Method of solidification of magnesium alloy for investment casting and investment casting method

Abstract

The present application relates to the alloy casting technical field, especially to a kind of investment casting magnesium alloy solidification method and investment casting method.The investment casting magnesium alloy solidification method includes the following steps: (a) the mold shell with magnesium alloy liquid is placed in the sealed chamber containing cooling medium, and the mold shell riser is leaked in the cooling medium;(b) the pressure in the sealed chamber is regulated, and the magnesium alloy in the mold shell is solidified under varying pressure.The investment casting magnesium alloy solidification method of the present application makes the magnesium alloy liquid solidify under pressure, which is beneficial to the liquid metal feeding;During the metal solidification process, the varying pressure is applied, the volume of magnesium alloy liquid is constantly changed, the dendrites formed during solidification are constantly washed, the dendrites are constantly broken and the grains are fine, and the feeding path is more smooth, thereby improving the microstructure density of the casting obtained by solidification, and the mechanical properties are improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of alloy casting technology, in particular to a method for solidification of magnesium alloy by investment casting and an investment casting method. BACKGROUND

[0002] In recent years, the demand for light weight materials is increasing, and magnesium alloy as a structural material has been widely used due to its small specific gravity, high specific strength and specific stiffness, good thermal and electrical conductivity, good cutting machinability, easy forming and recycling, etc.

[0003] According to different forming processes, magnesium alloy materials are mainly divided into two categories: cast magnesium alloy and wrought magnesium alloy. The former mainly obtains magnesium alloy products through casting, including sand casting, investment casting, lost foam casting, die casting, etc. Among them, investment casting has been widely used because the castings have high dimensional accuracy and low surface roughness, and investment casting can cast complex castings of various alloys.

[0004] For magnesium alloy casting, due to the wide crystallization temperature range of magnesium alloy, it is easy to form developed dendritic structure, which causes magnesium alloy castings to produce defects such as porosity, cracks and difficulty in feeding during solidification.

[0005] Therefore, the present application is proposed. SUMMARY

[0006] An object of the present application is to provide a method for solidification of magnesium alloy by investment casting, to solve the technical problems of magnesium alloy investment casting in the prior art, such as the production of defects such as porosity, cracks and difficulty in feeding during solidification.

[0007] Another object of the present application is to provide a magnesium alloy investment casting method, which includes the above-mentioned method for solidification of magnesium alloy by investment casting, and the performance of the magnesium alloy castings obtained is improved.

[0008] In order to achieve the above-mentioned objects of the present application, the following technical solutions are adopted:

[0009] The method for solidification of magnesium alloy by investment casting comprises the following steps:

[0010] (a) placing the mold shell poured with magnesium alloy liquid in a sealed chamber containing a cooling medium, and making the mold shell sprue outside the cooling medium;

[0011] (b) regulating the pressure in the sealed chamber to make the magnesium alloy in the mold shell complete solidification under varying pressure.

[0012] The method for solidification of the magnesium alloy by the lost foam casting of the application makes the magnesium alloy liquid solidify under pressure, which is beneficial to the liquid metal feeding; and during the solidification of the metal, the changing pressure is applied to make the volume of the magnesium alloy liquid change constantly, which is equivalent to the flow of the magnesium alloy liquid, and the dendrite formed during the solidification is constantly broken and the grain is fine, and the feeding path is more smooth, thereby improving the microstructure compactness of the casting obtained by the solidification and the mechanical property.

[0013] In the detailed description of the application, the method for regulating the pressure in the sealed chamber comprises: first pressurizing the sealed chamber, and then depressurizing; repeating the pressurizing and depressurizing at least once.

[0014] In the detailed description of the application, the method for regulating the pressure in the sealed chamber comprises:

[0015] (b1) pressurizing the pressure in the sealed chamber from normal atmospheric pressure to 80-100 atmospheres;

[0016] (b2) depressurizing the pressure in the sealed chamber from 80-100 atmospheres to 1-2 atmospheres;

[0017] Repeating (b1) and (b2) at least once.

