Analysis on the compressive creep behaviors of Mg–Y alloys with various grain sizes

The creep behaviors of a hot-rolled Mg-4.5wt.%Y alloy sheet in the grain size ranging from d = 10 μm to d = 160 μm were carefully investigated in this work. It was shown that both loading direction and grain size exhibited effects on the creep behavior. The creep resistance along the ND was always greater than that along the RD, and the increased grain size contributed to the improved creep resistance along both directions. For the fine-grained samples (d = 10 μm to d = 25 μm), the dominant mechanisms were independent of the loading direction, including grain boundary migration (GBM), cross-slip made by basal dislocations and prismatic dislocations, and < c + a > dislocations slipping on the prismatic planes. The undifferentiated dominant mechanisms led to the extremely low creep anisotropy. For the coarse-grained samples (d = 60 μm to d = 160 μm), the dominant mechanisms were different along two loading directions. Specifically, all RD samples shared the dominant mechanisms of cross-slip and {101¯2} twinning, while the dominant mechanisms of all ND samples were dislocation climb and < c + a > dislocations slipping on pyramidal planes. The easy activation of {101¯2} twinning replaced GBM and induced the creep anisotropy, resulting in a low incremental speed of creep resistance along the RD. Differently, the primary dislocation climb and pyramidal < c + a > slip brought a high incremental speed of creep resistance along the ND. Consequently, the coarsen-grained samples had a strong creep anisotropy.