Effects of high-speed deformation on the phase stability and interdiffusion in ultrasonically joined aluminum and zinc foils

The effects of high strain-rate deformation on the phase stability and interdiffusion were investigated for Al-Zn welds produced by ultrasonic welding at 513 K. The welds exhibited three distinct regions: a featureless region indicative of local melting on the zinc side, a solidified mushy layer and a layer of fee grains enriched with zinc. Al-Zn phase diagrams calculated from vacancy-modified Gibbs free energy curves indicate that local melting at the weld interface may result even at 513 K if the vacancy concentrations in the fee and hcp solutions approach 0.07 as a result of high strain-rate deformation. EDS analysis of the weld interface yielded an interdiffusivity of 1.9 μm 2/s, which is five orders of magnitude larger than the normal diffusivity of zinc in aluminum at 513 K. Application of the mono-vacancy diffusion mechanism to the diffusion data also yields a vacancy concentration of 0.07, indicating that such a high vacancy concentration may indeed resulted during the ultrasonic welding at 513 K. © 2005 Materials Research Society