Ceramic core for magnesium alloy investment casting and preparation method and application thereof

Abstract

The invention relates to the technical field of investment casting, in particular to a ceramic core for magnesium alloy investment casting and a preparation method and application of the ceramic core. The preparation method of the ceramic core for magnesium alloy investment casting comprises the following steps: coating magnesium alloy activity inhibitor slurry on the surface of a ceramic core, and baking at 90-120 DEG C for 0.5-1 hour to form an inhibitor layer; the magnesium alloy activity inhibitor slurry comprises powder and silica sol according to the mass ratio of 9: (30-40), and the powder comprises magnesium oxide powder and boric anhydride according to the mass ratio of 1: (0.5-0.7). The ceramic core disclosed by the invention is simple in preparation process and low in raw material price, and the prepared ceramic core is good in high-temperature stability, high in surface quality, high in dimensional precision, high in strength and easy to depoling after casting.

Description

Technical Field

[0001] The present invention relates to the technical field of investment casting, in particular to a ceramic core for magnesium alloy investment casting and a preparation method and application thereof. Background Art

[0002] Magnesium alloys, with their excellent properties such as low density and high specific strength, hold great promise for lightweighting in aerospace applications. Compared to traditional casting methods, investment casting offers unique advantages for producing large, complex, and complex components containing multiple oil pipes. Applying investment casting to magnesium alloy castings better meets the trend toward precision, thin-walled construction, and integrated aerospace components. However, when castings contain narrow internal piping structures, conventional coating slurry and sand cannot penetrate the pipes, resulting in casting defects such as inability to form the pipes, which can easily lead to batch rejection of castings. Using conventional coating processes combined with pre-embedded ceramic cores to assist in forming is a common method in actual production. Because ceramic cores play a crucial role in shaping key areas during the pouring process, and magnesium alloys are chemically more reactive, ceramic cores must be non-reactive with the molten metal and exhibit high dimensional accuracy, rigidity, and easy core removal. Furthermore, due to the inherent properties of magnesium alloys, significant casting shrinkage and the low coefficient of expansion of ceramic cores can generate significant stress. If the strength of the ceramic core material is insufficient, the ceramic core is prone to defects such as cracks and core deviation, which will lead to the scrapping of the casting.

[0003] The Chinese patent application with publication number CN106927798A records a water-soluble ceramic core and a preparation method thereof. By adding water-soluble inorganic salts such as potassium carbonate, sodium chloride, and sodium carbonate to the fused corundum powder, the problem of difficulty in core removal of the core material is solved. However, since magnesium alloy materials are easily corroded, the addition of sodium salts and potassium salts increases the hygroscopicity of the core material, which is easy to corrode the surface of the casting and affects the surface quality of the casting. The Chinese patent application with publication number CN118385442A records a ceramic core material for magnesium alloy precision casting and a preparation method thereof. The ceramic core material is prepared from carbon-coated aluminum nitride powder, a sintering aid, an ethanol solvent, and a binder. The preparation process requires cold isostatic pressing and debonding treatment. The production process and cost are relatively high, making it difficult to realize the engineering application of magnesium alloy investment castings.

[0004] In view of this, the present invention is proposed. Summary of the Invention

[0005] The purpose of the present invention is to provide a ceramic core for magnesium alloy investment casting, a preparation method and application thereof. The ceramic core for magnesium alloy investment casting prepared by the preparation method of the present invention has no interfacial reaction with the magnesium alloy liquid, and has the advantages of high surface quality, high dimensional accuracy, easy core removal and low cost.

[0006] In order to achieve the above-mentioned object of the present invention, the first aspect of the present invention provides a method for preparing a ceramic core for magnesium alloy investment casting, comprising the following steps:

[0007] Apply magnesium alloy active inhibitor slurry on the surface of the ceramic core and bake it at 90-120°C for 0.5-1h to form an inhibitor layer;

[0008] The magnesium alloy activity inhibitor slurry comprises powder and silica sol in a mass ratio of 9: (30-40), and the powder comprises magnesium oxide powder and boric anhydride in a mass ratio of 1: (0.5-0.7).

