shell is dewaxed, use a gas furnace to sinter the mold shell. The sintering temperature is 1150°C, and the sintering time is 2 hours. After sintering, a Y2O3 - SiO2 - Al2O3 composite ceramic mold shell suitable for investment casting of magnesium alloys can be obtained.

5. The method according to claim 2, wherein In step 1, (1) in the preparation of the surface layer coating, yttrium oxide is specifically selected with a 325 - mesh specification.

6. The method according to claim 2, wherein In step 1, (1) in the preparation of the surface layer coating, low - sodium corundum powder is selected with a 1000 - mesh specification, yttrium oxide sand is selected with an 80 - mesh specification, the lubricant is specifically the JFC reagent, and the defoaming agent is specifically n - octanol.

7. The method according to claim 2, wherein Before adding both the wetting agent and the defoaming agent, they are diluted with distilled water at a ratio of 1:

1.

8. The method according to claim 2, wherein In step 1(2), corundum powder is selected with a 325 - mesh specification; in step 1(3), coal gangue powder is selected with a 320 - mesh specification, and in step 1(3), the diameter of the activated carbon fiber filaments should be less than 10 μm.

9. The method according to claim 2, characterized in that, In step 2(1), yttrium oxide sand is specifically selected with an 80 - mesh specification; in step 2(2), corundum sand is specifically selected with a 60 - mesh specification.

10. The method according to claim 2, wherein In (3) of Step 2, the coal gangue refractory sand is specifically selected as 46 mesh. In (4) of Step 2, the coal gangue refractory sand is specifically selected in the range of 30 mesh to 60 mesh.