A method for producing a fine-grained large bloom

Abstract

The application provides a preparation method of fine-grain large casting blank, and the steps comprise the following: carrying out purification treatment on the metal melt in the inner cavity of a mold, and controlling the mold to rotate at a set speed; vertically inserting an inner mold into the inner cavity of the mold, so that an annular chamber is formed between the inner mold and the inner wall of the mold; covering the cover plate of the mold, connecting the mold to a vacuumizing device, and carrying out vacuumizing treatment; stopping the vacuumizing when the vacuum degree reaches-0.06 to-0.09 MPa, and then filling inert gas into the mold after pressure maintaining for 1 to 3 minutes; controlling the temperature of the four heating areas on the periphery of the mold to be within a set temperature range respectively; controlling the mold to rotate at a set speed two, and vibrating at a set frequency simultaneously; and then disassembling the mold and taking out the casting blank in the inner mold after the metal melt in the inner mold is completely solidified. The application integrates the melt purification and the casting blank forming into the same set of equipment, and can save about 60% of the floor space compared to the existing casting blank production line, and can form the large casting blank with fine grains without using the melt conveying facilities.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of magnesium alloy ingot manufacturing, and particularly relates to a preparation method of fine-grain large ingot (diameter not less than 1.2 m, length not less than 0.8 m). BACKGROUND

[0002] In the manufacturing process of large ingot with a diameter of Φ600-800 mm or more, due to the large difference between the inner and outer cooling rates of the ingot, the long solidification time, serious composition segregation or ingot core cracking is prone to occur. For high-strength heat-resistant magnesium alloys with high rare earth content such as EW75, WE83, WE91, the smelting and casting temperature is relatively higher, the thermal conductivity is lower, the solidification shrinkage is very large, the cooling strength is small during the ingot casting process, the solidification time is long, the composition segregation is serious, and the ingot core cracking is easily caused.

[0003] In order to solve the problems of complicated process, high preparation difficulty and poor forming performance of the existing large-size rare earth magnesium alloy ingot preparation process, a preparation method of large-size rare earth magnesium alloy ingot is developed in the early stage. First, the rare earth alloy melt is input into a solidification mold, then the solidification mold is placed in a vacuum tank for vacuum treatment, and then inert gas is filled into the solidification mold. The solidification mold filled with inert gas is moved to the lifting platform of the cooling device, the temperature of the four heating zones of the cooling device is controlled in the range of 200-700 DEG C, the circulating water of the cooling device is started, and the temperature at different positions of the ingot is monitored. When the temperature of the ingot is less than 400 DEG C, the lifting mechanism of the cooling device is started to slowly immerse the solidification mold in the cooling water until the ingot is solidified. Although the magnesium alloy ingot grain can be refined to about 50 microns by using this scheme, it is very important for the application of magnesium alloy to further refine the grain of such large ingot.

[0004] In addition, in the process of preparing the magnesium alloy ingot, two independent processes are adopted, that is, the magnesium alloy melt is first purified, and then input into the mold for casting forming. The melt purification equipment and melt conveying facility used have a large occupied space. SUMMARY

[0005] The application aims to provide a new preparation method of fine-grain large ingot, which integrates the melt purification and ingot forming into the same set of equipment, and can form the large ingot with fine grains without using the melt conveying facility.

[0006] In order to achieve the above-mentioned purpose, the application adopts the technical scheme as follows.

[0007] A preparation method of fine-grain large ingot, the steps comprising:

[0008] Step 1, the metal melt is input into the inner cavity of the mold, and the mold is placed on a rotary vibration platform;

[0009] Step 2, the metal melt in the inner cavity of the mold is purified, and the mold is controlled to rotate at a set speed;

[0010] Step 3, the inner mold is vertically inserted into the inner cavity of the mold, so that an annular chamber is formed between the inner mold and the inner wall of the mold;

[0011] Step 4, the cover plate of the mold is closed, the mold is connected to a vacuum pumping device and vacuum pumping is performed, when the vacuum degree reaches-0.06~ -0.09MPa, the vacuum pumping is stopped, and the mold is filled with inert gas after pressure maintaining for 1~3 minutes;

[0012] Step 5, the temperature of the four heating zones around the mold is controlled within a set temperature range respectively;

[0013] Step 6, the mold is controlled to rotate at a set speed two, and vibrates at a set frequency;

[0014] Step 7, after the metal melt in the inner mold is completely solidified, the mold is disassembled and the cast blank in the inner mold is taken out.

