INTERNAL-FRICTION IN FCC ALLOYS DUE TO SOLUTE DRAG ON DISLOCATION .2.EXPERIMENTAL STUDIES ON AL-SI ALLOYS

Internal friction (mechanical loss) experiments were carried out on si ngle crystal and polycrystalline Al-Si alloys with incoherent Si parti cles of varying size, spacing, and as a function of pre-strain. The re sulting internal friction spectra are correlated with microstructural investigations. The loss maximum at about 450 K (f approximately 1 Hz) , especially its ''low'' activation enthalpy of H = 1.14 eV, can be ex plained by our dislocation model described in the companion paper (Par t I), which considers the enhanced transverse diffusivity of solute at oms in the vicinity of the dislocation core. The model is also shown t o be in agreement with published data on Al-Si, Al-Mg, Cu-Si and Cu-Al . It is proposed that in many instances the internal friction maxima, even when characterized by a ''low'' activation enthalpy, need not be due to grain boundary or particle effects, but may well be explained b y core diffusion effects on solute drag acting on dislocations.