Method for preparing aluminum-magnesium bimetal by adopting pulse electromagnetic composite field and bimetal product

Abstract

The invention belongs to the technical field of bimetal part manufacturing, and particularly relates to a method for preparing aluminum-magnesium bimetal through a pulse electromagnetic composite field and a bimetal product, and the method comprises the following steps that a casting foam model is prepared according to the preset form of a workpiece, and a solid aluminum inlay and the casting foam model are assembled to form a composite model. And embedding the composite model into a sand box. During pouring, a pulsed magnetic field and a pulsed electric field are applied to the composite model in a vacuum environment. And cooling to obtain the aluminum-magnesium bimetal product. The invention further discloses the aluminum-magnesium bimetallic product prepared through the method. The method is suitable for manufacturing aluminum-magnesium bimetal castings with complex shapes, the process is simple, the bimetal interface is easy to control, the bimetal bonding performance is good, the alloy strengthening effect is good, grain refinement is effectively achieved, interface defects are overcome, and the method is suitable for producing various related parts in the fields of automobiles, spaceflight and the like.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of bimetallic part manufacturing, and particularly relates to a method for preparing aluminum-magnesium bimetal by using a pulse electromagnetic composite field and a bimetal product. BACKGROUND

[0002] Magnesium and aluminum are important engineering light metals, each having its own advantages and disadvantages. Magnesium alloy is light in quality, has good damping and heat conduction, but poor plasticity and poor corrosion resistance; aluminum alloy has good plasticity, good corrosion resistance and low cost, but the density is relatively large compared with magnesium alloy. If aluminum alloy and magnesium alloy are combined to prepare aluminum-magnesium bimetal, the advantages of the two materials can be combined, the strengths can be made up for the weaknesses, the performance requirements can be met, and the light weight requirements can be met, which has great application prospect in the fields of automobile, aviation, aerospace and the like.

[0003] However, it is found through research that during the combination of aluminum-magnesium bimetal, brittle intermetallic compounds such as Al3Mg2, Al 12 Mg 17 are formed at the interface; and due to the oxide film on the surface of the aluminum alloy, obvious oxidation inclusion defects are generated after the combination of the aluminum alloy and the magnesium alloy; meanwhile, it is found through experiments that there are problems such as coarse grains, preferred orientation and stress concentration at the interface of the aluminum-magnesium bimetal. These problems result in poor performance of the bimetal, thereby greatly restricting the development and application of the bimetal. Therefore, how to regulate and improve the interface structure through effective measures is a key problem that needs to be solved to improve the performance of aluminum-magnesium bimetal parts.

[0004] In view of the above problems of aluminum-magnesium bimetal, the current solutions include removing the oxide film on the surface of the insert, adding an intermediate layer, heat modification of the insert, constructing a three-dimensional structure on the surface of the insert, heat treatment, alloying and applying an external field.

[0005] Among them, applying an external field is a bimetal strengthening method that does not need pre-treatment to regulate the interface structure, and it can improve the matrix structure while strengthening the interface structure, realize the improvement of the overall performance of the bimetal, and has great potential in the regulation of the interface structure and performance of the bimetal. At present, the external fields commonly applied in aluminum-magnesium bimetal include mechanical vibration field and ultrasonic field.

[0006] Among them, the principle of mechanical vibration field is to disperse and refine the Mg2Si strengthening phase in the interface by mechanical vibration; its advantages lie in simple equipment, low cost and no need for special treatment process, and after mechanical vibration strengthening, the shear strength of the bimetal is also significantly improved; however, mechanical vibration is a three-dimensional vibration of the whole sand box, and cannot directly act on the interface, so the dispersion and refinement effect of Mg2Si is limited, and the influence on other structures in the interface is also small.

[0007] The ultrasonic field causes the vibration of the aluminum insert and the cavitation effect of the metal liquid by using ultrasonic waves, so as to realize the refinement of the crystal grains; the ultrasonic field can directly act on the interface, disperse the agglomerated strengthening phase in the interface, refine the entire interface structure, break the dendrites and the oxide film; however, the ultrasonic field has special requirements for the shape, size and volume of the alloy, and has limitations in the preparation of large complex bimetallic parts, and the process is complex and the cost is high.

[0008] Although the above two external fields can strengthen the aluminum-magnesium bimetal to a certain extent, they still face some problems, which cannot simply, low-cost and efficiently realize the strengthening of the complex aluminum-magnesium bimetal part.