[0009] In a specific embodiment of the present invention, the magnesium alloy activity inhibitor slurry is prepared by ball-milling a powder, adding silica sol, and stirring until uniform. Furthermore, the ball-milling conditions include a ball-to-powder ratio of (2-3):1, a rotation speed of 900-1100 rpm, and a ball-milling time of 6-8 hours.

[0010] In a specific embodiment of the present invention, the coating thickness of the magnesium alloy activity inhibitor slurry is 0.05 to 0.1 mm.

[0011] In a specific embodiment of the present invention, the preparation of the ceramic core includes: mixing the core material and the plasticizer to form a slurry, pressing to form a green body; and calcining the green body.

[0012] In a specific embodiment of the present invention, the mass ratio of the core material to the plasticizer is (400-500):91.

[0013] In a specific embodiment of the present invention, the core material comprises fused silica fine powder, fused silica coarse powder, and zirconium powder in a mass ratio of (5.5-6.5) : 1 : (2.5-3.5). Furthermore, the fused silica fine powder has a mesh size of 270-400, the fused silica coarse powder has a mesh size of 170-250, and the zirconium powder has a mesh size of 270-325.

[0014] In a specific embodiment of the present invention, the plasticizer includes paraffin wax and beeswax. Furthermore, the mass ratio of the paraffin wax to the beeswax is (42-43):3.

[0015] In a specific embodiment of the present invention, the roasting treatment includes: keeping the temperature at 200±10°C for 2-3 hours, heating to 350±10°C for 2-3 hours, and then heating to 800±10°C for 6-10 hours.

[0016] In a specific embodiment of the present invention, during the calcination process, the temperature is raised from room temperature to 200±10°C for 1.5±0.2 hours; the temperature is raised from 200±10°C to 350±10°C for 1.5±0.2 hours; and the temperature is raised from 350±10°C to 800±10°C for 1±0.2 hours. Furthermore, the calcination process further includes: maintaining the temperature at 800±10°C for 6-10 hours, followed by cooling to below 150°C in the furnace.

[0017] The second aspect of the present invention provides a ceramic core for magnesium alloy investment casting produced by the method for producing a ceramic core for magnesium alloy investment casting provided by the first aspect of the present invention.

[0018] The third aspect of the present invention provides the use of the ceramic core for magnesium alloy investment casting provided by the second aspect of the present invention in magnesium alloy investment casting.

[0019] Compared with the prior art, the present invention has the following beneficial effects:

[0020] (1) In the preparation of the ceramic core of the present invention, a magnesium alloy activity inhibitor slurry is coated on the surface of the ceramic core to form an inhibitor layer. During the process of baking the ceramic core with the mold shell, the components in the inhibitor layer will not volatilize. During pouring, it will form a molten state under the high temperature of the magnesium alloy liquid, which can fill the gaps on the surface of the ceramic core and block the reaction between the magnesium alloy and the material in the core. Secondly, the elemental boron obtained by the reaction in the magnesium alloy activity inhibitor can be embedded in the surface film of magnesium oxide, making it a dense oxide film, further isolating the magnesium alloy liquid from the ceramic core, so that it has no interface reaction with the magnesium alloy liquid during the pouring process.

[0021] (2) The ceramic core of the present invention has a simple preparation process and low raw material price. The obtained ceramic core has good high temperature stability, high surface quality, high dimensional accuracy, high strength and is easy to remove from the core after casting. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] In order to more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the specific embodiments or the description of the prior art. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0023] Figure 1 A diagram of the ceramic core firing system provided in an embodiment of the present invention;

[0024] Figure 2 This is a physical picture of the ceramic core prepared in Example 1 of the present invention;

[0025] Figure 3The following are appearance photos (a) and DR imaging schematics (b) of a magnesium alloy casting pipeline made using the ceramic core made in Example 1 of the present invention. DETAILED DESCRIPTION

[0026] The technical scheme of the present invention will be clearly and completely described below in conjunction with the accompanying drawings and specific embodiments, but it will be understood by those skilled in the art that the following described embodiments are part of embodiments of the present invention, rather than all embodiments, and are only used to illustrate the present invention, and should not be considered as limiting the scope of the present invention. Based on the embodiments in the present invention, all other embodiments obtained by those of ordinary skill in the art without making creative work are within the scope of protection of the present invention. Those who do not specify specific conditions in the embodiments are carried out according to conventional conditions or the conditions recommended by the manufacturer. Those whose reagents or instruments are not specified as manufacturers are conventional products that can be purchased commercially.

