A composite ceramic core for automobile turbine shell casting, preparation method and application

Abstract

The application discloses a composite ceramic core for an automobile turbine shell casting, a preparation method and application, and relates to the technical field of investment casting. The composite ceramic core is prepared from 200-mesh fused mullite powder, 325-mesh zirconium powder, fused quartz powder, and rare earth additive raw materials of lanthanum oxide or yttrium oxide through proportioning, forming and sintering. The fused quartz powder is prepared from 100-200-mesh, 200-mesh and 325-mesh quartz powders in an equal mass ratio. The rare earth additive generates a stable rare earth silicate phase at the mullite-quartz interface during the sintering process, and plays a role in releasing thermal stress and improving the high-temperature stability of the composite ceramic core. Through the regulation and control of the composite materials of low, medium and high expansion phases and the rare earth interface phase, the composite ceramic core realizes the synergistic balance of thermal expansion matching and high-temperature strength, reduces the sintering cracks of the ceramic core and the thermal cracking defects of the casting, improves the core removal performance and the surface smoothness of the flow channel of the casting, and is suitable for batch precision casting of automobile turbine shell castings.

Description

Technical Field

[0001] This invention relates to the field of investment casting technology, and in particular to a composite ceramic core for automotive turbine housing castings, its preparation method, and its application. Background Technology

[0002] As a key component for improving engine power and fuel efficiency, the turbocharger's turbine housing, a core component, is typically made of heat-resistant cast iron or nickel-based high-temperature alloys. The turbine housing casting contains multiple complex spiral flow channels and gas circulation chambers, requiring precise molding using ceramic cores. The ceramic core, serving as a temporary support structure for forming the internal cavity during investment casting, directly determines the dimensional accuracy and yield rate of the casting based on its thermal stability, strength, expansion matching, and core removal performance.

[0003] Currently, turbine housing ceramic cores are generally prepared using a silica sol binder system combined with mullite sand or fused silica sand. Therefore, turbine housing castings exhibit good plasticity and thermal shock stability at room temperature, but still have significant shortcomings under high-temperature casting conditions. While ceramic cores primarily composed of pure fused silica have a low coefficient of thermal expansion, reducing dimensional errors in castings, their high-temperature strength is relatively low, making them prone to deformation or fracture during pouring, leading to runner misalignment or sand inclusion defects. Conversely, although mullite ceramic cores have high strength, their large coefficient of thermal expansion results in poor compatibility with silica sol mullite shells, making them highly susceptible to thermal stress during cooling, thus inducing hot cracking in the casting.

[0004] To improve high-temperature performance and expansion matching, some studies have attempted to introduce high-strength ceramic fillers such as zirconium oxide (ZrO2) or cordierite, using composite formulations to control the overall performance of the ceramic core. However, simple multi-component mixtures often suffer from uneven material distribution and poor interfacial bonding, leading to uneven microstructure and large strength fluctuations after sintering. Furthermore, the significant differences in the thermal expansion coefficients of different components can easily cause microcracks or stress concentrations during high-temperature sintering and cooling, resulting in core cracking or deformation and reducing product yield. Simultaneously, high zirconium oxide content leads to a significant decrease in core removal, making it difficult to remove residual sand particles from the complex flow channels inside the turbine housing, affecting subsequent sand removal and airflow performance.

[0005] Furthermore, traditional ceramic core forming methods, such as manual slip casting or hot-press molding, make it difficult to precisely control their density and porosity distribution. This results in significant dimensional fluctuations within the same batch of products, affecting the smoothness and consistency of the flow channels inside the turbine housing. For demanding automotive turbine housing casting production lines, these issues directly impact product yield and economic efficiency. While existing literature proposes improving binder systems or using surface coatings to enhance core removal and surface quality, a systematic preparation scheme that balances high-temperature strength, thermal expansion matching, ease of core removal, and high yield has not yet been established.

