Achieving exceptionally high strength and rapid degradation rate of Mg-Er-Ni alloy by strengthening with lamellar γ′ and bulk LPSO phases

Abstract

As-extruded Mg-Er-Ni alloys with different volume fractions of long-period stacking ordered (LPSO) phase and density of lamellar γ′ phase were prepared, and the microstructure, mechanical, and degradation properties were investigated. Coupling the bulk LPSO phase and the lamellar γ′ phase, and controlling the dynamic recrystallization processes during deformation by adjusting the volume fraction of LPSO and the density of the γ′ phase, a synergistic increase in strength and degradation rate can be achieved. On the one hand, the increase in corrosion rate was related to the increased volume fraction of the bulk LPSO phase and the densities of the lamellar γ′ phase, which provide more galvanic corrosion. Moreover, high densities of the lamellar γ′ phase can provide more corrosion interface by inhibiting the recrystallization process to refine dynamic recrystallized (DRXed) grains during the hot extrusion. On the other hand, the ultimate tensile strength (UTS) and tensile yield strength (TYS) of the Mg-Er-Ni alloy increased from 345 and 265 MPa to 514 MPa and 358 MPa, respectively, which was mainly attributed to grain boundary and texture strengthening, bulk LPSO phase and lamellar γ′ phase strengthening. Overall, Mg-14Er-4Ni alloy, which contains the highest volume fraction bulk LPSO phase and the densities of lamellar γ′ phase, realized a synergistic enhancement of strength and degradation rate. The UTS, TYS, and degradation rate of Mg-14Er-4Ni were 514 MPa, 358 MPa, and 142.5 mg cm–2 h–1 (3 wt% KCl solution at 93 ℃), respectively. This research provides new insight into developing Mg alloys with high strength and degradation rates for fracturing tool materials in the application of oil and gas exploitation in harsh environments.