Microstructure, Texture, Mechanical Properties, and Corrosion Behavior of Biodegradable Zn-0.2Mg Alloy Processed by Multi-Directional Forging

Abstract

This study systematically investigated the microstructure, mechanical properties, and corrosion behavior of an extruded Zn-0.2Mg alloy processed by multi-directional forging (MDF) at 100 °C. The mean grain size was remarkably decreased from 17.2 ± 0.5 µm to 1.9 ± 0.3 µm, and 84.4% of the microstructure was occupied by grains of below 1 µm in size after applying three MDF passes. Electron backscattered diffraction examinations revealed that continuous dynamic recrystallization, progressive lattice rotation, and particle-stimulated nucleation mechanisms were recognized as contributing to microstructural evolution. Furthermore, transmission electron microscopy results showed that nanoparticles of Mg/Zn dynamically formed under high strain MDF, while the initial extrusion fiber texture was altered to be < 0001 > parallel to the final forging axis. A synergistic effect of grain refinement, texture evolution, second-phase precipitates, and dislocation strengthening resulted in an increased ultimate tensile strength of 232 ± 5 MPa after three MDF passes. However, this was accompanied by a reduction in the elongation (8 ± 2.1%). Additionally, a high corrosion rate of 0.59 mm/year was measured for the experimental alloy fabricated by 3 MDF passes. In agreement with the latter, electrochemical impedance spectroscopy results indicated that the grain refinement improved the passivation kinetics of the oxide layer.