[0018] In the detailed description of the application, after repeating (b1) and (b2) at least once, the pressure in the sealed chamber is pressurized to 80-100 atmospheres and kept for 5-10 minutes.

[0019] In the detailed description of the application, in step (b1), the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 80-100 atmospheres within 20-40 seconds.

[0020] In the detailed description of the application, in step (b2), the pressure in the sealed chamber is depressurized from 80-100 atmospheres to 1-2 atmospheres within 5-10 seconds.

[0021] In the detailed description of the application, the magnesium alloy comprises ZM5. Further, in the pouring, the pouring temperature of the magnesium alloy is 750-755℃, and the temperature of the mold shell is 360-365℃.

[0022] In actual operation, after the casting is solidified and cooled, the mold shell is taken out, and the casting is detected, heat treated, etc.

[0023] In the specific embodiment of the present application, the cooling medium comprises quenching oil and / or and / or lipophilic oil. Further, when the wall thickness of the casting is > 10mm, quenching oil is used as the cooling medium; when the wall thickness of the casting is ≤ 10mm, lipophilic oil is used as the cooling medium. The cooling medium is placed in the sealed chamber, which helps to achieve rapid pressurization and depressurization.

[0024] In the specific embodiment of the present application, the sealed chamber is formed by the closure of the tank body and the sealing cover; the tank body sidewall is provided with a gas inlet, and the sealing cover is provided with a gas outlet.

[0025] In the specific embodiment of the present application, the gas inlet is circumscribed by a positive pressure source, and the gas outlet is circumscribed by a negative pressure source.

[0026] In the specific embodiment of the present application, a first electromagnetic valve is arranged between the gas inlet and the positive pressure source; a second electromagnetic valve is arranged between the gas outlet and the negative pressure source.

[0027] In the specific embodiment of the present application, the first electromagnetic valve and the second electromagnetic valve are connected with a controller; the controller controls the on-off of the first electromagnetic valve and the second electromagnetic valve.

[0028] In the specific embodiment of the present application, a gas pressure sensor is arranged in the sealed chamber for detecting the gas pressure in the sealed chamber; the gas pressure sensor is connected with the controller. The pressure value of the sealed chamber transmitted by the gas pressure sensor to the controller controls the on-off of the first electromagnetic valve and the second electromagnetic valve.

[0029] The present application also provides a method for magnesium alloy investment casting, comprising any one of the above-mentioned methods for magnesium alloy investment casting solidification.

[0030] Compared with the prior art, the present application has the following beneficial effects:

[0031] The method for magnesium alloy investment casting solidification of the present application is accompanied by pressure during solidification, which is beneficial to the liquid metal feeding; during the metal solidification process, the pressure is changing, and with the change of the pressure, the metal volume changes. This change process is equivalent to the continuous flushing of the liquid flow on the dendrites formed during the solidification process, which makes the dendrites continuously broken and the grains finer, and makes the feeding path more smooth, thereby improving the organization density of the casting obtained by solidification, and the porosity degree is reduced compared with the existing investment casting casting, even without porosity, and the mechanical properties of the obtained casting can be improved by about 10%. BRIEF DESCRIPTION OF DRAWINGS

[0032] In order to more clearly illustrate the technical solutions in the specific embodiments or the prior art of the present application, the drawings needed to be used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings in the following description are some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative effort on the basis of these drawings.

[0033] Figure 1 The structural schematic diagram of the device for magnesium alloy solidification in investment casting provided by the embodiments of the present application.

[0034] Reference signs:

[0035] 1 - pot body; 2 - sealing cover; 3 - sealing chamber;

[0036] 4 - cooling medium; 5 - mold shell; 11 - gas inlet;

[0037] 12 - positive pressure source; 13 - first electromagnetic valve; 21 - gas outlet;

[0038] 22 - negative pressure source; 23 - second electromagnetic valve; 51 - riser. DETAILED DESCRIPTION

[0039] The technical solutions of the present application will be described clearly and completely in combination with the drawings and specific embodiments below, but those skilled in the art will understand that the following described embodiments are part of the embodiments of the present application, not all the embodiments, and are only used to illustrate the present application, and should not be regarded as limiting the scope of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present application. The specific conditions not mentioned in the embodiments are carried out according to the conventional conditions or the conditions recommended by the manufacturer. The reagents or instruments used are not marked with the manufacturer, which are conventional products that can be purchased in the market.

