Magnesium-lithium alloy low-overheating overpressure rapid mold filling sand mold exhaust top box and method

Abstract

The invention relates to a sand mold exhaust top box and method for magnesium-lithium alloy low-overheating and overpressure rapid mold filling, and belongs to the technical field of magnesium-lithium alloy casting. Comprising an exhaust unit, a low-pressure transition tank, a sucking pump and an exhaust pipe which are sequentially connected, the low-pressure transition tank is used for balancing pressure during exhausting and preventing smoke dust from being accumulated in the sucking pump; the exhaust unit comprises an exhaust floater, a guide pipe and a valve; the exhaust floater is connected with the low-pressure transition tank through a guide pipe, and a valve is installed on the guide pipe. The exhaust floater is used for exhausting gas and preventing the solution from overflowing after exhaust gas is exhausted. The combined sand mold exhaust top box is adopted to regulate and control the mold filling back pressure of the mold cavity, gas in the mold cavity is rapidly exhausted, and it is ensured that the mold cavity is rapidly filled with melt in the overpressure state.

Description

Technical Field

[0001] This invention relates to an alloy-filled exhaust top box and method, belonging to the field of magnesium-lithium alloy casting technology. Background Technology

[0002] Existing technologies employ modules and slider assemblies to form the cavity for casting aluminum alloy products. For example, publication number CN112338166B, entitled "An Aluminum Alloy Product Extrusion Casting Mold Structure," describes a technical solution applicable to aluminum alloys. The aluminum alloy forming process is almost unaffected by the reactivity of the melt and the mold. The mold is an extrusion casting mold structure, and to meet high forming pressure requirements, the mold material is metal, thus representing a completely different molding material system from magnesium-lithium alloys. For the production of complex magnesium alloy castings with contour dimensions exceeding 800mm, sand casting with anti-gravity is the primary method. Resin sand casting is widely used in magnesium alloy anti-gravity casting due to its high precision and ability to create complex structures. The lithium content in cast ultralight magnesium-lithium alloys typically ranges from 8% to 14%. Due to the high chemical reactivity of magnesium and lithium, when the lithium content exceeds 8%, for every 10°C increase in pouring temperature, the average reactivity of the magnesium-lithium alloy melt with the mold material or surrounding environment (oxygen, nitrogen, water vapor, etc.) increases by approximately 50%. When the pouring temperature reaches above 700°C, even with inert gas protection, violent combustion can easily occur, leading to a large amount of oxide inclusions in the molten metal, severely affecting the internal quality of near-net-shape castings. To ensure high specific modulus, high specific strength, and improved absolute strength, high-performance ultralight cast magnesium-lithium alloys incorporate a large number of alloying elements, increasing the viscosity of the alloy melt and significantly reducing its filling capacity. Traditional anti-gravity casting process parameters for magnesium alloys cannot meet the high internal quality requirements for casting large, complex components.

[0003] Currently used methods such as vacuum melting and inert atmosphere melting can only ensure a near-inert environment during the casting of magnesium-lithium alloys. However, fatal problems still exist when casting large and complex components using anti-gravity casting: the molten metal reacts violently with the mold material after filling, resulting in poor internal quality of the casting and poor stability in controlling the alloy composition. Even after filling, the high-temperature environment inside the casting causes a slow oxidation process within the alloy, known as "sneak fire." When the casting is large and thick-walled, this "sneak fire" can occur inside the casting and spread outwards, leading to either poor internal quality or, in severe cases, spontaneous combustion. When using differential pressure casting with a fully inert gas environment, the high mold pressure (typically 0.6-0.8 MPa) slows down the actual filling process, creating significant back pressure within the mold cavity. This prolonged contact between the magnesium-lithium alloy molten metal and the mold increases the chance of reaction between the molten metal and the mold material after filling, further reducing the internal quality of the casting. The root cause of these problems is the excessively high reactivity of the molten metal and the mold material during the filling process. Therefore, how to reduce the activity of the ultralight magnesium-lithium alloy melt resin sand mold anti-gravity casting process and how to rapidly reduce the casting temperature to below the critical temperature are the key issues that urgently need to be solved in the anti-gravity casting of large and complex magnesium-lithium alloy components.

