Preheating-assisted ultrasonic welding of AA 6061: FEM analysis and experimental investigation

Ultrasonic welding (USW) is widely employed for assembling aluminum components in lightweight structures and lithium-ion battery systems; however, achieving uniform interfacial bonding remains challenging. This study investigates preheating-assisted ultrasonic welding of AA6061 aluminum alloy to clarify the thermo-mechanical principles governing joint formation. A coupled three-dimensional thermo-mechanical finite element model and empirical lap-shear testing were employed to evaluate the influence of preheating temperature on interfacial temperature evolution, stress distribution, plastic deformation, and mechanical performance. The simulations indicate that raising the preheating temperature improves thermal uniformity and expands the effective plastic strain region at the interface, hence enlarging the bonded area. Experimental results demonstrate that lap-shear strength progressively increases from 25 °C to 125 °C, corresponding with enhanced interfacial deformation and reduced unbonded regions. At 150 °C, localized thermal concentration reduces the effective zone of plastic deformation, leading to diminished joint strength. A preheating temperature of 125 °C was established as the most effective, yielding enhanced mechanical performance. The combined computational-experimental framework demonstrates that preheating is a critical factor in controlling bonding area development and provides guidance for improving ultrasonic welding of precipitation-hardened aluminum alloys.