Closed-cell aluminum foam is a new type of lightweight material with structural and functional properties concurrently. Because of its unique porous structure characteristics, closed-cell aluminum foam shows high specific strength/stiffness, energy absorption, sound absorption and insulation, damping vibration, heat insulation, electromagnetic shielding and many other excellent performances. For these reasons, closed-cell aluminum foam has important applications in automobile industry, traffic facilities, building materials and other fields. With the deepening of the research and application development, closed-cell aluminum foam will make outstanding contributions to the development of human beings in more areas.This paper is based on the existing technology of our group, the melt foaming method is used to prepare closed-cell aluminum foams. Then the macroscopic analysis for samples is made. After that, the further research on the melt viscosity which is the most critical factor in the process is carried on, and the temperature of introducing thickener Ca and thickening stirring time are explored on the pore structure. Research shows that:the temperature of introducing thickener Ca can not be less than 730 ℃, otherwise it will reduce dissolution rate of Ca in the aluminum melt drastically, and has serious influence on subsequent experimental processes, and 750℃ is appropriate temperature at last. Thickening stirring time has a huge impact on melt viscosity. With the extension of stirring time, the bubble-free layer in closed-cell aluminum foam samples decreases, and the pore distribution is also more uniform.Then, the macro-micro structure characteristics of the aluminum foams are investigated. The results indicate that the pore walls mainly consist of aluminum matrix, Al4Ca phases at the grain boundary and some defects including cracks, compound particulate collections on the pore inner walls.At last, the electromagnetic interference shielding effectiveness of the aluminum foams with different porosity is investigated. The results show that aluminum foams possess good EMI shielding effectiveness of 25dB-75dB to the space plane electromagnetic wave within the frequency of 130MHz to 1800MHz. Its EMI shielding effectiveness generally increases with increasing porosity and decreases with increasing frequency. Furthermore, the electromagnetic shielding mechanism is systematically explored and the EMI shielding equation applied to aluminum foams is also proposed, which is correlated to reflection loss, absorption loss, multiple reflections loss, eddy-current loss, wave-current interaction and any other factors. The experimental results can be well explained qualitatively. |