CN120818715A - Preparation process of foamed aluminum with specific pore size - Google Patents

Abstract

A method for preparing foamed aluminum with a specific pore size includes foaming, wherein a composite foaming agent and stearic acid are added to tackified molten aluminum, followed by stirring and dispersion, followed by heat preservation and foaming. The composite foaming agent comprises titanium hydride as a main component, zirconium hydride, and calcite as auxiliary agents, with the mass ratio of titanium hydride, zirconium hydride, and calcite being 5:1-2:0.5-0.8. The present invention utilizes a composite of _TiH2 , _ZrH2 , and calcite as a foaming agent, and combines calcite with stearic acid to regulate the pore size structure and pore distribution uniformity in the foamed aluminum. The pore size is primarily distributed between 1 and 2 mm, with a pore size coefficient of variation of 0.49. The foamed aluminum has a porosity of 88.4%, a density retention rate of 108.2-120.4%, and excellent structural stability, offering significant advantages as a thermal and sound insulation material. Extending this preparation process to the preparation of aluminum-scandium alloy foam can promote uniform distribution of Sc, making the yield platform stress and energy absorption efficiency significantly higher than those of foamed aluminum made from pure aluminum.

Description

Preparation process of foamed aluminum with specific pore diameter

Technical Field

The invention relates to the technical field of preparation of foamed aluminum and aluminum scandium alloy foamed materials, in particular to a preparation process of foamed aluminum with specific pore diameters.

Background

The foamed aluminum is a novel material with structural and functional characteristics, has the performances of light weight, sound absorption, heat insulation, flame retardance, shock absorption, damping, energy absorption, electromagnetic shielding and the like, and is widely applied to the fields of automobiles, rail transit, military equipment, aerospace and the like. The foamed aluminum is divided into closed-cell foamed aluminum and open-cell foamed aluminum according to the pore structure characteristics, the pore size of the closed-cell foamed aluminum is closely related to the performance of the closed-cell foamed aluminum, the application scene of the closed-cell foamed aluminum is directly determined by the performance, researches show that the heat conductivity of the closed-cell foamed aluminum with the pore size of about 1mm is 30% lower than that of a traditional heat insulation material (such as rock wool), and the fire resistance is better (the metal matrix is incombustible), so that the closed-cell foamed aluminum is commonly used for heat insulation of an outer wall of a passive building, and the closed-cell foamed aluminum with the pore size range of 1-2 mm has good heat insulation and sound insulation performances and is commonly applied to the fields of building partition walls, pipeline heat insulation materials, sound insulation barriers and the like.

The closed-cell foamed aluminum prepared by the melt foaming method has the advantages of low cost, easy operation, easy regulation and control of the cell structure and the like, and is suitable for industrial production. The foamed aluminum prepared by the method is usually mainly prepared from thermal decomposition foaming agents such as TiH ₂、ZrH₂ and the like, and the quality of the prepared foamed aluminum is closely related to the dispersion degree of the foaming agents. However, the wettability of the aluminum melt and the foaming agent is poor, the foaming agent is often aggregated, so that the uniformity of pore structures in the foamed aluminum is influenced, and the problems of local macropores, thicker bubble-free layers, gas escape and the like are generated, so that the mechanical strength of the foamed aluminum is attenuated, the thermophysical performance is deteriorated, the functional characteristics are invalid and the like are caused. The prior art has mostly alleviated such drawbacks by increasing the stirring rate or modification. For example, CN107254597A delays the decomposition temperature of TiH ₂ by coating the TiH ₂ with phenolic resin to improve the dispersibility and pore-forming uniformity, but phenolic resin is decomposed to release toxic substances such as phenol, formaldehyde and the like in high-temperature preparation and have health and environmental hazards, for example, CN112746192A proposes to prepare a foaming agent by ball milling of magnesium carbonate and metal powder to enhance the wettability of a melt and improve the uniformity of cells, but magnesium carbonate has the characteristics of high decomposition temperature and low foaming efficiency and is easy to cause insufficient porosity.

In general, the above methods have problems of increasing process costs, increasing process complexity by modifying a foaming agent or an aluminum melt, and adversely affecting the properties or environment of the final product. Therefore, the selection of the foaming agent and the foaming process for dispersing the foaming agent are beneficial to preparing high-quality foamed aluminum, and the pore size structure, the pore size distribution and the pore size uniformity of the foamed aluminum are regulated and controlled.

