Superior strength-ductility synergy of Mg-Nd-Zn-Zr alloy rod achieved by drawing at elevated temperatures

Abstract

Mg alloys with superior strength-ductility synergy is highly desired for applications. In this study, the as-extruded Mg-Nd-Zn-Zr (JDBM) alloy rod was subjected to single-pass drawing over a range of temperature 200 ∼ 600 °C to enhance the properties. After drawing, a more homogeneous and refined microstructure developed because of dynamic recrystallization (DRX) and dynamic precipitation (DP). With the increase of drawing temperature, grain sizes increased first and then decreased due to the competition of grain nucleation and growth, while the sizes of the secondary phase particles varied in the same way. And a nearly basal texture evolved from a rare earth texture of the as-extruded sample. The yield strength of the as-drawn samples increased by ∼2.2 times with a sacrifice of elongation to fracture at different level. The high yield strength mainly originats from grain boundary and dislocation strengthening. An optimal combination of high yield strength (∼301 MPa) and good ductility (elongation to fracture of ∼19 % and improved strain hardening capacity) was obtained after drawing at 500 °C. The yield strength enhancement is mainly derived from texture and dislocation strengthening. Grain and secondary phase particle refinement, large volume fraction of low angle grain boundaries and reduced geometrically necessary dislocations are considered to be beneficial to the good ductility. In addition, a novel method has been proposed to fabricate materials with superior strength-ductility synergy by deformation with large strain at high temperatures to activate severe DP.