Metal injection molding aluminum alloy product with rigid outside and soft inside and preparation method of metal injection molding aluminum alloy product

Abstract

The invention provides an outer-rigid inner-soft metal injection molding aluminum alloy product and a preparation method thereof.The product comprises an inner layer structure and an outer layer structure which are connected together, the inner layer structure is made of aluminum alloy, and the outer layer structure is made of a composite material of the aluminum alloy and a reinforcing phase; the aluminum alloy in the inner-layer structure and the aluminum alloy in the outer-layer structure are the same in component. The whole product has the characteristics of being rigid outside and soft inside, so that the outer surface of the product has the advantages of high hardness and collision prevention, and meanwhile, the inner surface can be subjected to common machining.

Description

Technical Field

[0001] The invention belongs to the field of powder metallurgy aluminum alloy metal injection molding, and specifically relates to a metal injection molding aluminum alloy product which is rigid on the outside and flexible on the inside and a preparation method thereof, and belongs to a functional material. Background Art

[0002] Metal injection molding (MIM) has developed rapidly in recent years. It is an important technology for manufacturing complex small parts because of its low process cost, high efficiency, and ability to customize and process complex structural metal parts.

[0003] The density of aluminum is only 2.7g / cm 3 , has a strong specific strength and strong corrosion resistance. It can be made into various appearance colors through anodizing or PVD. It has important value in weight-reducing appearance products, such as mobile phone frames, smart watch cases, wireless headset cases, and even drone products, aerospace products, etc. However, conventional aluminum alloys do not have strong wear resistance, and the elastic modulus is usually 70-80 GPa. The ability to resist elastic deformation is relatively low compared to common metals such as steel. In daily use, aluminum alloy metal injection molding products are easily deformed by bumps, which limits the scope of application.

[0004] Metal Matrix Composite (MMC) is a composite material that is artificially synthesized with metal and its alloy as the matrix and one or more non-metallic reinforcement phases. Most of its reinforcement materials are inorganic non-metals, such as oxide ceramics, tungsten carbide ceramics, carbon, metal fibers, etc. In aluminum-based composite materials, by selecting appropriate reinforcement phases, the prepared materials have the advantages of light weight, high strength and high modulus. For example, commonly used reinforcement phases include silicon carbide (SiC), titanium carbide (TiC), aluminum oxide (Al2O3), and more expensive diamond (C), cubic boron nitride (CBN), etc. The above reinforcement phases have high hardness and high elastic modulus. When made into composite materials together with aluminum alloys, they have the advantages of lightweight and corrosion resistance of aluminum alloys, and the characteristics of high elastic modulus, wear resistance and high hardness of the reinforcement phases. They are relatively ideal materials.

[0005] Among the common products of aluminum alloy injection molding, although injection molding is a near-net-shape process, there are also some areas that require machining, such as threaded holes, micropores, etc. However, the high hardness of the reinforcing phase in aluminum-based composite materials increases the difficulty of machining, and even brings high machining costs. For example, using diamond or cubic boron nitride as a reinforcing phase is almost impossible with ordinary turning, milling and drilling, and the cost of using electric spark machining is too high. Common mobile phone frames, smart watch cases, wireless earphone cases and other products have simple and smooth outer surface structures, which can be MIM molded without additional machining; but the threaded holes, micropores and other structures on the inner surface require certain machining. Summary of the invention

[0006] In order to solve the problems of the above-mentioned prior art, the present invention provides a metal injection molded aluminum alloy product which is hard on the outside and soft on the inside and a preparation method thereof. The overall product has the characteristics of being hard on the outside and soft on the inside, so that the outer surface of the product has the advantages of high hardness and anti-collision, and the inner surface can also be subjected to ordinary machining.

[0007] The present invention is achieved through the following technical solutions: A metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside, comprising an inner layer structure and an outer layer structure connected together, wherein the inner layer structure is made of aluminum alloy, and the outer layer structure is made of a composite material of aluminum alloy and a reinforcement phase; the aluminum alloy in the inner layer structure has the same composition as the aluminum alloy in the outer layer structure.

[0008] Preferably, the aluminum alloy is a 6-series aluminum alloy, a 7-series aluminum alloy, a 2-series aluminum alloy or an Al-Mg-Cu alloy.

[0009] Preferably, the aluminum alloy contains 0.1 wt%-10 wt% of metallic tin.