Disclosure of Invention

In order to solve the problems that in the prior art, in the process of preparing closed-cell foamed aluminum by adopting a melt foaming method, the foaming performance of a foaming agent is not controlled in the foaming process, the pore size is difficult to adjust due to the fact that the foaming performance is reduced, and the uniformity of pore size distribution and pore size is poor, the invention aims to provide a preparation process of the foamed aluminum with specific pore size, which improves the foaming performance of the foaming agent, the pore size adjustment and the uniformity of pore size distribution in the foamed aluminum, and improves the mechanical strength, the thermophysical performance and the functional characteristics of materials.

The invention aims at realizing the following technical scheme:

The preparation method of the foamed aluminum with the specific pore diameter comprises demolding pretreatment, melting, tackifying, foaming and cooling solidification, and is characterized in that a composite foaming agent and stearic acid are added into the molten aluminum after tackifying, and the mixture is stirred and dispersed for heat preservation foaming, wherein the composite foaming agent takes titanium hydride as a main body and zirconium hydride and calcite as auxiliary agents, and the mass ratio of the titanium hydride to the zirconium hydride to the calcite is 5:1-2:0.5-0.8.

Further, the mass ratio of the stearic acid to the calcite is 0.2-0.5:2.

Further, the composite foaming agent is divided into 5-15 parts by weight, and then the aluminum foil is used for wrapping the composite foaming agent into balls, wherein the weight of each part of foaming agent is 0.2wt.% of the aluminum liquid, and the foaming agent is added into molten aluminum in a dispersing way.

Further, the heat preservation foaming is carried out by firstly preserving heat for 3-5 min at 500-600 ℃, then preserving heat for 5-8 min at a rate of 20-25 ℃ per minute to 700-720 ℃.

Further, the stirring and dispersing are carried out for 15-35 s under the condition of 1400-2200 r/min.

Further, the molten aluminum is prepared by weighing industrial pure aluminum and heating the industrial pure aluminum at 680-750 ℃ for 1.5-2 hours.

And further, the tackifying is to take particles Ca with the diameter of about 1.5mm, wrap and put the particles Ca into molten aluminum by using aluminum foil, stir the particles Ca for 1 to 3 minutes at the rotating speed of 1500 to 160 r/min, and keep the temperature for 10 to 30 minutes after the stirring is finished to obtain a mixed melt, wherein the mass of the particles Ca is 1 to 3 percent of that of pure aluminum.

Most specifically, the preparation method of the foamed aluminum with the specific pore diameter is characterized by comprising the following steps of:

(1) The demoulding pretreatment, namely adding water into a release agent ZnO for emulsification, smearing the ZnO on the inner wall of a stainless steel crucible, and drying the ZnO in a drying furnace at 100 ℃ for 2 hours;

(2) Melting, namely weighing industrial pure aluminum, placing the industrial pure aluminum into a crucible, and placing the crucible into a well type heating furnace for heating at 680-750 ℃ for 1.5-2 hours to ensure that aluminum ingots are completely melted;

(3) Tackifying, namely weighing granular Ca with the diameter of about 1.5mm, wrapping the granular Ca with aluminum foil, putting the granular Ca into molten aluminum, pressing and stirring the granular Ca by adopting an elliptical three-blade stirring paddle (with the blade pressing angle of 45 degrees and the blade diameter of 6 mm), stirring the granular Ca at the rotating speed of 1500-160 r/min for 1-3 min, and preserving the temperature for 10-30min after stirring to obtain a mixed melt, wherein the mass of the granular Ca is 1-3% of that of pure aluminum;

(4) The foaming process comprises the steps of weighing a composite foaming agent with the mass of 1-3% of that of aluminum liquid, equally dividing the foaming agent into 5-15 parts, wrapping the foaming agent into balls by using aluminum foil, wherein the mass of each part of foaming agent is 0.2wt.% of the aluminum liquid, the aluminum foil is 50mm multiplied by 50mm, the temperature of a mixed melt is reduced to 500-600 ℃, the wrapped composite foaming agent is put into the mixed melt, stearic acid is added, stirring paddles are rapidly pressed down and stirred, stirring is carried out for 15-35 s under the condition of 1400-2200r/min, after stirring is finished, the stirring paddles are rapidly lifted out, a heating furnace cover is covered for segmented heat preservation, and foaming is carried out fully to form a foam body, the composite foaming agent consists of titanium hydride, zirconium hydride and calcite according to the mass ratio of 5:1-2:0.5-0.8, the mass ratio of the stearic acid to the calcite is 0.2-0.5:2, and the segmented heat preservation is carried out at the temperature of 500-600 ℃ for 3-5 min, then the temperature is 20-25 ℃ per min, and the segmented heat preservation is carried out for 5-700 ℃ and the temperature is carried out;

