Perpendicular ultrasonic joining of steel to aluminium alloy plates

Standard and high strength steel plates were successfully joined to A2017 and A6061 aluminium plates by applying ultrasonic power perpendicular to the joint interface instead of tangentially, as in other ultrasonic joining methods Using a 2.9 mm diameter tip, cross tensile strengths of 281 N and 460 N were obtained when joining 0.5 mm thick A6061 plates to 0.5 mm thick commercial and high steel plates, respectively. When joining 0.5 mm thick A2017 plates, the cross tensile strengths were 343 N and 437 N, respectively. Temperature measured at less than 1 mm from the joining interface did not exceed 135 °C in any case. The joining mechanisms and resulting joint characteristics are investigated and discussed, alongside parameters affecting the resulting joint performance. Under optimal joining conditions, the cross tensile tests and cross section observations revealed that material fracture resulted in plug failure. No intermetallic layer has been detected with SEM analysis. The joint strengths obtained under those conditions were the maximum attainable for the tip diameter used, provided that they correspond to the stress intensities required to propagate cracks in the aluminium. These results support the conclusion that this ultrasonic joining method, being operationally similar to the method used in resistance spot welding, and providing good performance joints, could be used successfully for high throughput industrial applications taking advantage of the available spot welding tooling and operational procedures, as tangential movement of the whole plate is not required.