[0006] In summary, the existing technology has at least the following technical problems:

[0007] Existing ceramic cores have technical problems such as difficulty in balancing high-temperature strength and thermal expansion, which can easily lead to hot cracking of castings or breakage of ceramic cores; uneven distribution of ceramic core components, which can lead to high sintering stress; and poor core removal properties. Summary of the Invention

[0008] The purpose of this invention is to provide a composite ceramic core for automotive turbine housing castings, its preparation method, and its application, in order to solve the technical problems of existing ceramic cores, such as difficulty in balancing high-temperature strength and thermal expansion matching, which easily leads to hot cracking of castings or ceramic core fracture, uneven distribution of ceramic core components resulting in high sintering stress, and poor core removal properties.

[0009] The preferred technical solutions among the many technical solutions provided by this invention can produce a variety of technical effects, which are described in detail below.

[0010] To address the aforementioned technical problems, the present invention provides the following technical solution:

[0011] This invention provides a composite ceramic core for automotive turbine housing castings. The composite ceramic core is prepared by molding and sintering composite ceramic core powder with the following mass percentages: 15%–25% 200-mesh fused mullite powder; 10% 325-mesh zircon powder; and 65%–75% fused silica powder. The fused silica powder is a mixture of quartz powders of three particle sizes (100-200 mesh, 200 mesh, and 325 mesh) in equal mass ratios. It also includes 0.1%–1.0% of rare earth additives such as lanthanum oxide or yttrium oxide, used to form a stable rare earth silicate phase at the mullite-quartz interface during the sintering process of the composite ceramic core to mitigate thermal stress.

[0012] In one embodiment, the fused mullite powder is composed of 60-75% Al2O3 and 25-40% SiO2 by mass.

[0013] In one embodiment, the rare earth additive is added in the form of acetate or nitrate precursors, and after sintering, La2Si2O7 or Y2Si2O7 is formed at the interface to improve thermal shock stability and high-temperature strength.

[0014] A method for preparing a composite ceramic core for automotive turbine housing castings is also provided, comprising the following steps:

[0015] S1. Mixing: Weigh out 15%–25% of 200-mesh fused mullite powder, 10% of 325-mesh zircon powder, 65%–75% of fused silica powder (a mixture of the three particle sizes), and 0.1%–1.0% of rare earth additives by weight percentage, and dry mix for 2–4 hours to obtain composite powder.

[0016] S2. Slurry preparation: Mix the composite powder and silica sol binder at a mass ratio of 100:35-45, and stir evenly in a vacuum mixer to obtain a bubble-free slurry.

[0017] S3. Molding: The bubble-free slurry is injected into the mold by pressure injection molding and molded. After demolding, the ceramic core green body is obtained.

[0018] S4. Drying: Place the ceramic core green body in an environment with a temperature of 25±2℃ and a relative humidity of 40~50% and dry for 12~24 hours;

[0019] S5. Sintering: The dried ceramic core blank is placed in a sintering furnace, heated to 1150-1200℃ according to the set sintering curve and held for 2-3 hours; finally, it is cooled with the furnace to obtain the composite ceramic core.

[0020] In one embodiment, in the mixing process of step S1, the fused silica powder of the three particle size powders is composed of quartz powders of three particle size grades: 100-200 mesh, 200 mesh, and 325 mesh, mixed in equal mass ratios.

[0021] In one embodiment, a molding aid is added to the slurry in step S2. The molding aid is 0.5 to 1.5% polyvinyl alcohol by mass, which is used to improve the fluidity of the bubble-free slurry and the density of the molded ceramic core green body.

[0022] In one embodiment, after the ceramic core green body is dried in step S4, it is subjected to ultrasonic pre-degreasing treatment before entering the sintering process in step S5. This process is used to promote the decomposition of the silica sol binder, improve the internal venting uniformity of the ceramic core green body during sintering, and reduce the internal stress during sintering.

[0023] In one embodiment, the sintering curve is as follows: the temperature is increased to 200-300°C at a rate of 1-2°C / min and held for 1-2 hours, then increased to 1150-1200°C at a rate of 2-3°C / min and held for 2-3 hours; finally, the temperature is cooled to room temperature.

