Abstract: Mg₂Si/AZ91D composites were synthesized by stirring casting method using addition different content of fly ash cenospheres to AZ91D Mg alloy substrate as raw materials. The microstructure, composition and damping capacities of the Mg₂Si/AZ91D composite materials were investigated by means of optical microscope, XRD and dynamic mechanical thermal analysis. The results show that there is Mg₂Si phase in the composites after adding milling cenosphere particles, compared with the Mg alloy. With the increase of mass fraction of cenosphere, Mg₂Si phase shows irregular shape, and the damping capacities of the composites increase.After the solution treatment, the distribution of Mg₂Si particles in Mg₂Si/AZ91D composite becomes more uniform, and the damping capacities are higher than those of as-cast composite. The damping capacity of Mg₂Si/AZ91D composites prepared by stirring 6 min is higher than those by stirring 3 min at both room temperature and elevated temperature. Damping capacities of Mg₂Si/AZ91D composites can be explained by the G-L theory at room temperature.