A method for preparing open-cell aluminum foam

Abstract

This invention discloses a method for preparing open-cell aluminum foam. The method optimizes the powder mixing process by using a vacuum mill jar, alternating forward and reverse rotation during the milling process with a certain time interval between the alternations, etc., to achieve uniform mixing of pore-forming agent particles and aluminum powder. This makes it easier to completely remove the pore-forming agent particles, preventing residual pore-forming agent from corroding the open-cell aluminum foam during its service life and affecting its performance. This invention does not require a vacuum hot-pressing sintering furnace, reducing equipment requirements. The equipment is simple and convenient to operate, and the cost is low.

Description

Technical Field

[0001] This invention relates to the field of foam metal preparation technology, and in particular to a method for preparing functional open-cell aluminum foam with fine pore size. Background Technology

[0002] Foamed metal is a novel material that combines structural and functional properties, and is considered one of the most promising materials of the 21st century. Among all metallic elements, aluminum has become a research hotspot due to its high reserves, low cost, low density, and good plasticity. Foamed aluminum consists of an aluminum (or aluminum alloy) matrix and pores. This unique porous structure gives it characteristics such as low relative density, high specific strength, and large specific surface area, resulting in excellent energy absorption, damping, acoustic, electromagnetic shielding, and thermal properties, leading to its widespread application in the construction industry, electronic packaging, transportation, aerospace, and other fields. Based on whether the internal pores of foamed aluminum are interconnected, it can be divided into closed-cell foamed aluminum and open-cell foamed aluminum. Open-cell foamed aluminum uses aluminum or its alloys as a framework, with the interior of the framework filled with interconnected pores.

[0003] In recent years, with the development and exploration of open-cell aluminum foam preparation technology by researchers, there are more and more methods for preparing open-cell aluminum foam. Common preparation methods include investment casting, infiltration casting, additive manufacturing, and powder metallurgy. CN111850338A discloses a method for preparing a pore-forming agent, a preform, and open-cell aluminum foam. This method uses a granulator to manufacture the pore-forming agent and uses an infiltration method to prepare open-cell aluminum foam. This method requires the preparation of a pore-forming agent, the process is complex, and it uses a variety of raw materials, resulting in high production costs. CN114054722A discloses a method for preparing open-cell aluminum-zinc alloy foam using an infiltration method. This method first forms a preform composite of aluminum alloy tube and NaCl pore-forming agent particles in an infiltration mold. Then, the zinc-aluminum eutectoid alloy melt is poured into the preheated infiltration mold, and the zinc-aluminum eutectoid alloy melt infiltrates into the pores of the NaCl pore-forming agent particles under the pressure of the injected air. After the NaCl pore-forming agent particles are completely dissolved in water, the open-cell aluminum foam is obtained. The method for preparing foamed aluminum is greatly affected by the bulk density of the pore-forming agent. If the bulk density of the pore-forming agent is too high, the aluminum liquid will not easily penetrate; if the bulk density is too low, the pore-forming agent particles will not come into contact with each other, resulting in incomplete removal of the pore-forming agent particles during hydrolysis. This leads to poor open-cell foamed aluminum with poor porosity, and the remaining pore-forming agent may also cause corrosion problems during use. CN116329551A discloses a method for preparing ultra-thin open-cell foamed aluminum. This method involves mixing foamed aluminum with a foaming agent, pressing it into a block, hot-pressing and sintering it, and finally hot rolling and anodizing to obtain ultra-thin open-cell foamed aluminum. However, this method results in uneven mixing of foamed aluminum and foaming agent, making it difficult to completely remove the foaming agent after impregnation with organic solvents. Furthermore, it requires secondary processing of the foamed aluminum, making the preparation method relatively cumbersome. In the process of preparing open-cell aluminum foam using powder metallurgy, the pore size, pore shape, and porosity of the open-cell aluminum foam can be controlled by adjusting the size, shape, and volume fraction of the pore-forming agent particles. This method has significant advantages over other methods. However, due to reasons such as uneven mixing of the pore-forming agent particles and aluminum powder, and the instability and high reactivity of aluminum powder, which makes it easily oxidized, there is currently little research on the preparation of open-cell aluminum foam using powder metallurgy, especially on the powder mixing process. A suitable powder mixing process can ensure that the aluminum powder and pore-forming agent particles are mixed evenly to ensure that the pore-forming agent particles can be completely removed during the subsequent dissolution process. Summary of the Invention

