A method for preparing high-uniformity foamed aluminum by blowing

Abstract

This invention relates to the field of aluminum foam technology and discloses a method for preparing highly uniform aluminum foam by blowing, comprising the following steps: (1) raw material preparation; (2) smelting treatment; (3) setting up the blowing device; (4) blowing and foaming; (5) cooling and molding; (6) post-treatment. This invention achieves full-process control from bubble nucleation, growth, shaping to finished product molding through the synergistic matching of raw material pretreatment, composite foam stabilization, combined stirring, bubble homogenization, segmented cooling and post-treatment, significantly improving the uniformity and comprehensive performance of aluminum foam. The solution of this invention fundamentally solves the problems of uneven bubble cell size, low closed-cell rate, fluctuating mechanical properties and large dimensional deviation in the traditional blowing method through the synergistic effect of each step and parameter, and finally obtains highly uniform aluminum foam with uniform bubble cell size, excellent mechanical properties, high dimensional accuracy and good appearance quality, meeting the needs of high-end application scenarios.

Description

Technical Field

[0001] This invention relates to the field of aluminum foam technology, specifically a method for preparing highly uniform aluminum foam by blowing air. Background Technology

[0002] Aluminum foam, a porous metallic material with multiple advantages such as lightweight, high specific strength, energy absorption and cushioning, sound insulation and noise reduction, and electromagnetic shielding, is widely used in rail transportation, aerospace, automobile manufacturing, building vibration reduction, and electronic equipment packaging. The air-blowing method, due to its short process flow, high production efficiency, and ease of large-scale manufacturing, has become the mainstream technical route for the industrial production of aluminum foam.

[0003] The traditional blowing method still has significant technical problems in actual production: First, the dispersion uniformity of the foaming agent and foam stabilizing components in the aluminum melt is insufficient, which easily leads to local agglomeration, uncontrolled bubble nucleation and growth, resulting in large differences in bubble size, low closed-cell rate, and poor structural consistency. Second, it is difficult to achieve uniform mixing of the entire melt by simply relying on mechanical stirring. The temperature field and component field in the melt have gradients, which further aggravates the dispersion of bubble distribution. Third, the lack of homogenization constraints during the rise of bubbles makes them prone to merging, growing, and breaking, forming interconnected holes or local collapse. Fourth, the cooling process is mostly natural cooling, and the cooling rate inside and outside the billet is mismatched, resulting in internal stress and dimensional deformation. The final product's uniformity, mechanical stability, and appearance quality are difficult to meet the requirements of high-end equipment for high-precision and high-consistency foamed aluminum components.

[0004] Therefore, developing a foam aluminum blowing technology with uniform cell distribution, stable structure, excellent mechanical properties, and high dimensional consistency has become a key issue that urgently needs to be addressed in the industry. Summary of the Invention

[0005] To address the problems in the prior art, this invention provides a method for preparing highly uniform aluminum foam by blowing.

[0006] The technical solution adopted by this invention to solve its technical problem is: a method for preparing highly uniform aluminum foam by blowing, comprising the following steps: (1) Raw material preparation: High-purity aluminum ingots are selected as the base material, and foaming agent and composite foam stabilizing system are added and mixed evenly to obtain a raw material mixture; the composite foam stabilizing system is composed of silicon carbide particles and nano alumina particles, and the nano alumina particles are surface modified by silane coupling agent; the foaming agent is pretreated by vacuum drying. (2) Smelting process: The raw material mixture is placed in a smelting furnace and heated until the aluminum ingot is completely melted. The mixture is stirred evenly by a combination of mechanical stirring and electromagnetic stirring to make the foaming agent and composite foam stabilizing system evenly dispersed in the aluminum melt, so as to obtain an aluminum-based melt with uniform composition. (3) Setting of air blowing device: Use air blowing head and immerse the air blowing head into the bottom of the aluminum-based melt to a preset depth; set the bubble homogenization component at a preset position below the surface of the aluminum-based melt; (4) Blowing and foaming: Inert gas is introduced into the blowing head, and the blowing pressure, initial value of gas flow rate and blowing time are controlled to keep the temperature of aluminum-based melt stable and promote the uniform growth of bubbles to the preset size. (5) Cooling and molding: The foamed aluminum-based melt is cooled to room temperature in a segmented uniform cooling method. During the cooling process, a combination of water bath cooling and furnace insulation is used to ensure that the foamed aluminum billet is cooled evenly in all parts, resulting in a highly uniform foamed aluminum billet. (6) Post-processing: The aluminum foam blank is surface trimmed and homogenized by heat treatment to finally obtain a high-uniformity aluminum foam finished product.

[0007] As a further technical solution, in step (1), the purity of the high-purity aluminum ingot is ≥99.8%; the foaming agent is aluminum titanium hydride with a particle size of 20-50μm and an addition amount of 0.4-0.7wt% of the aluminum ingot mass; the composite foam stabilizing system is composed of silicon carbide particles and nano-alumina particles in a mass ratio of 3-5:1, wherein the particle size of the silicon carbide particles is 15-40μm, the particle size of the nano-alumina particles is 50-100nm, and the total addition amount of the composite foam stabilizing system is 1.5-2.5wt% of the aluminum ingot mass; the mixing is carried out using a high-speed mixer with a mixing temperature of 25-30℃, a rotation speed of 800-1000rpm, and a mixing time of 10-15min.

[0008] As a further technical solution, in step (1), the silane coupling agent is KH-550, and the modification process is as follows: the nano-alumina particles are placed in a silane coupling agent ethanol solution with a mass fraction of 2-3%, ultrasonically dispersed at 25-30℃ for 30-40 min, and then dried at 110-120℃ for 2-3 h for later use. The amount of silane coupling agent added is 1.5-2.5 wt% of the mass of the nano-alumina particles; the vacuum drying pretreatment of titanium hydride is performed with a vacuum degree of 0.06-0.08 MPa, a drying temperature of 85-95℃, and a drying time of 2.0-2.8 h. The moisture content after pretreatment is ≤0.1 wt%.

