Quantification of pitting in two tempers of 7075 aluminium alloy by non-destructive evaluation

An attempt was made to use the damage parameter, β obtained from non-linear ultrasonic assessment, to quantify pitting damage in 7075 aluminium alloy. β values were found to be different for the two tempers, T6 and T73. β reflected the pitting damage quite well in the initial stages of pitting, during which the non-linearity change in the lattice was mostly governed by the creation of free surfaces due to pitting. However, on prolonged pitting, the β values showed anomalous behaviour. The findings are explained by the operation of counteracting microstructural influences on lattice non-linearity.