CN110483087A - Turbine blade of gas turbine hot investment casting alumina based ceramic core manufacturing method - Google Patents

Abstract

The invention relates to a method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades, which effectively solves the problems of broken cores and partial cores caused by insufficient high-temperature mechanical properties of the core during the casting process of large-scale gas turbine blades, and the difficulty of core removal after the blade is cast. including step 1: making resin molds, step 2: preparing ceramic slurry, step 3: preparing ceramic core blanks; step 4: pre-firing and degreasing; step 5: high-temperature sintering; The ceramic core is impregnated with silica sol to obtain secondary mullite. The present invention prepares a ceramic core with an internal flow channel structure through light-curing rapid prototyping and gel injection molding, so that the core can be removed during the core removal process. The core liquid enters the interior of the core through the flow channel, and the two ends of the core and the interior can be in contact with the core removal liquid at the same time, thereby increasing the removal rate of the core material. At the same time, mullite whiskers are synthesized in situ in the core, Improve the high temperature mechanical properties of the core.

Description

Manufacturing method of alumina-based ceramic core for precision casting of gas turbine blades

technical field

The invention relates to the technical field of investment precision casting, in particular to a method for manufacturing an alumina-based ceramic core for precision casting of turbine blades of gas turbines.

Background technique

Hollow turbine blades are the core components of aero-engines and gas turbines, which contain complex cooling channel structures. At present, blades are mainly formed by investment casting method, and ceramic core manufacturing is one of the main links of blade investment casting. For large-sized gas turbine blades, the core needs to be kept in the high-temperature molten metal for a long time during the directional solidification process of the blade. It is easy to break the core and eccentrically under the action of the gravity and thermal stress of the molten metal, resulting in unqualified blade manufacturing. Therefore, the core needs to have excellent high temperature mechanical properties.

At present, there are mainly two kinds of core materials: silicon oxide and aluminum oxide. Among them, aluminum oxide has excellent chemical stability at high temperature and is not easy to chemically react with high-temperature molten metal, so it is gradually widely used. The poor reactivity of the core liquid makes it difficult to remove the core after the blade is cast. In addition, for large-sized gas turbine blades, core removal is particularly difficult due to the large core length and cross-sectional dimensions. The methods to improve the removal rate of alumina-based ceramic cores mainly include high temperature and high pressure, pressure stirring and high pressure jetting, etc., but the requirements for equipment are relatively high. Another method is to increase the porosity of the core to facilitate the entry of the core removal liquid into the core and increase the contact area between the core removal liquid and the core, thereby increasing the core removal rate. However, since there will be a certain amount of non-connected holes inside the core, this method has limited effect on improving the core removal rate.

Therefore, the present invention provides a method for manufacturing an alumina-based ceramic core for precise casting of gas turbine blades to solve this problem.

Contents of the invention

In view of the above situation, in order to overcome the defects of the prior art, the present invention provides a method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades. It can also effectively improve the core removal performance of the core after the blade is cast and formed. It is mainly based on the light-curing rapid prototyping method to manufacture the core resin mold. There are several resin filaments inside the resin mold, and then through solidification The plastic injection molding method pours alumina-based ceramic slurry into the resin mold to manufacture the ceramic core blank; the resin filament in the resin mold burns out and forms a connected hole structure inside the core, which helps to improve the core At the same time, during the core sintering process, mullite whiskers can be synthesized in the core, which improves the high temperature mechanical properties of the core.

A method for manufacturing an alumina-based ceramic core for precise casting of gas turbine blades, characterized in that it comprises the following steps:

Step 1: making a resin mold; using a light-curing rapid prototyping method to manufacture a resin mold for core gel injection molding. The resin mold includes a resin mold shell and a resin wire inside it, and the resin wire and the resin mold shell are integrally formed;

Step 2: preparing ceramic slurry; dissolving monomer, crosslinking agent, and dispersant in deionized water, and then adding evenly mixed ceramic powder to make ceramic slurry;

Step 3: Prepare the ceramic core blank; pour the ceramic slurry described in step 2 into the cavity between the resin mold shell and the resin wire in step 1, and prepare the ceramic after the ceramic slurry is solidified in situ core wet blank, and then through freeze-drying to remove the internal moisture of the ceramic core wet blank, to obtain a ceramic core green blank;

Step 4: pre-firing and degreasing; pre-firing and degreasing the ceramic core blank in the step 3 to obtain a pre-firing and degreasing ceramic core;

Step five: high-temperature sintering; place the ceramic core after pre-burning and degreasing in step four in a corundum crucible, put 3% to 6% aluminum fluoride powder inside the corundum crucible, cover the crucible lid, and then carry out High temperature sintering, in situ synthesis of mullite whiskers inside the ceramic core;

Step 6: impregnating the synthesized ceramic core with silica sol, then drying the moisture in the silica sol in the ceramic core, and sintering the ceramic core at high temperature again to obtain secondary mullite.

