CN103691911A - Magnesium alloy casting method and device thereof - Google Patents

Abstract

The invention discloses a magnesium alloy casting method. The method comprises: smelting and removing slag from the magnesium alloy; preheating the gypsum casting mold; Pressurize the lower tank at an air pressure of 1-5Kpa for 1-2 minutes; vacuumize the upper tank to reach the specified negative pressure value k ₁ , add 1-10% sulfur hexafluoride and 90-99% argon The mixed gas is injected into the upper tank and raised to the specified negative pressure value k ₂ ; the lower tank is pressurized with a pressure of 10-80KPa to realize pressurized pouring. The invention discloses a magnesium alloy casting device. According to the technical scheme disclosed in the invention, the average wall thickness of the castings produced is 1.0-1.5mm, the tensile strength reaches 190MPa, the elongation reaches 2-3%, the surface quality is high, there are no oxidation, cold shut and slag inclusion defects, and the internal structure Compact, good performance, simple process, convenient operation and low cost.

Description

A kind of magnesium alloy casting method and its device

technical field

The invention relates to a casting technology, in particular to a magnesium alloy casting method and a device thereof. the

Background technique

Magnesium alloy has low density, high specific strength/specific stiffness, stable size, good thermal and electrical conductivity, damping and vibration reduction, electromagnetic shielding and other advantages. At present, as an important structural material, it is widely used in aviation, aerospace, automobile, electronic communication and other industrial fields. In the field of national defense, due to the relatively high requirements for individual combat, magnesium alloys also have a place as weight-reducing materials. As early as the 1950s, the skins, frames and engine casings of my country's imitated aircraft and missiles had used magnesium rare earth alloys. After the 1970s, with the rapid development of my country's aerospace technology, magnesium alloys have been gradually promoted and applied in products such as attack aircraft, helicopters, missiles, and satellites. At present, the urgent need for weight reduction in my country's aviation, aerospace, and national defense fields provides opportunities and challenges for the development and application of new materials and processes for magnesium alloys. the

At present, one of the main factors limiting the application of magnesium alloy materials in the fields of aviation, aerospace, and national defense is the difficulty in casting magnesium alloy castings. The difficulty in casting lies in how to make complex parts form smoothly and ensure that they do not burn in the cavity, so as to increase the size of castings precision and reduce surface roughness. However, magnesium alloy castings are mainly manufactured by die casting and sand casting. Die casting is the most common magnesium alloy forming process at present, but die casting can only form castings with small size and simple structure; due to the existence of pores, castings cannot be heat treated or welded. It is also not possible to carry out relatively deep machining; traditional sand casting can form magnesium alloy castings with large size, complex shape and large wall thickness, which is currently a widely used forming process for large and complex magnesium alloy castings. However, due to the high thermal conductivity of the sand mold, it is impossible to reduce the weight of magnesium alloy castings with smaller wall thickness by sand casting; in addition, sand castings have low dimensional accuracy, poor surface quality, and large machining allowances, which increase The workload of follow-up processing. Gypsum investment casting has simple casting process and good reproducibility. It can form castings with extremely complex shape and internal structure and small wall thickness. If the quality of gypsum is good, castings with high precision and good surface quality can be cast. However, relying on the existing casting methods, due to the poor anti-oxidation effect of the gypsum casting, even if vacuum casting is used, it is difficult to ensure that the magnesium alloy melt does not react with the gypsum or even burn, which hinders the popularization of the gypsum cast magnesium alloy. the

Contents of the invention

(1) Technical problems to be solved

The technical problem to be solved by the present invention is: how to provide a magnesium alloy casting method to overcome the technical problem in the prior art that the magnesium alloy is easily oxidized and combustible during the pouring process; and provide a magnesium alloy casting device. the

(2) Technical plan

In order to solve the above technical problems, on the one hand, the present invention provides a magnesium alloy casting method, the method comprising: casting under negative pressure conditions. the

On the other hand, the present invention also provides a casting method of magnesium alloy, the method comprising:

Step 1. After smelting and removing slag, the magnesium alloy melt at a temperature of 730°C to 820°C is put into a crucible, the crucible is built into the lower tank, and the lower tank is sealed with a sealing cover;

Step 2. Put the preheated plaster mold with a temperature of 200°C to 400°C on the sealing cover plate, and cover the lower pot with the upper pot;