[0024] In one embodiment, the method further includes step S6, density and porosity testing: the composite ceramic core obtained from the sintering in step S5 is tested using a bulk density tester and a porosity tester, and the obtained bulk density is between 1.55 and 1.65 g / cm³. 3 The porosity was between 12% and 18% to confirm that the composite ceramic core's density and porosity were suitable for use in automotive turbine housing casting.

[0025] The invention also provides an application of the composite ceramic core in automotive turbine housing castings, wherein the composite ceramic core is used to form iron-based or nickel-based high-temperature alloy turbine housing castings with complex internal flow channels.

[0026] This invention addresses the technical problems of high-temperature strength, thermal expansion matching, component uniformity and core removal of ceramic cores used in automotive turbine housing castings, and proposes a composite ceramic core formulation system based on rare earth interface control. This composite ceramic core formulation has the following beneficial effects in terms of material system, microstructure and process adaptability: (1) Achieving a synergistic balance between high-temperature strength and thermal expansion matching; by using low-expansion fused silica as the matrix, medium-expansion electrofused mullite as the reinforcing phase and high-expansion zirconium oxide as the strengthening phase in a composite ratio, and introducing 0.1% to 1.0% of rare earth oxides as rare earth additives such as lanthanum oxide or yttrium oxide into this system, the overall thermal expansion coefficient of the ceramic core is precisely controlled within the range that matches the silica sol-mullite shell system.

[0027] Furthermore, the rare earth silicate phases La2Si2O7 or Y2Si2O7 generated during the sintering process can effectively buffer the expansion differences between different crystal phases, thereby significantly reducing the thermal stress concentration of the composite ceramic core and preventing cracks or deformation of the composite ceramic core under high-temperature casting injection, thus greatly reducing the hot cracking rate of the casting.

[0028] (2) Improve the uniformity and dimensional stability of the ceramic core structure; by compounding fused silica powder in equal proportions of three particle sizes of 100-200 mesh, 200 mesh and 325 mesh, a dense particle packing structure is formed, which reduces the porosity between particles and the difference in sintering shrinkage; the rare earth oxides of electrofused mullite and rare earth additives promote the uniform crystallization of the quartz glass phase during sintering, avoiding the concentration of internal stress caused by uneven component distribution; thus, the sintering shrinkage rate of the composite ceramic core is significantly reduced, the dimensional deviation is reduced, the yield is high, and it is suitable for mass industrial production.

[0029] (3) Significantly improves core removal performance and casting surface quality; This invention uses fused silica as the main matrix, which ensures that the composite ceramic core maintains good collapsibility and chemical cleanability after casting. Combined with its uniform and dense sintered structure, the surface of the composite ceramic core is smooth and the pores are uniform. It can be quickly and completely removed during alkaline explosion or high-pressure water sand removal without leaving any fragments; It significantly reduces the surface roughness of the inner cavity flow channel of the turbine housing casting, which is beneficial to improving the turbine airflow efficiency.

[0030] (4) Enhanced high-temperature mechanical and anti-corrosion properties; fused mullite provides excellent thermal shock stability, zirconium oxide significantly improves the strength against molten metal impact, and rare earth silicate interface layer enhances grain boundary bonding; the synergistic effect of the three makes the high-temperature bending strength, impermeability and corrosion resistance of the composite ceramic core significantly better than that of the traditional fused silica ceramic core.

[0031] In summary, this invention, through multiphase composite and rare earth interface control design, achieves a ceramic core for turbine housing castings that balances high-temperature strength, thermal expansion matching, core removal capability, and production stability. This results in a performance balance and process controllability of the ceramic core material system, significantly improving the yield and quality consistency of automotive turbine housing castings. Attached Figure Description

[0032] To more clearly illustrate the technical solution of the present invention, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the composite ceramic core structure of the present invention;

[0034] Figure 2 This is one of the flowcharts of the first embodiment of the composite ceramic core preparation method of the present invention;

[0035] Figure 3 This is a second schematic flowchart of the first embodiment of the composite ceramic core preparation method of the present invention;

[0036] Figure 4 This is a schematic flowchart of the second embodiment of the composite ceramic core preparation method of the present invention;

[0037] Figure 5 This is a schematic flowchart of the third embodiment of the composite ceramic core preparation method of the present invention.

