Synchronous enhancement of mechanical properties and degradation rates of as-extruded Mg−Er−Ni alloys by controlling Er content

Abstract

The synchronous enhancement mechanism of the mechanical properties and degradation rate of as-extruded Mg−xEr−1.6Ni alloys (x=17, 12, and 9.5, wt.%) was investigated by controlling Er content. Results indicate that, as the Er content decreases, the overall content and the distribution of secondary phases did not change evidently, while the type of the secondary phases changed from single long-period stacking ordered (LPSO) phase to coexistence of the LPSO phase and γ′ phase. Notably, the tensile yield strength (TYS) and degradation rate of the Mg alloy with a lower Er content (i.e., Mg−9.5Er−1.6Ni alloy) are increased by 22.3% and 51.5% respectively compared to those of the Mg alloy with a higher Er content (i.e., Mg−17Er−1.6Ni). The enhancement of mechanical properties of the Mg alloy with a lower Er content is attributed to the formation of γ′ phase, which can refine the grain size by inhibiting dynamic recrystallization, leading to enhanced TYS by secondary phase and grain boundary strengthening. Meanwhile, finer grains and the γ′ phase also provide more corrosion sites and inhibit the formation of corrosion-resistant Er₂O₃ film, thereby accelerating the corrosion of Mg alloy.