Effect of aging on damping capacity of AZ91 alloy

Changes in microstructure and damping capacity with aging time for solutionized AZ91 (Mg-9%AI-1%Zn-0.2%Mn) alloy have been investigated based on experimental results front optical micrography, X-ray diffractometry, hardness test and damping capacity measurement vibrating in a flexural mode. Discontinuous beta (Mg17Al12) precipitates form along the primary grain boundaries, the amount of which increases as the aging time increases. The hardness of alpha matrix with respect to aging shows a typical "S" shape, indicating a generation of fine continuous precipitation in the matrix during aging. The peak level of damping capacity for the AZ91 alloy is obtained after 1 hour of aging, over which the damping capacity becomes deteriorated continuously. The optimum density of continuous beta precipitates with fine morphology, which may well act as pinning points for dislocation lines, might be responsible for the improvement of damping capacity.