[0010] Preferably, the reinforcing phase is one or more of aluminum oxide, silicon carbide, titanium carbide, tungsten carbide, zirconium carbide, vanadium carbide, titanium nitride, tantalum nitride, cubic boron nitride and diamond.

[0011] Preferably, in the outer layer structure, the volume proportion of the reinforcement phase is 1%-30%.

[0012] There are three methods for preparing the metal injection molded aluminum alloy product with rigid exterior and flexible interior described in the present invention, which can be selected according to actual conditions.

[0013] Solution 1 includes the following steps: S01, mixing aluminum alloy powder and binder to form feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and binder to form feed material, recorded as B powder; S02, injection molding the B powder to obtain an outer layer structure green body, placing the outer layer structure green body in a mold, injection molding the A powder into the mold containing the outer layer structure green body to obtain an inner layer structure green body, the outer layer structure green body and the inner layer structure green body are bonded as a whole to obtain a green body; or injection molding the A powder to obtain an inner layer structure green body, placing the inner layer structure green body in a mold, injection molding the B powder into the mold containing the inner layer structure green body to obtain an outer layer structure green body, the outer layer structure green body and the inner layer structure green body are bonded as a whole to obtain a green body; S03, degreasing the green body to obtain a brown body; S04, sintering the brown blank to obtain a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside.

[0014] Solution 2 includes the following steps: S11, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S12, injection molding the A powder to obtain an inner layer structure green body; injection molding the B powder to obtain an outer layer structure green body; S13, combining the inner layer structure green body and the outer layer structure green body together, and performing a degreasing treatment to obtain a brown body; S14, sintering the brown blank to obtain a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside.

[0015] Preferably, in S13, the degreasing treatment is catalytic degreasing or thermal degreasing.

[0016] Solution 3 includes the following steps: S21, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S22, injection molding the A powder to obtain an inner layer structure green body; injection molding the B powder to obtain an outer layer structure green body; S23, degreasing and sintering the inner layer structure green body to obtain the inner layer structure; degreasing and sintering the outer layer structure green body to obtain the outer layer structure; S24, the inner structure and the outer structure are combined and welded together.

[0017] In the above scheme, the binder includes polyethylene, polypropylene, polyoxymethylene and polyethylene glycol; or, the binder includes paraffin, stearic acid, polyoxymethylene and dimethyl oxalate.

[0018] Compared with the prior art, the present invention has the following beneficial effects: The metal injection molded aluminum alloy product provided by the present invention is rigid on the outside and flexible on the inside. The outer layer structure uses an aluminum-based composite material containing a reinforcement phase, and the inner layer structure uses a conventional aluminum alloy. The inner and outer aluminum alloy matrices are the same material, so that the inner and outer layers can have similar shrinkage rates during sintering and can be combined together. The outer layer structure has rigid characteristics, and the inner layer structure has flexible characteristics. Therefore, the overall product has the characteristics of rigid on the outside and flexible on the inside, so that the outer surface of the product has the advantages of high hardness and anti-collision, and the inner surface can also be processed by ordinary machining.

[0019] Furthermore, in aluminum alloy metal injection molding, metallic tin needs to be added to the aluminum alloy formula to lower the melting point, promote sintering, slow down the generation rate of AlN, etc. This is crucial for obtaining high-density products by aluminum alloy metal injection molding.

[0020] The preparation method of the metal injection molded aluminum alloy product with a rigid outer layer and a flexible inner layer of the present invention adopts the injection molding method for both the inner layer structure and the outer layer structure, so the product has the characteristics of conventional metal injection molding, including the ability to mold complex product parts. At the same time, for common products on the market, the present invention provides three different production schemes for rigid outer layer and flexible inner layer products. In scheme one, the outer layer structure and the inner layer structure are integrally injection molded. This scheme can be used for most products and is also the preferred scheme. If the product has a thin-walled structure or a slender piece, such as the mobile phone middle frame in Example 2 of the present invention, scheme two needs to be adopted. This is because there is a slight difference in the sintering shrinkage rate of the outer layer structure and the inner layer structure material. This slight inconsistency in sintering shrinkage rate in thin-walled or slender products will cause product warping. During the sintering process, the main driving force for the reduction of porosity and the increase of density is the reduction of surface energy, while sintering welding is mainly based on diffusion. In the second scheme, the main change during sintering is that the outer layer structure and the inner layer structure are first densified separately, and then sintered and welded together (actually they happen at the same time, but the early stage is mainly densification, and the later stage is mainly diffusion). This can avoid large deformation due to the difference in sintering change rate. Generally speaking, when the product is large, it is not suitable for metal injection technology. Generally speaking, metal injection molded products are less than 200g. The present invention wants to further expand the scope of application of metal injection molding. For example, some gears, pulleys, etc. are heavy and have high requirements on the mechanical properties of the contact surface. Therefore, the third scheme is proposed, by molding the outer layer structure and the inner layer structure, sintering them to density respectively, and then welding them together by brazing. In this way, a product with slightly heavier weight can be made. Therefore, the preparation method of the present invention has a very wide range of application. BRIEF DESCRIPTION OF THE DRAWINGS