Preferably, in the step 1, the resin mold for core gel injection molding is prepared by photosensitive resin through photocuring rapid prototyping.

Preferably, the resin filaments in the step 1 include trunk resin filaments and branch resin filaments, and the cross-sections of the trunk resin filaments and branch resin filaments can be square or circular;

For the main resin wire, when the cross-section is square, the side length is 1.0-1.5mm; when the resin wire cross-section is circular, the cross-sectional diameter is 1.0-1.5mm;

For branched resin filaments, when the cross section is square, the side length is 0.3-0.6mm, and when the cross-section of the resin filament is circular, the cross-sectional diameter is 0.3-0.6mm.

Preferably, the ceramic powder in the second step is composed of alumina as a base material and a small amount of silica as a mineralizer, wherein the alumina ceramic powder is made of fused corundum powder with a particle size of 40-60 μm, 5-10 μm and 1-3 μm. Mixing accounts for 30%, 50% and 17% of the mass of the solid phase powder respectively. The silicon oxide powder is silicon oxide with a particle size of 1-3 μm, which accounts for 3% of the mass of the solid phase powder.

Preferably, the monomer and crosslinking agent in the step 2, wherein the monomer is an acrylamide monomer, the crosslinking agent is N, N'-methylenebisacrylamide, and the monomer and crosslinking agent are according to (15 ～25):1 mass ratio is made into mixture, and monomer and crosslinking agent are dissolved in deionized water to make the premix solution that mass concentration is 10%～20%;

The dispersant is 1% to 3% sodium polyacrylic acid solution, the amount of which is 2.0% to 3.0% of the mass of the ceramic powder; the ceramic powder in the ceramic slurry accounts for 50% to 60% of the slurry volume, and the balance is to Ionized water, monomers, crosslinking agents and dispersants; initiators and catalysts are ammonium persulfate aqueous solution and tetramethylethylenediamine aqueous solution, and the addition amounts of the two are 0.5-1% and 0.1%- 1%.

Preferably, the ceramic core needs to be placed in the crucible during the synthesis process of mullite whiskers in the step 5, the crucible needs to be covered with a crucible lid, and aluminum fluoride powder needs to be laid on the bottom of the crucible; the aluminum fluoride powder is 3% to 6% of the sum of the mass of alumina and silica.

Preferably, the pre-burning and degreasing in the step 4 adopts a slow heating method first and then a fast heating method, and the heating equipment is a box-type resistance heating furnace, and the room temperature is heated to 300 ° C at 30 ° C per hour, and the temperature is kept for 0.5 to 1 hour;

Then heat up to 600°C at 100°C-150°C per hour, and keep warm for 0.5-1 hour;

Then raise the temperature at 200-300°C per hour to 900-1000°C, keep it warm for 3-5 hours, and cool to room temperature with the furnace.

Preferably, in the step 5, the mullite whiskers are synthesized by high-temperature sintering at 200°C to 300°C per hour to 1100°C to 1200°C, kept for 1 to 1.5 hours, and then heated to 1400°C at 200°C to 300°C per hour. ℃～1500℃, keep warm for 3～4 hours.

Preferably, in the step 6, after synthesizing the mullite whiskers, impregnate the ceramic core body with silica sol, the mass fraction of silica sol is 40%, and perform secondary high-temperature sintering at 200°C to 200°C per hour after impregnating silica sol Raise the temperature from 300°C to 1200°C-1300°C, and keep it warm for 2-3 hours.

Compared with the prior art, the present invention has the following technical effects:

The present invention prepares complex structure ceramic core resin molds by light-curing rapid prototyping method, and prepares several resin wire structures in the mold at the same time, and then pours ceramic slurry in the resin mold by gel injection molding method to prepare ceramic cores, because The resin mold and its internal wires can be burned in the subsequent degreasing process, and a micro-connected flow channel structure is formed inside the core, so that the core removal liquid can enter the interior of the core through the flow channel during the core removal process, and the two ends of the core The core and the interior can be in contact with the core removal liquid at the same time, thereby increasing the removal rate of the core material.

