Foamed aluminum component with controllable pore structure gradient and preparation method

Abstract

The invention discloses a porous structure gradient controllable foamed aluminum component and a preparation method, and belongs to the technical field of porous metal material preparation. According to the method, a thin-wall stainless steel mold is adopted, a density gradient pre-foaming blank is formed through a hot forging and pressing process, and a composite process of induction pulse pretreatment and staged induction heating foaming is combined, so that the porous structure gradient controllable foamed aluminum component composed of a core material with the axial density gradient larger than or equal to 0.2 g / dm < 4 > and an aluminum sheet with the thickness ranging from 0.12 mm to 0.25 mm is prepared. According to the process system provided by the invention, the thickness of a surface compact layer can be remarkably increased while the gradient distribution of pores is effectively regulated and controlled, so that the two major problems of poor controllability and insufficient surface strengthening of a gradient structure are synchronously solved, and a new method is provided for controllable preparation of a high-performance gradient foamed aluminum component.

Description

Technical Field

[0001] This invention belongs to the field of porous metal material preparation technology, and relates to a foamed aluminum component with controllable pore structure gradient and its preparation method. Background Technology

[0002] Aluminum foam, as a typical porous metallic material, possesses low density, high specific strength, excellent energy absorption characteristics, and damping properties due to its unique pore structure, making it valuable for applications in lightweight structures and impact protection. Traditional aluminum foam manufacturing processes (such as melt foaming and powder metallurgy) typically produce homogeneous structures with uniformly distributed pores. Their isotropic properties are insufficient to meet the complex requirements of modern engineering for spatially gradient distribution of material properties. Density gradient aluminum foam components, by controlling the spatial distribution of material density, construct non-uniform structures with specific functional gradients, representing an effective way to improve the overall performance of the material.

[0003] Aluminum foam prepared by traditional heating methods has characteristics such as uniform sample density, inability to be formed in one step, and difficulty in connecting with other components due to the lack of a dense aluminum layer. This results in disadvantages such as a low upper limit for material processing and unpredictable deformation processes during practical applications. Furthermore, molds prepared by traditional heating methods are generally too thick, increasing the production cost of the samples.

[0004] Although existing technologies have proposed achieving a pore size gradient structure in aluminum foam from the surface inward by controlling heating and extending cooling time, they also point out that this method has poor process controllability, and the evolution behavior of the cells during the forming process is difficult to grasp. In addition, although existing processes can form a dense skin on the surface of aluminum foam, its thickness is generally thin, and its effect on enhancing the overall mechanical properties of the component is relatively limited. Summary of the Invention

[0005] To address the aforementioned problems, the purpose of this invention is to propose an economical and efficient method for preparing aluminum foam components with a controllable core material density gradient. This invention proposes a composite preparation process that utilizes a thin-walled stainless steel mold to hot-forge a density gradient pre-foamed blank, combined with induction pulse pretreatment and staged induction heating foaming. This process effectively controls the pore gradient distribution while significantly increasing the thickness of the surface dense layer, thus simultaneously solving the two major problems of poor controllability of the gradient structure and insufficient surface reinforcement, providing a new method for the controllable preparation of high-performance gradient aluminum foam components.

[0006] This invention proposes a method for preparing aluminum foam components with controllable pore structure gradient, comprising the following steps:

[0007] Step 1: Alloy melting: After melting industrial pure aluminum or aluminum alloy, heat it to 750℃-780℃, and add Si, Mg and Cu to adjust the melt composition.

[0008] Step 2: Casting the pre-foamed blank: Add thickening particles to the alloy, cool it down, stir and add the pretreated foaming agent, stir evenly and pour it into a preheated cuboid mold to prepare the pre-foamed blank.

[0009] Step 3: Hot forging to prepare density gradient pre-foamed samples: After heating the strip-shaped pre-foamed blank, it is locally forged by a hydraulic press to form a pre-foamed sample with a density gradient.

[0010] Step 4: Assemble the foaming mold: Place the blank to be foamed prepared in Step 3 into the cavity of the steel thin-walled foaming mold. Use two graphite blocks to seal the openings at both ends of the mold.

[0011] Step 5: Induction Pulse Pretreatment: The sample is subjected to 3-5 pulse heating cycles using a high-power current to pretreat the titanium hydride in the sample skin. Under the action of the induced current, an induction heating layer is formed on the sample surface, raising the sample surface temperature to above 640℃. Heating is stopped after holding at this temperature for 10-30 seconds, causing the foaming agent in the surface aluminum skin to decompose and become ineffective in subsequent foaming processes.

