Metal foam refers to a new type of material with voids distributed in the metal matrix. According to its pore structure, it can be divided into open-cell foam and closed-cell foam. Metal foam has two elements: one is that the material contains a large number of pores; the other is that the pores are used to meet some or some of the design requirements to achieve the desired performance index. The pores in the metal foam are functional phases that are used to optimize the properties of the material. The metal foam not only retains the characteristics of the lightweight, high-strength, high-temperature resistant structural materials of the metal materials, but also has the characteristics of functional materials such as energy absorption, heat insulation, shock absorption, flame resistance, heat resistance and permeability. Therefore, metal foam has broad application prospects in the fields of aerospace, atomic energy, petrochemical, medical, metallurgy, machinery, construction, etc. It can be used to make filters, catalyst carriers, porous electrodes, energy absorbers, silencers, shock absorption buffers. , heat exchangers, electromagnetic shields, etc. Research institutions in some developed countries have made metal foam one of the research priorities of new materials in the 21st century.
The light alloy foam sandwich structure is a three-layer composite structure composed of a panel, a low-density foam core and a panel developed on the basis of metal foam research. As shown in FIG. 1 , the panel may be a metal panel or a non-metal panel, and the low density foam core may be aluminum foam, titanium foam or the like. The preparation methods of the light alloy foam sandwich structure include a direct bonding method, a thermal spraying method, a powder metallurgy method and a cumulative stack rolling method, wherein the powder metallurgy method is the most mature method currently developed, and the method realizes the between the panel and the aluminum foam. Metallurgical bonding, combined with plastic forming techniques, enables the fabrication of complex structures in three-dimensional shapes. The foam sandwich structure has the following characteristics:
Low density and high specific stiffness. Metal foam is a metal material with a certain pore in the metal matrix, so the density is low. The thickness ratio of the panel material and the panel to the metal foam can be appropriately selected to form a low-density metal foam sandwich structure, and the metal foam sandwich is effectively The deformation mode of the panel under static and dynamic loads is improved, and the specific strength and specific stiffness of the structure are greatly improved.
Energy absorption performance. Metal foam can absorb a large amount of energy during deformation, and has impact resistance, but its strength is low, it is not suitable for structural materials, and it is combined with metal panel to become a metal foam sandwich structure, which can meet the strength of structural parts. With the requirement of rigidity, the demand for energy absorption characteristics can be satisfied at the same time.
Excellent damping characteristics. Aluminum foam is a highly damped material that combines with a metal panel to form a sandwich structure with enhanced damping characteristics. This is because, in the event of vibration, the aluminum foam core will be forced to expand and contract with the panel, resulting in greater shear stress and strain, reducing vibration energy and reducing vibration. At the same time, if the aluminum foam sandwich is between the panel and the panel A small range of slip can be produced by the shock pressure, which creates additional interface damping, which further reduces the energy of the shock.
Thermal insulation and sound insulation. The closed-cell metal foam has low thermal conductivity and absorbs sound and reduces noise. Therefore, the metal foam sandwich structure has a lower thermal conductivity than a dense metal, and has a property of absorbing sound.
Metal foam and its sandwich structure are advanced materials and structures suitable for the development of future aircraft, which can meet the requirements of system weight reduction, structural load bearing and functional integration. Its application will certainly promote the comprehensive performance of the aircraft. Several aspects have a good application prospect:
The wing, tail and skin structure of the aircraft. The light weight and high specific stiffness of the metal foam determine its wide application prospects in the wing, tail and skin structure of the aircraft, and can meet the requirements of aircraft stealth and surface anti-insulation during high-speed flight. Boeing's sandwich structure made of titanium foam has been used in the rear wing of the helicopter. Airbus is also currently conducting research on the structure of metal foam wings. The goal is to design and manufacture a new type of ribless and raft for light aircraft. Strip sandwich wing structure.
Filtration and flow control structures in aircraft. Metal foam has excellent permeability and is an ideal filter material. It has excellent mechanical properties and strong corrosion resistance. It is suitable for use in aircraft with very harsh working conditions, such as wide temperature range and wide pressure range (from vacuum to high pressure). ), inert or corrosive gases, liquids, high overload and filtration and flow control under thermal vibration conditions, so flow control is one of the uses of metal foam materials in aviation, used to make plugs for pipes placed in the flow path, It can be calibrated to meet the flow rate/pressure under severe conditions of use. Aluminum foam vent plugs produced by ERG in the United States have been used in the F22 Raptor for pressure release during high-speed switching. Metal foam will exhibit superior performance in similar constructions.
Armor protection structure in tanks and tanks. Metal foam and its structure exhibit excellent energy absorption performance during compression or impact. Therefore, metal foam is also an excellent armor material used in protective structures in tanks and tanks. The US military used aluminum foam as the energy absorbing layer, made composite armor, and carried out blasting tests. The results were satisfactory, indicating that foamed metal with the same structure is suitable for such structures.
The excellent performance and broad application prospects of metal foam and its sandwich structure have attracted the attention of domestic scholars. Some universities and research institutions have also carried out related research and made certain progress, but compared with foreign development, there are still some Big gap. In recent years, under the auspices of the National Natural Science Foundation of China, Aviation Support, and the Group's Innovation Fund, the company has carried out a large number of researches on the preparation of foamed aluminum by powder metallurgy, gas capture and bulk titanium sintering. The research work has accumulated rich experience in the preparation of metal foam and its sandwich structure, pore structure characterization and performance evaluation, and has a certain research foundation.
Metal foam and its sandwich structure are widely used as lightweight structural materials with excellent structure and function. They have broad application prospects in aerospace, shipbuilding, weapons, biology, etc., especially have become ultra-long-time aircraft lightweight. One of the important choices of structure. Therefore, mastering the basic theoretical problems existing in the manufacturing process of metal foam and its structure, and breaking through the key technologies of manufacturing, is of great significance for promoting the application of metal foam and its sandwich structure in new weapons and equipment.