Step 3, using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon, and an air pressure of 1-5Kpa to carry out the lowering of the tank between the sealing cover plate and the crucible for 1-2 minutes Squeeze to make the sulfur hexafluoride float on the magnesium alloy melt to form a protective layer;

Step 4. Vacuum the upper tank through the negative pressure vacuum pipeline located on the upper part of the upper tank, so that the negative pressure value of the upper tank reaches the specified negative pressure value k ₁ , and then put 1-10% hexafluoride The mixed gas of sulfur and 90-99% argon is injected into the upper tank from the upper part of the upper tank, so that the negative pressure of the upper tank rises to the specified negative pressure value k ₂ ;

Step 5. Pressurize the lower tank from the middle and lower part of the lower tank with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the upper tank through the liquid riser built in the crucible. In the cavity in the tank, pressurized pouring is realized. the

Preferably, the mixed gas described in step 3 and step 4 is a mixed gas of 10% sulfur hexafluoride and 90% argon; or a mixed gas of 5% sulfur hexafluoride and 95% argon. the

Preferably, the prescribed negative pressure value k ₁ described in step 4 is -20 to -50KPa, and the prescribed negative pressure value k ₂ is -10 to -30KPa.

Preferably, step 5 also includes adjusting process parameters, said process parameters comprising:

The liquid lifting speed is 30-40mm/s, the liquid lifting pressure is 5-8KPa, the filling speed is 30-60mm/s, the filling pressure is 30-50KPa, the crusting time is 2-5s, and the crusting boost pressure is 3-8KPa, the crystallization time is 150-350s, the crystallization boost pressure is 3-8KPa and the resistance coefficient is 1.2-1.5. the

Preferably, when producing magnesium alloy ZM10 castings with a wall thickness of 1.5mm, the melting temperature of the magnesium alloy is 780°C, and the preheating temperature of the gypsum mold is 380°C, the specified value _k1 is -30KPa, so The specified value k2 is -20KPa, the liquid lifting speed is 35m/s, the liquid lifting pressure is 6KPa, the filling speed is 40mm/s, the filling pressure is 38KPa, the crusting time is 5s, and the crusting boost pressure is 3KPa, the crystallization time is 150s, the crystallization boost pressure is 3KPa and the drag coefficient is 1.2.

Preferably, when producing magnesium alloy ZM5 castings with a wall thickness of 1.4mm, the melting temperature of the magnesium alloy is 820°C, the preheating temperature of the gypsum mold is 400°C, the specified value _k1 is -20KPa, the The specified value k2 is -10KPa, the liquid lifting speed is 40m/s, the hydraulic pressure is 5KPa, the filling speed is 50mm/s, the filling pressure is 40KPa, the crusting time is 3s, the crusting boost pressure is 5KPa, crystallization The time is 250s, the crystallization boost pressure is 5KPa and the drag coefficient is 1.5.

In another aspect, the present invention also provides a magnesium alloy casting device, the device comprising:

The lower tank 1, the middle and lower part of the lower tank 1 is connected with the pressurizing device 2; the top of the lower tank 1 is sealed with a sealing partition 15; the lower tank 1 has a built-in melting furnace 3 and is used to hold magnesium alloy melting A crucible 4 for the liquid, the crucible 4 has a built-in liquid riser 17, the lower end of the riser 17 has a certain distance from the bottom of the crucible 4, and the upper port of the riser 17 passes through the sealing partition 15; Between the crucible 4 and the sealing partition 15, the lower tank 1 is connected to the first protective gas pipeline 7;

Upper tank 13, the top or side wall of the upper tank 13 is connected with the negative pressure vacuum pipeline 12 and the second protective gas pipeline 16; the upper tank 13 has a built-in plaster mold 8 with a cavity 14, and the plaster cast Type 8 is directly placed on the sealing partition 15, and asbestos 10 and asbestos pressing plate 11 are successively arranged on the top of the gypsum casting mold 8, and the asbestos pressing plate 11 is fixedly connected with the sealing dividing plate 15 through a stud 9; The upper tank 13 and the sealing partition 15 are locked by the locking mechanism 5 . the