[0027] The first aspect of the present invention provides a method for preparing a ceramic core for magnesium alloy investment casting, comprising the following steps: coating a magnesium alloy active inhibitor slurry on the surface of the ceramic core, and baking at 90 to 120° C. for 0.5 to 1 hour to form an inhibitor layer;

[0028] The magnesium alloy activity inhibitor slurry comprises powder and silica sol in a mass ratio of 9: (30-40), and the powder comprises magnesium oxide powder and boric anhydride in a mass ratio of 1: (0.5-0.7).

[0029] In the preparation of the ceramic core of the present invention, a specific magnesium alloy activity inhibitor is applied to the surface of the ceramic core. The components of the resulting inhibitor layer do not volatilize during the subsequent firing of the ceramic core and the mold shell. During casting, under the high temperature of the magnesium alloy liquid, the inhibitor layer becomes molten, filling the voids on the surface of the ceramic core and preventing the magnesium alloy from reacting with SiO2 and Al2O3 in the core. Furthermore, the components of the magnesium alloy activity inhibitor react (B2O3 + 3Mg = 2B + 3MgO), forming elemental boron that can be embedded in the magnesium oxide surface film, forming a dense oxide film that further isolates the magnesium alloy liquid from the ceramic core, preventing interfacial reaction with the magnesium alloy liquid during casting.

[0030] The present invention regulates the mass ratio of the powder and the silica sol in the magnesium alloy activity inhibitor slurry within the range of 9: (30-40), for example, it can be 9:30, 9:32, 9:35, 9:38, 9:40 or a range consisting of any two of them, thereby further helping to improve the surface quality and dimensional accuracy of investment castings, while making it easier to de-core the ceramic core.

[0031] The present invention regulates the mass ratio of magnesium oxide powder and boric anhydride in the magnesium alloy activity inhibitor slurry within the range of 1: (0.5-0.7), for example, it can be 1:0.5, 1:0.55, 1:0.6, 1:0.65, 1:0.7 or a range consisting of any two of them, so as to better balance the surface quality, dimensional accuracy and difficulty of removing the ceramic core of the investment casting.

[0032] In a specific embodiment of the present invention, the magnesium alloy activity inhibitor slurry is prepared by ball-milling a powder, adding silica sol, and stirring until uniform. Furthermore, the ball-milling conditions include a ball-to-powder ratio of (2-3) to (1), a rotation speed of 900-1100 rpm, and a ball-milling time of 6-8 hours.

[0033] In actual operation, during the preparation of magnesium alloy activity inhibitor slurry, silica sol can be added in batches to ensure mixing uniformity.

[0034] In a specific embodiment of the present invention, the silica sol contains 29 wt% to 31 wt% SiO2 and ≤ 0.5 wt% Na2O. Furthermore, the average particle size of the SiO2 in the silica sol is 800 to 900 nm, for example, 800 nm, 820 nm, 850 nm, 880 nm, 900 nm, or any combination thereof. The present invention does not impose strict limitations on the specific type of silica sol; it is understood that any silica sol that can be used to prepare ceramic cores may be used.

[0035] In a specific embodiment of the present invention, the magnesium oxide powder is 150-250 mesh, for example, it can be 150 mesh, 175 mesh, 200 mesh, 250 mesh or a range consisting of any two thereof.

[0036] In a specific embodiment of the present invention, the coating thickness of the magnesium alloy activity inhibitor slurry is 0.05-0.1 mm, for example, 0.05 mm, 0.06 mm, 0.07 mm, 0.08 mm, 0.09 mm, 0.1 mm or any two thereof.

[0037] In actual operation, the magnesium alloy activity inhibitor slurry can be evenly applied to the surface of the billet using a brush or other tool to ensure that the magnesium alloy inhibitor slurry covers the entire surface of the billet.

[0038] In a specific embodiment of the present invention, the preparation of the ceramic core includes: mixing the core material and the plasticizer to form a slurry, pressing to form a green body; and calcining the green body.

[0039] In a specific embodiment of the present invention, the mass ratio of the core material to the plasticizer is (400-500):91, for example, it can be 400:91, 420:91, 450:91, 480:91, 500:91 or a range consisting of any two thereof.

