Preparation method of gradient porous metal material

Abstract

The invention relates to a gradient porous metal material and a preparation method and application thereof, belongs to the technical field of porous metal materials, and solves the problems that an existing porous metal material is low in preparation efficiency, the pore size distribution state is difficult to regulate and control, and the sound absorption frequency band is narrow. The preparation method comprises the following steps: mixing the hollow microspheres and the binder according to the requirements of different structural layers to obtain mixtures of different specifications; different inner cavities of a mold are filled with the mixtures of different specifications respectively; the binder is degreased, and the movable baffle is decomposed; melting a matrix alloy, and injecting the matrix alloy into the mold until the melt submerges the whole blank in the mold; and demolding after cooling to obtain the gradient porous metal material. The gradient porous metal material obtained through the preparation method is good in sound absorption performance, and the material cracking probability is reduced.

Description

Technical Field

[0001] The invention relates to the technical field of porous metal materials, and in particular to a gradient porous metal material and a preparation method and application thereof. Background Art

[0002] Porous materials have the characteristics of large specific surface area, light weight, enhanced heat and mass transfer, etc., and have great application potential in aerospace, energy, machinery, etc. For example, porous materials can be used in the field of sound absorption. There are a large number of micropores or gaps inside porous materials. The pores are small and evenly distributed inside the material. The sound absorption mechanism of porous materials is achieved through the air viscosity, air flow friction, heat exchange, etc. inside the material. Since high-frequency sound waves can accelerate the vibration of air particles in the pores, the heat exchange between the air and the pore wall is also accelerated, making the porous material have good high-frequency sound absorption performance.

[0003] At present, the structure of traditional porous materials is relatively simple, and the narrow sound absorption frequency band may limit its use scenarios. Gradient porous materials have different structural voids distributed inside, which broaden their sound absorption frequency band on the basis of strengthening sound absorption performance. There are not many studies on the preparation process of gradient porous materials. D.print uses powder wet spraying technology to spray multiple layers of powder with decreasing powder particle size on the outer wall or inner wall of the substrate. After spraying, a special sintering technology is used to control the sintering shrinkage of powders of different particle sizes to different degrees, so that the porosity of the coating is distributed along the gradient perpendicular to the substrate. However, this preparation process is extremely inefficient due to the influence of the coating preparation speed, and is not suitable for mass industrial preparation. Moreover, the strength between different coatings is greatly affected by the sintering system. The sintering process needs to be processed step by step, and the process is complicated. Frank uses a slurry impregnation process to place a sponge organism with a gradient porous structure in a mold, and then mixes a powder slurry to impregnate the sponge forming blank. The sponge organism is decomposed by high-temperature sintering to obtain a gradient porous material. The material formed by this process is greatly affected by the sponge, and the powder slurry preparation and impregnation process is prone to powder stratification, resulting in uncontrolled pore size distribution of the final porous material. In summary, it is still challenging to prepare porous materials with good sound absorption effects. Summary of the invention

[0004] In view of the above analysis, the present invention aims to provide a gradient porous metal material and its preparation method and application, so as to solve one of the following technical problems: (1) the preparation efficiency of existing porous metal materials is low; 2) the pore size distribution state of existing porous metal materials is difficult to control; (3) the sound absorption frequency band of existing porous metal materials is relatively narrow.

[0005] The purpose of the present invention is mainly achieved through the following technical solutions:

[0006] The present invention provides a method for preparing a gradient porous metal material, comprising:

[0007] Step 1: Mix the hollow microspheres and the binder according to the requirements of different structural layers to obtain mixed materials of different specifications;

[0008] Step 2, filling the mixed materials of different specifications into different inner cavities of the mold respectively; the different inner cavities are separated by movable baffles;

[0009] Step 3, degreasing the binder and decomposing the movable baffle to form a body consisting of hollow microspheres;

[0010] Step 4: Melt the matrix alloy and inject it into the mold until the melt covers the entire blank in the mold; demold after cooling to obtain a gradient porous metal material.

[0011] Furthermore, in step 1, the movable baffle is pressed from paraffin.

[0012] Furthermore, in step 1, the binder is a paraffin-based binder.

[0013] Furthermore, in step 1, the binder comprises, by mass percentage, 3.5% to 8.5% of high-density polyethylene, 0.5% to 1.5% of stearic acid, 0.5% to 1.5% of matrix alloy powder, and the remainder is paraffin.

[0014] Furthermore, in step 2, the filling of mixed materials of different specifications into the mold is carried out simultaneously.