[0040] In the description of the present application, it should be noted that the orientations or positional relationships indicated by the terms "center", "upper", "lower", "left", "right", "vertical", "horizontal", "inner", "outer" and the like are based on the orientations or positional relationships shown in the drawings, and are only for the convenience of describing the present application and simplifying the description, and therefore cannot be understood as indicating or implying that the devices or elements referred to must have a particular orientation, be constructed and operated in a particular orientation, and therefore cannot be understood as limiting the present application. In addition, the terms "first", "second", "third" are only for the purpose of description, and cannot be understood as indicating or implying relative importance.

[0041] In the description of the present application, it is necessary to point out that unless otherwise explicitly specified and limited, the terms "mounting", "connecting", "connection" should be understood in a broad sense, for example, it can be fixed connection, or detachable connection, or integrally connected; it can be mechanical connection, or electrical connection; it can be directly connected, or indirectly connected through intermediate medium, or the communication inside two elements. For those skilled in the art, the specific meaning of the above terms in the present application can be understood according to the specific circumstances.

[0042] The method for solidification of magnesium alloy by investment casting provided by the embodiment of the present application comprises the following steps:

[0043] (a) the mold shell poured with magnesium alloy liquid is placed in a sealed chamber containing cooling medium, and the mold shell sprue is exposed to the cooling medium;

[0044] (b) the pressure in the sealed chamber is regulated, so that the magnesium alloy in the mold shell completes solidification under varying pressure.

[0045] The method for solidification of magnesium alloy by investment casting of the present application enables the magnesium alloy liquid to solidify under pressure, which is beneficial to the liquid metal feeding; and during the solidification of the metal, the varying pressure is applied, so that the volume of the magnesium alloy liquid changes constantly, which is equivalent to the flow of the magnesium alloy liquid, constantly flushing the dendrites formed during the solidification, so that the dendrites are constantly broken and the grains are fine, and the feeding path is smoother, thereby improving the microstructure density of the casting obtained by solidification, and the mechanical properties are improved.

[0046] In the specific embodiment of the present application, the method for regulating the pressure in the sealed chamber comprises: first pressurizing the sealed chamber, and then depressurizing; the pressurizing and depressurizing operations are repeated at least once.

[0047] In the specific embodiment of the present application, the method for regulating the pressure in the sealed chamber comprises: first pressurizing the pressure in the sealed chamber to X atmospheres, and then depressurizing the pressure in the sealed chamber to Y atmospheres; X-Y≥70. Further, 70≤X-Y≤100, more preferably, 90≤X-Y≤100.

[0048] If the pressure change in the sealed chamber is too small, the flushing of the dendrites cannot be achieved during the repeated pressurization and depressurization; and if the pressure change in the sealed chamber is too large, the pressurization time may be too long, and the magnesium alloy may be compacted before the repeated flushing of the dendrites is achieved.

[0049] In the specific embodiment of the present application, the method for regulating the pressure in the sealed chamber comprises:

[0050] (b1) pressurizing the pressure in the sealed chamber from normal atmospheric pressure to 80-100 atmospheres;

[0051] (b2) again depress the pressure in the sealed chamber from 80-100 atmospheres to 1-2 atmospheres;

[0052] Repeat (b1) and (b2) at least once.

[0053] As in different embodiments, in step (b1), the pressure can be pressurized to 80 atmospheres, 82 atmospheres, 84 atmospheres, 85 atmospheres, 86 atmospheres, 88 atmospheres, 90 atmospheres, 92 atmospheres, 94 atmospheres, 95 atmospheres, 96 atmospheres, 98 atmospheres, 100 atmospheres, etc.; in step (b2), the pressure can be depressurized to 1 atmosphere, 1.2 atmospheres, 1.4 atmospheres, 1.5 atmospheres, 1.6 atmospheres, 1.8 atmospheres, 2 atmospheres, etc.

