INTERNAL FRICTION ASSOCIATED WITH GRAIN BOUNDARY SEGREGATION IN Al-Mg AND Al-Na ALLOYS AFTER QUENCHING AND ANNEALING

Abstract
The infiuence of solute segregation on the parameters of the grain boundary internal friction peak (GBP) and the high temperature internal friction peak (NTP) is systematically studied in two kinds of aluminium alloys (Al--Mg and Al--Na). The results show that the behavior of internal friction measured in the two kinds of Al alloys is completely different, which is attributed to different types of grain boundary (GB) segregation. The formtion and resolution of second phase particles in GBs which are controled by Mg atoms' non-equilibrium segregation at and back diffusion from GBs after quenching is the main factor to change the GBP's parameters in Al--Mg alloys. A NTP which is found in Al--Ma alloy after annealing at appropriate temperature range, is surposed to be associated with Na atoms' equilibrium selective segregation at GBs which is sensitive to GB structure and temperature.