[0009] Therefore, it is urgent to adopt a method for preparing aluminum-magnesium bimetal by using a pulse electromagnetic composite field and a bimetal product to solve the above problems. SUMMARY

[0010] The purpose of the present application is to provide a method for preparing aluminum-magnesium bimetal by using a pulse electromagnetic composite field and a bimetal product to solve the above problems.

[0011] To achieve the above purpose, the present application provides the following solutions:

[0012] The method for preparing aluminum-magnesium bimetal by using a pulse electromagnetic composite field comprises the following steps:

[0013] A casting foam model is prepared according to the preset shape of the part, and a solid aluminum insert is assembled with the casting foam model to form a composite model.

[0014] The composite model is buried in a sand box.

[0015] When pouring, a pulse magnetic field and a pulse electric field are applied to the composite model in a vacuum environment.

[0016] After cooling, an aluminum-magnesium bimetal part is obtained.

[0017] Optionally, the preparation of the composite model comprises the following steps:

[0018] The casting foam model comprises a pouring system foam pattern and a magnesium melt filling part foam pattern.

[0019] The magnesium melt filling part foam pattern is pasted and fixed with the solid aluminum insert, and the pouring system foam pattern and the magnesium melt filling part foam pattern are pasted and fixed to form the composite model.

[0020] The composite model is brushed with paint.

[0021] Optionally, the step of brushing the composite model with paint comprises:

[0022] The lost foam coating powder is mixed with water in a predetermined volume ratio to form a mixture, and the mixture is stirred uniformly.

[0023] The mixture is uniformly coated on all outer surfaces of the composite model, and the composite model is dried.

[0024] The above steps are repeated to apply several layers of coating.

[0025] The volume ratio of the lost foam coating powder to water is 6-42.

[0026] The composite model is dried in a drying oven with a temperature of 50-60°C.

[0027] After the mixture is uniformly coated on all outer surfaces of the composite model, it is placed in a drying oven for drying, and finally the dried composite model is coated with another layer of the mixture and dried again.

[0028] Optionally, the step of embedding the composite model in the sand box comprises:

[0029] Dry sand is placed at the bottom of the sand box.

[0030] The composite model is placed in the sand box and above the dry sand at the bottom.

[0031] The generating end of the pulsed magnetic field and the generating end of the pulsed electric field are arranged in the sand box.

[0032] The dry sand is filled to fix the composite model, the generating end of the pulsed magnetic field, and the generating end of the pulsed electric field.

[0033] After the filling is completed, a pouring space is formed by the mutual isolation of the composite model and the dry sand, and the pouring opening of the pouring space is located on the surface of the sand box.

[0034] Optionally, the step of filling the dry sand to fix the composite model, the generating end of the pulsed magnetic field, and the generating end of the pulsed electric field comprises:

[0035] The sand box is placed on a vibrating table, and when the dry sand is filled, the vibrating table vibrates the sand box to make the dry sand fill densely.

[0036] The vibration frequency of the vibrating table is 50-150 Hz, and the amplitude is 0.6-1.2 mm.

[0037] Optionally, the step of forming the vacuum environment comprises:

[0038] After the dry sand is filled, a plastic film is covered on the top of the sand box, and the bottom of the sand box is communicated with a vacuum pump assembly, which draws vacuum in the sand box through the bottom of the sand box.

[0039] The vacuum degree in the sand box reaches 0.01-0.05 MPa.

[0040] Optionally, the pulse magnetic field generating end comprises an excitation coil arranged around the composite model, the excitation coil is embedded in the dry sand, the excitation coil is electrically connected with a pulse magnetic field generator, and the pulse magnetic field generator is located outside the sand box.

[0041] The inner diameter of the excitation coil is greater than the length and width of the composite model.

[0042] The inner diameter of the excitation coil is 1.2-1.5 times of the longest dimension of the composite model.

[0043] The height of the excitation coil is greater than the height of the magnesium melt filling part foam model, but not higher than the height of the sprue of the gating system foam model, the height of the excitation coil is 1.1-1.3 times of the magnesium melt filling part foam model, and the magnesium melt filling part foam model is located in the middle of the excitation coil.

[0044] The duty cycle, frequency, and forward-reverse switching time of the pulse magnetic field are 20%-40%, 20-40 Hz, and 0-20 s, respectively.

[0045] Optionally, the pulse electric field generating end comprises a pulse electric field generator, and two poles of the pulse electric field generator are connected with two ends of the solid aluminum insert through wires.