[0054] The repeated pressurization and depressurization processes using the above pressures can ensure the breaking of the dendrites and improve the densification effect; if the pressure is too large and the pressurization time is too long, the magnesium alloy will be compacted without repeated flushing of the dendrites, and the dendrites cannot be further broken or the densification cannot be improved; if the pressure is too small, on the one hand, the efficiency is slow, and on the other hand, the effect of breaking the dendrites cannot be achieved.

[0055] In a specific embodiment of the present application, (b1) and (b2) are repeated 8-12 times.

[0056] As in different embodiments, the number of times of repeating (b1) and (b2) can be 8 times, 9 times, 10 times, 11 times, 12 times, etc.

[0057] In a specific embodiment of the present application, after repeating (b1) and (b2) at least once, the pressure in the sealed chamber is pressurized to 80-100 atmospheres for 5-10 minutes.

[0058] As in different embodiments, the time of the pressure holding can be 5 minutes, 6 minutes, 7 minutes, 8 minutes, 9 minutes, 10 minutes, etc.

[0059] In a specific embodiment of the present application, after the pressure in the sealed chamber is pressurized to 80-100 atmospheres for 5-10 minutes, the pressure is depressurized to 1 atmosphere within 6-10 seconds, and the casting is taken out after the casting is solidified and cooled.

[0060] In a specific embodiment of the present application, in step (b1), the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 80-100 atmospheres within 20-40 seconds.

[0061] As in different embodiments, the time for pressurizing from normal atmospheric pressure to 80-100 atmospheres in step (b1) can be 20s, 22s, 24s, 25s, 26s, 28s, 30s, 32s, 34s, 35s, 36s, 38s, 40s, etc.

[0062] In a specific embodiment of the present application, the pressure in the sealed chamber is released from 80-100 atmospheres to 1-2 atmospheres within 5-10 seconds in step (b2).

[0063] As in different embodiments, the time for releasing from 80-100 atmospheres to 1-2 atmospheres in step (b2) can be 5s, 6s, 7s, 8s, 9s, 10s, etc.

[0064] In actual operation, the solidification method of the present application is used, and the pouring temperature of the magnesium alloy liquid and the mold shell is 10°C higher than that in the conventional process when the alloy is poured. In a specific embodiment of the present application, the magnesium alloy comprises ZM5. Further, in the pouring, the pouring temperature of the magnesium alloy is 750-755°C, and the temperature of the mold shell is 360-365°C.

[0065] In actual operation, after the castings are solidified and cooled, the mold shell is removed, and the castings are detected, heat treated, etc.

[0066] In a specific embodiment of the present application, the cooling medium comprises quenching oil and / or and / or synthetic oil. Further, when the wall thickness of the castings is >10mm, quenching oil is used as the cooling medium; and when the wall thickness of the castings is ≤10mm, synthetic oil is used as the cooling medium.

[0067] In an embodiment of the present application, step (b) comprises:

[0068] (b1) pressurizing the pressure in the sealed chamber from normal atmospheric pressure to 100 atmospheres within 30 seconds;

[0069] (b2) releasing the pressure in the sealed chamber from 100 atmospheres to 1 atmosphere within 6 seconds;

[0070] (b1) and (b2) are repeated 10 times, and then the pressure in the sealed chamber is pressurized to 100 atmospheres and maintained for 10 minutes.

[0071] In a specific embodiment of the present application, it further comprises: heat treating the solidified castings. The heat treatment can be performed according to the conventional heat treatment system of the alloy.

[0072] Figure 1 A structural schematic diagram of a device for solidification of magnesium alloy in investment casting is provided for the embodiments of the present application; as Figure 1As shown, the device for solidification of magnesium alloy in investment casting provided by the embodiment comprises a tank body 1 and a sealing cover 2, which are sealingly connected to form a sealed chamber 3. The sealing connection between the tank body 1 and the sealing cover 2 comprises snap fit, threaded connection, etc., and is not limited thereto, and other ways of sealingly connecting the two to form the sealed chamber 3 are also available.

