Research And Application Of Development Status Of Metal Foam

Metal foam is a porous metal material that forms numerous bubbles in the metal matrix, also known as porous metal foam. Because it has both metal properties and some special physical properties of non-metals, it has received widespread attention at home and abroad. In recent years, great progress has been made in the theoretical research on the development, application and development of foam metal and its structural properties.

1. Overview of the development of foam metal at home and abroad

Since SOSNIK in the United States first added mercury to aluminum to produce foamed aluminum in 1948, researchers have done a lot of work on the preparation, performance research, and application development of foamed metal. The method system is generally fixed, which can be divided into casting method, metal deposition method, powder metallurgy method, spray deposition method, etc. Among them, the casting method is the most economical, and has made great progress in practical application in recent years. For example, the American Roa Company and the United States and Japan have successfully produced the lead alloy grades of 7075 and ALMAG35 foam aluminum profiles by the direct foaming method and the investment casting method respectively.

From the appearance of metal foam to the 1970s and 1980s, the research mainly focused on the preparation of metal foam. For example, the solution of the problem of viscosity increase in the preparation of aluminum foam has a great impetus for the preparation of aluminum foam; in addition, the proposal and application of the bubble core mechanism is a great breakthrough in the preparation of foam metal. The theory is like adding a nucleating agent in the solidification process of metal, which makes the direct forming of metal foam possible.

Now the production of foamed aluminum has been able to carry out continuous production from foaming to forming process.

(A) For continuous production of large aluminum; (B) For continuous production of large plates with a certain thickness; (c) For castings that can be used to produce a certain shape; (D) For continuous production of a certain shape casting. This method is to obtain a stable molten metal foam according to the bubble core theory, and then draw it out for molding to obtain a finished product of the desired shape.

On the other hand, various countries have invested a lot of manpower and material resources to improve the properties of foam metal, and the research content mainly includes alloying, heat treatment, fiber reinforcement or other reinforcement methods of foam metal. Among them, the Gasser high-strength porous foam material developed by Ukrainian metallurgist Shapovalov is the most typical. This material has a high degree of structural integrity and has much higher strength and stiffness than conventional porous foam materials.

In addition, in recent years, a systematic study of metal foams has also been carried out in theory. First of all, in the research on the structural parameters of metal foam, people increasingly feel the particularity of metal foam in physical structure, it is not only a structural material, but a multifunctional material with many physical properties. Its special properties can be found out from its structure. For example, the measurement and research of the open porosity and closed porosity of foam metal pores, the statistical measurement of pore size, the measurement of specific surface area and the influence of these parameters on the performance of foam metal. Secondly, it is to study the properties of foam metal, such as deformation characteristics, sound absorption characteristics and damping internal friction characteristics of foam metal. These studies provide a theoretical basis for applied research.

Great achievements have been made in the application and research of foam metal, and small and large pieces have been prepared and entered the stage of trial production and application. For example, the aluminum foam produced by Japan's Sumitomo Electric Co., Ltd. is used to manufacture some heat-resistant and abrasion-resistant parts of automobiles and parts of speakers; on railways, aluminum foam is used to make soundproof walls for air-conditioning power generation rooms. In addition, foamed aluminum is also used as a shock-proof device material for precision instruments.

Domestic research on foam metal only started in the 1980s. After more than 10 years of exploration and research, some research units such as Southeast University, Guizhou Academy of Sciences, Dalian University of Technology, Southwest Aluminum Processing Factory have initially mastered the production method of foam metal. Among them, Southeast University and Guizhou Academy of Sciences are the most advanced. In particular, the Guizhou Academy of Sciences has successfully produced large-scale aluminum foam profiles by using the direct foaming method with cheap foaming agents. After testing by the Institute of Acoustics of the Chinese Academy of Sciences and other units, the sound absorption, shielding, shock absorption and impact resistance effects, specific gravity And other performance indicators, have reached the indicators of similar foreign products. At present, Southeast University is very active in the research on the preparation and properties of foamed metal. They mainly focus on the preparation of foamed aluminum by the seepage method, and have carried out simulation experiments on the seepage method and prepared the foamed aluminum by the seepage method. Polymer composite materials, Hebei University of Technology has successfully prepared high-melting iron foam by adding pore-forming agents, and achieved gratifying results.

