Apparatus and method for magnetic field assisted lost foam molding of magnesium-aluminum bimetallic castings

Abstract

The application belongs to the technical field of bimetal castings, and discloses a device and method for magnetic field assisted lost foam casting of magnesium-aluminum bimetal castings. The device comprises a sand box, a cast foam pattern, a solid insert, a steady magnetic field coil, a rotating magnetic field coil and an alternating current power supply. The sand box is filled with dry sand, the cast foam pattern is arranged in the dry sand, the solid insert is embedded in the cast foam pattern, and the opposite ends of the solid insert are connected to the alternating current power supply. The steady magnetic field coil is sleeved outside the cast foam pattern, and the rotating magnetic field coil is sleeved outside the periphery of the steady magnetic field coil. The rotating magnetic field coil can produce electromagnetic stirring in the melt. The electromagnetic stirring can make the melt flow strongly, promote the migration and diffusion of high melting point precipitated phases in the melt, and thus improve the uniformity of the solidification structure of the magnesium-aluminum bimetal interface.

Description

TECHNICAL FIELD

[0001] The present application belongs to the technical field related to bimetallic castings, and more particularly, to an equipment and method for magnetic field assisted lost foam casting of magnesium-aluminum bimetallic castings. BACKGROUND

[0002] With the rapid development of modern industry, the fields of automobiles, weapons and equipment, and aerospace have put forward higher and higher requirements for the lightweight, structural integration and comprehensive performance of materials, and the use of single materials has been increasingly difficult to meet the increasingly high requirements for the comprehensive performance of parts. Bimetallic materials are a new type of composite material prepared by using composite forming methods to produce metallurgical bonding between two different metals at the interface. In bimetallic materials, each metal can maintain independent performance, and can also realize synchronous improvement of strength, toughness, friction performance, heat resistance, etc. as a whole. At present, bimetallic materials, with their characteristics of excellent complementary performance of different metals, can further improve the performance of parts compared with single metals, and have been applied in the fields of mechanical engineering, automobiles, ships, and aerospace.

[0003] The main preparation methods of bimetallic materials are rolling composite, welding composite, and casting composite. Rolling composite can quickly and in large quantities prepare laminar or rod-shaped bimetallic blanks. The bimetallic material prepared by welding method has excellent rigidity and connection performance. However, it is difficult to prepare bimetallic parts with complex profile and large area contact section by these two methods. Casting combines the characteristics of casting process suitable for preparing complex shaped parts, and thus has more advantages in low-cost preparation of complex shaped bimetallic parts. However, there are still some problems in the preparation of magnesium / aluminum bimetallic castings by solid-liquid composite casting technology.

[0004] There is a dense oxide film on the surface of the solid insert, which will hinder the metallurgical bonding of the magnesium / aluminum bimetallic interface, and the continuous oxide film is easy to remain in the composite interface during the composite process to form inclusion defects. At the same time, due to the large heat input during the composite casting process, the surface of the solid insert melts more, and a large amount of brittle and hard Al12Mg17, Al3Mg2 intermetallic compounds are generated at the interface during the composite process. At the same time, due to the cooling effect of the insert, a temperature gradient perpendicular to the surface of the solid insert will be formed in the interface area during solidification, which will lead to the formation of coarse solidification structure of these intermetallic compounds. These will have a very adverse effect on the performance of the bimetallic material bonding interface. The existence of these problems greatly restricts the further development and application of the solid-liquid composite casting process.

[0005] In view of the problems of easy oxidation inclusion, coarse solidification structure and low bonding strength at the magnesium / aluminum bimetal interface in the solid-liquid composite casting process, relevant researches are also carried out. At present, mechanical vibration and ultrasonic vibration are mostly used for regulating the interface structure and performance of magnesium / aluminum bimetal by external physical field. The process of mechanical vibration is simple and low in cost, but it cannot directly act on the interface, and its improvement effect on the solidification structure is limited. Ultrasonic vibration can directly act on the bimetal interface, and thus has good regulating effect, but matching design is needed between the solid-state insert and the ultrasonic transducer, and the process is complex and high in cost. SUMMARY

[0006] In view of the above defects or improvement needs of the prior art, the present application provides a device and method for magnetic field assisted lost foam casting of magnesium / aluminum bimetal castings, which aims to provide an effective, easy-to-operate and low-cost device and method for regulating the interface structure and performance of magnesium / aluminum bimetal.

