Aluminum foam is a kind of porous material with numerous pores distributed in metal aluminum matrix. Its special structure determines that it has many special properties which are not found in dense metals. Features: low density, large pore size, diverse pore structure, large surface area, high porosity, high absorption impact ability, high temperature resistance, fire resistance, corrosion resistance, sound insulation and noise reduction, low thermal conductivity, high electromagnetic shielding, strong weather resistance, filtration ability, easy processing, easy installation, high forming accuracy, the surface can be painted, etc.
Aluminum foam can be designed to achieve the desired comprehensive performance by changing its density and pore structure. Because of its excellent physical and mechanical properties, aluminum foam can be used as both structural and functional materials. And it has both metallic and pore characteristics. That’s the charm of this unique material, therefore, it is widely used in many fields.
The performance of aluminum foams mainly depends on the structural parameters such as porosity, pore diameter, through-hole ratio and density. The pore structure parameters of aluminum foam mainly depend on the preparation techniques.
The followings are detailed introduction of aluminum foam preparation techniques:
1.Powder metallurgy foaming method
Aluminium or aluminium alloy powder and foaming agent are prepared in a certain proportion and mixed evenly, the preform is obtained under the appropriate pressure, then further processed into a semi-finished product and place it into the steel die of the required part shape, heat to a temperature close to the melting point of the preform, the foaming agent is decomposed to release gas to form bubbles. Finally, closed cell aluminum foam was prepared.
2.Melt foaming method
The melt foaming process takes place in the liquid phase, the main direct blowing method, foaming agent foaming method.
Direct blowing method: Firstly, SiC, Al203 are added to the molten metal and uniformly dispersed to improve the melt viscosity, gas is then blown into the bottom of the melt (such as nitrogen, inert gas, etc.), a large number of pores are formed in the metal liquid and solidified after cooling.
Foaming agent foaming method: add foaming agent to aluminum melt and stir evenly, heating make the foaming agent to breaks down and produce gases, the gas expands and foams, after cooling then get metal foam.
The foaming agent used is usually metal hydride such as TiH2 or ZrH2, etc. The foaming agent particles are rapidly and uniformly dispersed in the aluminum melt by high speed stirring, viscosifier (Ca) is used to increase the viscosity of the melt to prevent bubbles from escaping or growing together during the foaming process, it can improve the pore structure.
3.Secondary foaming method
It is a foamed aluminum preparation method which combines the advantages of powder metallurgy foaming method and melt foaming method.
Add a viscosifier (Ca, Al203) to the aluminum melt and stir evenly, then add foaming agent (TiH2) at suitable temperature and viscosity and disperse evenly, before the foaming agent decomposes, the melt is cast into the mold for rapid cooling and solidification, the foaming precursor is obtained. when heated to a certain temperature, the foaming agent TiH2 begins to decompose and foam, and aluminum foam is obtained.