Preferably, the first shielding gas pipeline 7 and the second shielding gas pipeline 16 are respectively connected to the first shielding gas device and the second shielding gas device; or connected to the same shielding gas device 6, controlled by a control system, disconnected Open the second protective gas pipeline 16, connect the first protective gas pipeline 7, inject protective gas into the lower tank 1; disconnect the first protective gas pipeline 7, and connect the second protective gas The pipeline 16 injects protective gas into the upper tank 13 . the

In another aspect, the present invention also provides a casting method using the casting device described above, the method comprising:

Step 1. After smelting and removing slag, the magnesium alloy melt at a temperature of 730°C to 820°C is put into the crucible 4, the crucible 4 is built into the lower tank 1, and the lower tank 1 is sealed with a sealing cover;

Step 2. Place the preheated plaster mold 14 at a temperature of 200°C to 400°C on the sealing cover plate 15, and cover the lower pot 1 with the upper pot 13;

Step 3, using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon at a pressure of 1-5Kpa to pressurize the lower tank 1 through the first protective gas pipeline 7 for 1-2 minutes, Make the sulfur hexafluoride float on the magnesium alloy melt to form a protective layer;

Step 4. Vacuum the upper tank through the negative pressure vacuum pipeline 12, so that the negative pressure value of the upper tank reaches -20～-50KPa; then 1-10% sulfur hexafluoride and 90-99% argon The mixed gas is injected into the upper tank 13 through the second protective gas pipeline 16, so that the negative pressure of the upper tank 13 is raised to -10～-30KPa;

Step 5, using the pressurizing device 2 to pressurize the lower tank 1 with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the cavity 14 through the liquid riser 17 to realize pressurization pouring. the

(3) Beneficial effects

A kind of magnesium alloy casting method and device thereof provided by the present invention have the following advantages:

In the present invention, the mixed gas of 1-10% sulfur hexafluoride and 90-99% argon is used to pressurize and protect the lower tank, so that sulfur hexafluoride with a relatively heavy specific gravity can float above the magnesium alloy melt to form a layer The dense protective film can not only prevent the magnesium alloy melt from continuing to react or evaporate, but also isolate the magnesium alloy melt from the air; vacuumize the upper tank, and the air in the cavity is discharged through asbestos; when the upper tank is in Under negative pressure, the protective gas is injected to prevent the magnesium alloy melt in the cavity from burning, insufficient pouring or cold shut, which is beneficial to filling the mold; and the pressure device is used to apply pressure to the lower tank to make the magnesium alloy The melt is injected into the mold cavity from bottom to top along the riser, and provides a large external force, which is beneficial to filling and solidification, and is beneficial to the production of thin-walled parts. Adopting the technical solution provided by the invention, the average wall thickness of the casting is 1.0-1.5mm, the tensile strength reaches 190MPa, the elongation reaches 2-3%, the surface quality is high, there are no oxidation, cold shut and slag inclusion defects, and the internal structure is compact , good performance, simple process, convenient operation, low cost and easy mass production. the

Description of drawings

Fig. 1 is the casting method flow diagram of embodiment one;

Fig. 2 is the casting method schematic flow sheet of embodiment two;

Figure 3a is a schematic diagram of a combustion casting with excessive negative pressure;

Figure 3b is a schematic diagram of the negative pressure forming the casting within the range of the specified negative pressure value;

Fig. 4 is a schematic diagram of the casting device of the fourth embodiment. the

Detailed ways

Below in conjunction with accompanying drawing and embodiment of description, the specific embodiment of the present invention is described in further detail. The following examples are only used to illustrate the present invention, but not to limit the scope of the present invention. the

Embodiment one

As shown in Figure 1, the present embodiment describes a casting method of magnesium alloy near pressure regulating gas protection, the method comprises the following steps:

Step 101. Put the molten magnesium alloy at a temperature of 730° C. to 820° C. after smelting and deslagging into a crucible. The crucible is built into a lower tank, and the lower tank is sealed with a sealing cover. the

On the one hand, due to the high pouring temperature of magnesium alloy thin-walled parts, the magnesium alloy melt and gypsum are prone to react; The reaction between liquid and gypsum, therefore, after many tests, the melting temperature of the magnesium alloy in this embodiment is 730°C-820°C. the

Step 102: Put the preheated plaster mold at a temperature of 200° C. to 400° C. on the sealing cover plate, and cover the lower jar with the upper jar. the