[0046] The voltage, waveform, frequency, peak value, and forward-reverse switching time of the pulse electric field are 100-400 V, a pulse electric field sine wave, 50-200 Hz, 50-150 A, and 0-20 s, respectively.

[0047] Optionally, during pouring, a sprue cup is placed on the top of the pouring gate, the sprue cup is communicated with the pouring gate, and the magnesium melt pouring liquid is poured through the sprue cup.

[0048] The temperature of the magnesium melt pouring liquid is 700-750℃.

[0049] The application time of the pulse magnetic field and the pulse electric field is from when the magnesium melt pouring liquid fills the mold to when the metal temperature decreases below the solidus.

[0050] An aluminum-magnesium bimetallic product is prepared by using the above-mentioned method for preparing an aluminum-magnesium bimetallic product by using a pulse electromagnetic composite field.

[0051] Compared with the prior art, the application has the following advantages and technical effects:

[0052] The aluminum-magnesium bimetal casting method provided by the application is suitable for manufacturing aluminum-magnesium bimetal castings with complex shapes, has simple process, easy control of the bimetal interface, good bimetal bonding performance, good alloy strengthening effect, effectively realizes grain refinement, solves interface defects, and is suitable for producing various related parts in the fields of automobiles and aerospace.

[0053] (1) The external pulsed electromagnetic field and the internal pulsed current can generate explosive instantaneous current, thereby playing the roles of stirring and oscillation, so that the Al / Mg eutectic layer thickness increases and the interface morphology changes from flat to irregular after the pulsed electromagnetic composite field is applied; under the action of oscillation and stirring force, the Mg2Si particles in the Al3Mg2 and Al 12 Mg 17 layers can be effectively refined and homogenized, so that the Mg2Si particles are uniformly distributed on the interface in smaller sizes, thereby inhibiting the segregation of Mg2Si and improving the uniformity of the interface; and the vibration of the aluminum insert and the scouring action of the molten metal are beneficial to destroying the oxide film and breaking the dendrites, thereby reducing the oxide inclusion defects and dendrites;

[0054] (2) After the composite pulsed electromagnetic field is applied, the more uniform microstructure and the more uniformly distributed magnesium-silicon particles prolong the crack propagation path, thereby improving the Al / Mg interface shear strength;

[0055] (3) The electromagnetic field can make the melt generate forced convection, has the effects of breaking dendrites, reducing temperature gradient and increasing element diffusion, thereby being expected to realize grain refinement, reduce stress concentration and homogenize composition, and has no special requirements for the shape and size of the part, perfectly combines the advantages of the mechanical vibration field and the ultrasonic field, avoids the shortcomings of the two, and is suitable for preparing complex aluminum / magnesium bimetal parts;

[0056] (4) The application is a kind of electromagnetic composite field, that is, the external pulsed electromagnetic field + solid-state insert pulsed current mode. Compared with the single electromagnetic field, the following two advantages are obtained. First, the aluminum insert generates self-resistance heat when electrified, which is equivalent to preheating the aluminum insert, which helps to reduce the temperature gradient and further reduce the stress concentration; second, although the electromagnetic field can cause the aluminum insert to vibrate, the vibration is relatively slight, and by passing current through the insert, it can make the insert vibrate more greatly under the alternating magnetic field, thereby helping to eliminate dendrites and increase the migration and dispersion of high-melting-point precipitates.

[0057] (5) The method can not only realize the strengthening of the interface, but also improve the performance of the matrix, realize the synchronous improvement of the interface and the matrix, and prepare high-quality aluminum-magnesium bimetal parts. BRIEF DESCRIPTION OF DRAWINGS

[0058] In order to more clearly illustrate the technical solutions in the embodiments of the present application or the prior art, the following will briefly introduce the drawings needed in the embodiments. Obviously, the drawings described below only illustrate some of the embodiments of the present application, and are not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0059] Figure 1 Flow chart of the method of the present application.

[0060] Figure 2 Structural diagram of the equipment of the present application.

[0061] Figure 3 、 Figure 4 Distribution comparison chart of Mg2Si in two regions of the magnesium-aluminum bimetal interface of casting body a of the present application.

[0062] Figure 5 、 Figure 6 Distribution comparison chart of Mg2Si in two regions of the magnesium-aluminum bimetal interface of casting body b of the present application.

[0063] Figure 7 、 Figure 8 Distribution comparison chart of Mg2Si in two regions of the magnesium-aluminum bimetal interface of casting body c of the present application.