[0004] The purpose of this invention is to address the problems existing in the current process of preparing open-cell aluminum foam using powder metallurgy technology, and to provide a method for preparing open-cell aluminum foam. This method optimizes the powder mixing process by using a vacuum mill jar, alternating forward and reverse rotation during the milling process, and ensuring a certain time interval between the alternations. This achieves uniform mixing of pore-forming agent particles and aluminum powder, making it easier to completely remove the pore-forming agent particles and preventing residual pore-forming agent from corroding the open-cell aluminum foam during its service life, thus avoiding its impact on performance. This invention eliminates the need for a vacuum hot-pressing sintering furnace, reducing equipment requirements. The equipment is simple and convenient to operate, low in cost, and avoids oxidation of aluminum powder during ball milling, further improving sintering quality and facilitating low-cost production of open-cell aluminum foam.

[0005] The technical solution of the present invention is as follows:

[0006] A method for preparing open-cell aluminum foam, the method comprising the following steps:

[0007] The first step is to place the weighed aluminum powder and pore-forming agent granules into desiccators and dry them in a vacuum drying oven at 60-80°C for 1-2 hours.

[0008] The volume of the pore-forming agent is 50-80% of the sum of the volumes of the aluminum powder and the pore-forming agent;

[0009] The second step involves mixing the dried aluminum powder with the pore-forming agent and placing the mixture into a ball mill jar, sealing it under a vacuum of 10. -2 ~10 -3 The ball milling time under Pa is 3 to 5 hours. After setting the operating mode, start the motor to start the ball milling.

[0010] The diameter of the grinding balls is 4-8 mm; the ball-to-material ratio is 3:1; during the ball milling process, the forward and reverse rotations alternate every 5-15 minutes, with the interval between alternations set to 5-15 minutes.

[0011] The third step is to separate the raw material from the grinding balls using a 100-300 mesh sieve after ball milling to obtain a mixed powder of aluminum powder and pore-forming agent particles. The mixed powder is then placed in a vacuum bag and sealed for later use.

[0012] The fourth step is to pour the mixture of aluminum powder and pore-forming agent particles into a steel mold, vibrate it evenly, and then place it on a pressure testing machine with an axial pressure of 300-400 MPa and a holding time of 3-5 minutes. After demolding, a preform is obtained.

[0013] The fifth step is to place the preform into a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level of 10. -2 ~10 -3Pa, heated to 600-650℃ at a heating rate of 5-8℃ / min and held for 2-3 hours, then cooled to room temperature in the furnace to obtain the precursor;

[0014] Step 6: Place the precursor in an aqueous solution, then place it in an ultrasonic cleaner, set the heating temperature to 40℃, and the time to 1-2 hours. After cleaning, take out the sample and place it in a vacuum drying oven at 60-80℃ for 1-2 hours to obtain the desired open-cell aluminum foam.

[0015] The pore-forming agent is one or more of sodium chloride, calcium chloride, urea, or sucrose, with a particle size range of 1-2 mm and a shape of spherical, cubic, or irregular.

[0016] The aluminum powder has a particle size of 100-300 μm and is stored in a sealed container under vacuum.

[0017] In the second step, the ball milling speed is 250-300 r / min.

[0018] In step five, the mold used to prepare the open-cell aluminum foam is a sleeve with upper and lower pressure heads and a gasket with a matching inner diameter of the sleeve, which is used to compact the powder and facilitate the removal of the sample after compaction.

[0019] In the above-described method for preparing open-cell aluminum foam, all raw materials are obtained through commercial purchase.