[0038] The accompanying figure is labeled as follows:

[0039] 1. Composite ceramic core. Detailed Implementation

[0040] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings.

[0041] The specific embodiment provides a composite ceramic core for automotive turbine housing castings, its preparation method, and its application. The composite ceramic core is prepared by proportioning, molding, and sintering 200-mesh fused mullite powder, 325-mesh zirconium powder, fused silica powder, and rare earth additives such as lanthanum oxide or yttrium oxide. The fused silica powder is composed of quartz powders of three particle sizes (100-200 mesh, 200 mesh, and 325 mesh) in equal mass ratios. During sintering, the rare earth additives generate a stable rare earth silicate phase at the mullite-quartz interface, thus mitigating thermal stress and improving the composite properties. The role of ceramic cores in high-temperature stability: Composite ceramic cores achieve a synergistic balance between thermal expansion matching and high-temperature strength through the composite material of low, medium and high expansion phases and the control of rare earth interface phases. This reduces sintering cracks in ceramic cores and hot cracking defects in castings, improves core removal performance and surface finish of casting flow channels, and is suitable for mass precision casting of turbine housings for automotive turbochargers. It effectively solves the technical problems of existing ceramic cores, such as the difficulty in balancing high-temperature strength and thermal expansion matching, which easily leads to hot cracking of castings or ceramic core fracture, uneven distribution of ceramic core components resulting in high sintering stress, and poor core removal performance.

[0042] The first implementation of the composite ceramic core is, for example Figure 1 As shown, the composite ceramic core 1 is prepared by molding and sintering composite ceramic core 1 powder composed of the following mass percentages: 200 mesh fused mullite powder: 15% to 25%; 325 mesh zircon powder: 10%; fused silica powder: 65% to 75%; the fused silica powder is composed of quartz powder of three particle sizes of 100-200 mesh, 200 mesh and 325 mesh in equal mass ratios; it also includes 0.1% to 1.0% of rare earth additives of lanthanum oxide or yttrium oxide, which are used to form a stable rare earth silicate phase at the mullite-quartz interface during the sintering process of composite ceramic core 1 to mitigate thermal stress.

[0043] Specifically, this invention addresses the technical problems of high-temperature strength, thermal expansion matching, compositional uniformity, and core removal in ceramic cores used for automotive turbine housing castings. It proposes a composite ceramic core 1 formulation system based on rare-earth interface control. This composite ceramic core 1 formulation offers several beneficial technical effects for automotive turbine housing castings in terms of material system, microstructure, and process adaptability: achieving a synergistic balance between high-temperature strength and thermal expansion matching; by using low-expansion fused silica as the matrix, medium-expansion fused mullite as the reinforcing phase, and high-expansion zirconium oxide as the strengthening phase in a composite ratio, and introducing 0.1%–1.0% rare-earth oxides (lanthanum oxide or yttrium oxide) as rare-earth additives into this system, the overall thermal expansion coefficient of the ceramic core is precisely controlled within a range matching the silica sol-mullite shell system.

[0044] Furthermore, the rare earth silicate phases La2Si2O7 or Y2Si2O7 generated during the sintering process can effectively buffer the expansion differences between different crystal phases, thereby significantly reducing the thermal stress concentration of the composite ceramic core 1 and preventing the composite ceramic core 1 from cracking or deforming under high temperature casting injection, thus greatly reducing the hot cracking rate of the casting.

[0045] The composite ceramic core exhibits improved uniformity and dimensional stability. By blending fused quartz powder in equal proportions of 100-200 mesh, 200 mesh, and 325 mesh, a dense particle packing structure is formed, reducing interparticle porosity and sintering shrinkage differences. The rare earth oxides of electrofused mullite and rare earth additives promote uniform crystallization of the quartz glass phase during sintering, avoiding stress concentration caused by uneven component distribution. Consequently, the sintering shrinkage rate of the composite ceramic core 1 is significantly reduced, dimensional deviations are minimized, and the yield is high, making it suitable for mass industrial production.