[0021] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative work.

[0022] Figure 1 This is a schematic diagram of the original design of a sports watch case in the prior art; Figure 2 A schematic diagram of the outer structure of the sports watch case of the present invention; Figure 3 A schematic diagram of a watch case of the present invention that is rigid on the outside and flexible on the inside; Figure 4 It is a schematic diagram of the original design of the pulley in the prior art; Figure 5 It is a schematic diagram of the outer structure of the pulley of the present invention; Figure 6 It is a schematic diagram of the inner layer structure of the pulley of the present invention; Figure 7 Schematic diagram of the outer rigid inner flexible pulley of the present invention Figure 8 It is a schematic diagram of the original structure of the mobile phone middle frame in the prior art; Fig. 9 This is a schematic diagram of the outer structure of the mobile phone middle frame of the present invention; Fig.10 The present invention is a schematic diagram of the inner structure of the mobile phone middle frame; Fig.11 The present invention is a schematic diagram of a mobile phone middle frame which is rigid on the outside and flexible on the inside. DETAILED DESCRIPTION

[0023] The following describes the embodiments of the present invention through specific examples, and those skilled in the art can easily understand other advantages and effects of the present invention from the contents disclosed in this specification. The present invention can also be implemented or applied through other different specific embodiments, and the details in this specification can also be modified or changed in various ways based on different viewpoints and applications without departing from the spirit of the present invention.

[0024] It should be noted that the process equipment or devices not specifically specified in the following embodiments are all conventional equipment or devices in the art.

[0025] It should be noted that the terms "include" and "have" and any variations thereof are intended to cover non-exclusive inclusions. For example, a process, method, system, product or device that includes a series of steps or units is not necessarily limited to those steps or units clearly listed, but may include other steps or units that are not clearly listed or inherent to these processes, methods, products or devices. Moreover, unless otherwise specified, the numbering of each method step is only a convenient tool for identifying each method step, and is not intended to limit the order of arrangement of each method step or to define the scope of the present invention. Changes or adjustments in their relative relationships should also be regarded as the scope of the present invention without substantially changing the technical content.

[0026] The metal injection molded aluminum alloy product with rigid exterior and flexible interior of the present invention comprises an inner layer structure and an outer layer structure connected together, wherein the material of the inner layer structure is aluminum alloy, and the material of the outer layer structure is a composite material of aluminum alloy and reinforcement phase; the aluminum alloy in the inner layer structure has the same composition as the aluminum alloy in the outer layer structure. This is to ensure that the sintering conditions required for the inner layer and the outer layer matrix aluminum alloy materials are the same, thereby avoiding the generation of additional defects.

[0027] The above-mentioned metal injection molded aluminum alloy product with a hard outer surface and soft inner surface has the characteristics of being hard outer and soft inner. The outer layer structure uses aluminum-based composite materials, and the inner layer structure uses conventional aluminum alloys. Therefore, the outer surface of the product has the advantages of high hardness and anti-collision, and the inner surface can also be processed by ordinary machines.

[0028] In order to realize the preparation of a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside, the present invention provides three preparation schemes.

[0029] Solution 1: a method for integrally forming a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside. The specific implementation process is as follows: S01, mixing aluminum alloy powder and binder to form feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and binder to form feed material, recorded as B powder; S02, use an injection molding machine equipped with B powder to perform injection molding to obtain an outer layer structure green body, transfer the outer layer structure green body to the mold of an injection molding machine equipped with A powder, injection mold the A powder to obtain an inner layer structure green body, the outer layer structure green body and the inner layer structure green body are bonded as a whole to obtain a green body; or, use an injection molding machine equipped with A powder to perform injection molding to obtain an inner layer structure green body, transfer the inner layer structure green body to the mold of an injection molding machine equipped with B powder, injection mold the B powder to obtain an outer layer structure green body, the outer layer structure green body and the inner layer structure green body are bonded as a whole, which is called a green body; whether to injection mold the outer layer structure or the inner layer structure first depends on the structure of the trial product.