[0004] Therefore, there is an urgent need to propose a sand-type exhaust top box and method for rapid filling of magnesium-lithium alloy with low overheating and overpressure, in order to solve the above-mentioned technical problems. Summary of the Invention

[0005] To address the aforementioned problems, a sand-cast exhaust top box and method for rapid filling with low overheating and overpressure using magnesium-lithium alloy are provided. A brief overview of the invention is given below to provide a basic understanding of certain aspects of the invention. It should be understood that this overview is not an exhaustive summary of the invention. It is not intended to identify key or essential parts of the invention, nor is it intended to limit the scope of the invention.

[0006] The technical solution of this invention: A magnesium-lithium alloy low-overheating, overpressure, and rapid-filling sand-mold exhaust top box, comprising: The exhaust unit, low-pressure transition tank, suction pump, and exhaust pipe are connected in sequence; the low-pressure transition tank is used to balance the pressure during exhaust and prevent soot from accumulating in the suction pump. The exhaust unit includes an exhaust float, a conduit, and a valve; the exhaust float is connected to the low-pressure transition tank via a conduit, and a valve is installed on the conduit; the exhaust float is used to exhaust gas and prevent molten material from overflowing after the exhaust gas is discharged.

[0007] Preferably, the exhaust float is connected to the cavity, the exhaust pipe is connected to the gas tank, and the gas tank contains inert gas.

[0008] Preferably, the exhaust unit, low-pressure transition tank, and air pump are installed inside the top box shell, and the ducts of several exhaust units are connected to the low-pressure transition tank. The top box shell is filled with resin sand.

[0009] Preferably, the exhaust float includes a float shell and a float. The float is a convex frustum structure. The inner cavity of the float shell is set in accordance with the shape of the float. One end of the float shell is connected to the exhaust hole at the top of the cavity, and the other end of the float shell is connected to the conduit.

[0010] Preferably, the conduit includes an air guide tube and an air guide bellows, and the float shell, air guide tube, valve, air guide bellows, and low-pressure transition tank are connected in sequence, and the valve is a solenoid valve.

[0011] A method for rapid filling of magnesium-lithium alloy with low overheating and overpressure, using a sand-mold exhaust top box for rapid filling of magnesium-lithium alloy with low overheating and overpressure, includes the following steps: Start the vacuum pump. After the melt fills the mold cavity and reaches the final holding pressure difference, turn off the vacuum pump after a delay of 20-50 seconds to fully expel the gas generated by the heat effect around the casting. Then the melt cools down to form a complete casting.

[0012] The preferred method specifically includes the following steps: Step 1: Calculate the area required for exhaust; Step 2: Determine the liquid lifting rate, pouring temperature, filling speed, and final overpressure holding pressure; Step 3: The differential pressure casting equipment reaches an ambient pressure of 0.8-1.0 MPa; Step 4: Begin the top venting method for filling the mold, and simultaneously turn on the vacuum pump. In conjunction with the differential pressure casting equipment, the low-overheat inert melt is used to achieve the function of rapid filling under high pressure. After the melt fills the casting cavity and reaches the final holding pressure differential, the vacuum pump is turned off after a delay of 20-50 seconds to fully expel the gas generated by the heat effect around the casting. Subsequently, the melt cools down to form a complete casting.

[0013] Preferably, in step one, the ratio of the area of ​​the exhaust unit to the cross-sectional area of ​​a single exhaust position in the casting cavity is between 0.7 and 2, and the number of exhaust units is between 10 and 15.

[0014] Preferred: In step two, the liquid lifting rate is calculated according to formula (1), the pouring temperature is 640-680℃, the filling rate is calculated according to formula (2), and the final environmental pressure is 0.8-1.0MPa; The liquid lifting rate is calculated using the following formula: (1) In the formula, b is the liquid rise coefficient of high-pressure rapid casting, which is 1.0 to 1.5 for magnesium-lithium alloys with a lithium content of 8 to 20 wt.%; a is the distance (m) from the liquid surface to the bottom of the casting cavity. The filling speed is calculated using the following formula: (2) In the formula, c is the overpressure rapid filling coefficient, which is 0.3 to 0.5 for magnesium-lithium alloys with a lithium content of 8 to 15 wt.%; h is the height of the casting (m); and a is the distance from the liquid surface to the bottom of the casting cavity (m).

