Metal foam: At present, metals for making porous metal materials are mainly silver, copper, nickel, titanium and alloys thereof, and stainless steel. The following methods are mainly used to manufacture porous metal materials:
Hot extrusion method. For example, magnesium, aluminum and their alloy powders are mixed with certain carbonates, formed under hot extrusion, and foamed at a higher temperature to form a porous material.
Molten metal method. This means that a low melting point metal is added to a certain blowing agent in a molten state, and a method of uniformly distributing the gas to generate bubbles in the metal under strong stirring is achieved. In order to obtain castings with less defects, it is common to use a metal with better fluidity to reduce the gas adsorbed in the molten metal, because the inclusion of bubbles in the metal reduces the strength of the metal. But the method of making porous metal is just the opposite. It requires bubbles in the metal, and it has to reach a high ratio. Therefore, the viscosity of the molten metal is increased, so that the gas is not easily removed, and the gas is inside the metal. Solidified.
Powder metallurgy. Sintered multi-body materials are the most studied and mature porous materials. The method is to add a blowing agent to the powder, and the blowing agent volatilizes when sintered, leaving pores. Electrochemical deposition method. Using a plastic skeleton with a high degree of foaming, the metal is deposited by electroplating, and then the plastic is burned off, leaving pores. Casting method. A method of casting using a gettering-deflation phenomenon of a metal.
Porous metal is widely used as a structural and decorative material and has been widely used in transportation equipment, construction, and residential construction. The metal foam represented by foamed aluminum has the characteristics of light weight, good rigidity, shielding electromagnetic wave, sound absorption, heat insulation, impact resistance and easy processing. It is widely used in soundproof rooms, soundproof walls, shockproof materials, recording and video recording rooms. Shielding materials for electromagnetic waves and other various building materials.
Can metal be like foam?
If someone tells you that a piece of iron can float in the water like a foam, would you believe it? Usually the metal materials we see are mostly dense and usually very hard. However, if a special production process is used, a large number of pores can be generated inside the metal, and this metal is called a porous metal. Porous metals can be classified into two types, a multi-foaming metal and a gas permeable metal. The difference between the two is that the former's pores are independent and have no connection with the outside, just like the honeycombs we see in our daily lives (however, the pores of the porous metal can be as large as the honeycomb holes, and its pores are extremely small. The even the naked eye can't see it, and the latter is in continuous communication.
The percentage of pores in the total volume of porous metal is called porosity. It is an important index to measure the metal of porous body. The larger the porosity, the more pores in the metal. Imagine if it is magnified, is it much like a foam? Therefore, people who have a porosity of more than 90%, a porous body metal with a certain strength and rigidity is called a metal foam. This metal has a high pore content and a pore diameter of up to the order of millimeters, which is almost a communicating hole, and thus it is a gas permeable metal. Metal foam can achieve the purpose of energy saving and capital saving, and meet the needs of the development of modern industrial products. Compared with bulk materials, metal foam has the following characteristics:
First, the strength decreases with increasing porosity, and large deformation is likely to occur under a large pressure, so the metal foam has a good function of absorbing energy.
Second, the thermal conductivity decreases as the porosity increases. When the porosity reaches 50% or more, the heat conduction is reduced by several tens of times. Thus its conduction to heat becomes very slow.
Third, the quality is light. Metals of the same size, the more pores they contain, the lighter they are. When the porosity is 90%, most of the metal is lighter than the same volume of water. When the porosity reaches 90% or more, iron can become foam iron floating on the water. However, it is also important that the size of the pores and the distribution inside the metal are uniform, otherwise the porosity of the metal may not float even if it is high. Therefore, how to make the pore size evenly distributed is a key and difficult problem in the manufacture of metal foam. In addition, the metal foam has better sound absorption characteristics in a wide frequency range, and has strong shielding electromagnetic waves and good heat resistance.