Abstract: To understand damping capacity of magnesium at different frequency and amplitude of vibration, damping-frequency curves of AZ91D, AZ31, aluminum alloy and steel are measured at room temperature. It reveals that AZ91D has the best damping capacity among the mentioned four materials and a damping peak is found at frequency 6 Hz. To know its damping action in real use, the dynamic mechanical charac-teristics of magnesium engine box cover and aluminum engine box cover are studied by means of the experimental modal analysis technique. It is found that the first and the second stages of modal damping ratio of magnesium engine box cover are 17.6% and 41.3%, higher than the aluminum engine box cover individually. The first and the second stages of the modal mass of magnesium engine box cover are 45.0％ and 15.3%, higher than the aluminum engine box cover individually. These reveal that magnesium alloys have better shock absorption and better stability in appliance.

Key words: Damping, Experimental modal analysis, Magnesium alloy