[0009] As a further technical solution, in step (2), the smelting furnace is a resistance smelting furnace with a rated power of 50-100kW, an inner diameter of 30-50cm, and an argon protective atmosphere inside the furnace; the heating rate is 10-15℃ / min, and the smelting temperature is 730-750℃; the mechanical stirring adopts a paddle stirrer with paddles made of heat-resistant alloy material, a diameter of 15-20mm, an insertion depth of 3-5cm into the molten aluminum, and a stirring speed of 350-450rpm; the electromagnetic stirring adopts a low-frequency electromagnetic stirrer with a frequency of 50-60Hz, a stirring intensity of 0.3-0.4T, an adjustment accuracy of 0.05T, and a stirring direction opposite to the mechanical stirring direction; the total stirring time is 12-14min, and the furnace temperature is recorded every 2min during the stirring process, with a temperature fluctuation ≤±2℃.

[0010] As a further technical solution, in step (3), the air blowing head is made of heat-resistant stainless steel with a heat resistance temperature ≥800℃, has a cylindrical structure, a diameter of 20-30mm and a length of 50-80mm, and 10-20 air holes with a diameter of 0.5-1.0mm are evenly distributed on the surface. The air holes are arranged in a regular hexagonal array with a hole spacing of 5-8mm and a hole wall thickness of 0.3-0.5mm. The air blowing head is vertically immersed into the aluminum-based melt to a depth of 6-9cm, and the distance between the air holes and the bottom of the melting furnace is ≥4cm.

[0011] As a further technical solution, in step (3), the bubble homogenization component is set 5-8cm below the surface of the aluminum-based melt. The material is corundum high-temperature resistant ceramic with a high temperature resistance of ≥1200℃ and a thickness of 10-15mm. The ratio of the component diameter to the inner diameter of the furnace chamber is 1:3-4, and the distance between the edge of the component and the inner wall of the furnace chamber is 5-8cm. The holes are distributed in a regular hexagonal shape, with a hole wall thickness of 0.2-0.3mm and a hole diameter of 0.8-1.2mm, which is 1.2-1.8 times the diameter of the air vent of the blowing head.

[0012] As a further technical solution, in step (4), the inert gas is argon, which is introduced after drying and impurity removal, and the moisture content in the gas is ≤10ppm and the impurity content is ≤5ppm.

[0013] As a further technical solution, in step (4), the blowing pressure is controlled at 0.1-0.3MPa, the gas flow rate is 5-15L / min, the blowing time is 3-8min, and the foaming temperature is maintained at 680-720℃ with temperature fluctuation ≤±5℃.

[0014] As a further technical solution, in step (5), the segmented uniform cooling is specifically as follows: in the first stage, the temperature is cooled from the foaming temperature to 500℃ at a rate of 12-14℃ / min, and the water bath temperature is maintained at 30-35℃; in the second stage, the temperature is cooled from 500℃ to room temperature at a rate of 6-7℃ / min, and the water bath temperature is maintained at 25-30℃; the water bath uses deionized water, and the ratio of the water bath volume to the volume of the foamed aluminum billet is 5-8:1.

[0015] As a further technical solution, in step (6), the surface finishing adopts wet mechanical grinding with a grinding wheel grit of 80-120 mesh and a grinding speed of 15-20 m / min to remove 1.2-1.8 mm of uneven surface layer on the blank surface. After grinding, the surface roughness Ra≤1.6 μm. Deionized water is used for cooling during the grinding process. The homogenization heat treatment adopts a box-type resistance furnace with a temperature control accuracy of ±1℃, a heating rate of 5-8℃ / min, a heat treatment temperature of 320-340℃, a holding time of 1.2-1.8h, and a holding temperature fluctuation ≤±2℃. After heat treatment, the furnace is cooled with a cooling rate ≤5℃ / min.

[0016] The beneficial effects of this invention are: 1. This invention achieves full-process control from bubble nucleation, growth, shaping to finished product molding through the coordinated matching of raw material pretreatment, composite foam stabilization, combined stirring, bubble homogenization, segmented cooling and post-treatment, which significantly improves the uniformity and comprehensive performance of aluminum foam.

[0017] 2. In the raw material and melt control stage, high-purity aluminum ingots are selected to ensure the purity of the matrix composition and reduce the interference of impurities on bubble growth; vacuum drying pretreatment of titanium hydride effectively reduces the moisture content of the foaming agent, avoids defects such as pores and pinholes caused by moisture, and improves the stability of the foaming process; a foam stabilizing system is formed by combining nano-alumina modified with silane coupling agent and silicon carbide. The modified nano-alumina can be uniformly dispersed in the aluminum melt and adsorbed at the bubble interface, improving the strength and stability of the bubble film. Silicon carbide particles act as a skeleton support phase to prevent bubble merging and rupture. The two are compounded in a specific ratio to synergistically stabilize the bubble structure and reduce the coefficient of variation of bubble diameter; the combination of mechanical stirring and reverse electromagnetic stirring can form a global convection field in the aluminum melt, eliminate local concentration gradients and temperature gradients, and make the foaming agent and the foam stabilizing system uniformly dispersed, providing a stable environment for uniform nucleation and growth of bubbles.