[0046] Significantly improves core removal performance and casting surface quality; the present invention uses fused silica as the main matrix, ensuring that the composite ceramic core 1 maintains good collapsibility and chemical removability after casting. Combined with its uniform and dense sintered structure, the surface of the composite ceramic core 1 is smooth and the pores are uniform. It can be quickly and completely removed during alkaline explosion or high-pressure water sand removal without leaving any fragments; it significantly reduces the surface roughness of the inner cavity flow channel of the turbine housing casting, which is beneficial to improving the turbine airflow efficiency.

[0047] Enhanced high-temperature mechanical and corrosion resistance; fused mullite provides excellent thermal shock stability, zirconium oxide significantly improves resistance to molten metal impact, and rare earth silicate interface layer enhances grain boundary bonding; the synergistic effect of the three makes the high-temperature bending strength, impermeability and corrosion resistance of composite ceramic core 1 significantly better than that of traditional fused silica ceramic core.

[0048] In summary, this invention, through multiphase composite and rare earth interface control design, achieves a balance between high-temperature strength, thermal expansion matching, core removal capability, and production stability in the ceramic core used in turbine housing castings. This results in a performance balance and process controllability of the ceramic core material system, which can significantly improve the yield and quality consistency of automotive turbine housing castings.

[0049] As one alternative implementation method:

[0050] Regarding the composition of the above-mentioned fused mullite powder, the fused mullite powder is composed of 60-75% Al2O3 by mass and 25-40% SiO2 by mass.

[0051] In application, fused mullite powder, as the medium-expansion reinforcing phase in the composite ceramic core 1 system, forms a stable interfacial transition layer with the fused silica matrix during sintering. The high Al2O3 content effectively improves the rigidity and high-temperature strength of the crystalline phase and inhibits the phase transformation expansion of fused silica at high temperatures, while the SiO2 component ensures its chemical compatibility with the quartz matrix, thereby achieving lattice matching and stress relief at the microscopic level. This composition design enables the fused mullite to maintain high structural integrity under the high-temperature environment of casting and forms a synergistic strengthening effect with the rare earth silicate phase at the interface, improving the bending strength and thermal shock stability of the composite ceramic core 1. Through this structural composite effect, the composite ceramic core 1 can withstand the instantaneous impact of molten iron or nickel-based alloy liquid during casting without cracking or collapsing, fundamentally solving the problem of insufficient high-temperature strength and thermal cracking caused by thermal expansion mismatch in traditional ceramic cores.

[0052] Furthermore, the particle size of the fused mullite powder can be adjusted within the range of 150 to 250 mesh according to the inner cavity size and wall thickness requirements of the casting, so as to balance the packing density and gas discharge rate of composite ceramic cores 1 of different sizes; at the same time, the interfacial wettability between the fused mullite powder and the silica sol binder can be improved by surface modification treatment, coating with silane coupling agent or plasma surface activation, thereby further improving the density and structural consistency of the ceramic core green body.

[0053] The second embodiment of the composite ceramic core differs from the first embodiment in that rare earth additives are added in the form of acetate or nitrate precursors, and La2Si2O7 or Y2Si2O7 is formed at the interface after sintering to improve thermal shock stability and high temperature strength.

[0054] When applied, rare earth additives are added via a solution precursor route, allowing rare earth ions to form a uniform adsorption layer on the powder surface during the mixing stage. After molding, as the sintering temperature rises, rare earth elements react with SiO2 in the quartz and mullite phases to generate stable phases of La2Si2O7 or Y2Si2O7. These phases act as a "micro-interface control layer" at the grain boundaries, which can passivate the thermal crack propagation path and absorb the energy of local stress concentration. The formed rare earth silicate layer not only enhances the grain boundary bonding strength but also significantly suppresses the α-β phase transformation volume change of quartz near 573℃, thereby effectively improving the thermal shock lifetime of the composite ceramic core 1 during the heating-cooling cycle.

[0055] The close packing structure of rare earth silicate layers and multi-grade fused silica powder works together to disperse thermal stress during sintering and casting, resulting in more uniform shrinkage and more stable dimensions of the ceramic core. This helps maintain a precise shape and prevent localized spalling during high-temperature alloy casting.

