Vibration damping and noise reduction effects of magnesium alloy AZ31 was researched with the impulse response decay method (IRDM). The free vibration of magnesium alloy sheet was excited by a pulse excitation, and the sound pressure near the magnesium alloy sheet was measured. The radiated sound pressure due to one normal vibration mode or the complex sound pressure due to few normal vibration modes in one frequency band was isolated by a band-pass filter from the measured sound pressure signals. The damping loss factor (DLF) of the magnesium alloy was obtained by the slope of the polynomial fitting curve for the sound pressure signal, and compared with that of steel. The results showed that the DLF of magnesium alloy decreases with the increase of frequency. Many damping peaks appear at 660, 1 090, 1 230 and 1 760 Hz, which are most suitable for the vibration reduction. In the low-mid frequency range, the damping capacity of magnesium alloy is 2 to 3 times higher than steel's. Therefore, magnesium alloy components will show excellent shock absorption, vibration damping and noise reduction performance.
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