An Approach to Eddy-Current Evaluation of the Structural State in a Cast Aluminum–Silicon Alloy Subjected to Surface Laser Heat Treatment

Abstract

The effect of surface laser heat treatment on the eddy-current parameters of the cast Al–6.34Si–0.32Mg alloy has been studied at excitation frequencies of f = 6–136 kHz. It has been established that the laser heat treatment affects both the amplitude A and the phase angle φ of the eddy-current probe signal. The observed changes in the eddy-current parameters of the laser-treated alloy are caused by the changes in the structural state of the alloy, particularly, by the high dispersity of the structure, increased content of alloying elements in the solid solution, and residual stresses resulting from accelerated cooling under laser melting. The depth of the molten zone and the homogeneity of the structure at different depths can be estimated by measuring the amplitude A, whereas the presence and level of residual stresses can be estimated by measuring the phase angle φ at different probe excitation frequencies. The results clearly show the advantage of separate measurements of the amplitude A and the phase angle φ from the perspective of eddy-current evaluation of the structural state of the laser-treated alloy.