[0064] Figure 9 Scanning electron microscope image of the aluminum-magnesium bimetal interface of casting body a of the present application.

[0065] Figure 10 Scanning electron microscope image of the aluminum-magnesium bimetal interface of casting body b of the present application.

[0066] Figure 11 Scanning electron microscope image of the aluminum-magnesium bimetal interface of casting body c of the present application.

[0067] 1, sprue cup; 2, foamed pattern of gating system; 3, excitation coil; 4, solid aluminum insert; 5, soldering point for connecting sample and wire; 6, dry sand; 7, pulse magnetic field generator; 8, pulse electric field generator; 9, foamed pattern filled with magnesium melt; 10, magnesium melt pouring liquid; 11, vibration table; 12, sand box; 13, plastic film. DETAILED DESCRIPTION

[0068] The technical solutions in the embodiments of the present application will be described clearly and completely below with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, and not all the embodiments. Based on the embodiments of the present application, all other embodiments obtained by a person of ordinary skill in the art without creative labor are within the scope of protection of the present application.

[0069] In order to make the above objectives, features and advantages of the present application more obvious and easy to understand, the present application will be further described in detail below with reference to the drawings and specific embodiments.

[0070] With reference to Figures 1 to 11 The present application discloses a method for preparing aluminum-magnesium bimetal by using pulse electromagnetic composite field, which comprises the following steps:

[0071] A cast foam model is prepared according to the preset shape of the product, and a solid aluminum insert 4 is assembled with the cast foam model to form a composite model.

[0072] The composite model is buried in a sand box 12.

[0073] During pouring, a pulse magnetic field and a pulse electric field are applied to the composite model under vacuum environment.

[0074] After cooling, an aluminum-magnesium bimetal product is obtained.

[0075] The aluminum-magnesium bimetal cast product prepared by the method provided by the present application is suitable for manufacturing aluminum-magnesium bimetal cast products with complex shape, has simple process, easy-to-control bimetal interface, good bimetal bonding performance, good alloy strengthening effect, effectively realizes refined dendrites, solves interface defects, and is suitable for producing various related parts in the fields of automobiles and aerospace.

[0076] By simultaneously applying pulsed magnetic fields, pulsed electric fields, and a vacuum environment during the casting process, the molten metal is subjected to reciprocating Lorentz forces through the pulsed magnetic field, promoting the flow of the molten metal. This leads to the breakage of intermetallic compounds and the refinement of dendrites, improving the interfacial structure of the aluminum-magnesium bimetallic compound and enhancing the casting performance. Compared to other magnetic field application methods, pulsed magnetic fields can release high-intensity magnetic fields (up to tens of Tesla) in extremely short times (microseconds to milliseconds). This characteristic allows for the generation of strong electromagnetic forces through intermittent pulses without continuous energy consumption, resulting in lower average power requirements and avoiding the long-term energy consumption problems of other traditional continuous magnetic fields. Compared to the traditional method of continuously applying a magnetic field to the entire molten metal, pulsed magnetic fields can concentrate the electromagnetic force on a specific area of ​​the ingot through coil design (such as axial or radial gradient coils), overcoming the disadvantages of energy dispersion and low utilization rate of traditional magnetic field application methods. After applying an electric field to the solid aluminum inlay 4, the atoms, driven by the electric field force, more easily overcome the interfacial barrier and interact with the atoms on the other side, forming a denser and more uniform interfacial bonding layer. Rapid atomic diffusion can improve the bonding strength and stability of bimetals and reduce interface defects. By organically combining the advantages of electric field strengthening and pulsed magnetic field strengthening, not only can the instantaneous high-energy impact of the pulsed magnetic field more effectively break the inlay oxide film and produce a more significant grain refinement effect, but when the solid aluminum inlay 4 is energized, it will also be subjected to Lorentz force due to being in the pulsed magnetic field environment, thereby generating vibration, which can further break the oxide structure and refine the dendrites.

[0077] In summary, the method for strengthening aluminum-magnesium bimetallic castings using a pulsed electromagnetic composite field provided by this invention involves the solid inlay in the magnetic field vibrating under the influence of the Lorentz force. This vibration directly acts on the bimetallic interface, causing the continuous oxide film on the inlay surface to gradually break down and dissolve during the composite process, preventing the oxide film from remaining in the interface region during solidification. Simultaneously, because the vibration directly acts on the bimetallic interface region, the dendrites formed in the early stages of solidification in the interface region break down, generating a large number of free crystal nuclei, increasing the nucleation rate during solidification, thereby refining the solidification structure of the bimetallic interface and improving the overall comprehensive performance of the casting.