[0015] Further, step 2 specifically comprises:

[0016] Step 21, the filter part of the filtering device is inserted into the inner cavity of the mold until the bottom end of the filter part abuts against the bottom wall of the inner cavity of the mold;

[0017] Step 22, the mold is controlled to rotate at a speed of 800-1000r / min;

[0018] Step 23, after step 22 is performed for 20-30 minutes, the rotating speed of the mold is first reduced to zero, and then the filter part is taken out upward;

[0019] The filter part comprises a tungsten steel frame connected to the connecting plate, a ceramic filter element vertically extractable but horizontally limited is arranged in the tungsten steel frame, a through hole is arranged on the connecting plate directly above the tungsten steel frame, the ceramic filter element can pass through the through hole, and one side end of the ceramic filter element faces the axis of the inner cavity of the mold. By adopting such a scheme, the suspended impurities in the melt during high-speed rotation can be introduced into the ceramic filter element, which is more conducive to purifying the melt, and the ceramic filter element can be quickly and flexibly replaced.

[0020] In order to better purify the melt, six ceramic filter elements are uniformly arranged along the circumferential direction, the width of each ceramic filter element is 1 / 2~2 / 3 of the diameter of the inner cavity of the mold, and the length of each ceramic filter element is equal to the height of the inner cavity of the mold.

[0021] Further, the inner mold is a cylinder with open ends, the lower end of the cylinder can abut against the bottom wall of the inner cavity of the mold, and the upper end of the cylinder can abut against the bottom wall of the cover plate. By adopting the scheme, the cast blank can be quickly taken out.

[0022] As a preferred scheme, four electric heating zones are arranged along the vertical direction on the periphery of the mold, wherein the temperatures of the four heating zones from bottom to top satisfy 50℃≤Ⅳ-Ⅲ≤150℃, 50℃≤Ⅲ-Ⅱ≤150℃, and 50℃≤Ⅱ-Ⅰ≤150℃.

[0023] As a preferred scheme, in step 6, the speed two is set to 40 rpm, and the vibration frequency is 60 Hz.

[0024] As a preferred scheme, the temperature of the heating zone I is 350℃, the temperature of the heating zone II is 500℃, the temperature of the heating zone III is 650℃, and the temperature of the heating zone IV is 700℃, and the large cast blank is Mg-6Gd-3Y-0.5Zr magnesium alloy.

[0025] As a preferred scheme, the temperature of the heating zone I is 300℃, the temperature of the heating zone II is 400℃, the temperature of the heating zone III is 500℃, and the temperature of the heating zone IV is 600℃, and the large cast blank is Mg-8.5Gd-4.5Y-0.4Zr magnesium alloy.

[0026] As a preferred scheme, the temperature of the heating zone I is 340℃, the temperature of the heating zone II is 470℃, the temperature of the heating zone III is 530℃, and the temperature of the heating zone IV is 620℃, and the large cast blank is Mg-8Gd-3Y-0.6Zr magnesium alloy.

[0027] Further, the bottom wall of the inner cavity of the mold is provided with a limiting groove, and the limiting part at the lower end of the inner mold can be clamped into the limiting groove, so that the mold and the inner mold can rotate synchronously.

