Abstract
The bonding formation for ultrasonic welding of dissimilar metals has been shrouded in mystery because of the complex thermomechanical behavior at the bonding interface. We investigated the microstructure and phases at the bonding interface of ultrasonically welded aluminum to copper joints using transmission electron microscopy, and found a ~10 nm thick transition layer composed of amorphous phase and nanocrystallines, which was believed to form the bonding between these two metals in addition to mechanical interlocking observed at a larger scale. Interdiffusion of parent elements (i.e. Al and Cu) was noticed in the amorphous phase, which was mainly driven by plastic deformation in solid state introduced by ultrasonic vibration. High densities of dislocations and stacking faults were also observed in the parent metals close to the transition layer, confirming the effects of severe plastic deformation.
Highlights
Multi-material structures are of increasing demand to improve product performance and satisfy functional needs
Based on the diffraction contrast produced under the bright-field observation, low-magnification cross-sectional transmission electron microscopy (TEM) image illustrates the structure of parent Al, Cu and the Al-Cu interface (Fig. 1E)
It is known that Al has a high stacking-fault energy[16], high density stacking faults (SFs) are observed in Al grains, as illustrated by the low-magnification bright-field TEM image and its inset high-resolution transmission electron microscopy (HRTEM) image (Fig. 2C), which usually appear during severe plastic deformation
Summary
Multi-material structures are of increasing demand to improve product performance and satisfy functional needs. Based on the diffraction contrast produced under the bright-field observation, low-magnification cross-sectional transmission electron microscopy (TEM) image illustrates the structure of parent Al, Cu and the Al-Cu interface (Fig. 1E).
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