In terms of the preparation of foam metal, there are many domestic researches on foaming method, metallurgical method and percolation method, and they have basically caught up with the level of foreign developed countries, but the research on continuous production method is still blank, and needs to be developed to adapt to domestic conditions. Continuous production method.

In terms of theoretical performance, domestic research is relatively early, and the research field is basically at the international leading level, such as the measurement of structural parameters of foam metal, noise reduction performance, underwater sound absorption performance, damping performance, etc. A lot of research has been done , and achieved considerable results. The number of pores in the foam metal is huge and the sizes are different. It is extremely difficult to manually measure these structural parameters. In the literature, the graphic information of the foam metal is input into the computer and data processing is performed to measure the average diameter and pore size distribution of the pores. It solves the problem of measuring the structural parameters of foam metal. Metal foam is a kind of lightweight and high damping material with high energy absorption seeds. Its damping characteristic is nonlinear internal friction which is closely related to the strain amplitude, but has no significant relationship with the strain frequency. The research in this area was only reported abroad in 1998.

In terms of application, there are few domestic researches. Although the research on theoretical performance has proposed a lot of application possibilities, it is decoupled from application development, and there is no report on the application of foam metal.

2. Preparation status of foamed iron

Although metal foam has a history of nearly 50 years, the research and development of metal foam is mostly based on light metals, especially the research on foamed aluminum is the most extensive. This is due to the low melting point of aluminum and its alloys, good casting properties, and easy handling of molten metal. In addition, the materials that can be used to make foam metal include low melting point metals such as cu, Zn and their alloys, but these materials are far less extensive than the research and development of foam aluminum.

For the research of high melting point metal foam, there are mainly Ni-based, Ti-based and D-based alloys, and the production method is mainly powder metallurgy sintering. Reports in this regard have only appeared in recent years, such as the use of Ni-based alloys to produce thin porous electrodes.

The research reports on foamed iron are even rarer, only a few related reports on iron-containing Taiwan gold foam metal are found, one is Cu-Fe. The production of sn foam metal, in which the Fe content (mass fraction) is 60% to 80%, and the cu is 10% to 30%, which is obtained by powder metallurgy sintering, and its porosity is 10% to 35% [3U]; Another Fe-Cr-AI. RE Taijin, Fe accounts for 70% ~ 8O%, also produced by sintering method, Fe exists in the form of fibers"; there is also a Fe powder and another metal powder adhered to a sticky resin grid structure , and then sintered to obtain a thin metal foam sheet, which is used as an electrode. In addition, there are reports on the preparation of iron foam by the seepage method, and reports on the preparation of iron foam by the hollow ball method, but they have not been popularized.

In a word, the preparation and application of high-melting iron foam is only in its infancy, and the method is relatively complex and simple. Therefore, it is necessary to research and develop preparation methods for high-melting iron foam and other high-melting-point metals and their alloys, in order to use them as soon as possible This functional material with many special properties contributes to mankind.

3. Characteristics and applications of metal foam

Since there are many holes in the foam metal, the size, number, uniformity, connectivity and closure of the holes will affect its performance.

3.1 Structural parameters and characteristics

1) Pore size: Pore size generally refers to the average diameter of pores, which is the basic parameter of foam metal. The pore size of foam metal is generally larger, O. 1～10mm or more (generally, the aperture of powder metallurgy metal is not more than 0.3mm).

2) Total porosity, effective porosity: Total porosity refers to the ratio of the volume occupied by pores to the total volume (which can be obtained by the weighing method). Since not all pores are connected to each other, the ratio of the connected pores to the total volume is called the effective porosity. Only when all pores are connected, the total L porosity is equal to the effective L porosity. The porosity of metal foam is relatively high, and its porosity is between 40% and 90%.

3) Through porosity: the ratio of the average pore channel diameter to the average pore diameter on any section is the through porosity.

