Correlation between anelastic response and microstructure of 5N-Al thin foils

Highlights: • The microstructure evolution of thin Al foils following thickness reduction has been investigated by TEM and XRD. • Foils with thicknesses 10, 50 and 125 µm have been investigated by means of Mechanical Spectroscopy from 300 to 720 K. • Two relaxation peaks P1 and P2 and a relevant high temperature background were observed in the thinnest samples (10 µm). • The origin of P1 and P2 peaks is connected to the vibration dynamics of isolated dislocations not organized in networks. • Permanent grain boundary sliding seems to contribute to the high temperature background observed in the thinnest foils. -- Abstract: The anelastic behavior of 5N-Al thin foils with three different thicknesses (10, 50 and 125 µm) was investigated in the temperature range from 300 to 720 K through Mechanical Spectroscopy (MS) measurements performed by using a completely automated vibrating reed analyser. Two relaxation peaks P1 and P2 and a relevant high temperature background were observed in the thinnest samples whereas only the grain boundary peak (P_GB) was observed in the thickest ones. Detailed TEM observations and X-ray diffraction (XRD) measurements indicate that defective structures depend on foil thickness and suggest that the origin of P1 and P2 peaks is connected to the vibration dynamics of isolated dislocations not organized in networks. P1 has been attributed to the combination of dislocatio n motion through the stress field of other dislocations and thermally activated cross slip, while P2 is due to the movement of jogs assisted by pipe diffusion. In addition to anelastic effects due to dislocation vibration, permanent grain boundary sliding seems to contribute to the high temperature background observed in the thinnest foils.