[0030] S03, degreasing the green body to remove the plastic binder to obtain a brown body; S04, sintering the brown blank, and then obtaining a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside through a post-process.

[0031] Solution 2, a method of separately forming green bodies and sintering and diffusion welding, the specific implementation process is as follows: S11, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S12, using an injection molding machine equipped with A powder to perform injection molding to obtain an inner layer structure green body; using an injection molding machine equipped with B powder to perform injection molding to obtain an outer layer structure green body; S13, combining the inner layer structure green body and the outer layer structure green body together, and performing a degreasing treatment on the whole assembly to remove the plastic binder, thereby obtaining a brown body; S14, sintering the brown blank, and then obtaining a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside through a post-process.

[0032] Scheme 3, forming green bodies separately, sintering, and then brazing and welding. The specific implementation process is as follows: S21, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S22, performing injection molding using an injection molding machine equipped with powder A to obtain an inner layer structure green body; performing injection molding using an injection molding machine equipped with powder B to obtain an outer layer structure green body; S23, degreasing and sintering the inner layer structure green body to obtain the inner layer structure; degreasing and sintering the outer layer structure green body to obtain the outer layer structure; S24, the inner layer structure and the outer layer structure are combined together, brazed, and then a metal injection molded aluminum alloy product with a rigid outer surface and a flexible inner surface is obtained through a post-process.

[0033] In the above three schemes of the present invention, the aluminum alloy powder used contains one or more other metals other than aluminum without any specific restrictions. It is preferred to use 6 series aluminum alloy, 7 series aluminum alloy, 2 series aluminum alloy or Al-Mg-Cu alloy as the main alloy material, and preferably add 0.1%-10% of metal tin (Sn) to the main alloy material, and preferably 0.5%-2.0% Sn is selected. Sn mainly acts as a capture agent for oxygen and moisture during sintering, lowers the melting point to promote sintering, slows down the generation rate of AlN, etc. According to the present invention, metals such as bismuth, lead, indium or rare earth are not required, but if desired, they can still be added as alloy matching components to obtain a sintered body of the corresponding alloy. 6 series aluminum alloy, mass percentage: Si 0.4%-0.8%, Cu0.15%-0.4%, Mg 0.8%-1.2%, Cr 0.04%-0.35%, Fe≤0.7%, Mn≤0.15%, Zn≤0.25%, Ti≤0.15%, Al balance; 2 series aluminum alloy, mass percentage: Si 0.3%-0.5%, Cu 3.8%-4.9%, Mg 1.4%-2.0%, Cr≤0.1%, Fe≤0.7%, Mn 0.3%-1.0%, Zn≤0.25%; 7 series aluminum alloy, mass percentage: Si 0.2-0.4, Cu0.14-2.2, Mg 2.1-2.9, Cr 0.1-0.3, Fe≤0.5, Mn≤0.3, Zn≤5.5-6.5, Ti≤0.15, Al balance.

[0034] The aluminum alloy powder is prepared by gas atomization: the aluminum ingot and the additional added elements are smelted and atomized together, and it can be considered that the elements in the powder have been completely alloyed. Sn can be added additionally, and Sn can be used as a single powder mixed with the gas atomized aluminum alloy powder. The aluminum alloy powder particle size D90 is less than 28μm, and the specific surface area is greater than 0.4m 3 / g, oxygen content <1700ppm.

[0035] In the above three schemes of the present invention, the reinforcing phase used is also called the second phase. Common reinforcing phases include oxide series, such as aluminum oxide (Al2O3); carbide series, such as silicon carbide (SiC), titanium carbide (TiC), tungsten carbide (WC), zirconium carbide (ZrC), vanadium carbide (VC); nitride series, such as titanium nitride (TiN), tantalum nitride (TaN), cubic boron nitride (CBN); superhard series, such as diamond (C). SiC and Al2O3 are preferred. The particle size of the reinforcing phase is between 1-150μm, preferably 2-20μm. The difficulty of mixing uniformity of excessive particle size increases, and the injection head is more easily worn during injection molding. In theory, one reinforcing phase can be selected, or several can be used in combination, but the present invention believes that the use of one reinforcing phase can meet the performance of high strength and high wear resistance, and it is not recommended to use several in combination. In the outer layer structure, the volume proportion of the reinforcing phase is 1%-30%, and the four volume proportions of 5%, 10%, 15%, and 20% are preferred.