[0018] 3. In the bubble control and cooling forming stage, a specially structured air blowing head can output uniform and stable small bubbles. Combined with a bubble homogenizing component below the liquid surface, the rising bubbles are further regularized, reducing the difference in bubble size and improving overall uniformity. Segmented uniform cooling combined with water bath and furnace insulation ensures that the cooling rates inside and outside the billet are matched, reducing internal stress and deformation, and ensuring dimensional accuracy and structural stability. Subsequent wet polishing and homogenization heat treatment can eliminate surface defects and internal residual stress, improving surface quality and mechanical property stability. This invention, through the synergistic effect of various steps and parameters, fundamentally solves the problems of uneven bubble size, low closed-cell rate, fluctuating mechanical properties, and large dimensional deviations in traditional air blowing methods. Ultimately, it obtains highly uniform aluminum foam with uniform bubbles, excellent mechanical properties, high dimensional accuracy, and good appearance quality, meeting the needs of high-end applications. Detailed Implementation

[0019] The technical solutions in the embodiments of the present invention will be clearly and completely described below. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0020] This invention provides a method for preparing highly uniform aluminum foam by blowing, comprising the following steps: (1) Raw material preparation: High-purity aluminum ingots are selected as the base material, and foaming agent and composite foam stabilizing system are added and mixed evenly to obtain a raw material mixture; the composite foam stabilizing system is composed of silicon carbide particles and nano alumina particles, and the nano alumina particles are surface modified by silane coupling agent; the foaming agent is pretreated by vacuum drying.

[0021] (2) Smelting process: The raw material mixture is placed in a smelting furnace and heated until the aluminum ingot is completely melted. The mixture is stirred evenly by a combination of mechanical stirring and electromagnetic stirring to disperse the foaming agent and the composite foam stabilizing system evenly in the aluminum melt, so as to obtain an aluminum-based melt with uniform composition.

[0022] (3) Setting of air blowing device: Use air blowing head and immerse the air blowing head into the bottom of the aluminum-based melt to a preset depth; set the bubble homogenization component at a preset position below the surface of the aluminum-based melt.

[0023] (4) Blowing and foaming: Inert gas is introduced into the blowing head, and the blowing pressure, initial value of gas flow rate and blowing time are controlled to keep the temperature of aluminum-based melt stable and promote the uniform growth of bubbles to the preset size.

[0024] (5) Cooling and molding: The foamed aluminum-based melt is cooled to room temperature in a segmented and uniform manner. During the cooling process, a combination of water bath cooling and furnace insulation is used to ensure that the foamed aluminum billet is cooled evenly in all parts, resulting in a highly uniform foamed aluminum billet.

[0025] (6) Post-processing: The aluminum foam blank is surface trimmed and homogenized by heat treatment to finally obtain a high-uniformity aluminum foam finished product.

[0026] In this invention, the purity of the high-purity aluminum ingot is preferably greater than or equal to 99.8%. The foaming agent is preferably aluminum titanate, with a particle size of 20-50 μm, and the addition amount is preferably 0.4-0.7 wt% of the aluminum ingot mass. The composite foam stabilizing system is composed of silicon carbide particles and nano-alumina particles in a mass ratio of 3-5:1, wherein the particle size of the silicon carbide particles is preferably 15-40 μm, the particle size of the nano-alumina particles is preferably 50-100 nm, and the total addition amount of the composite foam stabilizing system is preferably 1.5-2.5 wt% of the aluminum ingot mass. Mixing is performed using a high-speed mixer, with a mixing temperature of preferably 25-30℃, a rotation speed of preferably 800-1000 rpm, and a mixing time of preferably 10-15 min.

[0027] In this invention, the preferred silane coupling agent is KH-550. The modification process is as follows: nano-alumina particles are placed in a 2-3% (w / w) silane coupling agent ethanol solution and ultrasonically dispersed at 25-30°C for 30-40 min, followed by drying at 110-120°C for 2-3 h. The preferred amount of silane coupling agent is 1.5-2.5 wt% of the mass of the nano-alumina particles. For the vacuum drying pretreatment of aluminum hydride, the preferred vacuum degree of the vacuum drying oven is 0.06-0.08 MPa, the preferred drying temperature is 85-95°C, and the preferred drying time is 2.0-2.8 h. The preferred moisture content after pretreatment is less than or equal to 0.1 wt%.

[0028] In this invention, the melting furnace is preferably a resistance melting furnace with a rated power of 50-100kW and an inner diameter of 30-50cm, and the furnace is filled with an argon protective atmosphere. The heating rate is preferably 10-15℃ / min, and the melting temperature is preferably 730-750℃. Mechanical stirring uses a paddle-type stirrer with blades made of heat-resistant alloy material, preferably 15-20mm in diameter, inserted into the molten aluminum to a depth of 3-5cm, and a stirring speed of 350-450rpm. Electromagnetic stirring uses a low-frequency electromagnetic stirrer with a frequency of 50-60Hz, a stirring intensity of 0.3-0.4T, an adjustment accuracy of 0.05T, and a stirring direction opposite to that of mechanical stirring. The total stirring time is preferably 12-14min, and the furnace temperature is recorded every 2min during stirring, with temperature fluctuation preferably less than or equal to ±2℃.

[0029] In this invention, the air blowing head is made of heat-resistant stainless steel, preferably with a heat resistance temperature of ≥800℃. It has a cylindrical structure with a diameter of 20-30mm and a length of 50-80mm. The surface has 10-20 evenly distributed vent holes with a diameter of 0.5-1.0mm, arranged in a regular hexagonal array. The hole spacing is preferably 5-8mm, and the hole wall thickness is preferably 0.3-0.5mm. The air blowing head is vertically immersed in the molten aluminum to a depth of 6-9cm, and the distance between the vent holes and the bottom of the melting furnace is preferably ≥4cm.