[0073] Further, the tank body 1 is provided with a gas inlet 11, and the sealing cover 2 is provided with a gas outlet 21.

[0074] Further, the gas inlet 11 is externally connected with a positive pressure source 12, and the gas outlet 21 is externally connected with a negative pressure source 22. The positive pressure source 12 injects gas into the sealed chamber 3 to increase the pressure in the sealed chamber 3, and the negative pressure source 22 sucks out the gas in the sealed chamber 3 to decrease the pressure in the sealed chamber 3.

[0075] In actual operation, the gas injected by the positive pressure source 12 can be argon.

[0076] Further, a first electromagnetic valve 13 is arranged between the gas inlet 11 and the positive pressure source 12, and a second electromagnetic valve 23 is arranged between the gas outlet 21 and the negative pressure source 22. When the first electromagnetic valve 13 is turned on, the sealed chamber 3 is connected to the positive pressure source 12 through the gas inlet 11 to inject gas into the sealed chamber 3, thereby increasing the pressure in the sealed chamber 3; when the second electromagnetic valve 23 is turned on, the sealed chamber 3 is connected to the negative pressure source 22 through the gas outlet 21 to suck out the gas in the sealed chamber 3, thereby decreasing the pressure in the sealed chamber 3.

[0077] Further, the first electromagnetic valve 13 and the second electromagnetic valve 23 are connected with a controller, and the controller controls the on-off of the first electromagnetic valve 13 and the second electromagnetic valve 23.

[0078] In actual operation, when pressurizing the sealed chamber 3, the controller opens the first solenoid valve 13 and closes the second solenoid valve 23, allowing the positive pressure source 12 to inject argon gas into the sealed chamber 3, increasing the pressure inside. When the pressure inside the sealed chamber 3 reaches a preset pressure (e.g., 80-100 atmospheres), the controller closes the first solenoid valve 13, and the positive pressure source 12 stops injecting argon gas into the sealed chamber 3. When depressurizing the sealed chamber 3, the controller closes the first solenoid valve 13 and opens the second solenoid valve 23, allowing the negative pressure source 22 to draw gas out of the sealed chamber 3, reducing the pressure inside. When the pressure inside the sealed chamber 3 reaches a preset pressure (e.g., 1-2 atmospheres), the controller closes the second solenoid valve 23, and the negative pressure source 22 stops drawing gas out of the sealed chamber 3. To maintain pressure during the process, both the first solenoid valve 13 and the second solenoid valve 23 can be closed. By controlling the positive pressure source 12, the first solenoid valve 13, the negative pressure source 22, and the second solenoid valve 23, the pressure is increased, decreased, and maintained in the sealed chamber 3. The specific operation can be adjusted according to actual needs.

[0079] Furthermore, a pressure sensor may be installed inside the sealed chamber 3 to detect the gas pressure inside the sealed chamber 3; the pressure sensor is connected to the controller. The pressure value of the sealed chamber transmitted to the controller by the pressure sensor controls the opening and closing of the first solenoid valve 13 and the second solenoid valve 23.

[0080] In practice, the flow rate of injected / extracted gas can be adjusted by regulating the opening degree of the solenoid valve according to the required pressurization and depressurization time.

[0081] When solidification is required, a certain amount of cooling medium 4 is placed in the sealed chamber 3. Then, the mold shell 5, filled with molten magnesium alloy, is placed in the sealed chamber 3 containing the cooling medium 4, with the riser 51 of the mold shell 5 protruding into the cooling medium 4, and the rest completely immersed in the cooling medium 4. The gas inlet 11 is higher than the height of the cooling medium 4. Then, according to the requirements of the solidification method, the pressure in the sealed chamber 3 is adjusted to allow the magnesium alloy inside the mold shell 5 to solidify under varying pressure, resulting in a casting.

[0082] The method of the present invention immerses the entire mold shell in the cooling medium, which reduces the empty space in the sealed chamber and is more conducive to rapid pressurization and depressurization.