[0040] In a specific embodiment of the present invention, the core material comprises fused silica fine powder, fused silica coarse powder, and zirconium powder in a mass ratio of (5.5-6.5) : 1 : (2.5-3.5). For example, in different embodiments, the mass ratio of fused silica fine powder to fused silica coarse powder in the core material can be 5.5:1, 5.8:1, 6:1, 6.2:1, 6.5:1, or any combination thereof; and the mass ratio of fused silica coarse powder to zirconium powder can be 1:2.5, 1:2.8, 1:3, 1:3.2, 1:3.5, or any combination thereof. Adjusting the core material composition to meet the above conditions further helps improve the strength and core removal performance of the ceramic core.

[0041] In a specific embodiment of the present invention, the fused quartz fine powder is 270-400 mesh, for example, 270 mesh, 325 mesh, 400 mesh, etc.; the fused quartz coarse powder is 170-250 mesh, for example, 170 mesh, 200 mesh, 250 mesh, etc.; the zirconium powder is 270-325 mesh, for example, 270 mesh, 300 mesh, 325 mesh, etc.

[0042] In a specific embodiment of the present invention, the plasticizer includes paraffin wax and beeswax. Furthermore, the mass ratio of paraffin wax to beeswax is (42-43):3, for example, 42:3, 42.2:3, 42.5:3, 42.8:3, 43:3, or any combination thereof. This further improves the green compact's compacting performance while ensuring a consistent calcination process.

[0043] In a specific embodiment of the present invention, mixing the core material and the plasticizer to form a slurry includes: mixing the core material and the plasticizer in proportion and then ball milling to obtain the slurry; wherein the ball milling conditions include: a ball-to-material ratio of (2-4) : 1, a rotation speed of 900-1100 rpm, and a ball milling time of 12-16 hours.

[0044] In a specific embodiment of the present invention, the green body is formed by pressing the green body, which includes adding the slurry into a mold and pressing the green body. Specifically, a ceramic core making machine can be used to press the green body.

[0045] In a specific embodiment of the present invention, the calcination treatment includes: keeping the temperature at 200±10°C for 2-3 hours, heating to 350±10°C for 2-3 hours, and then heating to 800±10°C for 6-10 hours.

[0046] In a specific embodiment of the present invention, during the calcination process, the temperature is raised from room temperature to 200±10°C for 1.5±0.2 hours; the temperature is raised from 200±10°C to 350±10°C for 1.5±0.2 hours; and the temperature is raised from 350±10°C to 800±10°C for 1±0.2 hours. Furthermore, the calcination process includes: maintaining the temperature at 800±10°C for 6-10 hours, followed by cooling to below 150°C in the furnace.

[0047] Figure 1 A diagram of the firing system for the ceramic core provided in an embodiment of the present invention. The green body obtained according to the method of the present invention corresponds to the step-by-step temperature rising firing system of the present invention, which is more conducive to taking into account the strength and high-temperature stability of the ceramic core. When the firing temperature is too low or the firing time is insufficient, the strength of the obtained ceramic core is insufficient, and the ceramic core is prone to breakage during the casting process, affecting the quality of the casting; when the firing temperature is too high or the firing time is too long, the brittleness of the ceramic core increases, affecting its performance.

[0048] The second aspect of the present invention provides a ceramic core for magnesium alloy investment casting produced by the method for producing a ceramic core for magnesium alloy investment casting provided by the first aspect of the present invention.

[0049] The third aspect of the present invention provides the use of the ceramic core for magnesium alloy investment casting provided by the second aspect of the present invention in magnesium alloy investment casting.

[0050] In a specific embodiment of the present invention, the magnesium alloy investment casting includes: installing a ceramic core on a wax part, then assembling it with a runner, preparing a shell, and pouring to obtain a magnesium alloy casting.

[0051] The installation of the ceramic core, its assembly with the runner, and the preparation of the mold shell can all be performed according to conventional procedures in the field of investment casting. For example, the preparation of the mold shell may include sequentially preparing a surface layer and a backing layer, followed by dewaxing and firing. For example, the preparation of the mold shell can be prepared by referring to the preparation method of the embodiment disclosed in Publication No. CN111036843A, but is not limited thereto.

