Achieving an ultra-high strength and moderate ductility in Mg–Gd–Y–Zn–Zr alloy via a decreased-temperature multi-directional forging

In this study, an ultra-high yield strength (~417 MPa) and moderate ductility (~12.9%) was obtained in Mg–8.2Gd–3.8Y–1.0Zn–0.4Zr (wt%) alloy through a method of decreased-temperature multi-directional forging (MDF) processing followed by aging treatment. The ultra-fine grained structure with average grain size of ~0.9 μm was prepared after 6 passes of forging progress, which was ascribed to the occurrence of dynamic recrystallization (DRX). Both the decreased MDF temperature and precipitation of fine Mg₅(Gd, Y) phase particles effectively hinder the DRX grain growth, so that the grain refinement can realize their full potential in strengthening effect. The formation of some DRX grains is also accompanied with the consumption of LPSO structures. Additionally, a weak fiber texture with c-axis perpendicular to normal direction was gradually formed during the reduplicative MDF process. As compared to the hot-extruded counterpart, the significant improvement in the yield strength of MDF-processed Mg-Gd-Y-Zn-Zr alloy can be attributed to the combined strengthening effects of the grain refinement, dynamic precipitation and broken secondary phase particles. Meanwhile, the homogenous microstructure induced by decreased-temperature MDF is also responsible for a resulting moderate ductility.