New materials application blue ocean expansion - foam aluminum
The properties of aluminum foam mainly depend on the pore characteristics distributed between the three-dimensional skeleton, ie the morphology and distribution of pores, including the type of pores (through or closed pores), the shape of pores, the distribution of pores, the structure of pores (pore diameter, pores). Rate, specific gravity, etc.).
1 physical properties
The most obvious characteristic of aluminum foam is light weight, low density, and change with the change of the hole. The specific gravity is only 0.1-0.6 times of the same volume of aluminum, but its firmness is more than 4 times that of foam. The aluminum foam material is much less conductive than the solid aluminum material, and the resistivity is much larger, which is a poor conductor of electricity. The thermal conductivity of aluminum foam is much smaller than that of solid aluminum, which is about 0.1-0.2 times that of solid aluminum. In addition, aluminum foam has the characteristics of large rigidity, non-flammability, non-oxidation, aging, weather resistance, and good recycling.
For devices subjected to bending loads, the material used should have a high specific strength through the specific strength values of aluminum foam and several common structural materials (aluminum, steel) (foam aluminum: aluminum: steel = 5:2.5:1) In comparison, it is known that aluminum foam has a high specific strength. Experimental studies have shown that proper heat treatment can increase the specific strength. Therefore, aluminum foam can be used to withstand large bending load devices.
2 mechanical properties
Like other porous materials, the elastic modulus, shear modulus, and elastic limit of aluminum foam decrease exponentially with increasing porosity.
(1) Tensile strength Aluminum foam has a low tensile strength, almost no elongation, and is semi-brittle. The experiment found that the pore size has a certain influence on its tensile properties. When the relative density is the same, the tensile strength with a small pore diameter is higher than that of the pore diameter.
(2) Compressive strength Although the tensile strength of aluminum foam is very low, its compressive strength is high. The foam aluminum compressive stress-strain curve can be divided into three regions: a linear elastic region, a yielding platform region, and a densified region. The shape of the compressive stress-strain curve of aluminum foam with different pore diameters is basically similar. The difference is mainly at the height of the plastic platform. It is found that the height of the pore size and the height of the plastic platform are not a simple linear relationship, but at a certain aperture. The lower plastic platform is the highest. From the relationship between the compressive strength of aluminum foam and its density and compressibility, it is known that the density increases and the compressive strength increases.
3 energy absorption characteristics
A porous structural material can be used as the energy absorbing material. A material with a small unit mass and a large energy absorption capacity has a large effect. Foamed aluminum has a small mass and high strength, so foamed aluminum has a high energy absorption capacity. During the compression process, aluminum foam has a high and wide stress platform that absorbs energy through strain under substantially constant stress. The energy absorption capacity is determined by the area under the stress-strain curve, so the energy absorption capacity is greater when the yielding platform is high and wide. The size of the aperture has a certain influence on the height of the yielding platform, so a suitable aperture can be found to make the yielding platform higher to improve its energy absorption capacity. In addition, its energy absorption capacity varies non-monotonously with porosity, and has the largest energy absorption capacity at a certain porosity.
4 damping performance
The damping property of a material refers to the ability of a material to irreversibly convert mechanical vibration energy into thermal energy for internal reasons. With this ability of materials, unwanted noise and vibration can be reduced. According to Zener's classical theory, one of the important ways to improve the damping properties of metal materials is to try to maximize the interaction between defects to obtain the maximum linear damping, or to introduce the mechanical amplification mechanism to obtain higher Nonlinear damping. Porous materials clearly conform to the structural characteristics of highly damped materials, and experiments have demonstrated that the presence of pores can play an important role in the damping response of certain non-metallic or metallic materials.
As a macroscopic porous material, aluminum foam consists of a metal skeleton and pores, the structure is extremely uneven, the strain strongly lags behind the stress, and the compressive stress-strain curve contains a long plateau, so it is a kind of high energy absorption. The characteristic lightweight and high damping material has considerable application prospects in the fields of noise reduction and shock absorption. Experimental research found that:
(1) When the pore diameter is constant, the internal friction of aluminum foam increases with the increase of porosity;
(2) When the porosity is constant, the internal friction of the aluminum foam increases as the pore size decreases;
(3) The internal friction of aluminum foam is closely related to the strain amplitude and increases with the increase of amplitude;
(4) The internal friction of aluminum foam has no significant relationship with the change of frequency in the low frequency range.
After adding a large number of holes in the low-damping aluminum, the damping power can be significantly improved. It is caused by the softness of the hole's own elastic modulus of nearly zero and the large number of interfaces formed between the hole and the matrix. In addition, there are many other microscopic and macroscopic defects in the foam aluminum. The damping mechanism of aluminum foam is the comprehensive effect of its defects, and the defect damping is its main damping mechanism.