[0083] Specifically,

[0084] (1) Place the mold shell 5 filled with magnesium alloy liquid into the sealed chamber 3 containing the cooling medium 4, and make the riser 51 of the mold shell 5 leak out into the cooling medium 4.

[0085] (2) open the first electromagnetic valve 13, the positive pressure source 12 injects high pressure argon into the sealed chamber 3 through the gas inlet 11, the pressure in the sealed chamber 3 increases until it reaches 80-100 atmospheres, and the first electromagnetic valve 13 is closed;

[0086] (3) open the second electromagnetic valve 23, the negative pressure source 22 sucks out the gas in the sealed chamber 3 through the gas outlet 21, the pressure in the sealed chamber 3 decreases until it reaches 1-2 atmospheres, and the second electromagnetic valve 23 is closed;

[0087] (4) repeat the operations of steps (2) and (3) 8-12 times, then open the first electromagnetic valve 13, the positive pressure source 12 injects high pressure argon into the sealed chamber 3 through the gas inlet 11, the pressure in the sealed chamber 3 increases until it reaches 80-100 atmospheres, the first electromagnetic valve 13 is closed, pressure is maintained for 5-10 minutes, the second electromagnetic valve 23 is opened, and the pressure is released to normal pressure, after the casting is solidified and cooled, the mold shell 5 is taken out.

[0088] Example 1

[0089] The present embodiment provides a method for solidification of a magnesium alloy ZM5 by investment casting, comprising the following steps:

[0090] (1) ZM5 alloy melting and mold shell baking are performed by using existing processes; then the obtained ZM5 alloy liquid is poured into the mold shell, the pouring temperature of the ZM5 alloy is 750°C, and the temperature of the mold shell is 360°C.

[0091] (2) the mold shell poured in step (1) is placed in a sealed chamber containing quenching oil (quenching oil U8132), only the opening parts such as the mold shell sprue are exposed to the cooling medium, the rest parts are completely immersed in the cooling medium, and the sealing cover is buckled.

[0092] (3) high pressure argon is injected into the sealed chamber, the pressure in the sealed chamber is increased from normal atmospheric pressure to 100 atmospheres within 30 seconds; then the gas in the sealed chamber is sucked out, the pressure in the sealed chamber is decreased from 100 atmospheres to 1 atmosphere within 6 seconds; after repeating the foregoing pressurization and depressurization operations 10 times, high pressure argon is injected into the sealed chamber, the pressure in the sealed chamber is increased from normal atmospheric pressure to 100 atmospheres within 30 seconds, pressure is maintained for 10 minutes, then it is depressurized to 1 atmosphere within 10 seconds, after the casting is solidified and cooled, the casting is taken out.

[0093] (4) the mold shell of the casting is cleaned to obtain the casting, the wall thickness is >10 mm; after the casting is detected to be qualified, heat treatment is performed; the heat treatment condition is: T6 heat treatment system (T6 heat treatment system: solid solution treatment at 415°C for 10h, aging treatment at 190°C for 8h).

[0094] Example 2

[0095] This example refers to the method of Example 1, the only difference being that step (3) is different.

[0096] Step (3) of this example is: inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 80 atmospheres in 30 seconds; then the gas in the sealed chamber is sucked out, so that the pressure in the sealed chamber is depressurized from 80 atmospheres to 1 atmosphere in 6 seconds; after repeating the foregoing pressurization and depressurization operations 10 times, inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 80 atmospheres in 30 seconds, and then held for 10 minutes, and then depressurized to 1 atmosphere in 10 seconds. After the casting solidifies and cools, the mold shell is removed.

[0097] Example 3

[0098] This example refers to the method of Example 1, the only difference being that step (3) is different.

[0099] Step (3) of this example is: inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 70 atmospheres in 30 seconds; then the gas in the sealed chamber is sucked out, so that the pressure in the sealed chamber is depressurized from 70 atmospheres to 1 atmosphere in 6 seconds; after repeating the foregoing pressurization and depressurization operations 10 times, inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 70 atmospheres in 30 seconds, and then held for 10 minutes, and then depressurized to 1 atmosphere in 10 seconds. After the casting solidifies and cools, the mold shell is removed.