[0078] As an optional implementation method, the preparation of the composite model includes the following steps:

[0079] The casting foam model includes foam pattern 2 for the gating system and foam pattern 9 for the magnesium melt filling part.

[0080] The magnesium melt filling part foam pattern 9 is glued and fixed to the solid aluminum insert 4, and the casting system foam pattern 2 and the magnesium melt filling part foam pattern 9 are glued and fixed to form a composite model.

[0081] Apply paint to the composite model.

[0082] As an optional embodiment, the step of brushing the coating on the composite model comprises:

[0083] The lost foam casting coating powder is mixed with water in a predetermined volume ratio to form a mixture, and the mixture is stirred uniformly.

[0084] The mixture is uniformly coated on all outer surfaces of the composite model, and the composite model is dried.

[0085] The above steps are repeated to apply several layers of coating.

[0086] The volume ratio of the lost foam casting coating powder to water is 6-42.

[0087] The composite model is dried in a drying oven with a temperature of 50-60°C.

[0088] After uniformly coating the mixture on all outer surfaces of the composite model, it is placed in the drying oven for drying, and finally the dried composite model is coated with another layer of mixture and dried again.

[0089] As an optional embodiment, the step of burying the composite model in the sand box 12 comprises:

[0090] Dry sand 6 is placed at the bottom of the sand box 12.

[0091] The composite model is placed in the sand box 12 and placed above the dry sand 6 at the bottom.

[0092] The generating end of the pulsed magnetic field and the generating end of the pulsed electric field are arranged in the sand box 12.

[0093] The dry sand 6 is filled to fix the composite model, the generating end of the pulsed magnetic field and the generating end of the pulsed electric field.

[0094] After filling, a pouring space is formed by the composite model and the dry sand 6, and the pouring port of the pouring space is located on the surface of the sand box 12.

[0095] As an optional embodiment, the step of filling the dry sand 6 to fix the composite model, the generating end of the pulsed magnetic field and the generating end of the pulsed electric field comprises:

[0096] The sand box 12 is placed on the vibration table 11, and when the dry sand 6 is filled, the vibration table 11 vibrates the sand box 12 to make the dry sand 6 fill tightly.

[0097] As an optional embodiment, the step of forming a vacuum environment comprises:

[0098] After the dry sand 6 is filled, a plastic film 13 is covered on the top of the sand box 12, and the bottom of the sand box 12 is communicated with the vacuum pump assembly, and the vacuum pump assembly draws a vacuum in the sand box 12 through the bottom of the sand box 12.

[0099] The vacuum degree in the sand box 12 reaches 0.01-0.05 MPa.

[0100] As an optional embodiment, the generating end of the pulse magnetic field comprises an excitation coil 3 arranged around the composite model, the excitation coil 3 is embedded in the dry sand 6, the excitation coil 3 is electrically connected with a pulse magnetic field generator 7, and the pulse magnetic field generator 7 is located outside the sand box 12.

[0101] The inner diameter of the excitation coil 3 is greater than the length and width of the composite model.

[0102] The inner diameter of the excitation coil 3 is 1.2-1.5 times the longest dimension of the composite model.

[0103] The height of the excitation coil 3 is greater than the height of the magnesium melt filling part foam pattern 9, but not higher than the height of the sprue of the gating system foam pattern 2, and the height of the excitation coil 3 is 1.1-1.3 times the height of the magnesium melt filling part foam pattern 9. The magnesium melt filling part foam pattern 9 is located in the middle of the excitation coil 3.

[0104] The duty cycle, frequency, and forward-reverse switching time of the pulse magnetic field are 20%-40%, 20-40 Hz, and 0-20 s, respectively.

[0105] As an optional embodiment, the generating end of the pulse electric field comprises a pulse electric field generator 8, and the two poles of the pulse electric field generator 8 are connected with the two ends of the solid aluminum inlay 4 through wires.

[0106] The voltage, waveform, frequency, peak value, and forward-reverse switching time of the pulse electric field are 100-400 V, a pulse electric field sine wave, 50 Hz-200 Hz, 50 A-150 A, and 0-20 s, respectively.

