Influence of vibrational treatment on thermomechanical response of material under conditions identical to friction stir welding

Nonuniform-to-uniform structural transitions induced by ultrasonic vibrations

“…The temperature of the thermal layers was controlled by the Nose–Hoover method 38 to maintain the temperature of the Mg–Al nanolayer at T e . For the consideration of applying a uniform action of UVs on the sample and avoiding a frictional motion between the two sides of the interface, UVs were realized by applying an X-direction periodical motion functioned by f ( x ) = B sin 2π ft to only the atoms in the sliding slab as in the literature 31 where the UV effect first acts on the driving Al block and then on the driving Mg block, rather than to the entire driving block including the sliding slab and the free slab as mentioned in the studies 32–34 where the UV effect was obviously accompanied by strong fractional motions at the interface of the two blocks or to an external tool as mentioned in the studies 27,30 where the UV effect is nonuniform. The vibration amplitude ( B ) and the vibration frequency ( f ) were typically set on the scales separately approaching those (approximately 0.01 nm and 100 GHz) of the thermal vibration of atoms, such as 0.03–50 nm and 4–1000 GHz.…”

“…the UV effect first acts on the driving Al block and then on the driving Mg block, rather than to the entire driving block including the sliding slab and the free slab as mentioned in the studies [32][33][34] where the UV effect was obviously accompanied by strong fractional motions at the interface of the two blocks or to an external tool as mentioned in the studies 27,30 where the UV effect is nonuniform. The vibration amplitude (B) and the vibration frequency ( f ) were typically set on the scales separately approaching those (approximately 0.01 nm and 100 GHz) of the thermal vibration of atoms, such as 0.03-50 nm and 4-1000 GHz.…”

“…On the atomic scale, molecular dynamics (MD) simulations have exerted attention on the atomic and strain-energy distributions at Al/Al, Cu/Al, Cu/Cu and Ti/Al interfaces joined via an UV-assisted method, 27–35 giving insights into the effect of UVs on the structural evolution of joints. However, there are still no direct images capturing atomic-scale motions of dislocations which, together with atomic diffusion, are involved and essential in material flow and plastic deformation in Mg/Al UVeFSW processes.…”

“…Computer simulations can therefore be an effective tool for probing relative problems. [20][21][22][23][24][25][26][27][28][29][30][31][32][33][34][35] Wu's group [20][21][22][23][24] employed the computational fluid dynamics method and proposed novel constitutive models to investigate the action of UVs on material flow. Their models are based on the Eulerian formulation where materials are treated as non-Newtonian fluids with high viscosity, together with the consideration of the acoustic softening effect.…”

“…However, their numerical investigations focused on the dynamic processes occurring at a large scale (a few millimeters), and lack of motion profiles of dislocations on an atomic scale, even though their measurement of flow stress consists of the plastic-deformation term which is established based on the motions of dislocations. 25,26 On the atomic scale, molecular dynamics (MD) simulations have exerted attention on the atomic and strain-energy distributions at Al/Al, Cu/Al, Cu/Cu and Ti/Al interfaces joined via an UV-assisted method, [27][28][29][30][31][32][33][34][35] giving insights into the effect of UVs on the structural evolution of joints. However, there are still no direct images capturing atomic-scale motions of dislocations which, together with atomic diffusion, are involved and essential in material flow and plastic deformation in Mg/ Al UVeFSW processes.…”