[0007] To achieve the above-mentioned purpose, according to one aspect of the present application, the present application provides a device for magnetic field assisted lost foam casting of magnesium / aluminum bimetal castings, which comprises a sand box, a casting foam pattern, a solid-state insert, a steady magnetic field coil, a rotating magnetic field coil and an alternating current power supply. The sand box is filled with dry sand, the casting foam pattern is arranged in the dry sand, the solid-state insert is embedded in the casting foam pattern, and its opposite ends are connected to the alternating current power supply; the steady magnetic field coil is sleeved outside the casting foam pattern, and the rotating magnetic field coil is sleeved outside the periphery of the steady magnetic field coil.

[0008] Further, the device further comprises a pouring system foam pattern and a sprue cup, and the pouring system foam pattern is arranged in the dry sand and connected to the sprue cup.

[0009] Further, the device further comprises a three-dimensional vibration table, and the sand box is arranged on the three-dimensional vibration table.

[0010] Further, the device comprises a vacuum pipe connected to the sand box to perform vacuumizing treatment on the sand box.

[0011] Further, the device comprises a film for covering the opening of the sand box.

[0012] Further, the height of the solid-state insert protruding from the casting foam pattern is 5mm-20mm.

[0013] The present application also provides a use method of the device for magnetic field assisted lost foam casting of magnesium / aluminum bimetal castings as described above. The sand box is vacuumized by the vacuum pipe to make the vacuum degree in the sand box 0.015Mpa-0.04Mpa.

[0014] Further, the alternating current applied to the solid-state inlay by the alternating power supply has a frequency of 50Hz-200Hz and a current value of 50A-150A.

[0015] Further, the steady magnetic field generated by the steady magnetic field coil after starting has a value of 0.4T-1.5T.

[0016] Further, the excitation current of the rotating magnetic field coil is 80A-400A, the excitation field frequency is 20Hz-150Hz, and the positive and negative reversal switching time is 0s-20s.

[0017] Overall, compared with the prior art, the equipment and method for magnetic field assisted lost mold casting of magnesium-aluminum bimetal castings provided by the present application mainly have the following advantages

[0018] Advantages:

[0019] 1. The rotating magnetic field coil of the present application can generate electromagnetic stirring in the melt, which can cause the melt to flow strongly and promote the migration and diffusion of high-melting-point precipitated phases in the melt, thereby improving the uniformity of the magnesium-aluminum bimetal interface solidification structure.

[0020] 2. The present application is based on the method of warm constant magnetic field + rotating magnetic field + alternating current to regulate the magnesium-aluminum bimetal interface solidification structure by magnetic field, and through the synergistic effect of steady magnetic field and alternating current to produce vibration, combined with the stirring of the rotating magnetic field on the melt, the effect of the composite external field is realized, which can better regulate the structure and performance of the magnesium-aluminum bimetal interface. Compared with the prior art, the process is simple, the regulation effect on the solidification structure of the bimetal interface is good, and the balance between regulation effect and process cost can be realized.

[0021] 3. The present application passes alternating current through the two ends of the solid-state inlay, and generates a steady magnetic field outside the inlay through the steady magnetic field coil. During the compounding process, the solid-state inlay in the warm constant magnetic field is subjected to Lorentz force and vibrates, and the vibration can directly act on the bimetal interface, so that the continuous oxide film on the surface of the inlay gradually breaks and dissolves during the compounding process, avoiding the residual of the oxide film in the interface region during the solidification process. At the same time, due to the direct action of vibration on the bimetal interface region, the dendrites formed in the initial stage of solidification of the interface region are broken, a large number of free nuclei are generated, the nucleation rate of the solidification process is improved, and the solidification structure of the bimetal interface is refined.

[0022] 4. Lost foam casting uses loose sand for molding, and the sand mold is compacted by vacuum suction, so the installation of the magnetic field generating coil is more convenient, which can be directly placed in the sand box, avoiding the shielding effect of the sand box on the magnetic field. BRIEF DESCRIPTION OF DRAWINGS

[0023] Figure 1 is a schematic view of a device for magnetic field assisted lost foam casting of magnesium-aluminum bimetallic castings provided by the present application.