[0056] Alternatively, cerium oxide (CeO2) can be selected as a rare earth additive, which can also form Ce2Si2O7 after sintering, achieving a similar interfacial buffering and lattice stabilizing effect. The concentration of the rare earth precursor solution is adjusted between 0.05 and 0.2 mol / L according to the thickness of the ceramic core to control the rare earth distribution depth and the thickness of the interfacial layer, thereby achieving optimized mixing of composite materials for composite ceramic cores of different sizes.

[0057] Based on the above embodiments of composite ceramic cores for automotive turbine housing castings, a method for preparing composite ceramic cores for automotive turbine housing castings is provided, comprising the following steps according to S1 to S5, as follows: Figure 2 As shown, S1, mixing: Weigh 15% to 25% of 200-mesh fused mullite powder, 10% of 325-mesh zircon powder, 65% to 75% of fused silica powder (a mixture of the three particle sizes), and 0.1% to 1.0% of rare earth additives by weight percentage, and dry mix for 2 to 4 hours to obtain composite powder;

[0058] S2. Slurry preparation: Mix the composite powder and silica sol binder at a mass ratio of 100:35-45, and stir evenly in a vacuum mixer to obtain a bubble-free slurry.

[0059] S3. Molding: The bubble-free slurry is injected into the mold by pressure injection molding and molded. After demolding, the ceramic core green body is obtained.

[0060] S4. Drying: Place the ceramic core green body in an environment with a temperature of 25±2℃ and a relative humidity of 40~50% and dry for 12~24 hours;

[0061] S5. Sintering: The dried ceramic core blank is placed in a sintering furnace, heated to 1150-1200℃ according to the set sintering curve and held for 2-3 hours; finally, it is cooled with the furnace to obtain the composite ceramic core.

[0062] In step S1, the fused silica powder of the three particle size powders is made by mixing quartz powders of three particle size grades, namely 100-200 mesh, 200 mesh and 325 mesh, in equal mass ratios.

[0063] like Figure 3 As shown, a molding aid is added to the slurry in step S2. The molding aid is 0.5% to 1.5% polyvinyl alcohol by mass, which is used to improve the fluidity of the bubble-free slurry and the density of the molded ceramic core green body.

[0064] In step S5, the sintering curve is as follows: the temperature is increased to 200-300℃ at a rate of 1-2℃ / min and held for 1-2 hours, then the temperature is increased to 1150-1200℃ at a rate of 2-3℃ / min and held for 2-3 hours; finally, the temperature is cooled to room temperature.

[0065] The composite ceramic core preparation method forms a complete process chain through steps S1 to S5, with each stage—mixing, slurry preparation, molding, drying, and sintering—working in synergy. By precisely controlling the mixing ratio and sintering curve, the three-phase components of fused mullite powder, zirconium powder, and fused silica form a stable composite structure during sintering. The equal-mass blending of multi-grade quartz powder ensures minimum porosity of the powder packing and uniform density of the sintered body. The added polyvinyl alcohol molding aid effectively improves the fluidity of the slurry during vacuum slurry preparation, resulting in a uniform internal structure and stable pore distribution in the injection-molded ceramic core green body. Combined with a low-speed heating-segmented heat preservation sintering curve, internal stress concentration caused by rapid decomposition of the binder is avoided, ensuring coordinated overall shrinkage and sufficient interfacial phase formation of the composite ceramic core. This achieves a balance between high strength, low shrinkage, and thermal expansion matching at high temperatures, solving the problems of cracking, warping, and uneven strength that easily occur in traditional ceramic core preparation.

[0066] In actual production, the holding time of the high-temperature holding sintering (1150-1200℃) after the second stage of heating in the sintering curve is adjusted to 2-3.5 hours according to the size of the composite ceramic core structure, in order to adapt to different thickness areas of the ceramic core; an online degassing system or a spiral stirring device can be introduced in the vacuum slurry stage to further reduce residual bubbles in the slurry and improve the repeatability of molding, thereby improving the stability of mass production.