The present invention synthesizes mullite whiskers inside the core through a gas phase reaction method, which can effectively improve the high-temperature mechanical properties of the core during blade casting and forming, help reduce fracture and partial core of the core, and improve the success rate of blade manufacturing; in addition , because the whiskers are synthesized inside the core by the in-situ reaction synthesis method, the process is simpler compared with interspersing continuous fibers inside the core, and compared with adding short fibers in the ceramic slurry, it can also reduce the increase in fiber size. The influence of slurry viscosity on the filling performance of ceramic slurry.

Description of drawings

Figure 1 is a schematic diagram of a ceramic core resin mold.

Figure 2 is a schematic diagram of the prepared ceramic core.

Fig. 3 is a schematic cross-sectional view of a ceramic core resin mold.

Fig. 4 is a schematic cross-sectional view of the ceramic core.

Figure 5 is a schematic diagram of the microstructure of the ceramic core.

Wherein, 1: resin mold split body A; 2: resin mold split body B; 3: resin mold split body C; 4: ceramic core A; 5: ceramic core B; 6: ceramic core C; 7: form The resin wire material of the inner runner structure of the ceramic core A; 7a: the main resin wire material; 7b: the branch resin wire material; 8: the resin wire material forming the inner flow channel structure of the ceramic core B; 9: the resin wire material forming the ceramic core C Resin wire with inner runner structure; 10: inner runner structure of ceramic core A; 10a: main channel; 10b: branch runner; 11: inner runner structure of ceramic core B; 12: inner flow of ceramic core C channel structure; 13: core matrix material alumina; 14: mullite whiskers generated inside the core.

Detailed ways

The aforementioned and other technical contents, features and functions of the present invention will be clearly presented in the following detailed description of the embodiments with reference to the accompanying drawings 1 to 5 . The structural contents mentioned in the following embodiments are all based on the accompanying drawings of the description.

In order to realize above-mentioned task, the present invention takes following technical solution:

Step 1: First, the core resin mold is manufactured by light-curing rapid prototyping technology. The mold includes a resin shell and an internal resin wire, and the resin wire and the resin mold shell are integrally formed;

The resin wire is composed of the main resin wire and the branch resin wire. The main resin wire will form the main flow channel inside the core after burning out, and the branch resin wire will form the branch flow channel inside the core after the main resin wire is burned out. The cross section of wood and branched resin wire is square or round;

For the main resin wire, when the cross-section is square, the side length is 1.0-1.5mm; when the cross-section of the resin wire is circular, the diameter of the cross-section is 1.0-1.5mm; When it is square, the side length is 0.3-0.6mm, and when the cross-section of the resin wire is circular, the diameter of the cross-section is 0.3-0.6mm.

Step 2: Next, dissolve the monomer and the organic matter of the crosslinking agent in deionized water, then add the dispersant and uniformly mixed alumina and a small amount of silicon oxide ceramic powder in turn, and make a ceramic slurry after being uniformly mixed by ball milling. Add initiator and catalyst before pouring, stir and mix evenly, wherein:

The organic matter is acrylamide monomer and N,N′-methylenebisacrylamide cross-linking agent, and the two are formulated into a mixture according to the mass ratio of (15～25):1, and the organic matter is dissolved in deionized water to make a mass concentration of 10% ~ 20% premix;

The dispersant is 1% to 3% polyacrylic acid sodium solution, and the amount added is 2.0% to 3.0% of the mass of the ceramic powder;

Alumina ceramic powder is composed of a mixture of fused corundum powder with a particle size of 40-60 μm, 5-10 μm and 1-3 μm, and the three account for 30%, 50% and 17% of the solid phase powder mass respectively;

The particle size of silicon oxide powder is 1-3 μm, accounting for 3% of the mass of solid phase powder;

The ceramic powder in the ceramic slurry accounts for 50% to 60% of the slurry volume, and the balance is deionized water, monomer, crosslinking agent and dispersant;

The initiator is an aqueous solution of ammonium persulfate, and the catalyst is an aqueous solution of tetramethylethylenediamine, and the addition amounts of the two are respectively 0.5-1% and 0.1-1% of the mass of the premixed liquid.

Step 3: Pour the ceramic slurry into the resin mold, fill the cavity area between the inner wall of the resin mold shell and the resin filament, and obtain a wet ceramic core containing the resin filament after the ceramic slurry is solidified in situ. The green body is then freeze-dried to remove moisture inside the green body to obtain a ceramic core green body.

