Nanoindentation creep behavior of coarse-grained and ultrafine-grained pure magnesium and AZ31 alloy

Ultrafine-grained (UFG) pure magnesium and AZ31 alloy were prepared by sliding friction treatment (SFT). Nanoindentation tests of UFG Mg and AZ31 alloy were performed under a wide range of loading strain rates from 0.004/s to 0.4/s with a holding time of 500 s at room temperature to study the grain size and alloy element influence on the creep behavior and the corresponding deformation mechanisms. It is shown that the refined grain size could promote creep behavior, while the alloy elements would enhance the creep resistance. Creep stress exponent deduced in the ending of the holding regime were used to illustrate the creep diversity in these materials. The UFG samples exhibit a reduced creep stress exponent because of significantly increased grain boundary activities. Besides that, the solute atoms of Al and Zn endow the material with an improved creep resistance by limiting interactions between dislocations and boundaries.