[0012] Step Six: Staged Induction Heating Foaming: Medium- and high-frequency induction current is used to rapidly heat and melt the sample. Once the sample enters the molten state, the input current is reduced until the sample further expands and fully fills the mold cavity.

[0013] Step 7: Cooling: After the foam fills the cavity, turn off the power to the induction furnace and cool the sample to room temperature.

[0014] Step 8: Disassemble the thin-walled mold to obtain a foamed aluminum component with a core material gradient.

[0015] In step one, the adjusted aluminum alloy composition is: Si 7.6wt%-9.5wt%, Mg 0.2wt%-0.5wt%, Cu 0-2.0wt%, with the remainder being aluminum.

[0016] In step two, the pretreatment of TiH2 is either vacuum treatment or air atmosphere heating treatment, with a treatment temperature of 450℃-520℃. When vacuum treatment is used, the gas pressure is 100Pa-400Pa.

[0017] Thickening granules, which are Ca powder or Al2O3 powder, are added during stirring. The addition temperature of the thickening granules is between 680℃ and 700℃; when the thickening granules are Ca, the addition amount is between 1wt% and 2wt%, and when the thickening granules are Al2O3, the addition amount is between 2wt% and 4wt%. The foaming agent added during stirring is preferably pretreated TiH2, added at a temperature between 640℃ and 650℃, and in an amount between 0.8wt% and 1.0wt%. The stirring time is 1min to 3min, and the stirring speed is 800rpm to 900rpm. The preheating temperature of the cuboid mold is 500℃ to 600℃. The density of the pre-foamed preform is 1.5g / cm³. 3 -1.7g / cm 3 .

[0018] In step three, the heating temperature of the strip-shaped pre-foamed preform is 460℃-510℃, and the hot forging pressure is 80MPa-150MPa. The density gradient of the resulting pre-foamed sample is 0.20 g / dm³. 4 -0.40g / dm 4 .

[0019] In step four, the foaming mold is a thin-walled steel pipe with an inner cavity size that matches the size of the blank to be foamed in step three, and the graphite block matches the size of the mold port to provide a sealing function; the wall thickness of the thin-walled steel pipe is 0.8mm-1.5mm, and the preferred material of the steel pipe is 304 stainless steel.

[0020] In step five, the pulse heating power used is 50kW-80kW, the pulse time is 5s-10s, and the time interval is 10s-30s.

[0021] In step six, the induction heating equipment used is a 10kHz-30kHz all-solid-state induction heating power supply, which performs segmented induction heating foaming on the preform. Initially, the heating current is adjusted to 0.38A-0.40A to raise the sample temperature to 580℃-620℃ within 5-6 minutes. After the sample enters a molten state, the input current is reduced to maintain it at 0.27A-0.29A to stabilize the sample temperature at 610℃-630℃, and the heating process continues until the sample further expands and fully fills the mold cavity.

[0022] In step seven, after the foaming process is completed, immediately cut off the induction heating power supply and cool the sample to room temperature by air cooling or wind cooling.

[0023] In step eight, after cooling is complete, the thin-walled mold is disassembled to obtain a foamed aluminum component with a core material gradient.

[0024] A second aspect of this invention provides a foamed aluminum component with controllable pore structure gradient, prepared using the aforementioned method. The foamed aluminum component is cylindrical and consists of a closed-cell foam-like core material with axial pore size and density gradients, and an aluminum sheet; the axial density gradient of the closed-cell foamed aluminum core material is ≥0.2 g / dm³. 4 The aluminum sheet thickness is 0.12mm~0.25mm.

[0025] The key point of this invention is:

[0026] 1. A dense aluminum skin is formed using pulse heating, which improves the mechanical properties of the component.

[0027] 2. Active design of density gradient foamed aluminum components is achieved by preparing density gradient pre-foamed materials.

[0028] 3. By designing thin-walled molds and a variable current induction heating process, heat transfer efficiency is improved, preparation time is shortened, and preparation costs are reduced.