(5) And (3) cooling and solidifying, namely taking out the crucible after heat preservation is finished, and putting the obtained foaming body into a cooling barrel for cooling and solidifying to obtain closed-pore foamed aluminum with the pore size distribution of 1-2 mm, wherein the liquid level of cooling water is 5-8cm.

In the whole foaming process, tiH ₂ is used for leading gas production to release H ₂ to foam to form bubble cores at the temperature of 500-600 ℃, zrH ₂ is used for leading gas production when the temperature is raised to 700-720 ℃, calcite is used for continuously decomposing the gas production in the process, the strength of bubble walls at each stage is regulated in a coordinated manner with stearic acid, and the collapse or combination of the bubbles is restrained, so that the uniformity of pore size and the structural stability are improved.

Compared with pure CaCO ₃, the calcite has MgCO ₃ and other impurities, so that the decomposition starting temperature is lower, the decomposition temperature interval is wider, gas can be released to foam at a lower temperature, the energy consumption is reduced, the calcite is foamed in the gas production in the whole heat preservation foaming process, the foaming process is favorably regulated, the slow nucleation is realized by utilizing the decomposition temperature difference between different components in the calcite, the foaming process of rapid expansion after slow nucleation is realized, and the uniformity of pore nucleation and growth is optimized. Secondly, mgO generated by calcite decomposition and stearic acid form a composite surface activity, the stearic acid reduces surface tension to promote bubble nucleation, mgO particles increase the strength of bubble films, improve interface stability, inhibit bubble combination or collapse, realize the dual effects of rapid nucleation and long-acting stability, and especially improve structural stability in high-porosity foamed aluminum.

The invention has the following technical effects:

According to the invention, tiH ₂、ZrH₂ and calcite are compounded to serve as a foaming agent, and the calcite and stearic acid are combined to reduce surface tension in the foaming process to promote bubble nucleation, so that the pore diameter structure and pore distribution uniformity in the foamed aluminum are regulated and controlled, the pore diameter is mainly distributed between 1 and 2mm, the pore diameter variation coefficient is 0.49, the porosity of the foamed aluminum is improved, 88.4% is achieved, the density retention rate of the material is increased along with the strain, and the foamed aluminum has excellent structural stability and obvious advantages as a heat-insulating and sound-insulating material.

Because the closed-cell aluminum foam prepared by the invention has huge specific surface area and through pores, the closed-cell aluminum foam can have high specific surface area and three-dimensional through pores, and can provide a rapid mass transfer channel for subsequent vacuum infiltration Sc or Al-Sc melt infiltration-diffusion. The aluminum foam preparation process is popularized to aluminum-scandium alloy foam preparation, so that Sc distribution is promoted to be uniform, and nano Al ₃ Sc strengthening phases are uniformly separated out, so that the stress and energy absorption efficiency of a yield platform are obviously higher than those of pure aluminum for preparing aluminum foam.

Drawings

FIG. 1 is a graph showing the microscopic morphology of aluminum foam prepared in example 1 of the present invention.

FIG. 2 is a graph of the microscopic morphology of aluminum foam prepared in each comparative example.

FIG. 3 stress-strain curves for static compression testing of aluminum foams prepared in the examples and comparative examples.

Detailed Description

The present invention is described in detail below by way of examples, which are necessary to be pointed out herein for further illustration of the invention and are not to be construed as limiting the scope of the invention, since numerous insubstantial modifications and adaptations of the invention will be to those skilled in the art in light of the foregoing disclosure.

The calcite used in the invention is common calcite with a purity of about 90%.

