Study of solid state joints of copper processed by ultrasonic welding

By means of ultrasonic welding, solid-state joints of copper sheets with the initial coarse-grained structure were obtained. It is shown that in the course of ultrasonic welding, significant structural changes occur in the material in the joint region. A layer with an ultrafine-grained structure with a grain size of less than 1 μm is formed near the contact interface of the sheets, and elongated grains with developed substructure are observed in the bulk of the sheets in the welding zone. There are no structural changes outside the weld spot zone. The average lap shear strength of the specimens was 36 MPa. It is shown that the structural changes occurring during welding result in an increase in microhardness by factors of 1.2 and 1.5 in the bulks of sheets in the weld spot zone and in the weld joint as compared to that of the initial sheet (950, 1200, and 790 MPa, respectively).