[0029] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0030] The induction heating method for preparing density gradient aluminum foam components provided by this invention offers the following comprehensive advantages: First, the pulse heating method allows for the in-situ formation of a dense aluminum skin (thickness not less than 0.1 mm) on the component surface, effectively improving overall mechanical properties and facilitating connection with other components. Second, by pre-preparing a pre-foamed body with a density gradient and coordinating with hot forging parameter control, the density gradient distribution of the foam core material can be actively designed, achieving controllable density changes along the axial direction. This allows for a gradual increase in stress and orderly transmission of deformation behavior during deformation, significantly enhancing the predictability and controllability of structural design and expanding its applicability in energy-absorbing components and other fields. Furthermore, the use of thin-walled molds combined with a variable current induction heating process greatly improves heat transfer efficiency, shortens the preparation cycle, and reduces mold and overall production costs. The rapid cooling of the thin-walled molds also helps suppress shrinkage and ensure the surface flatness of the components, making it suitable for large-scale production.

[0031] These characteristics together give density gradient aluminum foam components a wide range of applications and potential in the manufacture of high-performance, low-cost energy-absorbing structures. Attached Figure Description

[0032] Figure 1 This is a schematic diagram of the heating device used in this invention.

[0033] Figure 2 This is a CT cross-sectional image of the Al-7.6Si0.2Mg1Ca density gradient aluminum foam component prepared according to the present invention.

[0034] Figure 3This is a longitudinal cross-sectional CT slice of the Al-7.6Si0.2Mg1Ca density gradient aluminum foam component prepared according to the present invention.

[0035] Figure 4 The Al-7.6Si0.2Mg1Ca prepared according to this invention has an average density of 0.6 g / cm³. 3 Stress-strain curves of density gradient aluminum foam components.

[0036] Figure 5 The Al-7.6Si0.2Mg1Ca prepared according to this invention has an average density of 0.6 g / cm³. 3 Energy absorption and energy absorption efficiency of density gradient aluminum foam components.

[0037] Figure 6 This is a CT cross-sectional image of the Al-9.5Si0.5Mg2Al2O3 density gradient foam aluminum component prepared according to the present invention.

[0038] Figure 7 The Al-9.5Si0.5Mg2Al2O3 prepared according to this invention has an average density of 0.7 g / cm³. 3 Stress-strain curves of density gradient aluminum foam components.

[0039] Figure 8 The Al-9.5Si0.5Mg2Al2O3 prepared according to this invention has an average density of 0.7 g / cm³. 3 Energy absorption and energy absorption efficiency of density gradient aluminum foam components.

[0040] Figure 9 The average density of Al-9.5Si0.5Mg1.5Al2O3 prepared by conventional methods is 0.6 g / cm³. 3 CT slice image of the transverse section.

[0041] Figure 10 The average density of Al-9.5Si0.5Mg1.5Al2O3 prepared by conventional methods is 0.6 g / cm³. 3 The stress-strain curve of aluminum foam.

[0042] Figure 11 The average density of Al-9.5Si0.5Mg1.5Al2O3 prepared by conventional methods is 0.6 g / cm³. 3 The energy absorption and energy absorption efficiency of aluminum foam. Detailed Implementation

[0043] This invention provides a method for preparing aluminum foam components with controllable pore structure gradient, comprising the following steps:

[0044] Step 1: Alloy melting: After melting industrial pure aluminum or aluminum alloy, heat it to 750℃-780℃ and adjust the composition so that the melt contains Si 7.6wt%-9.5wt%, Mg 0.2wt%-0.5wt%, Cu 0-2.0wt%, with the balance being Al.

[0045] Step 2: Casting the pre-foamed blank: Add 1-2wt% Ca powder or 2wt%-4wt% Al2O3 powder to the melt at 680℃-700℃ and stir until homogeneous. Treat TiH2 under vacuum or air atmosphere at 450℃-520℃. When using vacuum treatment, the gas pressure should be 100Pa-400Pa. After the melt cools to 640℃-650℃, add 0.8wt%-1.0wt% of the pretreated TiH2 to the melt and stir at 800rpm-900rpm for 1-3 minutes. After stirring, quickly pour the melt into a preheated cuboid mold at 500℃-600℃. After cooling, a density of 1.5g / cm³ is obtained. 3 ~1.7g / cm 3 The pre-expanded foam blank.

