Interlaminar subgrain refinement in ultrasonic consolidation

This research presents microscopic evidence of dislocation propagation and sub-grain refinement in 3003-TO aluminium undergoing high frequency fully reversed loading conditions during the Ultrasonic Consolidation process. Dual Beam Focused Ion Beam etching techniques and Transmission Electron Microscopy were used to characterize sub-grain size, morphology and dislocation structure in regions that were subjected to high levels of multi-axial ultrasonic micro-strain and resultant plastic deformation. This Deformation Affected Zone is characterized by regions of reduced sub-grain sizes that form a gradual transition into larger equiaxed grains well below the interface. While ultrasonic weldi~g has been explored for some time, there has been little agreement on the specific softening mechanisms that allow an ultrasonic weld to occur. Usually, the unexplained effect is vaguely referred to as "acoustic softening," or "ultrasonic softening", generic terms that do not identify a specific mechanism. This uncertainty has led to many disparate theories as to the specific nature of ultrasonic welding. The presented interface characterization discoveries challenge many of these ideas and prescribes a fundamental operative "ultrasonic softening" mechanism that is similar in character to the Bauschinger Effect.