[0024] In all the drawings, the same reference signs are used to denote the same elements or structures, wherein: 1 - composite model, 101 - gating system foam pattern, 102 - cast foam pattern, 103 - solid insert, 104 - sprue cup, 105 - metal liquid pouring position, 2 - magnetic field generating device, 201 - steady magnetic field coil, 202 - rotating magnetic field coil, 203 - wire, 204 - alternating current power supply, 3 - sand box system, 301 - sand box, 302 - dry sand, 303 - three-dimensional vibration table, 304 - film, 305 - vacuum pipe. DETAILED DESCRIPTION

[0025] In order to make the objectives, technical solutions and advantages of the present application clearer, the present application is further described in detail below with reference to the drawings and examples. It should be understood that the specific examples described herein are only used to explain the present application and do not limit the present application. In addition, the technical features involved in each embodiment of the present application described below can be combined with each other as long as they do not conflict with each other.

[0026] Please refer to Figure 1 The present application provides a device for magnetic field assisted lost foam casting of magnesium-aluminum bimetallic castings, which comprises a composite model 1, a magnetic field generating device 2 and a sand box system 3, wherein the composite model 1 and the magnetic field generating device 2 are respectively installed on the sand box system 3.

[0027] The composite model 1 comprises a gating system foam pattern 101, a cast foam pattern 102, a solid insert 103 and a sprue cup 104, wherein the gating system foam pattern 101 and the cast foam pattern 102 are connected and both are arranged in the dry sand 302 of the sand box system 3. The sprue cup 104 is connected to the gating system foam pattern 101 and protrudes from the sand box system 3. The solid insert 103 is embedded in the sand box system 3 and is connected to the magnetic field generating device 2. The sprue cup 104 is provided with a metal pouring position, and the metal liquid is poured into the composite model 1 from the metal pouring position.

[0028] The sand box system 3 comprises a sand box 301, dry sand 302, a three-dimensional vibration platform, a film 304 and a vacuum pipe 305, wherein the dry sand 302 is arranged in the sand box 301, and the sand box is arranged on the three-dimensional vibration platform. The vacuum pipe 305 is connected to the sand box to perform vacuumization on the sand box. The film 304 covers the sand box during work to close the opening of the sand box.

[0029] The pouring system foam pattern 101 and the casting foam pattern 102 are both set in the dry sand 302 in the sand box.

[0030] The magnetic field generating device 2 includes a constant magnetic field coil 201, a rotating magnetic field coil 202, a wire 203, and an AC power supply 204. The constant magnetic field coil 201 is mounted outside the casting foam pattern 102, and the rotating magnetic field coil 202 is mounted outside the constant magnetic field coil 201. The AC power supply 204 is located outside the sand box, and both ends of the solid inlay 103 are connected to the AC power supply 204 via the wires 203.

[0031] According to the size of the casting, the distance between the constant magnetic field coil 201 and the composite model 1 needs to be adjusted to not less than 2cm to 10cm. The height of the solid inlay 103 extending out of the casting model is 5mm to 20mm.

[0032] The present invention also provides a method for using the magnetic field-assisted lost foam casting device for magnesium-aluminum bimetallic castings, the method mainly comprising the following steps:

[0033] (1) Place the composite model 1 in a sand box, and place the constant magnetic field coil 201 and the rotating magnetic field coil 202 in sequence near the composite model 1. Connect the top and bottom of the solid inlay 103 to the AC power supply 204 through the wire 203.

[0034] (2) Then, the sand is vibrated and filled into the sand box. After the sand box is filled, a film 304 is covered on the top, and the sand box is vacuumed through the vacuum tube 305 to compact the dry sand 302 in the sand box. Then, the pouring cup 104 is installed on the top of the pouring system of the composite model 1 to complete the molding process.

[0035] (3) Turn on the AC power supply 204 of the magnetic field generating device 2 to apply AC current to the solid inlay 103, and simultaneously start the constant magnetic field coil 201.

[0036] (4) Pour the molten metal from the pouring cup 104 . After the pouring is completed, start the rotating magnetic field coil 202 in the magnetic field generating device 2 .

[0037] (5) After the molten metal in the sand box solidifies, the magnetic field generating device 2 is turned off and cleaned, the composite model 1 is removed, and finally a bimetallic casting is obtained.

