A method for producing closed cell foam aluminum by gas blowing
By employing techniques such as foam stabilizer coating modification, rotary jet degassing, interface activation, and gradient cooling, the problems of uneven bubble nucleation and easy cooling rupture in traditional blowing foaming processes have been solved, enabling the production of closed-cell aluminum foam with high closed-cell ratio and uniform pore size, thereby improving the mechanical properties and production stability of the product.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- ANHUI NEOFOUND TECH
- Filing Date
- 2026-04-22
- Publication Date
- 2026-06-30
AI Technical Summary
In traditional air blowing foaming processes, uneven dispersion of foam stabilizers, insufficient cleanliness of aluminum melt, uncontrolled bubble nucleation and growth, and easy brittle cracking of pore walls during the cooling process result in low closed-cell rate, large pore size dispersion, and large fluctuations in mechanical properties, making it difficult to achieve a stable and continuous closed-cell structure.
By employing methods such as foam stabilizer coating modification, rotary jet degassing, interface activation, dynamic synergistic control of temperature and pressure, and gradient cooling, foam stabilizers such as titanium-based compounds are added to the aluminum melt. Combined with rotary jet degassing, refinement treatment, and interface activation, along with porous air blowing and vibration treatment, uniform nucleation and stable growth of bubbles are achieved. Gradient cooling reduces internal stress, forming a continuous closed-cell structure.
It improves the finished product quality of closed-cell aluminum foam, enhances the rupture resistance of the bubble walls, improves the closed-cell rate, pore size uniformity and mechanical properties, solves the problem of poor molding stability in traditional processes, and improves the product qualification rate.
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Abstract
Description
Technical Field
[0001] This invention relates to the field of aluminum foam technology, specifically a method for producing closed-cell aluminum foam by blowing. Background Technology
[0002] Closed-cell aluminum foam possesses properties such as lightweight, high specific strength, energy absorption and cushioning, sound insulation and noise reduction, and electromagnetic shielding, making it promising for applications in rail transportation, aerospace, new energy vehicles, and building protection. The air-blowing foaming method, due to its short process flow, high controllability, and suitability for large-scale production, has become the mainstream technology for the industrial preparation of closed-cell aluminum foam.
[0003] The traditional blowing foaming process still faces several technical bottlenecks in actual production: First, the foam stabilizer is unevenly dispersed in the aluminum melt, easily agglomerates, or decomposes prematurely, resulting in insufficient bubble nucleation, uncontrolled growth, low closed-cell rate, and large pore size dispersion in the finished product. Second, the aluminum melt is not clean enough, has coarse grains, and poor interfacial activity, making the bubble walls prone to segregation, loosening, and microcracks. These cracks are likely to merge, break, and penetrate during the foaming and cooling process, making it difficult to form a stable and continuous closed-cell structure. Third, the gas pressure and melt temperature are mostly controlled at constant levels during the foaming stage, which cannot match the dynamic process of bubble nucleation, growth, and shaping, making it difficult to accurately control the bubble size and distribution. Fourth, the cooling process often uses direct rapid cooling or natural slow cooling, which can easily cause internal stress concentration and pore wall brittleness, resulting in large fluctuations in the mechanical properties of the final product and a low pass rate.
[0004] Therefore, developing a closed-cell aluminum foam blowing foaming production method with high foaming efficiency, controllable foaming process, and stable molding quality is of great practical significance for improving product performance and promoting industrial application. Summary of the Invention
[0005] To address the problems in the prior art, this invention provides a method for producing closed-cell aluminum foam by air blowing.
[0006] The technical solution adopted by this invention to solve its technical problem is: a method for producing closed-cell aluminum foam by blowing, comprising the following steps: (1) Raw material preparation: Select aluminum alloy matrix raw material and foam stabilizer raw material; the foam stabilizer raw material is at least one of titanium-based compound, rare earth compound, and Zr compound, and its addition amount is 0.1-0.5% of the mass of the aluminum alloy matrix raw material; the foam stabilizer raw material is coated and modified. (2) Preparation of aluminum melt: The aluminum alloy matrix raw material is melted to complete melting to obtain aluminum melt; the aluminum melt is subjected to degassing and refining treatment in sequence, and interface activation treatment is performed simultaneously; the degassing treatment adopts the rotary jet degassing method, and argon gas is introduced into the aluminum melt; the refining treatment is to add Al-5Ti-1B refining agent to the aluminum melt; the interface activation treatment is to add Al-Ti-B-Ce master alloy to the aluminum melt; (3) Foam stabilizer mixing: First, the coated and modified foam stabilizer raw material is crushed to a preset particle size, and then mixed evenly with a small amount of aluminum alloy matrix raw material powder to form a pre-dispersion; the pre-dispersion is added to the aluminum melt after interface activation treatment, and stirred to obtain the aluminum melt to be foamed; (4) Air blowing foaming: The aluminum melt to be foamed is transferred to a closed foaming mold. The inert gas is first dried and purified for pretreatment. Then, the pretreated inert gas is introduced into the aluminum melt to be foamed through the porous air blowing device inside the mold. During the air blowing process, the temperature and pressure are dynamically coordinated and controlled. At the same time, the closed foaming mold is vibrated to complete the foaming and obtain the foamed aluminum billet. (5) Cooling and shaping: The aluminum foam blank is cooled together with the closed foaming mold using a gradient cooling method. After cooling, it is demolded to obtain the closed-cell aluminum foam finished product.
