Twinning-detwinning assisted reversible plasticity in thin magnesium wires prepared by one-step direct extrusion

Abstract

The present study examines the micromechanisms of plastic deformation in magnesium wires with diameters of 250μm, which were prepared by one-step direct extrusion with a high reduction ratio of 576:1 at a temperature of 577K. It is shown that small wire diameter combined with appropriate microstructure (grain size 14±2μm and strong texture) can yield convenient mechanical properties even in pure Mg. Reversible bending plasticity is achieved by abundant 101̅2 twinning-detwinning of selected variants in the compression zone and moderate dislocation activity in the tensile zone of bended wires. The 101̅2 twinning during bending is facilitated by the medium grain size and by the strong texture with the c-axis of grains roughly perpendicular to the extrusion direction. Intense or repeated plastic bending of wires results in twinning-induced grain refinement in the compression zone. Tensile tests conducted at room temperature and at strain rates of 10−3 and 10−1s−1 reveal maximum true stresses of 198±2 and 246±4MPa and ductility values of 10 and 8%, respectively. In contrast with bending, tensile deformation of wires almost exclusively includes dislocation mechanisms, and a minor contribution of any twinning mode is observed.