[0028] Beneficial effects: The present application integrates melt purification and cast blank forming into the same set of equipment, which can save about 60% of the floor space compared with the existing cast blank production line, and can form a large cast blank with fine grains without using melt conveying facilities, and the grain size of the obtained magnesium alloy large cast blank is 35±3 μm. In the present application, the melt is cleverly moved towards the inner cavity edge of the mold by high-speed rotation, thereby introducing most of the impurities in the melt into the ceramic filter element and a small part of the impurities into the melt in the annular chamber, thereby realizing the purification of the melt, and the specific structure also has the advantages of facilitating quick and flexible replacement of the ceramic filter element. BRIEF DESCRIPTION OF DRAWINGS

[0029] Figure 1 is an external structure schematic diagram of the mold and the filter device in the embodiment;

[0030] Figure 2is a schematic axial section of the mould and filter device in the example;

[0031] Figure 3 is a schematic radial section of the mould and filter device in the example;

[0032] Figure 4 is a schematic partial view of the filter device in the example;

[0033] Figure 5 is a schematic view of the melt flow in the mould cavity during rotation of the melt in the example, the direction of the arrow indicating the direction of the melt flow;

[0034] Figure 6 is a schematic view of the mould with the insert mould inserted in the example, the direction of the arrow indicating the direction of rotation of the mould. DETAILED DESCRIPTION

[0035] The following description of the examples is merely intended to help understand the principles of the application and its core idea, and is not intended to limit the scope of protection of the application. It should be noted that improvements to the application made by those of ordinary skill in the art without departing from the principles of the application also fall within the scope of protection of the claims of the application.

[0036] The mould and filter device used in the example will first be described, as shown in Figures 1 to 6As shown, the filter part includes a tungsten steel frame 5 connected to the connecting plate, a ceramic filter element 4 is arranged in the tungsten steel frame 5 and can be vertically taken out but is limited in the horizontal direction, the tungsten steel frame 5 is essentially a frame structure, the inner cavity of the frame structure is used to accommodate the ceramic filter element 4, a through hole 2 is arranged on the connecting plate 3 directly above the tungsten steel frame 5, the ceramic filter element 4 can pass through the through hole 2, one side end of the ceramic filter element 4 is directed to the axis of the inner cavity of the mold 1; the connecting plate 3 is connected with a displacement mechanism (which can be a lifting facility or a three-dimensional displacement mechanism), the displacement mechanism is used to control the fixing or movement of the filter device to a specified position; along the circumferential direction, six ceramic filter elements 4 are uniformly arranged, the width of each ceramic filter element 4 is 1 / 2 of the diameter of the inner cavity of the mold 1, and the length of each ceramic filter element 4 is equal to the height of the inner cavity of the mold 1. Among them, the inner mold 7 is a cylinder with two open ends, the lower end of the cylinder can abut against the bottom wall of the inner cavity of the mold 1, and the upper end of the cylinder can abut against the bottom wall of the cover plate 14. Four electric heating zones are arranged along the vertical direction on the periphery of the mold 1, the electric heating element 10 arranged from bottom to top corresponds to heating zone I, the electric heating element 11 corresponds to heating zone II, the electric heating element 12 corresponds to heating zone III, and the electric heating element 13 corresponds to heating zone IV; the bottom wall of the inner cavity of the mold 1 is provided with a limiting groove 6, and the limiting part at the lower end of the inner mold 7 can be clamped into the limiting groove 6, so that the mold 1 and the inner mold 7 can rotate synchronously, and an annular chamber 8 is formed between the inner mold 7 and the inner wall of the mold 1. In order to facilitate demolding, the acute angle between the inner side wall of the mold 1 and the horizontal plane is 85°, that is, the inner side wall of the mold 1 is in a conical surface structure (the diameter corresponding to the upper part of the inner side wall of the mold 1 is larger than the diameter corresponding to the lower part of the inner side wall of the mold 1). When demolding, the cover plate 14 of the mold 1 is first removed, then the solidified body in the annular chamber 8, the inner mold 7 and the solidified body in the inner mold 7 are taken out as a whole, then the solidified body in the inner mold 7 is taken out from the inner mold 7, and the solidified body in the inner mold 7 is used as a cast blank, and the solidified body in the annular chamber 8 is recycled and reused.