[0007] As a further technical solution, in step (1), the aluminum alloy matrix raw material is any one of industrial-grade pure aluminum, Al-Si industrial aluminum alloy, and Al-Mg industrial aluminum alloy; the titanium-based compound is at least one of TiH2 and TiC; the rare earth compound is at least one of La2O3 and CeO2; and the Zr compound is at least one of ZrO2 and ZrC.
[0008] As a further technical solution, in step (1), the coating modification treatment specifically involves uniformly coating the foam stabilizer particles with an Al2O3 coating layer, with the coating layer thickness controlled at 1-3 μm. After coating, the particles are dried at 80-100℃ until the moisture content is ≤0.1%. The Al2O3 coating layer is prepared by the sol-gel method, specifically by using tetraethyl orthosilicate as a precursor, ethanol as a solvent, and nitric acid as a catalyst, and mixing them at a volume ratio of precursor:ethanol:water = 1:3:0.5. The pH value of the reaction system is controlled at 4-6, the reaction temperature at 60-80℃, and the reaction time at 2-3h. After the reaction is completed, the foam stabilizer particles are coated and then dried and calcined.
[0009] As a further technical solution, in step (2), the aluminum alloy matrix raw material is smelted in a medium-frequency induction melting furnace at 720-750℃; the rotary blowing degassing method has a blowing speed of 150-200 r / min, an argon flow rate of 8-12 L / min, a degassing time of 5-10 min, and the aluminum melt temperature is maintained at 700-720℃ during the degassing process; the Al-Ti-B-Ce master alloy is added at 0.01-0.03% of the mass of the aluminum alloy matrix raw material, and after addition, it is kept at 700-720℃ for 3-5 min, and the mass fractions of Ti, B, and Ce in the master alloy are 4-6%, 0.8-1.2%, and 0.5-1%, respectively, with the remainder being Al; the Al-5Ti-1B refining agent is added at 0.05-0.2% of the mass of the aluminum alloy matrix raw material, and after the Al-5Ti-1B refining agent is added, it is stirred evenly and kept at 2-3 min.
[0010] As a further technical solution, in step (3), the foam stabilizer raw material is pulverized to a particle size of 5-10μm using an air jet mill; the mass ratio of the foam stabilizer raw material to the aluminum alloy matrix raw material powder in the pre-dispersion is strictly controlled to be 1:2-3; the stirring adopts a combination of mechanical stirring and electromagnetic stirring, with a mechanical stirring speed of 300-500r / min, an electromagnetic stirring frequency of 50-60Hz, a stirring time of 2-5min, and the temperature of the aluminum melt is strictly maintained at 650-720℃ during the stirring process, with temperature fluctuation not exceeding ±5℃.
[0011] As a further technical solution, in step (4), the aluminum melt to be foamed is transferred at a constant speed to a closed foaming mold, and after the transfer, the temperature of the aluminum melt is stabilized at 680-700℃ before blowing gas; the inert gas pretreatment specifically involves sequentially passing through molecular sieve drying and activated carbon purification, with a drying temperature of 25-35℃ and a time of 10-15min, and the gas moisture content after drying is ≤0.01%; the purification flow rate is 3-5L / min, and the inert gas is any one of argon, nitrogen or helium.
[0012] As a further technical solution, in step (4), the porous air blowing device is a porous ceramic tube or a stainless steel porous tube with a pore diameter of 10-50μm. The air outlet end is completely immersed in the aluminum melt to be foamed, with an immersion depth of 10-30mm. The dynamic coordinated control mode of temperature and pressure is as follows: the initial blowing pressure is 0.2-0.3MPa, the initial temperature of the aluminum melt is 680-700℃, and as the blowing time increases, the pressure increases at a rate of 0.05-0.1MPa / min, and the temperature decreases at a rate of 5-8℃ / min. Finally, the blowing pressure is controlled to be 0.6-0.8MPa, the aluminum melt temperature is 620-640℃, the gas flow rate is maintained at 5-20L / min throughout the process, and the total blowing time is 10-30s.
[0013] As a further technical solution, in step (4), the vibration frequency of the vibration treatment is 20-50Hz, the amplitude is 1-3mm, the vibration direction is perpendicular to the bottom surface of the mold, and the entire process is accompanied by the blowing and foaming process; the inner wall of the sealed foaming mold is uniformly coated with a high-temperature resistant release agent.
[0014] As a further technical solution, the release agent is boron nitride or graphite release agent, with a coating thickness of 5-10μm. After coating, it is naturally dried before being loaded into the aluminum melt to be foamed.
[0015] As a further technical solution, in step (5), the gradient cooling process keeps the mold sealed throughout, first cooling to 400-450℃ at a rate of 10-15℃ / min, holding at this temperature range for 10-15min, and then slowly cooling to room temperature at a rate of 2-5℃ / min; during the holding period, the same type of inert gas as in step (4) is introduced into the sealed mold at a flow rate of 2-3L / min, and the pressure inside the mold is maintained at 0.1-0.15MPa.
[0016] The beneficial effects of this invention are: 1. This invention utilizes a foam stabilizer coating modification to form a continuous and dense Al2O3 barrier layer on the surface of the foam stabilizer particles. This delays direct contact and rapid decomposition between the foam stabilizer and the molten aluminum, resulting in a smoother gas release. Simultaneously, it improves the wettability and dispersibility of the particles in the melt, preventing agglomeration and achieving uniform bubble nucleation and stable growth. This solves the problems of rapid foam stabilizer failure and poor dispersion in traditional processes. The synergistic treatment of rotary jet degassing, grain refinement, and interface activation effectively removes harmful gases such as hydrogen from the molten aluminum, refines the matrix grains, and enhances the activity of the melt interface. This results in a denser bubble wall structure and higher bonding strength, thereby strengthening the bubble wall's resistance to rupture and penetration, and improving the stability of the closed-cell structure. The use of pre-dispersion of the foam stabilizer combined with composite stirring reduces the agglomeration tendency when the foam stabilizer is directly added, ensuring uniform distribution of the foam stabilizer throughout the melt. Combined with mechanical-electromagnetic composite stirring, this achieves thorough mixing without dead zones, ensuring uniform bubble density and size and reducing localized macropores and defects.
