Exploring the effect of bimodal microstructure on the mechanical properties of Mg–15Er binary alloy by regulating the extrusion ratio

Abstract

Bimodal-grained Mg–Gd alloys exhibits excellent mechanical strength due to the high solid solubility of Gd element, which facilitates the strong precipitation strengthening. Er element has a higher solid-solubility than Gd in Mg, which may have a great potential in achieving high strength for Mg alloy. In the study, the Mg–15Er alloy with bimodal microstructure of different proportion of two components is fabricated by adjusting the extrusion ratio and microstructures and mechanical properties for the bimodal-structured Mg–15Er alloy are systematically investigated. The results suggest that the ErH2 phase in the Mg–15Er alloys is stable, regardless of the casting state, solid solution state, or extrusion state. Only a small number of dynamic precipitates is formed during extrusion due to the high solid solubility of Er in Mg. Moreover, the formation of dynamic precipitated MgEr3 phase, where the number of Er atoms is greater than that of Mg atoms, also leads to the inability to form high-density precipitates. The larger extrusion ratio results in higher volume fraction of dynamic recrystallization (from 24 % to 89 %), and larger grain size (from 4.1 μm to 7.9 μm). The results show that the ultimate tensile strength decreases from 301 MPa to 235 MPa, and the elongation increases from 12.5 % to 23.5 % with the increase of the extrusion ratio, which are primarily related to the components of unrecrystallized grains and recrystallized grains rather than dynamic precipitates.