[0015] Preferably, the method is applicable to an anti-gravity casting process capable of adapting to ultralight magnesium-lithium alloys with a lithium content of 8% to 15 wt%.

[0016] The present invention has the following beneficial effects: This invention can reduce the activity of the ultralight magnesium-lithium alloy melt resin sand casting process, solve the key problem of casting and forming large and complex magnesium-lithium alloy components, and realize the high internal quality casting and forming of large and complex ultralight magnesium-lithium alloy structures.

[0017] This invention inertizes the alloy melt by reducing its superheat (superheat refers to the difference between the actual temperature of the melt and the liquidus temperature of the melt; superheat control can be achieved by controlling the temperature or power of the melting furnace after the alloy melts, which is a general operation in the melting process). This reduces the intrinsic reactivity of the magnesium-lithium alloy melt during the filling process, decreases the reaction between the magnesium-lithium alloy and the surrounding environment during filling, avoids oxidation inclusions in the casting, and improves the internal quality of the casting.

[0018] This invention employs high-pressure rapid filling to reduce filling time, allowing the melt to quickly fill the mold cavity under relatively high filling pressure. The melt flows a longer distance through the mold cavity per unit time, contacts more of the mold, and increases the heat dissipation capacity of the melt. Filling the mold cavity as early as possible can quickly achieve the cooling process of the entire casting. The temperature of the melt in the mold cavity drops rapidly to below the critical activity temperature, successfully preventing the alloy from oxidizing and "igniting," preventing secondary oxidation and combustion, and improving the internal quality of the casting.

[0019] This invention employs a combined sand mold exhaust top box to regulate the back pressure of the mold cavity filling, rapidly expelling the gas inside the cavity and ensuring that the melt quickly fills the cavity under overpressure. Attached Figure Description

[0020] Figure 1 This is a schematic diagram illustrating a sand-type exhaust top box of magnesium-lithium alloy with low overheating and overpressure rapid filling according to the present invention. Detailed Implementation

[0021] To make the objectives, technical solutions, and advantages of this invention clearer, the invention is described below with reference to specific embodiments shown in the accompanying drawings. However, it should be understood that these descriptions are merely exemplary and not intended to limit the scope of the invention. Furthermore, descriptions of well-known structures and technologies are omitted in the following description to avoid unnecessarily obscuring the concept of the invention.

[0022] Specific implementation method one: Combining Figure 1 This embodiment describes a magnesium-lithium alloy low-overheating, overpressure, rapid-filling sand-type exhaust top box, which includes: an exhaust unit, an air pump 5, an exhaust pipe 6, and a low-pressure transition tank 7. The exhaust unit, low-pressure transition tank 7, suction pump 5, and exhaust pipe 6 are connected in sequence; the low-pressure transition tank 7 is used to balance the pressure during exhaust and to prevent soot from accumulating in the suction pump 5. The exhaust unit includes an exhaust float 1, a conduit, and a valve 3; the exhaust float 1 is connected to the low-pressure transition tank 7 through the conduit, and the valve 3 is installed on the conduit; the exhaust float 1 is used to exhaust gas and prevent the melt from overflowing after the exhaust gas is discharged. This invention can reduce the activity of ultralight magnesium-lithium alloy melt resin sand casting process, solve the key problem of casting and forming large and complex magnesium-lithium alloy components, and realize high internal quality casting and forming of large and complex ultralight magnesium-lithium alloy structures. This invention adopts a combined sand mold exhaust top box to regulate the back pressure of the cavity filling, quickly discharge the gas in the cavity, and ensure that the melt quickly fills the cavity under overpressure.

[0023] Specific Implementation Method Two: Combining Figure 1 This embodiment describes a sand mold exhaust top box for rapid filling of magnesium-lithium alloy under low overheating and overpressure. The exhaust float 1 is connected to the cavity of the high-pressure differential pressure casting equipment, and the exhaust pipe 6 is connected to the gas tank of the high-pressure differential pressure casting equipment. The gas tank contains an inert gas, such as 99.99% high-purity argon, to balance the pressure and create an oxygen-free environment.