[0052] Example 1

[0053] This embodiment provides a method for preparing a ceramic core for magnesium alloy investment casting, comprising the following steps:

[0054] (1) Fused quartz powder (325 mesh, average particle size of 45 μm), fused quartz powder (200 mesh, average particle size of 75 μm) and zirconium powder (300 mesh, average particle size of 50 μm) were weighed in a mass ratio of 6:1:3 and mixed to obtain a core material; paraffin wax and beeswax were weighed in a mass ratio of 85:6 and mixed to obtain a plasticizer; the core material and the plasticizer (the plasticizer was pre-heated and melted at 80°C) were mixed in a mass ratio of 450:91 and added to a ball mill with a ball-to-material ratio of 3:1. The slurry was obtained by ball milling at a speed of 1000 rpm for 12 h.

[0055] (2) Pour the slurry into the mold and press it into a green body using a core making machine. Injection parameters: slurry cylinder 80±5℃, slurry barrel 80±5℃, nozzle temperature 80±5℃, injection time 30s±2s.

[0056] (3) The green body obtained in step (2) is added to a roasting furnace for roasting. The roasting system is as follows: Figure 1 , specifically including: heating from room temperature to 200℃ for 1.5h, and then keeping warm at 200℃ for 2.5h; then heating from 200℃ to 350℃ for 1.5h, and then keeping warm at 350℃ for 2.5h; then heating from 350℃ to 800℃ for 1h, and then keeping warm at 800℃ for 8h; then cooling with the furnace to below 150℃ and taking out.

[0057] (4) Magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride were weighed and mixed as powder in a mass ratio of 1:0.6, added to a ball mill with a ball-to-material ratio of 2.5:1, and ball-milled at a speed of 1000 rpm for 6 h. The mixture was taken out and placed in a blender, and then silica sol was added to the blender in batches. After the addition, the mixture was stirred for 30 min to obtain a magnesium alloy activity inhibitor slurry; wherein, the mass ratio of powder to silica sol was 9:35.

[0058] (5) Using a brush, evenly apply a layer (thickness of about 0.05 to 0.1 mm) of the magnesium alloy activity inhibitor slurry obtained in step (4) on the surface of the ceramic core after the calcination treatment in step (3), and then bake it at 100°C for 30 minutes and then take it out to obtain a ceramic core for magnesium alloy investment casting, such as Figure 2 shown.

[0059] This embodiment also provides a method for magnesium alloy investment casting, comprising the following steps:

[0060] (a) Install the ceramic core for magnesium alloy investment casting prepared in this embodiment onto the wax part and affix the wax cover; assemble the wax part and the runner according to the design;

[0061] (b) A mold shell is prepared according to conventional methods, and then the smelted ZM2 magnesium alloy liquid is poured into the mold shell. After the casting cools down, the ceramic core inside the pipe is cleaned by hydraulic shell cleaning, and then the surface quality and internal quality of the pipe are checked. Figure 3 Among them, in the hydraulic shell cleaning method, the shell cleaning pressure is 40MPa.

[0062] In the preparation of the magnesium alloy casting of this embodiment, core cleaning is easy. Figure 3 As shown, the surface of the cast pipe is smooth, and its metallurgical quality meets the requirements of aviation standard HB7780-2005 Class I castings, and no inclusions (slag) are found in X-ray examination.

[0063] The difficulty of core cleaning is judged as follows: if the shell is cleaned at 40 MPa and the cleaning is completed within 30 seconds, it is considered easy; if the cleaning is completed within 30 seconds, it is considered difficult.

[0064] Example 2

[0065] This embodiment refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, with the difference being that in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0066] Step (4) of this embodiment includes: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.5 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 hours, taking the mixture out and placing it in a blender, and then adding silica sol to the blender in batches, stirring for 30 minutes after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:40.

[0067] In the preparation of the magnesium alloy casting of this embodiment, core cleaning is easy. The surface of the cast pipe is smooth and its metallurgical quality meets the requirements of aviation standard HB7780-2005 Class I castings. X-ray examination shows no inclusions (slag).

[0068] Example 3

[0069] This embodiment refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, with the difference being that in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0070] Step (4) of this embodiment includes: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.7 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 hours, taking the mixture out and placing it in a blender, and then adding silica sol to the blender in batches, stirring for 30 minutes after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:30.