[0036] In the above three schemes of the present invention, the binders (plastic binders and skeleton binders) used for feeding include polyethylene, polypropylene, polyoxymethylene and polyethylene glycol; or, the binders include paraffin, stearic acid, polyoxymethylene and dimethyl oxalate.

[0037] The present invention adopts nitrogen protection during feeding and production to prevent the aluminum alloy powder from being oxidized or even catching fire.

[0038] In the preparation scheme 1 of the present invention, two injection molding machines are required to inject powder A and powder B into a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside. The specific implementation steps are as follows: use the first injection molding machine to injection mold the outer layer structure with powder B, then remove the outer layer structure and move it to the specified position of the metal mold of the second injection molding machine, and use the second injection molding machine to injection mold the inner layer structure with powder A, so that a green body of a product that is rigid on the outside and flexible on the inside can be produced.

[0039] In the preparation schemes 2 and 3 of the present invention, the product is decomposed into two products, an outer layer structure and an inner layer structure, and the corresponding green bodies are formed using B powder and A powder respectively, so that one injection molding machine can be used for the completion.

[0040] In the above three schemes of the present invention, the degreasing process can be carried out by using a continuous furnace process, or by using a separate degreasing furnace. Common degreasing methods include thermal degreasing, catalytic degreasing, and solvent degreasing. The degreasing methods of schemes one and three can be freely selected according to the feeding formula, while in scheme two, because the green body needs to assemble the outer layer structure and the inner layer structure together for degreasing, the density of aluminum alloy is relatively low, which is not suitable for solvent degreasing, and catalytic degreasing or thermal degreasing is required.

[0041] In the above three schemes of the present invention, the sintering can be carried out by using a continuous furnace process or a vacuum furnace. The sintering requires inert gas protection, the dew point is less than -40 degrees Celsius, and the sintering temperature is usually between 590-640°C.

[0042] In the third solution of the present invention, the sintered outer layer structure and the inner layer structure are assembled together and welded together by vacuum brazing. During vacuum brazing, no brazing flux is required, and the vacuum degree needs to be 10-2Pa. Alternatively, brazing flux can be placed in the middle.

[0043] In the above three schemes of the present invention, the post-processing of the sintered product, such as polishing, grinding, machining, anodizing, etc., are common technologies in the industry and are not described.

[0044] Example 1: A product with a rigid outer shell and flexible inner shell.

[0045] like Figure 1 As shown in the figure, it is a sports watch case, which is usually produced by aluminum alloy CNC machining. In this example, the MIM aluminum alloy process is used to make the outer rigid and inner flexible sports watch case. Figure 2 As shown, the outer side is injection molded using B powder with added reinforcing phase powder, and the inner side is injection molded using conventional aluminum alloy powder. Since the product is thicker and is not easily deformed during sintering, the process of scheme 1 in the content of the present invention can be adopted.

[0046] The specific implementation is as follows: The 6061 aluminum alloy atomized powder was selected, and its mass percentage was: Si 0.65%, Cu 0.28%, Mg 1.02%, Cr0.11%, Fe0.25%, and Al balance. The powder particle size D90 was 20μm, the oxygen content was 1700ppm, and the specific surface area was 0.46m 3 According to the weight ratio, 99 parts of the above 6061 aluminum alloy aerosol powder and 1 part of tin powder were taken and mixed in a three-dimensional mixer for 30 minutes. The mixed powder was marked G6061.

[0047] The mass percentages of the binder components are as follows: Polyethylene 12% Polypropylene 5% Polyoxymethylene 78% Polyethylene glycol 5% A powder production: The binder and the G6061 aluminum alloy powder were mixed in an atmosphere-protected mixer at a mass ratio of 20:80, granulated, and made into G6061 aluminum alloy MIM feed, recorded as A powder.

[0048] B powder production: 90 parts of the 6061 alloy powder were taken by weight, and 5 parts of 23 μm aluminum oxide and 5 parts of 8 μm titanium carbide were selected by weight, and put into a three-dimensional mixer, and mixed for 1 hour under nitrogen protection. The obtained powder was recorded as BM powder.