[0037] Example 1

[0038] A method for preparing a fine-grained large cast blank, using the aforementioned mold and filter device to prepare a Mg-6Gd-3Y-0.5Zr magnesium alloy ingot with a diameter of 1300mm and a length of 1200mm, the steps comprising:

[0039] Step 1, placing the mold 1 on the rotating vibration platform 9, and inputting the metal melt into the inner cavity of the mold 1;

[0040] Step 2, purifying the metal melt in the inner cavity of the mold 1, and controlling the mold 1 to rotate at a set speed; specifically including steps 21-23, as follows:

[0041] Step 21, first insert the ceramic filter element 4 from the through hole 2 on the connecting plate 3, then insert the filter part (the tungsten steel frame 5 with the ceramic filter element 4) of the filter device into the inner cavity of the mold 1 until the bottom end of the filter part abuts against the bottom wall of the inner cavity of the mold 1, and keep the filter device fixed (two schemes can be adopted, scheme 1 is to control the connecting plate 3 to remain in a fixed position by means of a displacement mechanism; scheme 2 is to fix the connecting plate 3 by means of fasteners / locking members, and the embodiment adopts scheme 2);

[0042] Step 22, control the mold 1 to rotate at a speed of 850 rpm, and keep the filter device fixed during the process;

[0043] Step 23, after 30 minutes of step 22, first reduce the rotating speed of the mold 1 to zero, and then take out the filter part upward, which is actually to take out the whole of the ceramic filter element 4, the tungsten steel frame 5 and the connecting plate 3;

[0044] Step 3, vertically insert the inner mold 7 into the inner cavity of the mold 1 to form an annular chamber 8 between the inner mold 7 and the inner wall of the mold 1, at this time, the limiting part at the lower end of the inner mold 7 is just clamped into the limiting groove 6;

[0045] Step 4, cover the cover plate 14 of the mold 1, connect the mold 1 to the vacuumizing equipment and perform vacuumizing treatment, stop vacuumizing when the vacuum degree reaches-0.06 Mpa, and after pressure maintaining for 2 minutes, fill inert gas into the mold 1 and the inner mold 7;

[0046] Step 5, control the temperature of the four heating zones of the mold 1 to be within the set temperature range, wherein the temperature of the heating I zone 9 is controlled to be 350±2℃, the temperature of the heating II zone 8 is controlled to be 500±2℃, the temperature of the heating III zone 7 is controlled to be 650±2℃, and the temperature of the heating IV zone 6 is controlled to be 700±2℃;

[0047] Step 6, control the mold 1 to rotate at a speed of 30 rpm, and simultaneously vibrate at a frequency of 60 Hz;

[0048] Step 7, after the metal solution in the inner mold 7 is completely solidified, disassemble the mold (during the process when the ingot temperature is higher than 400℃, adopt natural cooling for cooling; during the process when the ingot temperature is lower than 400℃, adopt air cooling for cooling), and take out the cast billet in the inner mold 7.

[0049] Embodiment 2

[0050] A method for preparing a fine-grained large cast billet, which adopts the aforementioned mold and filter device to prepare a Mg-8.5Gd-4.5Y-0.4Zr magnesium alloy ingot with a diameter of 1500 mm and a length of 800 mm, and the steps include:

[0051] Step 1, placing the mold 1 on the rotary vibration platform 9, and inputting the metal melt into the inner cavity of the mold 1;

[0052] Step 2, purifying the metal melt in the inner cavity of the mold 1, and controlling the mold 1 to rotate at a set speed; specifically including steps 21-23, as follows:

[0053] Step 21, first inserting the ceramic filter element 4 from the through hole 2 on the connecting plate 3, and then inserting the filter part (the tungsten steel frame 5 with the ceramic filter element 4) of the filter device into the inner cavity of the mold 1 until the bottom end of the filter part abuts against the bottom wall of the inner cavity of the mold 1;

[0054] Step 22, controlling the mold 1 to rotate at a speed of 820 rpm, and keeping the filter device stationary during the process;

[0055] Step 23, after 28 minutes of step 22, first reducing the speed of the mold 1 to zero, and then taking out the filter part upward, which is essentially taking out the whole of the ceramic filter element 4, the tungsten steel frame 5 and the connecting plate 3;