[0030] In this invention, the bubble homogenizing component is positioned 5-8 cm below the surface of the aluminum-based molten metal. It is made of corundum high-temperature resistant ceramic, preferably with a high-temperature resistance of ≥1200℃, and a thickness of 10-15 mm. The ratio of the component diameter to the inner diameter of the furnace chamber is preferably 1:3-4, and the distance between the edge of the component and the inner wall of the furnace chamber is preferably 5-8 cm. The holes are distributed in a regular hexagonal pattern, with a hole wall thickness preferably of 0.2-0.3 mm and a hole diameter preferably of 0.8-1.2 mm, which is 1.2-1.8 times the diameter of the air vent hole in the blowing head.

[0031] In this invention, the inert gas is preferably argon, which is introduced after being dried and purified. The moisture content in the gas is preferably less than or equal to 10 ppm and the impurity content is preferably less than or equal to 5 ppm.

[0032] In this invention, the blowing pressure is preferably controlled at 0.1-0.3 MPa, and the gas flow rate is preferably 5-15 L / min. The blowing time is preferably 3-8 min. The foaming temperature is preferably maintained at 680-720℃, and the temperature fluctuation is preferably less than or equal to ±5℃.

[0033] In this invention, the segmented uniform cooling specifically comprises: a first stage cooling from the foaming temperature to 500°C at a rate of 12-14°C / min, with the water bath temperature preferably maintained at 30-35°C; and a second stage cooling from 500°C to room temperature at a rate of 6-7°C / min, with the water bath temperature preferably maintained at 25-30°C. Deionized water is used in the water bath, and the ratio of the water bath volume to the volume of the foamed aluminum billet is preferably 5-8:1.

[0034] In this invention, surface finishing is performed using wet mechanical grinding, with a preferred grinding wheel grit size of 80-120 mesh and a preferred grinding speed of 15-20 m / min. This removes a 1.2-1.8 mm uneven surface layer from the blank, and the surface roughness Ra after grinding is preferably less than or equal to 1.6 μm. Deionized water is used for cooling during the grinding process. Homogenization heat treatment is performed using a box-type resistance furnace with a temperature control accuracy of ±1℃, a preferred heating rate of 5-8℃ / min, a preferred heat treatment temperature of 320-340℃, a preferred holding time of 1.2-1.8 h, and a preferred temperature fluctuation of less than or equal to ±2℃. After heat treatment, the furnace is cooled, with a preferred cooling rate of less than or equal to 5℃ / min.

[0035] The preparation method provided by this invention significantly improves the cell uniformity, structural stability and mechanical properties of aluminum foam through the synergistic effect of a composite foam stabilizing system, combined stirring, bubble homogenization components, segmented uniform cooling and precise post-processing. It solves the problems of uneven cell size, excessively high connectivity, local collapse and large performance dispersion in traditional blowing methods, and achieves stable preparation of highly uniform aluminum foam.

[0036] To further illustrate the present invention, the following detailed description is provided through the examples and comparative examples.

[0037] Example 1:

[0038] (1) Raw material preparation: High-purity aluminum ingots with a purity of 99.8% were selected as the base material, and aluminum hydride was used as the foaming agent. The particle size of aluminum hydride was 20 μm, and the addition amount was 0.4 wt% of the aluminum ingot mass. The composite foam stabilizing system was composed of silicon carbide particles and nano-alumina particles in a mass ratio of 3:1. The particle size of silicon carbide particles was 15 μm, and the particle size of nano-alumina particles was 50 nm. The total addition amount of the composite foam stabilizing system was 1.5 wt% of the aluminum ingot mass. The nano-alumina particles were placed in a 2% KH-550 silane coupling agent ethanol solution and ultrasonically dispersed at 25℃ for 30 min. Then, they were dried at 110℃ for 2 h for later use. The addition amount of silane coupling agent was 1.5 wt% of the nano-alumina particle mass. The aluminum hydride was placed in a vacuum drying oven and pretreated at a vacuum degree of 0.06 MPa, a drying temperature of 85℃, and a drying time of 2.0 h. The moisture content after pretreatment was ≤0.1 wt%. Aluminum ingots, pretreated foaming agent, and composite foam stabilizing system are added to a high-speed mixer. The mixing temperature is 25℃, the speed is 800rpm, and the mixing time is 10min. The mixture is then homogeneous to obtain the raw material mixture.

[0039] (2) Melting process: The raw material mixture was placed in a resistance melting furnace with a rated power of 50kW and an inner diameter of 30cm. The furnace was filled with an argon protective atmosphere. The mixture was heated to 730℃ at a heating rate of 10℃ / min until the aluminum ingots were completely melted. Mechanical stirring was performed using a paddle-type stirrer with heat-resistant alloy blades, 15mm in diameter, inserted 3cm into the molten aluminum, and a stirring speed of 350rpm. Electromagnetic stirring was performed using a low-frequency electromagnetic stirrer with a frequency of 50Hz, a stirring intensity of 0.3T, and an adjustment accuracy of 0.05T. The stirring direction was opposite to the mechanical stirring direction. The total stirring time was 12min. The furnace temperature was recorded every 2min during the stirring process, with temperature fluctuations ≤±2℃, resulting in a uniformly composed aluminum-based melt.

[0040] (3) Air blowing device setup: A heat-resistant stainless steel air blowing head with a heat resistance temperature ≥800℃ is used. It has a cylindrical structure with a diameter of 20mm and a length of 50mm. Ten air vents with a diameter of 0.5mm are evenly distributed on the surface. The air vents are arranged in a regular hexagonal array with a spacing of 5mm and a wall thickness of 0.3mm. The air blowing head is vertically immersed into the bottom of the aluminum-based melt to a depth of 6cm. The distance between the air vents and the bottom of the melting furnace is ≥4cm. A bubble homogenizing component is set 5cm below the surface of the aluminum-based melt. The component is made of corundum high-temperature resistant ceramic with a heat resistance temperature ≥1200℃ and a thickness of 10mm. The ratio of the component diameter to the furnace inner diameter is 1:3, and the distance between the edge of the component and the inner wall of the furnace is 5cm. The holes of the component are distributed in a regular hexagonal array with a wall thickness of 0.2mm and a diameter of 0.8mm, which is 1.6 times the diameter of the air vents of the air blowing head.