[0049] The binder and the BM powder were mixed in an atmosphere-protected mixer at a mass ratio of 20:80, granulated, and made into particle-reinforced G6061 aluminum alloy MIM feed, which was recorded as B powder.

[0050] Injection molding green body: Use the injection molding machine equipped with B powder to inject the outer layer structure of the product into the green body, see Figure 2 The outer layer structure green body is transferred to the injection molding machine equipped with A powder, and injection molded into the inner layer structure green body. After cooling and demoulding, it naturally bonds to form a whole green body part. The schematic diagram of the whole part is shown in Figure 3 shown.

[0051] Debinding sintering: The integral green body obtained by injection molding with rigid outer surface and soft inner surface is subjected to catalytic degreasing and vacuum sintering. This example uses an oxalic acid furnace at 130°C for degreasing for 10 hours and vacuum sintering at 645°C for 12 hours. During the vacuum sintering stage, a small amount of inert gas can be introduced to increase the partial pressure in order to avoid the loss of Mg. In this example, nitrogen is introduced and the vacuum degree is 1KPa.

[0052] Post-process: The sintered products are processed according to the product requirements, such as machining, PVD coloring, etc. Since the MIM process tolerance is relatively high, the outer structure does not require additional machining, and the inner structure is ordinary aluminum alloy, and CNC machining of fine structures is relatively easy.

[0053] Example 2: Dual-material pulley product with rigid exterior and flexible interior.

[0054] like Figure 4 As shown in the figure, it is a pulley product, which is usually produced by aluminum alloy CNC machining. This example uses MIM aluminum alloy technology to make a dual-material pulley product with a rigid outer surface and a flexible inner surface. Figure 7 As shown. Among them, the outer side is injection molded using B powder with added reinforcing phase powder, such as Figure 5 The inner side is made of conventional aluminum alloy powder injection molding, such as Figure 6 As shown. Since the pulley products are relatively large, the process in the second solution of the present invention can be adopted, and a continuous furnace sintering method can be adopted.

[0055] The specific implementation is as follows: The AlMgCu aluminum alloy gas atomization powder was selected, and its mass percentage was: Si 0.36%, Cu 4.2%, Mg 1.8%, and Al balance. The powder particle size D90 was 20μm, the oxygen content was 1700ppm, and the specific surface area was 0.46m 3 According to the weight ratio, 99.5 parts of the above AlMgCu aluminum alloy atomized powder and 0.5 parts of tin powder were taken and mixed in a three-dimensional mixer for 30 minutes. Since its composition is similar to that of 2024 aluminum alloy, the mixed powder is marked G2024.

[0056] The binder of this embodiment includes the following components in terms of mass percentage: Paraffin 15%; Stearic acid 2%; Polyoxymethylene 80%; Dimethyl oxalate 3%; A powder production: The binder and the G2024 aluminum alloy were mixed in an atmosphere-protected mixer at a mass ratio of 25:75, granulated, and made into G2024 aluminum alloy MIM feed, recorded as A powder.

[0057] B powder production: 90 parts by weight of the G2024 alloy powder, 5 parts by weight of 35 μm aluminum oxide, and 10 parts by weight of 8 μm silicon carbide were put into a three-dimensional mixer, and mixed for 1 hour under nitrogen protection. The obtained powder was recorded as BM powder.

[0058] The binder and the BM powder were mixed in an atmosphere-protected mixer at a ratio of 25:75, granulated, and made into particle-reinforced G2024 aluminum alloy MIM feed, which was recorded as B powder.

[0059] Injection molding green body: Use the injection molding machine equipped with B powder to inject the outer layer structure of the product into the green body, see Figure 5 shown.

[0060] Use the injection molding machine equipped with A powder to inject the inner layer structure of the product into the green body, see Figure 6 shown.

[0061] Assemble the outer layer structure green body to the inner layer structure green body to obtain a green body. Figure 7 shown.