Step 4: Put the dried core into a box-type electric heating furnace, burn off the resin mold, the internal wire material of the mold and the organic gel inside the core blank by pre-firing and degreasing;

Pre-burning and degreasing adopts the heating method of slow first and then fast. When entering the furnace at room temperature, the temperature is raised to 300°C at 30°C per hour and kept for 0.5 to 1 hour; then the temperature is raised to 600°C at 100°C to 150°C per hour and held for 0.5 to 1 hour. ; Finally, the temperature is raised from 200°C to 300°C per hour to 900°C to 1000°C, kept for 3 to 5 hours, and cooled to room temperature with the furnace.

Step 5: Place the pre-fired and degreased core in a corundum crucible, lay aluminum fluoride powder on the bottom of the crucible, the mass of aluminum fluoride powder is 3% to 6% of the mass of ceramic powder, and then cover the crucible The crucible cover is put into the box-type electric heating furnace again for high-temperature sintering;

High-temperature sintering generates whiskers at 200-300°C per hour to 1100-1200°C, heat preservation for 1-1.5 hours, then heat-up at 200-300°C per hour to 1400-1500°C, and heat preservation for 3-4 hours;

In a high temperature environment, mullite whiskers are generated inside the core through a gas phase reaction method, and the reaction equations are shown in equations (1) to (4):

6AlF ₃ +3O ₂ →6AlOF+12F (1)

Al ₂ O ₃ +2F→2AlOF+0.5O ₂ (2)

SiO ₂ +8F→2SiF ₄ +2O ₂ (3)

6AlOF+2SiF ₄ +3.5O ₂ →3Al ₂ O ₃ 2SiO ₂ +14F (4)

Step six: using 40% mass fraction of silica sol to impregnate the core, then drying the moisture in the silica sol in the core, and sintering the core again at high temperature;

High-temperature sintering again at 200°C-300°C per hour to 1200°C-1300°C and keep warm for 2-3 hours;

The nano-silica in the silica sol reacts with the core matrix material alumina at high temperature to form secondary mullite, which increases the interface bonding area and bonding strength between the mullite whiskers and the core matrix material alumina, Thus, the reinforcing effect of the whiskers on the core is improved; at the same time, the secondary mullite itself is also a high-temperature strengthening phase, which can further improve the high-temperature mechanical properties of the core.

The detailed structure and principle in each step will be described in detail below:

The invention is a method for manufacturing an alumina-based ceramic core for precise casting of gas turbine blades, comprising the following steps:

step one

The core resin mold is manufactured by light-curing rapid prototyping method, and the wall thickness of the resin mold is about 0.8-1.5mm.

The resin mold includes resin mold split body A1, resin mold split body B2 and resin mold split body C3, which are respectively used for gel injection molding three different ceramic cores A4, ceramic core B5 and ceramic core C6. In the resin mold split A1, the resin mold split B2 and the resin mold split C3, the resin filament 7 used to form the internal flow channel structure of the ceramic core A and the resin wire material 7 used to form the internal flow channel structure of the ceramic core B were prepared respectively. The resin filament 8 and the resin filament 9 forming the internal channel structure of the ceramic core C. Wherein the resin wire material 7 forming the internal runner structure of the ceramic core A is made up of the main resin wire material 7a and the branch resin wire material 7b; the resin wire material 8 forming the internal flow channel structure of the ceramic core B is composed of the main resin wire material 7a and the branch resin wire material 7b Composed of branched resin filaments 7b; the resin filaments 9 forming the inner channel structure of the ceramic core C are composed of trunk resin filaments 7a and branched resin filaments 7b. The cross-sectional size of the main resin wire forming the main channel structure is 1mm×1mm, the cross-sectional size of the branch resin wire forming the branch flow channel structure is 0.4mm×0.4mm, and the distance between the two ends of the branch resin wire is 2mm from the outer edge of the core. -3mm.

step two

Preparation of gel-cast ceramic core greens.

First, dissolve the organic matter in deionized water to make a premix, then add ceramic powder to make a ceramic slurry, add an initiator and a catalyst before pouring, and mix evenly, wherein the volume ratio of the ceramic powder to the slurry is 50% to 60% ; The organic matter is a mixture of acrylamide monomer and N,N'-methylenebisacrylamide according to the mass ratio of (15-25):1, and the mass concentration in deionized water is 10%-20%; the initiator The catalyst is an aqueous solution of ammonium persulfate and an aqueous solution of tetramethylethylenediamine, and the addition amounts of the two are respectively 0.5-1% and 0.1-1% of the mass of the premixed liquid.

