Aluminum foam preparation method

Due to different preparation processes, aluminum foam can be classified into closed-cell aluminum foam, semi-closed-cell aluminum foam, and open-cell aluminum foam based on how the holes are linked. The preparation methods of aluminum foam can be broadly classified into three categories: liquid phase, solid phase, and deposition.

(1) Liquid phase method

The liquid-phase method is the more mature preparation method of aluminum foam, with broad research potential and application prospects, mainly including gas blowing into the metal liquid method, metal liquid blowing agent method, investment casting method, and seepage casting method.

Gas blowing into the metal liquid method: in the molten metal aluminum melt add thickener particles, to improve the viscosity of the melt, commonly used thickeners have silicon carbide, alumina magnesium oxide, etc. Subsequently, to the molten metal into the air, nitrogen, hydrogen, or a mixture of these gases, and constantly stirring, the molten metal can be obtained after cooling the porosity of 80% ~ 97.5% of the foam aluminum, as shown in Figure 1.

Fig.1 Macromorphology of aluminum foam prepared by gas injection method

(2) Metal liquid blowing agent method: to the molten aluminum melt add a blowing agent, by heating the blowing agent decomposition into gas release, gas thermal expansion of the molten metal into a foam, after cooling can be obtained for 91% ~ 93% of the porosity of the foam aluminum. Foaming agent used in the production ofaluminum foam TiH2, ZrH2, and CaH2, and so on.

(3) Molten mold casting method: the use of fluid refractory materials to fill the pores in the spongy foam, to be hardened refractory materials, heating to make the plastic gasification and obtain the spongy pore structure of the casting, the molten aluminum poured into this casting, cooled and solidified to remove the refractory materials, can be obtained porosity of 80% ~ 97% of the foam aluminum.

(4) Seepage casting method: high-temperature liquid aluminum under a certain pressure seepage into the filler gap to get the metal filler composite, and then use immersion or ultrasonic vibration and other methods to remove the filler, to get the porosity of 70% or so of the foam aluminum. Commonly used fillers are soluble salt, insoluble porous ceramic balls, hollow corundum balls, foam carbon, and so on. This method can be subdivided into two types: the up-pressure percolation casting method and negative pressure percolation casting method.

2. Solid phase method

(1) Powder metallurgy method: The powder metallurgy method is to mix the aluminum powder with a blowing agent (commonly used TiH2) in a certain proportion, prepare the pre-germ body under appropriate pressure, and then the pressed pre-fabricated body is further processed, such as rolling, forging, etc., and then this semi-finished product is put into the required steel mold, heated to a certain temperature so that the blowing agent decomposes to form bubbles and get the foam aluminum. This method is more complicated, but the product quality is higher and the performance is stable, thus it develops rapidly, but this method can not be produced continuously due to the high cost of raw materials.

(2) Powder impregnation slurry method: configure a certain viscosity of aluminum powder slurry, the porous polymer foam material is immersed in this slurry, the powder is deposited in the pore wall of the polymer foam material, and then drying treatment, heating so that thermal decomposition of polymer foam material, spongy material in the decomposition process to play a temporary support role, and finally the aluminum powder is sintered together, and then cooled to get the porosity of 70% to 90% of the Aluminum foam.

(3) Add ball material method: add the ball material or hollow ball into the aluminum melt and stir, so that the ball material is uniformly distributed in the aluminum melt; continue to stir and cool to a sufficient viscosity, and inject the model to get the metal-ball material composite. When the added ball material is a soluble substance, the method of immersion washing can be used to dissolve the ball material, to get through-hole-type foam aluminum.

3. electrodeposition method

Foam by the conductive process as the cathode material, industrial pure aluminum plate for the anode material, in the alkyl aluminum solution plating, so that the aluminum deposited on the surface of the foam, after drying at a certain temperature sintering, thermal decomposition of the foam,aluminum foam. This method is complex and needs to adjust the variables, but the foam structure is more uniform. The structure of aluminum foam prepared by the electrodeposition method is shown in Figure 2.

Fig. 2 Macromorphology of aluminum foam prepared by electrodeposition