Abstract: The effects of macroscopic open-pores on the damping behavior of foamed commercially pure aluminum (FA) were studied.The damping characterization was conducted on a multifunction internal friction apparatus (MFIFA).The FA specimens were prepared by air pressure infiltration process.The size of macroscopic pores was in the order of a millimeter (0.8-1.4 mm) and in large proportions,typically up to 76 vol%.The internal friction (IF) of the FA specimen was measured at different temperatures,different frequencies,and different amplitude dependences.The measured IF showed that FA had an enhanced damping capacity in comparison with bulk commercially pure aluminum.In light of IF measurements,the possible operative damping mechanisms in the FA should include ① stress concentration and mode conversion around macroscopic pores;② elastic modulus difference between the matrix and the macroscopic pores that results in a marked inhomogeneous stress;③ inhomogeneous expansion deformation around macroscopic pores.