[0041] (4) Gas blowing and foaming: Dry and impurity-removed argon gas is introduced into the blowing head. The moisture content of the gas is ≤10ppm and the impurity content is ≤5ppm. The blowing pressure is controlled at 0.1MPa, the gas flow rate is 5L / min, the blowing time is 3min, and the foaming temperature is maintained at 680℃ with a temperature fluctuation of ≤±5℃ to promote the uniform growth of bubbles to the preset size.

[0042] (5) Cooling and forming: A segmented uniform cooling method is adopted. In the first stage, the temperature is cooled from 680°C to 500°C at a rate of 12°C / min, while the water bath temperature is maintained at 30°C. In the second stage, the temperature is cooled from 500°C to room temperature at a rate of 6°C / min, while the water bath temperature is maintained at 25°C. Deionized water is used in the water bath, and the volume ratio of the water bath to the foamed aluminum billet is 5:1 to obtain a highly uniform foamed aluminum billet.

[0043] (6) Post-treatment: The surface is finished by wet mechanical grinding with an 80-mesh abrasive wheel at a grinding speed of 15 m / min. The 1.2 mm uneven surface layer is removed from the billet. Deionized water is used for cooling during the grinding process. The surface roughness Ra after grinding is ≤1.6 μm. The finished billet is placed in a box-type resistance furnace for homogenization heat treatment with a temperature control accuracy of ±1℃. The temperature is increased to 320℃ at a rate of 5℃ / min and held for 1.2 h with a holding temperature fluctuation of ≤±2℃. Then, it is cooled with the furnace at a cooling rate of ≤5℃ / min to finally obtain a high-uniformity aluminum foam product.

[0044] Example 2:

[0045] (1) Raw material preparation: High-purity aluminum ingots with a purity of 99.8% were selected as the base material, and aluminum hydride was used as the foaming agent. The particle size of aluminum hydride was 50 μm, and the addition amount was 0.7 wt% of the aluminum ingot mass. The composite foam stabilizing system was composed of silicon carbide particles and nano-alumina particles in a mass ratio of 5:1. The particle size of silicon carbide particles was 40 μm, and the particle size of nano-alumina particles was 100 nm. The total addition amount of the composite foam stabilizing system was 2.5 wt% of the aluminum ingot mass. The nano-alumina particles were placed in a 3% KH-550 silane coupling agent ethanol solution and ultrasonically dispersed at 30℃ for 40 min. Then, they were dried at 120℃ for 3 h for later use. The addition amount of silane coupling agent was 2.5 wt% of the nano-alumina particle mass. The aluminum hydride was placed in a vacuum drying oven and pretreated at a vacuum degree of 0.08 MPa, a drying temperature of 95℃, and a drying time of 2.8 h. The moisture content after pretreatment was ≤0.1 wt%. Aluminum ingots, pretreated foaming agent, and composite foam stabilizing system are added to a high-speed mixer. The mixing temperature is 30℃, the speed is 1000rpm, and the mixing time is 15min. The mixture is mixed evenly to obtain the raw material mixture.

[0046] (2) Melting process: The raw material mixture was placed in a resistance melting furnace with a rated power of 100kW and an inner diameter of 50cm. The furnace was filled with an argon protective atmosphere. The temperature was increased to 750℃ at a rate of 15℃ / min until the aluminum ingot was completely melted. Mechanical stirring was performed using a paddle-type stirrer with heat-resistant alloy blades, 20mm in diameter, inserted 5cm into the molten aluminum, and a stirring speed of 450rpm. Electromagnetic stirring was performed using a low-frequency electromagnetic stirrer with a frequency of 60Hz, a stirring intensity of 0.4T, and an adjustment accuracy of 0.05T. The stirring direction was opposite to the mechanical stirring direction. The total stirring time was 14min. The furnace temperature was recorded every 2min during the stirring process, with temperature fluctuations ≤±2℃, resulting in a uniformly composed aluminum-based melt.

[0047] (3) Air blowing device setup: A heat-resistant stainless steel air blowing head with a heat resistance temperature ≥800℃ is used. It has a cylindrical structure with a diameter of 30mm and a length of 80mm. Twenty 1.0mm diameter vent holes are evenly distributed on the surface, arranged in a regular hexagonal array with a hole spacing of 8mm and a hole wall thickness of 0.5mm. The air blowing head is vertically immersed to the bottom of the aluminum-based melt to a depth of 9cm, with the distance between the vent holes and the bottom of the melting furnace ≥4cm. A bubble homogenizing component is set 8cm below the surface of the aluminum-based melt. The component is made of corundum high-temperature resistant ceramic with a heat resistance temperature ≥1200℃ and a thickness of 15mm. The component diameter is in a 1:4 ratio to the furnace inner diameter, and the distance between the component edge and the furnace inner wall is 8cm. The component holes are distributed in a regular hexagonal array with a hole wall thickness of 0.3mm and a hole diameter of 1.2mm, which is 1.2 times the diameter of the air blowing head's vent holes.

[0048] (4) Gas blowing and foaming: Dry and impurity-removed argon gas is introduced into the blowing head. The moisture content in the gas is ≤10ppm and the impurity content is ≤5ppm. The blowing pressure is controlled at 0.3MPa, the gas flow rate is 15L / min, the blowing time is 8min, and the foaming temperature is maintained at 720℃ with a temperature fluctuation of ≤±5℃ to promote the uniform growth of bubbles to the preset size.

