High ductility of a bi-modal Mg-7wt.%Y alloy at low temperature prepared by high pressure boriding and semi-solid extrusion

A bi-modal Mg-7wt.%Y alloy has been successfully prepared by a novel route of high pressure boriding and semisolid extrusion. It reveals superplasticity at a temperature of similar to 170 degrees C at the strain rate of 1 x 10(-3) s(-1). The grain size ranges from hundreds nanometer to 150 pm, wherein the fine grains provide good strength in terms of Hall-Petch relationship, while the coarse grains offer high ductility due to high dislocation storage efficiency. Compared with conventional single fine or coarse grains, this bi-modal structure is confirmed as a more effective pathway in promoting the deformability of Mg alloys because of the occurrence of extension twinning, the presence of large angle grain boundaries and stable nano-scale YB12 particles with a high melting point. (C) 2015 Elsevier Ltd. All rights reserved.