[0100] Example 4

[0101] This example refers to the method of Example 1, the only difference being that step (3) is different.

[0102] Step (3) of this example is: inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 100 atmospheres in 60 seconds; then the gas in the sealed chamber is sucked out, so that the pressure in the sealed chamber is depressurized from 100 atmospheres to 1 atmosphere in 6 seconds; after repeating the foregoing pressurization and depressurization operations 10 times, inject high pressure argon into the sealed chamber, so that the pressure in the sealed chamber is pressurized from normal atmospheric pressure to 100 atmospheres in 60 seconds, and then held for 10 minutes, and then depressurized to 1 atmosphere in 10 seconds. After the casting solidifies and cools, the mold shell is removed.

[0103] Example 5

[0104] This example refers to the method of Example 1, the only difference being that step (3) is different.

[0105] Step (3) of this example is: high-pressure argon is injected into the sealed chamber, so that the pressure in the sealed chamber is increased from normal atmospheric pressure to 100 atmospheres in 30 seconds; then the gas in the sealed chamber is sucked out, so that the pressure in the sealed chamber is decreased from 100 atmospheres to 10 atmospheres in 6 seconds; after the foregoing pressurization and depressurization operation is repeated for 10 times, high-pressure argon is injected into the sealed chamber, so that the pressure in the sealed chamber is increased from normal atmospheric pressure to 100 atmospheres in 30 seconds, and then kept for 10 minutes; then the pressure is decreased to 1 atmosphere in 10 seconds; after the casting is solidified and cooled, the mold shell is taken out.

[0106] Example 6

[0107] This example refers to the method of Example 1, and the only difference is that step (3) is different.

[0108] Step (3) of this example is: high-pressure argon is injected into the sealed chamber, so that the pressure in the sealed chamber is increased from normal atmospheric pressure to 120 atmospheres in 30 seconds; then the gas in the sealed chamber is sucked out, so that the pressure in the sealed chamber is decreased from 120 atmospheres to 1 atmosphere in 7 seconds; after the foregoing pressurization and depressurization operation is repeated for 10 times, high-pressure argon is injected into the sealed chamber, so that the pressure in the sealed chamber is increased from normal atmospheric pressure to 120 atmospheres in 30 seconds, and then kept for 10 minutes; then the pressure is decreased to 1 atmosphere in 10 seconds; after the casting is solidified and cooled, the mold shell is taken out.

[0109] Example 7

[0110] This example refers to the method of Example 1, and the only difference is that the wall thickness of the casting is <10 mm, and the combined fat oil is used as the cooling medium.

[0111] Example 8

[0112] This example refers to the method of Example 1, and the only difference is that step (1) is different.

[0113] Step (1) of this example is: the existing process is used to smelt ZM5 alloy and to bake the mold shell; then the obtained ZM5 alloy liquid is poured into the mold shell, and the pouring temperature of the ZM5 alloy is 740°C, and the temperature of the mold shell is 350°C.

[0114] Comparative Example 1

[0115] Comparative Example 1 refers to the method of Example 1, and the only difference is that step (3) is different.

[0116] Step (3) of Comparative Example 1 is: high-pressure argon is injected into the sealed chamber, so that the pressure in the sealed chamber is increased from normal atmospheric pressure to 100 atmospheres in 30 seconds, and then kept for 10 minutes; then the pressure is decreased to 1 atmosphere in 10 seconds; after the casting is solidified and cooled, the mold shell is taken out.

[0117] Comparative Example 2

[0118] Comparative Example 2 refers to the method of Example 1, with the difference that step (3) is different.

[0119] Step (3) of Comparative Example 2 is: injecting argon protective gas into the sealed chamber to make the pressure in the sealed chamber normal atmospheric pressure, and taking out the mold shell after the casting is solidified and cooled.

