“…They also observed a structural change from fcc to an amorphous structure during the UW process. Recently, Li et al [ 18 ] investigated UW welding of Mg–Al nanolayers according to heat and ultrasonic vibrations. They reported that structure transitions and increasement of Mg–Ag interface thickness were observed under large vibration amplitudes and low vibration frequency due to facilitation of atomic diffusion and dislocations motions.…”