[0017] 2. By employing dried and purified inert gas and porous blowing elements, the oxidation of the melt and porosity defects caused by moisture and impurities in the gas are avoided. The porous structure breaks the gas into microbubbles, improving the nucleation density and uniformity of the bubbles. The use of dynamic temperature-pressure control combined with vibration-assisted foaming allows for matching pressure and temperature according to the bubble growth stage. Vibration eliminates local viscous resistance in the melt, resulting in more uniform bubble growth and more consistent wall thickness, solving the problems of uncontrolled foaming and uneven pore size under traditional constant parameters. The use of closed-loop gradient cooling and inert gas protection allows for the step-by-step release of internal stress, preventing rapid cooling from causing pore wall cracking, while also suppressing oxidation at high temperatures, thereby improving the dimensional accuracy and structural integrity of the finished product.
[0018] 3. This invention forms a closed-loop control system through the orderly coordination of key steps such as coating with a foam stabilizer, melt purification and activation, pre-dispersion and mixing, dynamic temperature and pressure foaming, and gradient cooling and shaping. The coating with a foam stabilizer provides stable bubble nuclei, the purified and activated melt provides a strong pore wall matrix, pre-dispersion and composite stirring ensure uniform distribution of bubbles throughout the entire process, dynamic temperature and pressure and vibration achieve precise bubble growth, and gradient cooling ensures a stable and crack-free final structure. Each step supports and synergistically strengthens the others, resulting in a continuous, uniform, and complete closed-cell network within the aluminum foam. This significantly improves the closed-cell rate, pore size uniformity, and compressive mechanical properties, while also enhancing production stability and finished product qualification rate. It can stably produce high-performance closed-cell aluminum foam that meets 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 producing closed-cell aluminum foam by blowing, including the steps of raw material preparation, aluminum melt preparation, foam stabilizer mixing, blowing foaming, and cooling and shaping.
[0021] This invention first involves raw material preparation, selecting an aluminum alloy matrix and a foam stabilizer. The foam stabilizer is at least one of a titanium-based compound, a rare earth compound, and a Zr compound, and its addition amount is 0.1%-0.5% of the mass of the aluminum alloy matrix. The foam stabilizer is then subjected to a coating modification treatment.
[0022] The aluminum alloy matrix material is preferably any one of industrial-grade pure aluminum, Al-Si industrial aluminum alloy, or Al-Mg industrial aluminum alloy. The Si content in Al-Si industrial aluminum alloy is 5%-12%, and the Mg content in Al-Mg industrial aluminum alloy is 3%-8%. The titanium-based compound is preferably at least one of TiH2 and TiC, the rare earth compound is preferably at least one of La2O3 and CeO2, and the Zr compound is preferably at least one of ZrO2 and ZrC.
[0023] The coating modification process involves uniformly coating the foam stabilizer particles with an Al2O3 coating layer, with the coating layer thickness controlled at 1μm-3μm. After coating, the particles are dried at 80℃-100℃ until the moisture content is ≤0.1%. The Al2O3 coating layer is prepared using the sol-gel method, specifically using tetraethyl orthosilicate as a precursor, ethanol as a solvent, and nitric acid as a catalyst. The precursor to ethanol to water are mixed in a volume ratio of 1:3:0.5. The pH of the reaction system is controlled at 4-6, the reaction temperature at 60℃-80℃, and the reaction time at 2-3 hours. After the reaction, the foam stabilizer particles are coated, and then dried and calcined to obtain the final product.
[0024] After raw material preparation, aluminum melt preparation is carried out by melting the aluminum alloy matrix raw material until it is completely melted to obtain aluminum melt. The aluminum melt is then subjected to degassing and refining treatments, while interface activation treatment is performed simultaneously. The degassing treatment uses a rotary jet degassing method, introducing argon gas into the aluminum melt. The refining treatment involves adding an Al-5Ti-1B refining agent to the aluminum melt. The interface activation treatment involves adding an Al-Ti-B-Ce master alloy to the aluminum melt.
[0025] The aluminum alloy matrix raw material is preferably smelted in a medium-frequency induction melting furnace at 720℃-750℃. The rotary jet degassing method uses a jetting speed of 150r / min-200r / min, an argon flow rate of 8L / min-12L / min, and a degassing time of 5min-10min, maintaining the aluminum melt temperature at 700℃-720℃ during degassing. The Al-Ti-B-Ce master alloy is added at 0.01%-0.03% of the aluminum alloy matrix raw material mass. After addition, it is held at 700℃-720℃ for 3min-5min. The mass fractions of Ti, B, and Ce in this master alloy are 4%-6%, 0.8%-1.2%, and 0.5%-1%, respectively, with the remainder being Al. The Al-5Ti-1B refining agent is added at 0.05%-0.2% of the aluminum alloy matrix raw material mass. After addition, the Al-5Ti-1B refining agent is stirred evenly and held at this temperature for 2min-3min.
[0026] After the aluminum melt is prepared, a foam stabilizer is mixed. First, the coated and modified foam stabilizer raw material is crushed to a preset particle size, and then mixed evenly with a small amount of aluminum alloy matrix raw material powder to form a pre-dispersion. The pre-dispersion is added to the aluminum melt after interface activation treatment and stirred to obtain the aluminum melt to be foamed.