[0015] Furthermore, in step 3, the degreasing of the binder and the decomposition of the movable baffle include: firstly performing solvent degreasing to remove the binder and the movable baffle to obtain a degreasing blank, and then performing thermal degreasing on the degreasing blank to degreasing the binder and decomposing the movable baffle.

[0016] Furthermore, in step 4, the melting temperature is 750-950° C., and the holding time is 0.5-2 h.

[0017] On the other hand, the present invention also provides a gradient porous metal material, which includes multiple structural layers, each structural layer is a porous material, and the pore structure of the porous material of each structural layer is different; the raw materials for preparing each structural layer of the gradient porous metal material include hollow microspheres and a binder, and the binder contains a small amount of matrix alloy.

[0018] Furthermore, the mass ratios of raw materials for preparing different structural layers of the gradient porous metal material are different.

[0019] The present invention also provides a sound absorbing material, which adopts the above-mentioned gradient porous metal material.

[0020] Compared with the prior art, the present invention can achieve at least one of the following beneficial effects:

[0021] (1) In the preparation method of the gradient porous metal material of the present invention, a mold with a movable baffle is adopted. The mold includes multiple inner cavities, and the material pores can be arranged in advance according to the needs. Then, the material skeleton is formed by pouring the metal melt to ensure that the pore structure of the porous material finally formed is accurate and adjustable. This not only simplifies the preparation process and improves the material preparation efficiency, but also can accurately and flexibly control the distribution of the material pore structure, and can prepare multilayer porous materials with different pore structure arrangements, thereby maximizing the sound absorption effect of the material, and preparing a gradient porous metal material with excellent sound absorption effect.

[0022] (2) In the preparation method of the gradient porous metal material of the present invention, the material of the movable baffle is the same as that of the adhesive, ensuring that it can be removed together with the adhesive during the degreasing process, thereby reducing the impurity content of the gradient porous metal material.

[0023] (3) In the preparation method of the gradient porous metal material of the present invention, hollow microspheres and a binder are mixed. The binder is a paraffin-based binder containing an appropriate amount of matrix alloy powder that can be decomposed at high temperature. The binder serves as a carrier for the flow filling of the hollow microspheres and the matrix alloy. The matrix alloy serves as a raw material for supporting and bonding the hollow microspheres after the binder is removed. The preparation method of the present invention reduces the probability of material cracking and ensures that a gradient porous metal material of qualified quality is obtained.

[0024] (4) The preparation method of the present invention has simple process, high efficiency and is suitable for large-scale industrial production.

[0025] (5) The gradient porous metal material of the present invention comprises a plurality of structural layers, each of which is a porous material, and the pore structure of the porous material of each structural layer is different; when used as a sound-absorbing material, the sound absorption frequency band is wide and the sound absorption performance is good; the raw materials for preparing the gradient porous metal material of the present invention comprise hollow microspheres and a binder, the binder contains a small amount of matrix alloy, the binder serves as a carrier for the flow filling of the hollow microspheres and the matrix alloy, and the matrix alloy serves as a raw material for supporting and bonding the hollow microspheres after degreasing; the raw materials for preparing the gradient porous metal material of the present invention reduce the probability of material cracking.

[0026] (6) The gradient porous metal material of the present invention comprises multiple structural layers, each of which is a porous material, and the pore structure of the porous material of each structural layer is different; by precisely controlling the number of structural layers and the porosity and pore size of each structural layer, when it is used as a sound-absorbing material, the sound absorption frequency band is wide and the sound absorption performance is excellent.

[0027] In the present invention, the above-mentioned technical solutions can also be combined with each other to achieve more preferred combination solutions. Other features and advantages of the present invention will be described in the subsequent description, and some advantages can become obvious from the description, or can be understood by practicing the present invention. The purpose and other advantages of the present invention can be realized and obtained through the contents pointed out in the embodiments of the description and the drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] The drawings are only for the purpose of illustrating particular embodiments and are not to be construed as limiting the invention.

[0029] Figure 1 It is a structural schematic diagram of the mold of the present invention.

[0030] Reference numerals

[0031] 1-mold, 2-removable baffle, 3-hollow microsphere, 4-binder. DETAILED DESCRIPTION

[0032] The preferred embodiments of the present invention will be described in detail below in conjunction with the accompanying drawings, wherein the accompanying drawings constitute a part of the present invention and are used together with the embodiments of the present invention to illustrate the principles of the present invention, but are not used to limit the scope of the present invention.

[0033] The present invention provides a gradient porous metal material, which includes multiple structural layers, each of which is a porous material, and the pore structure of the porous material in each structural layer is different; the raw materials for preparing each structural layer of the gradient porous metal material include hollow microspheres and a binder, and the binder contains a small amount of matrix alloy.

