Influence of alloying element Zn on the microstructural, mechanical and corrosion properties of binary Mg-Zn alloys after severe plastic deformation

Abstract

This work presents an analysis of the microstructural, mechanical and corrosion properties of two binary Mg-Zn alloys. Mg-6 wt%Zn and Mg-12 wt%Zn cast alloys were subjected to annealing followed by quenching and processed via equal channel angular pressing with applied back-pressure (ECAP-BP). After ECAP-BP, both alloys were thoroughly examined and showed partially recrystallized and highly deformed areas. High-angle annular dark-field imaging revealed a difference in Zn content across the α-Mg matrix of the Mg-12 wt%Zn after ECAP-BP due to the growth of MgZn2 nanoparticles. Electron energy-loss spectroscopy (EELS) was carried out to qualify an average Zn content in these areas, and a variation in Zn content up to 2at.% was found. Compression tests revealed mechanical anisotropy and a significant increase in the strength of both alloys after ECAP-BP. The yield strength, σ02, was in the range from 269 to 385MPa depending on the composition and compression axis. The initial state alloys showed yield strengths, σ02, of only 75–150MPa but improved ductility. The corrosion rates of the Mg-Zn alloys in the initial state, evaluated using a hydrogen evolution method in NaCl solution, were higher for Mg-12 wt%Zn. The corrosion rates of both alloys after ECAP-BP were higher than those of the initial state. Light microscopy observations did not reveal any preference for corrosion propagation, including transcrystalline, intercrystalline or interphase corrosion, in any of the materials.