[0027] The foam stabilizer raw material is preferably pulverized to a particle size of 5μm-10μm using an air jet mill. The mass ratio of the foam stabilizer raw material to the aluminum alloy matrix raw material powder in the pre-dispersion is strictly controlled at 1:2-3. Stirring is carried out using a combination of mechanical and electromagnetic stirring. The mechanical stirring speed is 300r / min to 500r / min, the electromagnetic stirring frequency is 50Hz-60Hz, and the stirring time is 2min-5min. During the stirring process, the temperature of the aluminum melt is strictly maintained at 650℃-720℃, and the temperature fluctuation does not exceed ±5℃.
[0028] After the foam stabilizer is mixed, air blowing foaming is performed. The aluminum molten material to be foamed is transferred into a closed foaming mold. The inert gas is first dried and purified for pretreatment, and then the pretreated inert gas is introduced into the aluminum molten material to be foamed through a porous air blowing device inside the mold. During the air blowing process, a dynamic and coordinated temperature and pressure control mode is adopted, accompanied by vibration treatment of the closed foaming mold, to complete the foaming and obtain the foamed aluminum billet.
[0029] The aluminum molten material to be foamed is preferably transferred at a uniform speed to a closed foaming mold. After transfer, the temperature of the aluminum molten material is allowed to stabilize at 680℃-700℃ before blowing. The inert gas pretreatment specifically involves sequentially passing the material through molecular sieve drying and activated carbon purification. The drying temperature is 25℃-35℃, and the time is 10min-15min. After drying, the gas moisture content is ≤0.01%. The purification flow rate is 3L / min-5L / min, and the inert gas is any one of argon, nitrogen, or helium.
[0030] The porous air blowing device is preferably a porous ceramic tube or a porous stainless steel tube with a pore diameter of 10μm-50μm. The air outlet end is completely immersed in the aluminum melt to be foamed, with an immersion depth of 10mm-30mm. The dynamic coordinated control mode of temperature and pressure is as follows: the initial blowing pressure is 0.2MPa-0.3MPa, the initial temperature of the aluminum melt is 680℃-700℃, and as the blowing time increases, the pressure increases uniformly at a rate of 0.05MPa / min-0.1MPa / min, while the temperature decreases uniformly at a rate of 5℃ / min to 8℃ / min. Finally, the blowing pressure is controlled at 0.6MPa-0.8MPa, the aluminum melt temperature is 620℃-640℃, the gas flow rate is maintained at 5L / min-20L / min throughout the process, and the total blowing time is 10s-30s.
[0031] The vibration treatment operates at a frequency of 20Hz-50Hz and an amplitude of 1mm-3mm, with the vibration direction perpendicular to the bottom surface of the mold, and is accompanied by an air blowing foaming process throughout. The inner wall of the sealed foaming mold is uniformly coated with a high-temperature resistant release agent. The release agent is preferably boron nitride or graphite release agent, with a coating thickness of 5μm-10μm. After coating, the mold is allowed to air dry before being filled with the molten aluminum to be foamed.
[0032] After the blowing and foaming process is completed, the aluminum foam blank is cooled and shaped. The aluminum foam blank is cooled together with the closed foaming mold using a gradient cooling method. After cooling, it is demolded to obtain the closed-cell aluminum foam finished product.
[0033] The gradient cooling process involves keeping the mold sealed throughout. First, the temperature is cooled to 400℃-450℃ at a rate of 10℃ / min-15℃ / min, held at this temperature for 10-15 minutes, and then slowly cooled to room temperature at a rate of 2℃ / min-5℃ / min. During the holding period, the same type of inert gas as used in the blowing foaming step is introduced into the sealed mold at a flow rate of 2L / min-3L / min, maintaining the pressure inside the mold at 0.1MPa-0.15MPa.
[0034] The closed-cell aluminum foam production method provided by this invention, through a series of synergistic processes such as foam stabilizer coating modification, aluminum melt interface activation, foam stabilizer pre-dispersion, dynamic temperature and pressure synergistic foaming, and gradient cooling, can produce closed-cell aluminum foam with high closed-cell rate, uniform pore size, and excellent mechanical properties. At the same time, it solves the problems of easy pore breakage, high connectivity, and poor molding stability of traditional foaming methods, thereby improving product qualification rate and production efficiency.
[0035] Example 1:
[0036] (1) Raw material preparation: Industrial-grade pure aluminum was selected as the aluminum alloy matrix raw material, and TiH2 was selected as the foam stabilizer raw material. The amount of foam stabilizer added was 0.1% of the mass of the aluminum alloy matrix raw material. The foam stabilizer particles were uniformly coated with an Al2O3 coating layer, and the coating layer thickness was controlled to be 1μm. After coating, the particles were dried at 80℃ until the moisture content was ≤0.1%. The Al2O3 coating layer was prepared by the sol-gel method, using tetraethyl orthosilicate as the precursor, ethanol as the solvent, and nitric acid as the catalyst. The mixture was prepared at a volume ratio of precursor:ethanol:water = 1:3:0.5. The pH value of the reaction system was controlled to be 4, the reaction temperature was 60℃, and the reaction time was 2h. After the reaction was completed, the foam stabilizer particles were coated and then dried and calcined.