[0034] Specifically, the above pore structure mainly refers to pore size and porosity.

[0035] Specifically, the mass ratios of raw materials for preparing different structural layers of the gradient porous metal material are different.

[0036] Specifically, the base alloy is preferably an aluminum alloy, and more preferably 6061 aluminum alloy. Aluminum alloy has a low melting temperature, good melt fluidity, is easy to cast, and has a low density, which has a good weight reduction effect. For example, using 6061 aluminum alloy can improve the surface quality of the material, and can also be heat-treated and strengthened according to actual needs.

[0037] like Figure 1 As shown, the present invention also provides a mold 1 used in the preparation process of the above-mentioned gradient porous metal material. The mold 1 is divided into different cavities by a movable baffle 2. During the preparation process of the gradient porous metal material, hollow microbeads 3 and adhesive 4 are placed in the inner cavity.

[0038] Specifically, the material of the mold 1 is preferably a graphite mold. Graphite has low cost and is easy to process, is resistant to high temperatures, can be used repeatedly, and is easy to repair.

[0039] Specifically, the movable baffle 2 is pressed from paraffin wax, because the paraffin wax decomposes at a relatively high temperature, thereby ensuring that the paraffin wax can be removed together with the binder during the degreasing process.

[0040] Specifically, different ratios of hollow microspheres and a binder mixture can be added to the above different inner cavities as required to achieve pre-regulation of the pore structure before forming, that is, the porosity of the porous material is controlled by the volume ratio of the hollow microspheres in the inner cavity. The pore size of the final material is controlled by the hollow size of the hollow microspheres.

[0041] The present invention also provides a method for preparing the above-mentioned gradient porous metal material, comprising:

[0042] Step 1: Mix the hollow microspheres and the binder according to the requirements of different structural layers to obtain mixed materials of different specifications;

[0043] Step 2: Filling mixed materials of different specifications into different inner cavities of the mold respectively;

[0044] Step 3, degreasing the binder and decomposing the movable baffle to form a body consisting of hollow microspheres;

[0045] Step 4: melt the matrix alloy and inject it into the mold until the melt covers the entire blank in the mold; demold after cooling, and grind or turn the outer matrix metal layer of the demolding material to obtain the internal gradient porous metal material.

[0046] Specifically, in the above step 1, the hollow microspheres can be hollow glass microspheres or hollow SiC particles. Hollow glass microspheres are low in cost and easy to obtain. Considering that hollow SiC particles have low density and good thermal stability and are not easily deformed or cracked when subjected to pressure or heat treatment, preferably, the hollow microspheres are hollow SiC particles.

[0047] Specifically, in the above step 1, the binder is preferably a paraffin-based binder, which has good thermoplasticity, is easy to be evenly mixed with the hollow microspheres during the mixing process, is easily decomposed by heat, and has little residue.

[0048] Specifically, in the above step 1, the binder comprises, by mass percentage, 3.5% to 8.5% of high-density polyethylene, 0.5% to 1.5% of stearic acid, 0.5% to 1.5% of matrix alloy powder, and the remainder is paraffin.

[0049] Specifically, in the above step 1, high-density polyethylene is used as the skeleton material in the binder; stearic acid is used to increase the surface activity of the mixture, making it easier to fill the mixture into the mold; and the matrix alloy powder is used as the bonding material of the hollow microspheres after degreasing.

[0050] Specifically, in the above step 1, the mass ratio of the binder to the hollow microspheres in different structural layers is determined according to the porosity requirements of the structural layers and the material density of the binder and the hollow microspheres. The mass ratio of the hollow microspheres to the binder is approximately ρ 空心微珠 φ:ρ 粘结剂 (1-φ) (φ is the porosity), therefore, the density of the binder and hollow microspheres should be tested before mixing to determine the porosity.

[0051] Specifically, in the above step 1, the p in the present invention is 空心微珠 :ρ 粘结剂 is 0.5.

[0052] Specifically, in the above step 1, the mixing of the binder and the hollow microspheres is carried out by a mixer or a twin-screw mixer. Considering that the mixing temperature is too high, the paraffin component in the binder will volatilize violently, affecting the actual composition ratio of the final mixture; if the mixing temperature is too low, the fluidity of the binder deteriorates, and the hollow microspheres and the binder are difficult to mix evenly, resulting in uneven distribution of hollow positions in the final material; if the mixing speed is too high, it is easy to cause the separation of materials with different specific gravities in the mixed material, resulting in uneven composition of the final mixed material; if the speed is too low, the material mixing efficiency is not high, and it is difficult to fully mix the materials; if the mixing time is too long, it affects the production efficiency and is easy to introduce impurities; if it is too short, it may not be fully mixed, and the material composition is uneven. Therefore, the mixing temperature is controlled to be 150-250°C, the mixing speed is 30-200r / min, and the mixing time is 3-6h.

