The effect of severe plastic deformation on the Mg properties after CEC deformation

Abstract

In this study, the effect of severe plastic deformation on the Mg grain refinement and recovery mechanism was investigated. Technical pure magnesium was deformed at room temperature by cycling extrusion-compression (CEC) process up to large deformation. Several steps of deformation have been used by applying 1, 2 and 4 passes of CEC giving a total effective plastic strain of ε = 3.1. Mechanical and structural properties of Mg in initial state and the states after successive steps of deformation were investigated. The mechanical properties were determined by microhardness and compression tests at room temperature. The structural investigations involved light microscope observations, electron back scattered diffraction and texture measurements by X-ray diffraction. It was found that the CEC process refines the grain size down to 6.4 µm and reduces strong rolling texture components. However, only the first two passes had a strong effect on mechanical properties while a larger number of CEC cycles (above 4) led to failure of the samples with a small effect on hardness. This observation correlates with texture evolution indicating a more random orientation distribution that slows down the typical for hcp metals rapid work hardening. It was found that the CEC process activated twin dynamic recrystallization in deformed Mg. This process led to the formation of new randomly oriented grains inside the twinned areas and as a consequence it reduced the strong rolling texture components.

Keywords

• Magnesium
• Cyclic extrusion compression
• Texture
• Microhardness