中文摘要：

由于镁为密排六方结构,室温塑性较差,目前纯镁的等通道挤压（equal channel angular pressing,ECAP）研究一般是在高温下进行的。为了实现纯镁在室温下的ECAP大变形,本次实验中采用创新性方法,将方铁套包套的工业纯镁圆棒在通道横截面尺寸为12 mm×12 mm的模具中进行室温等通道转角挤压,借助于纯铁优良的加工塑性以及在挤压过程中对纯镁产生的较强束缚力,成功制备了表面光滑且无明显裂纹的纯镁挤压试样,使用光学显微镜（OM）,微机控制电子万能试验机研究了一道次挤压后纯镁的组织和力学性能。最后,用扫描电子显微镜（SEM）对拉伸断口进行了观察。结果表明,一道次挤压后,纯镁的晶粒得到明显细化,晶粒尺寸由最初的几百微米下降到几个微米,屈服强度和拉伸强度分别达到97 MPa和118 MPa,比未挤压前明显提高。同时,由于在ECAP过程中试样发生了剧烈塑性形变,挤压前后断口形貌明显不同。

英文摘要：

At present,the study of pure magnesium （Mg ） based on equal channel angular pressing （ECAP ） is limited to elevated temperatures because of the poor formability of the metal at room temperature brought about by its close-packed hexagonal structure. To realize ECAP deformation of pure magnesium at room temperature, an innovative method was developed. In this method, an iron （ Fe ） -canned commercial pure magnesium bar was processed by ECAP at room temperature through a die with a transverse section size of 12 mm ×12 mm . By virtue of the excellent processing formability of Fe and the strong bonding force between Fe and M g ,an ex-truded Mg bar was successfully prepared; this bar presented a surface that w as smooth and free from apparent cracks. The microstructure of the prepared bar w as observed by optical microscopy,and its mechanical proper-ties were measured by an electromechanical universal testing machine. Finally, tensile fractures were observed by scanning electron microscopy. Results showed that the grains of the sample obviously became thinner after one-pass ECAP , decreasing from several hundred microns to several microns. T h e ultimate tensile and yield strengths of the prepared bar reached 118 and 97 MPa , respectively; these values are much higher than those obtained before extrusion. Because of significant plastic deformation during E C A P ,the fracture appearances of the Mg bar before and after extrusion were distinctly different.