[0038] The sand box is vacuumized by the vacuum pipe 305, so that the vacuum degree in the sand box is 0.015-0.04 MPa. The solid insert 103 is applied with an alternating current with a frequency of 50-200 Hz and a current value of 50-150 A by the alternating current power supply 204. The steady magnetic field generated by the steady magnetic field coil 201 is 0.4-1.5 T. The exciting current of the rotating magnetic field coil 202 is 80-400 A, the exciting field frequency is 20-150 Hz, and the positive and negative rotation switching time is 0-20 s.

[0039] The application is further described in detail below by way of several examples.

[0040] Example 1

[0041] The cast foam pattern is a cube with a size of 35x35x100 mm, and the solid insert is a cylinder with a diameter of 10 mm and a height of 110 mm. The material of the solid insert is A356 aluminum alloy, the poured metal liquid is AZ91D magnesium alloy, and the height of the solid insert protruding from the cast foam pattern in the composite model is 5 mm.

[0042] In use, the composite model is first placed in the sand box, and the steady magnetic field coil and the rotating magnetic field coil are sequentially placed near the composite model. The steady magnetic field coil is located inside the rotating magnetic field coil, and the distance between the steady magnetic field coil and the composite model is 2 cm. The wires are connected to the top and bottom of the solid insert and the alternating current power supply, respectively. The sand box is filled with sand by vibration until it is filled. After the sand box is filled, a thin film is covered on the top, and the sand box is vacuumized by the vacuum pipe to a vacuum degree of 0.015 MPa. Then, the sprue cup is installed on the top of the pouring system foam pattern of the composite model, and the molding process is completed.

[0043] Then, the alternating current power supply in the magnetic field generating device is turned on to apply an alternating current with a frequency of 50 Hz and a current value of 50 A to the solid insert, and the steady magnetic field coil is started to generate a steady magnetic field of 0.4 T.

[0044] The AZ91D magnesium alloy liquid is poured from the sprue cup at a pouring temperature of 750 ℃. After pouring is completed, the rotating magnetic field coil in the magnetic field generating device is started, the exciting current of the coil is 80 A, the exciting field frequency is 20 Hz, and the positive and negative rotation switching time is 20 s.

[0045] Implementation effect: The magnesium / aluminum bimetallic interface Al-Mg intermetallic compound is refined by more than 40%, the eutectic structure is refined by more than 30%, and the bimetallic interface bonding strength is improved by more than 35%.

[0046] Example 2

[0047] The casting foam model is a cube with a size of 35*35*100mm, and the solid-state insert is a cylinder with a diameter of 10mm and a height of 110mm. The material of the solid-state insert is A356 aluminum alloy, and the poured metal liquid is AZ91D magnesium alloy. The height of the solid-state insert protruding from the casting foam model in the composite model is 5mm.

[0048] During use, the composite model is first placed in the sand box, and the steady magnetic field coil and the rotating magnetic field coil are sequentially placed near the composite model. The steady magnetic field coil is located inside the rotating magnetic field coil, and the distance between the steady magnetic field coil and the composite model is 2cm. The top and bottom of the solid-state insert are respectively connected to the alternating current power source through wires. Vibration sand filling is performed until the sand box is filled. After the sand box is filled, a layer of plastic film is covered on the top, and the sand box is vacuumized through the vacuum pipe. The vacuum degree is 0.03MPa. Then, the sprue cup is installed on the top of the gating system foam model of the composite model, and the molding process is completed.

[0049] Then, the alternating current power source in the magnetic field generating device is turned on, and an alternating current with a frequency of 120Hz and a current value of 100A is applied to the solid-state insert. At the same time, the steady magnetic field coil is started to generate a steady horizontal magnetic field of 0.8T.

[0050] The AZ91D magnesium alloy liquid is poured from the sprue cup, and the pouring temperature is 720℃. After pouring is completed, the rotating magnetic field coil in the magnetic field generating device is started. The excitation current of the coil is 160A, the excitation field frequency is 80Hz, and the forward and reverse switching time is 10s.

[0051] Implementation effect: The Al-Mg intermetallic compound at the magnesium / aluminum bimetal interface is refined by more than 50%, the eutectic structure is refined by more than 45%, and the bimetal interface bonding strength is improved by more than 60%.

