The potential for friction stir weld inspection using transient eddy currents

The development of a growing range of new welding methods for high-strength alloys requires a method of monitoring the full weld profile to assist at both the development and production stages. The aim of this project was to investigate the potential for using transient eddy currents for friction stir weld (FSW) process monitoring and defect detection. As a result, transient eddy-current technology has proved to be remarkably well suited to FSW inspection for on-line process monitoring, being able to penetrate deep into the weld and produce a cross-sectional profile of a parameter related to the electrical conductivity. This is sufficient to indicate the 3D location of any changes in conductivity, as shown by scanning specimens with known conductivity changes at various depths. Comparison with high-frequency surface conductivity measurements has also shown good agreement. A model-based inversion to give a more accurate profile of conductivity is also thought to be possible and work has commenced on this. Further work is required to link electrical conductivity to the microstructure and important material properties of the weld. Better understanding of these relationships will considerably enhance the advantages of using transient eddy currents to monitor the friction stir weld process.