[0056] Step 3, vertically inserting the inner mold 7 into the inner cavity of the mold 1 to form an annular chamber 8 between the inner mold 7 and the inner wall of the mold 1, at this time, the limiting part at the lower end of the inner mold 7 is just clamped into the limiting groove 6;

[0057] Step 4, covering the cover plate 14 of the mold 1, connecting the mold 1 to the vacuum pumping equipment and performing vacuum pumping treatment, stopping vacuum pumping when the vacuum degree reaches -0.07 Mpa, and then filling inert gas into the mold 1 and the inner mold 7 after maintaining the pressure for 3 minutes;

[0058] Step 5, controlling the temperature of the four heating zones on the periphery of the mold 1 to be within the set temperature range, wherein the temperature of heating zone I is 300℃, the temperature of heating zone II is 400℃, the temperature of heating zone III is 500℃, and the temperature of heating zone IV is 600℃;

[0059] Step 6, controlling the mold 1 to rotate at a speed of 40 rpm, and vibrating at a frequency of 70 Hz;

[0060] Step 7, after the metal melt in the inner mold 7 is completely solidified, disassembling the mold (during the process when the temperature of the ingot is higher than 400℃, using natural cooling to cool down; during the process when the temperature of the ingot is lower than 400℃, using air cooling to cool down), and taking out the cast billet in the inner mold 7.

[0061] Example 3

[0062] A method for preparing a fine-grained large cast billet, using the aforementioned mold and filter device to prepare a Mg-8Gd-3Y-0.6Zr magnesium alloy ingot with a diameter of 1500 mm and a length of 1000 mm, the steps including:

[0063] Step 1, placing the mold 1 on the rotary vibration platform 9, and inputting the metal melt into the inner cavity of the mold 1;

[0064] Step 2, purifying the metal melt in the inner cavity of the mold 1, and controlling the mold 1 to rotate at a set speed; specifically including steps 21-23, as follows:

[0065] Step 21, first inserting the ceramic filter element 4 from the through hole 2 on the connecting plate 3, and then inserting the filter part (the tungsten steel frame 5 with the ceramic filter element 4) of the filter device into the inner cavity of the mold 1 until the bottom end of the filter part abuts against the bottom wall of the inner cavity of the mold 1;

[0066] Step 22, controlling the mold 1 to rotate at a speed of 800 revolutions per minute, and keeping the filter device stationary during the process;

[0067] Step 23, after 25 minutes of step 22, first reducing the speed of the mold 1 to zero, and then taking out the filter part upward, which is essentially taking out the whole of the ceramic filter element 4, the tungsten steel frame 5 and the connecting plate 3;

[0068] Step 3, vertically inserting the inner mold 7 into the inner cavity of the mold 1 to form an annular chamber 8 between the inner mold 7 and the inner wall of the mold 1, at this time, the limiting part at the lower end of the inner mold 7 is just clamped into the limiting groove 6;

[0069] Step 4, covering the cover plate 14 of the mold 1, connecting the mold 1 to the vacuum pumping equipment and performing vacuum pumping treatment, stopping vacuum pumping when the vacuum degree reaches -0.08 Mpa, and after maintaining the pressure for 1.5 minutes, filling inert gas into the mold 1 and the inner mold 7;

[0070] Step 5, controlling the temperature of the four heating zones of the mold 1 to be within the set temperature range, wherein the temperature of heating zone I is 340℃, the temperature of heating zone II is 470℃, the temperature of heating zone III is 530℃, and the temperature of heating zone IV is 620℃;

[0071] Step 6, controlling the mold 1 to rotate at a speed of 50 revolutions per minute, and simultaneously vibrating at a frequency of 60 Hz;

[0072] Step 7, after the metal melt in the inner mold 7 is completely solidified, disassembling the mold (during the process when the temperature of the ingot is higher than 400℃, cooling by natural cooling; during the process when the temperature of the ingot is lower than 400℃, cooling by air cooling), and taking out the cast billet in the inner mold 7.