[0071] In the preparation of the magnesium alloy casting of this embodiment, core cleaning is easy. The surface of the cast pipe is smooth and its metallurgical quality meets the requirements of aviation standard HB7780-2005 Class I castings. X-ray examination shows no inclusions (slag).

[0072] Comparative Example 1

[0073] Comparative Example 1 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that the preparation of the ceramic core does not include step (4) and step (5).

[0074] The magnesium alloy casting of Comparative Example 1 was easy to clean the core, but the surface of the cast pipe had a large area of ​​black oxide, and its metallurgical quality was lower than the requirements of aviation standard HB7780-2005 Class I castings. X-rays showed large areas of slag inclusions.

[0075] Comparative Example 2

[0076] Comparative Example 2 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that, in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0077] Step (4) of Comparative Example 2 comprises: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.4 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 h, taking the mixture out and placing it in a blender, and then adding silica sol to the blender in batches, stirring for 30 min after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:35.

[0078] In the preparation of the magnesium alloy casting of Comparative Example 2, core cleaning was difficult. The surface of the resulting casting pipe was smooth and its metallurgical quality met the requirements of aviation standard HB7780-2005 Class I castings, and no inclusions (slag) were found under X-ray examination.

[0079] Comparative Example 3

[0080] Comparative Example 3 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that, in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0081] Step (4) of Comparative Example 3 comprises: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.8 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 h, taking the mixture out and placing it in a blender, and then adding silica sol to the blender in batches, stirring for 30 min after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:35.

[0082] The magnesium alloy casting of Comparative Example 3 was easy to clean the core, but the surface of the cast pipe had a small amount of black oxide, and its metallurgical quality was lower than the requirements of aviation standard HB7780-2005 Class I castings. X-ray examination showed a small area of ​​inclusion (slag).

[0083] Comparative Example 4

[0084] Comparative Example 4 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0085] Step (4) of Comparative Example 4 comprises: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.6 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 h, taking the mixture out and placing it in a blender, and then adding silica sol into the blender in batches, stirring for 30 min after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:25.

[0086] In the preparation of the magnesium alloy casting of Comparative Example 4, core cleaning was difficult. The surface of the resulting casting pipe was smooth and its metallurgical quality met the requirements of aviation standard HB7780-2005 Class I castings, and no inclusions (slag) were found under X-ray examination.

[0087] Comparative Example 5

[0088] Comparative Example 5 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that in step (4), the composition of the magnesium alloy activity inhibitor slurry is different.

[0089] Step (4) of Comparative Example 5 comprises: weighing magnesium oxide powder (200 mesh, average particle size of 75 μm) and boric anhydride in a mass ratio of 1:0.6 as a mixture, adding the mixture into a ball mill with a ball-to-material ratio of 2.5:1, ball milling at a speed of 1000 rpm for 6 h, taking the mixture out and placing it in a blender, and then adding silica sol to the blender in batches, stirring for 30 min after the addition, to obtain a magnesium alloy activity inhibitor slurry; wherein the mass ratio of the powder to the silica sol is 9:45.

[0090] The magnesium alloy casting of Comparative Example 5 was easy to clean the core, but the surface of the cast pipe had a small amount of black oxide, and its metallurgical quality was lower than the requirements of aviation standard HB7780-2005 Class I castings. X-ray examination showed a small area of ​​inclusion (slag).

[0091] Comparative Example 6

[0092] Comparative Example 6 refers to the method for preparing a ceramic core for magnesium alloy investment casting and the method for magnesium alloy investment casting of Example 1, except that, in step (5), the baking temperature is different.

[0093] In step (5) of Comparative Example 6, the baking temperature is 150°C.

[0094] The magnesium alloy casting of Comparative Example 6 was easy to clean the core, but the surface of the cast pipe had an uneven morphology, and its metallurgical quality was lower than the requirements of aviation standard HB7780-2005 Class I castings. X-ray examination showed small areas of inclusions (slag).

[0095] Experimental example

[0096] The strength test was conducted on the ceramic cores for magnesium alloy investment casting according to different embodiments of the present invention and comparative examples. The three-point bending strength test results are shown in Table 1.

