Dynamic recrystallization behavior and strengthening mechanism of Mg-Gd-Y-Zn-Zr alloy during isothermal MDF process

As one of severe plastic deformation (SPD) methods, multi-directional forging (MDF) technology is an effective way to refine grains. The microstructure, texture evolution and mechanical properties of homogenized Mg-13Gd-4Y-2Zn-0.5Zr (wt. %) alloy during isothermal MDF process were synthetically investigated in the paper. The results showed that the mean grain size of the alloy decreased gradually with the MDF passes increased. After 4 passes, the average grain size of the alloy was refined to 2.7 mm, and the micro-structure distribution was uniform. On the one hand, with the increasing of the MDF passes, the massive intergranular LPSO phases are gradually broken up and formed a deformation zone. The plate-like Mg5(Gd,Y) precipitates were located interior the grains. On the other hand, the spherical Mg5(Gd,Y) phases were randomly distributed with the increasing of MDF passes. In addition, the maximum texture intensity of the MDFed alloy on (0001) basal plane gradually was weaken from 15.993 of the 1MDFed alloy to 4.245 of the 4MDFed alloy, which was attributed to the increasing of volume fraction of dynamic recrystallized (DRXed) grains via MDF method. And the dynamic recrystallization (DRX) mechanisms were continuous DRX (CDRX), discontinuous DRX (DDRX), particle stimulated nucleation (PSN) and kink induced DRX. The maximum ultimate tensile strength (UTS) and tensile yield strength (TYS) after 4 passes were 385 MPa and 360 MPa respectively. The excellent mechanical properties of the alloy were owing to the grain boundary strength-ening, dislocation strengthening, texture strengthening and precipitation strengthening. In addition, the second phase particles such as lamellar LPSO phases, broken block-shaped LPSO phases, spherical Mg5(Gd,Y) phases and plate-like Mg5(Gd,Y) phases were demon-strated to be the strengthening phases.(c) 2022 The Authors. Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).

Automated summary

The effects of isothermal multi-directional forging (MDF) on the microstructure, texture evolution, and mechanical properties of homogenized Mg-13Gd-4Y-2Zn-0.5Zr alloy were investigated in this study. The results showed that the MDF passes gradually decreased the average grain size of the alloy, resulting in a more uniform microstructure distribution. The MDF process also led to changes in the distribution of LPSO phases and Mg5(Gd,Y) precipitates within the grains. Additionally, the maximum texture intensity on the basal plane decreased with the increasing MDF passes due to the formation of dynamic recrystallized grains. The alloy exhibited excellent mechanical properties, attributed to various strengthening mechanisms such as grain boundary strengthening, dislocation strengthening, texture strengthening, and precipitation strengthening.