[0020] The essential features of this invention are:

[0021] (1) The process of using an axial press for pressure followed by vacuum sintering eliminates the need for a vacuum hot press furnace, reducing the equipment requirements for preparing aluminum foam using powder metallurgy. The equipment is also simple to operate and has a lower cost. (2) By using alternating forward and reverse rotation during ball milling with a certain time interval between the two rotations, the mill can be fully cooled. Insufficient cooling or no cooling will result in a high temperature in the milling tank, causing powder agglomeration during milling and resulting in uneven mixing of aluminum powder and pore-forming agent particles. Excessive cooling time will affect milling efficiency. The cooling time in this scheme allows for uniform mixing of aluminum powder and pore-forming agent, making it easier to remove pore-forming agent particles during subsequent hydrolysis, thus ensuring the porosity and pore uniformity of the prepared open-cell aluminum foam.

[0022] The beneficial effects of this invention are:

[0023] (1) This invention can be based on the density (ρ) of the pore-forming agent particles. s The density of aluminum powder (2.7 g / cm³) 3 To control the porosity (P) of open-cell aluminum foam, the appropriate mass ratio is adjusted. (where m1 is the mass of the pore-forming agent and m2 is the mass of the aluminum powder) It can achieve quantitative control of the porosity of aluminum foam, obtain open-cell aluminum foam with any desired porosity, and select pore-forming agent particles of different shapes to prepare open-cell aluminum foam with different pore types as needed.

[0024] (2) The present invention uses ball milling to mix pore-forming agent particles and aluminum powder, so that the pore-forming agent particles and aluminum powder can be evenly distributed after mixing. This allows the pore-forming agent particles in the preform after sintering can be completely dissolved and removed, and ensures that the pores of the aluminum foam can be interconnected. In addition, this ball milling process can save the mixing time under the condition of achieving the same dispersion effect, and greatly improve the mixing efficiency.

[0025] (3) In this invention, the ball milling process is stopped for a period of time after each period of operation to allow the ball milling jar to cool down. On the one hand, this prevents the aluminum powder and pore-forming agent particles from agglomerating due to excessive temperature caused by friction between the steel balls and the jar wall during the ball milling process, thus promoting the uniformity of powder dispersion and ensuring that the pore-forming agent particles can be completely dissolved and removed in the subsequent dissolution process. On the other hand, this allows the jar temperature to be cooled down in time during the ball milling process, ensuring the stability of the aluminum powder during the ball milling process and improving the safety of the preparation process.

[0026] (4) The present invention utilizes vacuum ball milling to avoid the active aluminum powder being oxidized to aluminum oxide during the ball milling process, thereby improving the sintering quality of the open-cell foam aluminum precursor and making the aluminum powder in the precursor after sintering more compact. In the subsequent ultrasonic cleaning process, the open-cell foam aluminum matrix will not be dispersed by ultrasonic waves, resulting in better molding effect.

[0027] (5) The present invention uses a self-made steel mold in the molding process, which can prepare open-cell aluminum foam of different thicknesses according to requirements without secondary processing. A layer of graphite powder is coated on the inner wall as a lubricant, which reduces the friction between the sample and the mold during demolding and prevents the edges of the aluminum foam preform from falling off during demolding. This allows the demolded open-cell aluminum foam to completely replicate the shape of the mold. Axial pressure is applied using a pressure testing machine, and after pressure molding, vacuum furnace sintering is used to separate the molding process from the sintering process. The vacuum hot pressing sintering furnace is not required for preparation, which reduces equipment requirements. The equipment is simple and convenient to operate and has low cost, which is conducive to the low-cost production of open-cell aluminum foam. Attached Figure Description

[0028] Figure 1 : Schematic diagram of the compression molding die used in this invention.

[0029] Figure 2 : A physical image of the open-cell aluminum foam prepared in Example 1.

[0030] Figure 3 Microscopic image of open-cell aluminum foam obtained in Example 1. Detailed Implementation

[0031] The present invention will be described in detail below with reference to specific embodiments. It should be noted that the following examples are only detailed descriptions of the preparation method of the present invention and do not represent that the scope of protection is limited thereto.

