Effect of solute atoms on grain boundary sliding in magnesium alloys

Abstract

The effect of solid-solution alloying on grain boundary sliding (GBS) was investigated using pure magnesium and six kinds of Mg–X (X = Ag, Al, Li, Pb, Y and Zn) dilute binary solid solutions with an average grain size of 10 µm. A sharp increase in damping capacity caused by GBS was observed above a certain temperature. The temperature at which a sharp increase in damping capacity occurred depended on the alloying element. The addition of Y and Ag markedly increased the onset temperature (more than 100 K) for a sharp increase in damping capacity, whereas the addition of Zn, Al and Li slightly increased the onset temperature (less than 50 K) as compared with that for pure magnesium. Tensile tests at a temperature of 423 K revealed that the higher the onset temperature, the lower the strain rate sensitivity of the flow stress. It is suggested that the former elements (Y and Ag) are more effective in suppressing GBS in magnesium alloys than the latter ones (Zn, Al and Li). The suppression of GBS was associated with low grain boundary energy, and the extent to which the energy is reduced depended on the alloying element. It was suggested that the change in the lattice parameter (the so-called c/a ratio) affects the grain boundary energy, and thus, the occurrence of GBS.