Sound absorption of open celled aluminium foam fabricated by investment casting method

Abstract

The sound absorption behaviour of an open celled aluminium foam fabricated by investment casting method was examined and correlated with the pore size, sample thickness and backing air gap depth in the present study. The foam shows low sound absorption coefficients at relatively low frequencies or with relatively thin sample thickness due to its 90% or higher open porosity. As frequency or sample thickness increases, the sound absorption is significantly enhanced. Furthermore, if the sample is backed with an air gap, the approximate periodical resonant absorption peaks emerge from the background and shift towards low frequencies with increasing the gap depth. It is also found that the present aluminium foam has even better absorption performance than polyurethane foam, with almost the same pore parameters as the former. The observation on the pore surface and further experiments demonstrate that the difference is attributed to rougher pore surface of the aluminium foam that makes the sound wave loss increase through enhanced friction between the air and the surface.

Sound Absorption Characteristics of Aluminum Foams Treated by Plasma Electrolytic Oxidation

“…Therefore, it is concluded that relatively small pores of the foams are beneficial to sound absorption. This tendency is consistent with those observed in aluminum foams [4,5,6]. …”

“…As mentioned above, two mechanisms are responsible for the sound absorption characteristics of Al foams, i.e. , the viscous losses resulting from the air flow and the thermal losses originating from the friction between the air and the cell wall through the vibration of air in the pores [4,5,6,9]. It can be found after the PEO treatment that there are small pores at micrometer level distributed in the surface of the aluminum foams.…”

“…There are increasing studies on the sound absorption characteristics of the aluminum foams [4,5,6,7,8,9]. Lu et al presented an experimental and theoretical study for the sound absorption of aluminum foams with semi-open cells.…”

“…Wang found that the sound absorption behavior of open-celled aluminum foam was correlated with the pore size, sample thickness, and backing air gap depth. As frequency or sample thickness increases, the sound absorption is significantly enhanced [6]. Masataka Hakamada fabricated the aluminum foams with porosities of 85%–95% by the spacer method.…”

Synthesis of ZnO micro-rods on the cell walls of open celled Al foam and their effect on the sound absorption behavior

“…The porosity and the average pore diameter are 92% and 1.0 mm, respectively. The detailed process and the cell characterization can be seen in reference [3]. Hydrothermal method was utilized to synthesize ZnO micro-rods on the cell surface of Al foam in the following steps: (1) soaking the Al foam samples with the size of f29 Â 30 mm in a solution of 0.015 mol/L zinc acetate dehydrate in ethanol for 1 min; (2) taking out the soaked Al foam samples from the solution and drying them with a hand electric dryer;…”