[0120] Experimental Example 1

[0121] In order to compare and illustrate the influence of the solidification methods of different examples and comparative examples on the compactness, porosity, grain size, etc. of the alloy structure, the structures of the castings after heat treatment obtained by different examples and comparative examples are characterized, and the test results are shown in Table 1 (wherein the porosity is evaluated according to HB7780-2005).

[0122] Table 1 Test results of structures of different castings

[0123]

[0124]

[0125] From the above table, it can be seen that the method for solidifying the magnesium alloy of the present application uses the process of rapid pressurization and depressurization during the solidification of the metal, so that the volume of the magnesium alloy continuously shrinks and expands, and the volume continuously changes, which is equivalent to the flow of the magnesium alloy liquid. Under the condition of large pressure change, the dendrites formed during the solidification process are continuously scoured and broken, and the grains become smaller. After the dendrites are broken, the feeding path is smoother, and the structure of the obtained casting is more compact, and the porosity is reduced or even without porosity.

[0126] Experimental Example 2

[0127] In order to further compare and illustrate the influence of the solidification methods of different examples and comparative examples on the properties of the alloy, the mechanical properties of the castings after heat treatment obtained by different examples and comparative examples are characterized, and the test results are shown in Table 2.

[0128] Table 2 Test results of mechanical properties of different castings

[0129]

[0130]

[0131] From the above table, it can be seen that the performance of the alloy casting obtained by the method for solidifying the magnesium alloy of the present application is significantly improved.

[0132] It should be noted that the above embodiments are only used to illustrate the technical solutions of the present application, and are not intended to limit the present application; although the present application has been described in detail with reference to the above embodiments, those skilled in the art should understand that the technical solutions recorded in the above embodiments can be modified, or some or all of the technical features can be replaced by equivalents; and these modifications or replacements do not make the essence of the corresponding technical solutions deviate from the scope of the technical solutions of the embodiments of the present application.

Claims

1. A method for solidifying magnesium alloys by investment casting, characterized in that, Includes the following steps: (a) The mold shell filled with molten magnesium alloy is placed in a sealed chamber containing a cooling medium, and the mold shell riser is exposed to the cooling medium. (b) Adjust the pressure inside the sealed cavity so that the magnesium alloy inside the mold shell can solidify under varying pressure; The method for regulating the pressure inside the sealed cavity includes: (b1) Increase the pressure inside the sealed chamber from normal atmospheric pressure to 80-100 atmospheres; (b2) Then depressurize the pressure in the sealed chamber from 80-100 atmospheres to 1-2 atmospheres; Repeat (b1) and (b2) at least once; In step (b1), the pressure inside the sealed chamber is increased from normal atmospheric pressure to 80-100 atmospheres within 20-40 seconds.

2. The method for solidification of magnesium alloy by investment casting according to claim 1, characterized in that, After repeating (b1) and (b2) at least once, pressurize the sealed chamber to 80-100 atmospheres and hold for 5-10 minutes.

3. The method for solidification of magnesium alloy by investment casting according to claim 1, characterized in that, In step (b2), the pressure inside the sealed chamber is reduced from 80 to 100 atmospheres to 1 to 2 atmospheres within 5 to 10 seconds.

4. The method for solidification of magnesium alloy by investment casting according to claim 1, characterized in that, The magnesium alloy includes ZM5; During the casting process, the casting temperature of the magnesium alloy is 750~755℃, and the temperature of the mold shell is 360~365℃. And / or, the cooling medium includes quenching oil and / or synthetic oil.

5. The method for solidification of magnesium alloy by investment casting according to claim 1, characterized in that, The sealed chamber is formed by the fastening of a tank body and a sealing cap; the side wall of the tank body is provided with a gas inlet, and the sealing cap is provided with a gas outlet.

6. The method for solidification of magnesium alloy by investment casting according to claim 5, characterized in that, The gas inlet is connected to a positive pressure source, and the gas outlet is connected to a negative pressure source. A first solenoid valve is provided between the gas inlet and the positive pressure source; a second solenoid valve is provided between the gas outlet and the negative pressure source.

7. A method for investment casting of magnesium alloys, characterized in that, The method for solidifying magnesium alloys by investment casting as described in any one of claims 1 to 6.

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