In order to prevent the temperature of the gypsum mold from being too low and reduce the temperature of the magnesium alloy melt in the cavity, resulting in insufficient pouring, cold shut and other defects, the gypsum mold is preheated first, generally at 200°C to 400°C. hot. the

Step 103, using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon at an air pressure of 1-5Kpa to place the lower tank between the sealing cover plate and the crucible for 1-2 minutes Pressing to make the sulfur hexafluoride float on the magnesium alloy melt to form a protective layer. the

In the mixed gas of 1-10% sulfur hexafluoride and 90-99% argon, sulfur hexafluoride with a large specific gravity floats on the surface of the magnesium alloy melt, reacts with the magnesium alloy melt, and produces a dense protective effect. The permanent protective film, on the one hand, can prevent the magnesium alloy melt from continuing to react, prevent the evaporation of the magnesium alloy melt, and isolate the magnesium alloy melt from the outside air to prevent the magnesium alloy from burning. the

Step 104, evacuate the upper tank through the negative pressure vacuum pipeline located on the upper part of the upper tank, so that the negative pressure value of the upper tank reaches the specified negative pressure value k ₁ , and then 1-10% hexafluoride The mixed gas of sulfur and 90-99% argon is injected into the upper tank from the upper part of the upper tank to raise the negative pressure of the upper tank to the specified negative pressure value k ₂ .

Vacuum the upper tank, the air in the cavity is discharged through asbestos, so that the upper tank is in a negative pressure state, and then inject a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon, and the mixed gas passes through Asbestos enters the mold cavity and reacts with the magnesium alloy melt entering the mold cavity to form a protective film, which can prevent the magnesium alloy melt from continuing to react, and isolate the magnesium alloy melt from the gypsum mold. It is in a negative pressure state, eliminating the condition of counterpressure during the filling process, so that the magnesium alloy melt driven by external force can easily overcome other external forces such as its own weight, viscous force and pressure in the cavity, which is conducive to realizing anti-gravity pouring. The specified negative pressure value k1 is generally -20 ~ -50KPa, and the specified negative pressure value _k2 is generally -10 ~ -30KPa. If the value is too large, the air turbulence in the liquid riser will be large, which will easily cause the magnesium alloy melt to burn in the liquid riser, forming a large number of inclusions, which is not conducive to mold filling. Figure 3a shows a schematic diagram of a burning casting with excessive negative pressure. The negative pressure shown in 3b is within the range of the specified negative pressure value; if it is too small, it is easy to cause insufficient pouring or cold shut.

Step 105: Pressurize the lower tank from the middle and lower part of the lower tank with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the upper tank through the liquid riser built in the crucible. In the cavity in the tank, pressurized pouring is realized. the

Pressurize the middle and lower part of the lower tank to avoid blowing away the sulfur hexafluoride above the magnesium alloy melt, which will not have a protective effect; at the same time, apply a certain external force to the lower tank so that the pressure on the surface of the magnesium alloy melt is greater than The pressure in the liquid riser, driven by external forces, the magnesium alloy melt overcomes its own gravity, viscous force and pressure in the cavity and other external forces, flows in the liquid riser along the opposite direction of gravity, and enters from bottom to top Cavity, so as to realize anti-gravity pouring, in the filling and solidification of castings, provide a large external force for the magnesium alloy melt, to overcome the resistance in thin-walled castings and complex castings, and improve the feeding of the magnesium alloy melt Ability to reduce casting defects such as shrinkage cavities, pores and pinholes, which is conducive to the formation of thin-walled parts. the

In step 105 of the present embodiment, adjustment process parameters are also included, and the specific selection principles are as follows:

1. Liquid rising speed, liquid rising speed refers to the rising speed of the melt in the liquid rising pipe. When the rising speed of the magnesium alloy melt into the cavity is too high, since the casting gate diameter is fixed, when the filling speed is constant, jetting will easily occur; if it is too small, the temperature drop of the magnesium alloy melt in the rising pipe If it is too large, it is easy to under-water or cold shut. the

2. Liquid lifting pressure, liquid lifting pressure refers to the corresponding pressure when the melt completes the liquid lifting process, reaches the liquid lifting nozzle, and connects the bottom contact. The value of this parameter is related to the amount of magnesium alloy melt, the less magnesium alloy melt, the larger the value of this parameter. According to this value, the device determines the end of the lifting process and the start of filling to ensure the filling quality of the casting. the

