Experimental investigation on ultrasonic spot welding of aluminum-cupronickel sheets under different parametric conditions

Variable-parameter NiTi ultrasonic spot welding with Cu interlayer

“…The material flow and plastic deformation volume of the welded area increased with increasing vibration amplitude due to the increment of the frictional heat. [26,28,29] Therefore, when a significantly higher vibration amplitude (>60 μm) was applied, excessive frictional energy intensity promoted the formation of microcracks in the Cu interlayer (Fig. 3(h,j)).…”

“…Then, the repeated motion of slippage and friction is generated at the weld interface, which is fundamental for frictional heat and plastic deformation to occur in the weld region. [25,26] The plastic deformation on the material surface occurred mainly due to two types of thermo-mechanical solicitation: surface friction dissipation and softening by volume ultrasonic effect. [27] These are credited for decreasing the yield strength of the joints, though contributing for the creation of a sound metallurgical bonding along the weld interface.…”

“…The experimental observations indicated that the 45 μm joint fractured along the weld interface, while the 50 μm joint failed through the upper NiTi. The fracture mode changed to BM fracture away from the weld spot with necking occurred when a 55 μm vibration amplitude was applied, after which fracture occurred at the edge of the weld spot, which was attributed to the reduced thickness of the welded region arising from the excessive heating generation at higher vibration amplitude [26]. To clarify the influences of vibration amplitude on the quality of the obtained joints, the fracture morphologies are shown in Fig.8(the observation locations were depicted with white line boxes in Fig.7).…”