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.

中文翻译：

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超晶粒细化对 ZK60 镁合金强度和应变率敏感性的影响

在此，阐明了镁合金ZK60中超细晶粒区域的晶粒尺寸与强度之间的关系。圆盘通过高压扭转加工以细化晶粒尺寸，并且一些样品经过退火以增加晶粒尺寸。显微硬度和压痕蠕变实验用于确定强度和应变率敏感性。此外，将压痕蠕变测试尖端下方的晶粒结构与测试前的对应物进行比较，以表明该合金中变形引起的晶粒生长非常有限。结果表明，不同晶粒尺寸范围内晶粒细化硬化的趋势不同。在粗晶粒（>1 μm）区域观察到晶粒细化硬化，在 ≈100 nm 范围内，超细晶粒范围内的斜率发生变化，硬化和可能的晶粒细化软化可忽略不计。它还表明，具有更细晶粒尺寸的样品表现出更高的应变率敏感性，表明变形机制发生了变化。目前的结果与晶界滑动变形模型一致。