[0053] Specifically, in the above step 2, the filling of mixed materials of different specifications into the mold should be carried out simultaneously to prevent the movable baffle from being broken due to imbalance of material pressure in different areas.

[0054] Specifically, in the above step 2, considering that the cold mixture has poor fluidity and is difficult to fill into the mold, the mixture becomes more fluid after heating, which can reduce the pressure of filling the mixture into the mold; however, the temperature of the mixture cannot be overheated, otherwise it will cause the volatilization loss of paraffin and the like in the binder. Therefore, the mixture should be heated when filling the mold, and the temperature of the mixture is preferably 125-175°C.

[0055] Specifically, in the above step 2, considering that too little pressure when filling the mixture into the mold makes it difficult to compact the mixture, and too much pressure easily causes the mixture to escape from the mold, the pressure of filling the mixture into the mold is controlled to be 5-25 MPa.

[0056] Specifically, in the above step 3, the degreasing of the binder and the decomposition of the movable baffle include: firstly performing solvent degreasing to remove the binder and the movable baffle to obtain a degreasing blank, and then performing thermal degreasing on the degreasing blank to decompose the binder and the movable baffle to form a blank composed of hollow microspheres.

[0057] Specifically, in the above step 3, the solvent used in solvent degreasing includes n-heptane or trichloroethylene.

[0058] Specifically, in the above step 3, the temperature of solvent degreasing is selected to be room temperature, and the degreasing time is 3 to 24 hours.

[0059] Specifically, in the above step 3, the hot degreasing is performed after the degreasing blank is dried. Considering that the degreasing temperature is too high, the matrix alloy in the binder will melt, causing the collapse and deformation of the blank after degreasing. If the temperature is too low, the binder is difficult to be completely removed, resulting in an increase in the residual carbon content of the material. If the degreasing time is too long, it will affect the production efficiency and bring the hidden danger of impurity pollution. If the degreasing time is too short, the binder is difficult to be completely removed. Therefore, the degreasing temperature is controlled to be 350-600°C and the degreasing time is 0.5-2h.

[0060] Specifically, in the above step 3, the combination of solvent degreasing and thermal degreasing can improve the degreasing efficiency and reduce the residual binder after degreasing. If thermal degreasing is performed directly, it is easy to cause deformation and cracking of the blank during the degreasing process, increasing the uncertainty of degreasing.

[0061] Specifically, in the above step 4, considering that too high a melting temperature or too long a holding time may cause the burning of alloy elements or an increase in the inclusion content in the melt, affecting the final performance of the material, the melting temperature is controlled to be 750-950°C and the holding time is 0.5-2h.

[0062] The present invention also provides an application of the above-mentioned gradient porous metal material, using the above-mentioned gradient porous metal material as a sound-absorbing material. The sound absorption frequency band is wide and the sound absorption performance is good. For example, the sound absorption coefficient at 200 Hz is above 0.12, for example, 0.12 to 0.15; the sound absorption coefficient at 500 Hz is above 0.51, for example, 0.51 to 0.95; the sound absorption coefficient at 1000 Hz is above 0.22, for example, 0.22 to 0.61; the sound absorption coefficient at 2000 Hz is above 0.45, for example, 0.45 to 0.85.

[0063] Preferably, the present invention provides a sound absorbing material, which adopts the above-mentioned gradient porous metal material.

[0064] It should be noted that the sound absorption mechanism of porous materials is to damp the sound waves through the air in the hollow microspheres. In addition, the interface between the hollow microspheres and the matrix will also weaken the sound waves due to structural differences. Under the premise of a certain porosity, the sound absorption coefficient will first increase and then decrease with the decrease of the pore size. After the pore size decreases, the interface between the hollow microspheres and the matrix increases, the specific surface area of ​​the pores per unit volume increases, and the sound absorption effect increases accordingly. However, after the size of the hollow microspheres is reduced to a certain extent, the sound waves tend to bypass the hollow microspheres and propagate from the matrix, resulting in a decrease in the sound absorption effect. Under the premise of a certain pore size, the sound absorption coefficient also shows a corresponding law with the change of porosity. After the porosity increases, the damping effect of the air in the hollow microspheres on the sound waves will increase the sound absorption coefficient of the material. However, after increasing to a certain extent, the density of the material decreases sharply, and the overall sound absorption effect will deteriorate.