Example 1

The preparation method of the mesoporous grade foamed aluminum comprises the following steps:

(1) The demoulding pretreatment, namely adding water into a release agent ZnO for emulsification, smearing the ZnO on the inner wall of a stainless steel crucible, and drying the ZnO in a drying furnace at 100 ℃ for 2 hours;

(2) Melting, namely weighing industrial pure aluminum, placing the industrial pure aluminum into a crucible, and placing the crucible into a well type heating furnace to heat for 1.5-2 hours at 700 ℃ to ensure that aluminum ingots are completely melted;

(3) Tackifying, namely weighing granular Ca with the diameter of about 1.5mm, wrapping the granular Ca with aluminum foil, putting the granular Ca into molten aluminum, pressing and stirring the granular Ca by adopting an elliptical three-blade stirring paddle (the blade pressing angle is 45 degrees and the blade diameter is 6 mm), stirring the granular Ca at the rotating speed of 1550r/min for 2min, and preserving heat for 20min after stirring to obtain a mixed melt, wherein the mass of the granular Ca is 2% of that of pure aluminum;

(4) The foaming process comprises the steps of weighing a compound foaming agent with the mass of 2% of aluminum liquid, equally dividing the foaming agent into 10 parts, wrapping the 10 parts by aluminum foil into balls, wherein the mass of each part of foaming agent is 0.2wt.% of the aluminum liquid, the aluminum foil is 50mm multiplied by 50mm, the temperature of a mixed melt is reduced to 550 ℃, putting the wrapped compound foaming agent into the mixed melt, adding stearic acid, rapidly pressing a stirring paddle to stir, stirring for 25 seconds under the condition of 2000r/min, rapidly lifting the stirring paddle after stirring, covering a heating furnace cover, firstly preserving heat for 4 minutes at 550 ℃, then preserving heat for 710 ℃ at the speed of 25 ℃ per minute, preserving heat for 6 minutes, and fully foaming to form a foam, wherein the compound foaming agent consists of titanium hydride, zirconium hydride and calcite according to the mass ratio of 5:1.5:0.6, and the mass ratio of the stearic acid to the calcite is 0.4:2;

(5) And (3) cooling and solidifying, namely taking out the crucible after heat preservation is finished, and putting the obtained foaming body into a cooling barrel for cooling and solidifying to obtain closed-pore foamed aluminum with the pore size distribution of 1-2 mm, wherein the liquid level of cooling water is 8cm.

Comparative example 1

In comparison with example 1, the pure CaCO ₃ was used in the composite foaming agent in place of calcite according to the CaCO ₃ content of calcite, the rest of the procedure being the same as in example 1.

Comparative example 2

In comparison with example 1, after adding the composite foaming agent to molten aluminum, SDBS (sodium dodecylbenzenesulfonate) was used instead of stearic acid, and the rest of the procedure was the same as in example 1.

Comparative example 3

In comparison with example 1, after the addition of the compound foaming agent and stearic acid in step (4), the temperature was raised to 710℃for 10 minutes at 10℃/min after the end of the heat preservation at 550 ℃. The remaining steps were the same as in example 1.

The porosity, pore size, pore uniformity and pore distribution uniformity of the aluminum foam are key structural parameters affecting the energy absorption performance of the closed-cell aluminum foam, and the action mechanism relates to stress distribution, energy dissipation paths and failure modes of material deformation. If the uniformity of the pore size is higher, the pore wall deformation synchronism is higher due to the uniform pore structure, the energy absorption is concentrated in the platform area, and the local advanced densification can be caused due to the poor uniformity of the pore size, so that the energy absorption of the platform area is reduced. And the buckling critical stress of the pore wall is consistent due to uniform pore size and pore distribution, so that the problem of uneven energy dissipation caused by weak Kong Xian collapse and strong pore post-collapse due to poor pore size and distribution uniformity is avoided. In addition, the uniformity of pore distribution in the foamed aluminum is improved, the load can be uniformly transmitted to the whole material, and the stability of the whole compressive strength and the whole tensile strength is improved. The pore structure of the aluminum foam prepared in the embodiment 1 is shown in fig. 1, and it can be seen that the prepared aluminum foam has uniform and compact pores and excellent uniformity of pore size distribution, and is mainly distributed in the range of 1-2 mm. The pore size structures of the aluminum foams prepared in comparative examples 1 to 3 are shown in fig. 2 ((a) (b) (c) correspond to comparative examples 1, 2 and 3, respectively), and it can be seen that the uniformity of pore size of the prepared aluminum foams is poor and the uniformity of pore size distribution is also not ideal.

