中文摘要：

在温度为285～380℃的条件下，采用循环镦一挤工艺成功获得AZ61镁合金的累积大塑性变形，并对铸态和循环镦一挤变形后合金的组织特征和力学性能进行研究。结果表明，在285℃的条件下，循环镦一挤变形3道次后，材料获得的累积应变为4．28，并得到了平均晶粒尺寸为3．5min的细小均匀的微观组织。晶粒细化的主要原因是局部应变引起的动态再结晶。结果还表明，显微组织演变受温度和累积变形程度的影响。晶粒细化使循环镦一挤变形的AZ61镁合金的力学性能得到明显的改善。此外，通过室温拉伸试验揭示了循环镦一挤工艺参数与力学性能之间的关系。

英文摘要：

The process of repetitive upsetting-extrusion （RUE） was used to achieve severe plastic deformation （SPD） for an as-cast AZ61 magnesium alloy in temperature range of 285-380 ℃. The microstructure and mechanical properties of the as-cast and RUE processed AZ61 alloys were investigated. The results indicated that homogeneous fine-grained structure with mean grain size of 3.5 μm was obtained as the accumulated true strain in the axial direction increased to 4.28 after three RUE passes at 285 ℃. The dominant reason of grain refinement was considered the dynamic recrystallization induced by strain localization. It was also found that the microstructural evolution was affected by temperature and accumulated deformation. The mechanical properties of RUE processed AZ61 alloys were significantly improved owing to grain refinement. Furthermore, the relationship between deformation parameters and mechanical properties of AZ61 alloy prepared by RUE processing was revealed by tensile tests carried out at room temperature.