[0046] Step 3: Hot forging to prepare density gradient pre-foamed samples: After heating the pre-foamed blank to 460℃-510℃, it is locally forged using a hydraulic press at a pressure of 80MPa-150MPa to form a density gradient of 0.20g / dm³ in the pre-foamed body. 4 -0.40g / dm 4 Pre-foamed samples.

[0047] Step 4: Assemble the foaming mold: Place the pre-foamed sample inside a thin-walled steel tube whose inner cavity size matches the pre-foamed sample. Select two graphite blocks that can achieve a sealing effect to seal the openings at both ends of the mold respectively. The wall thickness of the thin-walled steel tube is 0.8mm-1.5mm, and the material is preferably 304 stainless steel.

[0048] Step 5: Induction Pulse Pretreatment: The sample is pulsed 3-5 times with a power of 50kW-80kW, a pulse duration of 5s-10s, and a pulse interval of 10s-30s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, the foaming agent to dissipate, and the surface foaming agent to become ineffective.

[0049] Step Six: Staged Induction Heating Foaming: A 10kHz-30kHz all-solid-state induction heating power supply is used to perform staged induction heating foaming on the preform. In the initial stage, the heating current is adjusted to 0.38A-0.40A to raise the sample temperature to 580℃-620℃ within 5-6 minutes. After the sample enters the molten state, the input current is reduced and maintained at 0.27A-0.29A to stabilize the sample temperature at 610℃-630℃. The heating process continues until the sample further expands and fully fills the mold cavity.

[0050] Step 7: Cooling: After the foam fills the cavity, the foaming process is over. Turn off the all-solid-state induction heating power supply and air-cool or air-cool the sample to room temperature.

[0051] Step 8: Disassemble the thin-walled steel pipe mold to obtain a foamed aluminum component with a core material gradient.

[0052] This invention also provides a foamed aluminum component with controllable pore structure gradient, prepared using the above method. The foamed aluminum component is cylindrical and consists of a closed-cell foam-like core material with axial pore size and density gradient and an aluminum sheet; the axial density gradient of the closed-cell foamed aluminum core material is ≥0.2 g / dm³. 4 The aluminum sheet thickness is 0.12mm~0.25mm.

[0053] Example 1:

[0054] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0055] Step 1. Melt industrial pure aluminum ingots in a crucible and heat to 750°C. Add Si and Mg to adjust the composition so that the melt contains 7.6 wt% Si, 0.2 wt% Mg, and the balance is Al.

[0056] Step 2. Adjust the temperature to 680℃, add 1wt% Ca powder, and stir at 800 rpm for 1 min. Pretreat TiH2 at 520℃ and a vacuum of 100 Pa. Once the aluminum alloy melt temperature drops to 640℃, add 0.8wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 800 rpm for 1 min. After stirring, quickly pour the melt into a preheated cuboid mold at 500℃. After cooling, a density of 1.6 g / cm³ is obtained. 3 The pre-expanded foam blank.

[0057] Step 3. After removing the preform, heat it to 500℃ and perform local hot forging at a pressure of 80MPa using a hydraulic press to prepare a material with a density gradient of 0.20g / dm³. 4 Pre-foamed samples.

[0058] Step 4. As attached Figure 1 As shown, the pre-foamed sample is placed in the center of a 304 stainless steel mold with an inner cavity size that matches the pre-foamed sample and a wall thickness of 0.8 mm, and both ends are sealed with graphite blocks.

[0059] Step 5. Apply a 60kW current with a pulse duration of 5s and a time interval of 10s to heat the sample five times. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, releasing the foaming agent and rendering the surface foaming agent ineffective.

[0060] Step 6. Use a 10kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.38A current for 5 minutes to raise the specimen temperature to 610℃. After the sample enters the molten state, use a 0.28A current to stabilize the specimen temperature at 620℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0061] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and allow the sample to cool to room temperature using air cooling.

[0062] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0063] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.40 g / dm³. 4 Its average epidermal thickness is 0.18 mm.

[0064] It was scanned using an industrial CT scanner to obtain the following results: Figure 2 The CT image of the transverse section with gradient variation shown, and as follows Figure 3 The image shown is a longitudinal cross-sectional CT slice with a uniform aperture. Based on... Figure 2 As shown, quasi-static compression is performed with the low-density end facing upwards, resulting in... Figure 4 The stress-strain curves shown are calculated and plotted as follows. Figure 5 The diagram shows the energy absorption and energy absorption efficiency.

