4. Conclusions
A number of significant and encouraging results have been obtained using the C-scan technique; primarily it has been possible to obtain credible NDT assessments of resistance spot welds in aluminium. The results reported here have shown good correlation with actual peeled samples and metallographic cross sections. Importantly the results were relatively easy to attain, with each measurement taking less than 30 s to acquire, and without extensive operator training for NDT. This is a particular advantage with practical nature, compared to earlier air coupled systems, which required a few hours to obtain a useable image [13]. In addition it provided further fundamental understanding of aluminium RSW process through using the C-scan technique; in particular with respect to the presence of an outer fused ring, corresponding to the extremity of electrode indentation and force influence. The relatively simple, though perhaps obvious requirement, for a flat contact surface for the ultrasonic scanner was the major step in advancing the C-scan technique as a viable candidate NDT of aluminium spot welds.
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The NDT C-scan technique evaluated can provide information regarding aluminium spot weld size and shape.
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A prerequisite for obtaining reliable NDT results is the removal of any electrode surface indentation prior to scanning to provide a flat surface to prevent signal losses due to sound wave refraction.
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Use of the C-scan NDT technique suggests the presence of an outer fused ring at the faying surface corresponding to the outer extremity of the electrode indentation.
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Correlation between weld nugget diameters determined by C-scan and peeled plug measurement from a real assembly suggests practical applications of the technique.