Effect of Process Parameters On Interfacial Microstructures in Al-Zn-Mg-Cu Alloy Panels Fabricated by Ultrasonic Consolidation

Ultrasonic consolidation (UC) is a solid-state process that combines ultrasonic welding and computer control contour milling to bond thin metal foils in a layer-by-layer method. The successful bonding formation is dependent on proper setup of key control process parameters such as applied load, amplitude of oscillation, and travel speed of the sonotrode during the ultrasonic process. The objective of the study is to realize detailed understanding of the interfacial microstructure in various parameter conditions. In this work, aluminum alloy foils were welded to form block samples using the UC process with applied loads of 7000 N and 10000N, travel speeds of 34 mm/S and 102 mm/S, and amplitudes of 30 mm and 39 mm. Focused ion beam (FIB) was utilized to examine interfacial microstructure changes. The results showed that bonding mechanism should be related to plastic deformation and recrystallization near the welding interface. The plastic deformation of the bottom layer was larger than that of the upper one at the interface. In a fully bonded region, both layers formed a coherent plastic flow across the interface without voids or oxides. At a certain force level, increasing the amplitude produced a larger region of deformation and recrystallized fine-grains at the interface. Similarly, a slower travel speed of sonotrode obviously increased the region of interfacial microstructure change. At the current parameter levels, however, increasing the applied force had no significant effect on the region of microstructure change at the interface.