The pore size distribution can be calculated in addition to being observed from the scanning electron microscope. The uniformity of the aperture size is represented by data, wherein an image of the internal pore structure of the foamed aluminum is obtained through ct scanning, then the image is processed through image j image processing software, the aperture size in the image is calculated in a statistics mode, and after the aperture size is obtained, the variation coefficient of the aperture size is calculated to represent the uniformity of the aperture size, and the calculation formula is as follows:

In the middle of The smaller the aperture size variation coefficient, the more similar the aperture size, the more uniform the aperture size distribution;

-standard deviation;

pore size average.

The higher the porosity of the aluminum foam, the wider the energy absorption platform area, the porosity is measured by a drainage method, and the calculation formula is as follows:

Wherein, represents porosity;

m-sample mass, g;

ρAl-density of aluminum matrix (pure aluminum), g/cm ³;

v-sample drainage volume, cm ³.

The test results are shown in Table 1.

Table 1:

as can be seen from the calculation, the pore diameter variation coefficient of the aluminum foam prepared in example 1 was 0.49, while the pore diameter variation coefficient of the other comparative examples was significantly increased. Illustrating the excellent uniformity of pore size in the aluminum foam of example 1. From the above table it can be seen that the porosity of the closed cell aluminum foam prepared in example 1 of the present invention reached 88.4%, whereas the porosities of the aluminum foams prepared in comparative example 1, comparative example 2 and comparative example 3 were 76.7%, 74.3% and 78.9%, respectively, which resulted in a significant decrease compared to example 1.

The energy absorption mechanism of closed cell aluminum foam is mainly dependent on plastic deformation and elastic deformation of the porous structure. The energy absorption density and energy absorption performance efficiency of each group of aluminum foams were tested by static compression test (static energy absorption test), and the results are shown in table 2.

Table 2:

It can be seen that the aluminum foam prepared in example 1 has a static energy absorption density of 10.46 MJ/m ³ and a maximum energy absorption efficiency of 0.74, while the energy absorption density and the maximum energy absorption efficiency of the other comparative examples are both significantly reduced. The stress-strain curves for static compression testing of the aluminum foams prepared in example 1 and the respective comparative examples are shown in fig. 3.

In addition, the density retention is a visual index of the mechanical properties and structural stability of the aluminum foam, and the density retention is a ratio of the residual density to the original density of the aluminum foam after being stressed (such as compression, impact) or subjected to environmental effects (such as high temperature and aging), and is generally expressed in percentage:

density retention = ×100%

Thermal and acoustic insulation materials rely on air layers in porous structures to block heat or sound transfer. If the density retention rate is low (i.e. the porosity retention after loading is higher), the air layer retention is more complete, the heat/sound insulation performance is better, and if the density retention rate is too high (i.e. the pore size collapse is serious), the air layer is reduced, and the performance is reduced. Pore size uniformity and pore distribution uniformity in aluminum foam can significantly affect the degree of pore collapse during stress-strain, and thus the density retention variation. In the stress-strain test process, after the foamed aluminum in the embodiment 1 is loaded, the porosity retention effect is excellent, the density retention rate fluctuates between 108.2 and 120.4 percent along with the increase of strain in the static energy absorption detection process, and the density retention rate changes between 167.8 and 356.7 percent, 151.6 to 327.5 percent and 159.5 to 342.9 percent along with the increase of strain in the static energy absorption detection process and the dynamic energy absorption detection process respectively. The change in density retention allows an assessment of the compaction resistance of the aluminum foam.

Example 2

The preparation method of the mesoporous grade foamed aluminum comprises the following steps:

(1) The demoulding pretreatment, namely adding water into a release agent ZnO for emulsification, smearing the ZnO on the inner wall of a stainless steel crucible, and drying the ZnO in a drying furnace at 100 ℃ for 2 hours;

(2) Melting, namely weighing industrial pure aluminum, placing the industrial pure aluminum into a crucible, and placing the crucible into a well type heating furnace for heating at 680 ℃ for 2 hours to ensure that aluminum ingots are completely melted;

(3) Tackifying, namely weighing granular Ca with the diameter of about 1.5mm, wrapping the granular Ca with aluminum foil, putting the granular Ca into molten aluminum, pressing and stirring the granular Ca by adopting an elliptical three-blade stirring paddle (the blade pressing angle is 45 degrees and the blade diameter is 6 mm), stirring the granular Ca at the rotating speed of 1500r/min for 3min, and preserving the temperature for 10min after stirring to obtain a mixed melt, wherein the mass of the granular Ca is 1% of that of pure aluminum;