[0024] Specific implementation method three: Combining Figure 1 This embodiment describes a sand mold exhaust top box for rapid filling of magnesium-lithium alloy under low overheating and overpressure conditions. It includes a top box shell 8, exhaust units, a low-pressure transition tank 7, and a vacuum pump 5 disposed within the top box shell 8. The top box shell 8 is mounted on the mold cavity shell. The conduits of several exhaust units are connected to the low-pressure transition tank 7 to eliminate pressure differentials within the mold cavity and balance pressure. The exhaust floats 1 of several evenly arranged exhaust units are connected to exhaust holes at the top of the casting cavity. Exhaust pipes 6 extend from the top box shell 8 and connect to the gas tank. The top box shell 8 is filled with resin sand for fixation, facilitating disassembly and replacement.

[0025] Specific implementation method four: Combination Figure 1This embodiment describes a sand-cast exhaust top box for rapid filling of magnesium-lithium alloy under low overheating and overpressure. The exhaust float 1 includes a float shell and a float. The float is a convex frustum structure. The inner cavity of the float shell corresponds to the shape of the float. One end of the float shell is fixedly connected to the exhaust hole at the top of the cavity, and the other end of the float shell is fixedly connected to a conduit. The float shell and the float can be connected by a flexible rope to limit the float. The melt can push the float up to block the float shell, preventing the melt other than generated gas and other waste gases from overflowing. The structure is simple and reliable, and it is easy to control costs and maintain.

[0026] Specific Implementation Method Five: Combining Figure 1 This embodiment describes a magnesium-lithium alloy low-overheating, overpressure, and rapid-filling sand-type exhaust top box. The conduit includes an air guide pipe 2 and an air guide bellows 4. The float shell, air guide pipe 2, valve 3, air guide bellows 4, and low-pressure transition tank 7 are connected in sequence. The valve 3 is a solenoid valve.

[0027] Specific Implementation Method Six: Combination Figure 1 This embodiment describes a method for rapid filling of magnesium-lithium alloy with low overheating and overpressure, using a sand-mold exhaust top box for rapid filling of magnesium-lithium alloy with low overheating and overpressure, and includes the following steps: Start the vacuum pump 5. After the melt fills the cavity and reaches the final holding pressure difference, turn off the vacuum pump 5 after a delay of 20~50 seconds to fully expel the gas generated by the heat effect around the casting. Then the melt cools down to form a complete casting.

[0028] Specific implementation method seven: Combining Figure 1 This embodiment describes a method for rapid filling of magnesium-lithium alloys with low overheating and overpressure, which specifically includes the following steps: Step 1: Calculate the area required for exhaust; Step 2: Determine the liquid lifting rate, pouring temperature, filling speed, and final overpressure holding pressure; Step 3: Input key casting process parameters into the equipment, close the mold, install the casting mold, lock the upper and lower tanks, and then start to synchronously introduce air into the differential pressure casting equipment to make the upper and lower tanks simultaneously enter air to reach an ambient pressure of 0.8-1.0MPa. 99.99% high-purity argon is used. Step 4: Begin filling the mold using the top venting method. Simultaneously, turn on the vacuum pump 5 and activate the back pressure control function of the combined sand mold venting top box. This, in conjunction with the differential pressure casting equipment, enables the low-overheat inert melt to rapidly fill the mold under high pressure. After the melt fills the casting cavity and reaches the final holding pressure differential, delay for 20-50 seconds before turning off the vacuum pump 5 to fully expel the gas generated by the heat effect around the casting. Subsequently, the melt cools to form a complete casting.

[0029] Specific implementation method eight: Combination Figure 1This embodiment describes a method for rapid filling of magnesium-lithium alloy under low overheat and overpressure. In step one, the ratio of the area of ​​a single exhaust unit (the cross-section of the vent pipe) to the cross-sectional area of ​​a single exhaust position in the casting cavity is between 0.7 and 2, and the number of exhaust units is between 10 and 15.

