A model to characterize acoustic softening during ultrasonic consolidation

• Acoustic softening during UC is shown to reduce the yield stress of Al 1100-0 foils by up to 82%.
• Thermal softening during UC is relatively minor, less than 5% compared to acoustic softening.
• Frictional heat generation is shown to be the dominant source of heat during UC.

Ultrasonic consolidation (UC) is a solid state bonding process in which thin metal foils are bonded under the influence of ultrasonic vibration and pressure. Large parts can be made by placing foils side by side or by stacking layers to create thicker parts. Thermal and acoustic softening of metals during UC leads to increased plastic deformation and plays an important role in bond formation. In this work, a thermo-mechanical finite element model is developed to quantify the degree of thermal and acoustic softening occurring in Al 1100-0 foils during UC. The model uses experimentally measured temperatures and changes in the foil's geometry during UC to quantify the amount of thermal and acoustic softening. Acoustic softening is shown to reduce the yield stress of Al 1100-0 foils by up to 82%. In addition, thermal softening is found to be relatively minor, typically less than 5% of the total material softening. This method to quantify acoustic softening during UC allows for a better overall understanding of the bonding process and allows several aspects of the UC bonding process to be optimized and improved.