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Characterisation of early fatigue damage in AZ31 magnesium alloy using a non-linear ultrasound technique

Abstract An experimental test system was established to determine the ultrasonic non-linearity parameter β in a magnesium alloy. The β values of five AZ31 magnesium alloy specimens were measured and the surface microstructure was observed in situ using optical microscopy at various stages of fatigue. The results showed that there was a significant increase in β with an increasing number of fatigue cycles. This was shown to be linked to the accumulation of the number of persistent slip bands and the length of micro-cracks. The trend for the change of the value of β in areas without a concentration of stress was the same as in the stress concentration zone. However, the amplitude of β in areas without a concentration of stress was only 27% of that in the stress concentration zone. This shows the change in the original value of β resulted from micro-defects caused by material fatigue.