[0065] Therefore, the inventors conducted a lot of in-depth research on the pore size distribution and porosity arrangement characteristics of gradient porous materials, and obtained a gradient design scheme with the highest sound absorption coefficient and the best sound absorption efficiency.

[0066] Specifically, the number of structural layers of the sound absorbing material is 3 to 5, and the porosity difference between adjacent structural layers is preferably 5% to 25%.

[0067] Specifically, the pore size of the hollow microbeads of the sound absorbing material is 0.1-1 mm.

[0068] Specifically, the average porosity of the sound absorbing material is preferably 20% to 60%.

[0069] Specifically, when the number of structural layers of the sound absorbing material is 3, the porosity difference between adjacent structural layers is 5% to 25%, and the pore size difference of the hollow microbeads between adjacent structural layers is (0.2±0.05) mm.

[0070] Specifically, when the number of structural layers of the sound absorbing material is 4 or 5, the porosity difference between adjacent structural layers is 5% to 15%, and the pore size difference of the hollow microbeads between adjacent structural layers is (0.15±0.10) mm.

[0071] Specifically, the porosity and pore size of different structural layers of the above-mentioned sound absorbing material have the same variation trend, that is, as the porosity increases, the pore size of the hollow microbeads of the structural layer increases accordingly.

[0072] Specifically, the sound absorption material has a wide sound absorption frequency band and good sound absorption performance. For example, the sound absorption coefficient at 200 Hz is 0.12 or more, for example, 0.12-0.13; the sound absorption coefficient at 500 Hz is 0.87 or more, for example, 0.87-0.95; the sound absorption coefficient at 1000 Hz is 0.55 or more, for example, 0.55-0.61; the sound absorption coefficient at 2000 Hz is 0.75 or more, for example, 0.75-0.85.

[0073] Compared with the prior art, the preparation method of the gradient porous metal material of the present invention adopts a mold with a movable baffle, and the mold includes multiple cavities. The material pores can be arranged in advance according to needs, and then the material skeleton is formed by pouring the metal melt, thereby ensuring that the pore structure of the porous material finally formed is accurate and adjustable. It not only simplifies the preparation process and improves the material preparation efficiency, but also can accurately and flexibly control the distribution of the material pore structure, and can prepare multi-layer porous materials with different pore structure arrangements, thereby maximizing the sound absorption effect of the material, and preparing a gradient porous metal material with excellent sound absorption effect.

[0074] In the preparation method of the gradient porous metal material of the present invention, the material of the movable baffle is the same as that of the adhesive, which ensures that the movable baffle can be removed together with the adhesive during the degreasing process, thereby reducing the impurity content of the gradient porous metal material.

[0075] In the preparation method of the gradient porous metal material of the present invention, a paraffin-based binder containing an appropriate amount of matrix alloy powder that can be decomposed at high temperature is selected as the binder, the binder serves as a carrier for the flow filling of hollow microspheres and the matrix alloy, and the matrix alloy serves as a raw material for supporting and bonding the hollow microspheres after degreasing; the preparation method of the present invention reduces the probability of material cracking and ensures that a gradient porous metal material of qualified quality is obtained.

[0076] The preparation method of the invention has simple process and high efficiency and is suitable for large-scale industrial production.

[0077] When the gradient porous metal material of the present invention is used as a sound absorbing material, the sound absorbing frequency band is wide and the sound absorbing performance is good.

[0078] Example 1

[0079] The present embodiment provides a gradient porous metal material and a preparation method thereof. The size of the gradient porous metal material of the present embodiment is 300*300*60mm, and the gradient porous metal material includes 3 structural layers, each structural layer is a porous material, and the thickness of each structural layer is 20mm. The porosity of the three structural layers is 20%, 40%, and 60%, respectively, and the pore sizes of the three structural layers are 0.2mm, 0.4mm, and 0.6mm, respectively.

[0080] The preparation method comprises: mixing three hollow SiC microbeads with different pore sizes with a paraffin-based binder (the binder comprises 4% high-density polyethylene, 1% stearic acid, 0.5% 6061 aluminum alloy powder, and the balance is paraffin) in a mass ratio of 1:8, 1:3 and 3:4, respectively, and then mixing them with a twin-screw mixer, the mixing temperature is 170°C, the mixing speed is 130r / min, and the mixing time is 5h, so as to obtain mixed materials of different specifications; after the mixed material is heated to 150°C, it is injected into a mold at a pressure of 15MPa and filled into three inner cavities of the mold, and the pore sizes of the hollow microbeads in the three adjacent inner cavities are 0.2mm, 0.4mm and 0.6mm respectively; the filled material is immersed in n-heptane for 24h and dried, the mixed material is heated to about 550°C in a degreasing furnace, degreased for 0.8h, and the hollow SiC microbeads in the mold are bonded into a blank by the 6061 aluminum alloy powder in the binder.