3. Filling speed refers to the rising speed of the melt in the cavity. The value of this parameter is very important to the quality of the casting. If the value is too large, it will cause unstable mold filling, causing melt splashing or gas suffocation; if the value is too small, it will cause cold shut or under-casting. The specific size is related to the height, wall thickness and complexity of the casting. In general, the average wall thickness of castings is larger and the value is smaller; the average wall thickness of castings is smaller and the value is larger. the

4. Filling pressure refers to the pressure when the melt reaches the top of the cavity. The value of this parameter is related to the amount of melt in the melting and holding furnace and the height of the casting. The less melt in the furnace, the greater the value; the higher the casting, the greater the value. the

5. The crusting time refers to the time required from filling the mold to solidifying the crust on the surface of the casting. If the value of this parameter is too large, the crust is too thick, and even the casting is in the mushy solidification stage, which affects solidification feeding and shrinkage, and eventually leads to shrinkage porosity and micro-shrinkage porosity. the

6. Incrustation pressurization pressure refers to the pressure increase provided to make the casting crust under a certain pressure, that is, on the basis of the melt filling the cavity, a certain pressure is added. It can ensure that the melt is crusted under pressure and at the same time improve the feeding capacity. If the value of this parameter is too large, sand sticking will occur, and even the mold will be deformed. the

7. Crystallization time refers to the time required for the casting to completely solidify after the crust has solidified. If the value of this parameter is too small, the casting cannot be completely solidified, and premature pressure relief will cause the structure of the casting to be less dense, and the purpose of feeding will not be achieved; if the value is too large, the riser will freeze and affect work efficiency. The specific value of this parameter is related to the weight and wall thickness of the casting. the

8. Crystallization supercharging pressure refers to the larger supercharging value provided to make the casting crystallize under higher pressure, and the unit is KPa. The reason why this boost value is provided is to make the casting achieve better feeding during solidification and make the structure more compact. According to the rated working pressure of the tooling and equipment used, give a larger value as much as possible. the

9. The value of the drag coefficient is mainly to consider the complexity of the cavity. For the same filling height, the more complex the cavity, the greater the pressure required, so the more complex the casting, the greater the value of this parameter. the

After many tests, according to the amount of molten magnesium alloy, the average wall thickness of the casting, the height of the casting, the weight of the casting and the rated working pressure of the tooling and equipment used, the liquid rising speed in this embodiment can be 30-40mm/s , the lifting pressure can be 5-8KPa, the filling speed can be 30-60mm/s, the filling pressure can be 30-50KPa, the crusting time can be 2-5s, and the crusting boost pressure can be 3-8KPa, The crystallization time can be 150-350s, the crystallization boost pressure can be 3-8KPa, and the resistance coefficient can be 1.2-1.5. the

Adopting the technical solution of this embodiment, the average wall thickness of the casting is 1.0-1.5mm, the tensile strength reaches 190MPa, the elongation reaches 2-3%, the surface quality is high, there are no oxidation, cold shut, slag inclusion defects, and the internal structure is dense. It has good performance, simple process, convenient operation, low cost and easy mass production. the

Example two

The following ZM10 magnesium alloy, gypsum-type ingredients (mass fraction) are: 15% to 20% of quartz powder, 6% to 8% of talc powder, 60% to 85% of α hemihydrate gypsum, 18% to 25% of MgS0 ₄ , water and other materials, the mixed gas ratio is 10% sulfur hexafluoride and 90% argon as raw materials, combined with the casting device structure diagram shown in Figure 4, this embodiment is specifically introduced, as shown in Figure 2, The concrete steps of the casting method of a kind of magnesium alloy near pressure regulating gas protection described in this embodiment are as follows:

In step 201, the ZM10 magnesium alloy is smelted at 780° C., and the slag is removed, and the slag-removed magnesium alloy melt is put into a crucible, and the lower tank is sealed with a sealing partition. the

Step 202, preheating the gypsum mold at 380°C, closing the tank and putting the upper tank cover on and off the tank. the

Step 203, pressurizing the lower tank for 1 minute with a mixed gas of 10% sulfur hexafluoride and 90% argon at a pressure of 5KPa. the