5 sound absorption performance
The aluminum foam material is especially a through-hole foamed aluminum. When the sound passes through the foamed aluminum, the sound wave is also a kind of vibration, and scattering, interference and diffuse reflection can be generated inside the material, and the sound is absorbed in the pores thereof to vibrate the internal skeleton. Part of the acoustic energy is converted into heat energy and consumed by heat transfer, which plays a role in sound absorption. Therefore, aluminum foam has good sound absorption ability. The sound absorption performance is measured by the sound absorption coefficient. The larger the sound absorption coefficient, the better the sound absorption performance. The sound absorption performance of aluminum foam mainly depends on the pore characteristics, and the sound absorption performance of the through hole is better. The finer the hole, the better the sound absorption performance.
Application of aluminum foam
1 building materials
Because of the light weight per unit volume of foam aluminum, anti-vibration, anti-flammability, non-combustible, heat preservation and other properties, it can be used to build unloaded inner walls, partition walls, doors, ceilings, and exterior decorative materials. It can also be used in any building that requires airtightness and ventilation. When used for surface decoration, it is also possible to achieve the effect of foam, marble and other decorative materials, and in the case of frequent changes in the wiring piping of computer rooms, physical and chemical laboratories, etc., it is suitable for the construction of so-called mobile flooring. . For this purpose, honeycomb structural materials, die-cast materials, and the like are used, but foam aluminum can be used instead. The exterior of large buildings is designed to avoid the use of heavy materials on the upper floors, and aluminum foam is just right for this need. This is not only lightweight, but also allows for a free design. When there are special requirements for strength, it is possible to use aluminum foam made of steel.
2 decorative materials
Aluminum foam can be used as a decorative material inside and outside the building and other decorative materials, and can also be made into materials such as stone, marble, wood, glass and the like. Since the engravings, statues and other objects created by it are large and light, it is extremely easy to carry.
3 soundproof materials
It can be effectively used as a wall to adjust the sound effects of radio, music, lectures, theaters, etc. It is suitable for use as a power generation room, an engine test room, a soundproofing platform for airports, and a platform for sounding machinery in the industrial sector. It is used as a structural part of a phonograph or a stereo camera, a soundproofing of an indoor cooler, a soundproofing part of a hotel, etc. in daily life.
4 anti-vibration material
Aluminum foam is the best material for use as a car bumper and other accessory parts to slow down the impact for safety. In contrast, it can also be used as a moderate vibration material for collisions with equipment along the road. It is desirable as a vibration-proof material for transportation, installation, and the like of heavy and expensive articles. This material is used under the landing gear of the Apollo 11 LM when landing on the surface of the moon. It adapts to the unevenness of the lunar surface when landing, and mitigates the vibration by the destruction of aluminum foam. Also suitable as a pad material for valuables.
This material can be used because the foamed styrene model and other large models used at high temperatures are operationally capable of reducing weight. Honeycomb structures and other materials have traditionally been used in the trial production of automobiles and other large-scale models, but they have the disadvantage of high cost, while aluminum foam is inexpensive and easy to shape, and is very suitable for repeated trials when the mold changes. of.
6 in the automotive industry
The excellent properties of aluminum foam determine its wide range of applications and broad application prospects. Especially in the automotive industry, foam aluminum is considered a good material for future promising cars and other transportation vehicles. In order to protect the global environment and natural resources, developed countries such as Europe, North America, and Japan have formulated laws and regulations to improve the fuel efficiency of automobiles. Reducing self-weight is the best way to improve fuel efficiency and reduce the weight of the car: (1) improved structure, and (2) lightweight materials. The former has reached its end, and only the latter has the potential to dig. This provides a good opportunity for the development and application of aluminum foam materials. The bright European plan implemented by the European Economic Community is to study the application of aluminum foam in automobiles. The self-weight is reduced by 1kg, and the fuel efficiency can be increased by 0.01km/L. At present, all-aluminum vehicles have appeared in foreign countries. Compared with aluminum, foamed aluminum materials have lighter weight characteristics and can improve fuel efficiency.
Foreign studies have shown that the stiffness of the car frame is enhanced by the use of foamed aluminum components. About 20% of the body structure in automobile manufacturing can be made of foamed aluminum. The foamed aluminum parts of a medium-sized car can reduce the weight by about 27.2 kg. At the same time, the structural system can be simplified, and the number of parts can be reduced by at least 1/3. The cost of the car. Aluminum foam material is a good energy absorber, and the energy absorbed per unit volume can reach 6-9M J. The strong energy absorption capacity indicates its superiority as a bumper for automobile bumpers. The use of suitable components made of aluminum foam in the impact zone of the car controls the deformation of the maximum energy consumption. For example, filling the hollow steel or aluminum casing with foamed aluminum allows these components to have good deformation behavior during loading. The foamed aluminum material is used for the deformable material before and after the passenger seat of the car to improve safety. Foam aluminum is heat-resistant and flame-retardant. At the same time, it does not release toxic gases under heat. Therefore, the use of foam aluminum in transportation tools instead of foam or foamed resin materials can improve service life and reduce maintenance. It eliminates the harmful gases generated by traditional materials in vehicle accidents, greatly reduces the losses and casualties in traffic accidents, and also plays an environmental protection role.