The pulsed eddy current response to applied loading of various aluminium alloys

In this paper the pulsed eddy current (PEC) response of a range of heat treatable and non-heat treatable aluminium alloys (AA-1050, 2024, 5083 and 7075) to applied stress well below the elastic limit is studied. The effect of prior heat treatment and prior plastic deformation on the stress dependency of the pulsed eddy current response is quantified using the peak value of the PEC difference signal. In certain cases non-linear stress responses are measured. Because it is well known that the effect of stress on conductivity is anisotropic both isotropic (circular) probes and directional (rectangular) probes are compared. It is found that both prior plastic work and heat treatment condition can have a strong effect on the stress coefficients, even changing the sign of the stress dependence. The implications of these effects for the future characterisation of residual stress state by PEC are discussed.