Friction Stir Back Extrusion of Mg AZ31B-F: a Preliminary Investigation

Abstract

The limited room-temperature ductility of magnesium and its alloys inhibits their fabrication without the introduction of heat to the process; that’s why magnesium alloys are typically associated with warm or hot forming operations. This work presents a unique approach to heating magnesium alloys during bulk forming by utilising “friction stirring”; the same phenomenon on which friction stir welding (FSW) and friction stir processing (FSP) are based. The proposed friction stirring can be combined with particular forms of forging and back extrusion, thus generating the heat needed to soften the metal and ease its deformation. Moreover, and just like the case with FSW and FSP, the proposed bulk friction stir forming processes have the additional advantage of refining the grainstructure of the processed material, and thus the potential to enhance its performance. A close look is provided here to a particular form of bulk processing, referred to as friction stir back extrusion (FSBE). Magnesium AZ31B-F round bar samples are processed by FSBE at selected set of conditions producing sound tubular specimens. Microstructural examination and microhardness testing are performed at key locations to examine the changes to microstructure of the material due to processing. The preliminary results shown here provide a general validation to the proposed processing concept, showing significant grain refinement in the material.