[0062] Debinding sintering: The green body is placed in the degreasing zone of the atmosphere continuous furnace for degreasing. Because the product is large and has relatively high strength, the heating rate can be increased and the degreasing time needs to be extended. The degreasing process is as follows: heat up to 330°C at 5°C / min, keep at 330°C for 30 minutes, heat up to 420°C at 5°C / min, and keep at 420°C for 80 minutes. The degreasing atmosphere is 1 part of gas from the sintering zone and the burn-off zone flowing to the degreasing zone and 1.5 parts of air, and the atmosphere pressure is 0.2MPa; After degreasing, the product moves to the burn-off area to burn off the skeleton binder. The burn-off process is to increase the temperature to 500°C at 10°C / min and keep it at 510°C for 60 minutes. The volume percentage of the atmosphere used is: nitrogen 99.4%, oxygen 0.6%; The product continues to move to the sintering area in the furnace for high-temperature sintering. The high-temperature sintering process is as follows: the temperature is raised to 615℃ at 10℃ / min, and kept at 615℃ for 60 minutes. The atmosphere in the high-temperature sintering area is pure nitrogen, with a dew point below -60℃ and an oxygen content of less than 5ppm. The dew point in the high-temperature sintering furnace is lower than -40℃, which is used as the standard for controlling the atmosphere flow rate; Cool under nitrogen protection, and wait until the product temperature is below 50℃ before taking it out of the furnace; After degreasing and sintering, the outer layer structure green body and the inner layer structure green body can be sintered and diffused together, and have a certain strength.

[0063] Post-process: Generally speaking, pulleys require inner hole shaping or machining to achieve assembly accuracy.

[0064] Example 3: A mobile phone middle frame product that is tough on the outside and flexible on the inside.

[0065] like Figure 8 The figure shows a mobile phone middle frame product. The original product uses aluminum alloy CNC machine processing four pieces and then splices them together. Usually the elastic modulus of aluminum alloy is only 70GPa, and mobile phones will inevitably encounter bumps or fall from high places in daily use. The low elastic modulus of aluminum alloy is more likely to deform under stress. This example uses MIM aluminum alloy technology to make a mobile phone middle frame with a rigid exterior and a soft interior. Fig.11 As shown, the mobile phone middle frame can be made into an integral structure without the need for four pieces to be spliced. The outer side is injection molded with B powder with added reinforcing phase powder, and the inner side is injection molded with conventional aluminum alloy powder. Because the product is thin and easily deformed during sintering, the process of scheme 3 in the invention content is adopted.

[0066] The specific implementation is as follows: The 7075 aluminum alloy atomized powder was selected, and its mass percentage was: Si 0.40%, Fe 0.50%, Cu 0.16%, Mn 0.30%, Mg 2.2%, Zn 0.58%, Cr 0.21%, Ti 0.2%, and Al balance. The powder particle size D90 was 20 μm, the oxygen content was 1700 ppm, and the specific surface area was 0.46 m 3 According to the weight ratio, 98.8 parts of the above 7075 aluminum alloy aerosol powder and 1.2 parts of tin powder were taken and mixed in a three-dimensional mixer for 30 minutes. The mixed powder was marked G7075.

[0067] The mass percentages of the binder components are as follows: Polyethylene 20% Polypropylene 5% Polyoxymethylene 70% Polyethylene glycol 5% A powder production: The binder and the G7075 aluminum alloy were mixed in an atmosphere-protected mixer at a mass ratio of 20:80, granulated, and made into G7075 aluminum alloy MIM feed, recorded as A powder.

[0068] B powder production: 90 parts by weight of the G7075 alloy powder and 20 parts by weight of 6 μm silicon carbide were put into a three-dimensional mixer, and mixed for 1 hour under nitrogen protection. The obtained powder was recorded as BM powder.

[0069] The binder and the BM powder were mixed in an atmosphere-protected mixer at a mass ratio of 20:80, granulated, and made into particle-reinforced G7075 aluminum alloy MIM feed, which was recorded as B powder.

[0070] Injection molding green body: Use the injection molding machine equipped with B powder to inject the outer layer structure of the product into the green body, see Fig. 9 shown.

[0071] Use the injection molding machine equipped with A powder to inject the inner layer structure of the product into the green body, see Fig.10 shown.

[0072] Debinding sintering: The outer layer structure green body and the inner layer structure green body are catalytically degreased and vacuum sintered respectively. In this example, the oxalic acid furnace is used for degreasing at 130°C for 10 hours and vacuum sintering at 600°C for 12 hours. During the vacuum sintering stage, a small amount of inert gas can be introduced to increase the partial pressure in order to avoid the loss of Mg and Zn. In this example, nitrogen is introduced and the vacuum degree is 1KPa.

[0073] Product shaping: The degreased and sintered products are shaped to prevent excessive deformation caused by uncontrollable factors during sintering.