[0032] Example 1

[0033] Step 1: Prepare raw materials: In this embodiment, analytical grade cubic sodium chloride granules are selected as the pore-forming agent, with a purity of 99.5% and a density of 2.165 g / cm³. 3 Analytical grade aluminum powder with a purity of 97% and a density of 2.70 g / cm³ was selected. 3 .

[0034] The second step is to prepare aluminum foam with a porosity of 60%, that is, NaCl particles account for 60% of the total volume of aluminum powder and sodium chloride particles. After calculation, the required mass of NaCl particles is 12.24g and the mass of aluminum powder is 10.18g.

[0035] The relationship between the pore-forming agent and the mass ratio of aluminum powder is based on the desired porosity (P) of the aluminum foam and the density of the aluminum powder (2.7 g / cm³). 3 ) and pore-forming agent density (ρ s ),according to The mass of the pore-forming agent (m1) and the mass of the aluminum powder (m2) were calculated.

[0036] The third step is to place the weighed NaCl particles and aluminum powder into separate desiccators and dry them in a vacuum drying oven at 60°C for 1 hour before use.

[0037] Fourth step: Divide the dried aluminum powder and NaCl into two equal portions by mass and place them into two separate ball mill jars. Simultaneously, add grinding balls of Φ6mm diameter to each jar at a ball-to-powder ratio of 3:1. Connect a vacuum pump to the ball mill jars and evacuate to a vacuum level of 10. -3 After vacuuming, close the air extraction channel on the grinding jars; then place the two grinding jars into the planetary ball mill, close the cover and set the operating mode, set the ball mill speed to 300 r / min, the ball milling time to 3 h, and alternate between forward and reverse rotation every 15 min, with the interval between alternating operations set to 15 min. After setting the operating mode as described above, start the motor to perform ball milling.

[0038] Fifth step: After ball milling, use a 100-mesh sieve to separate the raw material obtained in the fourth step from the grinding balls to obtain a mixed powder of aluminum powder and NaCl particles. Then, put the mixed powder into a vacuum bag and seal it for later use.

[0039] The sixth step is to coat the inner surface of the designed steel mold with a layer of graphite powder, then pour the mixed powder of aluminum powder and pore-forming agent particles from the fifth step into the steel mold, vibrate it evenly, and then place it on a pressure testing machine to apply an axial pressure of 565kN at a speed of 0.1kN / s and hold the pressure for 3 minutes. After demolding, a preform of a certain shape is obtained.

[0040] Step 7: Place the preform obtained in step 6 into a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level of 10. -3 Pa was heated to 630°C at a heating rate of 8°C / min and held at that temperature for 3 hours before being cooled to room temperature in the furnace to obtain the precursor.

[0041] Step 8: Place the precursor obtained in step 7 into a beaker containing 100ml of aqueous solution, then place the beaker into an ultrasonic cleaner, set the heating temperature to 40℃ and the time to 2h. After cleaning, take out the sample and place it in a vacuum drying oven to dry at 60℃ for 1h to obtain the desired open-cell aluminum foam.

[0042] Figure 1 This is a schematic diagram of the mold used for pressing and molding in this embodiment.

[0043] Figure 2 The image shows a photograph of the open-cell aluminum foam obtained in this embodiment. As can be seen from the image, the prepared open-cell aluminum foam has very small and uniformly distributed pores, with no residual NaCl particles, indicating that the pore-forming agent particles have been fully dissolved.

[0044] Figure 3 The image shows a microscopic photograph of the open-cell aluminum foam obtained in this embodiment. As can be seen from the image, the pores are interconnected, the porosity is high, and the shape of the obtained pores is consistent with that of the NaCl particles used.

[0045] Example 2

[0046] Step 1: Prepare raw materials: In this embodiment, analytical grade cubic sodium chloride granules are selected as the pore-forming agent, with a purity of 99.5% and a density of 2.165 g / cm³. 3 Analytical grade aluminum powder with a purity of 97% and a density of 2.70 g / cm³ was selected. 3 .

