Study on sound absorption valley and acoustic absorption performance of small-pore aluminum foam composited with 304 stainless steel fibers

Abstract

Open-cell aluminum foam exhibits a sound absorption valley (SAV) in the 2500–4000 Hz frequency range, reducing its acoustic absorption in the range of 1000–6300 Hz. A small-pore aluminum foam composited with 304 stainless steel fibers (SP-SS304F aluminum foam) with a porosity of 82 % was fabricated via infiltration casting, and its pore structure, acoustic absorption performance, and mechanism were investigated. The pore structure of SP-SS304F aluminum foam consisted of 223–676 μm main pores, 125–373 μm cell wall pores, and 30–60 μm 304 stainless steel fibers. The fibers existed completely embedded in the cell walls, partially or completely embedded in the cell cavities. As the pore diameter decreases, the SAV value increases and then decreases. With increasing fiber content, the SAV value showed a similar trend. The increased SAV value benefits the enhancement of the average sound absorption coefficient (SAC). The SP-SS304F foam aluminum reaches an optimal SAC value of 0.899. Its static resistivity value is 24,345 Pa.s/m2. Finite element simulations reveal the reasons for the improved acoustic absorption performance of SP-SS304F aluminum foam: First, the small-diameter and pore-embedded fibers improve the acoustic impedance matching, reducing sound reflections at the SAV frequency. Second, the reduced pore diameters and partially or completely pore-embedded fibers increase the pore surface areas, intensifying the acoustic absorption by pore structure.