Pour the ceramic slurry into the resin mold, fill the cavity area between the inner wall of the resin mold shell and the internal resin wire, and make a ceramic core wet body after the ceramic slurry is solidified in situ, and then remove the mold by freeze drying. Moisture inside the core to obtain a ceramic core blank.

step three

Pre-fire and degrease the ceramic core to remove the resin filament inside the core.

Pre-burning and degreasing adopts the heating method of slow first and then fast. The heating equipment is a box-type resistance heating furnace. The room temperature is heated to 300°C at 30°C per hour, and the temperature is kept at 0.5 to 1 hour; then the temperature is raised at 100°C to 150°C per hour. to 600°C, keep warm for 0.5-1 hour; then raise the temperature at 200°C-300°C per hour to 900°C-1000°C, keep warm for 3-5 hours; cool down to room temperature with the furnace, and get ceramic core A with internal flow channel structure Internal flow channel structure 10, ceramic core A internal flow channel structure 10 is composed of main channel 10a and branch flow channel 10b; ceramic core B internal flow channel structure 11 is composed of main channel 10a and branch flow channel 10b; ceramic core C The internal channel structure 12 is composed of a main channel 10a and a branch channel 10b.

The flow channel will remain in the core after the core is sintered at high temperature and the blade casting is completed, so that the core removal efficiency of the core can be improved during the core removal process.

step four

Fabrication of whisker-reinforced ceramic cores.

Aluminum fluoride is laid on the bottom of the corundum crucible, the mass of aluminum fluoride accounts for 4% of the total mass of the ceramic core, then the core is placed in the crucible and the crucible lid is covered, and then the crucible is placed in a box-type resistance heating furnace for heating. High temperature sintering into mullite whiskers.

The sintering process for synthesizing whiskers is to raise the temperature from 200°C to 300°C per hour to 1100°C to 1200°C, keep it warm for 1 to 1.5 hours, then raise the temperature to 1400°C to 1500°C at 200°C to 300°C per hour, and keep it warm for 3 to 4 hours .

Aluminum fluoride reacts with oxygen at high temperature to generate gas, and reacts with alumina and silicon oxide in the gas phase to form mullite whiskers 14 generated inside the core, and the mullite whiskers 14 generated inside the core are bridged to form the core matrix The material is aluminum oxide 13, which in turn acts as a reinforcement for the ceramic core.

step five

The mandrel is impregnated with silica sol, and the mass fraction of silica sol is 40%.

Then the core is placed in an oven, the moisture in the silica sol in the core is dried, and the core is sintered at high temperature again.

High-temperature sintering is carried out at a rate of 200°C-300°C per hour to 1200°C-1300°C and heat preservation for 2-3 hours. The nano-silica in the silica sol reacts with alumina at high temperature to form secondary mullite, which can increase the gap between the mullite whiskers 14 generated inside the core and the core matrix material alumina 13. The interfacial bonding area and bonding strength are improved, thereby improving the reinforcing effect of whiskers on the core. At the same time, as a high-temperature strengthening phase, secondary mullite can further enhance the high-temperature mechanical properties of the core. The three-point high-temperature bending test experiment shows that the high-temperature strength of the prepared core sample can reach 17-18 MPa at 1500 °C.

In summary, the manufacturing center of the present invention has a gas turbine turbine blade alumina-based ceramic core with a fine flow channel structure and mullite whiskers inside, and its biggest advantage is that it can improve the aluminum oxide-based ceramic core of a large-scale industrial gas turbine blade. The core stripping performance of the core can effectively solve the problems of insufficient high-temperature mechanical properties of the core and easy core breakage and partial core during the blade investment casting process. In addition, the present invention adopts a photocuring rapid prototyping method to manufacture a core resin mold with a fine resin filament structure inside. The size of the resin filament structure is easy to adjust and form, so the process is simple and easy to control.