[0037] (2) Preparation of aluminum melt: Industrial-grade pure aluminum was heated to 720℃ and melted completely in a medium-frequency induction melting furnace to obtain aluminum melt. Degassing was performed by rotary jet degassing at a speed of 150 r / min, an argon flow rate of 8 L / min, and a degassing time of 5 min. The temperature of the aluminum melt was maintained at 700℃ during the degassing process. Al-5Ti-1B refining agent was added to the aluminum melt at a rate of 0.05% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was stirred evenly and held at the temperature for 2 min. Al-Ti-B-Ce master alloy was added to the aluminum melt at a rate of 0.01% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was held at 700℃ for 3 min. The mass fractions of Ti, B, and Ce in this master alloy were 4%, 0.8%, and 0.5%, respectively, with the remainder being Al.
[0038] (3) Foam stabilizer mixing: The coated and modified foam stabilizer raw material was pulverized to a particle size of 5μm using an air jet mill. The pulverized foam stabilizer raw material was mixed with industrial-grade pure aluminum powder at a mass ratio of 1:2 to form a pre-dispersion. The pre-dispersion was added to the aluminum melt after interface activation treatment, and mechanical stirring and electromagnetic stirring were used in combination. The mechanical stirring speed was 300r / min, the electromagnetic stirring frequency was 50Hz, and the stirring time was 2min. During the stirring process, the temperature of the aluminum melt was maintained at 650℃, and the temperature fluctuation did not exceed ±5℃, to obtain the aluminum melt to be foamed.
[0039] (4) Gas blowing and foaming: The aluminum melt to be foamed is transferred uniformly to a closed foaming mold. Gas blowing is performed after the temperature of the aluminum melt stabilizes at 680℃. Argon is selected as the inert gas and is successively dried by molecular sieve and purified by activated carbon. The drying temperature is 25℃ and the time is 10min. The moisture content of the gas after drying is ≤0.01%, and the purification flow rate is 3L / min. A porous ceramic tube is used as a porous blowing device with a pore diameter of 10μm. The outlet end is immersed 10mm into the aluminum melt to be foamed. The initial blowing pressure is 0.2MPa, the initial temperature of the aluminum melt is 680℃, the pressure increases uniformly at a rate of 0.05MPa / min, and the temperature decreases uniformly at a rate of 5℃ / min. The final blowing pressure is 0.6MPa, the temperature of the aluminum melt is 620℃, the gas flow rate is 5L / min, and the total blowing time is 10s. The vibration treatment frequency is 20Hz, the amplitude is 1mm, the vibration direction is perpendicular to the bottom surface of the mold, and it accompanies the blowing process throughout. The inner wall of the mold is coated with boron nitride release agent to a thickness of 5μm, and then used after natural drying.
[0040] (5) Cooling and shaping: The aluminum foam blank is cooled in a gradient manner with the mold, and the whole process is sealed. First, it is cooled to 400℃ at a rate of 10℃ / min and held for 10min. Then, it is cooled to room temperature at a rate of 2℃ / min. Argon gas is introduced during the holding period at a flow rate of 2L / min. The pressure inside the mold is maintained at 0.1MPa. After cooling, the closed-cell aluminum foam product is obtained by demolding.
[0041] Example 2:
[0042] (1) Raw material preparation: Al-Mg industrial aluminum alloy was selected as the aluminum alloy matrix raw material with a Mg content of 8%. CeO2 and ZrO2 were selected as foam stabilizer raw materials, and the amount of foam stabilizer added was 0.5% of the mass of the aluminum alloy matrix raw material. The foam stabilizer particles were uniformly coated with an Al2O3 coating layer with a coating thickness of 3μm. After coating, the particles were dried at 100℃ until the moisture content was ≤0.1%. The Al2O3 coating layer was prepared by the sol-gel method, using tetraethyl orthosilicate as a precursor, ethanol as a solvent, and nitric acid as a catalyst. The mixture was prepared at a volume ratio of precursor:ethanol:water = 1:3:0.5. The pH value of the reaction system was controlled at 6, the reaction temperature was 80℃, and the reaction time was 3h. After the reaction was completed, the foam stabilizer particles were coated and then dried and calcined.
[0043] (2) Preparation of aluminum melt: Al-Mg industrial aluminum alloy was heated to 750℃ and melted completely in a medium-frequency induction melting furnace to obtain aluminum melt. Degassing was performed by rotary jet degassing at a speed of 200 r / min, an argon flow rate of 12 L / min, and a degassing time of 10 min. The temperature of the aluminum melt was maintained at 720℃ during the degassing process. Al-5Ti-1B refining agent was added to the aluminum melt at a rate of 0.2% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was stirred evenly and held at the temperature for 3 min. Al-Ti-B-Ce master alloy was added to the aluminum melt at a rate of 0.03% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was held at 720℃ for 5 min. The mass fractions of Ti, B, and Ce in this master alloy were 6%, 1.2%, and 1%, respectively, with the remainder being Al.
[0044] (3) Foam stabilizer mixing: The coated and modified foam stabilizer raw material was pulverized to a particle size of 10 μm using an air jet mill. The pulverized foam stabilizer raw material was mixed with Al-Mg industrial aluminum alloy powder at a mass ratio of 1:3 to form a pre-dispersion. The pre-dispersion was added to the aluminum melt after interface activation treatment, and mechanical stirring and electromagnetic stirring were used in combination. The mechanical stirring speed was 500 r / min, the electromagnetic stirring frequency was 60 Hz, and the stirring time was 5 min. During the stirring process, the temperature of the aluminum melt was maintained at 720℃, and the temperature fluctuation did not exceed ±5℃, to obtain the aluminum melt to be foamed.
