Non-linear ultrasonic response of plastically deformed aluminium alloy AA 7009

Using non-linear longitudinal wave and non-linear surface wave, the effect of plastic deformation on the non-linear ultrasonic parameter of aluminium alloy AA 7009 was studied. The results reveal that the second-order non-linear coefficient (<inline-graphic xmlns:xlink="http://www.w3.org/1999/ xlink" xlink:href="mst-29-11-1304-e05.tif"/>) increased with increasing the plastic strain for both types of non-linear waves. A simple power-law relation was developed between the ratio of <inline-graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="mst-29-11- 1304-e06.tif"/> and the plastic strain. The stress exponent index was found to be ∼2·35 and 1 for the non-linear longitudinal wave and the non-linear surface wave respectively. The difference of the non-linear ultrasonic responses was likely due to the microstructural difference between the near surface material and the material far away from the surface.