[0107] As an optional embodiment, during pouring, a sprue cup 1 is placed on the top of the pouring gate, the sprue cup 1 is communicated with the pouring gate, and the magnesium melt pouring liquid 10 is poured through the sprue cup 1.

[0108] The temperature of the magnesium melt pouring liquid 10 is 700-750℃.

[0109] The application time of the pulse magnetic field and the pulse electric field is from when the magnesium melt pouring liquid 10 fills the mold to when the metal temperature decreases below the solidus.

[0110] As one of the specific embodiments, the specific operation process of the pulse electromagnetic composite field reinforced aluminum-magnesium bimetallic casting method is as follows:

[0111] Step 1, mold making.

[0112] The preparation of the composite model comprises the following steps:

[0113] (1) preparing the solid aluminum insert 4, the gating system foam pattern 2, and the magnesium melt filling portion foam pattern 9.

[0114] (2) sticking the magnesium melt filling portion foam pattern 9 to the solid aluminum insert 4, and bonding the gating system foam pattern 2 and the magnesium melt filling portion foam pattern 9 to form a composite pattern.

[0115] The second step is coating.

[0116] The coating of the composite pattern includes the following steps:

[0117] (1) preparing a mixed solution by mixing the expendable pattern coating powder and water according to a predetermined volume ratio, and stirring the mixed solution uniformly.

[0118] (2) uniformly coating the mixed solution on all outer surfaces of the composite pattern, and drying the composite pattern in a drying oven with a temperature of 50-60°C.

[0119] (3) coating the dried composite pattern with another layer of the mixed solution and drying.

[0120] The third step is sand embedding.

[0121] The sand embedding of the composite pattern includes the following steps:

[0122] (1) welding the solid aluminum insert 4 at both ends with a wire.

[0123] (2) adding the binderless dry sand 6 to the bottom surface of the sand box 12, and then placing the composite pattern into the sand box 12. Then, the excitation coil 3 is placed inside the sand box 12, and the excitation coil 3 is welded with a wire long enough. The position of the magnetic field coil and the composite pattern is adjusted, and finally the binderless dry sand 6 is added to the sand box 12 for fixation.

[0124] (3) using the vibration table 11 to vibrate and compact the dry sand 6 and the composite pattern in the sand box 12. The vibration frequency of the vibration table 11 is 50-150 Hz, and the amplitude is 0.6-1.2 mm.

[0125] The fourth step is vacuumizing.

[0126] A layer of plastic film 13 is arranged on the top end of the sand box 12, covering the top opening of the sand box 12. Then, the sand box 12 is vacuumized from the bottom by a vacuum pump assembly, so that the vacuum degree in the sand box 12 reaches 0.01-0.05 MPa.

[0127] The fifth step is adding the sprue cup 1.

[0128] The sprue cup 1 is arranged on the top of the gating system foam pattern 2. In this embodiment, the bottom of the sprue cup 1 is provided with refractory clay.

[0129] Sixth step, smelting.

[0130] Specifically, smelting magnesium in an electric resistance furnace to obtain a magnesium melt pouring liquid 10.

[0131] Seventh step, pouring.

[0132] Specifically, first, the magnesium melt pouring liquid 10 is poured from the sprue cup 1 to the composite model, the pouring temperature is 730-750 DEG C, until the composite model is filled. At the same time, the composite model vaporizes, and the vaporization product is a reducing gas.

[0133] Eighth step, applying a pulsed electromagnetic composite field.

[0134] The wire connected to the excitation coil 3 is connected to the pulsed magnetic field generator 7, and the wire on the solid aluminum insert 4 is connected to the pulsed electric field generator 8. Start the pulsed magnetic field generator 7 and the pulsed electric field generator 8.

[0135] Ninth step, cleaning.

[0136] After the magnesium melt pouring liquid 10 in the sand box 12 cools and solidifies, cleaning is performed to obtain an aluminum / magnesium bimetallic casting.

[0137] The method for strengthening aluminum / magnesium bimetallic castings provided by the application has the advantages of the lost foam solid-liquid composite casting method, i.e. the insert does not need to be fixed additionally, is suitable for preparing large-size complex parts, and large heat input and slow cooling rate are beneficial to realize metallurgical bonding. The application of the pulsed electromagnetic composite field can effectively solve the problems of brittle intermetallic compounds, coarse grains and stress concentration in the interface structure. In addition, the foam vaporization product is a reducing gas, which avoids the oxidation of the alloy liquid and aluminum during pouring, and improves the quality of the casting. The grains of the casting are refined, the strength, hardness and other properties are improved, and the overall comprehensive performance of the casting is improved.