[0045] (4) Air blowing and foaming: The aluminum melt to be foamed is transferred at a constant speed to a closed foaming mold. Air blowing is performed after the temperature of the aluminum melt stabilizes at 700℃. Nitrogen is selected as the inert gas and is successively dried by molecular sieve and purified by activated carbon. The drying temperature is 35℃ and the time is 15min. The moisture content of the gas after drying is ≤0.01%, and the purification flow rate is 5L / min. A stainless steel porous tube is used as a porous air blowing device with a pore diameter of 50μm. The air outlet end is immersed in the aluminum melt to be foamed for 30mm. The initial air blowing pressure is 0.3MPa, the initial temperature of the aluminum melt is 700℃, the pressure increases at a constant rate of 0.1MPa / min, and the temperature decreases at a constant rate of 8℃ / min. The final air blowing pressure is 0.8MPa, the aluminum melt temperature is 640℃, the gas flow rate is 20L / min, and the total air blowing time is 30s. The vibration treatment frequency is 50Hz, the amplitude is 3mm, the vibration direction is perpendicular to the bottom surface of the mold, and it accompanies the air blowing process throughout. The inner wall of the mold is coated with a graphite release agent with a thickness of 10μm, and then used after natural drying.
[0046] (5) Cooling and shaping: The aluminum foam blank is cooled in a gradient manner with the mold, and the whole process is sealed. First, it is cooled to 450°C at a rate of 15°C / min and held for 15 min, and then cooled to room temperature at a rate of 5°C / min. Nitrogen gas is introduced during the holding period at a flow rate of 3L / min, and the pressure inside the mold is maintained at 0.15MPa. After cooling, the closed-cell aluminum foam product is obtained by demolding.
[0047] Example 3:
[0048] (1) Raw material preparation: Al-Si industrial aluminum alloy was selected as the aluminum alloy matrix raw material with a Si content of 8%. TiC, La2O3, and ZrC were selected as foam stabilizer raw materials, and the amount of foam stabilizer added was 0.3% of the mass of the aluminum alloy matrix raw material. The foam stabilizer particles were uniformly coated with an Al2O3 coating layer with a coating thickness of 2μm. After coating, the particles were dried at 90℃ until the moisture content was ≤0.1%. The Al2O3 coating layer was prepared by the sol-gel method, using tetraethyl orthosilicate as a precursor, ethanol as a solvent, and nitric acid as a catalyst. The mixture was prepared at a volume ratio of precursor:ethanol:water = 1:3:0.5. The pH value of the reaction system was controlled at 5, the reaction temperature at 70℃, and the reaction time at 2.5h. After the reaction was completed, the foam stabilizer particles were coated and then dried and calcined.
[0049] (2) Preparation of aluminum melt: Al-Si industrial aluminum alloy was heated to 735℃ and melted completely in a medium-frequency induction melting furnace to obtain aluminum melt. Degassing was performed by rotary jet degassing at a speed of 175 r / min, an argon flow rate of 10 L / min, and a degassing time of 7.5 min. The temperature of the aluminum melt was maintained at 710℃ during the degassing process. Al-5Ti-1B refining agent was added to the aluminum melt at a rate of 0.12% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was stirred evenly and held at the temperature for 2.5 min. Al-Ti-B-Ce master alloy was added to the aluminum melt at a rate of 0.02% of the mass of the aluminum alloy matrix raw material. After addition, the mixture was held at 710℃ for 4 min. The mass fractions of Ti, B, and Ce in this master alloy were 5%, 1%, and 0.7%, respectively, with the remainder being Al.
[0050] (3) Foam stabilizer mixing: The coated and modified foam stabilizer raw material was pulverized to a particle size of 7.5 μm using an air jet mill. The pulverized foam stabilizer raw material was mixed with Al-Si industrial aluminum alloy powder at a mass ratio of 1:2.5 to form a pre-dispersion. The pre-dispersion was added to the aluminum melt after interface activation treatment, and mechanical stirring and electromagnetic stirring were used in combination. The mechanical stirring speed was 400 r / min, the electromagnetic stirring frequency was 55 Hz, and the stirring time was 3.5 min. During the stirring process, the temperature of the aluminum melt was maintained at 685℃, and the temperature fluctuation did not exceed ±5℃, to obtain the aluminum melt to be foamed.
[0051] (4) Gas blowing and foaming: The aluminum melt to be foamed is transferred at a constant speed to a closed foaming mold. Gas blowing is performed after the temperature of the aluminum melt stabilizes at 690℃. Helium is selected as the inert gas and is successively dried by molecular sieve and purified by activated carbon. The drying temperature is 30℃ and the time is 12min. The moisture content of the gas after drying is ≤0.01%, and the purification flow rate is 4L / min. A porous ceramic tube is used as a porous blowing device with a pore diameter of 30μm. The outlet end is immersed 20mm into the aluminum melt to be foamed. The initial blowing pressure is 0.25MPa, the initial temperature of the aluminum melt is 690℃, the pressure increases at a constant rate of 0.075MPa / min, and the temperature decreases at a constant rate of 6.5℃ / min. The final blowing pressure is 0.7MPa, the temperature of the aluminum melt is 630℃, the gas flow rate is 12L / min, and the total blowing time is 20s. The vibration treatment frequency is 35Hz, the amplitude is 2mm, and the vibration direction is perpendicular to the bottom surface of the mold, accompanied by air blowing throughout the process. The inner wall of the mold is coated with boron nitride release agent with a thickness of 7.5μm and is used after natural drying.
[0052] (5) Cooling and shaping: The aluminum foam blank is cooled in a gradient manner with the mold, and the whole process is sealed. First, it is cooled to 425°C at a rate of 12°C / min and held for 12min. Then, it is cooled to room temperature at a rate of 3.5°C / min. During the holding period, helium gas is introduced at a flow rate of 2.5L / min, and the pressure inside the mold is maintained at 0.12MPa. After cooling, the closed-cell aluminum foam product is obtained by demolding.
