Strain-induced heterogeneous bimodal microstructure behavior of Mg-Gd-Y-Zn-Zr alloy containing LPSO phase during hot compression

Abstract

In this study, the isothermal compression experiments of Mg-Gd-Y-Zn-Zr alloy at 450 °C and 0.01 s−1 under different strains were carried out to investigate the microstructure evolution and the formation mechanism of the heterogeneous microstructure. The microstructure of the sample with a strain of 1.4 exhibited significant heterogeneous microstructure characteristics with bimodal grain and bimodal texture distribution. The particle-stimulated nucleation (PSN) mechanism activated by intergranular block-shaped LPSO phases and the continuous dynamic recrystallization (CDRX) mechanism developed layer by layer towards grain interior promoted grain refinement and the formation of the bimodal grain distribution characteristics. Moreover, the stress-induced dynamic precipitation of Mg5RE particles became more significant with increasing strain, and the interaction of Mg5RE particles with dynamic recrystallization (DRX) grains further refined the DRX grains and exacerbated the degree of bimodal grain distribution. The grains with the <0001> axis between CD and TD and grains with the <0001> axis perpendicular to CD slipped along basal and prismatic planes, respectively, leading to the gradual deflection of the <0001> axis toward CD and the formation of a strong basal texture with <0001> axis parallel to CD during thermal compression. At the same time, the coarse deformed grains with strong basal texture were preserved during compression deformation due to small strain energy storage. Inhomogeneous plastic deformation, randomly oriented refined DRX-ed grains and dynamically precipitated Mg5RE particles together lead to the formation of the heterogeneous microstructure. This study provides theoretical guidance for preparing of high-performance Mg-RE alloys with heterogeneous microstructure.