Electrical resistivity measurements to assess vacancy concentration in aluminum during ultrasonic deformation and vibratory consolidation of aluminum-carbon nanotube composites

• Online Access: http://hdl.handle.net/2047/d20002067

Ultrasonic welding (USW) of metals is a widely used commercial process for bonding electrical connections in the solar, automobile and semiconductor industries. USW utilizes high strain rate plastic deformation to create a metallurgical bond but there is not a complete understanding of the bonding mechanisms. In the present work, the measured increase of electrical resistivity during ultrasonic deformation of aluminum indicated the generation of excess vacancy concentrations (Xv) orders of magnitude larger than equilibrium values. TEM observation of ultrasonically deformed aluminum revealed dislocation structures that reflected concurrent strain hardening and dynamic recovery. Dislocation loops were also observed indicating the generation of a large excess Xv during ultrasonic deformation. The very large amount of excess vacancies generated during ultrasonic deformation increases diffusion by orders of magnitude and as such may be an important bonding mechanism of USW. Gaining a better understanding of USW bonding mechanisms including the resulting effects of enhanced diffusion will help to determine the temperature-pressure parameters required to create full-density, metal powder composites using the ultrasonic powder consolidation (UPC) technique.