[0053] Comparative Example 1: Compared with Example 3, Comparative Example 1 did not undergo foam stabilizer coating modification treatment, and the remaining process parameters were exactly the same as those of Example 3.
[0054] Comparative Example 2: Compared with Example 3, Comparative Example 2 did not undergo aluminum melt interface activation treatment, did not add Al-Ti-B-Ce master alloy, and the remaining process parameters were exactly the same as those in Example 3.
[0055] Comparative Example 3: Compared with Example 3, Comparative Example 3 does not adopt the dynamic coordinated control mode of temperature and pressure. The blowing process maintains a constant pressure of 0.25 MPa and a temperature of 690°C, and the other process parameters are exactly the same as those in Example 3.
[0056] Comparative Example 4: Compared with Example 3, Comparative Example 4 did not use gradient cooling and was directly cooled to room temperature at a rate of 15°C / min. The remaining process parameters were exactly the same as those in Example 3.
[0057] test: Experiment 1: Closed-cell ratio test: Experimental methods: The closed-cell rate of aluminum foam was tested using a combination of the water displacement method and microscopic observation. Samples were taken in sizes of 50mm × 50mm × 50mm, and each sample was tested three times, with the average value taken. First, the sample volume and apparent density were determined using the Archimedes water displacement method. Then, the pore state of the cross-section was observed using a metallographic microscope. The ratio of closed pores to total pores was calculated to determine the closed-cell rate.
[0058] Experimental data: Table 1 Results of closed-pore ratio test
[0059] In all examples, the closed-cell rate was higher than 94%. Comparative Example 1 lacked a foam stabilizer, which easily agglomerated and decomposed too quickly, leading to easy pore rupture and interconnection, resulting in a significant decrease in the closed-cell rate. Comparative Example 2 lacked interface activation treatment, resulting in uneven surface tension of the aluminum melt, poor pore wall stability, and a reduced closed-cell rate. Comparative Example 3 lacked dynamic temperature and pressure control, leading to uncontrolled bubble growth, numerous interconnected pores, and the lowest closed-cell rate. Comparative Example 4 had an excessively rapid cooling rate, resulting in uneven pore wall shrinkage, rupture of some pores, and a lower closed-cell rate than the examples.
[0060] Experiment 2: Average pore size and pore size uniformity test: Experimental methods: The cross-sectional images of the samples were acquired using a metallographic microscope. The pore diameters of no less than 200 pores were counted using image analysis software. The average pore diameter and the coefficient of variation of the pore diameter were calculated. The smaller the coefficient of variation, the more uniform the pore diameter.
[0061] Experimental data: Table 2. Test results of average pore size and pore size uniformity
[0062] The average pore size in the examples was stable at 2.1 mm-2.3 mm, with a coefficient of variation below 8.5%, exhibiting excellent pore size uniformity. Comparative Example 1 showed poor foam stabilizer dispersion, significant variations in bubble size, and a large coefficient of variation. Comparative Example 2 exhibited insufficient melt interfacial activity, resulting in uneven bubble nucleation and growth, and large pore size deviations. Comparative Example 3, with its constant temperature and pressure, led to excessive bubble growth, resulting in larger pore sizes and the worst uniformity. Comparative Example 4, with its rapid cooling, resulted in uneven pore size distribution, with uniformity worse than the examples.
[0063] Experiment 3: Compressive Yield Strength Test Experimental methods: According to relevant material mechanics testing methods, a quasi-static compression test was conducted using a universal testing machine. The sampling size was Φ30mm×30mm, the compression rate was 1mm / min, and the compressive yield strength was recorded. Each group of tests was performed 3 times and the average value was taken.
[0064] Experimental data: Table 3 Results of compressive yield strength test
[0065] The compressive yield strength of all examples was higher than 8.5 MPa. Comparative Example 1, due to its low closed-cell ratio and thin pore walls, had poor load-bearing capacity and significantly reduced strength. Comparative Example 2 lacked interface activation, resulting in insufficient pore wall bonding strength and lower overall strength. Comparative Example 3 had numerous pore structure defects and the worst overall mechanical properties. Comparative Example 4 had high cooling internal stress, making it prone to microcracks in the pore walls, and its strength was lower than that of the examples.
[0066] 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 producing closed-cell aluminum foam by air blowing, characterized in that, Includes the following steps: (1) Raw material preparation: Select aluminum alloy matrix raw material and foam stabilizer raw material; the foam stabilizer raw material is at least one of titanium-based compound, rare earth compound, and Zr compound, and its addition amount is 0.1-0.5% of the mass of the aluminum alloy matrix raw material; the foam stabilizer raw material is coated and modified. (2) Preparation of aluminum melt: The aluminum alloy matrix raw material is melted to complete melting to obtain aluminum melt; the aluminum melt is subjected to degassing and refining treatment in sequence, and interface activation treatment is performed simultaneously; the degassing treatment adopts the rotary jet degassing method, and argon gas is introduced into the aluminum melt; the refining treatment is to add Al-5Ti-1B refining agent to the aluminum melt; the interface activation treatment is to add Al-Ti-B-Ce master alloy to the aluminum melt; (3) Foam stabilizer mixing: First, the coated and modified foam stabilizer raw material is crushed to a preset particle size, and then mixed evenly with a small amount of aluminum alloy matrix raw material powder to form a pre-dispersion; The pre-dispersed material is added to the aluminum melt after interface activation treatment, and the mixture is stirred to obtain the aluminum melt to be foamed. (4) Air blowing foaming: The aluminum melt to be foamed is transferred to a closed foaming mold. The inert gas is first dried and purified for pretreatment. Then, the pretreated inert gas is introduced into the aluminum melt to be foamed through the porous air blowing device inside the mold. During the air blowing process, the temperature and pressure are dynamically coordinated and controlled. At the same time, the closed foaming mold is vibrated to complete the foaming and obtain the foamed aluminum billet. (5) Cooling and shaping: The aluminum foam blank is cooled together with the closed foaming mold using a gradient cooling method. After cooling, it is demolded to obtain the closed-cell aluminum foam finished product.
2. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (1), the aluminum alloy matrix raw material is any one of industrial-grade pure aluminum, Al-Si industrial aluminum alloy, and Al-Mg industrial aluminum alloy; the titanium-based compound is at least one of TiH2 and TiC; the rare earth compound is at least one of La2O3 and CeO2; and the Zr compound is at least one of ZrO2 and ZrC.
3. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (1), the coating modification treatment specifically involves uniformly coating the foam stabilizer particles with an Al2O3 coating layer, with the coating layer thickness controlled at 1-3 μm. After coating, the particles are dried at 80-100℃ until the moisture content is ≤0.1%. The Al2O3 coating layer is prepared by the sol-gel method, specifically by using tetraethyl orthosilicate as a precursor, ethanol as a solvent, and nitric acid as a catalyst, mixed at a volume ratio of precursor:ethanol:water = 1:3:0.5, controlling the pH of the reaction system to be 4-6, the reaction temperature to be 60-80℃, and the reaction time to be 2-3 h. After the reaction is completed, the foam stabilizer particles are coated and then dried and calcined.
4. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (2), the aluminum alloy matrix raw material is smelted in a medium-frequency induction melting furnace at 720-750℃; the rotary blowing degassing method has a blowing speed of 150-200 r / min, an argon flow rate of 8-12 L / min, a degassing time of 5-10 min, and the aluminum melt temperature is maintained at 700-720℃ during the degassing process; the Al-Ti-B-Ce master alloy is added at 0.01-0.03% of the mass of the aluminum alloy matrix raw material, and after addition, it is kept at 700-720℃ for 3-5 min, and the mass fractions of Ti, B, and Ce in the master alloy are 4-6%, 0.8-1.2%, and 0.5-1%, respectively, with the remainder being Al; the Al-5Ti-1B refining agent is added at 0.05-0.2% of the mass of the aluminum alloy matrix raw material, and after the Al-5Ti-1B refining agent is added, it is stirred evenly and kept at 2-3 min.
5. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (3), the foam stabilizer raw material is pulverized to a particle size of 5-10 μm using an air jet mill; the mass ratio of the foam stabilizer raw material to the aluminum alloy matrix raw material powder in the pre-dispersion is strictly controlled to be 1:2-3; the stirring adopts a combination of mechanical stirring and electromagnetic stirring, with a mechanical stirring speed of 300-500 r / min, an electromagnetic stirring frequency of 50-60 Hz, a stirring time of 2-5 min, and the temperature of the aluminum melt is strictly maintained at 650-720℃ during the stirring process, with temperature fluctuation not exceeding ±5℃.
6. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (4), the aluminum melt to be foamed is transferred at a constant speed to a closed foaming mold. After the transfer, the temperature of the aluminum melt is stabilized at 680-700℃ before blowing. The inert gas pretreatment specifically involves sequentially passing through molecular sieve drying and activated carbon purification. The drying temperature is 25-35℃ and the time is 10-15min. After drying, the gas moisture content is ≤0.01%. The purification flow rate is 3-5L / min, and the inert gas is any one of argon, nitrogen, or helium.
7. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (4), the porous blowing device is a porous ceramic tube or a stainless steel porous tube with a pore diameter of 10-50 μm. The outlet end is completely immersed in the aluminum melt to be foamed, with an immersion depth of 10-30 mm. The dynamic coordinated control mode of temperature and pressure is as follows: the initial blowing pressure is 0.2-0.3 MPa, the initial temperature of the aluminum melt is 680-700℃, and as the blowing time increases, the pressure increases uniformly at a rate of 0.05-0.1 MPa / min, and the temperature decreases uniformly at a rate of 5-8℃ / min. Finally, the blowing pressure is controlled to be 0.6-0.8 MPa, the aluminum melt temperature is 620-640℃, the gas flow rate is maintained at 5-20 L / min throughout the process, and the total blowing time is 10-30 s.
8. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (4), the vibration frequency of the vibration treatment is 20-50Hz, the amplitude is 1-3mm, the vibration direction is perpendicular to the bottom surface of the mold, and the entire process is accompanied by blowing and foaming; the inner wall of the sealed foaming mold is uniformly coated with a high-temperature resistant release agent.
9. The method for producing closed-cell aluminum foam by air blowing according to claim 8, characterized in that, The release agent is boron nitride or graphite release agent, with a coating thickness of 5-10 μm. After coating, it is allowed to air dry naturally before being loaded into the aluminum melt to be foamed.
10. The method for producing closed-cell aluminum foam by air blowing according to claim 1, characterized in that, In step (5), the mold is kept sealed throughout the gradient cooling process. First, it is cooled to 400-450℃ at a rate of 10-15℃ / min, and then kept at this temperature for 10-15min. Then, it is slowly cooled to room temperature at a rate of 2-5℃ / min. During the heat preservation period, the same type of inert gas as in step (4) is introduced into the sealed mold at a flow rate of 2-3L / min, and the pressure inside the mold is maintained at 0.1-0.15MPa.