Step 204, vacuumize the upper tank, so that the negative pressure of the upper tank reaches -30KPa, and then inject the mixed gas of 10% sulfur hexafluoride and 90% argon into the upper tank, so that the negative pressure of the upper tank rises to -20Kpa. the

Step 205, adjust the process parameters, and use the air pressure of 50KPa to perform pressure pouring on the lower tank. the

Among them, the liquid lifting speed is 35m/s, the liquid lifting pressure is 6KPa, the filling speed is 40mm/s, the filling pressure is 38KPa, the crusting time is 5s, the crusting boost pressure is 3KPa, and the crystallization time is 150s. The boost pressure is 3KPa, and the drag coefficient is 1.2. The lower tank 1 is pressurized by the pressurizing device 2, and the applied pressure is 50KPa, so as to realize pressurized pouring. the

Adopt the technical scheme recorded in this embodiment to produce four gypsum-type thin-walled castings in a mold, the average wall thickness of the castings is 1.5mm, and the surface finish is 3.6. the

Embodiment three

The casting method of a magnesium alloy close to the pressure-regulating gas protection described in this embodiment is basically the same as the technical solution described in the above-mentioned preferred embodiment, except that the raw materials and process parameters are different:

1. The raw materials are different, the magnesium alloy is ZM5, and the mixed gas ratio is 5% sulfur hexafluoride + 95% argon;

2. The temperature of magnesium alloy ZM5 melt is 820°C, and the preheating temperature of gypsum type is 400°C;

3. Vacuumize the upper tank to make the negative pressure of the upper tank reach -20KPa, and then inject the mixed gas into the upper tank to raise the negative pressure of the upper tank to -10KPa;

4. Pressurize the lower tank for 2 minutes with a mixed gas of 5% sulfur hexafluoride and 95% argon at a pressure of 3Kpa

5. Use the air pressure of 55KPa to pressure pour the lower tank, the liquid lifting speed is 40m/s, the liquid lifting pressure is 5Kpa, the filling speed is 50mm/s, the filling pressure is 40Kpa, the crusting time is 3s, and the filling time is 3s. Shell supercharging pressure is 5Kpa, crystallization time is 250s, crystallization supercharging pressure is 5Kpa, drag coefficient is 1.5. the

The technical solution recorded in this embodiment is used to produce one piece of plaster-type thin-walled casting, the average wall thickness of the casting is 1.4mm, and the surface finish is 3.6. the

Embodiment four

As shown in Fig. 4, a kind of casting device of magnesium alloy described in this embodiment, as shown in Fig. 4, this device comprises: lower tank 1, the middle and lower part of lower tank 1 is connected with pressurizing device 2; The top is sealed with a sealing partition 15; the lower tank 1 has a built-in melting furnace 3 and a crucible 4 for containing the magnesium alloy melt. At a certain distance, the upper port of the riser pipe 17 passes through the sealing partition 15 ; between the crucible 4 and the sealing partition 15 , the lower tank 1 is connected to the first protective gas pipeline 7 . the

The upper tank 13, the top or side wall of the upper tank 13 is connected with the negative pressure vacuum pipeline 12 and the second protective gas pipeline 16; the upper tank 13 has a built-in plaster mold 8 with a cavity 14, and the plaster mold 8 is directly placed On the partition 15, asbestos 10 and asbestos pressure plate 11 are successively arranged on the top of the plaster mold 8, and the asbestos pressure plate 11 and the sealing partition 15 are fixedly connected by studs 9; the upper tank 13 and the sealing partition 15 are locked by the locking mechanism 5 tight. the

The first shielding gas pipeline 7 and the second shielding gas pipeline 16 in this embodiment can be connected to the first shielding gas device and the second shielding gas device respectively, or can be connected to the same shielding gas device 6, and controlled by the control system. Disconnect the second protective gas pipeline 16, connect the first protective gas pipeline 7, and inject protective gas into the lower tank 1; disconnect the first protective gas pipeline 7, connect the second protective gas pipeline 16, and inject protective gas into the upper tank 13 . the

Embodiment five

This embodiment describes a casting method using the device casting described above, the method includes. the

Step 501, step 1, putting the molten magnesium alloy at a temperature of 730° C. to 820° C. after smelting and deslagging into the crucible 4 , the crucible 4 is built into the lower tank 1 , and the lower tank 1 is sealed with a sealing cover. the