(4) The foaming process comprises the steps of weighing 3% of composite foaming agent by mass of aluminum liquid, equally dividing the foaming agent into 15 parts, wrapping the 15 parts by aluminum foil into balls, wherein the mass of each part of foaming agent is 0.2wt.% of the aluminum liquid, the aluminum foil is 50mm multiplied by 50mm, the temperature of a mixed melt is reduced to 500 ℃, the wrapped composite foaming agent is put into the mixed melt, stearic acid is added, stirring paddles are rapidly pressed and stirred under the condition of 1400r/min, stirring paddles are rapidly lifted after stirring is finished, a heating furnace cover is covered, firstly, the temperature is kept for 5min at 500 ℃, then the temperature is kept at the speed of 20 ℃ to 700 ℃, the temperature is kept for 8min, and foam is fully foamed to form a foam, and the composite foaming agent is formed by titanium hydride, zirconium hydride and calcite according to the mass ratio of 5:1:0.8, and the mass ratio of the stearic acid to calcite is 0.2:2;

(5) And (3) cooling and solidifying, namely taking out the crucible after heat preservation is finished, and putting the obtained foaming body into a cooling barrel for cooling and solidifying to obtain closed-pore foamed aluminum with the pore size distribution of 1-2 mm, wherein the liquid level of cooling water is 6cm.

Example 3

The preparation method of the mesoporous grade foamed aluminum comprises the following steps:

(1) The demoulding pretreatment, namely adding water into a release agent ZnO for emulsification, smearing the ZnO on the inner wall of a stainless steel crucible, and drying the ZnO in a drying furnace at 100 ℃ for 2 hours;

(2) Melting, namely weighing industrial pure aluminum, placing the industrial pure aluminum into a crucible, and placing the crucible into a well type heating furnace to heat for 1.5 hours at 750 ℃ to ensure that aluminum ingots are completely melted;

(3) Tackifying, namely weighing granular Ca with the diameter of about 1.5mm, wrapping the granular Ca with aluminum foil, putting the granular Ca into molten aluminum, pressing and stirring the granular Ca by adopting an elliptical three-blade stirring paddle (the blade pressing angle is 45 degrees and the blade diameter is 6 mm), stirring the granular Ca at the rotating speed of 1600r/min for 1min, and preserving the temperature for 30min after stirring to obtain a mixed melt, wherein the mass of the granular Ca is 3% of that of pure aluminum;

(4) The foaming process comprises the steps of weighing a composite foaming agent with the mass of 1% of aluminum liquid, equally dividing the foaming agent into 5 parts, wrapping the 5 parts by aluminum foil into balls, wherein the mass of each part of foaming agent is 0.2wt.% of the aluminum liquid, the aluminum foil is 50mm multiplied by 50mm, the temperature of a mixed melt is reduced to 600 ℃, putting the wrapped composite foaming agent into the mixed melt, adding stearic acid, rapidly pressing a stirring paddle to stir, stirring for 15s under 2200r/min, rapidly lifting the stirring paddle after stirring, covering a heating furnace cover, firstly preserving heat for 3min at 600 ℃, then preserving heat to 720 ℃ at a rate of 20 ℃ per min, preserving heat for 5min, and fully foaming to form a foam, wherein the composite foaming agent consists of titanium hydride, zirconium hydride and calcite according to a mass ratio of 5:1:0.5, and the mass ratio of the stearic acid to the calcite is 0.2:2;

(5) And (3) cooling and solidifying, namely taking out the crucible after heat preservation is finished, and putting the obtained foaming body into a cooling barrel for cooling and solidifying to obtain closed-pore foamed aluminum with the pore size distribution of 1-2 mm, wherein the liquid level of cooling water is 5cm.

Claims (8)

1. The preparation method of the foamed aluminum with the specific pore diameter comprises demolding pretreatment, melting, tackifying, foaming and cooling solidification, and is characterized in that a composite foaming agent and stearic acid are added into the molten aluminum after tackifying, and the mixture is stirred and dispersed for heat preservation foaming, wherein the composite foaming agent takes a titanium hydride main body, zirconium hydride and calcite as auxiliary agents, and the mass ratio of the titanium hydride to the zirconium hydride to the calcite is 5:1-2:0.5-0.8.

