连续变断面循环挤压制备细晶材料的新方法

Technology of Producing Refined Grain Materials by Continuous Variable Cross-Section Recycled Extrusion

提出了一种新的制备细晶材料的大变形方法——连续变断面循环挤压。其工作原理是:先将圆柱体试样在位于同一中心线上的挤压筒、锥形模内挤压成圆台体,再镦粗成圆柱体。换向180°继续挤压和镦粗,四道工序完成一个循环,重复以上过程,使应变量累积而获得大变形。挤压成的圆台体镦粗时,由上底面至下底面各单元层的变形逐渐减小,不会出现鼓形或失稳现象。文中推导了应变量与变形前后试样高度H和h之间关系的算式,得出n次循环挤压后的累积应变量εn=4nlnh/H。通过对铸态纯铝1A85挤压后的宏观及微观组织观察,其晶粒被反复拉长、压缩而破碎成等轴晶,挤压4循环后的晶粒平均尺寸被细化到1μm。

A kind of severe deformation method of producing refined grain materials was introduced continuous variable cross-section recycled extrusion in this paper. During the whole experiment period, the columned workpiece was pressed to circular cone and consequently the circular cone work piece was compressed into columned one; after that, the workpiece was rotated by 180° and repeated the forward procedure. All of procedures mentioned above constitute a cycle. The accumulative large deformation was achieved through repeating the whole cycle procedure. When the workpieee was extruded into circular cone, the deformation of each layer from the top surface to the underneath one decrease gradually and convex and instable situation did not happen. The formula among the strain, the height （H） before deforming and height （h） after deforming was deduced and the accumulative strain after n cycled deformation is calculated according to the formula, εn=4nln h/H The experiment presented that the grain was elongated and compressed repeatedly sothat it was broken into equiaxed grains. The grain size was fined to 1 μm after 4 cycled deformation.