[0047] The second step is to prepare aluminum foam with a porosity of 70%, that is, the volume fraction of NaCl particles is 70%. After calculation, the required mass of NaCl particles is 14.28g and the mass of aluminum powder is 7.63g.

[0048] The third step is to place the weighed NaCl particles and aluminum powder into separate desiccators and dry them in a vacuum drying oven at 60°C for 1 hour before use.

[0049] Fourth step: Divide the dried aluminum powder and NaCl into two equal portions by mass and place them into two separate ball mill jars. Simultaneously, add grinding balls of Φ6mm diameter to each jar at a ball-to-powder ratio of 3:1. Connect a vacuum pump to the ball mill jars and evacuate to a vacuum level of 10. -3 After vacuuming, close the air extraction channel on the grinding jars; then place the two grinding jars into the planetary ball mill, close the cover and set the operating mode, set the ball mill speed to 300 r / min, the ball milling time to 4 h, and alternate between forward and reverse rotation every 5 min, with the interval between alternating operations set to 15 min. After setting the operating mode as described above, start the motor to perform ball milling.

[0050] Fifth step: After ball milling, use a 100-mesh sieve to separate the raw material obtained in the fourth step from the grinding balls to obtain a mixed powder of aluminum powder and NaCl particles. Then, put the mixed powder into a vacuum bag and seal it for later use.

[0051] The sixth step is to coat the inner surface of the designed steel mold with a layer of graphite powder, then pour the mixed powder of aluminum powder and pore-forming agent particles from the fifth step into the steel mold, vibrate it evenly, and then place it on a pressure testing machine to apply an axial pressure of 565kN at a speed of 0.1kN / s and hold the pressure for 3 minutes. After demolding, a preform of a certain shape is obtained.

[0052] Step 7: Place the preform obtained in step 6 into a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level of 10. -3 Pa was heated to 640℃ at a heating rate of 8℃ / min and held at that temperature for 3 hours before being cooled to room temperature in the furnace to obtain the precursor.

[0053] Step 8: Place the precursor obtained in step 7 into a beaker containing 200ml of aqueous solution, then place the beaker into an ultrasonic cleaner, set the heating temperature to 40℃ and the time to 1h. After cleaning, take out the sample and place it in a vacuum drying oven to dry at 60℃ for 1h to obtain the desired open-cell aluminum foam.

[0054] Example 3

[0055] Step 1: Prepare raw materials: In this embodiment, analytical grade cubic sodium chloride granules are selected as the pore-forming agent, with a purity of 99.5% and a density of 2.165 g / cm³. 3 Analytical grade aluminum powder with a purity of 97% and a density of 2.70 g / cm³ was selected. 3 .

[0056] The second step is to prepare aluminum foam with a porosity of 80%, that is, the volume fraction of NaCl particles is 80%. After calculation, the required mass of NaCl particles is 16.33g and the mass of aluminum powder is 5.09g.

[0057] The third step is to place the weighed NaCl particles and aluminum powder into separate desiccators and dry them in a vacuum drying oven at 60°C for 1 hour before use.

[0058] Fourth step: Divide the dried aluminum powder and NaCl into two equal portions by mass and place them into two separate ball mill jars. Simultaneously, add grinding balls of Φ6mm diameter to each jar at a ball-to-powder ratio of 3:1. Connect a vacuum pump to the ball mill jars and evacuate to a vacuum level of 10. -3 After vacuuming, close the air extraction channel on the grinding jars; then place the two grinding jars into the planetary ball mill, close the cover and set the operating mode, setting the ball mill speed to 250 r / min, the ball milling time to 5 h, and alternating forward and reverse operation every 10 min, with the alternation interval set to 15 min. After setting the operating mode as described above, start the motor to perform ball milling.

[0059] Fifth step: After ball milling, use a 100-mesh sieve to separate the raw material obtained in the fourth step from the grinding balls to obtain a mixed powder of aluminum powder and NaCl particles. Then, put the mixed powder into a vacuum bag and seal it for later use.

