Abstract
Magnesium and its alloys are of interest because they can potentially have various practical applications. However, due to poor ductility at low temperatures the use of magnesium is largely limited. Unlike “hot” deformation methods, “cold” deformation at room temperature or lower temperatures leads to the formation of a fine-grained structure and improved mechanical properties. Development of new methods for cold deformation of magnesium and optimization of the existing techniques is an increasingly growing trend. Backward extrusion is one of such existing techniques. This paper describes an original method that involves creating a backpressure during backward extrusion to prevent cracking of magnesium and ensure successful deformation of metal at room temperature. As part of the experiment, a magnesium workpiece is placed in a steel container, with a copper tube attached to its end. When the punch goes down, it first burnishes the copper tube and then it penetrates the workpiece material forming cup walls. The punch presses the copper tube to the container. The resultant friction serves as a backpressure counteracting the growing Mg-wall. The copper tube creates additional compressive stresses which help prevent material cracking. The paper also calculates the level of backpressure, and the calculated data are confirmed through experiment. Depending on the copper tube thickness, cups of magnesium and magnesium alloys were obtained through deformation by backward extrusion with backpressure at room temperature with solid 1 to 4 mm thick walls. After such deformation, the average grain size of magnesium is 5 μm. The described method of back extrusion with backpressure is of scientific and practical interest as it can be used for fabrication of thin-walled magnesium tubes, as well as sheets and foils with a fine-grained structure.
Keywords
Magnesium, backward extrusion, backpressure, severe plastic deformation, structure.
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