2. The method for preparing foamed aluminum with specific pore diameters according to claim 1, wherein the mass ratio of stearic acid to calcite is 0.2-0.5:2.

3. The method for preparing the foamed aluminum with specific pore diameters according to claim 1 or 2, wherein the composite foaming agent is divided into 5-15 parts by weight, aluminum foil is used for wrapping the foamed aluminum into balls, and the weight of each part of foaming agent is 0.2wt.% of aluminum liquid and the foaming agent is added into molten aluminum in a dispersing manner.

4. A method for preparing foamed aluminum with specific pore diameters according to any one of claims 1 to 3, wherein the heat preservation foaming is carried out by firstly preserving heat at 500-600 ℃ for 3-5 min, then preserving heat at a rate of 20-25 ℃ per minute to 700-720 ℃ for 5-8 min.

5. The method for preparing aluminum foam with specific pore diameters according to claim 4, wherein stirring and dispersing are carried out for 15-35 s under the condition of 1400-2200 r/min.

6. The method for preparing aluminum foam with specific pore size according to claim 5, wherein the molten aluminum is prepared by weighing industrial pure aluminum and heating at 680-750 ℃ for 1.5-2 hours.

7. The method for preparing foamed aluminum with specific pore diameter as set forth in claim 6, wherein the tackifying is carried out by taking Ca particles with a diameter of about 1.5mm, wrapping the Ca particles with aluminum foil, putting the Ca particles into molten aluminum, stirring the Ca particles for 1-3 min at a rotating speed of 1500-160 r/min, and preserving heat for 10-30 min after stirring to obtain a mixed melt, wherein the Ca particles are 1-3% of the pure aluminum.

8. The preparation method of the foamed aluminum with the specific pore diameter is characterized by comprising the following steps of:

(1) The demoulding pretreatment, namely adding water into a release agent ZnO for emulsification, smearing the ZnO on the inner wall of a stainless steel crucible, and drying the ZnO in a drying furnace at 100 ℃ for 2 hours;

(2) Melting, namely weighing industrial pure aluminum, placing the industrial pure aluminum into a crucible, and placing the crucible into a well type heating furnace for heating at 680-750 ℃ for 1.5-2 hours to ensure that aluminum ingots are completely melted;

(3) Tackifying, namely weighing granular Ca with the diameter of about 1.5mm, wrapping the granular Ca with aluminum foil, putting the granular Ca into molten aluminum, pressing and stirring the granular Ca by adopting an elliptical three-blade stirring paddle (with the blade pressing angle of 45 degrees and the blade diameter of 6 mm), stirring the granular Ca at the rotating speed of 1500-160 r/min for 1-3 min, and preserving the temperature for 10-30min after stirring to obtain a mixed melt, wherein the mass of the granular Ca is 1-3% of that of pure aluminum;

(4) The foaming process comprises the steps of weighing a composite foaming agent with the mass of 1-3% of that of aluminum liquid, equally dividing the foaming agent into 5-15 parts, wrapping the foaming agent into balls by using aluminum foil, wherein the mass of each part of foaming agent is 0.2wt.% of the aluminum liquid, the aluminum foil is 50mm multiplied by 50mm, the temperature of a mixed melt is reduced to 500-600 ℃, the wrapped composite foaming agent is put into the mixed melt, stearic acid is added, stirring paddles are rapidly pressed down and stirred, stirring is carried out for 15-35 s under the condition of 1400-2200r/min, after stirring is finished, the stirring paddles are rapidly lifted out, a heating furnace cover is covered for segmented heat preservation, and foaming is carried out fully to form a foam body, the composite foaming agent consists of titanium hydride, zirconium hydride and calcite according to the mass ratio of 5:1-2:0.5-0.8, the mass ratio of the stearic acid to the calcite is 0.2-0.5:2, and the segmented heat preservation is carried out at the temperature of 500-600 ℃ for 3-5 min, then the temperature is 20-25 ℃ per min, and the segmented heat preservation is carried out for 5-700 ℃ and the temperature is carried out;

(5) And (3) cooling and solidifying, namely taking out the crucible after heat preservation is finished, and putting the obtained foaming body into a cooling barrel for cooling and solidifying to obtain closed-pore foamed aluminum with the pore size distribution of 1-2 mm, wherein the liquid level of cooling water is 5-8cm.