New discoveries in ultrasonic consolidation nano-structures using emerging analysis techniques

Abstract

This paper examines the influence of ultrasonic consolidation (UC) on the bonding interface and challenges existing opinion regarding the mechanism of oxide dispersal during UC bond formation. The findings presented in this paper were achieved through the use of dual beam focused ion beam (DBFIB) etching and transmission electron microscopy (TEM), enabling the close examination of the weld interface, sub-grain morphology, and dislocation structure in ultrasonically consolidated aluminium (Al) 3003-T0 samples. As a result of this investigation, it has been established that a persistent oxide layer between bonded foils often remains after UC with this material. The level of sub-grain refinement in ultrasonically consolidated components was seen to decrease as the distance from the weld interface increases. This trend was characterised by the nanoscale sub-grain and gradient sub-grain regions, between which a distinct stepped transition was apparent. Direct contact with the sonotrode surface during the deposition of each new layer was also seen to cause significantly more sub-grain refinement than interface dynamics alone. Nano-grain colonies were also discovered in areas surrounding material flaws, manganese particles, or non-planar interface regions, and persistent dislocation slip bands were seen near the UC weld interface. In light of these results, the context of previously proposed methods of bond formation in UC is discussed.