Exploring the dependence of creep behavior on the grain size of a peak-aged Mg-10.5Y alloy

Abstract

In this work, the effects of grain size on the compressive creep behavior of a peak-aged Mg-10.5 wt%Y alloy were studied. Compressive creep tests were conducted at 523 K using three group samples, each having an average grain size of d = 25 µm, d = 50 µm and d = 90 µm along the rolling direction. An inverse Hall-Petch relationship for mechanical strength could be used to evaluate the dependence of creep behavior on the grain size, and the creep resistance was continuously deteriorated with decreasing grain size. The dominant creep mechanisms were pyramidal <c+a> slip, cross-slip and prismatic slip in the d = 25 µm sample whilst pyramidal <c+a> slip, cross-slip and basal slip controlled the creep process in both the d = 50 µm and d = 90 µm samples. In addition, precipitate-free zones (PFZs) decorated randomly the grain boundaries during creep. Both the PFZs width and PFZs amounts were increased as the average grain size decreased, and the softening effects from the frequent activated prismatic slip and profuse PFZs induced the worst creep resistance in the d = 25 µm sample. Thus, the creep resistance of the fine-grained samples was always unsatisfactory even though grain boundary sliding was absent at creep duration. It hopes that this work can enrich the understanding of creep theories and offer important reference to the microstructure design of heat-resistant Mg-RE alloys.