Low energy ultrasonic welding for Cu-Cu joining accelerated via Cu nanoparticles

Decreasing welding energy input with enhanced welding quality is difficult to achieve in ultrasonic welding. In this study, a nanoparticle-accelerated ultrasonic welding technique using a Cu nanoparticle (Cu NP) interlayer was proposed. Lap shear tests revealed that the addition of Cu NPs drastically increased the load carry capacity by 253 % for Cu-Cu joints welded with an ultrasonic energy as low as 200 J, reducing the energy input to half of that without Cu NPs. This low energy requirement was attributed to the increase in peak temperature. The clamping force drove Cu NPs to fill and sinter in the interfacial gaps, which also significantly reduced the welding energy required for intimate contact in the early stage of welding. Furthermore, severe plastic deformation, enhanced friction, and nanosized grains induced by the Cu NPs facilitated material flow, accelerated elemental diffusion, and grain refinement at the interface. The enhancement of dynamic recrystallization in the base metal caused by the Cu NPs was confirmed by the calculated Zener-Hollomon parameter and critical recrystallization strain.