[0030] Specific Implementation Method Nine: Combining Figure 1 This embodiment describes a method for rapid filling of magnesium-lithium alloy with low overheating and overpressure. In step two, the liquid lifting rate is calculated according to formula (1), the pouring temperature is 640-680℃, the filling rate is calculated according to formula (2), and the final environmental pressure is 0.8-1.0MPa. The liquid lifting rate is calculated using the following formula: (1) In the formula, b is the liquid rise coefficient of high-pressure rapid casting, which is 1.0 to 1.5 for magnesium-lithium alloys with a lithium content of 8 to 20 wt.%; a is the distance (m) from the liquid surface to the bottom of the casting cavity. The filling speed is calculated using the following formula: (2) In the formula, c is the overpressure rapid filling coefficient, which is 0.3 to 0.5 for magnesium-lithium alloys with a lithium content of 8 to 15 wt.%; h is the height of the casting (m); a is the distance from the liquid surface to the bottom of the casting cavity (m). This invention employs high-pressure rapid filling to reduce filling time, allowing the melt to quickly fill the mold cavity under relatively high filling pressure. The melt temperature rapidly decreases below the critical activity temperature, successfully preventing the alloy from undergoing oxidation and "sneaking" and preventing secondary oxidation and combustion, thereby improving the internal quality of the casting.

[0031] Specific Implementation Method Ten: Combining Figure 1This embodiment describes a method for rapid filling of magnesium-lithium alloys under low superheat and high pressure. The invention addresses the aforementioned problems through three approaches. First, it reduces the intrinsic reactivity of the magnesium-lithium alloy melt during the filling process. Specifically, this is achieved by reducing the melt superheat to inertize the alloy melt. Reducing the melt superheat decreases the reaction between the magnesium-lithium alloy and the surrounding environment during filling, reducing the direct formation of oxide inclusions and defects in the casting. It also reduces the total heat carried by the entire casting, rapidly lowering the temperature inside and outside the casting to below the critical temperature to prevent "sneak fire." However, ultralight magnesium-lithium alloys have a viscosity 50-80% higher than ordinary magnesium alloys at low superheat, significantly reducing the melt's filling capacity. Although the melt activity is reduced, the ability to form complex structural castings also decreases. Traditional differential pressure casting processes cannot guarantee the complete forming of large, complex components. Therefore, a second measure is needed: employing a rapid filling process under high pressure to reduce filling time, allowing the melt to quickly fill the mold cavity under relatively high filling pressure, ensuring both melt inertization and filling capacity. Here, overpressure refers to the state of non-equilibrium forces in the micro-units of the melt flow process, where the applied filling pressure exceeds the pressure required for the net external force to balance. The micro-units of the melt are constantly in an accelerated state, which allows the melt to fill the mold under pressure, increasing the filling capacity. When the melt fills the mold rapidly under overpressure, the back pressure in the mold cavity that hinders filling will increase significantly. Therefore, a third measure is needed, namely, using a self-developed combined sand mold exhaust top box during filling to achieve active control of the back pressure in the mold cavity during rapid filling, quickly expelling the gas in the mold cavity. This, combined with the melt rapidly filling the mold cavity under overpressure, enables the overpressure rapid filling process to be realized on the basis of existing differential pressure casting equipment, saving equipment investment and facilitating the capacity upgrade of existing equipment. This invention proposes a resin sand casting method for ultralight magnesium-lithium alloy complex structure castings with low overheating and overpressure, and a combined sand mold exhaust top box; it also provides an anti-gravity casting method and a combined sand mold exhaust top box suitable for ultralight magnesium-lithium alloys with lithium content of 8%~15wt.%; by reducing the superheat of the alloy melt to inert it, this invention can reduce the intrinsic reactivity of the magnesium-lithium alloy melt during the filling process, reduce the reaction between the magnesium-lithium alloy and the surrounding environment during filling, avoid oxidation inclusion defects in the castings, and improve the internal quality of the castings.

