Abstract: In order to research the effect of welding heat input and vibratory acceleration on internal friction, the amplitude-dependent internal friction (ADIF) of welded metal under different vibration welding condition is tested by using dynamic mechanical analyzer (DMA). The influences of the dislocation shape and density on the dynamic mechanical property are analyzed. It shows that higher heat input leads to coarser microstructure and lesser internal friction in weld under 0.001% strain amplitude at the vibratory acceleration of 0 m/s2, which reveals the effect of grain size on ADIF with different heat inputs. When the vibratory acceleration is 6 m/s2, the internal friction at 31.6 kJ/cm increases obviously with the increase of strain amplitude, which shows the character after pinned dislocation and strain-strengthening. When the vibratory acceleration is 10 m/s2, dislocation density at 26.6 kJ/cm is the highest and dislocation tangle is most serious. The internal friction firstly reaches the peak with the increase of strain amplitude, such a change of the internal friction is related with the movable dislocation length and dislocation density.

Key words: Heat input, Internal friction, Vibration, Micro-grinding machines, Micro-grinding tools, Micro-spindles, Micro-grinding