Low-frequency damping behavior of foamed commercially pure aluminum

Experiments have been carried out to investigate the damping behavior of foamed commercially pure aluminum (FA). The FA specimens were prepared using pressure infiltration process. The damping characterization was conducted on a multifunction internal friction apparatus (MFIFA). The internal friction (IF), as well as the relative dynamic modulus, was measured at frequencies of 0.5, 1.0 and 3.0 Hz over the temperature range of 20–400 °C. The size of macroscopic pore is on the order of a millimeter (1.0 mm) and in large proportions, typically up to 69 vol.%. The measured IF shows that FA has a damping capacity that is enhanced in comparison with bulk commercially pure aluminum. Especially, an IF peak was found and corresponding to a rapid drop of relative dynamic modulus (vs. temperature) in the FA specimen. The average values for the activation energy of the IF peak is approximately 1.39±0.03 eV. The microstructural analysis was performed using transmission electron microscopy (TEM). TEM observations showed that dislocation substructures exist near the grain boundaries. Accordingly, one can propose that such substructures intersecting and interacting with the grain boundaries are dragged along with the grain boundary during the viscous sliding of the boundary, so that the sliding process is limited with the appearance of this IF peak. Finally, a four-parameter mechanical model used for describing the operative damping mechanism of the IF peak in the FA were discussed in light of IF measurements and microstructural studies. An approximate expression for IF is derived, which is based on the four-parameter mechanical model in FA specimen and the experimental results have been better explained.