[0073] Example 4

[0074] A method for preparing a fine-grained large cast billet, using the aforementioned mold and filter device to prepare a Mg-9Gd-3.5Y-0.8Zr magnesium alloy ingot with a diameter of 1800 mm and a length of 1500 mm, the steps including:

[0075] Step 1, placing the mold 1 on the rotary vibration platform 9, and inputting the metal melt into the inner cavity of the mold 1;

[0076] Step 2, purifying the metal melt in the inner cavity of the mold 1, and controlling the mold 1 to rotate at a set speed; specifically including steps 21-23, as follows:

[0077] Step 21, first inserting the ceramic filter element 4 from the through hole 2 on the connecting plate 3, and then inserting the filter part (the tungsten steel frame 5 with the ceramic filter element 4) of the filter device into the inner cavity of the mold 1 until the bottom end of the filter part abuts against the bottom wall of the inner cavity of the mold 1;

[0078] Step 22, controlling the mold 1 to rotate at a speed of 800 rpm, and keeping the filter device fixed during the process;

[0079] Step 23, after 25 minutes of step 22, first reducing the speed of the mold 1 to zero, and then taking out the filter part upward, which is essentially taking out the whole of the ceramic filter element 4, the tungsten steel frame 5 and the connecting plate 3;

[0080] Step 3, vertically inserting the inner mold 7 into the inner cavity of the mold 1 to form the annular chamber 8 between the inner mold 7 and the inner wall of the mold 1, at this time, the limiting part at the lower end of the inner mold 7 is just clamped into the limiting groove 6;

[0081] Step 4, covering the cover plate 14 of the mold 1, connecting the mold 1 to the vacuum pumping equipment and performing vacuum pumping treatment, stopping vacuum pumping when the vacuum degree reaches -0.08 MPa, and then filling the inert gas into the mold 1 and the inner mold 7 after pressure maintaining for 1.5 minutes;

[0082] Step 5, controlling the temperature of the four heating zones of the mold 1 to be within the set temperature range, wherein the temperature of heating zone I is 310℃, the temperature of heating zone II is 450℃, the temperature of heating zone III is 580℃, and the temperature of heating zone IV is 700℃;

[0083] Step 6, controlling the mold 1 to rotate at a speed of 60 rpm, and vibrating at a frequency of 90 Hz;

[0084] Step 7, after the metal melt in the inner mold 7 is completely solidified, disassembling the mold (during the process when the temperature of the ingot is higher than 400℃, cooling by natural cooling; during the process when the temperature of the ingot is lower than 400℃, cooling by air cooling), and taking out the cast blank in the inner mold 7.

[0085] Two samples were prepared by using each embodiment scheme respectively, the grain size of the sample taken from the core of the cast blank prepared in each embodiment (randomly taking one to cut and sample) was detected, and the slag removal rate of the sample taken from the core of the cast blank prepared in each embodiment and then remelted was detected, and the results are shown in Table 1.

[0086] Table 1 Grain size of the cast billet and deslagging rate

[0087] Examples Grain size Metal-solvent refining rate in the inner mold Example 1 34 μm 94.5％ Example 2 37 μm 93.8％ Example 3 34 μm 92.3％ Example 4 36 μm 93％

[0088] The present application integrates melt purification and cast billet forming into the same set of equipment, and can save about 60% of the floor space compared to the existing cast billet production line, and can form a large cast billet with fine grains without using melt conveying facilities, and the grain size of the obtained magnesium alloy large cast billet is 35±3 μm. In the present application, the melt is moved towards the inner cavity edge of the mold by means of high-speed rotation, and then the impurities suspended in the melt are mainly introduced into the ceramic filter element, and a small part of the suspended impurities are introduced into the melt in the annular chamber, so that the purification of the melt is realized, and in particular, the deslagging rate of the melt in the inner mold is higher than 90%, and the specific structure also has the advantages of facilitating quick and flexible replacement of the ceramic filter element. By using the scheme of the present application, a rare earth magnesium alloy ingot with a diameter of 1.5-2 meters and a length of 1-2 meters can be successfully prepared, and a magnesium alloy ingot with a diameter of 1.5-2 meters and a length of 1-2 meters can be obtained.