[0067] A second embodiment of the composite ceramic core preparation method is as follows: Figure 4 As shown, the difference between this embodiment and the first embodiment is that it also includes a degreasing step: after the ceramic core green body is dried in step S4, the ceramic core green body is subjected to ultrasonic pre-degreasing treatment before entering the sintering in step S5, which is used to promote the decomposition of silica sol binder, improve the internal exhaust uniformity of the ceramic core green body during sintering and reduce the internal stress during sintering.

[0068] In application, an ultrasonic pre-degreasing step is introduced after S4 drying. High-frequency vibration promotes the uniform release of residual silica sol binder and gas in the ceramic core green body. The cavitation effect of ultrasound can form microbubbles and pressure waves in the micropores, thereby opening the exhaust channels between particles and making the degreasing process more thorough and uniform. In conjunction with the subsequent S5 segmented heating sintering, ultrasonic pre-degreasing can significantly reduce the problems of local gas expansion and microcracks caused by residual organic binder. At the same time, it reduces the internal stress concentration of the composite ceramic core during the initial heating stage of sintering, making the internal structure of the composite ceramic core more homogeneous and dense, and improving thermal shock stability and dimensional accuracy. The addition of the degreasing step is particularly suitable for ceramic cores with large wall thickness or complex geometry, which can effectively improve sintering yield and product consistency.

[0069] A third embodiment of the composite ceramic core preparation method, for example Figure 5As shown, this embodiment differs from the first embodiment in that it further includes step S6, density and porosity testing: the composite ceramic core obtained from sintering in step S5 is tested using a bulk density tester and a porosity tester, and the obtained bulk density is between 1.55 and 1.65 g / cm³. 3 The porosity ranged from 12% to 18% to confirm that the composite ceramic core's density and porosity were suitable for use in automotive turbine housing casting.

[0070] In application, the density and porosity testing in step S6 is used for structural verification and production quality monitoring of the sintered body. Through bulk density testing and porosity determination, the internal density and gas channel distribution of the ceramic core can be accurately reflected. This testing step, together with the aforementioned particle size distribution design in S1, molding aid regulation in S2, and segmented sintering process in S5, forms a closed-loop control system. If the test results fall within the target range of bulk density 1.55–1.65 g / cm³ and porosity 12%–18%, it indicates that the ceramic core possesses both sufficient strength and appropriate permeability, capable of withstanding the impact of high-temperature molten metal while ensuring easy core removal after casting. The quality verification mechanism through density and porosity testing ensures the stable performance of the ceramic core and its suitability for mass production of turbine housings, guaranteeing the quality of the composite ceramic core before it enters the casting stage and reducing the scrap rate of castings.

[0071] Based on the above embodiments of composite ceramic cores for automotive turbine housing castings, an application of composite ceramic cores for automotive turbine housing castings is provided, specifically: composite ceramic cores are used to form iron-based or nickel-based high-temperature alloy turbine housing castings with complex internal flow channels.

[0072] In application, this composite ceramic core serves as a precision forming structure for the internal gas flow channels and circulation chambers during turbine housing casting. Its core function is to maintain a stable geometry and sufficient pressure-bearing capacity during the high-temperature casting stage. The electrofused mullite reinforcing phase of the composite ceramic core provides high-temperature structural support, the zirconium oxide reinforcing phase enhances resistance to molten metal impact and erosion, while the multi-grained fused silica matrix ensures the overall thermal expansion and compatibility with the external shell. The rare earth silicate interface layer generated during sintering plays a stress-relieving role at high temperatures, inhibiting interface thermal cracking and ceramic core fragmentation. Thus, the composite structure of the composite ceramic core and the dense, smooth surface formed by precision molding on the outer surface of the composite ceramic core work together to ensure precise forming of the complex flow channels inside the turbine housing casting, a smooth surface, and reduced molten metal turbulence and inclusions.

