We all know that metal, but what is metal foam? In which areas is it applied?
Metal foam may not be familiar to everyone, but simply mentioning foam or metal may not be known to everyone.
Foamed metals are special metal materials that contain foam pores. Through its unique structural characteristics, metal foam has a series of good materials with a small density, good thermal insulation performance, good sound insulation performance and the ability to absorb electromagnetic waves. It is a new type of material that has been gradually developed with human science and technology.
*The nature of metal foam*
The metal foam has high gas permeability, almost all of the communicating pores, the pore specific surface area is large, and the material bulk density is small.
The metal material containing the foamed pores has a higher porosity and a larger pore size of up to 7 mm than the generally sintered porous metal. Since the metal foam is a two-phase composite composed of a continuous phase of a metal matrix skeleton and a dispersed phase of a pore or a continuous phase, its properties depend on the metal matrix used, the porosity and the pore structure, and are affected by the preparation process. Generally, the mechanical properties of foamed metal decrease with increasing porosity, and the electrical conductivity and thermal conductivity decrease exponentially. When the metal foam is subjected to pressure, the foamed metal has excellent impact energy absorption characteristics due to an increase in the area of the force caused by the collapse of the pores and the strain hardening effect of the material.
How is metal foam made?
The preparation of the metal foam is by powder metallurgy and electroplating. The former produces a foamed metal by adding a blowing agent to the molten metal; the latter is replicated into a metal foam on the polyurethane foam skeleton by an electrodeposition process.
The powder metallurgy process produces a foamed metal by adding a blowing agent (such as NH4Cl) to the powder, and the blowing agent volatilizes when sintered, leaving pores. Metal foam with regular shape pores and porosity of up to 95% can be obtained by electrochemical deposition, including foams with metals and alloys such as Cu, Ni, NiCrFe, ZnCu, NiCu, NiCrW, NiFe. The metal electrochemically deposited on the porous body is sintered to connect the deposition components into a whole body, and the strength of the high-porosity metal foam is required to be high, and the porosity is high, and more substances such as a catalyst and an electrolyte can be filled in use.
*Type of metal foam*
Practical metal foams are known as aluminum, nickel and their alloys. In addition, foamed copper also has a certain space for development.
Aluminum foam and its alloys are light in weight, with sound absorption, heat insulation, vibration damping, shock absorption and electromagnetic waves. They are suitable for impact protection of missiles, aircraft and their recycling parts, automobile buffers, electromechanical vibration damping devices, and pulses. Power electromagnetic shields, etc.
Due to its connected pore structure and high porosity, foamed nickel has high air permeability, high specific surface area and capillary force. It is used as a functional material for the production of fluid filters, atomizers, catalysts, battery electrode plates and Heat exchangers, etc.
The copper foam has good electrical conductivity and ductility, and has a lower preparation cost than the foamed nickel, and has better electrical conductivity, and can be used for preparing a battery negative electrode (carrier) material, a catalyst carrier, and an electromagnetic shielding material. In particular, the use of copper foam as a base material for batteries as electrodes has some significant advantages, but its corrosion resistance is not as good as that of nickel, which limits its applications.
I understand! So where are the metal foams commonly used?
Metal foam is widely used in various high-tech fields such as aerospace, aviation, transportation, environmental protection, energy, biology, and general industrial fields.
*Application of metal foam*
Because foamed metal has a certain strength, ductility and additivity, it can be used as a lightweight structural material. This material has long been used in the core of aircraft clamps. In the aerospace and missile industries, metal foam is used as a lightweight, heat transfer support structure. Because it can be welded, glued or plated onto the structure, it can be made into a sandwich bearing member. Such as the support of the metal shell of the wing, the anti-shell high-temperature inverted support of the missile nose cone (because of its good thermal conductivity) and the landing gear of the spacecraft. In construction, metal foam is required to make light, hard, refractory components, railings or supports for these things. The high-speed and high-speed acceleration and deceleration of modern elevators also requires metal foam, a lightweight structure with both energy absorption and load-bearing characteristics to reduce energy consumption. Cylindrical housings are widely found in engineering structures such as aircraft fuselages and oil well platforms that are remote from the shore. A thin-walled cylindrical shell is susceptible to damage when subjected to a load, but if the outer casing is supported by a continuous foam: coil, the structure has greater strength than an unreinforced central casing of the same diameter and size. Foamed copper is easier to manufacture and is easy to deform, so it is suitable as a fastener. Metal foams are also used as reinforcements for many organic, inorganic and metallic materials. For example, when foamed nickel is filled with molten aluminum to be solidified, a foamed nickel reinforced aluminum alloy (NFRA) material or the like is formed.
Metal foam is well suited for use as a lightweight laminate of a variety of load-bearing panels, casings and tubes for a variety of laminated composites. A typical example of a porous material for a structural member is the fabrication of a sandwich panel. The sandwich panels used in modern aircraft use glass or carbon fiber composite skins. This layer of skin is made of aluminum foam or paper. The resin honeycomb material is spaced apart and may also be separated by a rigid polymeric foam to provide the sandwich panel with a large specific bending stiffness and specific bending strength. The same technology has been extended to other applications where weight is a key indicator: spaceships, sleds, rowing boats and movable buildings.
Buffer protection is also one of the main uses of metal foam. It must have the ability to absorb energy while controlling the maximum force acting on the protected object below the limit that causes damage. Porous foams are well suited for this application. By controlling its relative density, the strength of the metal foam can be adjusted over a wide range. In addition, the material can withstand a large compressive strain under almost constant stress, so a large amount of energy is absorbed without causing high stress. In the preparation of artificial bone, according to the requirement of a pore diameter of 150 ～m to 250 ̈m and a large porosity, the inorganic material cannot meet the requirements for use due to the strength at this time, and thus the artificial bone of metal foam is gradually developed. These metal foams are produced by conventional methods, mainly electroplating, etc., and they are subjected to load during processing such as molding and in the human body. Maintaining high mechanical properties while achieving the large porosity required for human bones, ie maintaining high porosity while meeting the large porosity required for human bones, which is the vast majority of human bone materials that do not have a self-healing effect. It is extremely important. 【1】