[0074] Vacuum brazing: The above-mentioned shaped products are spliced ​​in order, with the outer layer structure made of B powder on the outside and the inner layer structure made of A powder on the inside. After splicing, they are put into an aluminum alloy vacuum brazing furnace for vacuum brazing.

[0075] Post-process: The sintered products will be processed according to the product requirements, such as machining, PVD coloring, etc.

[0076] The elastic modulus of the final product of the outer layer structure of this example can exceed 100 GPa. Compared with the product of aluminum alloy CNC, the elastic modulus is increased by more than 43%.

Claims

1. A metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside, characterized in that: It comprises an inner layer structure and an outer layer structure connected together, wherein the inner layer structure is made of aluminum alloy, and the outer layer structure is made of a composite material of aluminum alloy and a reinforcement phase; the aluminum alloy in the inner layer structure has the same composition as that in the outer layer structure.

2. The metal injection molded aluminum alloy product with rigid exterior and flexible interior according to claim 1, characterized in that: The aluminum alloy is a 6-series aluminum alloy, a 7-series aluminum alloy, a 2-series aluminum alloy or an Al-Mg-Cu alloy.

3. The metal injection molded aluminum alloy product with rigid exterior and flexible interior according to claim 1, characterized in that: The aluminum alloy contains 0.1 wt% to 10 wt% of metallic tin.

4. The metal injection molded aluminum alloy product with rigid exterior and flexible interior according to claim 1, characterized in that: The reinforcing phase is one or more of aluminum oxide, silicon carbide, titanium carbide, tungsten carbide, zirconium carbide, vanadium carbide, titanium nitride, tantalum nitride, cubic boron nitride and diamond.

5. The metal injection molded aluminum alloy product with rigid exterior and flexible interior according to claim 1, characterized in that: In the outer layer structure, the volume proportion of the reinforcement phase is 1%-30%.

6. The method for preparing a metal injection molded aluminum alloy product with rigid exterior and flexible interior as claimed in claim 1, characterized in that: The following steps are involved: S01, mixing aluminum alloy powder and binder to form feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and binder to form feed material, recorded as B powder; S02, injection molding the B powder to obtain an outer layer structure green body, placing the outer layer structure green body in a mold, injection molding the A powder into the mold containing the outer layer structure green body to obtain an inner layer structure green body, and the outer layer structure green body and the inner layer structure green body are bonded as a whole to obtain a green body; or injection molding the A powder to obtain an inner layer structure green body, placing the inner layer structure green body in a mold, injection molding the B powder into the mold containing the inner layer structure green body to obtain an outer layer structure green body, and the outer layer structure green body and the inner layer structure green body are bonded as a whole to obtain a green body; S03, degreasing the green body to obtain a brown body; S04, sintering the brown blank to obtain a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside.

7. The method for preparing a metal injection molded aluminum alloy product with rigid exterior and flexible interior as claimed in claim 1, characterized in that: The following steps are involved: S11, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S12, injection molding the A powder to obtain an inner layer structure green body; injection molding the B powder to obtain an outer layer structure green body; S13, combining the inner layer structure green body and the outer layer structure green body together, and performing a degreasing treatment to obtain a brown body; S14, sintering the brown blank to obtain a metal injection molded aluminum alloy product that is rigid on the outside and flexible on the inside.

8. The method for preparing a metal injection molded aluminum alloy product with rigid exterior and flexible interior according to claim 7, characterized in that: In S13, the degreasing treatment is catalytic degreasing or thermal degreasing.

9. The method for preparing a metal injection molded aluminum alloy product with rigid exterior and flexible interior as claimed in claim 1, characterized in that: The following steps are involved: S21, mixing aluminum alloy powder and a binder to form a feed material, recorded as A powder; mixing aluminum alloy powder, reinforcing phase powder and a binder to form a feed material, recorded as B powder; S22, injection molding the A powder to obtain an inner layer structure green body; injection molding the B powder to obtain an outer layer structure green body; S23, degreasing and sintering the inner layer structure green body to obtain the inner layer structure; degreasing and sintering the outer layer structure green body to obtain the outer layer structure; S24, the inner structure and the outer structure are combined and welded together.

10. The method for preparing a metal injection molded aluminum alloy product with rigid exterior and flexible interior according to any one of claims 6 to 9, characterized in that: The binder includes polyethylene, polypropylene, polyoxymethylene and polyethylene glycol; or, the binder includes paraffin, stearic acid, polyoxymethylene and dimethyl oxalate.

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