[0081] 6061 aluminum alloy is melted at 800°C and kept at a temperature of 1h. The molten aluminum is injected into and fills the mold. The mold is demolded after cooling, and the outer layer of matrix metal is simply machined to obtain a gradient porous metal material with three layers of porosity of 20%, 40%, and 60% respectively and pore sizes of 0.2mm, 0.4mm, and 0.6mm distributed in a gradient manner.

[0082] Example 2

[0083] The present embodiment provides a gradient porous metal material and a preparation method thereof. The size of the gradient porous metal material of the present embodiment is 300*300*60mm, and the gradient porous metal material includes 4 structural layers, each structural layer is a porous material, and the thickness of each structural layer is 15mm. The porosity of the 4 structural layers is 20%, 35%, 45%, and 60%, respectively, and the pore sizes of the 4 structural layers are 0.2mm, 0.35mm, 0.5mm, and 0.75mm, respectively.

[0084] The preparation method comprises: mixing four hollow SiC microspheres with different pore sizes and a paraffin-based binder (the binder comprises 6% high-density polyethylene, 1.2% stearic acid, 1% 6061 aluminum alloy powder, and the balance is paraffin) at a mass ratio of 1:8, 1:3.7, 2:5, and 3:4, respectively, and then mixing them in a twin-screw mixer at a mixing temperature of 200°C, a mixing speed of 120 r / min, and a mixing time of 4 hours to obtain mixed materials of different specifications; mixing After the material is heated to 175°C, it is injected into the mold at a pressure of 20 MPa and filled into the four inner cavities of the mold. The pore sizes of the hollow microbeads in the four adjacent inner cavities are 0.2 mm, 0.35 mm, 0.5 mm, and 0.75 mm, respectively; the filled material is soaked in n-heptane for 24 hours and dried, and the mixture is heated to about 550°C in a degreasing furnace and degreased for 1 hour. The hollow SiC microbeads in the mold are bonded into a green body by the 6061 aluminum alloy powder in the binder.

[0085] 6061 aluminum alloy is melted at 850°C and kept at a temperature of 1h. The molten aluminum is injected into and fills the mold. The mold is demolded after cooling, and the outer layer of matrix metal is simply machined to obtain 4 layers of gradient porous metal materials with porosities of 20%, 35%, 45%, and 60% respectively and pore sizes of 0.2mm, 0.35mm, 0.5mm, and 0.75mm.

[0086] Example 3

[0087] The present embodiment provides a gradient porous metal material and a preparation method thereof. The size of the gradient porous metal material of the present embodiment is 300*300*60mm, and the gradient porous metal material includes 5 structural layers, each structural layer is a porous material, and the thickness of each structural layer is 12mm. The porosity of the 5 structural layers is 24%, 32%, 40%, 48%, and 56%, respectively, and the pore sizes of the 5 structural layers are 0.2mm, 0.3mm, 0.4mm, 0.5mm, and 0.6mm, respectively.

[0088] The preparation method comprises: mixing 5 hollow SiC microspheres with different pore sizes and a paraffin-based binder (the binder comprises 7% high-density polyethylene, 1.5% stearic acid, 1.5% 6061 aluminum alloy powder, and the balance is paraffin) at a mass ratio of 1:6.3, 1:4.2, 1:3, 1:2.2, and 7:11, respectively, and then mixing them in a twin-screw mixer at a mixing temperature of 220°C, a mixing speed of 80 r / min, and a mixing time of 3 hours to obtain mixed materials of different specifications. After the mixture is heated to 150°C, it is injected into the mold at a pressure of 15 MPa and filled into the five inner cavities of the mold. The pore sizes of the hollow microbeads in the five adjacent inner cavities are 0.2 mm, 0.3 mm, 0.4 mm, 0.5 mm, and 0.6 mm, respectively. The filled material is soaked in n-heptane for 24 hours and dried. The mixture is heated to about 550°C in a degreasing furnace and degreased for 1 hour. The hollow SiC microbeads in the mold are bonded into a green body by the 6061 aluminum alloy powder in the binder.

[0089] 6061 aluminum alloy is melted at 900°C and kept at a temperature of 1h. The molten aluminum is injected into and fills the mold. The mold is demolded after cooling, and the outer layer of base metal is simply machined to obtain 5 layers of gradient porous metal materials with porosities of 24%, 32%, 40%, 48%, and 56% respectively and pore sizes of 0.2mm, 0.3mm, 0.4mm, 0.5mm, and 0.6mm distributed in a gradient manner.