Step 502 , place the preheated plaster mold 14 at a temperature of 200° C. to 400° C. on the sealing cover plate 15 , and cover the lower jar 1 with the upper jar 13 . the

Step 503, using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon at a pressure of 1-5 Kpa to pressurize the lower tank 1 through the first protective gas pipeline 7 for 1-2 minutes, The sulfur hexafluoride is made to float on the molten magnesium alloy to form a protective layer. the

Step 504, evacuate the upper tank through the negative pressure vacuum pipeline 12, so that the negative pressure value of the upper tank reaches -20～-50KPa; The mixed gas is injected into the upper tank 13 through the second protective gas pipeline 16, so that the negative pressure of the upper tank 13 rises to -10～-30KPa. the

Step 505, using the pressurizing device 2 to pressurize the lower tank 1 with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the cavity 14 through the liquid riser 17 to realize pressurization pouring. the

The sulfur hexafluoride in the protective gas injected into the lower tank reacts with the magnesium alloy melt to form a dense protective film that prevents the magnesium alloy melt from continuing to burn or evaporate. The protective gas enters the gypsum mold through the asbestos and asbestos pressure plate, so that the air in the cavity can be discharged, which can realize the isolation of the magnesium alloy melt and the gypsum mold, and help to achieve negative pressure pouring, and the magnesium in the lower tank The alloy melt, under the external force applied by the pressurizing device, on the one hand avoids blowing away the sulfur hexafluoride on the surface of the magnesium alloy melt, on the other hand, makes the magnesium alloy melt overcome its own gravity and viscosity under the drive of external force External forces such as stagnation and pressure in the cavity are injected into the cavity from bottom to top along the riser for pressurized pouring. the

The above is only a preferred embodiment of the present invention, it should be pointed out that for those of ordinary skill in the art, without departing from the technical principle of the present invention, some improvements and modifications can also be made, these improvements and modifications It should also be regarded as the protection scope of the present invention. the

Claims (10)

