Evolution of Mg–Zn second phases during ECAP at different processing temperatures and its impact on mechanical properties of Zn-1.6Mg (wt.%) alloys

Abstract

In this study, the Zn-1.6 Mg alloy was processed by multi-pass equal channel angular pressing (ECAP) at three different temperatures to investigate its microstructural evolutions and mechanical properties. The obtained results showed that the microstructure of the as-cast alloy consisted of α-Zn primary phase and a three-component eutectic structure: α-Zn + Mg2Zn11 + MgZn2. The α-Zn and Mg2Zn11 phases exhibited typical rod eutectic morphology, and MgZn2 nanoscale particles were precipitated within Mg2Zn11 phase. Multi-pass ECAP stimulated dynamic recrystallization (DRX) of primary α-Zn grains and crush of eutectic structure gradually. High ECAP temperature accelerated the growth of α-Zn and Mg2Zn11 grains, while MgZn2 nanoscale particles showed no obvious growth owing to their good thermostability. Moreover, low temperature promoted the formation of a bandlike microstructure, while high temperature resulted in a homogeneous microstructure. Tensile tests demonstrated that the 12p ECAP alloy processed at 150 °C possessed the optimal mechanical properties with ultimate tensile strength of 423 MPa, yield strength of 361 MPa and elongation of 5.2%. The simultaneously enhanced strength and ductility could be ascribed to the combined effect of fine DRX grains, refined Mg2Zn11 s phase particles, MgZn2 nanoscale particles, and the precipitation of new MgZn nano-particles within α-Zn grains.