[0032] The technology mentioned in CN112338166B in the prior art is applicable to aluminum alloys, which is different from the magnesium-lithium alloy system used in this invention. Compared with magnesium-lithium alloys, aluminum alloy forming is almost unaffected by the reactivity of the melt and the mold, so they are not comparable. The mold mentioned in CN112338166B is a squeeze casting mold structure. To meet the high forming pressure requirements, the mold material is metal, which is a completely different molding material system compared with the resin sand mold used in this invention. Therefore, the usage methods and processes are fundamentally different. The strength of the metal mold is more than two orders of magnitude higher than that of the resin sand mold. When forming complex structure castings, some parts cannot be separated from the metal mold after pouring using squeeze casting. Resin sand molds can quickly obtain complete castings through sand removal.

[0033] Example 1: Combination Figure 1 A method for rapid filling of magnesium-lithium alloy with low overheating and overpressure is provided to form complete castings with high internal quality, avoid oxidation and slag inclusion defects in castings, and prevent combustion and "sneak fire" during the forming process; Example 2: This embodiment is basically the same as Embodiment 1, except that the casting diameter is 950mm, the height is 800mm, the wall thickness is 4mm, the lithium content is 15%, and in the first step, the area required for venting is calculated to be approximately 600mm². 2 Fifteen venting locations were set up. The ratio of the area of ​​a single venting unit in the combined sand mold venting top box to the cross-sectional area of ​​a single venting location in the casting cavity was 2, and the number of venting units was 15. The pouring temperature was 680℃, and the final overpressure holding pressure was 1.0MPa. The liquid rising speed V1 was calculated to be 13.35cm / s, and the filling speed V2 was calculated to be 23.4KPa / s. After the melt filled the cavity and reached the final holding pressure difference, the air pump was turned off after a delay of 25s (5).

[0034] Example 2 provides a method for rapid filling of magnesium-lithium alloy with low overheating and overpressure to form complete castings with high internal quality, avoiding defects such as oxidation and slag inclusions in the castings, and without combustion or "sneak fire" during the forming process.

[0035] Comparative Example 1: Compared with Example 1, this comparative example did not use a combined sand mold exhaust top box; the formed casting was incomplete, and there were some oxide inclusions at the top of the casting. No combustion or "sneak fire" occurred during the forming process.

[0036] Comparative Example 2: Compared with Example 1, the liquid lifting speed in this comparative example was V1 = 10 cm / s; the filling speed was the traditional differential pressure casting filling speed V2 = 5 kPa / s. The formed casting was incomplete, with some oxide inclusions at the top. No combustion or "sudden combustion" occurred during the forming process.

[0037] Comparative Example 3: Compared with Example 1, this comparative example had a pouring temperature of 720°C, and the formed casting was complete. However, the casting had some oxide inclusions and severe surface oxidation during the forming process.

[0038] Comparative Example 4: Compared with Example 2, this comparative example did not use a combined sand mold exhaust top box; the formed casting was incomplete, and there were some oxide inclusions at the top of the casting. No combustion or "sneak fire" occurred during the forming process.

[0039] Comparative Example 5: Compared with Example 2, the liquid lifting speed of this comparative example is V1=12cm / s; the filling speed adopts the traditional differential pressure casting filling speed V2=5KPa / s; the formed casting is incomplete, and there are some oxide inclusions at the top of the casting. No combustion or "sneak fire" occurred during the forming process.

[0040] Comparative Example 6: Compared with Example 2, this comparative example had a casting temperature of 720°C. The surface reaction during the forming process was severe, the casting had serious oxidation inclusions, and the casting had incomplete forming of oxidation inclusion defects.

[0041] It should be noted that in the above embodiments, as long as the technical solutions are not contradictory, they can be permuted and combined. Those skilled in the art can exhaust all possibilities based on the mathematical knowledge of permutation and combination. Therefore, the present invention will not describe the technical solutions after permutation and combination one by one, but it should be understood that the technical solutions after permutation and combination have been disclosed by the present invention.

[0042] The above description is merely a preferred embodiment of the present invention and is not intended to limit the invention. Various modifications and variations can be made to the present invention by those skilled in the art. Any modifications, equivalent substitutions, improvements, etc., made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy, characterized in that: include: The exhaust unit, low-pressure transition tank (7), air pump (5), and exhaust pipe (6) are connected in sequence; the low-pressure transition tank (7) is used to balance the pressure during exhaust and prevent smoke and dust from accumulating in the air pump (5); The exhaust unit includes an exhaust float (1), a conduit, and a valve (3); the exhaust float (1) is connected to the low-pressure transition tank (7) through the conduit, and the valve (3) is installed on the conduit; the exhaust float (1) is used to exhaust gas and prevent the melt from overflowing after the exhaust gas is discharged.

