Damping capacity of sand cast magnesium alloy AZ91

Abstract

Measurements of damping properties have been carried out on sand cast specimens of the most widely used commercial magnesium alloy AZ91. Damping properties of specimens in both as cast and heat treated (T4 and T6) conditions were determined by measurements of the logarithmic decrement of free bending beam vibration at various frequencies. The best damping properties were found in the as cast specimens. This is directly related to the microstructure, which consists of α magnesium, large inclusions of β phase (Mg₁₇Al₁₂), as well as lamellar eutectoid Mg₁₇Al₁₂ precipitating as a result of low cooling rate. For homogenised and annealed specimens, the maxima of the hardness and of the damping capacity as a function of annealing time was found. The measurements of the logarithmic decrement can be explained using a model of Granato and Lücke.