[0065] from Figure 2 A clear density gradient distribution can be seen in the foamed aluminum component, corresponding to Figure 3 The stress-strain curves show that the stress gradually increases with the increase of the axial density gradient at the beginning of the plateau stage.

[0066] Example 2:

[0067] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0068] Step 1. After melting the aluminum alloy in a crucible, heat it to 770℃, and add Si, Mg and Cu to adjust the composition so that the melt contains 8wt% Si, 0.3wt% Mg and 1.0wt% Cu, with the balance being Al.

[0069] Step 2. Adjust the temperature to 685℃, add 1.2wt% Ca powder, and stir at 800rpm for 3 minutes. Pretreat TiH2 at 480℃ in air. Once the aluminum alloy melt temperature drops to 645℃, add 0.9wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 850rpm for 1 minute. After stirring, quickly pour the melt into a preheated cuboid mold at 550℃. After cooling, a density of 1.6g / cm³ is obtained. 3 Pre-foamed samples.

[0070] Step 3. After removing the preform, heat it to 460℃ and perform local hot forging at a pressure of 150MPa using a hydraulic press to prepare a material with a density gradient of 0.30g / dm³. 4 The pre-expanded foam blank.

[0071] Step 4. As attached Figure 1 As shown, the pre-foamed blank is placed in the center of a 304 stainless steel mold with an inner cavity size that matches the pre-foamed sample and a wall thickness of 0.8 mm, and both ends are sealed with graphite blocks.

[0072] Step 5. Perform four pulse heating pretreatments on the pre-foamed sample using a power of 80kW, a pulse duration of 8s, and a time interval of 15s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, resulting in the release of the foaming agent and the inactivation of the surface foaming agent.

[0073] Step 6. Use a 20kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.40A current for 5 minutes to raise the specimen temperature to 620℃. After the sample enters the molten state, use a 0.27A current to stabilize the specimen temperature at 610℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0074] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and use air cooling to cool the sample to room temperature.

[0075] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0076] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.30 g / dm. 4 Its average epidermal thickness is 0.12 mm.

[0077] Example 3:

[0078] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0079] Step 1. After melting the aluminum alloy in a crucible, heat it to 760℃, add Si and Mg to adjust the composition to 9wt% Si and 0.4wt% Mg in the melt, with the balance being Al;

[0080] Step 2. Adjust the temperature to 685℃, add 1.5wt% Ca powder, and stir at 900rpm for 1min. Pretreat TiH2 at 450℃ and a vacuum of 200Pa. Once the aluminum alloy melt temperature drops to 645℃, add 0.9wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 900rpm for 2.5min. After stirring, quickly pour the melt into a preheated cuboid mold at 600℃. After cooling, a density of 1.7g / cm³ is obtained. 3 Pre-foamed samples.

[0081] Step 3. After removing the preform, heat it to 480℃ and perform local hot forging at a pressure of 130MPa using a hydraulic press to prepare a material with a density gradient of 0.25g / dm³. 4 The pre-expanded foam blank.

[0082] Step 4. As attached Figure 1 As shown, the pre-foamed blank is placed in the center of a 304 stainless steel mold with an inner cavity size matching the pre-foamed sample and a wall thickness of 1.0 mm, and both ends are sealed with graphite blocks.

[0083] Step 5. Perform three pulse heating pretreatments on the pre-foamed sample using a power of 60kW, a pulse duration of 7s, and a time interval of 22s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, resulting in the release of the foaming agent and the inactivation of the surface foaming agent.

[0084] Step 6. Use a 10kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.38A current for 6 minutes to raise the specimen temperature to 600℃. After the sample enters the molten state, use a 0.29A current to stabilize the specimen temperature at 620℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0085] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and use air cooling to cool the sample to room temperature.

[0086] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0087] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.42 g / dm³. 4 Its average epidermal thickness is 0.22 mm.

[0088] Example 4:

[0089] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0090] Step 1. Melt industrial pure aluminum ingots in a crucible and heat to 750℃. Add Si, Mg, and Cu to adjust the composition so that the melt contains 9.5wt% Si, 0.5wt% Mg, 2.0wt% Cu, and the balance is Al.