1. A casting method of a magnesium alloy, characterized in that the method comprises: pouring under negative pressure conditions. 2. a casting method of magnesium alloy, is characterized in that, the method comprises the steps: Step 1. After smelting and removing slag, the magnesium alloy melt at a temperature of 730°C to 820°C is put into a crucible, the crucible is built into the lower tank, and the lower tank is sealed with a sealing cover; Step 2. Put the preheated plaster mold with a temperature of 200°C to 400°C on the sealing cover plate, and cover the lower pot with the upper pot; Step 3, using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon, and an air pressure of 1-5Kpa to carry out the lowering of the tank between the sealing cover plate and the crucible for 1-2 minutes Pressing to make the sulfur hexafluoride float on the magnesium alloy melt to form a protective layer; Step 4. Vacuum the upper tank through the negative pressure vacuum pipeline located on the upper part of the upper tank, so that the negative pressure value of the upper tank reaches the specified negative pressure value k ₁ , and then put 1-10% hexafluoride The mixed gas of sulfur and 90-99% argon is injected into the upper tank from the upper part of the upper tank, so that the negative pressure of the upper tank rises to the specified negative pressure value k ₂ ; Step 5. Pressurize the lower tank from the middle and lower part of the lower tank with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the upper tank through the liquid riser built in the crucible. In the cavity in the tank, pressurized pouring is realized. 3. The casting method according to claim 2, wherein the mixed gas in step 3 and step 4 is a mixed gas of 10% sulfur hexafluoride and 90% argon; or 5% sulfur hexafluoride Mixed gas with 95% argon. 4. The casting method according to claim 2 or 3, characterized in that the prescribed negative pressure value _k1 described in step 4 is -20 to -50KPa, and the prescribed negative pressure value _k2 is -10 to - 30KPa. 5. The casting method according to any one of claims 1 to 4, characterized in that step 5 also includes adjusting process parameters, said process parameters comprising: The liquid lifting speed is 30-40mm/s, the liquid lifting pressure is 5-8KPa, the filling speed is 30-60mm/s, the filling pressure is 30-50KPa, the crusting time is 2-5s, and the crusting boost pressure is 3-8KPa, the crystallization time is 150-350s, the crystallization boost pressure is 3-8KPa and the resistance coefficient is 1.2-1.5. 6. The casting method according to claim 5, characterized in that, when producing magnesium alloy ZM10 castings with a wall thickness of 1.5mm, the melting temperature of the magnesium alloy is 780°C, and the preheating temperature of the gypsum mold is 380°C , the specified negative pressure value k ₁ is -30KPa, the specified negative pressure value k ₂ is -20KPa, the liquid lifting speed is 35m/s, the liquid lifting pressure is 6KPa, the filling speed is 40mm/s, The filling pressure is 38KPa, the crusting time is 5s, the crusting boost pressure is 3KPa, the crystallization time is 150s, the crystallization boost pressure is 3KPa and the resistance coefficient is 1.2. 7. The casting method according to claim 5, characterized in that, when producing magnesium alloy ZM5 castings with a wall thickness of 1.4mm, the melting temperature of the magnesium alloy is 820°C, and the preheating temperature of the gypsum mold is 400°C , the specified negative pressure value _k1 is -20KPa, the specified negative pressure value k2 is -10KPa, the liquid lifting speed is 40m/s, the liquid lifting pressure is 5KPa, the filling speed is 50mm/s, the filling pressure is 40KPa, crusting time is 3s, crusting boost pressure is 5KPa, crystallization time is 250s, crystallization boost pressure is 5KPa and drag coefficient is 1.5. 8. A magnesium alloy casting device, characterized in that the device comprises: The lower tank (1), the middle and lower part of the lower tank (1) is connected with the pressurizing device (2); the top of the lower tank (1) is sealed with a sealing partition (15); the lower tank (1) A built-in melting furnace (3) and a crucible (4) for containing magnesium alloy melt, the crucible (4) has a built-in riser (17), and the lower end of the riser (17) is connected to the crucible ( 4) has a certain distance from the bottom, and the upper port of the riser pipe (17) passes through the sealing partition (15); between the crucible (4) and the sealing partition (15), the lower tank ( 1) Connect with the first protective gas pipeline (7); An upper tank (13), the top or side wall of the upper tank (13) is connected with the negative pressure vacuum pipeline (12) and the second protective gas pipeline (16); the upper tank (13) has a built-in cavity ( 14) the gypsum casting mold (8), the gypsum casting mold (8) is directly placed on the sealing partition (15), and the top of the gypsum casting mold (8) is provided with asbestos (10) and asbestos Pressing plate (11), the asbestos pressing plate (11) and the sealing partition (15) are fixedly connected by studs (9); the upper tank (13) and the sealing partition (15) are connected by a locking mechanism (5) Lock tight. 9. The casting device according to claim 8, characterized in that, the first shielding gas pipeline (7) and the second shielding gas pipeline (16) are respectively connected to the first shielding gas device and the second shielding gas device; Or connect with the same protective gas device (6), control it through the control system, disconnect the second protective gas pipeline (16), connect the first protective gas pipeline (7), and send to the lower tank ( 1) Inject protective gas; disconnect the first protective gas pipeline (7), connect the second protective gas pipeline (16), and inject protective gas into the upper tank (13). 10. A casting method using the device according to any one of claims 8 to 9, characterized in that the method comprises: Step 1. After smelting and removing slag, put the molten magnesium alloy at a temperature of 730°C to 820°C into the crucible (4), the crucible (4) is built into the lower tank (1), and the lower tank (1) is sealed with a sealing cover plate. tank(1); Step 2. Place the preheated plaster mold (14) at a temperature of 200°C to 400°C on the sealing cover (15), and cover the lower pot (1) with the upper pot (13); Step 3. Using a mixed gas of 1-10% sulfur hexafluoride and 90-99% argon at a pressure of 1-5Kpa to pass through the first protective gas pipeline (7) to the lower tank (1) for 1- Press for 2 minutes to make the sulfur hexafluoride float on the magnesium alloy melt to form a protective layer; Step 4. Vacuum the upper tank through the negative pressure vacuum pipeline 12, so that the negative pressure value of the upper tank reaches -20～-50KPa; then 1-10% sulfur hexafluoride and 90-99% argon The mixed gas is injected into the upper tank (13) through the second protective gas pipeline (16), so that the negative pressure of the upper tank (13) rises to -10～-30KPa; Step 5. Using a pressurizing device (2), pressurize the lower tank (1) with an air pressure of 10-80KPa, so that the magnesium alloy melt enters the cavity ( 14) to achieve pressurized pouring.

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