[0097] Table 1 Three-point bending strength test results of different ceramic cores

[0098] serial number Three-point bending strength (MPa) Example 1 32.5 Example 2 31.6 Example 3 31.2 Comparative Example 1 27.2 Comparative Example 2 37.2 Comparative Example 3 28.5 Comparative Example 4 38.1 Comparative Example 5 26.3 Comparative Example 6 32.1

[0099] According to the embodiments and comparative examples of the present invention, the ceramic core for magnesium alloy investment casting prepared by the embodiments of the present invention is easy to remove from the core after casting, and the surface and interior of the formed pipeline are of good quality.

[0100] If the magnesium alloy activity inhibitor slurry is not applied, as in Comparative Example 1, the reaction between the molten magnesium alloy liquid and the ceramic core cannot be avoided, and a large amount of black reactants will appear on the surface of the pipe; if the composition of the coated magnesium alloy activity inhibitor slurry is not suitable, it is impossible to simultaneously take into account the core removal performance of the ceramic core and avoid the reaction between the magnesium alloy liquid and the ceramic core; if the baking temperature after applying the magnesium alloy activity inhibitor slurry is not suitable, it will cause the surface of the ceramic core to peel, resulting in an uneven casting pipe, which cannot meet the surface requirements of the casting pipe.

[0101] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of the present invention, rather than to limit it. Although the present invention has been described in detail with reference to the above embodiments, those skilled in the art should understand that they can still modify the technical solutions described in the above embodiments, or replace some or all of the technical features therein with equivalents. However, these modifications or replacements do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of the present invention.

Claims

1. A method for preparing a ceramic core for magnesium alloy investment casting, characterized in that: The method comprises the following steps: coating a magnesium alloy active inhibitor slurry on the surface of the ceramic core, and baking the slurry at 90 to 120° C. for 0.5 to 1 hour to form an inhibitor layer; The magnesium alloy activity inhibitor slurry comprises powder and silica sol in a mass ratio of 9: (30-40), and the powder comprises magnesium oxide powder and boric anhydride in a mass ratio of 1: (0.5-0.7).

2. The preparation method according to claim 1, characterized in that The preparation of the magnesium alloy activity inhibitor slurry comprises: ball-milling the powder, adding the silica sol, and stirring uniformly; Preferably, the ball milling conditions include: a ball-to-material ratio of (2-3):1, a rotation speed of 900-1100 rpm, and a ball milling time of 6-8 h.

3. The preparation method according to claim 1, characterized in that The coating thickness of the magnesium alloy activity inhibitor slurry is 0.05 to 0.1 mm.

4. The preparation method according to claim 1, characterized in that The preparation of the ceramic core comprises: mixing the core material and the plasticizer to prepare slurry, pressing to form a green body; and calcining the green body.

5. The preparation method according to claim 4, characterized in that The mass ratio of the core material to the plasticizer is (400-500):

91.

6. The preparation method according to claim 4, characterized in that The core material comprises fused silica fine powder, fused silica coarse powder and zirconium powder in a mass ratio of (5.5-6.5) : 1 : (2.5-3.5); Preferably, the fused quartz fine powder is 270-400 mesh; Preferably, the fused quartz coarse powder is 170-250 mesh; Preferably, the zirconium powder is 270-325 mesh.

7. The preparation method according to claim 4, characterized in that The plasticizers include paraffin and beeswax; Preferably, the mass ratio of the paraffin wax to the beeswax is (42-43):

3.

8. The preparation method according to claim 4, characterized in that The calcination process comprises: keeping the temperature at 200±10°C for 2-3 hours, heating the temperature to 350±10°C for 2-3 hours, and then heating the temperature to 800±10°C for 6-10 hours; Preferably, in the calcination process, the time for heating from room temperature to 200±10°C is 1.5±0.2h; the time for heating from 200±10°C to 350±10°C is 1.5±0.2h; the time for heating from 350±10°C to 800±10°C is 1±0.2h; Preferably, the calcination treatment further comprises: heat preservation treatment at 800±10°C for 6 to 10 hours, and then cooling to below 150°C along with the furnace.

9. A ceramic core for magnesium alloy investment casting, characterized in that: The ceramic core is prepared by the method for preparing a ceramic core for magnesium alloy investment casting according to any one of claims 1 to 8.

10. Use of the ceramic core for magnesium alloy investment casting according to claim 9 in magnesium alloy investment casting.

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