[0138] An aluminum / magnesium bimetallic product is prepared by the method for preparing aluminum / magnesium bimetallic products using a pulsed electromagnetic composite field.

[0139] The application will be further described in detail in the following application examples.

[0140] Application Example 1:

[0141] The foam model of the casting is a cube with a size of 35x35x100mm, and the solid aluminum insert 4 is a cylinder with a diameter of 10mm and a height of 110mm. The material of the solid aluminum insert 4 is A356 aluminum alloy, the magnesium melt pouring liquid 10 is AZ91D magnesium alloy melt, and the height of the solid aluminum insert 4 protruding from the foam model of the casting in the composite model is 5mm.

[0142] During use, firstly, the composite model is placed in the sand box 12, and the top and bottom of the solid aluminum insert 4 are connected with the pulse electric field generator 8 respectively by wires. The excitation coil 3 is placed near the composite model, and the distance between the excitation coil 3 and the composite model is 2 cm. Vibration sand filling is performed until the sand box 12 is filled, and after the sand box 12 is filled, a layer of plastic film 13 is covered on the top, and the sand box 12 is vacuumized through the vacuum pipe, and the vacuum degree is 0.015 MPa. Then, the sprue cup 1 is installed on the top of the casting foam model of the composite model, and the molding process is completed.

[0143] Then, the magnesium melt pouring liquid 10 is poured from the sprue cup 1, the pouring temperature is 750 DEG C, and after the pouring is completed, the pulse magnetic field generator 7 and the pulse electric field generator 8 are started at the same time, the alternating current with a frequency of 100 Hz and a current value of 100 A is applied to the solid aluminum insert 4, at the same time, the pulse magnetic field frequency is 20 Hz, the duty cycle is 20%, and the positive and negative switching time is 20 s.

[0144] Implementation effect: The intermetallic compound A1-Mg of the magnesium-aluminum bimetal interface, the eutectic structure is refined, the bimetal interface bonding strength is improved, the precipitated phase is reduced by about 70%, and the strength of the bimetal casting is improved.

[0145] Application example 2:

[0146] Three completely same casting foam models, all are 35*35*100mm cubes, and three completely same solid aluminum inserts 4 marked as a, b, and c respectively (corresponding to the subsequent three castings a, b, and c) are all cylinders with a diameter of 10 mm and a height of 110 mm. The material of the solid aluminum insert 4 is A356 aluminum alloy, the magnesium melt pouring liquid 10 is AZ91D magnesium alloy melt, and the height of the solid aluminum insert 4 extending out of the casting foam model in the composite model is 5 mm.

[0147] During use, firstly, the three composite models are placed in the sand box 12 respectively, and the following operation setting is used for the control experiment: the top and bottom of the solid aluminum insert 4 marked as a are connected with the pulse electric field generator 8 respectively by wires. The excitation coil 3 is placed near the composite model, and the distance between the excitation coil 3 and the composite model is 2 cm. The top and bottom of the solid aluminum insert 4 marked as b are connected with the pulse electric field generator 8 respectively by wires. The excitation coil 3 is placed near the composite model of the solid aluminum insert 4 marked as c, and the distance between the excitation coil 3 and the composite model is 2 cm. The three sand boxes 12 are vibrationally filled with sand until the sand boxes 12 are filled, and after the sand boxes 12 are filled, a layer of plastic film 13 is covered on the top, and the sand boxes 12 are vacuumized through the vacuum pipe, and the vacuum degree is 0.015 MPa. Then, the sprue cup 1 is installed on the top of the casting foam model of the composite model, and the molding process is completed.

[0148] Then, the magnesium melt pouring liquid 10 is poured from the sprue cup 1, the pouring temperature is 750 DEG C, after pouring, the pulse magnetic field generator 7 and the pulse electric field generator 8 are started respectively, the pulse electric field generator 8 is started, and the pulse magnetic field generator 7 is started, for the three devices respectively. The alternating current with the frequency of 50 Hz and the current value of 50 A is applied to the three aluminum inserts, at the same time, the pulse magnetic field frequency is 40 Hz, the duty cycle is 20%, and the positive and negative switching time is 20 s.

