Ultrasonic spot welding of 5182 aluminum alloy: Evolution of microstructure and mechanical properties

The present study is focused on the evaluation of microstructures, tensile lap shear strength and fatigue resistance of ultrasonic spot welded joints of lightweight AA 5182 aluminum alloy. The temperature quickly increased during ultrasonic spot welding (USW), with the peak temperature increasing with increasing welding energy. A "necklace"-like ultrafine structure occurred at the weld interface due to the presence of dynamic recrystallization. The tensile lap shear strength increased with decreasing number of impedance setting. When the impedance was set below 5, the tensile lap shear failure load of nearly 6 kN was attained, surpassing the requirement for the average peak load of AWS D17.2 standards. The tensile lap shear strength, failure energy, and critical stress intensity factor first increased, reached their maximum and then decreased with increasing welding energy. The maximum tensile lap shear strength of -150 MPa was achieved at a welding energy of 4000 J and an impedance setting of 2. The load-controlled fatigue behavior displayed a bi-linear characteristic due to the change in the failure mode from interfacial failure at the higher cyclic loads to transverse-through thickness (TIT) crack growth mechanism at the lower cyclic loads.