Claims (9)

1. A method for manufacturing an alumina-based ceramic core for precision casting of a gas turbine blade, characterized in that it comprises the following steps: Step 1: making a resin mold; using a light-curing rapid prototyping method to manufacture a resin mold for core gel injection molding. The resin mold includes a resin mold shell and a resin wire inside it, and the resin wire and the resin mold shell are integrally formed; Step 2: preparing ceramic slurry; dissolving monomer, crosslinking agent, and dispersant in deionized water, and then adding evenly mixed ceramic powder to make ceramic slurry; Step 3: Prepare the ceramic core blank; pour the ceramic slurry described in step 2 into the cavity between the resin mold shell and the resin wire in step 1, and prepare the ceramic after the ceramic slurry is solidified in situ core wet blank, and then through freeze-drying to remove the internal moisture of the ceramic core wet blank, to obtain a ceramic core green blank; Step 4: pre-firing and degreasing; pre-firing and degreasing the ceramic core blank in the step 3 to obtain a pre-firing and degreasing ceramic core; Step five: high temperature sintering; place the ceramic core after pre-burning and degreasing in step four in the corundum crucible, put 3% to 6% aluminum fluoride powder inside the corundum crucible, cover the crucible lid, and then carry out High temperature sintering, in situ synthesis of mullite whiskers inside the ceramic core; Step 6: impregnating the synthesized ceramic core with silica sol, then drying the moisture in the silica sol in the ceramic core, and sintering the ceramic core at high temperature again to obtain secondary mullite. 2. the method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein the resin mold for core gel injection molding in said step 1 adopts photosensitive resin through photocuring rapid prototyping preparation . 3. the method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein the resin filament in the step 1 comprises a trunk resin filament and a branch resin filament, and the trunk resin The cross-section of the wire and the branched resin wire can be square or circular; For the main resin wire, when the cross-section is square, the side length is 1.0-1.5mm; when the resin wire cross-section is circular, the cross-sectional diameter is 1.0-1.5mm; For branched resin filaments, when the cross section is square, the side length is 0.3-0.6mm, and when the cross-section of the resin filament is circular, the cross-sectional diameter is 0.3-0.6mm. 4. the method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein the ceramic powder in said step 2 is made up of matrix material alumina and a small amount of mineralizer silicon oxide, wherein Alumina ceramic powder is mixed with fused corundum powder with a particle size of 40-60 μm, 5-10 μm and 1-3 μm, which account for 30%, 50% and 17% of the mass of solid phase powder respectively. Silicon oxide with a diameter of 1 to 3 μm accounts for 3% of the mass of the solid phase powder. 5. the method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein the monomer and crosslinking agent in the step 2, wherein the monomer is an acrylamide monomer, The cross-linking agent is N, N´-methylenebisacrylamide, the monomer and the cross-linking agent are prepared as a mixture according to the mass ratio of (15-25): 1, and the monomer and the cross-linking agent are dissolved in deionized water. Premix solution with a mass concentration of 10% to 20%; The dispersant is 1% to 3% polyacrylic acid sodium solution, the amount of which is 2.0% to 3.0% of the mass of the ceramic powder; the ceramic powder in the ceramic slurry accounts for 50% to 60% of the slurry volume, and the balance is to Ionized water, monomer, cross-linking agent and dispersant; initiator and catalyst are ammonium persulfate aqueous solution and tetramethylethylenediamine aqueous solution, the addition amount of the two is 0.5-1% and 0.1%- 1%. 6. the method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein the ceramic core needs to be placed in a crucible during the synthesis of mullite whiskers in the step 5, The crucible needs to be covered with a crucible lid, and aluminum fluoride powder needs to be placed on the bottom of the crucible; the aluminum fluoride powder is 3% to 6% of the sum of the mass of alumina and silica. 7. The method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein in said step 4, pre-firing and degreasing adopts a slow heating method and then a fast heating method, and the heating equipment is a box type Resistance heating furnace, enter the furnace at room temperature and raise the temperature from 30°C to 300°C per hour, and keep warm for 0.5 to 1 hour; Then heat up to 600°C at 100°C-150°C per hour, and keep warm for 0.5-1 hour; Then raise the temperature at 200-300°C per hour to 900-1000°C, keep it warm for 3-5 hours, and cool to room temperature with the furnace. 8. The method for manufacturing an alumina-based ceramic core for precise casting of gas turbine blades according to claim 1, characterized in that in step 5, the high-temperature sintering and synthesis of mullite whiskers is carried out at a rate of 200° C. to 300° C. per hour. Heat to 1100°C-1200°C, keep warm for 1-1.5 hours, then raise the temperature at 200-300°C per hour to 1400-1500°C, keep warm for 3-4 hours. 9. The method for manufacturing an alumina-based ceramic core for precision casting of gas turbine blades according to claim 1, wherein in said step 6, after the mullite whiskers are synthesized, the ceramic core blank is siliconized. Sol impregnation, the mass fraction of silica sol is 40%, after the impregnation of silica sol, the second high-temperature sintering is carried out at 200°C-300°C per hour to 1200°C-1300°C, and the temperature is kept for 2-3 hours.