Strain amplitude-dependent internal friction of as-cast high damping magnesium alloy during cyclic vibration

An investigation on strain amplitude-dependent internal friction (IF) of an as-cast high damping Mg-7 wt% Ni alloy was carried out. In the range of our tested strain amplitudes, whether the strain amplitude is increasing or decreasing, the strain amplitude-dependent IF curve can be divided into two stages: one is the strain amplitude weakly dependent part and the other is the strain amplitude strongly dependent part. However, after several cyclic vibrations, the IF values measured during the strain amplitude increasing are smaller than those obtained during the strain amplitude decreasing. The phenomenon is also observed at 100 A degrees C. Partial dislocations generate a short-range slip under the cyclic stress to be responsible for it. At the first certain cycle measurement, it was also found that IF value is completely reversible; no amplitude hysteresis loop appears. During the cycle number increasing, however, it was found that the IF value tested is smaller while increasing the strain amplitude than that obtained while decreasing the strain amplitude.