The Effect of Ultragrain Refinement on the Strength and Strain Rate Sensitivity of a ZK60 Magnesium Alloy
Amanda P. Carvalho, Roberto B. Figueiredo
Abstract
Herein, the relationship between the grain size and the strength in the magnesium alloy ZK60 in the ultrafine‐grained region is clarified. Discs are processed by high‐pressure torsion to refine the grain size and some samples are subjected to annealing to increase the grain size. Microhardness and indentation creep experiments are used to determine the strength and strain rate sensitivity. Also, the grain structure below the tip of an indentation creep test is compared with its counterpart before testing to show that deformation‐induced grain growth is very limited in this alloy. The results show different trends in grain refinement hardening at different grain size ranges. Grain refinement hardening is observed in the coarse‐grain (>1 μm) region, there is a change in slope in the ultrafine grain range and negligible hardening and possible grain refinement softening in the range of ≈100 nm. It is also shown that samples with finer grain sizes display higher strain rate sensitivities, suggesting a change in the deformation mechanism. The current results agree with a model of grain boundary sliding deformation.