The objective of this work is to demonstrate the feasibility of microstructural characterization via nondestructive techniques. Ultrasonic velocity and attenuation techniques have been used to characterize the microstructural evolution of a cross section of a friction stir welded joint with a focusing immersion C-scan system. One-to-one correspondence was observed between the Vickers hardness and the ultrasonic parameters in quantitatively characterizing the microstructure. Both the velocity and attenuation distribution coincide well with the microstructural evolution. The maximum and minimum values of the attenuation curve can be used to nondestructively characterize the edges of the zones (base metal, heat-affected zone, thermo-mechanically affected zone and nugget) in the quantitative segmentation of the joints. The results also imply the feasibility of further application for quantitative analysis of joint and mechanical properties prediction.
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