[0090] Example 4

[0091] The present embodiment provides a porous metal material and a preparation method thereof. The size of the porous metal material of the present embodiment is 300*300*60mm. The porous metal material includes two structural layers, each of which is a porous material. The thickness of each structural layer is 30mm, and the porosity of the two structural layers is 40% and 70% respectively. The pore diameter of the two structural layers is 0.3mm.

[0092] The preparation method comprises: mixing hollow SiC microbeads and a paraffin-based binder (the binder comprises 4% high-density polyethylene, 1% stearic acid, 0.5% 6061 aluminum alloy powder, and the balance is paraffin) in a mass ratio of 1:3 and 1.2:1 respectively, and then mixing them with a twin-screw mixer, the mixing temperature is 150°C, the mixing speed is 100r / min, and the mixing time is 2h, so as to obtain mixtures of different specifications; after the mixture is heated to 150°C, it is injected into a mold at a pressure of 15MPa and filled into two inner cavities of the mold, the filled material is immersed in n-heptane for 24h and dried, the mixture is heated to about 550°C in a degreasing furnace, degreased for 1h, and the hollow SiC microbeads in the mold are bonded into a blank by the 6061 aluminum alloy powder in the binder.

[0093] 6061 aluminum alloy is melted at a melting temperature of 800°C and a holding time of 1 hour. The molten aluminum is injected into and fills the mold, and the mold is demolded after cooling. The outer layer of the matrix metal is simply machined to obtain two layers of porous metal materials with porosities of 44% and 70% respectively.

[0094] Example 5

[0095] The present embodiment provides a porous metal material and a preparation method thereof. The size of the porous metal material of the present embodiment is 300*300*60mm. The porous metal material includes 3 structural layers, each structural layer is a porous material, the thickness of each structural layer is 20mm, the porosity of the 3 structural layers is 40%, and the pore sizes of the 3 structural layers are 0.2mm, 0.4mm, and 0.6mm, respectively.

[0096] The preparation method comprises: mixing hollow SiC microbeads and a paraffin-based binder (the binder comprises 4% high-density polyethylene, 1% stearic acid, 0.5% 6061 aluminum alloy powder, and the balance is paraffin) in a mass ratio of 1:3, and then mixing them in a twin-screw mixer at a mixing temperature of 180°C, a mixing speed of 100 r / min, and a mixing time of 2.5 hours to obtain mixtures of different specifications; after the mixture is heated to 150°C, it is injected into a mold at a pressure of 15 MPa and filled into three inner cavities of the mold, the filled material is immersed in n-heptane for 24 hours and dried, the mixture is heated to about 550°C in a degreasing furnace, degreased for 1 hour, and the hollow SiC microbeads in the mold are bonded into a green body by the 6061 aluminum alloy powder in the binder.

[0097] 6061 aluminum alloy is melted at a melting temperature of 850°C and a holding time of 1 hour. The molten aluminum is injected into and fills the mold, and the mold is demolded after cooling. The outer layer of the base metal is simply machined to obtain three layers of porous metal materials with a porosity of 40% and pore sizes of 0.2 mm, 0.4 mm, and 0.6 mm in a gradient distribution.

[0098] Example 6

[0099] The present embodiment provides a porous metal material and a preparation method thereof. The size of the porous metal material of the present embodiment is 300*300*60mm, and the porous metal material includes 5 structural layers, each structural layer is a porous material, and the thickness of each structural layer is 12mm. The porosity of the 5 structural layers is 24%, 32%, 40%, 48%, and 56%, respectively, and the pore sizes of the 5 structural layers are 0.6mm, 0.5mm, 0.4mm, 0.3mm, and 0.2mm, respectively.

[0100] The preparation method comprises: mixing five hollow SiC microbeads with different diameters with a paraffin-based binder (the binder comprises 7% high-density polyethylene, 1.5% stearic acid, 1.5% 6061 aluminum alloy powder, and the balance is paraffin) at a mass ratio of 1:6.3, 1:4.2, 1:3, 1:2.2 and 7:11, respectively, and then mixing them with a twin-screw mixer at a mixing temperature of 220°C, a mixing speed of 80 r / min, and a mixing time of 3 hours to obtain mixed materials of different specifications; after the mixed material is heated to 150°C, it is injected into a mold at a pressure of 15MPa and filled into five inner cavities of the mold, the filled material is immersed in n-heptane for 24 hours and dried, the mixed material is heated to about 550°C in a degreasing furnace, degreased for 1 hour, and the hollow SiC microbeads in the mold are bonded into a blank by the 6061 aluminum alloy powder in the binder.