[0060] The sixth step is to coat the inner surface of the designed steel mold with a layer of graphite powder, then pour the mixed powder of aluminum powder and pore-forming agent particles from the fifth step into the steel mold, vibrate it evenly, and then place it on a pressure testing machine to apply an axial pressure of 565kN at a speed of 0.1kN / s and hold the pressure for 3 minutes. After demolding, a preform of a certain shape is obtained.

[0061] Step 7: Place the preform obtained in step 6 into a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level of 10. -3 Pa was heated to 650°C at a heating rate of 8°C / min and held at that temperature for 3 hours before being cooled to room temperature in the furnace to obtain the precursor.

[0062] Step 8: Place the precursor obtained in step 7 into a beaker containing 300ml of aqueous solution, then place the beaker into an ultrasonic cleaner, set the heating temperature to 40℃ and the time to 1h. After cleaning, take out the sample and place it in a vacuum drying oven to dry at 60℃ for 1h to obtain the desired open-cell aluminum foam.

[0063] As can be seen from the above examples, by adjusting the mass fraction of the pore-forming agent and aluminum powder, open-cell aluminum foam with different porosities was prepared, realizing quantitative control of the porosity of open-cell aluminum foam. From the actual images of the open-cell aluminum foam, it can be seen that the sintered aluminum powder is tightly bonded, the pore-forming agent particles are completely dissolved, and the pores are evenly distributed without agglomeration, indicating that the aluminum powder and pore-forming agent particles are evenly distributed after ball milling, resulting in good molding effect. From the microscopic images, it can be seen that the shape of the pores completely replicates the shape of the pore-forming agent particles, and there are interconnected channels between the pores, ensuring the connectivity between the pores of the open-cell aluminum foam.

[0064] Matters not covered in this invention are common knowledge.

Claims

1. A method for preparing open-cell aluminum foam, characterized in that the method includes the following steps: The first step is to place the weighed aluminum powder and pore-forming agent granules into desiccators and dry them in a vacuum drying oven at 60-80°C for 1-2 hours. The volume of the pore-forming agent is 50-80% of the sum of the volumes of the aluminum powder and the pore-forming agent; the pore-forming agent is one or more of sodium chloride, calcium chloride, urea, or sucrose. The second step involves mixing the dried aluminum powder from the third step with the pore-forming agent and placing the mixture into a ball mill jar, sealing it under a vacuum of 10. -2 ~10 -3 The ball milling time under Pa is 3 to 5 hours. After setting the operating mode as described above, start the motor to perform ball milling. in, The diameter of the grinding balls is 4-8 mm; the ball-to-material ratio is 3:1; during the ball milling process, the forward and reverse rotations alternate every 5-15 minutes, with the interval between alternations set to 5-15 minutes. The third step is to separate the raw material from the grinding balls using a 100-300 mesh sieve after ball milling to obtain a mixed powder of aluminum powder and pore-forming agent particles. The mixed powder is then placed in a vacuum bag and sealed for later use. The fourth step is to pour the mixture of aluminum powder and pore-forming agent particles from the fifth step into a steel mold, vibrate it evenly, and then place it on a pressure testing machine. The axial pressure is 300-400 MPa, and the holding time is 3-5 minutes. After demolding, a preform is obtained. The fifth step is to place the preform into a vacuum sintering furnace, close the furnace door, and evacuate to a vacuum level of 10. -2 ~10 -3 Pa, heated to 600-650℃ at a heating rate of 5-8℃ / min and held for 2-3 hours, then cooled to room temperature in the furnace to obtain the precursor; Step 6: Place the precursor in an aqueous solution, then place it in an ultrasonic cleaner, set the heating temperature to 40℃, and the time to 1-2 hours. After cleaning, take out the sample and place it in a vacuum drying oven at 60-80℃ for 1-2 hours to obtain the desired open-cell foam. The particle size range of the pore-forming agent is 1-2 mm, and the shape can be spherical, cubic or irregular. The aluminum powder has a particle size of 100-300 μm and is stored in a sealed container under vacuum. In the second step described above, the ball mill speed is 250–300 r / min.

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