Enhanced diffusion and phase transformations during ultrasonic welding of zinc and aluminum

Effects of Vibration Amplitude on Microstructure Evolution and Mechanical Strength of Ultrasonic Spot Welded Cu/Al Joints

“…It is well known that the diffusion can be accelerated dramatically by the high concentrations of lattice defects. Significantly, the ratio of the enhanced diffusivity in Metals 2017, 7, 471 7 of 12 ultrasonic welding to the predicted diffusivity was much smaller than 1.57 × 10 5 previously examined for the ultrasonic welding of Al-Zn where a continuous intermetallic layer was not formed [22]. It was implied that the formation of lattice defects was likely to have the greatest influence on the nucleation of IMC islands in the early stages of ultrasonic welding.…”

“…The reasons for the acceleration of the intermetallic layer formation at a greater amplitude were as follows: first, the shear stain rate in ultrasonic welding increased with the amplitude [16]. The vacancy concentration in copper increased more significantly at the greater stain rate, thus accelerating the diffusion through the welding interface [22]. Second, a greater vibration amplitude generated more frictional energy, resulting in the more rapid increase of the interface temperature.…”

“…This might be related to the high-strain-rate plastic deformation during ultrasonic welding. The lattice defects, such as the excess concentration of vacancies, the high density of dislocations and substructures, were generated owing to the severe plastic deformation during ultrasonic welding [10,22]. It is well known that the diffusion can be accelerated dramatically by the high concentrations of lattice defects.…”

“…This finding suggested that local melting occurred at the periphery of the Cu/Al joints according to the eutectic reaction, α-Al + θ → L. However, for the amplitude of 22.5 µm, the peak temperature was measured as 593 K at the welding time of 0.8 s, which was significantly lower than the temperature of the eutectic reaction. It was more likely that the melting point was depressed by the high-strain-rate ultrasonic deformation [22]. Besides, A. Panteli reported that the melting point could also be depressed by the presence of additional elements [13].…”

Sheet Lamination Processes

“…Materials which have been successfully bonded using UAM include Al 3003 (H18 and O condition), Al 6061, Al 2024, Inconel ® 600, brass, SS 316, SS 347, Ni 201, and high purity copper. Ultrasonic weldabilities of a number of other metallic materials have been widely demonstrated [11,[13][14][15][16]. Thus, there is significant material flexibility for UAM processes.…”