Fatigue behaviour of a commercial zinc-aluminium eutectoid alloy

Constant-amplitude, flexural-fatigue tests have been carried out over the frequency range 8–100 Hz and the temperature range 293–373°K on a commercial zinc-aluminium alloy of basically eutectoid composition. This alloy is highly superplastic at 530°K, when the strain-rate sensitivity of the flow stress index, m, 0·5. At 293°K some residual superplasticity exists and this manifests itself as a frequency effect in the fatigue behaviour. This effect is almost certainly the result of room-temperature, strainrate sensitivity; it is shown by the fact that when the superplastic microstructure is destroyed, the frequency effect disappears. Finally, it is shown that the model proposed by Morrow successfully predicts the fatigue life of this alloy.