Internal friction in magnesium reinforced by short Al2O3 fibres after thermal cycling

This paper describes the influence of thermal cycling on the damping behavi our of composites with Mg matrix and two contents (26.0 and 34.1 vol.%) of Saffil short fibres. The composites were prepared by squeeze casting. The l ogarithmic decrement, as a characteristic of the process responsible for th e damping behaviour, was measured after ten thermal cycles between room tem perature and an upper temperature. The upper temperature was varied within the range from 100 to 450 degrees C. The strain dependence of the logarithmic decrement can be divided into two regions. A region of strain amplitude independent damping at low strains is followed by a region with amplitude dependent damping at higher strains. T he damping level in the strain amplitude independent region depends weakly on the upper temperature of the cycle whereas the values of the logarithmic decrement in the strain amplitude dependent region depend very sensitively on the upper temperature of cycles. The observed experimental data can be explained considering creation of new dislocations during thermal cycling f ollowing recovery processes at higher upper temperatures of the cycle.