Microstructure Evolution and Dynamic Recrystallization Behavior of Mg-Gd-Y-Zn-Zr Alloy during Rotating Backward Extrusion.

Yali Duan,Mu Meng,Huifang Zhang,Baohong Zhang,Hongyuan Hao,Huiling Liu,Zhimin Zhang,Ping Xu,Jianmin Yu,Mei Cheng,Beibei Dong

doi:10.3390/ma15031057

Abstract

Rotating backward extrusion (RBE) is one of severe plastic deformation (SPD) methods used to produce cylindrical components with a very large strain by a single pass. In this study, the microstructure and texture evolution in the different regions of Mg-12Gd-4Y-2Zn-0.5Zr (wt.%) alloys via RBE process were investigated by using optical microscopy (OM), X-ray diffraction (XRD), scanning electron microscopy (SEM) and electron back-scatter diffraction (EBSD). The results showed that the cup-shaped sample formed by RBE process exhibited typical gradient microstructure expanding from its inner wall to outer wall along the radial direction (RD). The average grain size of the RBEed sample decreased when the radius decreased from the edge region to the center region along the RD, which was attributed to the different strains and strain rates in the different regions. It also could be observed that the center region showed highest deformation and the edge region exhibited the lowest deformation in the RBEed sample along the RD. In addition, the grain refinement mechanisms of the experimental alloy containing long-period stacking ordered (LPSO) phases after RBE with 100 N were continuous dynamic recrystallization (CDRX), discontinuous dynamic recrystallization (DDRX) and particle stimulated nucleation (PSN).

Highlights

As the lightest structural and engineering material, magnesium (Mg) and Mg alloys have attracted considerable attention in the aeronautics and astronautics industries [1,2,3,4]
Applications of Mg alloys are still limited owing to their low strength and poor ductility both at room temperature (RT) and high temperature (HT) because of their special hexagonal close-packed (HCP) structure [5,6,7,8]
In order to improve their tensile strength with excellent ductility simultaneously [9] and make full use of their benefits, the hot extrusion method is widely applied in the manufacturing procedure for Mg alloys

Summary

Introduction

As the lightest structural and engineering material, magnesium (Mg) and Mg alloys have attracted considerable attention in the aeronautics and astronautics industries [1,2,3,4]. Applications of Mg alloys are still limited owing to their low strength and poor ductility both at room temperature (RT) and high temperature (HT) because of their special hexagonal close-packed (HCP) structure [5,6,7,8]. In order to improve their tensile strength with excellent ductility simultaneously [9] and make full use of their benefits, the hot extrusion method is widely applied in the manufacturing procedure for Mg alloys. An ultra-high yield strength of 417 MPa and moderate ductility of 12.9% were obtained in Mg-8.2Gd-3.8Y-1.0Zn-0.4Zr alloy through a method of decreasedtemperature MDF processing followed by ageing treatment by Tong et al [14]. Zhang et al [15] developed Mg-3.5Sm-2Yb-0.6Zn-0.4Zr alloy containing low RE with high strength using an extrusion and ageing treatment. The peak-aged sample exhibited superior tensile yield strength (TYS) of 449 MPa and acceptable failure elongation (FE) of 4.9%

Objectives

Methods