Influence of severe plastic deformation on intermetallic particles in Mg-12wt.%Zn alloy investigated using transmission electron microscopy

Abstract The in-depth microstructural characterization of intermetallic particles in an Mg-12 wt.%Zn binary alloy subjected to a severe plastic deformation is presented. The alloy was processed by four passes via equal channel angular pressing with an applied back pressure at a gradually decreasing temperature and analyzed using transmission electron microscopy techniques to observe the influence of processing on intermetallic particles. The results are compared with the initial state of the material prior to severe plastic deformation. The microstructural evolution of the α-Mg matrix and the Mg 21 Zn 25 , Mg 51 Zn 20 and MgZn 2 was analyzed using bright field imaging, selected area electron diffraction, high-resolution transmission electron microscopy and high-angle annular dark field imaging in scanning mode. The plastic deformation process influenced the α-Mg matrix and each type of intermetallic particle. The α-Mg matrix consisted of two types of areas. The first type of area had a highly deformed structure, and the second type of area had a partially recrystallized structure with an average grain size of approximately 250 nm. The Mg 21 Zn 25 microparticles exhibited distinct forms in the α-Mg matrix that were characterized as a single-crystalline form, a nano-crystalline form and a broken up form. No evidence of Mg 51 Zn 20 nanoparticles within the α-Mg matrix was found in the microstructure, which indicates their dissolution or phase transformation during the deformation process. MgZn 2 nanoparticles exhibited different behavior in both types of α-Mg matrix. Two orientation relationships toward the highly deformed α-Mg matrix were observed; however, there was no relationship toward the partially recrystallized α-Mg matrix. Additionally, the growth of the MgZn 2 nanoparticles was different in the two types of α-Mg matrix. The Mg 51 Zn 20 nanoparticles inside Mg 21 Zn 25 microparticles exhibited a distinct behavior within the single-crystalline or nano-crystalline form of the parent Mg 21 Zn 25 microparticles. The Mg 21 Zn 25  + Mg 51 Zn 20 eutectic compound was confirmed for both forms of the parent Mg 21 Zn 25 microparticles, and the growth of Mg 51 Zn 20 nanoparticles is discussed.