Ultrasonic C-scan imaging and analysis of the mechanical properties of resistance spot-welded joints of stainless steel

The quality of spot-welded joints of 1 mm-thick SUS304 stainless steel sheets was investigated using scanning acoustic microscopy. C-scan images were used to characterize the weld evolution characteristics of welds formed under different welding parameters, and A-scan signals of feature regions were collected and analysed. The mechanical properties of the spot-welded joints were described in terms of the peak load, failure energy, failure mode and the failure displacement. The results illustrate that C-scan images can provide information about the internal state of spot-welded joints. The A-scan signals in different feature regions were distinct from each other, and three regions in the spot-welded joints were distinguished on the basis of the A-scan signals and the C-scan images: the weld nugget zone, the heat-affected zone and the fusion zone. When the supply pressure was 0.15 MPa, both over-burn defects and splash defects were observed; when the welding current was greater than 8 kA, only splash defects were observed. The peak load, the failure energy and the failure displacement tended to first increase and then decrease with increasing welding current and increasing supply pressure.