[0149] The implementation effect is that, after the shear strength test, the average shear strength of the three castings a, b and c is 27.0, 22.1 and 22.3 MPa respectively. Compared with the single external field, the electromagnetic composite field effectively improves the shear performance of the casting. Figures 3-5 It can be seen that the interface structure of the electromagnetic composite field is more refined than the interface structure of the other two single external fields, and the grain is more effectively refined. The distribution of Mg2Si phase is shown in Figures 6-8 It is not difficult to see that the Mg2Si phase is more uniformly distributed on the aluminum / magnesium bimetal interface under the action of the electromagnetic composite field, and effectively avoids the segregation of the Mg2Si phase.

[0150] In the description of the present application, it should be understood that the terms "longitudinal", "transverse", "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer" and the like indicate the orientation or positional relationship based on the orientation or positional relationship shown in the drawings, and are only for the convenience of describing the present application, and do not indicate or imply that the device or element referred to must have a particular orientation, be constructed and operated in a particular orientation, therefore cannot be understood as a limitation on the present application.

[0151] The above-described embodiments are only preferred modes of the present application, and do not limit the scope of the present application, and various modifications and improvements to the technical solutions of the present application made by those skilled in the art without departing from the design spirit of the present application shall fall within the protection scope of the present application.

Claims

1. A method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field, characterized in that, Includes the following steps: A foam model of a casting is prepared according to the preset shape of the casting, and a solid aluminum inlay (4) is assembled with the foam model of the casting to form a composite model; The composite model is embedded in a sand box (12); During casting, a pulsed magnetic field and a pulsed electric field are applied to the composite model in a vacuum environment; After cooling, an aluminum-magnesium bimetallic part is obtained.

2. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 1, characterized in that, The preparation of the composite model includes the following steps: The casting foam model includes a gating system foam pattern (2) and a magnesium melt filling part foam pattern (9). The magnesium melt filling part foam pattern (9) is attached and fixed to the solid aluminum insert (4), and the casting system foam pattern (2) and the magnesium melt filling part foam pattern (9) are attached and fixed to form the composite model. The composite model is coated with paint.

3. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 2, characterized in that, The steps of applying paint to the composite model include: The lost foam casting coating powder and water are mixed in a predetermined volume ratio to form a mixture, and the mixture is stirred evenly. The mixture is uniformly coated on all the outer surfaces of the composite model, and the composite model is then dried. Repeat the above steps to apply several layers of paint.

4. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 1, characterized in that, The step of burying the composite model in the sand box (12) includes: Dry sand (6) is placed into the bottom of the sand box (12); The composite model is placed inside the sand box (12) and positioned above the dry sand (6) at the bottom. The generating end of the pulsed magnetic field and the generating end of the pulsed electric field are located inside the sand box (12); The dry sand (6) is used to fix the composite model, the generating end of the pulsed magnetic field, and the generating end of the pulsed electric field; After filling, the composite model and the dry sand (6) are isolated from each other to form a pouring space, and the pouring port of the pouring space is located on the surface of the sand box (12).

5. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 4, characterized in that, The steps of filling the composite model with dry sand (6) to fix the pulsed magnetic field generation end and the pulsed electric field generation end include: When the sand box (12) is placed on the vibration table (11) and the dry sand (6) is filled, the vibration table (11) causes the sand box (12) to vibrate so that the dry sand (6) is filled densely.

6. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 4, characterized in that, The steps for creating the vacuum environment include: After the dry sand (6) is filled, a plastic film (13) is covered on the top of the sand box (12), and the bottom of the sand box (12) is connected to the vacuum pump assembly. The vacuum pump assembly evacuates the sand box (12) through the bottom of the sand box (12).

7. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 4, characterized in that, The generating end of the pulse magnetic field includes an excitation coil (3) arranged around the composite model. The excitation coil (3) is buried in the dry sand (6). The excitation coil (3) is electrically connected to a pulse magnetic field generator (7). The pulse magnetic field generator (7) is located outside the sand box (12).

8. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 1, characterized in that, The pulse electric field generating end includes a pulse electric field generator (8), and the two poles of the pulse electric field generator (8) are respectively connected to the two ends of the solid aluminum inlay (4) through wires.

9. The method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field according to claim 4, characterized in that: During casting, a pouring cup (1) is placed on top of the pouring port and the pouring cup (1) is connected to the pouring port, and the magnesium melt pouring liquid (10) is injected through the pouring cup (1).

10. An aluminum-magnesium bimetallic product, characterized in that, It was prepared using the method for preparing aluminum-magnesium bimetal using a pulsed electromagnetic composite field as described in any one of claims 1-9.

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