Internal friction of powder metallurgy (P/M) and ingot metallurgy (I/M) Al-Fe alloys at elevated temperature

Abstract

Low-frequency internal friction measurements have been carried out on the powder metallurgy (P/M) and ingot metallurgy (I/M) Al–Fe alloy. Internal friction peaks can be seen at about 820–830 K and 530–620 K in the I/M alloys, but not in the P/M alloys. The former is probably due to the grain-boundary relaxation and the latter to recrystallization. Activation energies for the grain-boundary relaxation are estimated to be in two ranges: one is between 100 and 130 kJ mol−1 and the other is between 200 and 210 kJ mol−1, according to the iron content and fabrication processes. The high activation energy is given by the low iron content I/M alloys having a bamboo-like grain. It is suggested that such a difference in the activation energy is due to whether or not the solute iron diffuses into the grain boundary to lower the grain boundary energy.