[0049] (5) Cooling and forming: A segmented uniform cooling method is adopted. In the first stage, the temperature is cooled from 720°C to 500°C at a rate of 14°C / min, while the water bath temperature is maintained at 35°C. In the second stage, the temperature is cooled from 500°C to room temperature at a rate of 7°C / min, while the water bath temperature is maintained at 30°C. Deionized water is used in the water bath, and the volume ratio of the water bath to the foamed aluminum billet is 8:1 to obtain a highly uniform foamed aluminum billet.

[0050] (6) Post-treatment: The surface is finished by wet mechanical grinding with a grinding wheel of 120 mesh and a grinding speed of 20 m / min. The 1.8 mm uneven surface layer is removed from the blank. The grinding process is cooled with deionized water. The surface roughness Ra after grinding is ≤1.6 μm. The finished blank is placed in a box-type resistance furnace for homogenization heat treatment with a temperature control accuracy of ±1℃. The temperature is increased to 340℃ at 8℃ / min and held for 1.8 h with a holding temperature fluctuation of ≤±2℃. Then it is cooled with the furnace at a cooling rate of ≤5℃ / min to finally obtain a high-uniformity aluminum foam product.

[0051] Example 3:

[0052] (1) Raw material preparation: High-purity aluminum ingots with a purity of 99.9% were selected as the base material, and aluminum hydride was used as the foaming agent. The particle size of aluminum hydride was 35μm, and the addition amount was 0.55wt% of the aluminum ingot mass. The composite foam stabilizing system was composed of silicon carbide particles and nano-alumina particles in a mass ratio of 4:1. The particle size of silicon carbide particles was 27μm, and the particle size of nano-alumina particles was 75nm. The total addition amount of the composite foam stabilizing system was 2.0wt% of the aluminum ingot mass. The nano-alumina particles were placed in a 2.5% KH-550 silane coupling agent ethanol solution and ultrasonically dispersed at 27℃ for 35min. Then, they were dried at 115℃ for 2.5h for later use. The addition amount of silane coupling agent was 2.0wt% of the nano-alumina particle mass. The aluminum hydride was placed in a vacuum drying oven and pretreated at a vacuum degree of 0.07MPa, a drying temperature of 90℃, and a drying time of 2.4h. The moisture content after pretreatment was ≤0.1wt%. Aluminum ingots, pretreated foaming agent, and composite foam stabilizing system are added to a high-speed mixer. The mixing temperature is 27℃, the speed is 900rpm, and the mixing time is 12min. The mixture is then homogeneous to obtain the raw material mixture.

[0053] (2) Melting process: The raw material mixture was placed in a resistance melting furnace with a rated power of 75kW and an inner diameter of 40cm. The furnace was filled with an argon protective atmosphere. The temperature was increased to 740℃ at a rate of 12℃ / min until the aluminum ingot was completely melted. Mechanical stirring was performed using a paddle-type stirrer with heat-resistant alloy blades, 17mm in diameter, inserted 4cm into the molten aluminum, and a stirring speed of 400rpm. Electromagnetic stirring was performed using a low-frequency electromagnetic stirrer with a frequency of 55Hz, a stirring intensity of 0.35T, and an adjustment accuracy of 0.05T. The stirring direction was opposite to the mechanical stirring direction. The total stirring time was 13min. The furnace temperature was recorded every 2min during the stirring process, with temperature fluctuations ≤±2℃, resulting in a uniformly composed aluminum-based melt.

[0054] (3) Air blowing device setup: A heat-resistant stainless steel air blowing head with a heat resistance temperature ≥800℃ is used. It has a cylindrical structure with a diameter of 25mm and a length of 65mm. Fifteen air vents with a diameter of 0.75mm are evenly distributed on the surface. The air vents are arranged in a regular hexagonal array with a spacing of 6.5mm and a wall thickness of 0.4mm. The air blowing head is vertically immersed to the bottom of the aluminum-based melt to a depth of 7.5cm. The distance between the air vents and the bottom of the melting furnace is ≥4cm. A bubble homogenizing component is set 6.5cm below the surface of the aluminum-based melt. The component is made of corundum high-temperature resistant ceramic with a heat resistance temperature ≥1200℃ and a thickness of 12mm. The ratio of the component diameter to the furnace inner diameter is 1:3.5, and the distance between the edge of the component and the inner wall of the furnace is 6.5cm. The holes of the component are distributed in a regular hexagonal array with a wall thickness of 0.25mm and a diameter of 1.0mm, which is 1.3 times the diameter of the air vents of the air blowing head.

[0055] (4) Gas blowing and foaming: Dry and impurity-removed argon gas is introduced into the blowing head. The moisture content of the gas is ≤10ppm and the impurity content is ≤5ppm. The blowing pressure is controlled at 0.2MPa, the gas flow rate is 10L / min, the blowing time is 5.5min, and the foaming temperature is maintained at 700℃ with a temperature fluctuation of ≤±5℃ to promote the uniform growth of bubbles to the preset size.

[0056] (5) Cooling and forming: A segmented uniform cooling method is adopted. In the first stage, the temperature is cooled from 700℃ to 500℃ at a rate of 13℃ / min, while the water bath temperature is maintained at 32℃. In the second stage, the temperature is cooled from 500℃ to room temperature at a rate of 6.5℃ / min, while the water bath temperature is maintained at 27℃. Deionized water is used in the water bath, and the volume ratio of the water bath to the foamed aluminum billet is 6.5:1 to obtain a highly uniform foamed aluminum billet.