[0101] 6061 aluminum alloy is melted at 900°C and kept at a temperature of 1h. The molten aluminum is injected into and fills the mold. The mold is demolded after cooling, and the outer layer of base metal is simply machined to obtain 5 layers of porous materials with porosities of 24%, 32%, 40%, 48%, and 56% respectively and pore sizes of 0.6mm, 0.5mm, 0.4mm, 0.3mm, and 0.2mm distributed in a gradient.

[0102] The porous material of the embodiment is sampled according to φ100mm*60mm, and the sampling is required to be carried out along the direction of the pore structure gradient arrangement. The density of the sample is tested using a density tester, and the sound absorption coefficient of the material of the embodiment is tested by comparing it with a traditional porous aluminum alloy material (porosity 40%, 0.4mm pore size). During the test, the test sample is placed close to the surface of the rigid piston at the end of the standing wave tube, and the test vehicle is moved to test the sound pressure level difference of the test sample at different center frequencies (200Hz, 500Hz, 1000Hz, 2000Hz). The sound absorption coefficient of the sample at different frequencies is calculated by the sound pressure level difference.

[0103] Table 1 Density and sound absorption coefficient of the embodiments and comparative examples

[0104]

[0105]

[0106] From the sound absorption performance of the embodiments and comparative examples, it can be seen that the sound absorption performance of the gradient porous metal material of the present invention is significantly better than that of the conventional porous material with a single uniform porosity. Compared with Example 4, the improvement of the sound absorption coefficient of the gradient porous metal material of the 3-5 layers of the embodiments 1-3 of the present invention is more obvious than that of the double-layer gradient material. In addition, compared with the embodiments 5-6, the synchronous change of the pore size and porosity between different structural layers of the embodiments 1-3 is more conducive to the improvement of the sound absorption effect, but the pore size should maintain the same trend as the porosity change, and the improvement of the sound absorption coefficient will be more obvious.

[0107] The above description is only a preferred specific implementation manner of the present invention, but the protection scope of the present invention is not limited thereto. Any changes or substitutions that can be easily conceived by any technician familiar with the technical field within the technical scope disclosed by the present invention should be covered within the protection scope of the present invention.

Claims

1. A method for preparing a gradient porous metal material, characterized in that: include: Step 1: Mix the hollow microspheres and the binder according to the requirements of different structural layers to obtain mixed materials of different specifications; Step 2, filling mixed materials of different specifications into different inner cavities of the mold (1); the different inner cavities are separated by a movable baffle (2); Step 3, degreasing the binder and decomposing the movable baffle (2) to form a body consisting of hollow microspheres; Step 4: Melt the matrix alloy and inject it into the mold until the melt covers the entire blank in the mold; demold after cooling to obtain a gradient porous metal material.

2. The preparation method according to claim 1, characterized in that: In the step 1, the movable baffle (2) is pressed from paraffin.

3. The preparation method according to claim 1, characterized in that: In the step 1, the binder is a paraffin-based binder.

4. The preparation method according to claim 3, characterized in that: In the step 1, the binder comprises, by mass percentage, 3.5% to 8.5% of high-density polyethylene, 0.5% to 1.5% of stearic acid, 0.5% to 1.5% of matrix alloy powder, and the remainder is paraffin.

5. The preparation method according to claim 1, characterized in that: In step 2, the mixtures of different specifications are filled into the mold simultaneously.

6. The preparation method according to claim 1, characterized in that: In step 3, the degreasing of the binder and the decomposition of the movable baffle include: firstly performing solvent degreasing to remove the binder and the movable baffle to obtain a degreasing blank, and then performing thermal degreasing on the degreasing blank to degreasing the binder and decomposing the movable baffle.

7. The preparation method according to any one of claims 1 to 6, characterized in that: In step 4, the melting temperature is 750-950° C., and the holding time is 0.5-2 h.

8. A gradient porous metal material, characterized in that: The gradient porous metal material is prepared by the preparation method described in any one of claims 1 to 7, and the gradient porous metal material includes multiple structural layers, each structural layer is a porous material, and the pore structure of the porous material of each structural layer is different; the preparation raw materials of each structural layer of the gradient porous metal material include hollow microspheres and a binder, and the binder contains a matrix alloy.

9. The gradient porous metal material according to claim 8, characterized in that: The mass ratios of raw materials for preparing different structural layers of the gradient porous metal material are different.

10. A sound absorbing material, characterized in that: The sound absorbing material is a gradient porous metal material prepared by the preparation method according to any one of claims 1 to 7 or a gradient porous metal material according to claim 1 or 2.

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