Effect of weld tip geometry on ultrasonic welding of A6061 aluminium alloy

The authors ultrasonically welded A6061 aluminium alloy sheet using two types of weld tips with different contact face geometries, and investigated the effect of the weld tip on the performance and interface structure of the welds. One type of tip has a cylindrical contact face without knurl, which is called a C-tip in this study. The other type of tip has a flat contact face with knurl, which is a called K-tip in this study. The following main results were obtained.

The strength of the joints welded using the C-tip was higher than that welded using the K-tip and the fluctuation in joint strength with the C-tip was smaller. The C-tip could stably produce the higher strength joint. Using the K-tip, the knurl indentations were made on the workpiece surface due to the pyramidal projections on the weld tip, and the indentation size expanded with welding time, resulting in the deterioration of the joint property. On the other hand, the indentation made on a workpiece surface by using the C-tip showed a distinctive shape like an ellipse, elongated perpendicular to the ultrasonic vibration, and the indentation grew with welding time.

Using the K-tip, unbonded regions remained at the weld interface due to the concavity on the weld tip face. In the cross-sectional structure parallel to the workpiece width of the joint welded using the C-type tip, a distinctive feature was observed that the faying surface of the anvil workpiece was mixed with that of the sonotrode workpiece by intense plastic deformation and a horn-like protuberance intruding into the sonotrode workpiece was formed at the periphery of the welded area.