[0057] (6) Post-treatment: The surface is finished by wet mechanical grinding with a grinding wheel of 100 mesh and a grinding speed of 17 m / min. The uneven surface layer of 1.5 mm is removed from the blank. The grinding process is cooled with deionized water. The surface roughness Ra after grinding is ≤1.6 μm. The finished blank is placed in a box-type resistance furnace for homogenization heat treatment with a temperature control accuracy of ±1℃. The temperature is increased to 330℃ at 6℃ / min and held for 1.5 h with a holding temperature fluctuation of ≤±2℃. Then it is cooled with the furnace at a cooling rate of ≤5℃ / min to finally obtain a high-uniformity aluminum foam product.

[0058] Comparative Example 1: Compared with Example 3, Comparative Example 1 did not add a composite foam stabilizing system, but the other raw materials, process parameters and operating steps were exactly the same as those in Example 3.

[0059] Comparative Example 2: Compared with Example 3, Comparative Example 2 only used mechanical stirring and did not use electromagnetic stirring. The other raw materials, process parameters and operating steps were exactly the same as those in Example 3.

[0060] Comparative Example 3: Compared with Example 3, Comparative Example 3 does not have a bubble homogenization component, but the other raw materials, process parameters, and operating steps are exactly the same as in Example 3.

[0061] Comparative Example 4: Compared with Example 3, Comparative Example 4 uses conventional one-time cooling instead of segmented uniform cooling, and the other raw materials, process parameters, and operating steps are exactly the same as those in Example 3.

[0062] test: Experiment 1: Cell Uniformity Test Experimental methods Image analysis was used to cut aluminum foam samples into standard 10mm×10mm×10mm specimens. Cross-sectional images were acquired using a metallographic microscope, and the cell diameter, coefficient of variation, and closed-cell ratio were analyzed using Image-ProPlus software. Five different fields of view were selected for each sample, and the average value of the test results was taken.

[0063] Experimental data: Table 1 Results of bubble cell uniformity test

[0064] The coefficients of variation for cell diameter in Examples 1-3 were all less than 7%, and the closed-cell rate was higher than 91%, exhibiting excellent cell uniformity. Comparative Example 1, without the addition of a composite foam stabilizing system, lacked a stable bubble skeleton in the melt, leading to easy cell merging and growth, a significantly increased coefficient of variation, and a significantly decreased closed-cell rate. Comparative Example 2, using only mechanical stirring, resulted in uneven dispersion of the foaming agent and foam stabilizer, leading to localized bubble aggregation and poor uniformity. Comparative Example 3, lacking a bubble homogenization component, exhibited no regular constraint during bubble ascent, resulting in a discrete size distribution. Comparative Example 4, employing a single cooling method, showed a large difference in cooling rates between the inside and outside of the billet, resulting in uneven cell shrinkage and slightly lower uniformity than the Examples.

[0065] Experiment 2: Mechanical property testing: Experimental methods: According to the mechanical property testing specifications for aluminum foam, the compression performance was tested using a universal testing machine. The sample size was 50mm×50mm×50mm, the loading rate was 1mm / min, and the quasi-static compressive strength and energy absorption value were tested. Each sample was tested 3 times and the average value was taken.

[0066] Experimental data: Table 2 Mechanical property test results

[0067] The compressive strength and energy absorption values ​​of Examples 1-3 are superior to those of the Comparative Examples. Comparative Example 1, lacking a composite stabilizing system, has thin and uneven cell walls, making it prone to collapse under stress and exhibiting the worst mechanical properties. Comparative Example 2 suffers from uneven dispersion, resulting in weak local structures and lower mechanical properties. Comparative Example 3 exhibits inconsistent bubble sizes and poor overall structural integrity, leading to mechanical properties lower than the Examples. Comparative Example 4 suffers from uneven cooling, causing internal stress concentration and slightly lower mechanical properties than the Examples.

[0068] Experiment 3: Dimensional Uniformity and Appearance Quality Test Experimental methods: A 3D scanner was used to scan the finished aluminum foam, and the thickness, length, and width of the sample at different locations were measured to calculate the dimensional deviations. A roughness meter was used to measure the surface roughness Ra and to observe surface collapse and protrusion defects.

[0069] Experimental data: Table 3 Results of Dimensional Uniformity and Appearance Quality Tests

[0070] Examples 1-3 exhibited dimensional deviations of less than ±0.25 mm and surface roughness Ra below 1.5 μm, demonstrating excellent apparent quality. Comparative Example 1 lacked a stable foaming system, resulting in uncontrolled foaming, green body collapse, numerous pores, and significant dimensional deviations and roughness. Comparative Example 2 suffered from uneven mixing, leading to localized over-foaming, resulting in protrusions and exposed cells, and poor dimensional and surface quality. Comparative Example 3 lacked a homogenization component, resulting in poor cell and edge regularity. Comparative Example 4 experienced uneven cooling, leading to warping and a lower surface quality than the examples.

[0071] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. A method for preparing highly uniform aluminum foam by blowing air, characterized in that, Includes the following steps: (1) Raw material preparation: High-purity aluminum ingots are selected as the base material, foaming agent and composite foam stabilizing system are added, and the mixture is mixed evenly to obtain a raw material mixture; the composite foam stabilizing system is composed of silicon carbide particles and nano alumina particles, and the nano alumina particles are surface modified by silane coupling agent. The foaming agent undergoes vacuum drying pretreatment; (2) Smelting process: The raw material mixture is placed in a smelting furnace and heated until the aluminum ingot is completely melted. The mixture is stirred evenly by a combination of mechanical stirring and electromagnetic stirring to make the foaming agent and composite foam stabilizing system evenly dispersed in the aluminum melt, so as to obtain an aluminum-based melt with uniform composition. (3) Setting of air blowing device: Use air blowing head and immerse the air blowing head into the bottom of the aluminum-based melt to a preset depth; set the bubble homogenization component at a preset position below the surface of the aluminum-based melt; (4) Blowing and foaming: Inert gas is introduced into the blowing head, and the blowing pressure, initial value of gas flow rate and blowing time are controlled to keep the temperature of aluminum-based melt stable and promote the uniform growth of bubbles to the preset size. (5) Cooling and molding: The foamed aluminum-based melt is cooled to room temperature in a segmented uniform cooling method. During the cooling process, a combination of water bath cooling and furnace insulation is used to ensure that the foamed aluminum billet is cooled evenly in all parts, resulting in a highly uniform foamed aluminum billet. (6) Post-processing: The aluminum foam blank is surface trimmed and homogenized by heat treatment to finally obtain a high-uniformity aluminum foam finished product.

2. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (1), the purity of the high-purity aluminum ingot is ≥99.8%; the foaming agent is aluminum titanium hydride with a particle size of 20-50μm and an addition amount of 0.4-0.7wt% of the aluminum ingot mass; the composite foam stabilizing system is composed of silicon carbide particles and nano-alumina particles in a mass ratio of 3-5:1, wherein the silicon carbide particles have a particle size of 15-40μm and the nano-alumina particles have a particle size of 50-100nm, and the total addition amount of the composite foam stabilizing system is 1.5-2.5wt% of the aluminum ingot mass; the mixing is carried out using a high-speed mixer with a mixing temperature of 25-30℃, a rotation speed of 800-1000rpm, and a mixing time of 10-15min.

3. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (1), the silane coupling agent is KH-550, and the modification process is as follows: nano-alumina particles are placed in a silane coupling agent ethanol solution with a mass fraction of 2-3%, ultrasonically dispersed at 25-30℃ for 30-40 min, and then dried at 110-120℃ for 2-3 h for later use. The amount of silane coupling agent added is 1.5-2.5 wt% of the mass of nano-alumina particles; the vacuum drying pretreatment of aluminum hydride is performed with a vacuum degree of 0.06-0.08 MPa, a drying temperature of 85-95℃, and a drying time of 2.0-2.8 h. The moisture content after pretreatment is ≤0.1 wt%.

4. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (2), the melting furnace is a resistance melting furnace with a rated power of 50-100kW, an inner diameter of 30-50cm, and an argon protective atmosphere inside the furnace. The heating rate is 10-15℃ / min, and the melting temperature is 730-750℃. The mechanical stirring adopts a paddle stirrer with heat-resistant alloy blades of 15-20mm in diameter, 3-5cm deep into the molten aluminum, and a stirring speed of 350-450rpm. The electromagnetic stirring adopts a low-frequency electromagnetic stirrer with a frequency of 50-60Hz, a stirring intensity of 0.3-0.4T, an adjustment accuracy of 0.05T, and a stirring direction opposite to the mechanical stirring direction. The total stirring time is 12-14min, and the furnace temperature is recorded every 2min during the stirring process, with a temperature fluctuation ≤±2℃.

5. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (3), the air blowing head is made of heat-resistant stainless steel with a heat resistance temperature ≥800℃. It has a cylindrical structure with a diameter of 20-30mm and a length of 50-80mm. 10-20 air vents with a diameter of 0.5-1.0mm are evenly distributed on the surface. The air vents are arranged in a regular hexagonal array with a spacing of 5-8mm and a wall thickness of 0.3-0.5mm. The air blowing head is vertically immersed in the aluminum-based melt to a depth of 6-9cm, and the distance between the air vents and the bottom of the smelting furnace is ≥4cm.

6. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (3), the bubble homogenization component is set 5-8cm below the surface of the aluminum-based melt. The material is corundum high-temperature resistant ceramic with a high temperature resistance of ≥1200℃ and a thickness of 10-15mm. The ratio of the component diameter to the inner diameter of the furnace chamber is 1:3-4, and the distance between the edge of the component and the inner wall of the furnace chamber is 5-8cm. The holes are distributed in a regular hexagonal shape, with a hole wall thickness of 0.2-0.3mm and a hole diameter of 0.8-1.2mm, which is 1.2-1.8 times the diameter of the air vent of the blowing head.

7. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (4), the inert gas is argon, which is introduced after drying and impurity removal. The moisture content in the gas is ≤10ppm and the impurity content is ≤5ppm.

8. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (4), the blowing pressure is controlled at 0.1-0.3MPa, the gas flow rate is 5-15L / min, the blowing time is 3-8min, and the foaming temperature is maintained at 680-720℃ with temperature fluctuation ≤±5℃.

9. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (5), the segmented uniform cooling specifically refers to the following: in the first stage, the temperature is cooled from the foaming temperature to 500℃ at a rate of 12-14℃ / min, while the water bath temperature is maintained at 30-35℃; in the second stage, the temperature is cooled from 500℃ to room temperature at a rate of 6-7℃ / min, while the water bath temperature is maintained at 25-30℃; deionized water is used in the water bath, and the ratio of the water bath volume to the volume of the foamed aluminum billet is 5-8:

1.

10. The method for preparing highly uniform aluminum foam by blowing air according to claim 1, characterized in that, In step (6), the surface finishing is done by wet mechanical grinding with a grinding wheel grit of 80-120 mesh and a grinding speed of 15-20 m / min. This removes 1.2-1.8 mm of uneven surface layer from the blank. After grinding, the surface roughness Ra ≤ 1.6 μm. Deionized water is used for cooling during the grinding process. The homogenization heat treatment is done in a box-type resistance furnace with a temperature control accuracy of ±1℃, a heating rate of 5-8℃ / min, a heat treatment temperature of 320-340℃, a holding time of 1.2-1.8 h, and a holding temperature fluctuation ≤ ±2℃. After heat treatment, the furnace is cooled with a cooling rate ≤ 5℃ / min.

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