4) Specific gravity and specific surface area: the specific gravity of foam metal is light. Generally only 1/10-3/5 of the same volume of metal. Its specific surface area is larger, which is lO-40cm²/cm³

3.2 Performance characteristics

3.2.1 Light weight and small specific gravity

Due to the existence of many large and small holes in the metal matrix, this material is obviously light in weight. The specific gravity is small. The specific gravity of foamed aluminum ranges from 0.2 to 0.5 g/cm, and its average value is only 1/10 of that of aluminum.

3.2.2 Mechanical properties

The tensile strength of foam metal is relatively low. The specific strength is also relatively low, but the compressive strength and flexural strength are high. The tensile strength of foamed aluminum is only about 1/100 of that of aluminum, and the specific strength is about 1/10 of that of aluminum. Foamed aluminum has low severability. For example, aluminum foam does not have the ductility of metal aluminum, and almost no plastic deformation occurs under pressure. The elastic modulus of foamed aluminum measured by bending test is about 1/50-1/100 of that of aluminum alloy.

3.2.3 Shock energy absorption characteristics

The foam metal material has a unique network, non-directional porous structure, and no rebound effect. Through the stress-strain test of this material, it is found that its strain lags behind the stress strongly, and in the compressive stress-strain curve E line Containing a long plateau, metal foam is a material with high impact energy absorption properties.

3.2.4 Thermophysical properties

Foamed metal generally has high heat resistance, even if the temperature reaches the melting point of the base alloy, it will not dissolve. For example, ALMAG alloys have a temperature range of 560-640. C, but the ALMAG alloy foam alloy is heated to 1400 in the atmosphere. C does not dissolve either.

3.2.5 Transmission performance

Permeability is a fork-characteristic of through-cell metal foam. Through the adjustment of the foam metal pore structure (such as porosity, pore size, through porosity, etc.). Foamed metal materials with different permeability requirements can be obtained.

3.2.6 Acoustics and Electricity

For through-hole metal foam, when the sound wave touches the metal surface, it enters the hole of the metal foam through diffuse reflection, and the internal vibration of the metal converts the sound energy into heat energy, which plays a role in noise reduction. Electromagnetic waves were used to test foam metal, and it was found that foam metal also had the effect of absorbing electromagnetic waves, so foam metal also had a shielding effect on electromagnetic waves.

3.3 Application of foam metal

In view of the various kinds of foam metal mentioned above, there are many corresponding application fields of foam metal. The need for application is also the significance of the development of this new type of material.

3.3.1 Utilize excellent thermophysical properties

Foamed metal has a large specific surface area, and can be used to make heat exchangers and radiators for through-cell foamed metal; for closed-cell foamed metal, it can be used as a thermal insulation material.

3.3.2 Utilize the shock energy absorption characteristics

It is one of the important uses of foam metal for the manufacture of buffers and shock absorbers. Its applications range from the impact baffle of the car to the landing gear of the spacecraft, and it has been successfully used in elevators, conveyor safety pads, and energy-absorbing linings for high-speed grinder shields.

3.3.3 Utilizing permeability

Using the permeability of metal foam, it can be used as an important material for the preparation of filters. Compared with powder metallurgy porous metal, it has the characteristics of large pore size and high porosity, and the filter made with it has a wide range of applications, which can be used to filter out solid particles from liquid, air or other airflows.

3.3.4 Using acoustic and electromagnetic properties

Using the sound-absorbing properties of foam metal, it is mainly used for noise reduction and noise reduction, such as attenuation mufflers for steam power plants, pneumatic tools, cars, etc. In Japan, promising results have been obtained in high-speed train generator rooms, radio recording studios, and Shinkansen sound absorption.

3.3.5 Other uses

Bubble metal can also be used in the construction industry, such as interior and exterior decorative parts of buildings, curtain walls, walls, etc.; it can also be used as a computer stand; various packaging boxes, etc. … Using the fire resistance of foam metal, it can be used for refractory materials in industries such as construction; or by processing its holes, it can be used for flame retardant materials. In chemical industry, it can be used as a catalyst carrier. In addition, metal foam can also be used as a porous electrode.

To sum up, the application of foam metal is quite extensive, it can be used in many fields such as construction industry, aviation industry, computer industry, transportation and packaging industry, and with the continuous improvement of foam metal production process and its research and development With the continuous deepening, the application field of foam metal is still expanding. Therefore, the research and development of foam metal has great practical application value.