Claims

1. A method for producing a fine-grained bloom, characterized by the steps of The application relates to a method for preparing a large magnesium alloy casting blank. Step 1: metal melt is input into a mold cavity, and the mold is placed on a rotary vibration platform; Step 2: the metal melt in the mold cavity is purified, and the mold is controlled to rotate at a set speed; Step 3: an inner mold is vertically inserted into the mold cavity, so that an annular chamber is formed between the inner mold and the inner wall of the mold; Step 4: the cover plate of the mold is covered, the mold is connected to a vacuumizing device and is vacuumized, the vacuumizing is stopped when the vacuum degree reaches-0.06~-0.09MPa, and inert gas is filled into the mold after pressure maintaining for 1~3 minutes; Step 5: the temperature of the four heating zones on the periphery of the mold is controlled in a set temperature range respectively; Step 6: the mold is controlled to rotate at a set speed two, and is vibrated at a set frequency; Step 7: the mold is disassembled after the metal melt in the inner mold is completely solidified, and the casting blank in the inner mold is taken out.

2. The production method according to claim 1, characterized by, Step 2 specifically comprises the following steps: Step 21: the filter part of a filtering device is inserted into the mold cavity until the bottom end of the filter part abuts against the bottom wall of the mold cavity; Step 22: the mold is controlled to rotate at a speed of 800-1000r / min, Step 23: after step 22 is performed for 20-30 minutes, the rotating speed of the mold is first reduced to zero, and then the filter part is taken out upwards; The filter part comprises a tungsten steel frame connected to a connecting plate, a ceramic filter element is arranged in the tungsten steel frame and can be vertically taken out but is horizontally limited, a through hole is arranged on the connecting plate above the tungsten steel frame, the ceramic filter element can pass through the through hole, and one side end of the ceramic filter element faces the axis of the mold cavity.

3. The method of claim 2, wherein: Six ceramic filter elements are uniformly arranged along the circumferential direction, the width of each ceramic filter element is 1 / 2~2 / 3 of the diameter of the mold cavity, and the length of each ceramic filter element is equal to the height of the mold cavity.

4. The method of claim 3, wherein: The inner mold is a cylinder with open ends, the lower end of the cylinder can abut against the bottom wall of the mold cavity, and the upper end of the cylinder can abut against the bottom wall of the cover plate.

5. The method of claim 4, wherein: Four electric heating zones are arranged on the periphery of the mold along the vertical direction, wherein the temperatures of the four heating zones from bottom to top satisfy 50℃≤Ⅳ-Ⅲ≤150℃, 50℃≤Ⅲ-Ⅱ≤150℃ and 50℃≤Ⅱ-Ⅰ≤150℃.

6. The method of any one of claims 1-5, wherein: In step 6, the set speed two is 20~60r / min, and the vibration frequency is 40~120Hz.

7. The method of claim 6, wherein: The temperature of heating zone I is 350℃, the temperature of heating zone II is 500℃, the temperature of heating zone III is 650℃, the temperature of heating zone IV is 700℃, and the large casting blank is Mg-6Gd-3Y-0.5Zr magnesium alloy.

8. The method of claim 6, wherein: The temperature of heating zone I is 300℃, the temperature of heating zone II is 400℃, the temperature of heating zone III is 500℃, the temperature of heating zone IV is 600℃, and the large casting blank is Mg-8.5Gd-4.5Y-0.4Zr magnesium alloy.

9. The method of claim 6, wherein: The temperature of heating zone I is 340℃, the temperature of heating zone II is 470℃, the temperature of heating zone III is 530℃, the temperature of heating zone IV is 620℃, and the large casting blank is Mg-8Gd-3Y-0.6Zr magnesium alloy.

10. The method of any one of claims 7-9, wherein: The bottom wall of the mold cavity is provided with a limiting groove, and the limiting part at the lower end of the inner mold can be clamped into the limiting groove, so that the mold and the inner mold can rotate synchronously.

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