[0091] Step 2. Adjust the temperature to 685℃, add 2wt% Ca powder, and stir at 850 rpm for 2 minutes. Pretreat TiH2 at 480℃ and a vacuum of 400 Pa. After the aluminum alloy melt temperature drops to 650℃, add 1.0wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 900 rpm for 3 minutes. After stirring, quickly pour the melt into a preheated cuboid mold at 500℃. After cooling, a density of 1.5 g / cm³ is obtained. 3 Pre-foamed samples.

[0092] Step 3. After removing the preform, heat it to 490℃ and perform local hot forging at a pressure of 120MPa using a hydraulic press to prepare a material with a density gradient of 0.35g / dm³. 4 The pre-expanded foam blank.

[0093] Step 4. As attached Figure 1 As shown, the pre-foamed blank is placed in the center of a 304 stainless steel mold with an inner cavity size that matches the pre-foamed sample and a wall thickness of 1.5 mm, and both ends are sealed with graphite blocks.

[0094] Step 5. Perform four pulse heating pretreatments on the pre-foamed sample using a power of 65kW, a pulse duration of 10s, and a time interval of 30s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, resulting in the release of the foaming agent and the inactivation of the surface foaming agent.

[0095] Step 6. Use a 10kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.39A current for 6 minutes to raise the specimen temperature to 590℃. After the sample enters the molten state, use a 0.28A current to stabilize the specimen temperature at 615℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0096] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and use air cooling to cool the sample to room temperature.

[0097] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0098] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.28 g / dm³. 4 Its average epidermal thickness is 0.25 mm.

[0099] Example 5:

[0100] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0101] Step 1. Melt industrial pure aluminum ingots in a crucible and heat to 780℃. Add Si and Mg to adjust the composition to 9.5wt% Si and 0.5wt% Mg in the melt, with the balance being Al.

[0102] Step 2. Adjust the temperature to 685℃, add 2wt% Al2O3 powder, and stir at 900rpm for 1min. Pretreat TiH2 at 450℃ and a vacuum of 300Pa. Once the aluminum alloy melt temperature drops to 640℃, add 0.8wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 900rpm for 1min. After stirring, quickly pour the melt into a preheated cuboid mold at 580℃ and cool to obtain a density of 1.6g / cm³. 3 Pre-foamed samples.

[0103] Step 3. After removing the preform, heat it to 510℃ and perform local hot forging at a pressure of 100MPa using a hydraulic press to prepare a material with a density gradient of 0.40g / dm³. 4 The pre-expanded foam blank.

[0104] Step 4. As attached Figure 1 As shown, the pre-foamed blank is placed in the center of a 304 stainless steel mold with an inner cavity size that matches the pre-foamed sample and a wall thickness of 1.2 mm, and both ends are sealed with graphite blocks.

[0105] Step 5. Perform three pulse heating pretreatments on the pre-foamed sample using a power of 75kW, a pulse duration of 6s, and a time interval of 20s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, the foaming agent to dissipate, and the surface foaming agent to become ineffective.

[0106] Step 6. Use a 10kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.39A current for 5 minutes to raise the specimen temperature to 580℃. After the sample enters the molten state, use a 0.29A current to stabilize the specimen temperature at 630℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0107] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and use air cooling to cool the sample to room temperature.

[0108] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0109] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.50 g / dm. 4 Its average epidermal thickness is 0.15 mm.

[0110] The results of scanning it using an industrial CT scanner are shown in the attached image. Figure 6 The image shows a CT scan with gradient changes. Following the example shown in the image, quasi-static compression was performed with the low-density end facing upwards, resulting in the following... Figure 7 The stress-strain curves shown are calculated and plotted as follows. Figure 8 The diagram shows the energy absorption and energy absorption efficiency.

[0111] from Figure 5 A clear density gradient distribution can be seen in the foamed aluminum component, corresponding to Figure 7 The stress-strain curves show that the stress gradually increases with the increase of the axial density gradient at the beginning of the plateau stage.

[0112] Example 6:

[0113] This embodiment provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0114] Step 1. After melting the aluminum alloy in a crucible, heat it to 770℃ and add Si, Mg and Cu to adjust the composition so that the melt contains 9.5wt% Si, 0.5wt% Mg and 1.5wt% Cu, with the balance being Al.

[0115] Step 2. Adjust the temperature to 700℃, add 4wt% Al2O3 powder, and stir at 800rpm for 3 minutes. Pretreat TiH2 at 520℃ in air. Once the aluminum alloy melt temperature drops to 650℃, add 0.9wt% of the pretreated TiH2 to the aluminum alloy melt and stir at 850rpm for 2 minutes. After stirring, quickly pour the melt into a preheated cuboid mold at 550℃. After cooling, a density of 1.5g / cm³ is obtained. 3Pre-foamed samples.