[0052] Example 3

[0053] The casting foam model is a cube with a size of 35*35*100mm, and the solid-state insert is a cylinder with a diameter of 10mm and a height of 110mm. The material of the solid-state insert is A356 aluminum alloy, and the poured metal liquid is AZ91D magnesium alloy. The height of the solid-state insert protruding from the casting foam model in the composite model is 5mm.

[0054] During use, the composite model is first placed in the sand box, and the steady magnetic field coil and the rotating magnetic field coil are sequentially placed near the composite model. The steady magnetic field coil is located inside the rotating magnetic field coil, and the distance between the steady magnetic field coil and the composite model is 2cm. The top and bottom of the solid-state insert are respectively connected to the alternating current power source through wires. Vibration sand filling is performed until the sand box is filled. After the sand box is filled, a layer of plastic film is covered on the top, and the sand box is vacuumized through the vacuum pipe. The vacuum degree is 0.03MPa. Then, the sprue cup is installed on the top of the gating system foam model of the composite model, and the molding process is completed.

[0055] Then, the AC power supply in the magnetic field generating device is turned on, AC current with a frequency of 150 Hz and a current value of 140 A is applied to the solid-state inlay, and at the same time, the steady magnetic field coil is started to generate a steady transverse magnetic field of 1.3 T.

[0056] The AZ91D magnesium alloy liquid is poured from the pouring cup, the pouring temperature is 700 DEG C, after pouring, the rotating magnetic field coil in the magnetic field generating device is started, the excitation current of the coil is 350 A, the excitation field frequency is 120 Hz, and the forward and reverse switching time is 15 s.

[0057] The implementation effect is that the Al-Mg intermetallic compound of the magnesium / aluminum bimetal interface is refined by more than 70%, the eutectic structure is refined by more than 60%, and the bimetal interface bonding strength is improved by more than 85%.

[0058] Those skilled in the art can easily understand that the above description is only the preferred embodiment of the present application, and is not intended to limit the present application, and any modification, equivalent replacement and improvement made within the spirit and principle of the present application shall be included in the protection scope of the present application.

Claims

1. A magnetic field assisted lost foam casting device for magnesium-aluminum bimetallic castings, characterized by: The equipment includes a sand box, a casting foam pattern, a solid inlay, a steady magnetic field coil, a rotating magnetic field coil and an AC power supply. The sand box is filled with dry sand, the casting foam pattern is arranged in the dry sand, the solid inlay is embedded in the casting foam pattern, and its opposite ends are connected to the AC power supply; the steady magnetic field coil is sleeved outside the casting foam pattern, and the rotating magnetic field coil is sleeved on the outer periphery of the steady magnetic field coil.

2. The magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 1, characterized in that: The equipment also includes a pouring system foam pattern and a pouring cup. The pouring system foam pattern is arranged in the dry sand and connected to the pouring cup.

3. The magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 1, characterized in that: The equipment further comprises a three-dimensional vibration table, and the sand box is arranged on the three-dimensional vibration table.

4. The magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 3, characterized in that: The device includes a vacuum pipe connected to the sand box to vacuum the sand box.

5. The magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 3, characterized in that: The apparatus includes a film for covering an opening of the flask.

6. The magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 1, characterized in that: The height of the solid inlay extending out of the foam pattern portion of the casting is 5 mm to 20 mm.

7. A method for using the magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to any one of claims 1 to 6, characterized in that: The sand box is vacuumed through a vacuum pipe so that the vacuum degree in the sand box is 0.015Mpa~0.04Mpa.

8. The method for using the magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 7, characterized in that: The AC current applied to the solid inlay by the AC power supply has a frequency of 50 Hz to 200 Hz and a current value of 50 A to 150 A.

9. The method for using the magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 7, characterized in that: The steady magnetic field generated by the steady magnetic field coil after startup is 0.4T~1.5T.

10. The method for using the magnetic field assisted lost foam casting equipment for magnesium-aluminum bimetallic castings according to claim 7, characterized in that: The excitation current of the rotating magnetic field coil is 80A to 400A, the excitation field frequency is 20Hz to 150Hz, and the forward and reverse switching time is 0s to 20s.

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