2. The sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy according to claim 1, characterized in that: The exhaust float (1) is connected to the mold cavity, and the exhaust pipe (6) is connected to the inner cavity of the gas tank in which the entire mold is located. The gas tank contains inert gas.

3. The sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy according to claim 2, characterized in that: The exhaust unit, low-pressure transition tank (7), and air pump (5) are installed inside the top box shell (8). The ducts of several exhaust units are connected to the low-pressure transition tank (7). The top box shell (8) is filled with resin sand.

4. A sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy according to any one of claims 1-3, characterized in that: The exhaust float (1) includes a float shell and a float. The float is a convex truncated cone structure. The inner cavity of the float shell is set in accordance with the shape of the float. One end of the float shell is connected to the exhaust hole at the top of the cavity, and the other end of the float shell is connected to the conduit.

5. The sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy according to claim 4, characterized in that: The conduit includes an air duct (2) and an air bellows (4). The float shell, air duct (2), valve (3), air bellows (4), and low-pressure transition tank (7) are connected in sequence. The valve (3) is a solenoid valve.

6. A method for rapid filling of magnesium-lithium alloys with low overheating and overpressure, characterized in that: The sand-mold exhaust top box with low overheating and overpressure rapid filling of magnesium-lithium alloy as described in any one of claims 1-5 includes the following steps: Start the vacuum pump (5). After the melt fills the cavity and reaches the final pressure difference, turn off the vacuum pump (5) after a delay of 20~50s to fully discharge the gas generated by the heat effect around the casting. Then the melt cools down to form a complete casting.

7. The method for rapid filling of magnesium-lithium alloy with low overheating and overpressure according to claim 6, characterized in that: Specifically, the following steps are included: Step 1: Calculate the area required for exhaust; Step 2: Determine the liquid lifting rate, pouring temperature, filling speed, and final overpressure holding pressure; Step 3: The differential pressure casting equipment reaches an ambient pressure of 0.8-1.0 MPa; Step 4: Start the top venting method for filling the mold, and at the same time turn on the vacuum pump (5) to cooperate with the differential pressure casting equipment to realize the function of low overheat inert melt overpressure rapid filling. After the melt fills the casting cavity and reaches the final holding pressure difference, delay for 20~50s to turn off the vacuum pump (5) to fully exhaust the gas generated by the heat effect around the casting. Then the melt cools down to form a complete casting.

8. The method for rapid filling of magnesium-lithium alloy with low overheating and overpressure according to claim 7, characterized in that: In step one, the ratio of the area of ​​the exhaust unit to the cross-sectional area of ​​a single exhaust position in the casting cavity is between 0.7 and 2, and the number of exhaust units is between 10 and 15.

9. A method for rapid filling of magnesium-lithium alloy with low overheating and overpressure according to claim 8, characterized in that: In step two, the liquid lifting rate is calculated according to formula (1), the pouring temperature is 640-680℃, the filling rate is calculated according to formula (2), and the final environmental pressure is 0.8-1.0MPa; The liquid lifting rate is calculated using the following formula: (1) In the formula, b is the liquid rise coefficient of high-pressure rapid casting, which is 1.0 to 1.5 for magnesium-lithium alloys with a lithium content of 8 to 15 wt.%; a is the distance (m) from the liquid surface to the bottom of the casting cavity. The filling speed is calculated using the following formula: (2) In the formula, c is the overpressure rapid filling coefficient, which is 0.3 to 0.5 for magnesium-lithium alloys with a lithium content of 8 to 15 wt.%; h is the height of the casting (m); and a is the distance from the liquid surface to the bottom of the casting cavity (m).

10. A method for rapid filling of magnesium-lithium alloy with low overheating and overpressure according to any one of claims 7-9, characterized in that: The method is applicable to an anti-gravity casting process for ultralight magnesium-lithium alloys with a lithium content of 8% to 15 wt%.

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