[0116] Step 3. After removing the preform, heat it to 510℃ and perform local hot forging at a pressure of 100MPa using a hydraulic press to prepare a material with a density gradient of 0.30g / dm³. 4 The pre-expanded foam blank.

[0117] Step 4. As attached Figure 1 As shown, the pre-foamed blank is placed in the center of a 304 stainless steel mold with an inner cavity size that matches the pre-foamed sample and a wall thickness of 0.8 mm, and both ends are sealed with graphite blocks.

[0118] Step 5. Perform three pulse heating pretreatments on the pre-foamed sample using a power of 50kW, a pulse duration of 10s, and a time interval of 30s. This pretreatment of the sample surface forms an induction heating layer, causing the sample surface to heat up rapidly, resulting in the release of the foaming agent and the inactivation of the surface foaming agent.

[0119] Step 6. Use a 30kHz all-solid-state induction heating power supply to perform segmented induction heating foaming on the preform. First, heat with a 0.38A current for 5 minutes to raise the specimen temperature to 590℃. After the sample enters the molten state, use a 0.27A current to stabilize the specimen temperature at 610℃, and maintain the foaming temperature until the sample further expands and fully fills the mold cavity.

[0120] Step 7. After the aluminum foam fills the mold cavity, stop the foaming process. Turn off the all-solid-state induction heating power supply and use air cooling to cool the sample to room temperature.

[0121] Step 8. Disassemble the 304 stainless steel mold to obtain a foamed aluminum component with a core material gradient.

[0122] The axial density gradient of the core material of the foamed aluminum component prepared in this embodiment is 0.32 g / dm. 4 Its average epidermal thickness is 0.18 mm.

[0123] Comparative Example 1:

[0124] This comparative example provides a method for preparing a foamed aluminum component with controllable pore structure gradient, which is carried out according to the following steps:

[0125] Industrial pure aluminum ingots were melted in a crucible and heated to a predetermined temperature. 9.5 wt% Si and 0.5 wt% Mg were added sequentially, followed by adjusting the temperature to 690℃ and adding 1.5 wt% Al₂O₃, stirring at 850 rpm for 2 minutes. TiH₂ was pretreated at 470℃ under a vacuum of 400 Pa. The temperature of the aluminum alloy melt was then lowered to 645℃, and 0.9 wt% of the pretreated TiH₂ was added, stirring at 800 rpm for 3 minutes. After stirring, the melt was quickly poured into a preheated rectangular mold at 300℃. After cooling, a dense preform was obtained. The preform was cut into uniform strips using wire cutting. These strips were placed in the center of a 3mm thick 304 stainless steel mold, with both ends sealed with graphite blocks. Foaming was performed using a constant 0.32A current until the mold was filled. The mold was then removed, and the strips were allowed to cool naturally, yielding an average density of 0.6 g / cm³. 3 Cylindrical aluminum foam. Its surface thickness is 0.05 mm.

[0126] The thicker mold shell reduced heat transfer efficiency, resulting in noticeable defects on the sample surface. Furthermore, the isothermal foaming process extended the sample melting time to 15 minutes, significantly reducing production efficiency.

[0127] The results of scanning it using an industrial CT scanner are shown in the attached image. Figure 9 The CT image shown is relatively uniform. Quasi-static compression is then applied to obtain... Figure 10 The stress-strain curves shown are calculated and plotted as follows. Figure 11 The diagram shows the energy absorption and energy absorption efficiency.

[0128] contrast Figure 3 and Figure 4 It is evident that the component sample prepared using conventional methods has a significantly lower peak stress than the former, due to the lack of a dense and thick metal skin for support. The plateau region is stable, lacking proactive design of material properties, which reduces its application potential.