[0073] During the cooling and core removal stages after casting, the chemical disintegration and porous channel structure of the molten quartz matrix enable the ceramic core to be rapidly decomposed and peeled off in alkaline solution or high-pressure water rinsing, avoiding the problem of easy residue or difficult sand removal of traditional high-strength ceramic cores. This application solution significantly reduces the hot cracking rate of turbine housing castings and significantly improves the surface roughness of the flow channel, ensuring the airflow efficiency and thermal balance performance of the turbocharger at high speeds.

[0074] In addition, the composite ceramic core can be combined with an intelligent detection system, using online acoustic monitoring to reflect and judge the real-time heating state and deformation of the ceramic core during the casting process through spectral analysis, thereby realizing digital casting control and further improving the molding accuracy and production yield of complex turbine housing products.

[0075] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features in the above embodiments are described.

Claims

1. A composite ceramic core for automotive turbine housing castings, characterized in that, The composite ceramic core is prepared by molding and sintering composite ceramic core powder with the following mass percentages: 200-mesh fused mullite powder: 15%–25%; 325-mesh zirconium oxide powder: 10%; fused silica powder: 65%–75%; the fused silica powder is a mixture of quartz powder of three particle sizes (100-mesh, 200-mesh, and 325-mesh) in equal mass ratios; and also includes 0.1%–1.0% of rare earth additives such as lanthanum oxide or yttrium oxide, which are used to form a stable rare earth silicate phase at the mullite-quartz interface during the sintering process of the composite ceramic core to mitigate thermal stress.

2. The composite ceramic core according to claim 1, characterized in that, The fused mullite powder is composed of 60-75% Al2O3 and 25-40% SiO2 by mass.

3. A method for preparing a composite ceramic core for automotive turbine housing castings, characterized in that, Includes the following steps: S1. Mixing: Weigh out 15%–25% of 200-mesh fused mullite powder, 10% of 325-mesh zirconium oxide powder, 65%–75% of fused silica powder, and 0.1%–1.0% of rare earth additives of lanthanum oxide or yttrium oxide according to the mass percentage, and dry mix for 2–4 hours to obtain composite powder; wherein, the fused silica powder is composed of quartz powder of three particle sizes of 100 mesh, 200 mesh, and 325 mesh in equal mass ratio; S2. Slurry preparation: Mix the composite powder and silica sol binder at a mass ratio of 100:35-45, and stir evenly in a vacuum mixer to obtain a bubble-free slurry. S3. Molding: The bubble-free slurry is injected into the mold by pressure injection molding and molded. After demolding, the ceramic core green body is obtained. S4. Drying: Place the ceramic core green body in an environment with a temperature of 25±2℃ and a relative humidity of 40~50% and dry for 12~24 hours; S5. Sintering: The dried ceramic core blank is placed in a sintering furnace, heated to 1150-1200℃ according to the set sintering curve and held for 2-3 hours; finally, it is cooled with the furnace to obtain the composite ceramic core.

4. The method for preparing composite ceramic core according to claim 3, characterized in that, After drying in step S4, the ceramic core green body is subjected to ultrasonic pre-degreasing treatment before entering the sintering process in step S5. This process promotes the decomposition of the silica sol binder, improves the internal venting uniformity of the ceramic core green body during sintering, and reduces the internal stress during sintering.

5. The method for preparing composite ceramic core according to claim 3, characterized in that, The sintering curve is as follows: the temperature is increased to 200-300℃ at a rate of 1-2℃ / min and held for 1-2 hours, then increased to 1150-1200℃ at a rate of 2-3℃ / min and held for 2-3 hours; finally, it is cooled to room temperature.

6. The method for preparing composite ceramic cores according to any one of claims 3 to 5, characterized in that, The process also includes step S6, density and porosity testing: the composite ceramic core obtained from sintering in step S5 is tested using a bulk density meter and a porosity meter, and the obtained bulk density is between 1.55 and 1.65 g / cm³. 3 The porosity was between 12% and 18% to confirm that the composite ceramic core's density and porosity were suitable for use in automotive turbine housing casting.

7. An application of the composite ceramic core as described in claim 1 or 2 in automotive turbine housing castings, characterized in that, The composite ceramic core is used to form iron-based or nickel-based high-temperature alloy turbine housing castings with complex internal flow channels.

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