Claims

1. A method for preparing a foamed aluminum component with controllable pore structure gradient, characterized in that, Includes the following steps: Step 1. Alloy melting: After melting industrial pure aluminum or aluminum alloy, heat the mixture to 750℃-780℃ and add Si, Mg, and Cu to adjust the melt composition; Step 2. Casting the pre-foamed preform: After adding thickening particles to the alloy and stirring, the mixture is cooled to 640℃-650℃, and then 0.8wt%-1.0wt% of pretreated foaming agent is added while stirring. After stirring evenly, the mixture is poured into a preheated cuboid mold to prepare the pre-foamed preform; the density of the pre-foamed preform is 1.5 g / cm³. 3 -1.7g / cm 3 ; Step 3. Hot forging to prepare density gradient pre-foamed samples: After heating the pre-foamed preform, it is locally hot-forged using a hydraulic press to form a pre-foamed sample with a density gradient; wherein the heating temperature is 460℃-510℃, the hot forging pressure is 80MPa-150MPa, and the density gradient of the pre-foamed sample is 0.20 g / dm³. 4 -0.40g / dm 4 ; Step 4. Assemble the foaming mold: Place the blank to be foamed prepared in step 3 into the cavity of the steel thin-walled foaming mold, and use two graphite blocks to seal the openings at both ends of the mold respectively; the wall thickness of the thin-walled steel pipe is 0.8mm-1.5mm; Step 5. Induction pulse pretreatment: The sample is pulsed with a high-power current for 3-5 times to pretreat the titanium hydride in the sample skin; under the action of the induced current, an induction heating layer is formed on the sample surface, raising the sample surface temperature to above 640℃. After holding at this temperature for 10s-30s, heating is stopped, causing the foaming agent in the surface aluminum skin to decompose and become ineffective in the subsequent foaming process. Step 6. Staged induction heating foaming: Medium and high frequency induction current is used to heat the sample rapidly to melt it; after the sample enters the molten state, the input current is reduced until the sample expands further and fully fills the mold cavity; the induction heating equipment used has a frequency of 10kHz-30kHz. Step 7. Cooling: Once the foam fills the cavity, the foaming process is complete. Immediately turn off the induction heating power and cool the sample to room temperature. Step 8. Disassemble the thin-walled mold to obtain a foamed aluminum component with a core material gradient.

2. The method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1, characterized in that, In step 6, the staged induction heating foaming process is as follows: in the initial stage, the heating current is adjusted to 0.38A-0.40A to make the sample temperature reach 580℃-620℃ within 5min-6min; Once the sample has entered the molten state, reduce the input current to maintain it at 0.27A-0.29A to stabilize the sample temperature at 610℃-630℃, and continue the heating process until the sample expands further and fully fills the mold cavity.

3. The method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1 or 2, characterized in that, In step 1, after adjusting the composition, the melt composition is: Si 7.6wt%-9.5wt%, Mg 0.2wt%-0.5wt%, Cu 0-2.0wt%, with the remainder being Al.

4. A method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1 or 2, characterized in that, In step 2, the thickening particles are Ca powder or Al2O3 powder; the addition temperature of the thickening particles is 680℃-700℃. The foaming agent is TiH2, and the foaming agent pretreatment method is: heating to 450℃-520℃ under vacuum conditions or air atmosphere for treatment; wherein, during vacuum treatment, the gas pressure is 100Pa-400Pa; The stirring time is 1-3 minutes, and the stirring speed is 800-900 rpm. The preheating temperature of the rectangular mold is 500℃-600℃.

5. The method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 4, characterized in that, The thickening particles are Ca, and the addition amount is 1wt%-2wt%.

6. The method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 4, characterized in that, When the thickening particles are Al2O3, the addition amount is 2wt%-4wt%.

7. A method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1 or 2, characterized in that, In step 4, the inner cavity size of the thin-walled steel pipe matches the size of the sample to be foamed, and the size of the graphite block matches the size of the mold port. The thin-walled steel pipe is made of 304 stainless steel.

8. A method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1 or 2, characterized in that, In step 5, the pulse heating power is 50kW-80kW, the pulse time is 5s-10s, and the time interval is 10s-30s.

9. A method for preparing a foamed aluminum component with controllable pore structure gradient according to claim 1 or 2, characterized in that, In step 7, the cooling method is air cooling or air cooling.

10. A foamed aluminum component with controllable pore structure gradient, prepared using the method of claim 1 or 2, characterized in that, In this step, the aluminum foam component is cylindrical, composed of a closed-cell foam core material with axial pore size and density gradient and an aluminum sheet; the axial density gradient of the closed-cell aluminum foam core material is ≥0.2 g / dm³. 4 The aluminum sheet thickness is 0.12mm~0.25mm.

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